The effects of pressure on coal reactions during pulverised coal combustion and gasification

Wall, Terry; Liu, Guisu; Wu, Hongwei; Roberts, Daniel G.; Benfell, Katharine E.; Gupta, Sushil K.; Lucas, John; Harris, David

doi:10.1016/s0360-1285(02)00007-2

Cited by 277 publications

(166 citation statements)

References 109 publications

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“…At higher pressures as at 2.2 and 3.0 MPa, the formation of CO 2 and CH 4 has been observed from reactions R3 and R4 respectively, which can be explained by other mechanisms proposed by different authors [17,19,23,24]. With increasing the pressure further, the surface will be saturated with oxygen surface complexes which means that increases in pressure will not lead to the formation of further C(O) and the reaction rate will not increase so the impact of pressure becomes less significant to independent [19,25]. It appears that at pressures up to 1.65 MPa the controlling mechanism is adsorption because the oxygen surface complexes are increasing and at higher pressures, above 2.2 MPa the oxygen surface complexes approach saturation and the pressure effect becomes insignificant [16,19].…”

mentioning

confidence: 58%

“…It appears that at pressures up to 1.65 MPa the controlling mechanism is adsorption because the oxygen surface complexes are increasing and at higher pressures, above 2.2 MPa the oxygen surface complexes approach saturation and the pressure effect becomes insignificant [16,19]. Furthermore during C-CO 2 and C-H 2 O gasification the reaction rate decreases as the pressure increases due to the increased inhibiting effect by CO and H 2 respectively [16,19]. Fig.…”

Section: Effect Of Pressurementioning

confidence: 94%

“…In this mechanism the retarding effect of the produced H 2 is taken into account which inhibits the char--steam reaction [18]. Furthermore in a two-step adsorption-desorption reaction mechanism, widely accepted for the char--CO 2 reaction at atmospheric pressure, the inhibiting effect of CO which slows down the gasification rate of the char--CO 2 reaction is taken into account [19,20].Figs. 9 and 10 show respectively the effect of the H 2 O/CO 2 ratio on the gas production (mol/kg of sample) and the LHV (MJ/N m 3 ) of the product gas.…”

mentioning

confidence: 99%

“…13 shows that the quantity of carbon converted (X a ) is notably increased by progressively higher pressures up to 1.65 MPa, above this pressure the incremental conversion becomes smaller which indicates that the effect saturates (over the conditions tested herein). From atmospheric pressure up to 1.65 MPa, this effect can be explained by the two-step reaction mechanism of adsorption -desorption which is shown as the following for the reactions R3 and R4 respectively [19,[21][22][23]. C(O) are the adsorbed oxygen surface complexes and are determined by the forward adsorption reactions which influence the reaction rate.…”

mentioning

confidence: 99%

“…With increasing the pressure further, the surface will be saturated with oxygen surface complexes which means that increases in pressure will not lead to the formation of further C(O) and the reaction rate will not increase so the impact of pressure becomes less significant to independent [19,25]. It appears that at pressures up to 1.65 MPa the controlling mechanism is adsorption because the oxygen surface complexes are increasing and at higher pressures, above 2.2 MPa the oxygen surface complexes approach saturation and the pressure effect becomes insignificant [16,19]. Furthermore during C-CO 2 and C-H 2 O gasification the reaction rate decreases as the pressure increases due to the increased inhibiting effect by CO and H 2 respectively [16,19].…”

mentioning

confidence: 99%

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Experimental study on the impact of reactant gas pressure in the conversion of coal char to combustible gas products in the context of Underground Coal Gasification

Konstantinou

Marsh

2015

Fuel

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Underground Coal Gasification (UCG) is the process by which unmineable coal resources are converted in situ into a combustible gas. Pressurised oxidants such as steam and air or oxygen are injected into the coal seam in order to react with coal and form a product gas. The main gases produced are H 2 , CO, CH 4 and CO 2 , in proportions depending on temperature, pressure and the composition of the reactant gases injected [1][2][3]. Although it can be challenging to accurately measure or reproduce these conditions in a reliable fashion, it is generally believed that at high enough temperatures, free oxygen reacts completely with the solid carbon within a relatively short distance from the injection point. The heat evolved acts to pyrolyse the adjacent coal and the char formed then reacts with carbon dioxide, steam or other gases formed by combustion and pyrolysis [4][5][6]. The key substance, and hence driver of the net gasification process under these conditions is therefore CO 2 which is produced during the oxidation zone [5,7,8]. At the reduction zone CO 2 and steam, which is either introduced deliberately into the cavity or is flowing into the cavity from the oxidation of the surrounding strata, reacts with char and produces around 60% of the total gas product (by volume) during the UCG process. The remaining 40% is produced during the devolatilisation phase, although this is highly dependent on reactor condition, the type of coal and the gaseous reactants [4]. Fig. 1 illustrates the three reaction zones of a reacting channel during a UCG process, which are the oxidation, reduction and pyrolysis zones. During the oxidation zone, as the coal is consumed more coal falls into the growing void, which creates a high coal surface area available for reaction and permits contact between the hot gases and the coal [5,7]. This area is the final reduction zone which converts excess CO 2 to CO and is responsible for the uniform quality of the product gas. Measurement of the upstream gas composition in the oxidation zone has shown comparatively low heating values which demonstrate that the reactions in the oxidation zone do not have such a significant effect on the product gas composition [8,9]. Finally the pyrolysis zone is where the devolatilisation of the coal takes place, forming char that contains active sites for subsequent gas-solid reactions.Experimental study on the impact of reactant gas pressure in the conversion of coal char to combustible gas products in the context of Underground Coal Gasification AbstractThis paper describes an experimental investigation to determine the impact of pressurised reactor conditions within the reduction zone of a gasification process employing a semi-batch reactor with a bituminous coal. The conditions examined with this bespoke pressurised rig were designed to be representative of an Underground Coal Gasification (UCG) process, at pressures up to 3.0 MPa and temperatures up to 900 °C; coal samples were approximately 36 g per test. Current published literature suggests that one ...

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