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Show grade fuels include formation and composition of airborne emissions and solid products of combustion. Airborne emissions of concern include particulates, acid gases, oxides of nitrogen (NOJ, organics with particular attention to polynuclear aromatic hydrocarbons (PAH's) and dioxin and furan species, and trace metals. Ash composition considerations include both carbon content and trace metals content of the bottom ash and flyash, and these have significant implications for the growing concerns related to ash management. 1.2. Combustion Modeling for Low Grade Fuels In order to address the technical/economic and environmental considerations associated with combustion of low grade fuels in industrial settings, Ebasco Environmental has developed a model structure: SFCOMB. This model structure is constructed around a modified Gordon-McBride thermodynamic model [20] which is widely used in combustion analyses. Structurally it includes four components (see Fig. 1): 1) 2) 3) 4) PREP PRELIMS/G-M EFFICIENCY TRACE The model component accepting all of the data inputs; This model component adjusts inputs to the Gordon-McBride format and then calculates flame temperature and equilibrium products of combustion; This model component calculates the useful heat available from combustion of low grade solid fuels; and This model component calculates airborne emissions prior to the air quality control system (AQCS) and also estimates cenain compositional characteristics of the bonom ash product stream. The purpose of this model is to achieve a careful approximation of system efficiencies and emissions to facilitate process design, permitting analyses, and risk assessments. It is structured around existing data, and does not attempt to develop or utilize new data. It emphasizes the use of test information from full scale boilers and, secondarily, large scale pilot plants in order to have maximum use in the field. It is limited to grate fired systems. It does not address fluidized bed combustion, or suspension burning, at this time. 2.0. BACKGROUND The computer modeling of low grade fuel combustion was perfonned recognizing the extensive body of theory associated with the behavior of solid fuel in industrial boilers aDd kilns. Consistency with the general body of combustion theory became a governing principle in the effon. Because the model has been designed to approximate full scale system performance, however, recognition of large industrial grate fired system design principles became equally necessary. These twin constraints were used in guiding the 3 |