Investigation of gas-phase reactions in the mixing region for hydrocarbon autothermal reforming applications

Abstract

Mixture preparation technology plays a critical role in ensuring reformate quality during autothermal reforming of liquid fuels. Incomplete mixing can cause temperature overshoots and deposit formation within the catalyst bed. However, the time available for mixing is limited by unwanted gas-phase reactions that produce deposit precursors. We perform an analysis of the gas-phase reactions in the mixing region using a well-tested alkane oxidation mechanism taken from the literature. One particularly interesting prediction is that the time for significant reaction to occur does not monotonically decrease as the temperature increases. This is due to the negative temperature coefficient (NTC) kinetics. By mixing within the NTC temperature window, it should be possible to provide substantially more time for mixing. Similarly, one can expand the mixing time by suitable choices of mixture composition. These results provide important guidance criteria for the optimization of a mixer design to avoid undesirable reactions.