Development of an analytical equation for calculation of the blast furnace fuel rate
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INTRODUCTION
IN the 1960's Rist and Meysson developed a thermochemical model for the blast furnace process that relates, for the steady-state, fuel rate to blast conditions. ~The model has its basis in certain observations that have been found for the steady-state to remain fairly constant as changes are made to the process. These observations are that the gas composition in the stack approaches or reaches the conditions for equilibrium with wustite (FeO,; X = 1.05) and that this occurs at a location in the furnace where the gas and solids temperatures are nearly equal. 2 This allows the furnace to be divided conceptually into two stages, which, in turn, permits the fuel requirements for the bosh and hearth to be separated from the fuel requirements for the stack. Appropriate mass and heat balances are derived for the bottom stage as well as for the process as a whole, which along with the foregoing condition of chemical equilibrium, function as constraints in the model. The model is represented graphically as the Rist diagram (Figure 1), where the oxygen balance for the entire process is represented as an "operating" line in terms of the coordinates of gas composition and oxygen-level of the ironbearing burden. 3 The thermal balance for the bosh and hearth and the gas composition in the stack at the level where the higher oxides of iron have been reduced fully to wustite are represented by points P and W, respectively, on the operating line. In the model, point W refers to the "ideal" conditions of equilibrium of the gas phase with wustite and plug flow conditions for the gas and solid streams. With these points specified, the operating state of the furnace is defined completely; the top gas composition (point A), the amount of "direct" reduction by coke (FeO + C = Fe + CO2; point B) and the specific wind rate (point E) are all set with points P and W specified in the model. The essence of the Rist-Meysson model is to show graphically the effects of changes in the thermal conditions of the bosh and hearth on the slope of the operating line DAVID M. KUNDRAT is Senior Staff Engineer. Armco Inc., Middletown, OH 45043 and Adjunct Professor, Department of Materials Science and Metallurgical Engineering. University of Cincinnati, Cincinnati, OH 45221. Manuscript submitted February 6, 1986. METALLURGICALTRANSACTIONS B
when fixed at the ideal gas composition (point W), the slope, in turn, being directly the "ideal" fuel rate for the process, "ideal" referring to the furnace operation for which the assumptions of the model are obeyed. Recently, Peacey and Davenport have outlined a procedure for calculating the ideal fuel rate, for which a computer program of the model is employed. 4 In 1966, Nakatani et al. discussed from a different point of view the roles of the iron oxide-gas phase equilibrium and thermal requirements in setting the fuel rate for the blast furnace process. 5 They presented a plot, referred to as the Carbon-Direct Reduction Rate (C-DRR) diagram where the conditions of chemical equilibrium for the s
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