Statistics for Process Control Engineers

3Process Examples

Real process data has been used throughout to demonstrate how the techniques documented can be applied (or not). This chapter simply describes the data and how it might be used. Where practical, data are included as tables in Appendix 1 so that the reader can reproduce the calculations performed. All of the larger datasets are available for download.

The author’s experience has been gained primarily in the oil, gas and petrochemical industries; therefore much of the data used come from these. The reader, if from another industry, should not be put off by this. The processes involved are relatively simple and are explained here. Nor should the choice of data create the impression that the statistical techniques covered are specific to these industries. They are not; the reader should have no problem applying them to any set of process measurements.

3.1 Debutaniser

The debutaniser column separates C₄₋ material from naphtha, sending it to the de‐ethaniser. Data collected comprises 5,000 hourly measurements of reflux (R) and distillate (D) flows. Of interest is, if basic process measurements follow a particular distribution, what distribution would a derived measurement follow? In Chapter 10 the flows are used to derive the reflux ratio (R/D) to demonstrate how the ratio of two measurements might be distributed.

3.2 De‐ethaniser

The overhead product is a gas and is fed to the site’s fuel gas system, along with many other sources. Disturbances to the producers ...