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Abstract

Oxy-coal combustion steam system of near-zero emission (OCCSS) proposed by the authors' research group is a new power generation system which uses coal-based syngas or demineralized coal as fuel. The combustion process has the characteristics of high temperature, high pressure, high water vapor concentration and high oxygen concentration. The key point of understanding the combustion process is to study the combustion characteristics under complex conditions. As an important part of the combustion characteristics, the study of the flammable limit of syngas has important value for the design and operation of the burner. The paper introduces the study of the lower flammability limit (LFL) of hydrogen/carbon monoxide mixtures (H2/CO) based on a spherical explosion vessel. The internal diameter was 337 mm and the volume is 20.04 L. The experimental procedure was based upon ASTM E2079-07. Effects of initial temperature, H2/CO ratio, and different dilution with N2 or water vapor were studied. Results show LFL of the syngas decreases with the temperature, which indicates higher initial temperature can promote flame propagation. The study also shows the flame temperature at LFL is approximately constant regardless of the unburned gas temperature. Experiments on the effects of different H2 contents both which is from 0 to 100% in both pure oxygen and water vapor show more H2 in the mixed gas will help to lower the LFL, and the presence of H2O can promote the flame propagation. In addition, studies on the dilution effects of H2O and N2 on LFL show the addition of water vapor not only reduces the reactant concentration, but also affects the gas flame propagation through affecting the chemical process. Finally, Le Chatelier's rule is used to estimate the LFL of the H2/CO mixture and compared with the experimental data. The results indicate the mixing rule is appropriate for the predication of LFL of H2/CO in O2/H2O environment by considering N2 or CO2 as a kind of dilution in the combustible gas.