Hydrogen-enriched natural gas blend oxidation under high-pressure conditions: Experimental and detailed chemical kinetic modeling

Abstract

For the first time, experimental results were obtained for the kinetics of oxidation of hydrogen/natural gas mixtures in a fused silica jet-stirred reactor operating at 10 atm, over the temperature range 900–1200 K for equivalence ratios of 0.3, 0.6, and 1. The concentration profiles of the reactants, stable intermediates and the final products were measured by probe sampling followed by on-line FTIR analyses and off-line GC-TCD/FID analyses. The addition of hydrogen in variable concentrations significantly increases the reactivity of the natural gas blend used (methane–ethane 10:1), particularly under fuel-lean conditions. The present experiments were modeled by means of a detailed chemical kinetic reaction mechanism (97 species involved in 732 reversible reactions). We obtained an overall good agreement between the present data and the modeling. According to the proposed kinetic scheme, the enhanced oxidation of methane by hydrogen proceeds through an increased production of OH. The increase in hydrogen initial concentration boosts the formation of HO 2 radicals at low temperature, yielding higher concentrations of H 2 O 2 and OH. The oxidation of hydrogen, methane and ethane mostly proceeds via reaction with OH. The following sequence of reactions summarizes the mechanism yielding the observed reactivity increase in hydrogen-enriched mixtures: CH 3 + H 2 ⇒ CH 4 + H ; H + O 2 ⇒ HO 2 ; 2 HO 2 ⇒ H 2 O 2 + O 2 ; H 2 O 2 ⇒ 2 OH ; HO 2 + H ⇒ 2 OH ; OH + H 2 ⇒ H 2 O + H followed by reactions of hydrocarbons with OH. The proposed kinetic scheme was also used to simulate the burning velocities of methane–hydrogen–air mixtures over the pressure range 1–5 atm.