Deliverables Assessment of enhanced removal system of heavy metals from flue gas during coal and RDF co-combustion by dry sorbent injection and filtration The main environmental concern on waste co-combustion is related to toxic emission of heavy metals and organic compounds. The assessment of trace metal behaviour during co-combustion and the removal by dry sorbent injection and fabric filtration not only ensure the compliance with the stringent emission limit values fixed by 2000/76/EC Directive but even allow to demonstrate to European and national authorities and general public the environmental relevance of this application during waste co-combustion. With respect to the initial project, specific measurements on mercury removal have been performed as it resulted that mercury enrichment, speciation and removal is strongly dependent on type of RDF and coal burned and flue gas temperature. Comparison and synergy with other European and national projects have been fruitful for data exchange. As the industrial and economic relevance of the utilisation waste in energy production is growing, the assessment of potential emission and removal technique of heavy metals are of priority interest. These results can be used by power generation companies during the evaluation of the technical feasibility of dry sorbent injection or as base-line for further test on different waste stream impact during utilisation. Moreover, the data collected can represent useful information for authorities to define integrated pollution prevention and control strategy and promote the thermal recovery of waste in fossil fuel power generation plant. Method to characterise the composition of a waste mixture An advanced analytical tool in Excel was developed to analyse the composition of an unknown waste mixture. It includes the TG- and DTG-curves of more than 50 single compounds and some examples of waste mixtures. The TG-and DTG-data of a new mixture can be easily imported to the interface for analysis. Preparation and handling of SRF Grinding is an essential aspect concerning the economics of co-combustion of SRF in pulverised fuel firings, detailed investigations on grinding properties of several mixed waste materials and single components were carried out. At the Institute of Process Engineering and Power Plant Technology (IVD), several experimental facilities are available for these investigations on co-combustion. The grinding tests were performed at a hammer, a cutting and a beater wheel mill. The knowledge about the individual grinding properties of waste fuel components will help to choose the appropriate grinding technology for specific waste fuels. The experiences made in fuel handling provide valuable input for the design of the fuel handling system. Status quo of co-firing in Germany Although decreasing, the fuel mix in thermal power stations in Europe is still dominated by solid fuels, contributing about 55% of the total energy consumed in 1997. As an example in Germany in 1998 520, 000 million kWh of electricity was generated in 982 power plants. The share of coal was 52%, with 27% produced from hard coal and 25% from brown coal. For power production about 45.8 million tons of hard coal, equivalent to 1363PJ, and 151 million tons of brown coal, 1345PJ, were fired in German power plants. These numbers appear to have stabilised at this level over the past few years, after changes following the German reunification in 1990. The co-combustion of biomass, wastes or other residual matter in existing coal-fuelled power plants renders a range of advantages: - The high capacity installed in existing power stations offers a great capacity regarding biomass or waste utilisation, even with small shares of the additional fuel. It involves, however, that the site has to be tested for suitability. - The levels of efficiency of power production in industrial-scale combustion chambers are high. - In case of non-availability of the biomass, the output can be balanced by coal. - Previous studies have shown that there could be an economic advantage because of lower investment costs. For instance, the new construction of a decentralised biomass combustion plant requires investments up to 400 to 750 euros per kW of installed thermal capacity. In the case of retrofitting an existing coal-fuelled power plant for co-combustion with biomass, the additional investments are estimated to only 75 and 150 euros per kW of thermal capacity, the major part of the costs being required for fuel preparation. The quantities of supplemental fuels that could be co-fired in e.g. German power plants can be calculated on the basis of primary energy used. If 10% of the 2708PJ are replaced by a fuel with a lower heating value of 10MJ/kg, about 27 million metric tons could be co-fired in power stations. Though the potential for co-firing in the stoker and fluidised bed firings should not be neglected, the focus of this paper will be on pulverised fuel systems. However, most of the findings can be transferred to the other firing systems. Co-combustion of limited shares of supplemental fuel is technically feasible, even though detailed questions, like the changes on the composition of the residues and operational problems (e.g. slagging, fouling, corrosion), need further clarification. Sewage sludge co-firing in power stations can be considered as a functioning technique. Still, possibly higher emissions of volatile trace metals, e.g. mercury, have to be examined. There is a rather large base of knowledge in co-combustion of bio-fuels (straw, wood) already established through the last years. However, the potential of the large co-combustion capacity within the European power industry has yet to be recognised. For this, fuel qualities for the use in power plants have to be defined and fuel markets need to be established, while careful cost/benefit considerations are required under new boundary conditions as a consequence of the liberated electricity marked. Database of characteristic properties of fuels and fuel mixtures The characteristic properties of waste fuels and their single compounds are collected to an Excel-database. Reported proximate analysis, ultimate analysis and thermogravimetric properties can be used as a fingerprint of each material. Combustion behaviour of SRF This result includes information about several main areas of concern when co-firing SRF in a pulverised coal boiler. Basic information on combustion behaviour of SRF particles are presented as well as general operational observations encountered during the co-firing tests. The results represent a valuable input for evaluation of SRF qualities, important technical issues and emission characteristics, and therefore have high potential concerning the implementation of co-firing in large scale. Combustion experiments were carried out with some operational challenges concerning feeding, which required the installation of a new feeding system. Due to the significantly larger particle sizes of the SRF in comparison to the pulverised coal particles, heat up and consumption is retarded counteracting the benefits of the high volatile matter content. The effects encountered are: - Possible increase of CO and unburned particles in the ash by the coarser fuel grinding, altering the ash properties. - Changed flame geometry in dependence on the particle size of the SRF: A less defined and less homogeneous flame zone forms because of the discretely burning particles. This changes temperature and oxygen in the flame and affects the effectiveness of primary NOx reduction measures. - Possible impacting of burning single particles on tube surfaces: This could cause local temperature excursions and locally reducing atmosphere on the surface leading to increased slagging and fouling. - The aerodynamic properties (shape, density) of different plastic particles change on the path through the combustion. At high heating rates, PP foil formed droplets degrading in form of porous, hollow spheres; PA shavings and the compact PS/PP melt, blister and form very porous char structures; the compact HDPE melted and degraded from the surface. This diverse behaviour influences the residence time of the single particles and components in the combustion zone of a boiler. The deviances of the combustible matter and of the ash forming constituents have distinctive effects on operation and emissions: - Lower SO2 and primary NOx-emission levels due to lower input of fuel-S and fuel-N. - Lower SO2 emissions by increased sulfur capturing by higher concentrations of relevant ash constituents. - Altered slagging and fouling tendency, as sulfur and alkali metals selectively deposited on the relatively colder tube surface due to high Ca in the SRFs. - In combination with the above, co-firing of high ash containing SRF fuels like Stabilat could cause heavy and rapid deposit ash formation on heat transfer surfaces. - Heavy metals from the secondary fuel could reduce the melting temperature of the deposit ash. Searching for OpenAIRE data... There was an error trying to search data from OpenAIRE No results available
