Adaptive Control of Alumina Reduction Cells with Pointfeeders

Abstract

Cood alumina feeding control is important to obtain optimum cell operation. Cells with pointfceders may successfully be operated within narrow ranges of alumina concentration in the bath, to reduce anode effect frequency and stabilize cell operation. Control of an alumina reduction cell is difficult due to the lack of measurements which may give information about the internal state of the cell. Normally the only on-line measurement is the resistance of the cell, or more correctly the current and the voltage. ÅSV has developed an adaptiv controller to get as much information as possible from the resistance. The adaptive controller uses the Maximum Likelihood method for estimation of the process parameters. In ÅSV we have more than 1200 reduction cells. We are now installing one micromputer pr. cell. The microcomputer is developed by ÅSV. We have done this because we did not find any microcomputer in the market that satisfied our requirements. Our microcomputer is designed to operate in potroom conditions. The microcomputer is equiped with Intel 8086 microprocessor and a numeric dataprocessor, Intel 8087. This combination are running all the adaptive controller equations in real time. The results achived with adaptive controllers and microcomputers are very good. We have reached current efficencies of 94 - 95 % and energy consumption of 13.2 kWh/kg Al.