Final Report Summary - ENRSYS (Integrated Thermal Energy Reduction, Recovery & Re-use in Autoclave based Composites Processing)
Executive Summary:
The ENRSYS project has successfully developed a first of its kind integrated, computer controlled, heat recovery, reuse & thermal energy management system centred on the autoclave with potential re-use of thermal energy in the post-cure ovens or autoclaves, and possibly in the clean room air filtration/cooling system.
The system operates by extracting heat from the autoclave to match existing cooling rates that are specified by material manufacturers. The heat is stored in specially designed thermal stores and the control system manages the process of heat storage to maximise the potential and efficiency for reuse.
The ENRSYS system represents a near to market solution. A level of industrial readiness has been built in from the outset so that the system is ready for direct implementation within a real operating environment for use during the next steps.
Through introduction of this system the aim was to reduce initial energy use in the autoclave by at least 25% through reduction of the autoclave headspace and recover 50% of the energy wasted at the end of the autoclave processing stage for re-use in other energy intensive heating processes such as the post cure process.
A complex technical solution has been devised consisting of a multi tank, stratified energy store which is part pressurised. The control system enables the most efficient extraction and use of energy. Enhanced energy saving is also achieved through improved, retro-fittable thermal insulation of the autoclaves. Research and evaluation of end user operations demonstrated large losses through the main “hull” of the autoclave. As a result effort was redirected to improved insulation. This is a more efficient use of resources and offers a greater economic benefit when compared with the use of a thermally insulated space saving system.
The ENRSYS system was developed with a large industrial application using multiple autoclaves in mind, and whilst the prototype developed during the project is approximately 1/5th of this scale it is already well matched to some smaller industrial applications and the potential savings achievable from directly using the prototype are none the less substantial (up to €22,500 savings per anumn based on typical usage profile)
The test results (energy stored, energy transferred and efficiency) achieved with the ENRSYS prototype have been extrapolated and applied to the known commercially used autoclave system in order to determine potential benefits for the primary market. The data has been calculated for three scenario’s (low, medium and high enthalpy). Efficiencies of between 67% and 87% have been achieved across the three scenario’s and cost savings indicated in energy usage of up-to €56,500 for the commercial autoclave system studied across the three scenario’s.
A system scaling model has already been produced using the underpinning theory and substantiated by the prototype validation data. This tool shall be validated and optimised following the project by comparing to performance under continuous operational use. The aim is to ensure this gives a reliable indication of the system size and potential outputs (energy recovery level) for a range of usage scenarios and in turn this will become an extremely useful tool for specifying bespoke systems which are well matched to customer requirements.
During the test phase of the ENRSYS project a number of potential area’s for improving the system were identified which form the basis of the development plan for the next phase of ENRSYS. By doing so this will further enhance the efficiency of ENRSYS and also ensure the equipment can achieve regulatory compliance.
IP protection has already been initiated and based on the various searches no system which provided serious competition to the ENRSYS system has been found. The SMEs have also attracted the interest of a potential system distributor with substantial international presence and experience selling high value machinery to the automotive and aerospace sectors. In addition two large composite manufactures (both LEs) have expressed a considerable interest with an agreement in principal to install the system for long term operational use post project.
Project Context and Objectives:
The primary aim of the ENRSYS project was to develop a fully integrated computer controlled heat recovery and thermal energy management system for use with autoclaves. It was proposed to develop a system that following testing could be installed into an autoclave end-user post project.
This was to be achieved by extracting heat from an autoclave to match existing cooling rates specified by material manufacturers. Heat was to be stored in a specially designed thermal store at the highest enthalpy possible to maximise opportunities for re-use. The main objectives were to reduce initial energy use in the autoclave by at least 20% through reduction of the autoclave headspace and recover 50% of the energy wasted at the end for re-use in other energy intensive heating processes such as the post cure process. In addition, an investigation into the potential to recover compressed air (with its intrinsic compression energy and heat from the autoclave) was to be undertaken and heat from the air compressors that create the 7 to 10 bar pressure and integrate this with the ENRSYS system.
The technical objectives of the project were:
• Design & prototype a dead space heat saving system, to reduce the ‘dead space’ volume of hot air in autoclave and establish a method of insulation for the hull capable of significantly reducing energy loss during autoclave processing.
• Design & prototype a compact, low cost multiple stage thermal store able to store energy at high temp (at least 90ºc and possibly up to 135ºc ) from the heat pump for up to 48 hours with no more than 5ºc loss in temperature. The capacity of the store being sufficient to store heat recovered from 3 autoclave cycles (of our demonstrator system).
• A heat delivery system able to supply the stored heat back to the autoclave through the existing fan assisted finned heating matrix. This system can be used to pre-heat the air in the oven, before the electric elements are switched on to achieve and maintain the final operating temperature of 175ºc A larger scale specification and a smaller scale demo unit will be fabricated.
• A computer control system that measures temperatures and flow rates; calculates heat demands and energy availability and then controls heat flows through a system controlled by motorised pumps, valves and existing heat dumps (cooling towers) to optimise NET energy recovery.
The scientific objectives of the project were:
• Test a variety of lightweight; low thermal conductivity, low heat capacity ‘ceramic’ like particles & bagging materials and also a range of insulation products.
• Create a complete thermodynamic model of proposed system and determine heat flows & storage needs etc.
• From thermodynamic modelling carry out R&D to determine and select the most suitable heat store medium
• Prove the suitability and scalability of CO2 or Ammonia Hybrid heat pump technology for our large scale application.
• Develop experimental CO2 or Ammonia Hybrid heat pump for integration into our demo heat management system.
The proposed system will create the following benefits:
• A system that can be easily integrated into existing complex autoclave manufacturing processes
• Reduce primary energy used by at least 20% and recover 50% of thermal energy used in the autoclave.
• Storage & re-use of the recovered energy in the autoclave or post cure process.
• Reduce CO2 emissions by 318 tonnes per (case study scale) system per year.
• Create a new market for energy recovery systems in the composites sector worth up to €200m.
• A reduction in energy use of 639,000kW.hrs giving a saving for the end user of €66,000 per system per year.
Project Results:
1. Preparatory Research
A case-study system was identified which is a market leading composites manufacturer in the UK who uses multiple autoclaves as part of the manufacturing process. With their assistance data was compiled for key parameters of the ENRSYS system from which an initial specification was compiled. Using the compiled data, a thermodynamic model was created that represents various scenarios of the autoclave cooling and heating cycles. The calculated heat energy available in the autoclave cooling process is 1.88 GJ, translated into electrical energy equals 523 kWh. It has to be stated that the calculations are made on standard autoclave time-temperature diagram with the operating temperature at 185°C. However, a higher operating temperature will result in a larger amount of heat energy with higher average water temperatures, while a lower operating temperature will have the opposite effect.
Investigations were made into suitable high uplift heat-pumps for use with the system. These investigations took into account both current commercially available pumps as well as ones in development. Suitable pumps were identified that were capable of providing a temperature uplift of 90°C.
A process simulation model using Lab-view was designed and developed to represent existing autoclave systems. The model demands inputs based on the known operating parameters and efficiencies of a given system and can be utilised for multiple autoclaves. On running the simulation accurate data can be produced that predicts the energy savings to be gained by using the ENRSYS technology. A lot of the data in the model is determined by the data from the results of the ENRSYS system trials.
Investigations were undertaken to determine thermal storage of the energy taken from an autoclave and a three tank system was recommended consisting of three temperature ranges; high (140°C - 100°C), medium (100°C - 70°C) and low (<70°C). Specifications were produced for each tank. Naturally, the water stored in highest temperature range is pressurized, while the remaining tanks’ water is stored at atmospheric pressure.
Investigations were undertaken into reduction of head-space in the autoclave by use of a ‘bean-bag’ system. This included investigation into the best materials to fill the bean-bags and Pumice was identified as the best material. This is a naturally occurring volcanic rock where the TG designation refers to a grain size of 3 to 8mm.
To summarize, the above stated heat recovery systems with different composition design, have been proposed as a possible design solution:
• Heat recovery system without a heat pump, with the highest achievable heating temperature of 135°C.
• Heat recovery system with a heat pump included; the heat pump is commercially available, the maximum heat pump uplift temperature is 90°C, while the maximum water temperature (from the autoclave) is 135°C.
• Heat recovery system with no commercially available heat pump (heat pump uplift temperature is projected to 135°C). In this case the pressurized water is not being used due to high heat pump uplift temperature.
The designed system had an estimated efficiency of 72.3% which actually exceeds the proposed target from the Dow (40%). This is advantageous especially considering our finding that the heat recovery from the main hull is a substantially better source of recoverable energy compared with compressed air. This potential yield, gives higher than expected benefits and provides justification for focussing on heat recovery as the major innovation Using the heat pump for five hours, this equals the time in autoclave cycles, heat pump power should be 72kW. However, in order to sink the cost of the heat pump, higher units cost less per kW, three autoclave should be connected to one pump. In this case heat pump power is raised to 216kW.
2. Design of Sub-Systems
A broad market analysis of available heat pump technology to establish an optimal heat pump considering, performance, cost, availability and lead-time was undertaken.
Provisional detailed drawings were produced for the hot thermal storage tanks were produced and subjected to design reviews following which some refinements were made and CAD drawings produced.
The detailed design phase took into account the sizing and capacity requirements of the tanks by calculating the thermal storage requirements with uplift of 15%. A wide range of factors including regulatory requirements for the pressure tanks (to ensure safe operation), selection of materials (Stainless Steel S316) methods of insulation, corrosion protection, leak prevention were considered. Care was taken to ensure to minimize the cost of production and as a result tank 2 was designed as a flat wall tank making manufacture simpler and more efficient. The tank height to width ratio was designed to minimize the volume of water could be used to submerge the pumps fitted in the base of the tanks whilst remaining stable. Since tank 1 was a pressure vessel this had to be designed to comply with strict legislative requirements and required CE Marking in order to be used.
The auxiliary components such as system piping and flow monitoring equipment were also designed. Piping selection took into consideration the Pressure (outer, inner), temperature, medium flow velocity, pipe joining, water “chemical” aggressiveness etc. Suitable immersion heaters were specified to enable “top up heating” of the contents in order to simulate different use conditions. The tank designs allowed for installation of these within the tanks would enable higher temperatures to be simulated.
A feasibility analysis was completed to indicate that the rate of heat release from the planned thermal store should be sufficient to augment the normal electrical heating and it is also apparent that a thermal store of 0.65GJ capacity would contain enough energy to raise the temperature of the case study post cure ovens and contents to 80C.
Case study information gathered helped all aspects of the system design by provided specific constraints on the layout and guidance on sizing requirements based on spatial constraints and thermal capacity requirements.
Heat transfer calculations were performed and research into appropriate secondary (fluid to air) heat exchange technologies was carried out for the case study application and an example heat exchanger was identified.
To enable sensible, controlled validation of the heat transfer capacity a “simulation tank” was designed which required the calculation, specification and design of an integrated heat exchanger within. This simulation tank acts as a heat sink, just as an oven (air) would by using heat from the storage system to increase its own enthalpy and was sized according to the scaled down demo system requirements. Due to the higher specific heat capacity than air its use was more practical i.e. it occupies a significantly smaller volume thus reducing materials outlay. The contents of this tank can be “reused” therefore reducing the sizeable amounts of energy required to validate the system during industrial laboratory trials. Significantly though this offers a dependable means of assessing the heat delivery capabilities (rates, losses, control validation) of the system in practice and is also easily measureable.
The design of the demo unit was further developed to produce a more complex, “stratified” storage system consisting of three main tanks and a final traditional cooling pond. Within the scheme the thermal store is represented by two tanks a pressurised tank for storage of high temperature water and a secondary, lower heat tank which uses traditional (readily available) heat pump technology to store heat at approximately 80°C.
The “cold store” is also represented by two tanks. First a cold insulated tank which could be supplied as part of the ENRSYS solution to store low grade heat at only 30 degrees. This meets the initial requirements specification for the cold water store and minimises energy loss to atmosphere. This can be sized according to system requirements, fully insulated to and provides added system flexibility. Used in conjunction with existing cold stores it has the potential to feed heat pumps and or be recirculated during the autoclave curing cycle to achieve an up-lift in temperature. The traditional cold store therefore does not require insulation; the aim is to maintain this at a low temperature and can therefore promote efficient autoclave cooling at lower throughput rates. Use in this way offered the greatest range of potential use scenarios to be evaluated.
Detailed tank designs were produced for the cold insulated store which is similar in construction to tank 2. Rock wool insulation was selected for cost, performance and ease of manufacture. Drawings were passed forward for manufacture. In addition a specification was produced to ensure the correct sizing of a simple cold store which would represent the traditional cooling pond in the prototype system.
Flow chart logic’s have been created for the tanks initialisation phase, autoclave cooling cycle and the autoclave heating cycles. The control system is based on a Wago PLC with a PFC controller and is a modular system that supports various digital, analogue and speciality modules. An integrated web server provides the user with configuration options and status information from the controller. The software has been written using a compiler known as CodeSys which can be used across multiple language types. The system is interfaced via a digital touch screen.
The system can be run in one of three settings, manual, off and automatic. This allows the system to be tested without the PLC being connected and allows the operator to manually override the system if required.
A range of potential system configurations were considered for the recovery of heat and compressed air. Careful consideration was given to the feasibility and cost of these which demonstrated that the savings were minimal and did not justify the investment in such a solution. For example the conclusions from the consideration of an air re-use; turbine within an air re-circulation sub-system were investigated as a way of converting the waste air into electrical energy the main issue was the intermittent use of the turbine. This equated to an estimated 144 hours use per year for a single autoclave giving a low return on investment even in a site-wide system with a turbine costing in excess of €12,000 but only being used for a small proportion of available time each year.
• Investment costs Approx 12,000€
• Power DEPRAG GET (Green Energy Turbine) 5 kW
• Infeed remuneration 0.20 €/kWh
• Annual usage (single autoclave estimate) 144hrs
• Annual costs (Maintenance etc.) 400€
• Annual earnings 144€
• Payback period Approx. 88 years
To negate the impact of these findings on the overall novelty and energy saving potential of ENRSYS, a new stream of work was also introduced to investigate and develop a system for heat recovery from the autoclave cooling fans. This had been overlooked prior to the project when the concept was developed, however working. These offer much larger potential for energy savings and run for a much larger portion of the autoclave cycle and continuously produce excess heat energy.
Preliminary designs were considered to adapt the main heat recovery system and add an additional cooling circuit which would enable heat extraction from the cooling fans. A secondary cooling coil was specified within tank 3 (insulated cold store) to enable heat extraction from the fan cooling water into this tank and the cooling circuit also allowed for continuous, low level heat feed to the heat pump. These were reflected in the system P&ID and also incorporated into the control specifications For the purpose of simulation a heater was specified within the demo unit to mimic this heat source. The manufactured system is based upon these P&IDs.
The manufacturing techniques for the bean bags were assessed, a simple prototype has been built and the overall concepts were presented to the beneficiaries. Whilst initial interest into this solution was high, ISRI carried out initial evaluation of the performance by conducting provisional tests and calculations were made to estimate the potential energy saving capability of the bean bags. A known heating profile was used for the calculation; and the results suggested that a 17kW saving could be achieved per curing cycle using a 379m3 autoclave at a 15% bean bag loading.
During the evaluation of the end users sit it became evident that the hull presented the major source of heat loss. The bean bag system would not achieve any inherent reductions in this. As such new concepts for insulating the hull were presented and deemed to offer a much improved technical and economic benefit.
3. Build Sub-Systems of Demo Unit
The specifications for the heat-pump sub-systems were signed off for manufacture, this review ensured that the
Following the research, specification and design undertaken previously the outputs were signed off for manufacture of the hot thermal store system. A final design review was carried out to ensure the designs were fit for purpose and also to identify any associated project risks e.g. H&S, or procurement delays.
Design reviews were undertaken to of the pressure vessel in order to ensure that it would meet all relevant safety regulations. Initial tank data was compiled to satisfy the essential requirements including material conformity, weld procedure, tank inspection & pressure test certificates to comply with PD5500. Formal consultation was required from an independent risk management with expertise in the UK legislative requirements to ensure the tanks could be approved for use. The prototype simulation was manufactured which consists of a sealed tank an integrated heat-exchanger.
Final sizing calculations were performed to confirm the sizing of the cooling pond prior to order.
The unit was manufactured according to the designs produced. As with the hot thermal stores all necessary fittings were installed ready for integration with the other subsystems. The tank was reinforced to ensure integrity when filled with water. An additional cold water store was also procured to mimic a traditional cold water pond in an industrial facility. These were inspected and signed off ready for integration.
The control hardware has been procured and assembled in accordance with the designs and specifications created previously. The software has been programmed to utilise temperature, pressure flow and level sensors to control valves and pumps to control the flow of energy stored in each part of the system. The software is managed by a central PLC which is resident in the main control cabinet.
4. Integration & Commissioning of Sub-Systems
All necessary ancillary components were purchased by ISRI to allow for integration of the subsystems. Once initial integration had been carried out set to work commissioning of the heat pump system was performed to check for correct functionality of this and its associated valves and sensors.
The prototype subsystem was integrated with a heat source at ISRI via an interface heat exchanger within the “simulation tank” so that testing and validation of the system could be carried out in a safe and controlled manner. This work on the integration of the heat pump system was carried out concurrently with the subsequent tasks i.e. this was also connected with the other subsystems and piping as outlined in subsequent tasks.
Comprehensive safety checks on all tanks were undertaken. The various tanks were connected to the other sub-systems and tanks including the insulated cold store and the simulated cooling pond. Supplementary water heaters were fitted to tanks 1 & 2 to enable higher temperature outputs to be simulated in a laboratory environment. Full pipework checks were carried out to ensure no leakage, correct flow of water.
The simulation water tank and its associated pipework was connected to the range of thermal store tanks and the various components were located according to the proposed system layout. The remaining fittings and pipework was installed prior to welding of joints. Checks were carried out to ensure check valves and sensors function correctly.
Concurrently with the other installation activities the cold thermal store and simulated cooling tower were also connected with tanks, 1, 2 and the “simulation tank”. Checks were carried out to ensure these all functioned together. Set to work commissioning procedures were followed to document the initial commissioning of the system and ensure this was ready for lab validation and final handover.
All electrical hardware was installed within the system (including installation of the control panels, all system wiring i.e. to various sensors, actuators etc, integration with the power supply and initial testing to ensure the electrics were safe and functioned as expected. Following the initial integration work an extensive period of commissioning was carried out to i) debug the software ii) optimise the set-up prior to trials in WP4.
A Model to scale system for commercial application has been designed for use ‘post-project’ The model contains a detailed & refined thermodynamic model of the autoclave. A mathematic simulation has been undertaken including several scenarios taking into consideration key autoclave factors like autoclave electric heaters (autoclave heat energy input), process temperature. The process temperature is in correlation with the overall heat transfer coefficient enabling the heat energy transfer. Additionally, a new graphical user interface (GUI) was developed. The graphical user interface is a display in one or more windows containing controls that enable the user to perform interactive tasks without the need for typing a script or commands. The GUI is divided into 3 sections: User section, Water tank calculations section and Energy savings section. User section is where the user enters values in order for the GUI to calculate certain values. Water tank section is where the results of tank capacity and temperatures will be calculated. Energy savings section is where calculations of saved energy are displayed.
5. Field Trials & Validation
A D of E (Design of Experiments study) was undertaken to determine the required test program based on the following scenarios i) no heat pump ii) commercial heat pump iii) simulation of a “super” heat-pump using the electrical heaters. A matrix of tests was produced for implementation during the system validation work.
Validation of the control system was undertaken in a laboratory environment prior to any full-scale testing being undertaken. These trials were conducted in manual mode. During this time debugging issues were addressed and some minor improvements to the control system were made.
The output data from the trials has been analysed based on the computation of heat balance. This analysis has led to a number of conclusions regarding the usefulness of the system. The complete cooling (or heating if the reverse process of stored heat recovering is considered) tests have been undertaken to reproduce the complete energy storage process through heat transfer from the Autoclave to the tanks. This work was divided into three sub-tests, a) cooling of simulation tank, heating of tank 1 – high enthalpy, b) cooling of simulation tank, heating of tank 2 – medium enthalpy, c) cooling of simulation tanks, heating of tank 3 – low enthalpy.
The range of testing included preliminary cooling testing, heat pump testing, thermal stratification and followed the D of E study. The tests were based on increasing the initial temperature of the simulation tank in order to simulate three different enthalpy levels. The energy saving potential of all three scenarios (low, medium & high) have been calculated and the payback time of a large-scale system calculated for a known full-scale Autoclave installation. Considering an initial cost estimate of the full scale plant equal to 310,000 Euro, the best payback time is equal to five years and it is given by recovering heat at the highest temperature as possible, also considering an equivalent of the 40% of the energy stored spent by the heating pump to uplift and keep the temperature up to 120°C.
Initial screening trials were undertaken to evaluate the preferred insulation solution using the basic small-scale rig developed previously on the candidate materials identified. These enabled the choice to be narrowed to two main products:- Superfoil® SF40 and Rockwool Cladding (foil faced).
These materials were tested and compared with each other as well as with a non-insulated system using the second larger-scale rig. The results show that the fitting of a layer of SF40 could represent a significant energy saving per annum, potentially as much as 90%.
Based on the lessons learned throughout the build, integration, planning for testing and installation and also the trial phase ISRI have produced a number of recommendations for system improvement and have been included these include:
1. A two tank system in a commercial application as the low enthalpy scenario doesn’t produce enough energy savings vs the payback time.
2. Reduced complexity through use of a single tank so reducing the pipe-work and subsequent controls required.
3. 70°C Heat-Pump. This is the best option in the absence of a higher rated heat-pump that is commercially available.
4. Reduced tank temperature stratification: To improve the stratification agitation or recirculation pumps should be utilised.
5. Autoclave insulation: Use of Super-Foil SF40 is recommended.
6. Control System Improvements: By improving the variable speed drive logic in order to vary the flow rates which will help maintain the temperature profile.
7. FMEA Analysis: For all considered commercial applications in order to fully understand the process variables and outputs for a given system.
Potential Impact:
The ENRSYS project has provided the SME beneficiaries with an IP protectable technology to manufacture an integrated, computer controlled, heat recovery, reuse & thermal energy management systems for autoclaves. This is a bespoke system for each application(s) of an end-user.
Whilst the EU is a leader in aerospace composites processing, the aerospace and automotive industry is a global business with parts being manufactured further afield prior to being shipped for assembly by an OEM or within their 1st tier supply chain. Thus there is increasing pressure from processors based outside the EU. ENRSYS provides a real option for European autoclave users to reduce energy costs and thus overheads keeping them cost competitive with the rest of the supply market. End users of the ENRSYS technology will benefit in a number of ways. Firstly, the model to scale software will detail the current losses in their autoclave systems and accurately predict the energy savings for their system(s). This in turn will give accurate payback times for each bespoke installation and increased efficiencies. There is a further impact in using the ENRSYS technology, end-users will benefit from a reduction in the primary energy used as well as increased efficiencies for each autoclave cycle due to improved heating profiles by use of stored energy.
It is difficult to give actual figures because each installation is bespoke and the savings will depend on the number of autoclaves integrated into the ENRSYS technology, however, for the target application the following figures were obtained (per anum) for a system of 5 Autoclaves using a two tank system (>70°C, 70°C to 100°C) is:
• Energy transferred: 212MJ
• Efficiency: 77%
• Cost reduction: €70,000
There are approximately 1000 autoclave users in Europe with a current market growth of about 4% per annum. The total market of installed autoclaves onto which the ENRSYS technology could be retro-fitted is estimated to be approximately 2000 currently and could be about 2,340 five years post-project. The aim of the consortium is to have penetrated 2% of the market selling approximately 50 systems.
The ENRSYS project has successfully developed a first of its kind integrated, computer controlled, heat recovery, reuse & thermal energy management system centred on the autoclave with potential re-use of thermal energy in the post-cure ovens or autoclaves, and possibly in the clean room air filtration/cooling system.
The system operates by extracting heat from the autoclave to match existing cooling rates that are specified by material manufacturers. The heat is stored in specially designed thermal stores and the control system manages the process of heat storage to maximise the potential and efficiency for reuse.
The ENRSYS system represents a near to market solution. A level of industrial readiness has been built in from the outset so that the system is ready for direct implementation within a real operating environment for use during the next steps.
Through introduction of this system the aim was to reduce initial energy use in the autoclave by at least 25% through reduction of the autoclave headspace and recover 50% of the energy wasted at the end of the autoclave processing stage for re-use in other energy intensive heating processes such as the post cure process.
A complex technical solution has been devised consisting of a multi tank, stratified energy store which is part pressurised. The control system enables the most efficient extraction and use of energy. Enhanced energy saving is also achieved through improved, retro-fittable thermal insulation of the autoclaves. Research and evaluation of end user operations demonstrated large losses through the main “hull” of the autoclave. As a result effort was redirected to improved insulation. This is a more efficient use of resources and offers a greater economic benefit when compared with the use of a thermally insulated space saving system.
The ENRSYS system was developed with a large industrial application using multiple autoclaves in mind, and whilst the prototype developed during the project is approximately 1/5th of this scale it is already well matched to some smaller industrial applications and the potential savings achievable from directly using the prototype are none the less substantial (up to €22,500 savings per anumn based on typical usage profile)
The test results (energy stored, energy transferred and efficiency) achieved with the ENRSYS prototype have been extrapolated and applied to the known commercially used autoclave system in order to determine potential benefits for the primary market. The data has been calculated for three scenario’s (low, medium and high enthalpy). Efficiencies of between 67% and 87% have been achieved across the three scenario’s and cost savings indicated in energy usage of up-to €56,500 for the commercial autoclave system studied across the three scenario’s.
A system scaling model has already been produced using the underpinning theory and substantiated by the prototype validation data. This tool shall be validated and optimised following the project by comparing to performance under continuous operational use. The aim is to ensure this gives a reliable indication of the system size and potential outputs (energy recovery level) for a range of usage scenarios and in turn this will become an extremely useful tool for specifying bespoke systems which are well matched to customer requirements.
During the test phase of the ENRSYS project a number of potential area’s for improving the system were identified which form the basis of the development plan for the next phase of ENRSYS. By doing so this will further enhance the efficiency of ENRSYS and also ensure the equipment can achieve regulatory compliance.
IP protection has already been initiated and based on the various searches no system which provided serious competition to the ENRSYS system has been found. The SMEs have also attracted the interest of a potential system distributor with substantial international presence and experience selling high value machinery to the automotive and aerospace sectors. In addition two large composite manufactures (both LEs) have expressed a considerable interest with an agreement in principal to install the system for long term operational use post project.
Project Context and Objectives:
The primary aim of the ENRSYS project was to develop a fully integrated computer controlled heat recovery and thermal energy management system for use with autoclaves. It was proposed to develop a system that following testing could be installed into an autoclave end-user post project.
This was to be achieved by extracting heat from an autoclave to match existing cooling rates specified by material manufacturers. Heat was to be stored in a specially designed thermal store at the highest enthalpy possible to maximise opportunities for re-use. The main objectives were to reduce initial energy use in the autoclave by at least 20% through reduction of the autoclave headspace and recover 50% of the energy wasted at the end for re-use in other energy intensive heating processes such as the post cure process. In addition, an investigation into the potential to recover compressed air (with its intrinsic compression energy and heat from the autoclave) was to be undertaken and heat from the air compressors that create the 7 to 10 bar pressure and integrate this with the ENRSYS system.
The technical objectives of the project were:
• Design & prototype a dead space heat saving system, to reduce the ‘dead space’ volume of hot air in autoclave and establish a method of insulation for the hull capable of significantly reducing energy loss during autoclave processing.
• Design & prototype a compact, low cost multiple stage thermal store able to store energy at high temp (at least 90ºc and possibly up to 135ºc ) from the heat pump for up to 48 hours with no more than 5ºc loss in temperature. The capacity of the store being sufficient to store heat recovered from 3 autoclave cycles (of our demonstrator system).
• A heat delivery system able to supply the stored heat back to the autoclave through the existing fan assisted finned heating matrix. This system can be used to pre-heat the air in the oven, before the electric elements are switched on to achieve and maintain the final operating temperature of 175ºc A larger scale specification and a smaller scale demo unit will be fabricated.
• A computer control system that measures temperatures and flow rates; calculates heat demands and energy availability and then controls heat flows through a system controlled by motorised pumps, valves and existing heat dumps (cooling towers) to optimise NET energy recovery.
The scientific objectives of the project were:
• Test a variety of lightweight; low thermal conductivity, low heat capacity ‘ceramic’ like particles & bagging materials and also a range of insulation products.
• Create a complete thermodynamic model of proposed system and determine heat flows & storage needs etc.
• From thermodynamic modelling carry out R&D to determine and select the most suitable heat store medium
• Prove the suitability and scalability of CO2 or Ammonia Hybrid heat pump technology for our large scale application.
• Develop experimental CO2 or Ammonia Hybrid heat pump for integration into our demo heat management system.
The proposed system will create the following benefits:
• A system that can be easily integrated into existing complex autoclave manufacturing processes
• Reduce primary energy used by at least 20% and recover 50% of thermal energy used in the autoclave.
• Storage & re-use of the recovered energy in the autoclave or post cure process.
• Reduce CO2 emissions by 318 tonnes per (case study scale) system per year.
• Create a new market for energy recovery systems in the composites sector worth up to €200m.
• A reduction in energy use of 639,000kW.hrs giving a saving for the end user of €66,000 per system per year.
Project Results:
1. Preparatory Research
A case-study system was identified which is a market leading composites manufacturer in the UK who uses multiple autoclaves as part of the manufacturing process. With their assistance data was compiled for key parameters of the ENRSYS system from which an initial specification was compiled. Using the compiled data, a thermodynamic model was created that represents various scenarios of the autoclave cooling and heating cycles. The calculated heat energy available in the autoclave cooling process is 1.88 GJ, translated into electrical energy equals 523 kWh. It has to be stated that the calculations are made on standard autoclave time-temperature diagram with the operating temperature at 185°C. However, a higher operating temperature will result in a larger amount of heat energy with higher average water temperatures, while a lower operating temperature will have the opposite effect.
Investigations were made into suitable high uplift heat-pumps for use with the system. These investigations took into account both current commercially available pumps as well as ones in development. Suitable pumps were identified that were capable of providing a temperature uplift of 90°C.
A process simulation model using Lab-view was designed and developed to represent existing autoclave systems. The model demands inputs based on the known operating parameters and efficiencies of a given system and can be utilised for multiple autoclaves. On running the simulation accurate data can be produced that predicts the energy savings to be gained by using the ENRSYS technology. A lot of the data in the model is determined by the data from the results of the ENRSYS system trials.
Investigations were undertaken to determine thermal storage of the energy taken from an autoclave and a three tank system was recommended consisting of three temperature ranges; high (140°C - 100°C), medium (100°C - 70°C) and low (<70°C). Specifications were produced for each tank. Naturally, the water stored in highest temperature range is pressurized, while the remaining tanks’ water is stored at atmospheric pressure.
Investigations were undertaken into reduction of head-space in the autoclave by use of a ‘bean-bag’ system. This included investigation into the best materials to fill the bean-bags and Pumice was identified as the best material. This is a naturally occurring volcanic rock where the TG designation refers to a grain size of 3 to 8mm.
To summarize, the above stated heat recovery systems with different composition design, have been proposed as a possible design solution:
• Heat recovery system without a heat pump, with the highest achievable heating temperature of 135°C.
• Heat recovery system with a heat pump included; the heat pump is commercially available, the maximum heat pump uplift temperature is 90°C, while the maximum water temperature (from the autoclave) is 135°C.
• Heat recovery system with no commercially available heat pump (heat pump uplift temperature is projected to 135°C). In this case the pressurized water is not being used due to high heat pump uplift temperature.
The designed system had an estimated efficiency of 72.3% which actually exceeds the proposed target from the Dow (40%). This is advantageous especially considering our finding that the heat recovery from the main hull is a substantially better source of recoverable energy compared with compressed air. This potential yield, gives higher than expected benefits and provides justification for focussing on heat recovery as the major innovation Using the heat pump for five hours, this equals the time in autoclave cycles, heat pump power should be 72kW. However, in order to sink the cost of the heat pump, higher units cost less per kW, three autoclave should be connected to one pump. In this case heat pump power is raised to 216kW.
2. Design of Sub-Systems
A broad market analysis of available heat pump technology to establish an optimal heat pump considering, performance, cost, availability and lead-time was undertaken.
Provisional detailed drawings were produced for the hot thermal storage tanks were produced and subjected to design reviews following which some refinements were made and CAD drawings produced.
The detailed design phase took into account the sizing and capacity requirements of the tanks by calculating the thermal storage requirements with uplift of 15%. A wide range of factors including regulatory requirements for the pressure tanks (to ensure safe operation), selection of materials (Stainless Steel S316) methods of insulation, corrosion protection, leak prevention were considered. Care was taken to ensure to minimize the cost of production and as a result tank 2 was designed as a flat wall tank making manufacture simpler and more efficient. The tank height to width ratio was designed to minimize the volume of water could be used to submerge the pumps fitted in the base of the tanks whilst remaining stable. Since tank 1 was a pressure vessel this had to be designed to comply with strict legislative requirements and required CE Marking in order to be used.
The auxiliary components such as system piping and flow monitoring equipment were also designed. Piping selection took into consideration the Pressure (outer, inner), temperature, medium flow velocity, pipe joining, water “chemical” aggressiveness etc. Suitable immersion heaters were specified to enable “top up heating” of the contents in order to simulate different use conditions. The tank designs allowed for installation of these within the tanks would enable higher temperatures to be simulated.
A feasibility analysis was completed to indicate that the rate of heat release from the planned thermal store should be sufficient to augment the normal electrical heating and it is also apparent that a thermal store of 0.65GJ capacity would contain enough energy to raise the temperature of the case study post cure ovens and contents to 80C.
Case study information gathered helped all aspects of the system design by provided specific constraints on the layout and guidance on sizing requirements based on spatial constraints and thermal capacity requirements.
Heat transfer calculations were performed and research into appropriate secondary (fluid to air) heat exchange technologies was carried out for the case study application and an example heat exchanger was identified.
To enable sensible, controlled validation of the heat transfer capacity a “simulation tank” was designed which required the calculation, specification and design of an integrated heat exchanger within. This simulation tank acts as a heat sink, just as an oven (air) would by using heat from the storage system to increase its own enthalpy and was sized according to the scaled down demo system requirements. Due to the higher specific heat capacity than air its use was more practical i.e. it occupies a significantly smaller volume thus reducing materials outlay. The contents of this tank can be “reused” therefore reducing the sizeable amounts of energy required to validate the system during industrial laboratory trials. Significantly though this offers a dependable means of assessing the heat delivery capabilities (rates, losses, control validation) of the system in practice and is also easily measureable.
The design of the demo unit was further developed to produce a more complex, “stratified” storage system consisting of three main tanks and a final traditional cooling pond. Within the scheme the thermal store is represented by two tanks a pressurised tank for storage of high temperature water and a secondary, lower heat tank which uses traditional (readily available) heat pump technology to store heat at approximately 80°C.
The “cold store” is also represented by two tanks. First a cold insulated tank which could be supplied as part of the ENRSYS solution to store low grade heat at only 30 degrees. This meets the initial requirements specification for the cold water store and minimises energy loss to atmosphere. This can be sized according to system requirements, fully insulated to and provides added system flexibility. Used in conjunction with existing cold stores it has the potential to feed heat pumps and or be recirculated during the autoclave curing cycle to achieve an up-lift in temperature. The traditional cold store therefore does not require insulation; the aim is to maintain this at a low temperature and can therefore promote efficient autoclave cooling at lower throughput rates. Use in this way offered the greatest range of potential use scenarios to be evaluated.
Detailed tank designs were produced for the cold insulated store which is similar in construction to tank 2. Rock wool insulation was selected for cost, performance and ease of manufacture. Drawings were passed forward for manufacture. In addition a specification was produced to ensure the correct sizing of a simple cold store which would represent the traditional cooling pond in the prototype system.
Flow chart logic’s have been created for the tanks initialisation phase, autoclave cooling cycle and the autoclave heating cycles. The control system is based on a Wago PLC with a PFC controller and is a modular system that supports various digital, analogue and speciality modules. An integrated web server provides the user with configuration options and status information from the controller. The software has been written using a compiler known as CodeSys which can be used across multiple language types. The system is interfaced via a digital touch screen.
The system can be run in one of three settings, manual, off and automatic. This allows the system to be tested without the PLC being connected and allows the operator to manually override the system if required.
A range of potential system configurations were considered for the recovery of heat and compressed air. Careful consideration was given to the feasibility and cost of these which demonstrated that the savings were minimal and did not justify the investment in such a solution. For example the conclusions from the consideration of an air re-use; turbine within an air re-circulation sub-system were investigated as a way of converting the waste air into electrical energy the main issue was the intermittent use of the turbine. This equated to an estimated 144 hours use per year for a single autoclave giving a low return on investment even in a site-wide system with a turbine costing in excess of €12,000 but only being used for a small proportion of available time each year.
• Investment costs Approx 12,000€
• Power DEPRAG GET (Green Energy Turbine) 5 kW
• Infeed remuneration 0.20 €/kWh
• Annual usage (single autoclave estimate) 144hrs
• Annual costs (Maintenance etc.) 400€
• Annual earnings 144€
• Payback period Approx. 88 years
To negate the impact of these findings on the overall novelty and energy saving potential of ENRSYS, a new stream of work was also introduced to investigate and develop a system for heat recovery from the autoclave cooling fans. This had been overlooked prior to the project when the concept was developed, however working. These offer much larger potential for energy savings and run for a much larger portion of the autoclave cycle and continuously produce excess heat energy.
Preliminary designs were considered to adapt the main heat recovery system and add an additional cooling circuit which would enable heat extraction from the cooling fans. A secondary cooling coil was specified within tank 3 (insulated cold store) to enable heat extraction from the fan cooling water into this tank and the cooling circuit also allowed for continuous, low level heat feed to the heat pump. These were reflected in the system P&ID and also incorporated into the control specifications For the purpose of simulation a heater was specified within the demo unit to mimic this heat source. The manufactured system is based upon these P&IDs.
The manufacturing techniques for the bean bags were assessed, a simple prototype has been built and the overall concepts were presented to the beneficiaries. Whilst initial interest into this solution was high, ISRI carried out initial evaluation of the performance by conducting provisional tests and calculations were made to estimate the potential energy saving capability of the bean bags. A known heating profile was used for the calculation; and the results suggested that a 17kW saving could be achieved per curing cycle using a 379m3 autoclave at a 15% bean bag loading.
During the evaluation of the end users sit it became evident that the hull presented the major source of heat loss. The bean bag system would not achieve any inherent reductions in this. As such new concepts for insulating the hull were presented and deemed to offer a much improved technical and economic benefit.
3. Build Sub-Systems of Demo Unit
The specifications for the heat-pump sub-systems were signed off for manufacture, this review ensured that the
Following the research, specification and design undertaken previously the outputs were signed off for manufacture of the hot thermal store system. A final design review was carried out to ensure the designs were fit for purpose and also to identify any associated project risks e.g. H&S, or procurement delays.
Design reviews were undertaken to of the pressure vessel in order to ensure that it would meet all relevant safety regulations. Initial tank data was compiled to satisfy the essential requirements including material conformity, weld procedure, tank inspection & pressure test certificates to comply with PD5500. Formal consultation was required from an independent risk management with expertise in the UK legislative requirements to ensure the tanks could be approved for use. The prototype simulation was manufactured which consists of a sealed tank an integrated heat-exchanger.
Final sizing calculations were performed to confirm the sizing of the cooling pond prior to order.
The unit was manufactured according to the designs produced. As with the hot thermal stores all necessary fittings were installed ready for integration with the other subsystems. The tank was reinforced to ensure integrity when filled with water. An additional cold water store was also procured to mimic a traditional cold water pond in an industrial facility. These were inspected and signed off ready for integration.
The control hardware has been procured and assembled in accordance with the designs and specifications created previously. The software has been programmed to utilise temperature, pressure flow and level sensors to control valves and pumps to control the flow of energy stored in each part of the system. The software is managed by a central PLC which is resident in the main control cabinet.
4. Integration & Commissioning of Sub-Systems
All necessary ancillary components were purchased by ISRI to allow for integration of the subsystems. Once initial integration had been carried out set to work commissioning of the heat pump system was performed to check for correct functionality of this and its associated valves and sensors.
The prototype subsystem was integrated with a heat source at ISRI via an interface heat exchanger within the “simulation tank” so that testing and validation of the system could be carried out in a safe and controlled manner. This work on the integration of the heat pump system was carried out concurrently with the subsequent tasks i.e. this was also connected with the other subsystems and piping as outlined in subsequent tasks.
Comprehensive safety checks on all tanks were undertaken. The various tanks were connected to the other sub-systems and tanks including the insulated cold store and the simulated cooling pond. Supplementary water heaters were fitted to tanks 1 & 2 to enable higher temperature outputs to be simulated in a laboratory environment. Full pipework checks were carried out to ensure no leakage, correct flow of water.
The simulation water tank and its associated pipework was connected to the range of thermal store tanks and the various components were located according to the proposed system layout. The remaining fittings and pipework was installed prior to welding of joints. Checks were carried out to ensure check valves and sensors function correctly.
Concurrently with the other installation activities the cold thermal store and simulated cooling tower were also connected with tanks, 1, 2 and the “simulation tank”. Checks were carried out to ensure these all functioned together. Set to work commissioning procedures were followed to document the initial commissioning of the system and ensure this was ready for lab validation and final handover.
All electrical hardware was installed within the system (including installation of the control panels, all system wiring i.e. to various sensors, actuators etc, integration with the power supply and initial testing to ensure the electrics were safe and functioned as expected. Following the initial integration work an extensive period of commissioning was carried out to i) debug the software ii) optimise the set-up prior to trials in WP4.
A Model to scale system for commercial application has been designed for use ‘post-project’ The model contains a detailed & refined thermodynamic model of the autoclave. A mathematic simulation has been undertaken including several scenarios taking into consideration key autoclave factors like autoclave electric heaters (autoclave heat energy input), process temperature. The process temperature is in correlation with the overall heat transfer coefficient enabling the heat energy transfer. Additionally, a new graphical user interface (GUI) was developed. The graphical user interface is a display in one or more windows containing controls that enable the user to perform interactive tasks without the need for typing a script or commands. The GUI is divided into 3 sections: User section, Water tank calculations section and Energy savings section. User section is where the user enters values in order for the GUI to calculate certain values. Water tank section is where the results of tank capacity and temperatures will be calculated. Energy savings section is where calculations of saved energy are displayed.
5. Field Trials & Validation
A D of E (Design of Experiments study) was undertaken to determine the required test program based on the following scenarios i) no heat pump ii) commercial heat pump iii) simulation of a “super” heat-pump using the electrical heaters. A matrix of tests was produced for implementation during the system validation work.
Validation of the control system was undertaken in a laboratory environment prior to any full-scale testing being undertaken. These trials were conducted in manual mode. During this time debugging issues were addressed and some minor improvements to the control system were made.
The output data from the trials has been analysed based on the computation of heat balance. This analysis has led to a number of conclusions regarding the usefulness of the system. The complete cooling (or heating if the reverse process of stored heat recovering is considered) tests have been undertaken to reproduce the complete energy storage process through heat transfer from the Autoclave to the tanks. This work was divided into three sub-tests, a) cooling of simulation tank, heating of tank 1 – high enthalpy, b) cooling of simulation tank, heating of tank 2 – medium enthalpy, c) cooling of simulation tanks, heating of tank 3 – low enthalpy.
The range of testing included preliminary cooling testing, heat pump testing, thermal stratification and followed the D of E study. The tests were based on increasing the initial temperature of the simulation tank in order to simulate three different enthalpy levels. The energy saving potential of all three scenarios (low, medium & high) have been calculated and the payback time of a large-scale system calculated for a known full-scale Autoclave installation. Considering an initial cost estimate of the full scale plant equal to 310,000 Euro, the best payback time is equal to five years and it is given by recovering heat at the highest temperature as possible, also considering an equivalent of the 40% of the energy stored spent by the heating pump to uplift and keep the temperature up to 120°C.
Initial screening trials were undertaken to evaluate the preferred insulation solution using the basic small-scale rig developed previously on the candidate materials identified. These enabled the choice to be narrowed to two main products:- Superfoil® SF40 and Rockwool Cladding (foil faced).
These materials were tested and compared with each other as well as with a non-insulated system using the second larger-scale rig. The results show that the fitting of a layer of SF40 could represent a significant energy saving per annum, potentially as much as 90%.
Based on the lessons learned throughout the build, integration, planning for testing and installation and also the trial phase ISRI have produced a number of recommendations for system improvement and have been included these include:
1. A two tank system in a commercial application as the low enthalpy scenario doesn’t produce enough energy savings vs the payback time.
2. Reduced complexity through use of a single tank so reducing the pipe-work and subsequent controls required.
3. 70°C Heat-Pump. This is the best option in the absence of a higher rated heat-pump that is commercially available.
4. Reduced tank temperature stratification: To improve the stratification agitation or recirculation pumps should be utilised.
5. Autoclave insulation: Use of Super-Foil SF40 is recommended.
6. Control System Improvements: By improving the variable speed drive logic in order to vary the flow rates which will help maintain the temperature profile.
7. FMEA Analysis: For all considered commercial applications in order to fully understand the process variables and outputs for a given system.
Potential Impact:
The ENRSYS project has provided the SME beneficiaries with an IP protectable technology to manufacture an integrated, computer controlled, heat recovery, reuse & thermal energy management systems for autoclaves. This is a bespoke system for each application(s) of an end-user.
Whilst the EU is a leader in aerospace composites processing, the aerospace and automotive industry is a global business with parts being manufactured further afield prior to being shipped for assembly by an OEM or within their 1st tier supply chain. Thus there is increasing pressure from processors based outside the EU. ENRSYS provides a real option for European autoclave users to reduce energy costs and thus overheads keeping them cost competitive with the rest of the supply market. End users of the ENRSYS technology will benefit in a number of ways. Firstly, the model to scale software will detail the current losses in their autoclave systems and accurately predict the energy savings for their system(s). This in turn will give accurate payback times for each bespoke installation and increased efficiencies. There is a further impact in using the ENRSYS technology, end-users will benefit from a reduction in the primary energy used as well as increased efficiencies for each autoclave cycle due to improved heating profiles by use of stored energy.
It is difficult to give actual figures because each installation is bespoke and the savings will depend on the number of autoclaves integrated into the ENRSYS technology, however, for the target application the following figures were obtained (per anum) for a system of 5 Autoclaves using a two tank system (>70°C, 70°C to 100°C) is:
• Energy transferred: 212MJ
• Efficiency: 77%
• Cost reduction: €70,000
There are approximately 1000 autoclave users in Europe with a current market growth of about 4% per annum. The total market of installed autoclaves onto which the ENRSYS technology could be retro-fitted is estimated to be approximately 2000 currently and could be about 2,340 five years post-project. The aim of the consortium is to have penetrated 2% of the market selling approximately 50 systems.