Commissioning and Operation of a Direct Digital Control Computer on a Cement Plant

Abstract

The installation and commissioning of an on-line computer on a new cement plant is described. The computer carries out direct digital control, although conventional controllers are also provided. Part I of the paper gives an account of the background to the project, the process characteristics and the computer functions and an assessment of the value of the computer. The main functions performed are control of raw materials blending and of the kiln. A mathematical model has been used for the development of the kiln control scheme. The computer has assisted in learning about the process, in overcoming commissioning difficulties and in developing control schemes both with and without the use of models. Direct digital control has made possible finer adjustments to valves and set points, has allowed automatic calibration of an important feed flow meter and has made the implementation of alternative control loop configurations easier. Part II gives a detailed description of the computer system and an assessment of its reliability. The availability achieved over a three-year period is 99.1 per cent. Many of the faults which have occurred have been identified and could in future be eliminated in design. It is expected that the availability attainable after such improvements would be about 99.9 per cent.