Unlimited intermediate storage

The second operational philosophy that exploits intermediate storage is the unlimited intermediate storage (UIS) operational philosophy. This philosophy is similar to FIS philosophy, except that the availability of storage is always guaranteed. The implication thereof is that whenever the intermediate material is produced it can immediately be stored without limitations or constraints on storage capacity. In practical terms, this can be achieved if the capacity of storage is too large compared to the capacity of production units as shown in Fig. 1.5. 

Unlimited Intermediate Storage (UIS) the intermediate product is stable and can be stored without any problem. There are one or more dedicated vessels with unlimited storage capacity. 

Figure 12.12 Gantt chart with unlimited intermediate storage (UIS).

The so-called zero-wait transfer policy is used when a batch at any stage is immediately transferred to the next stage because there is no-intermediate storage vessel available or when it cannot be kept in the current vessel. This policy is extremely restrictive. The other extremum is the unlimited intermediate storage policy, where a batch can be stored without any capacity limit in a storage vessel. Finally, there is a transfer option called no-intermediate storage, which allows the batch to be kept inside the vessel. Normally, the zero-wait transfer reqnires the longest CT. In practice, plants normally have a mixtnre of the three transfer policies. 

The other operational philosophies that are generally encountered are the mixed intermediate storage (MIS), zero-wait (ZW), finite wait (FW) as well as the unlimited wait (UW) operational philosophies. The MIS philosophy is encountered in a situation where at least 2 of the aforementioned operating philosophies coexist in one process. It is indeed very seldom in most practical applications to have only one philosophy throughout the operation. A combination of different philosophies in often the case. 

Uncomfortable interactions, group friction, 907 UNIFAC model, phase equilibria simulation, 452 UNIQUAC model, phase equilibria simulation, 452 Unit performance, input/output models, 584 Unlimited intermediate product storage, uis-process, 113 Unsteady state operations, batch processing, 93 Unused reactants, recycle structure, 76 Unwanted products, ZZ, 888... 

Another important aspect of process flow requirements is reflected in inventory policies. These often involve finite and dedicated storage, although frequent cases include shared tanks as well as zero-wait, non-intermediate and unlimited storage policies. Material transfer is often assumed to be instantaneous, but in some cases such as in pipeless plants delay is significant and must be accounted for. 

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