Batch process control recipe

Batch run-to-run control can be viewed as implementing a series of set-point changes to the underlying batch process controllers at the end of each run. By analyzing the results of previous batches, the run-to-run controller adjusts the batch recipe in order to reduce quality variations. Thus, run-to-run control is equivalent to controlling a sequence of the controlled variable at times k, k + 1, k - - 2, analogous to a standard control problem. 

This control activity is primarily concerned with determining what products will be made in the batch plant and when those products will be made. This requires the control activity to interface with the process management, recipe management, and information management control activities. 

Fritz, M., Liefeldt, A. and Engell, S. (1999) Recipe-driven batch processes Event handling in hybrid system simulation. Proceedings of 1999 IEEE International Symposium on Computer Aided Control System Design (CACSD 99), Hawaii, USA, pp. 138-143. 

This section describes some of the tools available for intelligent development of process cycles, such as the time-temperature cycles used in curing composites. Current industrial practice is typically limited to the use of cure cycles. The cycles are based on a series of autoclave temperature and pressure states so that traditional linear, regulatory process control methods can be used. These recipes may not be the ideal method for process control of batch processes because they do not ... 

Applications to batch processes have been less common, but there has been some work done on the use of an ANN to control autoclave curing. Joseph et al. used an ANN successfully to cure a part, reducing cure times and improving qualities, such as thickness control and void content [37], When more variables were included, however, the computational problem became intractable. This particular approach to using an ANN broke variables down into time, temperature, and pressure recipes, which, as noted in the Section 15.3.2, can lead to exponential growth of necessary training cases. 

Recipe management refers to the assumption of such duties by the control system. Each batch of product is tracked throughout its production, which may involve multiple processing operations on various pieces of processing equipment. Recipe management ensures that all actions specified in the product recipe are performed on each batch of product made in accordance with that recipe. As the batch proceeds from one piece of processing equipment to the next, recipe management... 

The example is taken from a polymerization batch process and has also been referred to previously by Dahl et al. [1999] and Kosanovich et al. [1996], The dataset consists of 50 batches from which eight process variables are measured over approximately 120 time intervals. From this set of batches, two quality variables on the final product were also available. Both process and quality variables are listed in Table 10.7. The reactor in this chemical process (see Figure 10.26) converts the aqueous effluent from an upstream evaporator into a polymer product. The reactor consists of an autoclave and a cooling/heating system. It also has a vent to control the vapor pressure in the autoclave. The recipe specifies reactor and heat source pressure trajectories through five stages. 

The batch method is quite simple and can be used in many different types of polymerisations, although there is little control beyond the recipe, temperature, and agitation conditions. Because latex particles are usually nucleated in the early stages of a batch polymerisation, they can be made monodisperse, and polystyrene size standard particles have been made using this process. However, significant variations may still exist from batch to batch, making production of a consistent product difficult by the batch process. 

The master recipe is essential, as without it, control recipes cannot be created, hence no batch processing. 

The polymerization takes place in the presence of catalysis. The objective of the batch process is to maximize production of the product by controlling the amount and timing of added reactants along with the reactor s temperature profile. Of course, this objective is conditional on satisfying certain safety constraints. In the initial recipe the feedrates for components A and B, the temperature and the catalyst charge, which are also the decision variables in the optimization, are set. 

In batch production, a recipe that contains all requisite information for manufacturing the product determines the products processes. This includes ingredients or raw materials needed the order of process steps through which ingredients must pass the conditions of each step in the process, and the equipment to be used in the process. Because an individual batch can represent several million dollars worth of research and materials, the batch control is critical for batch manufacturers to ensure the repeatability, consistency, and long-term maintainability of the process. 

General and site recipes are non-equipment dependent and describe the technique of the process, or how to do it in principle, they may however, specify when known, data that may be required for the equipment, for example, pressure requirements. The general recipe is defined at the level of the enterprise, whilst the site recipe is specific to a particular site. Master and control recipes describe the task, i.e. how to do it with actual resources. The master recipe is the required recipe as without it no control recipe can be created and therefore no batches can be produced. 

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. 

In continuous processes, supervisory control is in charge of monitoring the system in order to detect when it is no longer in its optimal state and to act on the local control to compensate it. In the case of batch processes, the supervisory control has also to detect the end of each phase or step of the recipe and drive the system form one dynamic configuration to other dynamic configuration to achieve the final product of the recipe. 

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