Successful Application of Hierarchical Digital Control in the Pargas Cement Plant

Abstract

The shortening of the weekly hours for workers in continuous three-shift work from 40 hours to 36 hours, starting in 1980, forced many process industries to find solutions for decreasing the number of personnel per shift. Automation and concentration of the control to a few or only one control room was chosen also by Partek as a method for reaching this goal.The demand for high availability could be met by a microprocessor based, distributed control system, DAMATIC, which had been developed by Valmet, a Finnish company. In this system even the control room CRT displays are generated by microprocessors, thus eliminating the need for minicomputer or discbased data systems. The same data highways which carry information from the analogic measurement points are also used for motor start-stop control.The process computer, which has turned out easy to program and to operate, is a Hewlett-Packard 1000 with a 20 M byte disc memory. It is connected to DAMATIC through a serial digital channel. The progammes are written in FORTRAN. Besides control tasks going through the DAMATIC system, the computer also controls “intelligent” sensors like X-ray analysers and particle size analysers.Computer programs developed by Partek now control raw material mixing, cement rotary kiln operation, and cement finish grinding. A typical feature of these programs is that several measurements, both continuous and sampled, have to be combined to a model of the process in question to make control actions correct. Through computer control, 2-4 % savings in fuel consumption and 5-10 % savings in energy needed for finish grinding have been achieved.The hierarchical solution, where the process computer has been relieved of primitive routines, like analog data collecting, digital control of simple loops, interlocking, generating of control room displays etc., which all can be taken over by microcomputers, makes it possible for the operating personnel to take advantage of the smooth programming and operating properties of modern minicomputers without hazarding the reliability of the primary supervisory functions in the control room.