Coal conversion gasification

Synthesis gas is obtained either from methane reforming or from coal gasification (see Coal conversion processes). Telescoping the methanol carbonylation into an esterification scheme furnishes methyl acetate directly. Thermal decomposition of methyl acetate yields carbon and acetic anhydride,... 

Produced from Co l. Estimates of the cost of producing methanol from coal have been made by the U.S. Department of Energy (DOE) (12,17) and they are more uncertain than those using natural gas. Experience in coal-to-methanol faciUties of the type and size that would offer the most competitive product is limited. The projected costs of coal-derived methanol are considerably higher than those of methanol produced from natural gas. The cost of the production faciUty accounts for most of the increase (11). Coal-derived methanol is not expected to compete with gasoline unless oil prices exceed 0.31/L ( 50/bbl). Successful development of lower cost entrained gasification technologies could reduce the cost so as to make coal-derived methanol competitive at oil prices as low as 0.25/L ( 40/bbl) (17) (see Coal conversion processes). 

Coal can be converted to gas by several routes (2,6—11), but often a particular process is a combination of options chosen on the basis of the product desired, ie, low, medium, or high heat-value gas. In a very general sense, coal gas is the term appHed to the mixture of gaseous constituents that are produced during the thermal decomposition of coal at temperatures in excess of 500°C (>930°F), often in the absence of oxygen (air) (see Coal CONVERSION PROCESSES, gasification) (3). A soHd residue (coke, char), tars, and other Hquids are also produced in the process ... 

In this process, any sulfur present in the coal exits the gasifier as hydrogen sulfide which is removed by various processes such as a Hohnes-Stretford unit where the sulfide is absorbed and regenerated. The resulting sulfur is filtered out as a cake (39 wt %) which is sold as a valuable feedstock (see Coal CONVERSION PROCESSES, GASIFICATION SULFURREMOVAL AND RECOVERY). 

Gasification. Gasification converts soHd fuel, tars, and oils to gaseous products such as CO, H2, and CH that can be burned direcdy or used in synthesis gas (syngas) mixtures, ie, CO and mixtures for production of Hquid fuels and other chemicals (47,48) (see Coal conversion processes, gasification Euels, synthetic-gaseous fuel Hydrogen). 

C -Chemisty. A great deal of research has been undertaken on the development of PGM catalysts for the manufacture of chemicals and fuels from syngas, a mixture of CO and H2 obtained from coal gasification (see Coal conversion processes). 

Partial oxidation of heavy Hquid hydrocarbons requires somewhat simpler environmental controls. The principal source of particulates is carbon, or soot, formed by the high temperature of the oxidation step. The soot is scmbbed from the raw synthesis gas and either recycled back to the gasifier, or recovered as soHd peUitized fuel. Sulfur and condensate treatment is similar in principle to that required for coal gasification, although the amounts of potential poUutants generated is usually less (see Coal conversion processes, gasification). 

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). 

Goal Processing to Synthetic Fuels and Other Products. The primary approaches to coal processing or coal conversion are thermal decomposition, including pyrolysis or carbonization (5,6), gasification (6), and Hquefaction by hydrogenation (6). The hydrogenation of coal is not currently practiced commercially. 

Gasification. Gasification of coal is used to provide gaseous fuels by surface and underground appHcations, Hquid fuels by indirect Hquefaction, ie, catalytic conversion of synthesis gas, and chemicals from conversion of synthesis gas. There are also appHcations in steelmaking (see Coal conversion PROCESSES, gasification). 

See Coal CONVERSION PROCESSES, gasification Fuels, synthetic. 

Consequently, two semicommercial pilot plants have been operated for 1.5 years. One plant, designed and erected by Lurgi and South African Coal, Oil, and Gas Corp. (SASOL), Sasolburg, South Africa, was operated as a sidestream plant to a commercial Fischer-Tropsch synthesis plant. Synthesis gas is produced in a commercial coal pressure gasification plant which includes Rectisol gas purification and shift conversion so the overall process scheme for producing SNG from coal could be demonstrated successfully. The other plant, a joint effort of Lurgi and El Paso Natural Gas Corp., was operated at the same time at Petrochemie Schwechat, near Vienna, Austria. Since the starting material was synthesis gas produced from naphtha, different reaction conditions from those of the SASOL plant have also been operated successfully. 

Source Adapted from Hailong, X., The Shell Coal Gasification Process (SCGP), International Hi-Tech Symposium on Coal Chemical Industry Coal Conversion, Oct. 30-31, Shanghai, China, 2004. 

Because of the massive "unconventional" reserves of liquid hydrocarbons afforded by oil sand bitumens and heavy oils, Canadian interests in coal conversion are generally more likely to centre on gasification than on liquefaction, and to focus on long-term supply of fuel gas (which could in many cases be substituted for oil where coal can not, and thereby reduce projected oil supply shortfalls). 

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. 

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. 

---