Batch analogy

DCS sampling frequency too low or the response time for some analog instruments may be too slow for proper control of transient nature of batch processes and may lead to a process upset. 

Beim Batch-Verfahren wird analog zum Fermentations-Verfahren gearbeitet. Man hat jedoch den Vorteil, daG sich der Katalysator schnell und einfach abtrennen laBt. Fur die... 

Because of the difficulties of presses with HIPS cited earlier, it is usual to transfer the syrup to a suspension reactor containing water and a suspending agent for the completion of polymerization. Design problems for suspension reactors will be discussed in the next section. Design problems for HIPS prepoly batch-mass reactors are analogous to HIPS continuous reactors as discussed in Section 2.3. 

Chapter 1 treated the simplest type of piston flow reactor, one with constant density and constant reactor cross section. The reactor design equations for this type of piston flow reactor are directly analogous to the design equations for a constant-density batch reactor. What happens in time in the batch reactor happens in space in the piston flow reactor, and the transformation t = z/u converts one design equation to the other. For component A,... 

This is the piston flow analog of the variable-volume batch reactor. Equation (2.30). 

As an analogy, the human body performs a mixture of batch, semicontinuous and continuous processes in order to operate effectively. Sohds-handhng operations are conducted batchwise for transfer and semicontinuously for processing, whereas heat exchange (HEx), filtration, pumping, and so on, are performed continuously. 

Calcium caseinate and butter oil have been extruded directly at 50-60% moisture levels to obtain a cheese analog with no surface water or fat (Cheftel et ah, 1992). The fat emulsification and melting ability increased with screw speed or barrel temperature. The texture of the extmded analogs was similar to those obtained by batch cooking and was affected by pH (Cheftel et ah, 1992) and emulsifying salts (Cavalier-Salou and Cheftel, 1991). The product can be used as adjimcts for hamburger, pizza, and sauces. 

Nuclear decay is a random process, yet it proceeds in a predictable fashion. To resolve this paradox, consider an everyday analogy. An unstable nucleus in a sample of radioactive material is like a popcorn kernel in a batch of popcorn that is being heated. When a kernel pops, it changes form. Similarly, an unstable nucleus changes form when it decays. 

Analogous to time as a measure of batch process performance, space-time (r) can be defined for a continuous reactor ... 

As with continuous processes, the heart of a batch chemical process is its reactor. Idealized reactor models were considered in Chapter 5. In an ideal-batch reactor, all fluid elements have the same residence time. There is thus an analogy between ideal-batch reactors and plug-flow reactors. There are four major factors that effect batch reactor performance ... 

All of the control schemes mentioned previously can be accomplished using digital control or the traditional analog control methods. For many processes there is at present no economic justification for a digital control system if only physical disturbances are to be considered. One exception to this is a multiproduct batch processing plant, in which a number of operations are required. 

Since this is a batch system, it might be advisable to use direct digital control. Undoubtedly the throughput could be increased over that with the more traditional analog control system. However, the initial costs and maintenance expenses would also increase. To fully instrument the system would also greatly complicate the equipment required, especially for feeding the reactors (this is discussed later). An economic balance should be run to determine whether this is feasible. I feel it would not be warranted, and have chosen to instrument the plant in the traditional way. 

The tubular flow reactor is a convenient means of approaching the performance characteristics of a batch reactor on a continuous basis, since the distance-pressure-temperature history of the various plugs as they flow through the reactor corresponds to the time-pressure-temperature protocol that is used in a batch reactor. Although this analogy is often useful,... 

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