Rapid-rate methane formation

At temperatures greater than 1700°F the transient reactivity for rapid rate methane formation exists only briefly. For coals or coal chars prepared in inert atmospheres this period is seconds or less (6). IGT s studies suggest that for air-pretreated coal chars, this period is more extended although the total amounts of carbon which can be gasified by... 

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. 

PH2 = hydrogen partial pressure, atm /r = relative reactivity factor for rapid-rate methane formation dependent on the particular carbonaceous solid (defined as unity for air-pretreated Ireland mine coal char) a = kinetic parameter dependent on gas composition and pressure... 

Figure 3. Correlation of base carbon conversion for gasification in the rapid-rate methane formation stage (thermobalance data)...

COMPUTED CURVE ONLY FOR DEVOLATILIZATION AND LOW-RATE GASIFICATION (NO RAPID-RATE METHANE FORMATION)... 

Data obtained in experiments done at low temperatures, such as those in Figure 7, have been correlated using a more detailed model to describe the rapid-rate methane formation process prior to the completion of this reaction. This model is described in a previous publication (13). Certain characteristics of this model rationalize the independence of total base carbon conversion in the rapid-rate methane formation stage from heating rate and final temperature for tests done above 1500 °F. The following critical steps assumed in the model relate to this range of conditions ... 

A comparison of this expression with Equation 6 indicates that f3N°Ao = 0.0092 atm"1. Since no definition of the temperature history was required to develop Equation 13, the suggested model indicates that the amount of base carbon conversion to methane during the rapid-rate methane formation step is independent of heat-up rate or temperature level when the intermediate, A, has been completely deactivated. 

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