Discrete batch type operation

Discrete batch, also called intermittent, refers to a facility in which processes are organized into separate work centers and products are moved in lots through a sequence of work centers in which each work center is set up for a specific set of operations on that product and the setup and sequence is specific to a product family. This describes a facility that can make a large but relatively fixed set of products but only a few types of product at one time, so the same product is made at intervals. This also describes a facility in which the technology is common— the set of processes and the ordering is relatively fixed, but the details of the process in each work center may vary considerably from product to product in the mix. Examples include semiconductors and circuit boards, composite parts, firearms, and machined metal parts made in quemtity. 

In a retrofit batch design, we optimize the batch plant profitability defined as the total production value minus the cost of any new equipment. The objective is to obtain a modified batch plant structure, an operating strategy, the equipment sizes, and the batch processing parameters. Discrete decisions correspond to the selection of new units to add to each stage of the plant and their type of operation. Continuous decisions are represented by the volume of each new unit and the batch processing variables which are allowed to vary within certain bounds. 

Many industrial users of batch distillation (Chen, 1998 Greaves, 2003) find it difficult to implement the optimum reflux ratio profiles, obtained using rigorous mathematical methods, in their pilot plants. This is due to the fact that most models for batch distillation available in the literature treat the reflux ratio as a continuous variable (either constant or variable) while most pilot plants use an on-off type (switch between total reflux and total distillate operation) reflux ratio controller. In Greaves et al. 2001) a relationship between the continuous reflux ratio used in a model and the discrete reflux ratio used in the pilot plant is developed. This allows easy comparison between the model and the plant on a common basis. 

CFA is very often used in process control. In CFA, the sampling process consists of samples flowing sequentially and continuously in a tube, where each sequentially mixes with reagents in the same tube at the same point downstream and then flows sequentially into a detector. Another automated device type is the discrete analyzer where the analysis is made by taking a batch sample at selected intervals and subjecting it to analysis. The main advantage of CFA is the objectivity assured by operator elimination at the sample pickup and sampling steps. However, when the complexity of the sample that is to be analyzed increases, CFA does not offer reliable analytical information therefore, one should use discrete analyzers as an alternative. 

There are two types of analyser discrete and continuous (Figure 9.3). In discrete analysers, samples are taken at selected intervals, placed in individual containers and any required sample preparation steps are carried out. Samples are then analysed in batches, with the information being fed to the controller and operator in the usual way. Obviously... 

Batch processes are examples of discrete-event dynamic systems they include start-up and shutdown processes, valving operations, recipe execution. Different methodologies have been proposed to model, analyse and control this type of systems. 

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