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Show plant. Because the results of TRACE are based upon existing systems, they are somewhat conservative in approximating emissions. Such conservatism is based upon ever increasing technology to maximize combustion efficiency and minimize undesirable combustion biproducts. 4.0. DISCUSSION The combined results of TRACE AND G-M are shown in Tables 9 - 11. Table 9 presents the profile of a hypothetical lignite fIred system, Table 10 presents the profile of a hypothetical biomass fired system, and Table 11 presents the profile of a hypothetical MSW incinerator. These results are well within the realm of reason for well designed and constructed facilities, particularly as documented by source tests recently conducted for industrial boilers. It is useful to note that the reasonableness of results from this model implies certain limitations of operation. For all cases, the mcxlel assumes grate frred systems (i.e. pile burners and spreader-stokers), since such systems dominate industrial boilers fired with low grade fuels. Further, for all cases, there are significant excess air or stoichiometric ratio limitations as follows: lignite stoichiometric ratio range of 1.2 - 1.8 biomass stoichiometric ratio range of 1.25 - 2.0 MSW and RDF stoichiometric ratio range of 1.8 - 2.5 Further, for MSW it assumes that the grate stoichiometric ratio exceeds 1.0. Exceeding these limits may produce results which are less than reliable. The model is limited in other ways as well. It is limited to operator judgement regarding carbon conversion, the expected operational distribution of underfrre and overfire air, and the expected particle size distribution of the fuels employed (percent fines, percent large particles). If such data are defmed by design studies or vendor guarantees, reliance on the operator of the model is somewhat reduced. Given those limitations, however, the model has proven useful in developing approximation profiles of industrial size boilers. Its documentation with respect to the outcomes from existing facilities ensures considerable utility in supporting feasibility studies from both economic (EFFICIENCY module) and environmental (G-M and TRACE modules) perspectives. When coupled with the AQCS model now under development, it will provide a thorough analysis of all products from the combustion and post-combustion control systems. 15 |