Batch process control activity model

Model concept in a batch process helps in understanding its hierarchical structure, and is specified in Part 1 of ISA 88. This structure will assist in dividing the systems into smaller parts. In line with the standard. Fig. VI/3.1.2-1 shows the various model types. Fig. Vl/3.1.2-1 A (or Fig. 1 of ISA 88) shows how the entire process has been divided into smaller parts for analysis of the system. As shown, the process is subdivided into process stage, process action, etc. This is a process model of batch process. The entire process can be divided in terms of models in three ways, viz. physical model, procedural model, and control activity model, as shown in Fig. VI/3.1.2-IB. Therefore, it is better to start the discussion on the three types one by one. 

The sequential control logic required at each level of a control hierarchy in batch plants is still largely derived manually, perhaps with the aid of some structured approach. This is a time consuming and error prone activity in which safety issues are difficult to treat formally and efficiently. To overcome these problems, Alsop et al [21] and Sanchez and Machietto [22] proposed a formal method for computer aided synthesis of sequential control logic for processes modelled as state-transition systems such as the co-ordination control of batch processes. 

The blend of the two active ingredients (B1 and B2) is slugged and then the slugs are oscillated. Slugger model and tooling are listed in the batch instructions. The thickness of the slug is specified, but no information is recorded on the slugging operation, as control of this procedure is left to the experience of the press operator. The batch record permits the use of only one screen size. Since all of the batches have been made in the same manner, this important process step will not be included as one to be studied. 

As one of its major interests, a model represents an efficient tool for the kinetic analysis of cellular processes. It is able to account for the main phenomena that may simultaneously control the activities of cells. As such, depending on the culture conditions, composition of the medium and whether there is batch or continuous mode of operation, it can be used first to identify the rate-limiting factors and then to characterize quantitatively their relative importance. For instance, with a model it is possible to evaluate the kinetic effect of a depletion of glucose, glutamine and other amino acids or of an accumulation of ammonia and lactate on the rates of cell growth and death. 

The highest level in the procedural control model is the procedure, which defines the strategy for carrying out a major processing activity. The second level is the unit procedure, which is made up of a set of operations that take place within a unit, in a determined sequence. An operation usually involves a chemical or physical change, and is made up of a sequence of phases. An operation must be carried to completion in a single unit, and only one batch is assumed to be worked on at a time in a unit, however, several operations can be executed simultaneously in different units. 

With the exception of a few solution processes such as one used to make ethylene-propylene copolymers, traditional CCC ( Ziegler-Natta ) catalysts, which were used to make all linear polyethylenes until the advent of the metallocene catalysts, have multiple active center types and therefore yield polymers having a moderately broad MWD and CCD. Techniques used to control the distribution include blending, use of mixed catalysts or cocatalysts, and the use of staged batch reactors or multiple, cascaded continuous reactors. These techniques complicated the already poorly-defined MWD due to the heterogeneity of the catalyst, and as a result, the distribution could not be reliably modeled or described using the standard equations presented in Chapter 3. 

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