Dynamic Control of the Cement Process with a Digital Computer System

A control study of the cement manufacturing process has culminated in the installation of a direct digital control (DDC) system which automatically controls both the ball-mill blending of raw materials for kiln feed and the kiln-cooler combination. In each case, the control schemes were developed by determination of the process dynamics, computer simulation and analysis, and field application at the plant. The blending control scheme finally developed is based on measurement of ball-mill output composition with an X-ray analyzer, and on a concept of noninteracting feedforward-feedback control. The kiln-cooler control scheme utilizes conventional and advanced control techniques such as nonlinear, feedforward and adaptive compensations, and optimization. This control scheme includes coordinated loops for control of burning zone temperature by manipulation of fuel rate and/or kiln speed, for control of kiln exit temperature and oxygen by ID fan speed, and for maximization of production rate by trim manipulation of kiln speed. The control schemes are being applied at the plant with a DDC system which provides maximum operating flexibility with extensive simplification of the operator-computer interface. The direct digital control operating experience has been very favorable.