Carbon gasification

Thermodynamically, the formation of methane is favored at low temperatures. The equilibrium constant is 10 at 300 K and is 10 ° at 1000 K (113). High temperatures and catalysts ate needed to achieve appreciable rates of carbon gasification, however. This reaction was studied in the range 820—1020 K, and it was found that nickel catalysts speed the reaction by three to four orders of magnitude (114). The Hterature for the carbon-hydrogen reaction has been surveyed (115). 

Even at 1,500 F, equilibrium eonstants for the first two reactions are high enough (about 10) to expect reaction to go essentially to completion except for kinetic-rate limitations. The reaction zone might be expected to be sized by volume of rabbled carbon bed, considering that the carbon gasification reactions that occur in it are governed by kinetics and are reaction-rate limited. Actually, it is sized by hearth area. The area exposed to the gases controls mass transfer of reactants from the gas phase to the carbon and heat transfer to support the endothermic reactions. 

Catalyst presence as an example of this factor mention may be made of carbon gasification by water vapour ... 

Lahaye J., Dentzer J., Soulard P., Ehrburger P. Carbon gasification The active site concept. In Fundamental Issues of Control of Carbon Gasification Reactivity, Lahaye J, Ehrburger P. Ed., Academic Publishers, London, 1991, p. 143-158... 

L.R. Radovic, A.A. Lizzio, H. Jiang, in J. Lahaye, P. Ehrburger (Eds.), Fundamental Issues in Control of Carbon Gasification Reactivity, Kluwer Academic Publishers, Dordrecht (The Netherlands), 1991, p. 235. 

Predicted Relative Rates of Carbon Gasification in Reaction Zone III for Similar Shapes of Carbon Specimens and Constant Linear Gas Flow Rate... 

In ordar to determine the effect of coal rank (at established by reflectance measurement of vitrinite in coal) on the reactions of coal as related to carbonization, gasification, combustion, and other processes, a wide range of bituminous coals were studied. The results show that reflectance measurements can be used effectively (1) to determine accurately yields of coal carbonization products such as coke, tar, gas, light oil, and liquor from pilot and commercial coke oven (2) to obtain the heating value and specific gravity properties of gases from these processes (3) to determine the free swelling index and B.t.u. content of coals ... 

The reaction is described by two basic routes in (391) they are chosen so that carbon enters the reaction only in route A 1, and route N<2) results in the conversion of a part of CO formed in route N(1) into C02. With such a choice of the basis of routes, r u, the rate of the reaction along route Nil) is the rate of carbon gasification i.e., corresponds to symbol r(1) in (390). 

The volume percent of physical components of coal is used as an aid in the characterization of coal for use in carbonization, gasification, and combustion processes. To determine the volume percent of the physical components of coal (ASTM D-2799), the components in a representative crushed coal sample (ASTM D-2797) are identified under a microscope according to their reflectance, other optical properties, and morphology. The proportion of each component in the sample is determined by observation of a statistically adequate number of points and summing those representative of each component. Only area proportions of components are determined on a surface section of a sample. However, the area and volume proportions are the same when the components are distributed randomly throughout the sample. 

Dominant Oxidant. Carbon gasification in fluidized bed combustors can occur by both the CC /C and the O2/C reactions ... 

Heavy Duty catalysts are primarily for naphtha feeds that have even more tendency for carbon deposition. These catalysts contain complex stabilized alkali phases and other promoters that maximize carbon gasification activity70. 

The practical motivation for understanding the microscopic details of char reaction stem from questions such as How does the variability in reactivity from particle to particle and with extent of reaction affect overall carbon conversion What is the interdependence of mineral matter evolution and char reactivity, which arises from the catalytic effect of mineral matter on carbon gasification and the effects of carbon surface recession, pitting, and fragmentation on ash distribution How are sulfur capture by alkaline earth additives, nitric oxide formation from organically bound nitrogen, vaporization of mineral constituents, and carbon monoxide oxidation influenced by the localized surface and gas chemistry within pores ... 

D W McKee m Fundamental Issues in Control of Carbon Gasification (Eds J Lahaye, P Ehrburgcr), Kluwer Dordrecht, 1991, p 484-514... 

In order to establish the optimum chemisorption temperature, a series of isothermal chemisorption experiments were performed at different temperatures between 200 and 300 °C. The sample was first outgassed in Ar (15 °C min, 1000 C, 5 hours). The temperature was then lowered to the chemisorption temperature, and a flow rate of 75 mL min of oxygen was introduced to the TGA. In this way, an optimised chemisorption temperature of 250 °C was found, so that equilibrium could be achieved in a reasonable period of time, and simultaneous carbon gasification could be avoided. 

B. McEnaney, Fundamental Issues in Control of Carbon Gasification Reactivity, Kluwer Academic Publishers, Netherlands, 1991, 175. 

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