Final Report Summary - RESOLIVE (Adaptation of renewable energies technologies for the olive oil industry)
Project context and objectives:
Comprising pioneer countries in olive oil production throughout history, the European Union is the main olive oil producer in the world. The figures show that 80.2% of the world production, 2.056.200 tons, were produced in the countries of the Mediterranean region.
The European olive oil sector is nowadays facing several stresses that push towards the need of a new approach to production. Despite worldwide consumption rises (due to the acknowledgement of the consumers of olive oil's beneficial effects for health); new producer countries like Turkey, Syria and Tunisia enter the markets and increase competition, threatening European producers' dominant position.
Besides, the olive oil industry is defined by the polluting character of its residues, of which about 5.8 million tons are produced annually. This poses serious problems to the olive mills, especially in the case of small and medium ones. Actors from all the groups involved agree on the need for a more sustainable approach to production schemes, where environmental conditions are taken into consideration without damaging productivity.
In this sense, in the last years there has been new research exploring the possibilities of further use of the residues, olive mill waste water and olive pomace, and initiatives to provide solutions to the industry. Even though efforts have been made so far for bringing the results obtained to practice, many local producers associations still lack a clear guidance adapted to their needs in specific fields, resulting in giving up the implementation of these activities after the institutional framework which supported it disappears.
Against this situation, the proposing IAGs have attempted to take an integrated and more proactive approach to the problem: This polluting charge of olive mill waste (OMW) can be taken as an advantage to produce energy from it: olive mill solid waste has a wide range of uses in renewable energy: it can, for instance, be gasified to obtain hydrogen and CO, digested in an anaerobic process to obtain methane, or directly used in combustion.
Other processes to obtain a valuable outcome from olive mill residues: Solid residues can also be used, once properly processed, for animal feeding, or composted to be used in agriculture as a natural, chemical-free fertiliser.
In the light of such stresses, polluting characteristics and energy recovery opportunities pertaining to the olive oil sector, RESOLIVE aims at achieving the following objectives:
Overall objectives:
- To define the specific conditions for the implementation of renewable energy solutions specific to the olive oil industry.
- To enable the producers and their associations more independence from centralised energy systems.
- To increase the competitiveness of the European olive industry through the accession to state-of-the-art technologies.
Scientific and technological objectives:
- To build a prototype gasification system combined with a 30kW microturbine production to demonstrate its performance using different olive industry wastes as fuel.
- To carry out a full program of laboratory scale tests on anaerobic digestion to optimise the existing techniques for biogas production, which will enable producers to its implementation.
- To collect information about other renewable energy solutions for the industry, successful stories and implementation ranges.
Socio-economic objectives:
- To answer to the current need to increase the sustainability of European agricultural sectors by implementing solutions which result in a valuable output (in this case, energy) from their waste.
- To reduce production costs in the olive oil sector in the current scenario of constantly increasing prices of energy.
- To summarise the existing knowledge in olive waste valorisation by month 30 and transfer this knowledge to its end users (expected date of accomplishment, month 36), supporting them in the further implementation.
- To create a comprehensive set of guidelines by month 31 of the project that will advise the associates of olive oil producers' cooperatives deciding which of the available options for the implementation of renewable energy suits their conditions best.
- To enable the olive oil producers in Europe access to a new market: electricity production.
- To increase employment in the sector by capacity building in state-of-the-art technologies and creation of new jobs in the operation of the proposed systems.
Below, the entire structure of the RESOLIVE project is found, showing research focus areas and targets divided in its work packages (WPs).
WP1: Information assessment
This WP is the first devoted to research and technological development activities and was scheduled to be developed from month 1 of the project to month 12 and led by UNIPG. It was divided into 2 tasks that had the following main objectives:
- characterisation of needs and constraints of the sector,
- screening of current technologies.
WP2: Definition of prototype requirements
The main objective of this WP was to deal with the analyses necessary for the adaptation of the gasification system to the specific system conditions and to carry out the preliminary characterisations for the anaerobic digestion phase. WP2 was scheduled from month 4 to month 20 of the project. The WP leader was ISFTA. It was divided into six tasks that had the following objectives:
- chemical characterisation and analysis of the feedstock,
- gasification prototype placement,
- gasification prototype connection to the grid,
- gasification system modelling and analysis,
- gasification prototype design,
- lab scale anaerobic digestion tests.
The results obtained in these tasks showed that the proposed technologies for the prototype (gasification and microturbine) were not appropriate for the feedstocks to be used in RESOLIVE, which led to the request for an amendment in the description of work. Further details are given under the full descriptions of WP2, 3 and 7.
WP3: Prototype building and operation
WP3 was scheduled to be developed from month 15 to month 29 of the project, led by INYTE. The main objective of WP 3 was the process of building and operation of the gasification prototype. It was divided into two tasks with the following objectives:
- building of the gasification prototype,
- operation period of the gasification prototype.
The change in the technology used for the prototype during WP2 entailed a restructuring of this WP and the works on each task. Further details are given under the full description of WP7.
WP4: Assessment of operation stage results
WP4 is led by project partner INYTE and was scheduled to be developed from month 13 to month 34 of the project. It was divided into five tasks having the following main aims:
- assessment of the anaerobic digestion results,
- assessment of the gasification results,
- review of alternative technologies,
- economic analysis,
- preparation of operation manuals and result summaries.
From these, and due to the amendment of the DoW, only the first has started. The partners agreed in starting the economic analysis of the anaerobic digestion technology before planned in order to gain time and avoid further delays in the future.
WP6: Dissemination
This WP is devoted to dissemination activities and is expected to run continuously throughout the project, led by UNIOLIVA. It is divided into seven tasks that have the following objectives:
- setup and maintenance of the project web page,
- preparation of project dissemination materials,
- preparing RESOLIVE guidelines and materials for results dissemination,
- attending conferences and sectorial fairs,
- dissemination activities which are SME-oriented,
- organisation of national workshops on sustainable approaches in olive oil production,
- definition of a knowledge and IPR management permanent structure.
WP7: Project management
The aim of WP7 is to ensure an effective project management and co-ordination over the entire project duration. The work package was scheduled to cover the period from month 1 to month 36 of the project and is led by TTZ. It is divided into 3 main tasks with the following objectives:
- executive project coordination,
- general and financial project coordination,
- scientific project coordination.
Project results:
At the start of the project, needs and constraints of the olive-oil sector were characterised, collecting necessary information to adapt both the proposed systems, gasification and anaerobic digestion, to the real conditions found in olive mills throughout the producer countries in Europe. These two systems offer solutions for the olive residue treatment, at the same time, produce a valuable energy output for the mill or the electricity grid. Four alternatives to gasification and anaerobic digestion were also defined as use as fertiliser/soil conditioner and compost for plant nurseries, recovery of organic compounds, energy use with direct combustion and finally, use as animal feed. ttz started compiling relevant information on the olive oil sector in the main European producer countries. The search was divided between production methods and legislation concerning environmental risks that the production has to comply with. The information was completed with the collaboration of UNIPG. CERTH/ ISFTA contributed providing information on the needs and capacities of the olive mills and cooperatives in Greece. National statistics services were also contacted, providing data on olive products from the main olive oil production
Following a literature review, a comparison between two-phase decanting and three-phase decanting was completed along with data on the status of the olive oil sector in Greece, Spain, Portugal and Italy, comprising surface dedicated to this crop, irrigation, quality and amounts and composition of by-products. The critical issue of the disposal of by-products was analysed and the existing legislation concerning limiting values for the discharges of wastewaters were investigated.
Finally, social constrains regarding data for gross production in terms of product value were presented for the needs of this task.
All IAG partners (Paseges, Unioliva, Unaprol, Ceolpe and Vilaflor) participated in the validation of the information gathered. Finally, the conclusions were drawn with the help of the rest RTD and IAG partners. Deliverable 1, report on needs and constraints of the sector, was submitted to the Commission officers on 17 June 2009.
In a second step, UNIPG developed an intensive screening of research activity on current technologies for olive waste reuse and valorisation. They verified the best practices and the gaps in this field. This activity has been developed also in cooperation with task 1.1 leader (ttz). CERTH/ISFTA provided support on defining the technologies, the best practices worldwide and the gaps in knowledge that need to be overcome to reach full implementation status.
In addition, a literature review was carried out about the use of olive oil residues in the energy sector and specifically considered the potential of using this type of material as an alternative source for solid biofuels. Conventional combustion of residues from olive and olive oil production is already applicable in many regions. Based on the accumulated knowledge on previous and current projects for the energy exploitation of olive residues, the combustion technology is most widely applied. The potential of replacing this technology with a new one such as RESOLIVE proposes, under more 'environmental friendly' terms, is examined in this task, and biomass gasification process is presented in details along with gasifier types, including bubbling fluidised bed, circulating fluidised bed, fixed-bed and entrained flow reactor type. Furthermore, data concerning olive kernel gasification from the scientific literature and studies for olive kernel thermochemical conversion are reported in this task.
Finally, UNIPG included a SWOT analysis for those alternative uses of olive mill residues which show promising results so far, such as the extraction of organic compounds or the reuse of solid OMW as an amendment, fertiliser, herbicide or pesticide. Also, Deliverable 2 provides suggestions for further research on this topic, submitted to the European Commission on 8 January 2010.
Gasification
Prototype requirements
The prototype requirements were determined, including preliminary chemical analyses, pre-engineering and integration of the equipment, electric and heat transfer system, specifying equipment, parts, biomass fuels and lab materials for purchase, detailing a variety and range of parameters to be tested, specify data collection protocols, and data analysis methodologies.
The initial plan in the project was using a catalytic combustor enabled the microturbine to operate directly on low-Btu, low-pressure gas. However, the results obtained after tasks 2.1 ('Chemical characterisation and analysis of the feedstock') and 2.4 ('Gasification system modelling and analysis') confirmed that this would not be a feasible solution. As explained in the draft version of D05 submitted to the EC in April, 2010, the gasification product gas obtained with the substrates used in the project has about 10-20% of hydrogen. It has been indicated that the flashback produced in the microturbine by the hydrogen would cause malfunction and permanent damage. For this reason the partners concluded that the best solution to keep intact the initial objectives of the project was to adapt the prototype, using another power producing unit in the design instead of the microturbine. Based on the offers from other manufacturers and the research of the RTDs, the technical solution chosen, and proposed in the request for amendment to the EC was a gasifier with a gas engine.
Chemical characterisation and lab-scale tests were realised in ISFTA's facilities in order to evaluate gasification behaviour of the examined feedstocks. The following properties were measured: moisture content, proximate (thermo-chemical behaviour) and ultimate (elemental composition) analyses, calorific values and ash analyses. These analyses provide information on the volatility of the feedstock, its elemental analysis and heat content.
A variety of materials were supplied by PEZA, Unioliva, Sabina, Ceolpe, Melambianakis and Vilaflor, in order to achieve a significant number of feedstocks. Based on the chemical characterisation the most promising feedstocks were selected for the gasification experiments. A six-month delay was attained on the completion of the experiments since not all the samples had been delivered to ISFTA in due time course, while some adjustments on the fluidised bed facility were considered necessary to secure the safe and continuous supply of the biomass feedstock.
Prior to the fluidised bed gasification experiments, some cold tests were considered necessary in order to determine the operational conditions of the installation for optimum performance. The reactor was constructed from stainless steel cylindrical tube of 8.9 cm ID and 1.3 m in height, placed in an electrically heated oven.
Two sets of gasification experiments were performed using quartz sand and olivine for bed material for each biomass fuel. Taking into account the similarities of the composition of the examined fuels, experiments were conducted with representative materials Unioliva - leaves and prunings and Melambinakis - dry olive cake.
The results from the gasification experiments showed that olivine promotes H2 and CO2 formation and lowers CO. For similar air ratios the methane yield appears slightly lower with olivine. Olivine more significantly drops the amount of tars in the gas in all cases. Operation at 800°C derives slightly less tars than 770°C. Tars drop sharply with higher air, but so does the quality of the product gas (H2 and CO drop in favour of CO2 and H2O). The use of olivine significantly reduces the tar levels produced and is recommended for the application.
From the gasification tests it can be concluded that the product gas quality ranges between the following minimum and maximum (better) quality:
Based on the specifications of the commercially available micro gas turbines (Capstone) the gas has to be pressurised and cleaned but also the following criteria have to be met for low hydrogen content. There are even more strict specifications for tars which cannot be matched with gasification. Nevertheless, the operation of a micro gas turbine with product gas is theoretically feasible. The gasifier needs to be operated at pressures around 5 bar. An alternative option is to employ an atmospheric gasifier with an alternative power production other than the micro gas turbine (MGT) (i.e. solid oxide fuel cells or gas engine). So, the results is that either commercial MGT needs to be modified (feasible solution not recommended under the framework of the project) or change the MGT with another power producing unit in the design. As explained in the introduction of the work package, the partners decided, after discussing the best options internally and with the EC officers, to request a change in the technologies, using another power producing unit in the design instead of the microturbine. Based on the offers from other manufacturers and the research of the RTDs, the technical solution chosen, and proposed in the request for amendment to the EC was a gasifier with a gas engine.
In the proposed system, the hot fuel gases and the entrained ash/char are cooled in a tube-and-shell heat exchanger. Hot gas enters the heat exchanger at about 700°C and is cooled to approximately 100°C. The fuel gas flows inside of the tubes and a cooling fluid (liquid or air) on the shell side. There are clean out ports to allow inspection and cleaning of the tubes.
For woody biomass the clean fuel gas typically has an energy content of about 120 to 165 Btu/cu ft. The fuel gas is composed of about 20% CO, 20% H2 and 2% CH4. A pound of dry biomass will produce about 50 cubic ft of producer gas. The feedstock enters through the top of the downdraft gasifier. The control system will call for dry feed to be added on top of this flaming pyrolysis zone automatically when system temperatures reach required levels. As the feedstock particles approach the flaming pyrolysis zone, they are heated and dried, losing their moisture as steam. This steam and the gasification air that is automatically delivered travel quickly to the flaming pyrolysis zone below. As the feedstock particles travel further downward, they are heated to pyrolysis temperatures and begin to emit pyrolysis vapours. The combustion gases and residual tar vapours then travel down to the char oxidation zone, along with the char formed in the flaming pyrolysis zone.
In the char oxidation zone, secondary air is added by computer control to oxidise the char, producing carbon dioxide and heat. In the steady-state condition of the gasifier, the temperatures of the char oxidation zone are moderated by the endothermic reactions of steam and char to form hydrogen and carbon monoxide, as well as, carbon dioxide reacting with char to form carbon monoxide. These temperature-moderating reactions increase faster at the higher temperatures of this zone. The hot char and ash surfaces, along with free radicals present in this zone catalyse the destruction of the residual tar vapours.
The results from this task are compiled in D03 'Report on the results of chemical characterisation of fuels and lab scale gasification tests' which was submitted in month 8.
Prototype placement
INYTE, with the cooperation of Unioliva, worked in the land assessment for deciding the best placement for the prototype. Unioliva provided information on their facilities, which was then assessed using an AI-based method to determine the optimal supply area and location for an electric generation system based on biomass. The proposed AI-based method is a discrete binary version of the PSO algorithm, which makes use of the profitability index as objective function. The proposed approach assessed the land available to the cooperative or olive mill, dividing it in lots of the same area assessing their suitability with regard to several variables. This method reached convergence in a few iterations, which is equivalent to a computational cost more than a thousand times lower than that required for exhaustive on site comparison.
The region considered to apply the proposed method was the area of Úbeda, it was divided in 128 ×128 = 16.384 square parcels of constant surface, Si = 0.09766 km2. In particular, Úbeda is a town in the province of Jaén, in Spain's autonomous community of Andalusia. Úbeda has become in one of the biggest olive oil's producers and packers of the Jaén province. The Úbeda extension is 397-400 km2 approximately. The city is near the geographic centre of the province of Jaén, and it is the administrative seat of the surrounding 'Loma de Úbeda comarca'. The agricultural economy mainly works with olive cultivation and cattle ranching.
The results showed the optimal location of the biomass power plant for the best found solution and the profitability index evolution.
The permits and administrative procedures that need to be fulfilled to comply with the legislation in each of the countries addressed were also obtained. Paseges found this information for Greece. UNAPROL worked in the permits needed in Italy. Unioliva, with support of Ceolpe provided information on the administrative procedures for Spain and Vilaflor took over this task for Portugal. ttz provided these partners with extra support in this task. The results of task 2.2 were compiled in D04 'Prototype placement and connection to the grid report', explaining the method used for finding the best location for the prototype, which was submitted to the EC in October, 2009.
Prototype connection to the grid
Technical details were taken into consideration for the connection of the gasification prototype to the grid, as well as with the legislative framework in force in each of the countries addressed by the project regarding renewable energies production and connection of the necessary licenses to connect to the grid and act as an electricity provider.
INYTE carried out the task, with support from the IAG partners and ttz. The main role of INYTE was the preparation of the technical descriptions, and the IAGs provided information about the legal frameworks in their countries, which was supported by ttz.
The gasification system is intended to work for the production of energy for the own consumption of the association where it is placed. However, it is possible to connect the system to the grid so the olive mill becomes an energy provider. This possibility and the engineering needed to achieve it were defined by INYTE. CERTH/ISFTA provided support to INYTE in the engineering study of the system connection to the grid.
A microturbine is small gas turbine engine-generator, typically sized 25-500kW. The technologies for microturbine are evolved from automotive and truck turbochargers, auxiliary power units for airplanes, and small jet engines. A frequency inversion is required before a microturbine could be connected to the grid system. For the microturbine to self-support its own power usage (auxiliary supply), the power is supplied from the DC link between the rectifier and the inverter for the frequency inversion.
A digital controller is required in the microturbine package to control the microturbine's operation and function. The common type of digital controller is the programmable logic controller (PLC). A protective device is included as well.
The procedure for grid connection is basically as follows. In a feasibility study the network operator examines whether the system conditions prevalent at the planned point of connection are technically sufficient for operation of the generating unit.
Should the system conditions suffice for operation, the network operator submits a verifiable offer as to the network connection scheme. Should the system conditions at the system point of connection not be adequate, the network operator furnishes evidence of this inadequacy
Then, the network operator, together with the connection holder, examines appropriate modifications, such as network reinforcements. Following this feasibility study, a formal connection offer is made, and, if accepted, leads to detailed design work to determine the final connection charge and additional requirements. Eventually the project is commissioned.
As a result, the chapter dealing with these issues in D04 summarised the administrative procedures to follow in order to use the electricity produced by the prototype in the national grid. Special attention has been given to bonuses devised by the different administrations to foster renewable energies.
Deliverable 4 'Prototype placement and connection to the grid report' was submitted as planned on 31.10.2009 to the EC.
Gasification system modelling and analysis
Prior to the final design of the prototype, thermodynamic calculations aiming to improve the performance of the gasification unit was carried out by ISFTA. Microturbine thermodynamic cycle was modelled with the aid of GateCycle software which can handle more precisely advanced cycle calculations. The proposed system consists of one fluidised bed reactor thermally coupled with heat pipes, a product gas cleaning train and a micro gas turbine.
A steady state air gasifier model was composed to assess average gas compositions and perform heat and mass balance calculations. The air gasifier was modelled based on the combination of unit operations: biomass decomposition into its constituents and reaction of them with air. Char and methane formation was taken into account, while equilibrium reactions for the rest of the biomass components were considered by minimisation of the Gibb's free energy.
Pressurised gasification is in general advantageous compared to atmospheric when considering the utilisation of the product gas in gas turbines or fuel cells, since considerable savings occur from reductions in equipment size and avoidance of warm product gas compression power, while tar removal or cracking is not a major issue anymore, as the gas compressor, which is directly affected by tar condensation, is no longer necessary. Even a slightly pressurised operation (around 5 bar) is advantageous in the case of micro gas turbine utilisation with the gasifier. Two pressure levels have been tested in this study, near atmospheric and 4 bars, in order to establish the optimum operation in view of product gas quality.
From a thermodynamic point of view, biomass air gasification processes should be accomplished with the minimum air necessary for maximising carbon conversion. Increasing the gasifier temperature and, therefore, ER has an overall negative effect on the exergetic efficiency because major chemical exergy carrier components, i.e. combustibles in the product gas are minimised. Nevertheless, kinetic reasons such as advancement of tar reforming reactions, fluidisation limitations or heat losses might impose higher ER values in practice. The gasifier temperature was chosen as 1080 K, while two pressure levels were considered: 1.5 bar and 4 bars. The corresponding ER value in both atmospheric and pressurised modes of operation is 0.37. The model predicts a very slight exergetic effectiveness increase in the case of pressurised gasification. A higher moisture fuel would result in a penalty on the gasification efficiency because of dilution of the product gas.
As a concluding remark, gasification operates slightly better at elevated pressures, requiring less air flow and demonstrating a slightly improved efficiency over atmospheric operation, provided the carbon conversion is complete.
In the same task the existence of a gas cleaning stage had to be investigated by ISFTA. Gas cleaning is a critical step for the success of RESOLIVE gasification project and any other modular small biomass gasification unit. The stage of gas cleaning is necessary in order to remove some undesirable constituents such as:
- particles (char particles, ash and bed material),
- alkali metals (Na and K),
- nitrogen compounds,
- tars,
- sulphur and Chloride compounds, (H2S, COS and HCl).
The actual gas cleaning design for RESOLIVE is based on the following technologies and is under development. Figure 3 gives a comparative presentation of the different existing gas cleaning technologies that need to be combined for efficient gas cleaning.
Modelling of product gas thermal pathway in equilibrium phase with a typical set of initial contaminant values and calculations performed for a series of temperatures as the product gas might be gradually cooled as it exits the gasifier till it enters the turbine combustion chamber. Calculations were performed at higher operating pressures of the RESOLIVE reactor i.e. 3 bar. The operating temperature of the RESOLIVE gasification system was set at 800°C.
The main conclusions from this work can be summarised in the following way:
- To condense and, hence, remove alkalis by barrier filtration, temperature of 600°C or below must be reached. Tars will start to condense below 200°C. Tar condensation should be avoided, since sticky condensed tar material will destroy the filter elements.
- To reduce tar content, tar cracking or reforming must be employed in addition to cooling. Cooling alone will reduce tars to ppm values only if ambient temperatures are reached. If secondary catalysts are used, these must be tolerant to alkalis or else these should be employed after the alkali cleaning (<600°C). If higher temperatures for tar cracking are required then alkali tolerant catalysts should be employed or a catalytic bed reheating from the combustion bed of the RESOLIVE system.
- The product gas should be fed to the turbine at a temperature as high as possible. According to reported data this feed temperature value could be up to 600°C, i.e. a gaseous-tar tolerant turbine could be fed with the product gas immediately after the hot gas filtration (provided no NH3, H2S, HCl cleaning is required).
- If hot gas cleaning of NH3, H2S, HCl by sorbents is pursued these should be able to clean the gas from temperatures of 600°C (Alkali condensation) down to 200°C (tar condensation).
Before the microturbine modelling was carried out, a list of the leading microturbine manufactures was prepared along with the main technical characteristics of their products. In addition, economics of microturbines was investigated in order of capital cost, O&M cost and maintenance interval.
Furthermore, a literature review regarding the operation of microturbines using biomass as primary fuel, took place before the thermodynamic simulation, in order to identify possible issues that may need to pay more attention during the simulation and to lead in a complete study of the microturbine thermodynamic cycle.
Various microturbine models were analysed with the aid of Gate Cycle.
Several runs took place trying to optimise thermodynamic performance of gasification unit, changing variables such as pressure ratio at the compressor, air inlet temperature at combustor, exhaust gas temperature etc. in different power outputs. Due to the correlation between the system's efficiency and the temperature of the combustor, the temperature cases ranging from 1123 K to 1227 K were investigated.
A parametric study was applied in order to optimise the model and achieve higher efficiency level. Increases in turbine inlet temperature rapidly increase the power output of the turbine and to a lesser extent increase efficiency. The results for various inlet temperatures indicated that the optimum compressor's pressure ratio ranges from 1:4 to 1:5. Also the impact of recuperator on efficiency is important. Optimising recuperator's effectiveness better system efficiency can be assessed. The ambient conditions at the inlet of microturbine affect both the power output and efficiency. At inlet air temperatures above 288 K, both the power and efficiency decrease. The power decreases due to the decreased air density with increasing temperature, and the efficiency decreases because the compressor requires more power to compress higher temperature air. Similarly at high altitudes where air density is lower, power output and efficiency are also lower. Finally, the impact of fuel inlet temperature on efficiency is examined. As expected higher inlet fuel temperatures give higher efficiency while higher values for gasification outlet gas temperatures are desired.
In general the thermodynamic efficiency of the microturbine cycle can be improved by increasing the turbine inlet (or firing) temperatures, increasing the efficiencies of turbomachinery components (turbines and compressors) and by adding modifications to the basic cycle (intercooling, recuperation and reheating).
A short delay was necessary for the completion of this task due to the extensive data required accomplishing the modelling results, and thus the higher man-effort required compared to the initial projection. The results of this task were included in D05 ('Gasification prototype design'), which was prepared under task 2.5. Results of this task are also included in a publication (in press) of Vera, Jurado, Panopoulos, Grammelis in the International Journal of Energy Research with the following title, 'Modelling of biomass gasifier and microturbine for the olive oil industry'.
Prototype design
Based on the specifications provided by CERTH/ISFTA about the design requirements focused mainly on the gas properties and cleaning, INYTE conducted a market survey with potential equipment suppliers.
Due to the characteristics of the process detailed in the description for WP2 and task 2.4 numerous problems were found with the manufacturers of microturbines. Once the full gas characteristics were sent to a broad list of manufacturers, none of them accepted to sell this equipment to the consortium. The reasons argued for this were that the gas obtained from the fuels used in RESOLIVE would cause malfunction in the microturbine.
The companies contacted avoided these bad results reaching the market by all means. It is noteworthy that the information available from these manufacturers (especially Capstone, mentioned as preferred supplier in the description of work) to the partners of the project before proposing RESOLIVE and during the proposal preparation stage was always indicating that there would be no impediment for using their products and obtaining a satisfactory result.
It was concluded that the Capstone microturbine restriction for maximum 1% of hydrogen content, set to avoid flashback problems, could not be met, since the gasification product gas contains 10-20% of hydrogen. This information was forwarded to the European Commission through the coordinator, requesting an amendment to the DoW of the project, in which another power producing unit, such as a gas engine would be used instead of a microturbine of the gasification prototype design was requested. The requested amendment was accepted on 15 October 2010 and INYTE started the procedure for purchasing the prototype (gasifier with gas engine and generator).
The option chosen, after comparing different quotations, was the one from the company Ankur, as it complied with the budget allocated for the prototype in the project, and delivery time was quite fast (12 - 14 weeks). The completion of this task entailed the achievement of milestone M1: Completion of the prototype design.
Prototype building
The specifications in the prototype design phase were followed by the construction of the gas engine prototype. INYTE was in charge of the task, supported on-site by the staff of Unioliva.
A first step in the building of the prototype was the confirmation with the chosen supplier of the performance of the gas engine and its technological characteristics. For this reason, Cummins Ltd. carried out battery tests which are described in D07 'Gasification prototype built'. These are part of the building process of the prototype and have been used by the consortium of RESOLIVE during the test phase for the comparison of the prototype's performance when using olive oil production residues as a fuel.
The transport of the prototype to Spain took longer than initially planned, as the ship transporting it left the port of Mumbai later than planned. This circumstance led to a delay that affected the whole of the project. The system was dispatched by Ankur Scientific on 9 May 2011, and arrived in the Spanish port of Algeciras 8 June. The customs screening, clearance and transport to Úbeda took eleven days and the prototype arrived on 20 June. Erection and commissioning of the prototype took four weeks, from 25 July to 29 August. The operation started and a set of tests were carried out. These tests enabled the complete adaptation of the system to the specific conditions of olive mills, with special attention was given to the determination of the overall process efficiency and energy and mass balance. In this way, milestone M3: 'Gasification prototype built' was reached. During the operation stage, INYTE was in charge of adjusting the system to an optimal performance level.
Before the arrival of the prototype, its building site at Unioliva was prepared, with the construction of a concrete floor and walls to stabilise the terrain. Furthermore, prunings and leaves were selected and reserved by the staff at Unioliva in order to have all fuels ready for testing.
The prototype parts are as follows: the biomass is fed through the skip charger into feed shell having pneumatic double door assembly and is stored in the hopper. A limited and controlled amount of air for partial combustion enters through the air nozzles. The hearth ensures relatively clean and good quality gas production. The reactor holds charcoal for reduction of partial combustion products while allowing the ash to escape. The dry ash that falls out of reactor gets collected in the slanted table of reactor and from there it is taken out with the help of a screw conveyor. The screw conveyor outlet has a two valve dry ash collection box which holds the dry ash for a particular duration of time. The gas passes through the annulus area of the reactor from upper portion of perforated sheet. The gas outlet is connected with reactor outlet, and then bellow, bellow distance piece, cyclone, cyclone distance piece, Venturi scrubber, wet blower, separation box with gas control valve, heat exchanger with chiller, mist eliminator, parallel set of fine filters and pleated filters, header box with flare assembly and fully closed valve (FCV) valves for the engine, in order to facilitate running of the system in ultra clean gas mode. The gas is then brought to the adapted gas motor for the production of electricity.
The modelling and simulation of the process performed prior to the erection of the prototype provided data on the behaviour of the prototype with different fuels:
- Gasifiers as the one installed can handle biomass with moisture contents less than 20% and operate at atmospheric pressure with a reaction temperature about 800-1000ºC. In this specific gasifier, the biomass consumption is around 100 kg h-1 and the average LHV of fuel gas obtained (product gas) is 4.5 - 5.0 MJ Nm-3. Simulation results: air-biomass ratio, fuel consumption, needed air, water consumption, particles, ashes, gasification, electric and overall efficiency and specific air flow for the Otto cycle have been analysed. The CHP system has been modelled with Cycle-Tempo software.
- The gas engine chosen for the is a six cylinder (V-configuration) turbocharged- after cooler engine model Cummins GTA 855 G, supplied originally to operate on dilute natural gas (biogas fuel). These kind engines are marketed as bio-gas engines and are serving as days load power plants. This engine is adopted to operate on producer gas along with a specially designed gas carburetor, built from a diesel engine frame at modified compression ratio (CR) of 8.5 to operate on gaseous fuels in a spark-ignition mode.
This as well as the steps necessary for building the system, plan and schematic drawings for GAS-70 is explained in details in D07 'Gasification prototype built' which was submitted to the EC on 6 December 2010.
Operation
Once the prototype was ready, INYTE, with support from UNIOLIVA started its operation and carried out a set of tests that enabled the complete adaptation of the system to the specific conditions of the olive cooperative, as defined in task 1.2. These tests took into account the preliminary conditions to be met for a profitable exploitation. INYTE was in charge of adjusting the system to an optimal performance level.
ISFTA took part in the measurement campaign during the operation of the prototype. ISFTA brought its equipment (portable gas chromatograph, model of varian CP-4900) to Unioliva in order to measure the producer gas composition in different working modes of the gasifier. During the measurement campaign, ash and fuel samples were be collected and subjected to detailed analysis (major and trace elements, carbon content in ash) in the laboratory of ISFTA in Ptolemais, Greece.
The objective of the measurement campaign was to carry out a thorough assessment of the prototype operation by recording data for several parameters, such as composition of producer gas, pressure drop, temperature, electric output and engine emissions. Moreover, all the accrued results from ash analyses were be studied in order to investigate the alternative valorisation of solid residues into existing industrial practices as well as their environmentally safe disposal in fields or landfills. A technical meeting with personnel of INYTE and Unioliva was scheduled for the end of June in order to discuss all the details of the above campaign.
The only deliverable planned for the period comprised in this report was D8, 'Report on the operation stage of the gasification prototype'. Due to the delay in the delivery of the prototype and therefore, the start of the testing phase, this deliverable could not be finished in the date foreseen in the description of work. A draft version of D8 was, however, prepared and presented on 30 June, with the experimental plan for the months ahead in the testing of the gasification prototype. A final, updated version was submitted on 15 December, with the results obtained.
Gasification result assessment
When the operation period finished, INYTE compiled in month 35 all the results obtained in D10 'Report on the results obtained from the operation of the gasification prototype'. Possible failures in the operation and improvements in the system were proposed at this stage. The necessary improvements were accompanied by a thorough description of the materials and machinery needed. This would enable further implementation and improvement of the system by the SME-AGs. Special attention was given to the determination of the overall process efficiency and energy and mass balance.
A Varian CP4900 gas chromatograph was used by ISFTA in order to measure the composition of producer gas. The GC was calibrated using the following calibration gas mixture of CO:19%, H2:18%, CH4:3%, CO2:8% and N2:52%. Every five minutes (during operation of gasifier at full load) a gas chromatogram was monitored in the PC while pressure drop of gasifier (?PG) and pressure drop of nozzles (?PN) were recorded manually. The same measurement was repeated after 24 hours (second day) in order to check the repeatability of the gas composition results. The average composition of gas was N2:53.1%, O2-Ar:1.33%, H2:24.13%, CH4:4.18%, CO2:4.6% and CO:10.66%. Regarding heating value of gas the following values were calculated HHVgas=6.30 MJ/Nm3 and LHVgas=5.65 MJ/Nm3 taking into account the average values for gas species mole fractions.
Also ISFTA assessed not only the gas quality but also the quantity of ash residues produced from the gasifier. The collected bottom residues of gasification have been tested for their mineralogy by means of X-ray diffraction (XRD) spectroscopy, using a Bruker D8 Advance instrument. The loss on ignition tests were carried out by the use of thermogravimetric analysis (TGA), using a LECO TGA-701 instrument, up to 850°C. The morphology of the collected samples has been investigated by means of scanning electron microscopy, using a JSM-6300 JEOL instrument. The calorific value of the samples was determined through the calorimeter of LECO, model AC-350 whereas the chlorine and sulphur content of samples was determined through the use of photometric and turbidimetric method (Hach Lange, model DR2800). Finally, heavy metals were determined by flame atomic absorption spectrometry of Shimatzu (model AA-6300), after complete digestion of samples with an acid mixture of HCl/H2SO4 in a microwave oven.
According to the results, the char obtained from the gasification cannot be compared to the usual chars obtained through other similar gasification processes found elsewhere. The high operation temperature of the gasifier combined with the use of olive kernel residues results in chars with quite high thermal content and unburnt carbon. Due to this enhanced energy loss occurring in the gasifier, an optimisation of the gasifier operating conditions may be required. Since the gasifier is specifically designed for wood chips, the efficient system performance should be adapted to the specific fuel properties of olive kernel residues or prunings. This could mean changing the operation temperature, the air-fuel ratio etc.
However, if the gasifier keeps running in this mode then two alternatives seem to be the most promising for the optimal utilisation of its residues: use as a fuel and as a precursor for the production of activated carbons.
Based on the high calorific value of the bottom gasification residue - which can be safely considered biochar - its relatively low moisture content, and its high loss-on-ignition value, it is concluded that it can be utilised as a primary fuel for combustion boilers in the energy sector. Moreover, Cl is highly volatile and has been released early in the gasification process. This reduced chlorine content of the residue combined with the low sulphur percentages suggests minimal corrosion problems to the boiler. Additional to the low-corrosion-probability, the absence of quartz reveals a low-erosion-probability. On the other hand, a major drawback is the quite low initial deformation temperature (IDT) coming from the eutectic minerals of biochar. This is a basic factor for high slagging potential and should be seriously considered when used in a combustion installation.
Due to the highly porous structure of the residues and the high amount of unburnt carbon, an alternative utilisation option for these olive kernel gasification residues may be their use as precursors for activated carbons production. The special characteristics of these chars make attractive the possibilities of obtaining activated carbons directly from the gasification process or through upgrading of the resulting char. Since the demand for activated carbons is growing, it is very promising and interesting to convert the gasification process residues to high value-added products, particularly considering that low cost input materials could result in the production of high value end-product.
Anaerobic digestion
Lab scale anaerobic digestion tests
Anaerobic digestion presents a high potential for the biological disposal of OMWW. However, this technology presents many different options that so far have not been compared and ranked by their requirements and advantages therefore, there was a need of further information before it is fully implemented in olive mills.
TTZ carried out a series of tests and analyses at their facilities in order to determine three important parameters for the optimisation of anaerobic digestion:
- Substrates to be used: olive mill waste, pruning rests (twigs and leaves), and mixtures of both.
- Possible additives to be used: in some cases it has been reported that the addition of other components to the reactor feed improves the final gas yield. Possible additives, such as other agricultural wastes, were studied.
- Possible pre-treatment requirements. In many cases, hard substrates rich in lignin and hemicellulose require a mechanical, chemical or enzymatic pre-treatment that enables the conversion of these compounds into the final product, like crushing, NaOH baths or treatment with cellulases and hemicellulases.
This stage comprised preliminary tests, to select the best options, followed by batch test analysis to know the production of biogas and biogas composition in each of them.
The results obtained showed that olive mill wastes were quantitatively degraded to biogas during the anaerobic digestion and moreover, during the co-digestion with different co substrates which have been undergone in some case specific pre-treatments.
These results demonstrate that the co-fermentation tests have been satisfactory and justify the initial thesis being tested, that an improvement of the biogas yield and especially for the methane yield could be observed.
The best results were obtained with two-phase pomace mixed, the production of methane increases 25 Nml/goTS from the value observed in the simple anaerobic digestion and co-digestion (i.e. cow manure as co-substrate) concerning pomace from two-phase process. A biogas production of 262 Nml/goTS or 85 Nml/g FM was obtained, and potential produced methane was set about 110 Nml/goTS or 36 Nml/g FM. However, a considerable biogas quality of 61% has been proven. This is due to the fact that hen litter provides nutrients essential for the microbial consortia for an optimum fermentation.
For the case of pomace from three-phase process, the chemical and enzymatic pre-treatment of this waste before its anaerobic digestion presents many advantages since the organic dry matter removal after fermentation can reach up to 65%. The biogas production of pre-treated three-phase pomace was 283,72Nml/g oTS and the corresponding potential methane production was 174 Nml/g oTS. Moreover, the absence or the slight inhibition shows that a steady microbiological system has been enhanced.
For the olive mil waste water two-phases process, two fermentation tests systems present comparable results, co-digestion of OMWW and pomace and the OMWW and hen litter (HL). Both systems show, respectively, an average methane potential production of 229 Nml/g oTS and 223Nml/goTS; however, the system (OMWW + hen litter (HL)) proves a better microbial synergy since no strong inhibition has been observed in the three vessels during the batch test. On the other hand, the organic removal of this both systems stays insufficient (9 to 24%).
The results of this stage were compiled in deliverable D06 'Report on the anaerobic digestion phase', which was submitted to the EC in 30 April 2010, and D09, 'Report on the results from anaerobic digestion stage', submitted on 30 June 2010 The accomplishment of this task completed Milestone M2: 'Anaerobic digestion stage completed'.
Result assessment
TTZ appraised the results obtained in the previous months. The values obtained for each of the substrate possibilities tested were presented, comparing the performance in biogas production and quality of the gas obtained against the stability of the system.
The results obtained for anaerobic digestion were tested against the theoretical performance indicators as well as the different pre-treatments. The results obtained showed that olive mill wastes were quantitatively degraded to biogas during the anaerobic digestion and moreover, during the co-digestion with different co substrates which have been undergone in some case specific pre-treatments. These results demonstrate that the co-fermentation tests have been satisfactory and justify the initial thesis being tested, that an improvement of the biogas yield and especially for the methane yield could be observed.
The best results were obtained with two-phase pomace mixed, the production of methane increases 25 Nml/goTS from the value observed in the simple anaerobic digestion and co-digestion (i.e. cow manure as co-substrate) concerning pomace from two-phase process. A biogas production of 262 Nml/goTS or 85 Nml/g FM was obtained, and potential produced methane was set about 110 Nml/goTS or 36 Nml/g FM. However, a considerable biogas quality of 61% has been proven. This is due to the fact that hen litter provides nutrients essential for the microbial consortia for an optimum fermentation.
For the case of pomace from three-phase process, the chemical and enzymatic pre-treatment of this waste before its anaerobic digestion presents many advantages since the organic dry matter removal after fermentation can reach up to 65%. The biogas production of pre-treated three-phase pomace was 283,72Nml/g oTS and the corresponding potential methane production was 174 Nml/g oTS. Moreover, the absence or the slight inhibition shows that a steady microbiological system has been enhanced.
These results were also used for the economic assessment in task 4.4. The results of this task are compiled in Deliverable D9 'Report on the results from anaerobic digestion stage'; the final version of which was submitted to the EC by on 30 June 2010.
Alternative technologies
The most interesting technologies for the valorisation and reuse of OMW were evaluated in order to provide some possible solutions for those SME and territories where it is not possible to introduce the gasification prototype or anaerobic digestion. The structure used in this task was planned to provide results in a user-friendly form. Particular importance was given to the experiences available in literature in order to allow an easy understanding of the opportunity and feasibility of each technology proposed. A description of the all the alternative technology/reuses of OMWs, excluding gasification technology, was reported in deliverable D11.
Conclusions were made that the examined alternative technologies could be divided into two groups: the first one represents the alternatives which have an application at the present; the second one represents the alternatives which could have an interest in the future but which need more knowledge to improve their implementation. In the first group the main possible reuses are production of energy (i.e. briquetting and co-combustion), production of fertiliser, production of nursery substrates, and animal feeding. The best solutions for the reuse of OMW are diverse because of the vast differences among physical and chemical characteristics of OMWs (above all due to extraction system) and the complex scenario where OMWs are produced (above all oil mill size). For example, another alternative is the recuperation of valuable chemical compounds (polyphenols for the cosmetic industry) with membrane systems, but at a relative high price. Therefore, the possible application of each analyzed alternative is evaluated in relation to the economic, structural and cultural characteristics of each olive mill. The following four alternative uses and technologies which must be applied to treat the residues for such purposes were analysed in depth: as fertiliser/soil conditioner, organic compound recovery, as animal feed, and as energy from direct combustion.
Use as fertiliser / soil conditioner and compost for plant nurseries
From the prospective of its fertilising value, olive residue has a positive effect due to its high content of nitrogen, phosphorus, potassium and magnesium. The high organic matter content and its degree of humidification improves the physical and chemical properties of soil, which is important, given the progressive decrease in the organic matter content of soils subjected to intensive cultivation.
Here it is considered the recovery of the biomass (pruning, husks, wastewater) to obtain a quality product (compost) through a controlled and sustainable process that can partially or completely replace peat for producing potting substrates. Composting is a technique through which organic matter is decomposed. The proposed case study has been finalised in order to obtain quality compost, cheap and easily available, to use as fertiliser in the open field, or as a potting substrate in the nursery. The compost obtained can be produced through a composting process carried out in cumulus, on a cement platform. Results from the analysis show that:
- For spreading on soil as fertiliser and soil conditioner, it is particularly suitable for all owners of small and medium-sised olive mills who also own farmland. If laws are respected, cost are very low considering the gain of waste disposal and improvement of CO2 storage in the soil.
- For composting, It is particularly suitable for small and medium sized olive mill If laws are respected, cost are very low considering the gain of waste disposal and improvement of CO2 storage in the soil. In nurseries the compost can be used with appropriate% as a substitute for peat and they can be an adequate market for compost.
Recovery of organic compounds
Membrane technology offers several advantages (low energy consumption, no additive requirements, no phase change) over traditional techniques to recover phenolic compounds from OMWs. The performance OMW treatment by membrane filtration finalised to the recovery of polyphenols has been evaluated and this methodology was chosen because it has been patented and applied in different situations. This would reduce the cost of water disposal; it would provide flexibility in treatment and reuse technology for other applications during periods of non-olive milling. With regard to the economic analysis, it is particularly suitable for all owners of small and medium-sized two-phase oil mills. The initial cost is proportional to the amount of processed olives. It could be easily developed where there is market for cosmetics and medicine-based polyphenols. Since the membrane methodology does not change with the sizes of the olive mill (but change the initial costs of investment and working hours), the technology can be applied in different situations, from little-medium-sized mill to big one.
Use as animal feed
Some olive mill wastes can be used as animal feedstuff. OMWs have low digeribility and high content in compounds such as phenols which may be toxic for animals. Among OMWs, olive cake is indicated in scientific literature as the most suitable for such reuse because of the low content in phenols and water. Generally, no pre-treatments are needed even though for storage period longer than 15 days ensilage is recommended.
In the economic analysis, three study cases were considered (administration of olive cake to: lactating ewes, lactating cows and grazing lambs). Savings on the normal diet due to the introduction of olive cake were between EUR 27 and 161/ton for administration to lactating cows and grazing lambs, respectively. These results were estimated as the sum of diet cost reduction and the results (milk yield and live weight gain) obtained with administration thesis in comparison with normal diet. No transport cost or ensiling cost were added and a selling price was estimated as the half of the previous value, in order to allow a margin to both the seller (olive mill) and the animal raiser. On the other hand, such reuse requires large number of animals close to the plant where olive cake is produced. This because of the low daily intake of olive cake reported in literature and the transport cost which greatly varied depending on the distance and the viability. This suggests that such reuse may be affordable for traditional extraction plants (which generally yield olive cake and low volume of OMWs). Finally it should be considered that permits are needed for selling OMW as feedstuff. This could represent a barrier for olive mills.
As conclusion, olive mill wastes used as animal feedstuff could be affordable in olive mills which yield a low amount of OMW and in which extraction system yields a dry cake (pressure systems and three-phase olive mill). According to the economic analysis, profitability level could be considered interesting, but it should be taken into account that OMW intake per animal is fairly low. For this reason, it can be profitable on large scale only if animals could be potentially fed with it are largely available nearby the olive mill (<10 km in order to limit transport costs). Finally, it is largely advisable in case of farms in which both, olive mill and animal rising activity are just carried out.
Energy use with direct combustion
Waste treatment technologies aimed at direct energy production may represent an interesting alternative for the sustainable disposal of residues from olive oil production, able to reduce the environmental impact and generate electric energy for sale or to satisfy the needs of olive mills, when gasification technology find local or technical constrains in being adopted. The residual biomass from olive processing with potential energy use with pyrolysis technology (direct combustion) is classified into two groups. The first is constituted by residual biomass produced during olive tree cultivation (pruning and harvest residues). The second is made up of residual biomass produced during the various stages of the olive oil extraction process. The available energy from the by-product differs according to the extraction system. For instance, exhausted olive cake and TPOMW are characterised by an average heating value of 19 000 and 14 000 kJ/kg, respectively. Efficient use of olive cake in energy production solves two problems in one step: clean energy production and acceptable disposal of olive oil mill waste.
The pomace and pit can be used to produce electric and thermal energy or both (co-generation).The production of electric energy is accompanied by that of heat; therefore, it is also possible to produce thermal energy in conjunction with electric energy.
The boilers can be small size (below20 - 30 kW), medium size (30 to 100 kW) and large size (above 100 kW).
As conclusion, olive mill wastes used as energy source with pyrolysis technology is suitable for all kinds of olive mills. In case of small olive mill, energy produced can be used by the company itself or by private homes nearby the plant. In case of medium and large olive mills, energy can be also sold to the grid. Dry material can be sold as burning material to other customer.
Comprising pioneer countries in olive oil production throughout history, the European Union is the main olive oil producer in the world. The figures show that 80.2% of the world production, 2.056.200 tons, were produced in the countries of the Mediterranean region.
The European olive oil sector is nowadays facing several stresses that push towards the need of a new approach to production. Despite worldwide consumption rises (due to the acknowledgement of the consumers of olive oil's beneficial effects for health); new producer countries like Turkey, Syria and Tunisia enter the markets and increase competition, threatening European producers' dominant position.
Besides, the olive oil industry is defined by the polluting character of its residues, of which about 5.8 million tons are produced annually. This poses serious problems to the olive mills, especially in the case of small and medium ones. Actors from all the groups involved agree on the need for a more sustainable approach to production schemes, where environmental conditions are taken into consideration without damaging productivity.
In this sense, in the last years there has been new research exploring the possibilities of further use of the residues, olive mill waste water and olive pomace, and initiatives to provide solutions to the industry. Even though efforts have been made so far for bringing the results obtained to practice, many local producers associations still lack a clear guidance adapted to their needs in specific fields, resulting in giving up the implementation of these activities after the institutional framework which supported it disappears.
Against this situation, the proposing IAGs have attempted to take an integrated and more proactive approach to the problem: This polluting charge of olive mill waste (OMW) can be taken as an advantage to produce energy from it: olive mill solid waste has a wide range of uses in renewable energy: it can, for instance, be gasified to obtain hydrogen and CO, digested in an anaerobic process to obtain methane, or directly used in combustion.
Other processes to obtain a valuable outcome from olive mill residues: Solid residues can also be used, once properly processed, for animal feeding, or composted to be used in agriculture as a natural, chemical-free fertiliser.
In the light of such stresses, polluting characteristics and energy recovery opportunities pertaining to the olive oil sector, RESOLIVE aims at achieving the following objectives:
Overall objectives:
- To define the specific conditions for the implementation of renewable energy solutions specific to the olive oil industry.
- To enable the producers and their associations more independence from centralised energy systems.
- To increase the competitiveness of the European olive industry through the accession to state-of-the-art technologies.
Scientific and technological objectives:
- To build a prototype gasification system combined with a 30kW microturbine production to demonstrate its performance using different olive industry wastes as fuel.
- To carry out a full program of laboratory scale tests on anaerobic digestion to optimise the existing techniques for biogas production, which will enable producers to its implementation.
- To collect information about other renewable energy solutions for the industry, successful stories and implementation ranges.
Socio-economic objectives:
- To answer to the current need to increase the sustainability of European agricultural sectors by implementing solutions which result in a valuable output (in this case, energy) from their waste.
- To reduce production costs in the olive oil sector in the current scenario of constantly increasing prices of energy.
- To summarise the existing knowledge in olive waste valorisation by month 30 and transfer this knowledge to its end users (expected date of accomplishment, month 36), supporting them in the further implementation.
- To create a comprehensive set of guidelines by month 31 of the project that will advise the associates of olive oil producers' cooperatives deciding which of the available options for the implementation of renewable energy suits their conditions best.
- To enable the olive oil producers in Europe access to a new market: electricity production.
- To increase employment in the sector by capacity building in state-of-the-art technologies and creation of new jobs in the operation of the proposed systems.
Below, the entire structure of the RESOLIVE project is found, showing research focus areas and targets divided in its work packages (WPs).
WP1: Information assessment
This WP is the first devoted to research and technological development activities and was scheduled to be developed from month 1 of the project to month 12 and led by UNIPG. It was divided into 2 tasks that had the following main objectives:
- characterisation of needs and constraints of the sector,
- screening of current technologies.
WP2: Definition of prototype requirements
The main objective of this WP was to deal with the analyses necessary for the adaptation of the gasification system to the specific system conditions and to carry out the preliminary characterisations for the anaerobic digestion phase. WP2 was scheduled from month 4 to month 20 of the project. The WP leader was ISFTA. It was divided into six tasks that had the following objectives:
- chemical characterisation and analysis of the feedstock,
- gasification prototype placement,
- gasification prototype connection to the grid,
- gasification system modelling and analysis,
- gasification prototype design,
- lab scale anaerobic digestion tests.
The results obtained in these tasks showed that the proposed technologies for the prototype (gasification and microturbine) were not appropriate for the feedstocks to be used in RESOLIVE, which led to the request for an amendment in the description of work. Further details are given under the full descriptions of WP2, 3 and 7.
WP3: Prototype building and operation
WP3 was scheduled to be developed from month 15 to month 29 of the project, led by INYTE. The main objective of WP 3 was the process of building and operation of the gasification prototype. It was divided into two tasks with the following objectives:
- building of the gasification prototype,
- operation period of the gasification prototype.
The change in the technology used for the prototype during WP2 entailed a restructuring of this WP and the works on each task. Further details are given under the full description of WP7.
WP4: Assessment of operation stage results
WP4 is led by project partner INYTE and was scheduled to be developed from month 13 to month 34 of the project. It was divided into five tasks having the following main aims:
- assessment of the anaerobic digestion results,
- assessment of the gasification results,
- review of alternative technologies,
- economic analysis,
- preparation of operation manuals and result summaries.
From these, and due to the amendment of the DoW, only the first has started. The partners agreed in starting the economic analysis of the anaerobic digestion technology before planned in order to gain time and avoid further delays in the future.
WP6: Dissemination
This WP is devoted to dissemination activities and is expected to run continuously throughout the project, led by UNIOLIVA. It is divided into seven tasks that have the following objectives:
- setup and maintenance of the project web page,
- preparation of project dissemination materials,
- preparing RESOLIVE guidelines and materials for results dissemination,
- attending conferences and sectorial fairs,
- dissemination activities which are SME-oriented,
- organisation of national workshops on sustainable approaches in olive oil production,
- definition of a knowledge and IPR management permanent structure.
WP7: Project management
The aim of WP7 is to ensure an effective project management and co-ordination over the entire project duration. The work package was scheduled to cover the period from month 1 to month 36 of the project and is led by TTZ. It is divided into 3 main tasks with the following objectives:
- executive project coordination,
- general and financial project coordination,
- scientific project coordination.
Project results:
At the start of the project, needs and constraints of the olive-oil sector were characterised, collecting necessary information to adapt both the proposed systems, gasification and anaerobic digestion, to the real conditions found in olive mills throughout the producer countries in Europe. These two systems offer solutions for the olive residue treatment, at the same time, produce a valuable energy output for the mill or the electricity grid. Four alternatives to gasification and anaerobic digestion were also defined as use as fertiliser/soil conditioner and compost for plant nurseries, recovery of organic compounds, energy use with direct combustion and finally, use as animal feed. ttz started compiling relevant information on the olive oil sector in the main European producer countries. The search was divided between production methods and legislation concerning environmental risks that the production has to comply with. The information was completed with the collaboration of UNIPG. CERTH/ ISFTA contributed providing information on the needs and capacities of the olive mills and cooperatives in Greece. National statistics services were also contacted, providing data on olive products from the main olive oil production
Following a literature review, a comparison between two-phase decanting and three-phase decanting was completed along with data on the status of the olive oil sector in Greece, Spain, Portugal and Italy, comprising surface dedicated to this crop, irrigation, quality and amounts and composition of by-products. The critical issue of the disposal of by-products was analysed and the existing legislation concerning limiting values for the discharges of wastewaters were investigated.
Finally, social constrains regarding data for gross production in terms of product value were presented for the needs of this task.
All IAG partners (Paseges, Unioliva, Unaprol, Ceolpe and Vilaflor) participated in the validation of the information gathered. Finally, the conclusions were drawn with the help of the rest RTD and IAG partners. Deliverable 1, report on needs and constraints of the sector, was submitted to the Commission officers on 17 June 2009.
In a second step, UNIPG developed an intensive screening of research activity on current technologies for olive waste reuse and valorisation. They verified the best practices and the gaps in this field. This activity has been developed also in cooperation with task 1.1 leader (ttz). CERTH/ISFTA provided support on defining the technologies, the best practices worldwide and the gaps in knowledge that need to be overcome to reach full implementation status.
In addition, a literature review was carried out about the use of olive oil residues in the energy sector and specifically considered the potential of using this type of material as an alternative source for solid biofuels. Conventional combustion of residues from olive and olive oil production is already applicable in many regions. Based on the accumulated knowledge on previous and current projects for the energy exploitation of olive residues, the combustion technology is most widely applied. The potential of replacing this technology with a new one such as RESOLIVE proposes, under more 'environmental friendly' terms, is examined in this task, and biomass gasification process is presented in details along with gasifier types, including bubbling fluidised bed, circulating fluidised bed, fixed-bed and entrained flow reactor type. Furthermore, data concerning olive kernel gasification from the scientific literature and studies for olive kernel thermochemical conversion are reported in this task.
Finally, UNIPG included a SWOT analysis for those alternative uses of olive mill residues which show promising results so far, such as the extraction of organic compounds or the reuse of solid OMW as an amendment, fertiliser, herbicide or pesticide. Also, Deliverable 2 provides suggestions for further research on this topic, submitted to the European Commission on 8 January 2010.
Gasification
Prototype requirements
The prototype requirements were determined, including preliminary chemical analyses, pre-engineering and integration of the equipment, electric and heat transfer system, specifying equipment, parts, biomass fuels and lab materials for purchase, detailing a variety and range of parameters to be tested, specify data collection protocols, and data analysis methodologies.
The initial plan in the project was using a catalytic combustor enabled the microturbine to operate directly on low-Btu, low-pressure gas. However, the results obtained after tasks 2.1 ('Chemical characterisation and analysis of the feedstock') and 2.4 ('Gasification system modelling and analysis') confirmed that this would not be a feasible solution. As explained in the draft version of D05 submitted to the EC in April, 2010, the gasification product gas obtained with the substrates used in the project has about 10-20% of hydrogen. It has been indicated that the flashback produced in the microturbine by the hydrogen would cause malfunction and permanent damage. For this reason the partners concluded that the best solution to keep intact the initial objectives of the project was to adapt the prototype, using another power producing unit in the design instead of the microturbine. Based on the offers from other manufacturers and the research of the RTDs, the technical solution chosen, and proposed in the request for amendment to the EC was a gasifier with a gas engine.
Chemical characterisation and lab-scale tests were realised in ISFTA's facilities in order to evaluate gasification behaviour of the examined feedstocks. The following properties were measured: moisture content, proximate (thermo-chemical behaviour) and ultimate (elemental composition) analyses, calorific values and ash analyses. These analyses provide information on the volatility of the feedstock, its elemental analysis and heat content.
A variety of materials were supplied by PEZA, Unioliva, Sabina, Ceolpe, Melambianakis and Vilaflor, in order to achieve a significant number of feedstocks. Based on the chemical characterisation the most promising feedstocks were selected for the gasification experiments. A six-month delay was attained on the completion of the experiments since not all the samples had been delivered to ISFTA in due time course, while some adjustments on the fluidised bed facility were considered necessary to secure the safe and continuous supply of the biomass feedstock.
Prior to the fluidised bed gasification experiments, some cold tests were considered necessary in order to determine the operational conditions of the installation for optimum performance. The reactor was constructed from stainless steel cylindrical tube of 8.9 cm ID and 1.3 m in height, placed in an electrically heated oven.
Two sets of gasification experiments were performed using quartz sand and olivine for bed material for each biomass fuel. Taking into account the similarities of the composition of the examined fuels, experiments were conducted with representative materials Unioliva - leaves and prunings and Melambinakis - dry olive cake.
The results from the gasification experiments showed that olivine promotes H2 and CO2 formation and lowers CO. For similar air ratios the methane yield appears slightly lower with olivine. Olivine more significantly drops the amount of tars in the gas in all cases. Operation at 800°C derives slightly less tars than 770°C. Tars drop sharply with higher air, but so does the quality of the product gas (H2 and CO drop in favour of CO2 and H2O). The use of olivine significantly reduces the tar levels produced and is recommended for the application.
From the gasification tests it can be concluded that the product gas quality ranges between the following minimum and maximum (better) quality:
Based on the specifications of the commercially available micro gas turbines (Capstone) the gas has to be pressurised and cleaned but also the following criteria have to be met for low hydrogen content. There are even more strict specifications for tars which cannot be matched with gasification. Nevertheless, the operation of a micro gas turbine with product gas is theoretically feasible. The gasifier needs to be operated at pressures around 5 bar. An alternative option is to employ an atmospheric gasifier with an alternative power production other than the micro gas turbine (MGT) (i.e. solid oxide fuel cells or gas engine). So, the results is that either commercial MGT needs to be modified (feasible solution not recommended under the framework of the project) or change the MGT with another power producing unit in the design. As explained in the introduction of the work package, the partners decided, after discussing the best options internally and with the EC officers, to request a change in the technologies, using another power producing unit in the design instead of the microturbine. Based on the offers from other manufacturers and the research of the RTDs, the technical solution chosen, and proposed in the request for amendment to the EC was a gasifier with a gas engine.
In the proposed system, the hot fuel gases and the entrained ash/char are cooled in a tube-and-shell heat exchanger. Hot gas enters the heat exchanger at about 700°C and is cooled to approximately 100°C. The fuel gas flows inside of the tubes and a cooling fluid (liquid or air) on the shell side. There are clean out ports to allow inspection and cleaning of the tubes.
For woody biomass the clean fuel gas typically has an energy content of about 120 to 165 Btu/cu ft. The fuel gas is composed of about 20% CO, 20% H2 and 2% CH4. A pound of dry biomass will produce about 50 cubic ft of producer gas. The feedstock enters through the top of the downdraft gasifier. The control system will call for dry feed to be added on top of this flaming pyrolysis zone automatically when system temperatures reach required levels. As the feedstock particles approach the flaming pyrolysis zone, they are heated and dried, losing their moisture as steam. This steam and the gasification air that is automatically delivered travel quickly to the flaming pyrolysis zone below. As the feedstock particles travel further downward, they are heated to pyrolysis temperatures and begin to emit pyrolysis vapours. The combustion gases and residual tar vapours then travel down to the char oxidation zone, along with the char formed in the flaming pyrolysis zone.
In the char oxidation zone, secondary air is added by computer control to oxidise the char, producing carbon dioxide and heat. In the steady-state condition of the gasifier, the temperatures of the char oxidation zone are moderated by the endothermic reactions of steam and char to form hydrogen and carbon monoxide, as well as, carbon dioxide reacting with char to form carbon monoxide. These temperature-moderating reactions increase faster at the higher temperatures of this zone. The hot char and ash surfaces, along with free radicals present in this zone catalyse the destruction of the residual tar vapours.
The results from this task are compiled in D03 'Report on the results of chemical characterisation of fuels and lab scale gasification tests' which was submitted in month 8.
Prototype placement
INYTE, with the cooperation of Unioliva, worked in the land assessment for deciding the best placement for the prototype. Unioliva provided information on their facilities, which was then assessed using an AI-based method to determine the optimal supply area and location for an electric generation system based on biomass. The proposed AI-based method is a discrete binary version of the PSO algorithm, which makes use of the profitability index as objective function. The proposed approach assessed the land available to the cooperative or olive mill, dividing it in lots of the same area assessing their suitability with regard to several variables. This method reached convergence in a few iterations, which is equivalent to a computational cost more than a thousand times lower than that required for exhaustive on site comparison.
The region considered to apply the proposed method was the area of Úbeda, it was divided in 128 ×128 = 16.384 square parcels of constant surface, Si = 0.09766 km2. In particular, Úbeda is a town in the province of Jaén, in Spain's autonomous community of Andalusia. Úbeda has become in one of the biggest olive oil's producers and packers of the Jaén province. The Úbeda extension is 397-400 km2 approximately. The city is near the geographic centre of the province of Jaén, and it is the administrative seat of the surrounding 'Loma de Úbeda comarca'. The agricultural economy mainly works with olive cultivation and cattle ranching.
The results showed the optimal location of the biomass power plant for the best found solution and the profitability index evolution.
The permits and administrative procedures that need to be fulfilled to comply with the legislation in each of the countries addressed were also obtained. Paseges found this information for Greece. UNAPROL worked in the permits needed in Italy. Unioliva, with support of Ceolpe provided information on the administrative procedures for Spain and Vilaflor took over this task for Portugal. ttz provided these partners with extra support in this task. The results of task 2.2 were compiled in D04 'Prototype placement and connection to the grid report', explaining the method used for finding the best location for the prototype, which was submitted to the EC in October, 2009.
Prototype connection to the grid
Technical details were taken into consideration for the connection of the gasification prototype to the grid, as well as with the legislative framework in force in each of the countries addressed by the project regarding renewable energies production and connection of the necessary licenses to connect to the grid and act as an electricity provider.
INYTE carried out the task, with support from the IAG partners and ttz. The main role of INYTE was the preparation of the technical descriptions, and the IAGs provided information about the legal frameworks in their countries, which was supported by ttz.
The gasification system is intended to work for the production of energy for the own consumption of the association where it is placed. However, it is possible to connect the system to the grid so the olive mill becomes an energy provider. This possibility and the engineering needed to achieve it were defined by INYTE. CERTH/ISFTA provided support to INYTE in the engineering study of the system connection to the grid.
A microturbine is small gas turbine engine-generator, typically sized 25-500kW. The technologies for microturbine are evolved from automotive and truck turbochargers, auxiliary power units for airplanes, and small jet engines. A frequency inversion is required before a microturbine could be connected to the grid system. For the microturbine to self-support its own power usage (auxiliary supply), the power is supplied from the DC link between the rectifier and the inverter for the frequency inversion.
A digital controller is required in the microturbine package to control the microturbine's operation and function. The common type of digital controller is the programmable logic controller (PLC). A protective device is included as well.
The procedure for grid connection is basically as follows. In a feasibility study the network operator examines whether the system conditions prevalent at the planned point of connection are technically sufficient for operation of the generating unit.
Should the system conditions suffice for operation, the network operator submits a verifiable offer as to the network connection scheme. Should the system conditions at the system point of connection not be adequate, the network operator furnishes evidence of this inadequacy
Then, the network operator, together with the connection holder, examines appropriate modifications, such as network reinforcements. Following this feasibility study, a formal connection offer is made, and, if accepted, leads to detailed design work to determine the final connection charge and additional requirements. Eventually the project is commissioned.
As a result, the chapter dealing with these issues in D04 summarised the administrative procedures to follow in order to use the electricity produced by the prototype in the national grid. Special attention has been given to bonuses devised by the different administrations to foster renewable energies.
Deliverable 4 'Prototype placement and connection to the grid report' was submitted as planned on 31.10.2009 to the EC.
Gasification system modelling and analysis
Prior to the final design of the prototype, thermodynamic calculations aiming to improve the performance of the gasification unit was carried out by ISFTA. Microturbine thermodynamic cycle was modelled with the aid of GateCycle software which can handle more precisely advanced cycle calculations. The proposed system consists of one fluidised bed reactor thermally coupled with heat pipes, a product gas cleaning train and a micro gas turbine.
A steady state air gasifier model was composed to assess average gas compositions and perform heat and mass balance calculations. The air gasifier was modelled based on the combination of unit operations: biomass decomposition into its constituents and reaction of them with air. Char and methane formation was taken into account, while equilibrium reactions for the rest of the biomass components were considered by minimisation of the Gibb's free energy.
Pressurised gasification is in general advantageous compared to atmospheric when considering the utilisation of the product gas in gas turbines or fuel cells, since considerable savings occur from reductions in equipment size and avoidance of warm product gas compression power, while tar removal or cracking is not a major issue anymore, as the gas compressor, which is directly affected by tar condensation, is no longer necessary. Even a slightly pressurised operation (around 5 bar) is advantageous in the case of micro gas turbine utilisation with the gasifier. Two pressure levels have been tested in this study, near atmospheric and 4 bars, in order to establish the optimum operation in view of product gas quality.
From a thermodynamic point of view, biomass air gasification processes should be accomplished with the minimum air necessary for maximising carbon conversion. Increasing the gasifier temperature and, therefore, ER has an overall negative effect on the exergetic efficiency because major chemical exergy carrier components, i.e. combustibles in the product gas are minimised. Nevertheless, kinetic reasons such as advancement of tar reforming reactions, fluidisation limitations or heat losses might impose higher ER values in practice. The gasifier temperature was chosen as 1080 K, while two pressure levels were considered: 1.5 bar and 4 bars. The corresponding ER value in both atmospheric and pressurised modes of operation is 0.37. The model predicts a very slight exergetic effectiveness increase in the case of pressurised gasification. A higher moisture fuel would result in a penalty on the gasification efficiency because of dilution of the product gas.
As a concluding remark, gasification operates slightly better at elevated pressures, requiring less air flow and demonstrating a slightly improved efficiency over atmospheric operation, provided the carbon conversion is complete.
In the same task the existence of a gas cleaning stage had to be investigated by ISFTA. Gas cleaning is a critical step for the success of RESOLIVE gasification project and any other modular small biomass gasification unit. The stage of gas cleaning is necessary in order to remove some undesirable constituents such as:
- particles (char particles, ash and bed material),
- alkali metals (Na and K),
- nitrogen compounds,
- tars,
- sulphur and Chloride compounds, (H2S, COS and HCl).
The actual gas cleaning design for RESOLIVE is based on the following technologies and is under development. Figure 3 gives a comparative presentation of the different existing gas cleaning technologies that need to be combined for efficient gas cleaning.
Modelling of product gas thermal pathway in equilibrium phase with a typical set of initial contaminant values and calculations performed for a series of temperatures as the product gas might be gradually cooled as it exits the gasifier till it enters the turbine combustion chamber. Calculations were performed at higher operating pressures of the RESOLIVE reactor i.e. 3 bar. The operating temperature of the RESOLIVE gasification system was set at 800°C.
The main conclusions from this work can be summarised in the following way:
- To condense and, hence, remove alkalis by barrier filtration, temperature of 600°C or below must be reached. Tars will start to condense below 200°C. Tar condensation should be avoided, since sticky condensed tar material will destroy the filter elements.
- To reduce tar content, tar cracking or reforming must be employed in addition to cooling. Cooling alone will reduce tars to ppm values only if ambient temperatures are reached. If secondary catalysts are used, these must be tolerant to alkalis or else these should be employed after the alkali cleaning (<600°C). If higher temperatures for tar cracking are required then alkali tolerant catalysts should be employed or a catalytic bed reheating from the combustion bed of the RESOLIVE system.
- The product gas should be fed to the turbine at a temperature as high as possible. According to reported data this feed temperature value could be up to 600°C, i.e. a gaseous-tar tolerant turbine could be fed with the product gas immediately after the hot gas filtration (provided no NH3, H2S, HCl cleaning is required).
- If hot gas cleaning of NH3, H2S, HCl by sorbents is pursued these should be able to clean the gas from temperatures of 600°C (Alkali condensation) down to 200°C (tar condensation).
Before the microturbine modelling was carried out, a list of the leading microturbine manufactures was prepared along with the main technical characteristics of their products. In addition, economics of microturbines was investigated in order of capital cost, O&M cost and maintenance interval.
Furthermore, a literature review regarding the operation of microturbines using biomass as primary fuel, took place before the thermodynamic simulation, in order to identify possible issues that may need to pay more attention during the simulation and to lead in a complete study of the microturbine thermodynamic cycle.
Various microturbine models were analysed with the aid of Gate Cycle.
Several runs took place trying to optimise thermodynamic performance of gasification unit, changing variables such as pressure ratio at the compressor, air inlet temperature at combustor, exhaust gas temperature etc. in different power outputs. Due to the correlation between the system's efficiency and the temperature of the combustor, the temperature cases ranging from 1123 K to 1227 K were investigated.
A parametric study was applied in order to optimise the model and achieve higher efficiency level. Increases in turbine inlet temperature rapidly increase the power output of the turbine and to a lesser extent increase efficiency. The results for various inlet temperatures indicated that the optimum compressor's pressure ratio ranges from 1:4 to 1:5. Also the impact of recuperator on efficiency is important. Optimising recuperator's effectiveness better system efficiency can be assessed. The ambient conditions at the inlet of microturbine affect both the power output and efficiency. At inlet air temperatures above 288 K, both the power and efficiency decrease. The power decreases due to the decreased air density with increasing temperature, and the efficiency decreases because the compressor requires more power to compress higher temperature air. Similarly at high altitudes where air density is lower, power output and efficiency are also lower. Finally, the impact of fuel inlet temperature on efficiency is examined. As expected higher inlet fuel temperatures give higher efficiency while higher values for gasification outlet gas temperatures are desired.
In general the thermodynamic efficiency of the microturbine cycle can be improved by increasing the turbine inlet (or firing) temperatures, increasing the efficiencies of turbomachinery components (turbines and compressors) and by adding modifications to the basic cycle (intercooling, recuperation and reheating).
A short delay was necessary for the completion of this task due to the extensive data required accomplishing the modelling results, and thus the higher man-effort required compared to the initial projection. The results of this task were included in D05 ('Gasification prototype design'), which was prepared under task 2.5. Results of this task are also included in a publication (in press) of Vera, Jurado, Panopoulos, Grammelis in the International Journal of Energy Research with the following title, 'Modelling of biomass gasifier and microturbine for the olive oil industry'.
Prototype design
Based on the specifications provided by CERTH/ISFTA about the design requirements focused mainly on the gas properties and cleaning, INYTE conducted a market survey with potential equipment suppliers.
Due to the characteristics of the process detailed in the description for WP2 and task 2.4 numerous problems were found with the manufacturers of microturbines. Once the full gas characteristics were sent to a broad list of manufacturers, none of them accepted to sell this equipment to the consortium. The reasons argued for this were that the gas obtained from the fuels used in RESOLIVE would cause malfunction in the microturbine.
The companies contacted avoided these bad results reaching the market by all means. It is noteworthy that the information available from these manufacturers (especially Capstone, mentioned as preferred supplier in the description of work) to the partners of the project before proposing RESOLIVE and during the proposal preparation stage was always indicating that there would be no impediment for using their products and obtaining a satisfactory result.
It was concluded that the Capstone microturbine restriction for maximum 1% of hydrogen content, set to avoid flashback problems, could not be met, since the gasification product gas contains 10-20% of hydrogen. This information was forwarded to the European Commission through the coordinator, requesting an amendment to the DoW of the project, in which another power producing unit, such as a gas engine would be used instead of a microturbine of the gasification prototype design was requested. The requested amendment was accepted on 15 October 2010 and INYTE started the procedure for purchasing the prototype (gasifier with gas engine and generator).
The option chosen, after comparing different quotations, was the one from the company Ankur, as it complied with the budget allocated for the prototype in the project, and delivery time was quite fast (12 - 14 weeks). The completion of this task entailed the achievement of milestone M1: Completion of the prototype design.
Prototype building
The specifications in the prototype design phase were followed by the construction of the gas engine prototype. INYTE was in charge of the task, supported on-site by the staff of Unioliva.
A first step in the building of the prototype was the confirmation with the chosen supplier of the performance of the gas engine and its technological characteristics. For this reason, Cummins Ltd. carried out battery tests which are described in D07 'Gasification prototype built'. These are part of the building process of the prototype and have been used by the consortium of RESOLIVE during the test phase for the comparison of the prototype's performance when using olive oil production residues as a fuel.
The transport of the prototype to Spain took longer than initially planned, as the ship transporting it left the port of Mumbai later than planned. This circumstance led to a delay that affected the whole of the project. The system was dispatched by Ankur Scientific on 9 May 2011, and arrived in the Spanish port of Algeciras 8 June. The customs screening, clearance and transport to Úbeda took eleven days and the prototype arrived on 20 June. Erection and commissioning of the prototype took four weeks, from 25 July to 29 August. The operation started and a set of tests were carried out. These tests enabled the complete adaptation of the system to the specific conditions of olive mills, with special attention was given to the determination of the overall process efficiency and energy and mass balance. In this way, milestone M3: 'Gasification prototype built' was reached. During the operation stage, INYTE was in charge of adjusting the system to an optimal performance level.
Before the arrival of the prototype, its building site at Unioliva was prepared, with the construction of a concrete floor and walls to stabilise the terrain. Furthermore, prunings and leaves were selected and reserved by the staff at Unioliva in order to have all fuels ready for testing.
The prototype parts are as follows: the biomass is fed through the skip charger into feed shell having pneumatic double door assembly and is stored in the hopper. A limited and controlled amount of air for partial combustion enters through the air nozzles. The hearth ensures relatively clean and good quality gas production. The reactor holds charcoal for reduction of partial combustion products while allowing the ash to escape. The dry ash that falls out of reactor gets collected in the slanted table of reactor and from there it is taken out with the help of a screw conveyor. The screw conveyor outlet has a two valve dry ash collection box which holds the dry ash for a particular duration of time. The gas passes through the annulus area of the reactor from upper portion of perforated sheet. The gas outlet is connected with reactor outlet, and then bellow, bellow distance piece, cyclone, cyclone distance piece, Venturi scrubber, wet blower, separation box with gas control valve, heat exchanger with chiller, mist eliminator, parallel set of fine filters and pleated filters, header box with flare assembly and fully closed valve (FCV) valves for the engine, in order to facilitate running of the system in ultra clean gas mode. The gas is then brought to the adapted gas motor for the production of electricity.
The modelling and simulation of the process performed prior to the erection of the prototype provided data on the behaviour of the prototype with different fuels:
- Gasifiers as the one installed can handle biomass with moisture contents less than 20% and operate at atmospheric pressure with a reaction temperature about 800-1000ºC. In this specific gasifier, the biomass consumption is around 100 kg h-1 and the average LHV of fuel gas obtained (product gas) is 4.5 - 5.0 MJ Nm-3. Simulation results: air-biomass ratio, fuel consumption, needed air, water consumption, particles, ashes, gasification, electric and overall efficiency and specific air flow for the Otto cycle have been analysed. The CHP system has been modelled with Cycle-Tempo software.
- The gas engine chosen for the is a six cylinder (V-configuration) turbocharged- after cooler engine model Cummins GTA 855 G, supplied originally to operate on dilute natural gas (biogas fuel). These kind engines are marketed as bio-gas engines and are serving as days load power plants. This engine is adopted to operate on producer gas along with a specially designed gas carburetor, built from a diesel engine frame at modified compression ratio (CR) of 8.5 to operate on gaseous fuels in a spark-ignition mode.
This as well as the steps necessary for building the system, plan and schematic drawings for GAS-70 is explained in details in D07 'Gasification prototype built' which was submitted to the EC on 6 December 2010.
Operation
Once the prototype was ready, INYTE, with support from UNIOLIVA started its operation and carried out a set of tests that enabled the complete adaptation of the system to the specific conditions of the olive cooperative, as defined in task 1.2. These tests took into account the preliminary conditions to be met for a profitable exploitation. INYTE was in charge of adjusting the system to an optimal performance level.
ISFTA took part in the measurement campaign during the operation of the prototype. ISFTA brought its equipment (portable gas chromatograph, model of varian CP-4900) to Unioliva in order to measure the producer gas composition in different working modes of the gasifier. During the measurement campaign, ash and fuel samples were be collected and subjected to detailed analysis (major and trace elements, carbon content in ash) in the laboratory of ISFTA in Ptolemais, Greece.
The objective of the measurement campaign was to carry out a thorough assessment of the prototype operation by recording data for several parameters, such as composition of producer gas, pressure drop, temperature, electric output and engine emissions. Moreover, all the accrued results from ash analyses were be studied in order to investigate the alternative valorisation of solid residues into existing industrial practices as well as their environmentally safe disposal in fields or landfills. A technical meeting with personnel of INYTE and Unioliva was scheduled for the end of June in order to discuss all the details of the above campaign.
The only deliverable planned for the period comprised in this report was D8, 'Report on the operation stage of the gasification prototype'. Due to the delay in the delivery of the prototype and therefore, the start of the testing phase, this deliverable could not be finished in the date foreseen in the description of work. A draft version of D8 was, however, prepared and presented on 30 June, with the experimental plan for the months ahead in the testing of the gasification prototype. A final, updated version was submitted on 15 December, with the results obtained.
Gasification result assessment
When the operation period finished, INYTE compiled in month 35 all the results obtained in D10 'Report on the results obtained from the operation of the gasification prototype'. Possible failures in the operation and improvements in the system were proposed at this stage. The necessary improvements were accompanied by a thorough description of the materials and machinery needed. This would enable further implementation and improvement of the system by the SME-AGs. Special attention was given to the determination of the overall process efficiency and energy and mass balance.
A Varian CP4900 gas chromatograph was used by ISFTA in order to measure the composition of producer gas. The GC was calibrated using the following calibration gas mixture of CO:19%, H2:18%, CH4:3%, CO2:8% and N2:52%. Every five minutes (during operation of gasifier at full load) a gas chromatogram was monitored in the PC while pressure drop of gasifier (?PG) and pressure drop of nozzles (?PN) were recorded manually. The same measurement was repeated after 24 hours (second day) in order to check the repeatability of the gas composition results. The average composition of gas was N2:53.1%, O2-Ar:1.33%, H2:24.13%, CH4:4.18%, CO2:4.6% and CO:10.66%. Regarding heating value of gas the following values were calculated HHVgas=6.30 MJ/Nm3 and LHVgas=5.65 MJ/Nm3 taking into account the average values for gas species mole fractions.
Also ISFTA assessed not only the gas quality but also the quantity of ash residues produced from the gasifier. The collected bottom residues of gasification have been tested for their mineralogy by means of X-ray diffraction (XRD) spectroscopy, using a Bruker D8 Advance instrument. The loss on ignition tests were carried out by the use of thermogravimetric analysis (TGA), using a LECO TGA-701 instrument, up to 850°C. The morphology of the collected samples has been investigated by means of scanning electron microscopy, using a JSM-6300 JEOL instrument. The calorific value of the samples was determined through the calorimeter of LECO, model AC-350 whereas the chlorine and sulphur content of samples was determined through the use of photometric and turbidimetric method (Hach Lange, model DR2800). Finally, heavy metals were determined by flame atomic absorption spectrometry of Shimatzu (model AA-6300), after complete digestion of samples with an acid mixture of HCl/H2SO4 in a microwave oven.
According to the results, the char obtained from the gasification cannot be compared to the usual chars obtained through other similar gasification processes found elsewhere. The high operation temperature of the gasifier combined with the use of olive kernel residues results in chars with quite high thermal content and unburnt carbon. Due to this enhanced energy loss occurring in the gasifier, an optimisation of the gasifier operating conditions may be required. Since the gasifier is specifically designed for wood chips, the efficient system performance should be adapted to the specific fuel properties of olive kernel residues or prunings. This could mean changing the operation temperature, the air-fuel ratio etc.
However, if the gasifier keeps running in this mode then two alternatives seem to be the most promising for the optimal utilisation of its residues: use as a fuel and as a precursor for the production of activated carbons.
Based on the high calorific value of the bottom gasification residue - which can be safely considered biochar - its relatively low moisture content, and its high loss-on-ignition value, it is concluded that it can be utilised as a primary fuel for combustion boilers in the energy sector. Moreover, Cl is highly volatile and has been released early in the gasification process. This reduced chlorine content of the residue combined with the low sulphur percentages suggests minimal corrosion problems to the boiler. Additional to the low-corrosion-probability, the absence of quartz reveals a low-erosion-probability. On the other hand, a major drawback is the quite low initial deformation temperature (IDT) coming from the eutectic minerals of biochar. This is a basic factor for high slagging potential and should be seriously considered when used in a combustion installation.
Due to the highly porous structure of the residues and the high amount of unburnt carbon, an alternative utilisation option for these olive kernel gasification residues may be their use as precursors for activated carbons production. The special characteristics of these chars make attractive the possibilities of obtaining activated carbons directly from the gasification process or through upgrading of the resulting char. Since the demand for activated carbons is growing, it is very promising and interesting to convert the gasification process residues to high value-added products, particularly considering that low cost input materials could result in the production of high value end-product.
Anaerobic digestion
Lab scale anaerobic digestion tests
Anaerobic digestion presents a high potential for the biological disposal of OMWW. However, this technology presents many different options that so far have not been compared and ranked by their requirements and advantages therefore, there was a need of further information before it is fully implemented in olive mills.
TTZ carried out a series of tests and analyses at their facilities in order to determine three important parameters for the optimisation of anaerobic digestion:
- Substrates to be used: olive mill waste, pruning rests (twigs and leaves), and mixtures of both.
- Possible additives to be used: in some cases it has been reported that the addition of other components to the reactor feed improves the final gas yield. Possible additives, such as other agricultural wastes, were studied.
- Possible pre-treatment requirements. In many cases, hard substrates rich in lignin and hemicellulose require a mechanical, chemical or enzymatic pre-treatment that enables the conversion of these compounds into the final product, like crushing, NaOH baths or treatment with cellulases and hemicellulases.
This stage comprised preliminary tests, to select the best options, followed by batch test analysis to know the production of biogas and biogas composition in each of them.
The results obtained showed that olive mill wastes were quantitatively degraded to biogas during the anaerobic digestion and moreover, during the co-digestion with different co substrates which have been undergone in some case specific pre-treatments.
These results demonstrate that the co-fermentation tests have been satisfactory and justify the initial thesis being tested, that an improvement of the biogas yield and especially for the methane yield could be observed.
The best results were obtained with two-phase pomace mixed, the production of methane increases 25 Nml/goTS from the value observed in the simple anaerobic digestion and co-digestion (i.e. cow manure as co-substrate) concerning pomace from two-phase process. A biogas production of 262 Nml/goTS or 85 Nml/g FM was obtained, and potential produced methane was set about 110 Nml/goTS or 36 Nml/g FM. However, a considerable biogas quality of 61% has been proven. This is due to the fact that hen litter provides nutrients essential for the microbial consortia for an optimum fermentation.
For the case of pomace from three-phase process, the chemical and enzymatic pre-treatment of this waste before its anaerobic digestion presents many advantages since the organic dry matter removal after fermentation can reach up to 65%. The biogas production of pre-treated three-phase pomace was 283,72Nml/g oTS and the corresponding potential methane production was 174 Nml/g oTS. Moreover, the absence or the slight inhibition shows that a steady microbiological system has been enhanced.
For the olive mil waste water two-phases process, two fermentation tests systems present comparable results, co-digestion of OMWW and pomace and the OMWW and hen litter (HL). Both systems show, respectively, an average methane potential production of 229 Nml/g oTS and 223Nml/goTS; however, the system (OMWW + hen litter (HL)) proves a better microbial synergy since no strong inhibition has been observed in the three vessels during the batch test. On the other hand, the organic removal of this both systems stays insufficient (9 to 24%).
The results of this stage were compiled in deliverable D06 'Report on the anaerobic digestion phase', which was submitted to the EC in 30 April 2010, and D09, 'Report on the results from anaerobic digestion stage', submitted on 30 June 2010 The accomplishment of this task completed Milestone M2: 'Anaerobic digestion stage completed'.
Result assessment
TTZ appraised the results obtained in the previous months. The values obtained for each of the substrate possibilities tested were presented, comparing the performance in biogas production and quality of the gas obtained against the stability of the system.
The results obtained for anaerobic digestion were tested against the theoretical performance indicators as well as the different pre-treatments. The results obtained showed that olive mill wastes were quantitatively degraded to biogas during the anaerobic digestion and moreover, during the co-digestion with different co substrates which have been undergone in some case specific pre-treatments. These results demonstrate that the co-fermentation tests have been satisfactory and justify the initial thesis being tested, that an improvement of the biogas yield and especially for the methane yield could be observed.
The best results were obtained with two-phase pomace mixed, the production of methane increases 25 Nml/goTS from the value observed in the simple anaerobic digestion and co-digestion (i.e. cow manure as co-substrate) concerning pomace from two-phase process. A biogas production of 262 Nml/goTS or 85 Nml/g FM was obtained, and potential produced methane was set about 110 Nml/goTS or 36 Nml/g FM. However, a considerable biogas quality of 61% has been proven. This is due to the fact that hen litter provides nutrients essential for the microbial consortia for an optimum fermentation.
For the case of pomace from three-phase process, the chemical and enzymatic pre-treatment of this waste before its anaerobic digestion presents many advantages since the organic dry matter removal after fermentation can reach up to 65%. The biogas production of pre-treated three-phase pomace was 283,72Nml/g oTS and the corresponding potential methane production was 174 Nml/g oTS. Moreover, the absence or the slight inhibition shows that a steady microbiological system has been enhanced.
These results were also used for the economic assessment in task 4.4. The results of this task are compiled in Deliverable D9 'Report on the results from anaerobic digestion stage'; the final version of which was submitted to the EC by on 30 June 2010.
Alternative technologies
The most interesting technologies for the valorisation and reuse of OMW were evaluated in order to provide some possible solutions for those SME and territories where it is not possible to introduce the gasification prototype or anaerobic digestion. The structure used in this task was planned to provide results in a user-friendly form. Particular importance was given to the experiences available in literature in order to allow an easy understanding of the opportunity and feasibility of each technology proposed. A description of the all the alternative technology/reuses of OMWs, excluding gasification technology, was reported in deliverable D11.
Conclusions were made that the examined alternative technologies could be divided into two groups: the first one represents the alternatives which have an application at the present; the second one represents the alternatives which could have an interest in the future but which need more knowledge to improve their implementation. In the first group the main possible reuses are production of energy (i.e. briquetting and co-combustion), production of fertiliser, production of nursery substrates, and animal feeding. The best solutions for the reuse of OMW are diverse because of the vast differences among physical and chemical characteristics of OMWs (above all due to extraction system) and the complex scenario where OMWs are produced (above all oil mill size). For example, another alternative is the recuperation of valuable chemical compounds (polyphenols for the cosmetic industry) with membrane systems, but at a relative high price. Therefore, the possible application of each analyzed alternative is evaluated in relation to the economic, structural and cultural characteristics of each olive mill. The following four alternative uses and technologies which must be applied to treat the residues for such purposes were analysed in depth: as fertiliser/soil conditioner, organic compound recovery, as animal feed, and as energy from direct combustion.
Use as fertiliser / soil conditioner and compost for plant nurseries
From the prospective of its fertilising value, olive residue has a positive effect due to its high content of nitrogen, phosphorus, potassium and magnesium. The high organic matter content and its degree of humidification improves the physical and chemical properties of soil, which is important, given the progressive decrease in the organic matter content of soils subjected to intensive cultivation.
Here it is considered the recovery of the biomass (pruning, husks, wastewater) to obtain a quality product (compost) through a controlled and sustainable process that can partially or completely replace peat for producing potting substrates. Composting is a technique through which organic matter is decomposed. The proposed case study has been finalised in order to obtain quality compost, cheap and easily available, to use as fertiliser in the open field, or as a potting substrate in the nursery. The compost obtained can be produced through a composting process carried out in cumulus, on a cement platform. Results from the analysis show that:
- For spreading on soil as fertiliser and soil conditioner, it is particularly suitable for all owners of small and medium-sised olive mills who also own farmland. If laws are respected, cost are very low considering the gain of waste disposal and improvement of CO2 storage in the soil.
- For composting, It is particularly suitable for small and medium sized olive mill If laws are respected, cost are very low considering the gain of waste disposal and improvement of CO2 storage in the soil. In nurseries the compost can be used with appropriate% as a substitute for peat and they can be an adequate market for compost.
Recovery of organic compounds
Membrane technology offers several advantages (low energy consumption, no additive requirements, no phase change) over traditional techniques to recover phenolic compounds from OMWs. The performance OMW treatment by membrane filtration finalised to the recovery of polyphenols has been evaluated and this methodology was chosen because it has been patented and applied in different situations. This would reduce the cost of water disposal; it would provide flexibility in treatment and reuse technology for other applications during periods of non-olive milling. With regard to the economic analysis, it is particularly suitable for all owners of small and medium-sized two-phase oil mills. The initial cost is proportional to the amount of processed olives. It could be easily developed where there is market for cosmetics and medicine-based polyphenols. Since the membrane methodology does not change with the sizes of the olive mill (but change the initial costs of investment and working hours), the technology can be applied in different situations, from little-medium-sized mill to big one.
Use as animal feed
Some olive mill wastes can be used as animal feedstuff. OMWs have low digeribility and high content in compounds such as phenols which may be toxic for animals. Among OMWs, olive cake is indicated in scientific literature as the most suitable for such reuse because of the low content in phenols and water. Generally, no pre-treatments are needed even though for storage period longer than 15 days ensilage is recommended.
In the economic analysis, three study cases were considered (administration of olive cake to: lactating ewes, lactating cows and grazing lambs). Savings on the normal diet due to the introduction of olive cake were between EUR 27 and 161/ton for administration to lactating cows and grazing lambs, respectively. These results were estimated as the sum of diet cost reduction and the results (milk yield and live weight gain) obtained with administration thesis in comparison with normal diet. No transport cost or ensiling cost were added and a selling price was estimated as the half of the previous value, in order to allow a margin to both the seller (olive mill) and the animal raiser. On the other hand, such reuse requires large number of animals close to the plant where olive cake is produced. This because of the low daily intake of olive cake reported in literature and the transport cost which greatly varied depending on the distance and the viability. This suggests that such reuse may be affordable for traditional extraction plants (which generally yield olive cake and low volume of OMWs). Finally it should be considered that permits are needed for selling OMW as feedstuff. This could represent a barrier for olive mills.
As conclusion, olive mill wastes used as animal feedstuff could be affordable in olive mills which yield a low amount of OMW and in which extraction system yields a dry cake (pressure systems and three-phase olive mill). According to the economic analysis, profitability level could be considered interesting, but it should be taken into account that OMW intake per animal is fairly low. For this reason, it can be profitable on large scale only if animals could be potentially fed with it are largely available nearby the olive mill (<10 km in order to limit transport costs). Finally, it is largely advisable in case of farms in which both, olive mill and animal rising activity are just carried out.
Energy use with direct combustion
Waste treatment technologies aimed at direct energy production may represent an interesting alternative for the sustainable disposal of residues from olive oil production, able to reduce the environmental impact and generate electric energy for sale or to satisfy the needs of olive mills, when gasification technology find local or technical constrains in being adopted. The residual biomass from olive processing with potential energy use with pyrolysis technology (direct combustion) is classified into two groups. The first is constituted by residual biomass produced during olive tree cultivation (pruning and harvest residues). The second is made up of residual biomass produced during the various stages of the olive oil extraction process. The available energy from the by-product differs according to the extraction system. For instance, exhausted olive cake and TPOMW are characterised by an average heating value of 19 000 and 14 000 kJ/kg, respectively. Efficient use of olive cake in energy production solves two problems in one step: clean energy production and acceptable disposal of olive oil mill waste.
The pomace and pit can be used to produce electric and thermal energy or both (co-generation).The production of electric energy is accompanied by that of heat; therefore, it is also possible to produce thermal energy in conjunction with electric energy.
The boilers can be small size (below20 - 30 kW), medium size (30 to 100 kW) and large size (above 100 kW).
As conclusion, olive mill wastes used as energy source with pyrolysis technology is suitable for all kinds of olive mills. In case of small olive mill, energy produced can be used by the company itself or by private homes nearby the plant. In case of medium and large olive mills, energy can be also sold to the grid. Dry material can be sold as burning material to other customer.
