Case Studies where Variography is an Effective Tool to Discover and Quantify Structural Problems

Case study #1: A copper smelter monitors the copper content of slag every three hours. To prepare such sample several increments of the molten material are collected within three hours to make a three-hour composite. The plant must comply with the following specifications believed to work best for an economic optimization: the Targeted Average TA is set at 10%; the Upper Specification US , above which too much money is lost is 14%, and the Lower Specification LS , below which too much money is spent for the process to perform high copper recovery is 7%. At times, the plant encounters difficulties taming the process variability within the specifications. Explanations for these difficulties have eluded management for some time. The following sequence is a step-by-step strategy to approach such difficulties. Case Study #2: An unspecified chemical plant is monitored for the g/l solids of a precipitated valuable product at the underflow exit of a thickener. On a routine basis, a 1-liter, one-hour sample is collected to measure the g/l solids. The plant must comply with the following specifications believed to work best for economic optimization: a Targeted Average TA of 440g/l is set. The Upper Specification US , above which too much money is lost is 490g/l, and the Lower Specification LS , below which too much money is lost as well is 390g/l. On a regular basis, the plant encounters difficulties taming the process variability within the specifications. Explanations for these difficulties have eluded management for some time. Using a variographic approach explanations for these difficulties were revealed.