Liquefaction direct, coal gasification

This paper touches on the chemistry of coal gasification and liquefaction comments on the current status of conversion processes and the influence of coal properties on coal performance in such processes and examines the contributions which coal conversion could make towards attainment of Canadian energy self-sufficiency. Particular attention is directed to a possible role for the medium-btu gas in long-term supply of fuel gas to residential and industrial consumers to linkages between partial conversion and thermal generation of electric energy and to coproduction of certain petrochemicals, fuel gas and liquid hydrocarbons by carbon monoxide hydrogenation. 

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. 

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

Many processes have been developed for the removal of hydrogen sulfide from gas streams. They can be classified as liquid absorption, liquid oxidation, dry oxidation, and adsorption. One of these processes is usually included in a coal gasification or liquefaction flowsheet since the coal sulfur is converted to H2S and finally elemental sulfur. The Stretford and Townsend direct HpS to S processes and the Recti sol process followed by a Claus plant are frequently included on coal conversion flowsheets (1 ). Kohl and Riesenfeld (2) present pertinent details for many commercial processes. 

Direct liquefaction processes under development are typically carried out at temperatures from about 450 to 475°C and at high pressures from 10 to 20 MPa and up to 30 MPa. Despite the slow rate at which liquefaction proceeds, the process itself is thermally rather efficient, since it is only slightly exothermic. However, hydrogen must be supplied and its manufacture accounts for an important fraction of the process energy consumption and cost of producing the liquid fuel. The hydrogen itself may be produced, for example, by the gasification of coal, char, and residual oil. 

Recent years have seen vast experimentation with many different process designs for the liquefaction of coals. The degree of coal conversion and composition of the product oil vary with both the coal rank, maceral composition, mineral matter content, and conversion process. Whereas much attention has been focused on the separation and characterization of the product oil by chromatographic and spectroscopic means, less work has been done on the unconverted or process altered residues from liquefaction processes. Although many of the processes do incorporate some sort of bottoms processing , other possible uses of these residues include road materials, carbon electrodes, coal gasification feedstocks, and as direct combustion fuels. Recently, coal conversion by-products have been used as raw materials in the synthesis of thermosetting polyesters. ... 

The principal consideration of coal beneficiation is to upgrade the quality of coal for direct use in steam and power generation, or for special uses such as chemical feedstock, feed to liquefaction, and gasification. The properties and quantities of impurities in coal are known to be the major factors that place limitations on coal utilization. All coals are not the same (Chapters 1 and 2). Thus, the type of coal beneficiation technology and the extent of beneficiation depend mostly on the type of coal, the means of mining, and the clean coal utilization. 

In any text about coal (but more specifically in any chapter about coal gasification), it is appropriate to include a listing of the types of processes available as well as a description of the different processes. Thus, it is the intent here to give selected examples of specific processes. This is in direct contrast to the inclusion of an appendix to the chapter on coal liquefaction (Chapters 18 and 19) in fact, the situation is quite different with respect to liquefaction processes. 

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. 

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 utilization of gases as source of primary chemicals and fuels has increased steadily over the last half of this century. The development of the gas industry in Europe during the thirties and fourties included novel processes in the fuel gas industry that were related mainly to those for liquefaction and gasification of coal, e.g., by Fischer-Tropsch syntheses. With the expansion of petrochemistry after World War II, overwhelming activities were directed globally towards the... 

N. Berkowitz (Alberta Research Council) provided a stimulating account of the potential of coal in Canada s energy future. Coal can be used directly as an industrial fuel or be converted to other combustible hydrocarbons. Berkowitz described the three different conversion techniques gasification, liquefaction, and partial conversion techniques to produce gases, oils, and solid fuels. 

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