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6. Operating Conditions.

The main variables of the operation, such as pressure, temperature, space-velocity, gas composition are today practically the same, as in 1937-1938. Specifically, there was no improvement or change in the design of the ovens. Nevertheless there was no increase in the average yield expressed in gram/m³ feed gas from approximately 100 g to 130 g/m³. As Germany was faced with a serious lack of cobalt, the yield of product per ton of cobalt was of greatest importance, since this yield can be raised by keeping the space-velocity low, most plants were operated at less than 100 V/H/V (Vol feed gas/hr/unit volume catalyst).

The Essener Steinkohlen A.G. apparently had developed a somewhat improved method of operation, which resulted in a better yield based on feed, and longer catalyst life. This operation widely discussed by the FT group, was known as the “Essener Fahrweise”.

In principle, it consisted only in a rigorous control of operation, i.e.;

1. Absolute constant feedgas rate and composition
2. Countercurrent regeneration of all ovens.
3. Low-space velocity (increased number of ovens).
4. More equal distribution of load between stages.

With these means the Essener plant obtained the following results:

Flexibility of Operation. In order to show the variations possible in FT plant operation, yields and product qualities for 2 conditions listed below. The data are based on a report from Brabag and refer to their Ruhland Plant:

The difference is due to a variation in the amount of thermal cracking of the distillation fraction carried out in a separate unit.

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