Conceptual model of the iron blast furnace considering thermodynamic and kinetic constraints on the process
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I. I N T R O D U C T I O N
THE aim of the blast furnace
operator is to produce hot metal of a consistent quality at a desired rate and at the lowest possible consumption of fuel. Thus, hot metal temperature and chemistry, production rate, and fuel rate are the critical parameters of the process. The primary control variables are typically blast conditions for feedback control, and burden and coke properties for feedforward control. The relationship of these variables to the furnace parameters has been known empirically, yet these relationships are limited generally to a narrow range of operation. To extend the process to lower fuel rates and higher productivities while maintaining a consistent hot metal quality requires knowledge of the behavior of the process over a wide range of operating conditions. This is necessary not only for gradual improvements in efficiency of the conventional process but also for major changes to the process that are designed to dramatically increase productivity and substantially decrease fuel rate. m For this, it is desirable to anticipate the behavior of the process at the new operating regime from a mathematical model that accommodates all of the critical variables. While some progress has been made with regard to the development of models, it is difficult to verify them a priori. To facilitate verification of these models, a perspective of the relationships among the key variables of the process over a wide range of operating conditions is useful. Fundamental chemical and thermal relationships of key control variables to the parameters of the process can be deduced from a rudimentary analysis where the dictates of the First and Second Laws of Thermodynamics are imposed on a countercurrent, packed-bed reactor undergoing chemical reactions of finite duration. The thermodynamic constraints are principally the oxygen and heat balances, stoichiometry, and chemical equilibrium of the iron oxides and of carbon with the reducing gases. D.M. KUNDRAT is Senior Staff Engineer, Armco, Inc., Middletown, OH 45043 and Adjunct Professor, Department of Materials Science and Engineering, University of Cincinnati, Cincinnati, OH 45221. This paper is based on a presentation made in the T.B. King Memorial Symposium on "Physical Chemistry in Metals Processing" presented at the Annual Meeting of The Metallurgical Society, Denver, CO, February, 1987, under the auspices of the Physical Chemistry Committee and the FrD/ISS. METALLURGICAL TRANSACTIONS B
The chemical reactions are the reduction of iron oxide and regeneration of the product gas by reaction with coke. These constraints are also implicit in the inherent chemical and thermal stability of the process. For example, it can be deduced that satisfaction of the oxygen balance with the simultaneous superposition of the ore reduction and coke gasification reactions is responsible for the blast furnace having a degree of self-regulation as it responds to changes in control variables. The relationship of the chemical constraints to the fuel rate and produ
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