Synthol reactors Fischer-Tropsch synthesis

The Fischer-Tropsch synthesis of hydrocarbons is used on a large scale for fuel production in South Africa [78, 79]. Synthesis gas generated from coal in Lurgi fixed-bed gasifiers enters the Synthol reactor (Fig 18), where it is reacted over an iron catalyst at 340°C. The reactor works on the principle of the circulating fluidized bed. The mean porosity in the riser is 85%, and the gas velocity varies between 3 and 12ms1 [2]. Reaction heat is removed by way of heat-exchanger tube bundles placed inside the riser. 

Figure 18. Fischer Tropsch synthesis in the Synthol reactor [2, 78] (a) hopper, (b) standpipe, (c) riser, (d) cooler (coil), (e) reactor, (f) gooseneck...

Figure 1.16 High-temperature Fischer-Tropsch synthesis reactors, (a) Sasol Synthol circulating fluidized-bed reactor.

Sasol Fischer-Tropsch Process. 1-Propanol is one of the products from Sasol s Fischer-Tropsch process (7). Coal (qv) is gasified ia Lurgi reactors to produce synthesis gas (H2/CO). After separation from gas Hquids and purification, the synthesis gas is fed iato the Sasol Synthol plant where it is entrained with a powdered iron-based catalyst within the fluid-bed reactors. The exothermic Fischer-Tropsch reaction produces a mixture of hydrocarbons (qv) and oxygenates. The condensation products from the process consist of hydrocarbon Hquids and an aqueous stream that contains a mixture of ketones (qv) and alcohols. The ketones and alcohols are recovered and most of the alcohols are used for the blending of high octane gasoline. Some of the alcohol streams are further purified by distillation to yield pure 1-propanol and ethanol ia a multiunit plant, which has a total capacity of 25,000-30,000 t/yr (see Coal conversion processes, gasification). 

Change occurred in high-temperature Fischer-Tropsch reactor technology. The circulating fluidized bed Sasol Synthol reactors were replaced by fixed fluidized bed Sasol Advanced Synthol (SAS) reactors.44 This did not meaningfully affect the Fe-HTFT syncrude composition, but it reduced the operating cost of HTFT synthesis. 

There are processes in which the total amount of catalyst is entrained by the gas. The reactors then belong to the category of transport reactors. Examples are some of the present Fischer-Tropsch reactors for the production of hydrocarbons from synthesis gas and the modern catalytic cracking units. Fig 10.11 shows the Synthol circulating solids reactor. In the dilute side of the circuit, reactant gases carry suspended catalyst upward, and the fluidized bed and stand-pipe on the other side of the circuit provide the driving force for the smooth circulation of the solid catalyst. For the removal of heat, heat exchangers are positioned in the reactor. 

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