Algorithms for On-line Computer Control of Steel Ingot Processing

Abstract

A substantial proportion of steel production is provided in cast ingot form. These ingots are reheated in a soaking pit furnace to provide metallurgically acceptable conditions for the subsequent slabbing process. Substantial savings in processing cost can be realized as a direct consequence of efficient scheduling between successive operations. Efficiency is improved by appropriately choosing from a limited inventory of ingots of known thermal history, and by charging, and firing the furnaces according to strategies which can satisfy the slab mill demand while minimizing cost. An on-line model of ingot thermal behavior has been developed to provide estimates of thermal profile and heat content at each processing stage between teeming and slabbing. This algorithm provides a consistent basis for ranking the utility of various processing options for meeting slab mill demand.Once the charging decision has been made and firing has commenced, it is necessary to monitor and control the reheating process to meet actual demand. An on-line calculation of the thermal state is used to project ingot thermal profiles since these cannot usually be measured directly. The furnace set-point can be modified to insure that the ingots achieve the soaked condition as required by slabbing demand. This paper describes a compact, on-line interactive control algorithm using a suboptimal but practical firing strategy which minimizes fuel cost and slab mill delay.