(6c) Process Variability: Causes, Costs, and Cures

Excessive variability in product qualities and process operating conditions is a problem in many plants. It can have many causes and its reduction can be obtained by many different types of changes in equipment and control. Depending on the source, the magnitude and the frequency; process design and operating procedure changes may be justified. Variability can also often be reduced and control system performance improved by enhancing measurement and control valve performance, by dynamic analysis and scientific loop tuning and by implementation of advanced multivariable control technologies. To evaluate the economic return of these potential investments it is necessary to have a realistic estimate of the financial value of this reduction. Claims for these benefits are often made that are not supported by basic process industry financial norms. Equally, valuable associated benefits are sometimes ignored. In this presentation, realistic approaches to estimation of financial benefits from variability reduction are presented. A methodology to decide what types of changes should be made to reduce variability is also shown. Case studies showing applications of the methodology and results are presented.