Testing the Entire Process on a Small Scale

Since the high-boiling substance was not known before, it was not possible to include it in the mathematical simulation. Now that it has been discovered as a result of operating an integrated plant (micro- or miniplant), it can be characterized and incorporated in the simulation [Buschulte 1995]. Whereas the microplant is used to test the most important recycle streams at the laboratory stage, in the integrated miniplant all recycle streams are investigated. 

The process now leaves the research phase and enters the development phase. This is associated with a jump in costs, which makes disciplined milestoning and continuous cost and time control necessary. Today mainly miniplants are used as integrated test plants, and these are described in more detail in the following. 

The following design documents are required as a rninimum for constructing a miniplant  

In a miniplant, the hold-up for a given throughput is almost aWays greater than in an industrial-scale plant. The size of the vessels and column bottoms should therefore be minimized, othenvise it vdll take too long for the miniplant to reach a steady state because of long residence times. In the column bottoms, which are particularly critical, a hold up of 100 - 200 mL is normally the lower limit. Below this level, a laboratory evaporator can usually no longer be operated efficiently (because of excessive temperature differences, foaming, etc.). 

A miniplant produces a high-boiling residue at a rate of Ig h This residue is removedfrom the bottom of a distillation column with a distillation boiler capacity of200 ml, so that the mean residence time is 200 h. The time required to reach the steady state is consequently about 25 d (about 3 times the mean residence time). Only then will it be possible to assess this bottom residue and draw conclusions about its fouling behavior, composition, properties, and so on. 

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