OCR Text |
Show in Kalina and Leibowitz [29]. Of particular imponance in the analysis of this module is only the use of the stack gas composition as calculated in the adapted G-M model. TRACE, which is described in more detail below, addresses those airborne emissions and solid products of combustion not adequately addressed by the adapted Gordon-McBride model. In particular, TRACE is used to estimate particulates, NO., P AH's, dioxins and furans, trace metal emissions, and the composition of bottom ash. These aspects of combustion modeling are addressed in TRACE because formation of particulates and bottom ash or clinker products are not well considered in the G-M structure. The fate of trace metals can be predicted by the use of G-M, however the model has operational limitations in this regard. Oxides of nitrogen are not well addressed since the reactions forming NO. rarely if ever go to equilibrium [14, 15]. Similarly the PAH's are not necessarily equilibrium products. Finally, the G-M model does not address the formation of chlorinated dibenzo dioxins or chlorinated 'dibenzo furans at all, since these are largely post-flame and post-combustion zone phenomena [3, 21, 45]. In order to have a reasonable profile of the combustion process, such emissions and solid biproducts must be addressed. The results of the combined modules in SFCOMB offer an integrated analysis of any low grade fuel combustor. These results include the system efficiency and generation of useful heat, the flame temperature, the bulk gas composition, and all airborne emissions including acid gases, particulates, trace metals, oxides of nitrogen, polyaromatic hydrocarbons, dioxins and furans, and the composition of bottom ash. As such, these results are of considerable use to system engineers, risk assessment personnel, and environmental analysts. 3.0. CONSTRUCTION OF THE TRACE MODULE The most critical aspect of SFCOMB is the TRACE module. This component is responsible for estimating those emissions not readily predicted by thennodynamic or kinetic equations alone. 3.1. Governing Principles for Construction of TRACE A large amount of literature was surveyed in order to construct TRACE. This literature survey was designed to obtain emissions values for the classes of combustion biproducts to be treated by the module. Funher, it was designed to obtain values which could be evaluated according to the mechanisms discussed in Section 2.1 and shown in Figures 2, 4, 5, 6, and 7. In assessing the information obtained, a hierarchy of emissions data was established (from highest to lowest): 1) emissions values from operating full scale plants; 2) emissions values from large scale pilot plants, approaching full scale systems in size; 8 |