Numerical Simulation Of Oxygen - Enriched Combustion In Cement Rotary Kiln

With the rapid development of Chinses cement industry, cement industry’s annual consumption of coal is also increasing rapidly, which has brought great stress to China’s increasingly severe energy supply situation. It is a great challenge to reduce energy consumption of cement industry, and how to use coal energy effectively, to reduce CO2 emissions per unit output value. Oxygen enriched combustion technology has advantages of reducing the amount of air, reducing flue gas emissions, speeding up the combustion reaction rate, facilitating complete combustion. If oxygen enriched combustion technology is applied in the production of cement, it can save fuel and raw material, reduce exhaust emissions of the rotary kiln, and it is conducive to environment friendly.In this paper, a rotary cement kiln of 4000t/d yield in Yunnan province was simulated to investigate the characteristics of coal combustion in rotary cement kiln with a comprehensive computational fluid dynamics method. Numerical simulation results are compared with the data measured in experiment. In this paper, a three dimensional model of the four channel burner and rotary kiln is modeled according to the actual size. The mesh of the burner and kiln are structured and hexahedral mesh type. RNG k-e model for turbulence, P-1 radiation model for gas-phase radiation, Eddy dissipation model and discrete phase model (DPM) for coal combustion were used in 3-D structured grid CFD simulation.Simulation was conducted under five oxidant stream conditions with different O2/N2 volume ratios:21/79,24/76,27/73,30/70,33/67. Results show that there is strong entrainment, inside recirculation and outside recirculation zone. The oxygen-enriched combustion improves the max temperature of the kiln, however, uniformity of the temperature becomes worse. In addition, the use of oxygen enriched air, the concentration of N2 in furnace can be reduced by reducing the amount of the combustion air needed, which can improve the combustion efficiency. The high temperature zone in the kiln is mainly in the zone where the volatiles burn massively. At lower oxygen content (<27% concentration in volume), NOX emissions go up slowly with enlarging the oxygen content, whereas the increase of NOx is sharply when the oxygen content exceeds 27% concentrations in volume. It is suggested that the optimal oxygen content is no more than 27% concentrations for combustion of pulverized coal in cement kiln, which can not only improve the thermal efficiency of rotary kiln, but also can effectively control the emissions of pollutants.The results reflect a reasonable rule of velocity distribution, temperature distribution, NOx and component distribution in the rotary kiln. The finding of this work will provide a theoretical guidance to the cement industry.