Mathematical model of COREX melter gasifier: Part II. Dynamic model
- PDF / 171,931 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 76 Downloads / 232 Views
I. INTRODUCTION
III. THE MODEL
IN the COREX process, after the blow-in operation, the furnace passes through a transient period and eventually reaches a steady state. Besides, often it is required to shut down the furnace for routine maintenance, which leads to an unsteady state for a significant period of the total furnace operation time. It is of interest to characterize this unsteadystate behavior. Numerical investigation of the transient behavior of the melter gasifier has not been done to date, to the authors knowledge. In this article, an unsteady-state model is developed to investigate the dynamic response of the melter gasifier. The model is based on the steady-state model described in Part I of this article.[1] The dynamic response of the blast furnace has been studied by a number of investigators.[2–6] A one-dimensional (1-D) dynamic model of a blast furnace by Kubo et al.[2] simulates the empty-blowing-out and blowing-in operations. Hatano and Yamaoka[3] studied the transient behavior of a blast furnace due to changes in process parameters like oil injection, blast temperature, blast moisture, and ore-to-coke ratio. Their results[2,3] show good agreement with the plant data. Detailed analysis by Takatani et al.[4] predicted the blow-in and blow-off condition with respect to changes in the temperature of the hot metal and temperature and composition of the top gas. All these studies show that a blast furnace takes a long time to reach steady state, which is observed in plant operation also. Flierman et al.[5] have shown that it may take 10 to 20 hours before a noticeable change in Si content of hot metal occurs in response to any change of the process variables like blast moisture, blast temperature, coke charge, etc. A scrap-melting process of the moving-bed type[7] shows a much higher response than that of a blast furnace to reach steady state.
The mass, momentum, and energy-balance equations for all phases can be represented by a generalized governing equation: ⭸(ii) ⫹ ⵜ ⭈ (i ui i) ⫺ ⵜ ⭈ (⌫ ⵜ ⭈ i) ⫽ S ⭸t
[1]
Where is a scalar quantity and, for an appropriate value of , Eq. [1] becomes an equation of continuity, equation of motion, or heat-balance equation. The source term in the continuity equation has a mass source because of chemical reactions, whereas, for the momentum-balance equation of gas, the pressure gradient and interphase resistance terms are the source terms. The source of heat arises from the reaction heat, surface heat transfer due to convection, and radiation and phase-change heat transfer. Equation [1] has been written for all the species and phases considered in Part I of this article. The total number of species-continuity and heat-balance equations has given in detail in Part I. The primary gas- and solid-flow direction in the melter gasifier is axial, but, near the vicinity of the tuyere, the gasflow direction is radial. This poses a problem for the gas boundary condition. So, two-dimensional (2-D) mass, momentum, and heat-balance equations have been solved near the t
Data Loading...
