Syngas production using superadiabatic combustion of ultra-rich methane-air mixtures

Abstract

Two common methods for the production of synthesis gas (syngas) are: (1) methane partial oxidation and (2) methane steam re-forming. This paper discusses the experimental results obtained from the partial oxidation of "ultrarich," (φ = 4), methane-air mixtures in a new type of chemical reactor based on filtration combustion. Experimental results show that the reciprocal flow burner (RFB), due to its high heat recuperation efficiency (approximately 90%), can support self-sustained combustion of ultrarich methane-air mixtures up to an equivalence ratio of 8, well beyond the conventional flammability associated with a methane-air flame in free space. For the range of equivalence ratios (2 < φ < 8) and reactor pressures (1, 3, 5 atm) investigated, the maximum experimental conversion of methane to hydrogen (65%), carbon monoxide (75%), acetylene (10%), and ethylene (8%) were observed. Parametric studies demonstrate that the maximum temperature in the combustion zone, which varies from 1100 to 1400 °C, is a function of the equivalence ratio, filtration velocity, reactor pressure, and porous body diameter. Kinetic simulations reveal that methane partial oxidation occurs in a two-stage process: (1) ignition, a fast process that accounts for approximately 60% of the total hydrogen conversion relative to thermodynamic equilibrium and (2) steam reformation, a slow process where the remaining conversion of hydrogen occurs when water reacts with unburned methane.