Liquefaction indirect, coal gasification

Direct liquefaction is the conversion of coal directly to liquid products. In general chemical terms, coal liquefaction involves addition of hydrogen to the coal by various techniques so that the ratio of hydrogen to carbon in the product is increased to a level comparable to petroleum-based fuels. Indirect liquefaction is coal gasification followed by conversion of the synthesis gas (a carbon monoxide, CO, hydrogen, mixture) to liquid fuels. 

After World War II, direct liquefaction of coal became uneconomical as the use of lower-cost petroleum products became more widespread. However, the German process of indirect coal liquefaction, the Fischer-Tropsch process, continued to hold some interest. The Fischer-Tropsch process first involved production of a carbon monoxide and hydrogen-rich synthesis gas by the controlled gasification of coal followed by a catalytic reaction process to yield a valuable mixture of hydrocarbon products. Simplified Fischer-Tropsch reactions are shown by the following equations ... 

We will consider three processes in more detail to show how the sulfur in the original feedstock material (coal or oil shale) is recovered as elemental by-product sulfur. In this way yields of sulfur per barrel of product can be computed. The three processes will illustrate examples of coal gasification for production of SNG, methanol or indirect liquids, direct liquefaction for production of naphtha and synthetic crude oil and finally, oil shale retorting for production of hydrotreated shale oil. 

Indirect liquefaction of coal and conversion of natural gas to synthetic liquid fuels is defined by technology that involves an intermediate step to generate synthesis gas, CO + H2. The main reactions involved in the generation of synthesis gas are the coal gasification reactions. Combustion... 

The principal method of indirect liquefaction is to react carbon monoxide and hydrogen produced by coal gasification in the presence of a catalyst to form hydrocarbon vapors, which are then condensed to liquid fuels. This procedure for synthesizing hydrocarbons is based on the work of Fischer and Tropsch in Germany in the 1920s. Just prior to and during World War II, Germany produced... 

Of the indirect liquefaction procedures, methanol synthesis is the most straightforward and well developed [Eq. (6)]. Most methanol plants use natural gas (methane) as the feedstock and obtain the synthesis gas by the steam reforming of methane in a reaction that is the reverse of the methanation reaction in Eq. (5). However, the synthesis gas can also be obtained by coal gasification, and this has been and is practiced. In one modern low-pressure procedure developed by Imperial Chemical Industries (ICI), the synthesis gas is compressed to a pressure of from 5 to 10 MPa and, after heating, fed to the top of a fixed bed reactor containing a copper/zinc catalyst. The reactor temperature is maintained at 250 to 270°C by injecting... 

Much attention was then paid to developing processes for the indirect liquefaction of coal (coal gasification followed by synthesis), but the high level of investment required for coal conversion remains a major constraint on its commercial application. 

Coal carbonization is the earliest and most important method. Coal carbonization is mainly used to produce cokes for metallurgy and some secondary products like coal gas, benzene, and methylbenzene. Coal gasification takes up an important position in chemical industry. City gas and varieties of fuel gases can be produced by coal gasification. The common role of low-tanperature carbonization, direct coal liquefaction, and indirect coal Uqnefaction is to produce liquid fuels. 

The plant processes 26,840 TPSD of low sulfur North Dakota lignite. The sulfur is 1.3 wt%/DAF coal. The coal analysis is shown in Table II. Output from the plant is 268,700 MM Btu/day of SNG, equivalent to 45,000 BOE/day. Total production of by-product elemental sulfur is 161 tons/day. This represents 78 wt% of total sulfur input from the coal feedstock. Since goal gasification and indirect liquefaction facilities are most likely to use Western low sulfur lignite or subbituminous coals, this represents the low sulfur case for coal conversion. 

In addition 10 direct operations i<> remove or reduce sulfur content, coal liquefaction or gasification can accomplish similar results indirectly. 

Gasification-Based Liquid Fuels and Chemicals Liquid fuels and chemicals from gasification-based synthesis gas are described in the coal liquefaction section following this section. While the downstream areas of power system and indirect liquefaction plants will differ markedly, the gasification sections will be quite similar and are described in this section. 

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