Coal char gasification kinetics

Laurendeau N.M., Heterogeneous Kinetics of Coal Char Gasification and Combustion , Prog. Energy Combust. Sci. 4, 221-270(1978). 

The kinetics of coal char gasification can usually be interpreted in terms of the following set of reactions ... 

The inhibition effect of CO is widely accepted and reasonably well documented for coal char gasification but not for biomass. The lack of extensive literature for wood char CO2 gasification kinetics including CO has strongly motivated this investigation. 

Roberts, D.G. and Harris, D.J. A kinetic analysis of coal char gasification reactions at high pressures. Energy Fuels, 2006, 20, 2314. 

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

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,... 

In the present paper investigation are made in order to produce operational data for the gasification reactivity for biomass chars and coal chars. Furthermore the differences between chars derived from biomass and coal is illustrated. Thermogravimetric analyses have been used to obtain information about the kinetic values of the C-CO2 reaction. 

The kinetics of oil shale char gasification have been studied for Colorado oil shale from the Parachute Creek member. Reaction rate expressions similar to those previously reported for coal char were obtained for the H20-char, C02-char and water gas shift reactions. Evidence is presented to suggest that CaO, a product of mineral decomposition, catalyzes the H20-char reaction and that indigeneous iron catalyzes the water gas shift reaction. 

After the devolatilization and rapid-rate methane formation stages are completed, char gasification occurs at a relatively slow rate various models to describe the gasification kinetics of this material for various limited ranges of conditions have been proposed. The differential rates of reaction of devolatilized coal chars are a function of temperature, pressure, gas composition, carbon conversion, and prior history. 

It is generally assumed that a carbon surface is mainly composed of two types of planes basal and edge. The edge planes include all types of defects that may be present in the structure (mainly potentially unsaturated sp2-hybridized carbon atoms bound to only two other carbon atoms) and thus constitute the so-called active sites or active surface area (ASA). During the last four decades, the concept of active sites has been very useful in the study of carbon reactivity [52,79-81] as well as to the gasification kinetics of coal chars [82-85]. 

Attempts have been made to predict gasification rates using mathematical models. This area has been briefly reviewed by Rafsanjani et al. (2002) who discuss the use of (what are termed) the grain model, the random pore model, the simple particle model and the volume reaction model. They report that differential mass conservation equations are required for the oxidant gas and char particle. These authors use a simplified mathematical model (the quantise method (QM)) for activation of coal chars when both diffusion and kinetic effects have to be considered. Results are compared with other methods when it is found that QM predictions of rate are more accurate than predictions by the random pore model and the simple particle model. 

Reaction of steam with carbon is one of the basic processes involved in the gasification of coals or chars to produce clean fuels. The industrial importance of this reaction is considerable, particularly at this time of spiraling energy costs. In addition, the steam-carbon reaction finds other important industrial applications, such as preventing or minimizing the coking of olefin-plant cracker-tubes. Because of its commercial importance, the steam-carbon reaction has been studied extensively, and excellent reviews are available (1,2). In addition to reaction kinetics and mechanisms, the effects of carbon structure, catalysis by metals, and impurities (anions) have been investigated (3,4, .5) ... 

Because it is decisive for the overall carbon conversion, special emphasis should be placed on the most important conversion process during coal gasification the char conversion. The intention is to establish a coal-adapted kinetic submodel for a CFD case study. 

Kinetics of Chars from Four Commercially Significant Coals of Varying Rank. Proceedings of the Second Annual Conference on Coal Gasification, EPRI, Palo Alto, CA. 

A gasification reaction is composed of various kinds of chemical processes such as pyrolysis of coal, decomposition of tar, oxidation of char, combustion of gas, shift reaction, and formation of various organic compoimds. In order to elucidate the reaction process, the method to delve into the composition of gas for information on the reaction state in the reactor needs to be established. As has been mentioned, kinetic and equilibrium theories are not available for this purpose. 

It is generally accepted that j sification consists of more than five chemical processes such as pyrolysis, p>artial oxidation of char, further decompx)sition of tar, secondary reactions, and combustion of char or It is obviously difficult to simulate actual coal gasification precisely by applying reliable scientific analysis of fundamental exp>eriment. Since coal gasification is a very complicated both from experimental and theoretical pxiints of view, its chemical process cannot be completely understood merely by the accumulation of kinetic data. 

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