Section 1 Summary

Franz Fischer and Hans Tropsch are credited with the discovery, in the 1920’s, that carbon monoxide and hydrogen can be converted in the presence of a metal catalyst to a variety of hydrocarbon products. Just prior to and during World War II the “Fischer-Tropsch” reaction was commercialized in Germany and used to produce military fuels in fixed bed reactors. It was recognized from the start that this reactor system had severe operating and yield limitations and alternative reactor systems were sought. In 1955 the Sasol I complex, using an entrained bed (Synthol) reactor system, was started up in South Africa. Although this reactor was a definite improvement and is still operating, the literature is filled with proponents of other reactor systems, each claiming its own advantages. This report provides a summary of the results of a study to compare the development potential of three of these reactor systems with the commercially operating Synthol-entrained bed reactor system.

1.1 Description of Reactor System

The three reactor systems to be evaluated are:

1)    The tube-wall reactor, developed by the U. S. Bureau of Mines (1), resembling a shell and tube
         heat exchanger having catalyst flame-sprayed onto the cooling tubes

2)        The slurry reactor as proposed by Koelbel (2), with catalyst suspended in an inert liquid, cooled
         by immersed coils, with syngas bubbled through the catalyst slurry.

3)    An ebullating bed reactor, which is also a liquid phase reactor, but with larger size catalyst and heat
        removal from a circulating liquid stream that is also used to keep the bed expanded (3).

The three reactors and the entrained bed reactor are shown in Figure 1.1-1.

The commercial Synthol reactor is used as a benchmark against which the development potential of the other three reactors can be compared. This reactor system is operated by Sasol in South Africa. However, most of the information on which this study is based was supplied by Kellog Co. (4). No information beyond that in the literature on the operation of the Synthol reactor system was available for consideration in preparing this study, nor were any details of the changes made to the original Synthol system to overcome the operating problems reported in the literature (5).

Because of conflicting claims and results found in the literature, it was decided to concentrate a large part of this study on a kinetic analysis of the reactor systems, in order to provide a theoretical analysis of intrinsic strengths and weaknesses of the reactors unclouded by different catalysts, operating conditions and feed compositions. The remainder of the study considers the physical attributes of the four reactor systems, and compares their respective investments costs, yields, catalyst requirements and thermal efficiencies from simplified conceptual designs.