Gasification, coal compositions

The reactants, coal, water and oxygen are converted to hydrogen, carbon monoxide, carbon dioxide, methane, water vapour and hydrogen sulphide at a given temperature and pressure according to thermodynamic equilibria and the kinetics of gasification. A particular coal composition which is characteristic of a German hard coal was taken as a basis (Table I). 

Pyrolysis results are very important for coal characterization, as all conversion processes of coal such as combustion, liquefaction, and gasification start with a pyrolytic step. For this reason, pyrolysis was frequently used for the analysis of coals [17,18). Pyrolysis data were correlated with coal composition, coal characterization and ranking [18a], prediction of coal reactivity as well as of other properties related to coal utilization. Techniques such as Py-MS, Py-GC/MS with different ionization modes, Py-FTIR, or evolved gas analysis (EGA) [19] were described for coal analysis. Programmed temperature pyrolysis is another technique that has been proposed [17] for a complete evaluation of the two types of molecules present in coal. 

Table 1.17 Coal gasification. Typical composition of raw gas (vol%). Coal - lUinois...

Battaerd, HA. and Evans, D.G. (1979) An alternative representation of coal composition data. Fuel, 58 (2), 105-108. Mountouris, A., Voutsas, E., and Tassios, D. (2006) Solid waste plasma gasification equilibrium model development and exergy analysis. Energy Conversion and Management, 47 (13-14),... 

Texaco Research and Development Coordinating author plus Introduction and sections on Coal Production and Consumption, Origin and Classification, Coal Composition and Structure, Pyrolysis, and Gasification (2) Center for Applied Energy Research, University of Kentucky Coal Mining and Preparation (3) Advanced Fuel Research Combustion (4) Center for Applied Energy Research, University of Kentucky Direct Coal Liquefaction (5) Eastman Chemical Company Petrochemical Feedstocks. 

The gasification plant is equipped with two Texaco gasifiers, each capable of producing all of the synthesis gas required for operation of the complex. Eastman chose an entrained-bed gasification process for the Chemicals from Coal project because of three attractive features. The product gas composition using locally available coal is particularly suitable for production of the desired chemicals. Also, the process has excellent environmental performance and generates no Hquids or tars. EinaHy, the process can be operated at the elevated pressure required for the downstream chemical plants. 

It is not possible, however, to calculate accurately actual gas composition by using the relationships of reactions (27-14) to (27-19) in Table 27-12. Since the gasification of coal always takes place at elevated temperatures, thermal decomposition (pyrolysis) takes place as coal enters the gasification reactor. Reaction (27-15) treats coal as a compound of carbon and hydrogen and postulates its thermal disintegration to produce carbon (coke) ana methane. Reaction (27-21) assumes the stoichiometiy of hydrogasifying part of the carbon to produce methane and carbon. 

Cu will be unaffected by the atmosphere, whilst at other atmospheric compositions the pure oxides will be stable. Figure 7.76 illustrates a simplified diagram at 871°C for three metallic elements Cr/Mn/Ni-S-O in a heat-resisting alloy the range for coal gasification is also included. It is clear that CrjOj is stable in all these atmospheres, but NiS will be stable under these atmospheric conditions above 620°C in the form of a eutectic liquid with Ni. Thus, an alloy of Cr and Ni may produce either of these phases or their mixtures leading to corrosion problems. 

The composition of a gas derived by the gasification of coal is, volume percentage carbon dioxide 4, carbon monoxide 16, hydrogen 50, methane 15, ethane 3, benzene 2, balance nitrogen. If the gas is burnt in a furnace with 20 per cent excess air, calculate ... 

Schwartz, M., S. Gade, R. Schaller, and B. Berland, Novel Composite Membranes for Hydrogen Separation in Gasification Processes in Vision 21 Plants, 19th Annual International Pittsburgh Coal Conference, Pittsburgh, PA, September 2002. 

The heat required for gasification is essentially supplied by the partial oxidation of the coal. Overall, the gasification reactions are exothermic, so waste heat boilers often are used at the gasifier effluent. The temperature, and therefore composition, of the product gas is dependent upon the amount of oxidant and steam, as well as the design of the reactor that each gasification process utilizes. 

Two-constant equation of state phase behavior calculations for aqueous mixtures often require the use of temperature dependent binary interaction parameters. The methods used for evaluating these parameters for some of the typical aqueous binary pairs found in coal gasification and related process streams are described. Experimental and predicted phase compositions based on these methods are illustrated for aqueous pairs containing CO2. H2S, NH3, and other gases. 

Typical compositions for several oxygen-blown coal gasification products are shown in Table 9-4. 

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. 

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