Batch process intermediate storage

Chapter 3 presents a synthesis technique for multipurpose batch plants and further introduces an unexplored operational philosophy so called Process Intermediate Storage (PIS) operational philosophy. 

Whether parallel operations, larger or smaller items of equipment, and intermediate storage should be used can only be judged on the basis of economic tradeoffs. However, this is still not the complete picture as far as the batch process tradeoffs are concerned. So far the batch size has not been varied. Batch size can be varied as a function of cycle time. Overall, the variables are... 

Batch processes can be synthesized by first synthesizing a continuous process and then converting it to batch operation. A Gantt (time-event) diagram can be used to identify the scope for improved equipment utilization and the need for intermediate storage. 

No matter whether intermediate storage is available or not, some intermediates must be processed immediately because otherwise the batch will be off-grade. For instance, if the... 

Intermediate storage de-couples the process into periodically operated subprocesses in the sense that each of the subprocesses can be operated with its own limiting cycle time and batch size. If the storage capacity is sufficiently large to accommodate the intermediate product of an entire production campaign, then the subprocesses can be operated completely independently. Alternatively, the storage capacity can be selected so that it de-couples the... 

Finally, recycling of materials is difficult in batch processes because the connection in time cannot usually be made between the steps involved in the recycling. This is because different steps take place in different time periods. However, time can be bridged through the use of intermediate storage for the recycle. 

Production schedules for batch processes can be sequential, overlapping, parallel, use intermediate storage, or use a combination of these. Such schedules can be analyzed using Gantt charts. Batch processes often produce multiple products in the same equipment and can be distinguished as flowshop or multiproduct plants. Equipment cleaning and material transfer policy have a significant effect on the production schedule. 

In the analysis, synthesis and optimization of batch plants complexity arises from the various operational philosophies that are inherent in time dependent processes. In a situation where the intermediate is allowed to wait in the same unit from which it is produced until the next unit is available, the operational philosophy is commonly known as no intermediate storage (NIS) operational philosophy. This philosophy is depicted in Fig. 1.3. NIS operational philosophy is usually adopted if operational space is of essence, since intermediate storage tanks can occupy considerable area. 

The goal of a conceptual design for a continuous process is to select the process units and the interconnections between these units, identify the dominant design variables and estimate the optimum design conditions, and identify the process alternatives and find the best four or so alternatives. For batch processes, we must also decide which units should be batch and which should be continuous, whether or not some process operations should be carried out in the same process unit or separate units, whether or not parallel units should be used, and how much intermediate storage is required. Thus, batch processes require more decisions to fix the structure of the flowsheet (there are more alternatives to consider). Since there are many situations in which it must be decided whether to develop a batch or a continuous process, both procedures should be present in a general conceptual design code, whereas the current trend is to develop separate codes for batch processes. 

H3- Multiproduct campaign H4- No intermediate storage H5- No reuse of equipment except for the case of consecutive tasks H6- Processing time is a function of the batch size H7- Production demands are treated revenue. ... 

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