The effect of CH4 addition on high-H2 syngas combustion characteristics under N2/CO2 dilution

Abstract

The composition of biomass gas is complex, in order to promote the more extensive and efficient utilization of low-calorific syngas, it is necessary to master the basic combustion characteristics of low-calorific syngas under different compositions. In this paper, the effects of addition of CH4 (0% – 20%) on the combustion characteristics of laminar flow flame of high-H2 syngas (H2:CO = 3:1) were studied by experiments and numerical simulations under the dilution of N2 and CO2 (40%). The laminar burning velocity (LBV) and Markstein length are obtained by experiments. CHEMKIN-PRO software package was used to compare the prediction results of the four mechanisms with the measured data. Finally, GRI3.0 mechanism was selected as the simulation mechanism in this paper. The experimental results indicate that the LBV of N2 dilution is higher than that of CO2 dilution, and the flame is more stable, with adding CH4, the LBV of syngas mixtures is decreased, and the LBV of rich-fuel mixtures is decreased faster, but the stability of premixed flames of syngas is improved. Numerical simulation shows that the dominant branch chain reaction changes from R99 to R38 after CH4 is added, and the mole fraction of H, O decreases while the mole fraction of OH, CH3 increases. The dilution of CO2 results in a lower concentration of active radicals than N2 because CO2 inhibits the important reaction R99. The GRI 3.0 mechanism was used to simulate the formation of NO: the addition of CH4 promoted the formation of hot NO. The NO production of NNH and N2O intermediate mechanism is decreased, and a new way of N2 and CH reaction to HCN is increased. The dilution of CO2 can reduce NO emission more than that of N2. The insights gained from this study have practical implications in a variety of production applications. For example, optimizing mixture equivalence ratios can improve combustion efficiency, thereby increasing energy efficiency and reducing environmental emissions.