Automatic Kiln Control at Oregon Portland Cement Company´s Durkee Plant Utilizing Fuzzy Logic

The basis and experience in automating the control of a 1500- ton/day four-stage preheater cement kiln is described. The control substitutes the coordinative control actions formerly carried out by the kiln operators by utilzing a minicomputer to implement fuzzy logic control strategies. Operating decisions are made more consistent and quantitative and less subjective to human operator control philosophy variations. By making mathematical approximations of the relationship between changes in process variables through linear regression analysis and then by implementing verbally formulated control rules for corrective action, kiln fluctuations are reduced and more stable operation is achieved. The control is based upon a direct correlation between the nitric oxides measured in the kiln exit gases and the liter weight of the clinker in the burning zone. A consistent liter weight is the aim; however, a secondary control program assures the correct temperature/excess air after the preheater tower. Kiln speed and kiln feed are kept constant, and control actions are taken on the kiln draft by speed adjustments of the induced draft (ID) fan and fuel adjustments of a direct-fired coal mill by coal feeder adjustments into the mill. The system was installed durig March and April 1982, and the experience gained through the commissioning period and the first six months of operation is discussed. It appears that with the limited experience to date, a savings of about three to four percent in fuel efficiency is achieved. In addition, indications are that brick savings are substantial, as high as 50 percent.