Lurgi 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). 

Other coal gasifiers, eg Shell-Koppers and Texaco, have been commercially tested elsewhere. These operate at higher temperatures than the Lurgi reactors and consequently produce a gas with a lower CH. content and a lower H2/CO ratio. They use less steam but more oxygen. A discussion of xhe pros and cons of the various coal gasifiers is beyond the scope of this review. 

The base case for all calculations shown here is a 3.7 m diameter dry ash air-blown Lurgi reactor with a 3.0 m... 

In the Lurgi process a cooled tube reactor is applied. The catalyst particles are located in the tubes and cooling takes place by boiling water. The most important difference between the two reactor types is the temperature profile. In the Lurgi reactor it is much flatter than in a quench reactor. 

Table I. Base Operating Data for Ash Discharge (Lurgi) Reactor...

The Eastman process was the first modem coal-to-chemicals facility. Coal is converted to synthesis gas (CO + H ) by reaction with water in a Lurgi reactor. The synthesis gas is then purified and converted to methanol in a heterogeneous process. Reaction of methanol with acetic acid (which is recycled from applications of acetic anhydride) produces methyl acetate, which is the starting material for the Eastman carbonylation process. 

Since the coal is heated gradually as it passes slowly down through the bed, the Lurgi reactor produces light oils, tars, and phenols, as well as the usual Impurities of hydrogen sulfide and ammonia. A typical Lurgi gas from bituminous coal has the following dry composition ... 

Most of the ash leaves the reactor with the gas, so that particulate removal is a more difficult problem than with the Lurgi reactor. 

Figure 10.9. Lurgi reactor for a low-pressure methanol synthesis plant. Reproduced with permission from Lurgi Aktiengesellschraft.

In the Godrej-Lurgi process, olefins are produced by dehydration of fatty alcohols on alumina in a continuous vapor-phase process. The reaction is carried out in a specially designed isothermal multitube reactor at a temperature of approximately 300°C and a pressure of 5—10 kPa (0.05—0.10 atm). As the reaction is endothermic, temperature is maintained by circulating externally heated molten salt solution around the reactor tubes. The reaction is sensitive to temperature fluctuations and gradients, hence the need to maintain an isothermal reaction regime. 

Continuous slurry reactors are generally either of one of two designs. One type uses a reactor loop, generally known as a Buss loop design the other is a co-current hydrogen/fatty acid/catalyst system mainly marketed by Lurgi. Continuous slurry reactors are more popular in Europe, Asia, and South America than in the United States. 

Sasol uses both fixed-bed reactors and transported fluidized-bed reactors to convert synthesis gas to hydrocarbons. The multitubular, water-cooled fixed-bed reactors were designed by Lurgi and Ruhrchemie, whereas the newer fluidized-bed reactors scaled up from a pilot unit by Kellogg are now known as Sasol Synthol reactors. The two reactor types use different iron-based catalysts and give different product distributions. 

The Lurgi fixed-bed gasifier operates using lump coal of a noncaking type with an ash composition chosen to avoid a sticky, partly fused ash in the reactor. A slagging version of this gasifier has been tested in Westfield, Scotland. Other fixed-bed gasifiers have similar coal requirements. 

The first commercial operation of the Lurgi process was in Germany in 1936 using brown coal. The reactor was modified to stir the coal bed to permit utilization of bituminous coal. One plant was built at the Dorsten Works of Steinkohlengas AG, and the Sasol plants were built in South Africa to provide synthesis gas for Hquid fuels. 

Fig. 9. Lurgi-Rhurgas flash pyrolysis system, where 1 is a lift pipe 2, primary pyrolysis reactor 3, screw feeder 4, secondary pyrolysis reactor 5 and 7,...

Fig. 13. Flowsheet of medium pressure synthesis, fixed-bed reactor (Lurgi-Ruhrchemie-Sasol) having process conditions for SASOL I of an alkaline, precipitated-iron catalyst, reduction degree 20—25% having a catalyst charge of 32—36 t, at 220—255°C and 2.48 MPa (360 psig) at a fresh feed rate of...

Status of Indirect Liquefaction Technology The only commercial indirect coal liquefaction plants for the production of transportation fuels are operated by SASOL in South Africa. Construction of the original plant was begun in 1950, and operations began in 1955. This plant employs both fixed-bed (Arge) and entrained-bed (Synthol) reactors. Two additional plants were later constructed with start-ups in 1980 and 1983. These latter plants employ dry-ash Lurgi Mark IV coal gasifiers and entrained-bed (Synthol) reactors for synthesis gas conversion. These plants currently produce 45 percent of South Africa s transportation fuel requirements, and, in addition, they produce more than 120 other products from coal. 

But, so far as the number of reactors are concerned, I indicated that we have six. That s the maximum number that we require regardless of the quality of the syngas that we process. When we took the Lurgi gas and methanated it, starting with 38% methane already there, we required only four reactors. As a matter of fact, we could have gotten by with three. So it is really a question of how much work you have to do that determines the number of reactors that you would install in the system. 

L. Seglin Why has Lurgi selected the hot gas recycle process for methanation rather than the isothermal reactor (ARGE) design which they used for the Fischer-Tropsch plant in SASOL s plant in South Africa ... 

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