Gasification, coal chemistry

Coal gasification is actually comprised of several processes (a) evaporation of moisture (b) coal pyrolysis, releasing volatile matter (tar, CO, CIt, H2, C02, etc.) (c) reaction of volatiles in the gas phase (d) heterogeneous reaction of char with gas-phase species (such as H20 and C02) and (e) mineral matter release and transformation. Coal moisture is rank dependent low-rank coals such as lignites and subbituminous coals may have up to 35% moisture by weight, whereas bituminous coals generally contain less than 5% moisture by weight. The heat to evaporate this moisture must come from the combustion of volatiles and reduces the efficiency of 

---

Chemistry. Coal gasification iavolves the thermal decomposition of coal and the reaction of the carbon ia the coal, and other pyrolysis products with oxygen, water, and hydrogen to produce fuel gases such as methane by internal hydrogen shifts... 

Whereas near-term appHcation of coal gasification is expected to be in the production of electricity through combined cycle power generation systems, longer term appHcations show considerable potential for producing chemicals from coal using syngas chemistry (45). Products could include ammonia, methanol, synthetic natural gas, and conventional transportation fuels. 

D. Hebden and H. J. F. Stroud, "Coal Gasification Processes," iu M. A. Elliott, ed.. Chemistry of Coal Utilisyation, secoud supplemeutary volume,... 

M. Greenfeld described unique laboratory experiments designed to stimulate and understand the complex chemistry of in-situ coal gasification. Developed at the Alberta Research Council, the gasification simulator was heavily instrumented with calorimeters and gas chromatographs to determine the enthalpy, composition, and kinetics of formation of the product gases. Computer techniques were used to calculate mass and heat balances and to test kinetic models. 

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. 

In actual in-situ coal gasification, numerous processes, i.e. oxidation, reduction, thermal cracking and a variety of catalytic as well as non-catalytic reactions, occur in overlapping zones, and to explore the chemistry of these reactions as single or consecutive unit processes is virtually impossible. It is, however, feasible to study the individual reactions under controlled conditions by simulating in-situ gasification in the laboratory. 

C. .-Chemistry. 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). 

This type of approach is somewhat reminiscent of the chemistry of coal gasification, More detail is given in the Dostrovsky reference listed,... 

Lu, D.Y., Granatstein, D.L. and Rose, D.J. (2004) Study of mercury speciation from simulated coal gasification. Industrial and Engineering Chemistry Research, 43(17), 5400-404. 

MERC Hot Gas Cleanup Task Force, "Chemistry of Hot Gas Cleanup in Coal Gasification and Combustion," MERC/SP-78/2, February 1978. 

A computer model has been developed to provide numerical simulations of fluidized bed coal gasification reactors and to yield detailed descriptions, in space and time, of the coupled chemistry, particle dynamics and gas flows within the reactor vessels. Time histories and spatial distributions of the important process variables are explicitly described by the model. With this simulation one is able to predict the formation and rise of gas bubbles, the transient and quasi-steady temperature and gas composition, and the conversion of carbon throughout the reactor. 

The chemistry of coal gasification is usually depicted to involve the following reactions of carbon, oxygen, and steam (c/. Bodle and Schora, 1979). The standard enthalpy change (gram molecules) at 298 K is shown for each reaction. 

D. Hebden and H.J.F. Stroud, Coal gasification processes. In Chemistry of coal utilization, Ed. M.A. Elliott, John Wiley Sons Inc., New York, 1981... 

Johnson J.L, Fundamentals of coal gasification, in chemistry of coal utilization (1981), editor Elliott M.A... 

---