Batch process structural variations

Batch process structural variations. (A) Single stream batch process (B) parallel streams batch process (C) multiple pathways batch process. 

As an example, 80 batches with four observations per batch were each simulated for the following random variation forms normal, exponential, and lognormal, (see Fig. 5 A-C). x and R charts were constructed for each set as if the true random variation were normal. The charts appear in Figs. 2-4. The results appear in Table 2. This table shows that roughly the same number of points falls outside the x control limits, regardless of the form of the random variation. However, the lognormal distribution has many more R values outside the control limits than the other four distributions. The operator of the process would mistakenly think this process was frequently out of control. The R chart shows greater susceptibility to nonnormality in the random error structure. 

Because of the nonuniform temperature and complex flow pattern in the reactors, it is not possible to model the process in order to predict all the distributions required to describe the structure. In addition, it is not possible to characterize the structure of LDPE in any detail using analytical methods because of its complex and irreprodudble structure. Finally, different batches of polymer made in the same reactor often vary in their structure. These variations may not be detectable using standard test methods while stiU affecting the processing behavior of the melt [115]. 

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