Bituminous coal char gasification

Kinetics of Bituminous Coal Char Gasification with Gases Containing Steam and Hydrogen... 

In another test method (ASTM D-5515), a dilatometer is used to measure the swelling of bituminous coal. The test method is limited in applicability to coal that has a free swelling index < 1 (ASTM D-720). The principle of this test method is that the final volume of char obtained at the conclusion of a standard dilatation test is dependent on the mass of coal in the coal pencil and on the radius of the retort tube. This test method incorporates a procedure that determines the mass of air-dried coal in the coal pencil, provides a means to measure the average retort tube radii and employs a means to report coal expansion on an air-dried coal weight basis. The value of the dilatation properties of coals may be used to predict or explain the behavior of a coal or blends during carbonization or in other processes, such as gasification and combustion. 

Wccda, M., Abcouwer, H.H., Kapteijn, F. Moulijn, J.A. (1993).Steam gasification kinetics and bum-off behaviour for a bituminous coal derived char in the presence of H2, Fuel Processing Technology, Vol. 36, pp. 235-242,... 

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... 

Coals were devolatilized at rates comparable with those encountered in combustion and gasification processes. Rapid pyrolysis was attained with pulse-heating equipment developed for this purpose. This technique permitted control of the heating time and the final temperature of the coal samples. Subbituminous A to low volatile bituminous coals were studied. All bituminous coals exhibited devolatilization curves which were characteristically similar, but devolatilization curves of subbituminous A coal differed markedly. The products of devolatilization were gases, condensable material or tar, and residual char. Mass spectrometric analysis showed the gas to consist principally of H2, CHh, and CO. Higher hydrocarbons, up to C6, were present in small quantities. 

Table 1.3 Typical Weight Losses (%) Obtained for Gasification of a Bituminous Coal and Its Parent Char at About 1073 K...

As discussed previously, the Destec Plaquemine project is demonstrating the Destec coal gasification process on subbituminous coals. The use of this two-stage entrained flow technology for bituminous coals poses several technical concerns. Specifically, bituminous coal increases the potential for liquid hydrocarbon formation in the top stage and increases the recycle of char from the top stage to the bottom stage. 

Some work has been reported utilizing alcohols for supercritical extraction of coal. Makabe et al.(5) reported extraction of coal with ethanol-sodium hydroxide mixtures with the objective of maximizing extraction yield no sulfur data were reported. Methyl alcohol reaction with a low volatile bituminous West Virginia coal at higher temperatures (460-600 °C) was reported by Garner et al.(J>). Promotion of coal gasification was the objective of that study sulfur content of the resultant char was not reported. 

The pretreated coal is quite reactive. For example, at 25-30% carbon gasification with steam-hydrogen mixtures, the rate constant is more than twice that reported by Feldkirchner and Linden (6) in reactions of low temperature bituminous char with hydrogen. The greater reactivity is most likely attributable to the higher volatile content of our pretreated coal (25-26% ) than that of their char (17% ). 

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