Numerical simulation of flameless combustion of multi-source low calorific value gas

Abstract

Fuel can be produced from biomass, municipal solid waste, low-grade coal and other raw materials through anaerobic fermentation, pyrolysis gasification and other technologies. It can not only deal with solid waste, and make coal clean to use, but also generate utilizable gas, which has the dual benefits of energy and environmental protection. However, the produced gas has low calorific value, complex composition, more non-combustible components, and the composition changes greatly under the influence of raw materials and processes. There are some problems such as ignition difficulty, combustion instability, and difficult control of pollutants under traditional combustion. Flameless combustion is a mild combustion mode under low oxygen condition with low pollutant emission and high combustion efficiency, which helps to solve these problems. In this study, a detailed mechanism GRI Mech 3.0 and the eddy dissipation concept (EDC) model were used to simulate the flameless combustion process of three low caloric value gas by coupling the turbulent flow with the chemical reaction. The experimental data verify that the simulation method in this study can accurately simulate the flameless combustion in the actual burner. Subsequently, the numerical simulation of flameless combustion of biogas, biomass gasified gas and coal gasified gas was carried out, including temperature field, species, OH radical distribution and pollutant emission. The flameless combustion of biomass gasified gas and coal gasified gas was successfully realized by improving the burner. The results show that the temperature distribution of biomass gasified gas and coal gasified gas in flameless combustion is more uniform than that of natural gas and biogas, the reaction zone structure is larger, and NOx is close to "zero emission". The dilution of CO2 can promote flameless combustion, and CH4 will change the reaction zone and OH distribution, making the temperature distribution nonuniform. The horizontal comparison of flameless combustion of three low calorific value gas shows that even if the input power is the same, the lower the calorific value of gas, the lower the overall furnace temperature. However, the amount of flue gas is larger, so it is necessary to strengthen the heat utilization of flue gas to increase the thermal efficiency of the system.

Keywords

• flameless combustion
• mild combustion
• numerical simulation
• low calorific value gas
• nox emission