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U. S. Bureau of Mines Hydro. Demon. Plant Div.

Methane - Steam Reaction at High Pressure

By E. E. Donath, July 24, 1947

Summary

For the reaction

The equilibrium constants for various temperatures using approximation formulas have been calculated. Approximate equilibrium temperatures for 0.5 and 1% methane content in the dry reaction gas for various pressures are given in the following table. Steam methane ratios of 2 to 1 and 8 to 1 by volume were used. Furthermore, the influence of 0.5 vol. oxygen per 1 vol. methane has been taken in account as a means to deliver the heat of reaction.

Further engineering calculations could give the heat recovery attainable by heat exchange. With these data, the actual required amount of heat and oxygen respectively could be calculated. If an economic study would then show an advantage of the gasification at elevated pressures, more accurate equilibrium calculations could be made. This is necessary because in the present calculations, no consideration has been given to deviations from the ideal gas law.

Dr. T. E. Warren, Canadian Department of Mines, mentioned during his visit in Torrence, June 19, 1947, the possibility of an elimination of the hydrogen compression by a conversion of the hydrogenation of gases with steam and oxygen at full hydrogenation pressure. It is evident from equilibrium considerations that at higher pressures for this reaction higher temperatures are necessary. For the calculation of the equilibrium constant of the reaction

data can be derived from GUMZ, Feuerungs-Technik, 1942, P. 264-271.

Then, for the following reactions, formulas for the equilibrium constant are given:

From the values for Kp4 the methane partial pressure according to equation 4) can be calculated. In this calculation for the partial pressure of H₂O a ratio P E₂O/P CH₄ in the initial gas mixture of 2/1 and 8/1 respectively will be used. For the hydrogen partial pressure it will be assumed, that for 1 vol. methane in the initial gas 1/2 vol. oxygen has been used. Thereby according to the equation

the partial pressure of H₂ is decreased and of H₂O increased.

For low percentages of CH₄ in the reaction gas i.e. nearly complete conversion the following figures were obtained from Kp4 (Table 1):

These data are drawn in Fig. 1 and show the equilibrium methane content for the three mentioned pressures and two H₂O/CH₄ ratios at various temperatures.