| The global warming has become issue general concern to the international community, where CO2 is the main greenhouse gas. Change of energy structure, vigorous development of natural gas, and application of O2/CO2 combustion co-generation technologies to reduce CO2 emission are the most direct and effective way to deal with greenhouse effect. The number of natural gas boiler in power plant of China has increased. Applying O2/CO2 technology to natural gas combustion can greatly improve combustion efficiency and reduce CO2 emission, and injecting CO2 captured into oil well can enhance oil recovery. However, there are little researches about combustion characteristics of natural gas under O2/CO2 atmosphere at present. In this paper, the combustion characteristics of ethylene and natural gas in O2/CO2 atmosphere were studied by the combination of experiment and numerical simulation.Using ethylene diffusion flame experiment system of State Key Laboratory of Coal Combustion of Huazhong University of science and Technology, the combustion experiments were operated. The thermal properties test results indicated that, in O2/CO2 atmosphere the flame characteristics and temperature diffusion are similar with O2/N2 atmosphere. And the flame height are more higher in the O2/CO2 atmosphere, while combustion temperature are lower. The temperature shows the trend of increased with the oxygen concentration of two combustion atmosphere.Making the burner used in laboratory as a model, the modeling and solution of ethylene combustion in the experimental conditions are carried out by FLUENT software. The simulation results of combustion temperature are larger than the experimental results, and the average error is 8.06%. The FLUENT numerical simulation method is reasonable. It demonstrates the practicability of this method applied to gas-fired boiler under O2/CO2 combustion.In addition, change the fuel and simulate the natural gas combustion characteristics in O2/N2 atmosphere and O2/CO2 atmosphere. The results show that the change trends of natural gas combustion speed in the two kinds of atmosphere is same. The oxygen content is low, combustion speed difference is small in the two kinds of combustion atmosphere. With the increase of oxygen concentration, high speed combustion zone increase, and axial velocity gradient tends to be uniform. With same oxygen concentration, gas combustion speed in O2/N2 atmosphere rate was significantly lower than O2/CO2 atmosphere. Gas burns rapidly between 5 mm and 9 mm from nozzle with large temperature gradients. At different combustion condition,temperature distribution is low in the middle and high on all sides, and the maximum temperature occurred in the middle part of combustion region. With the increase of oxygen concentration, the exit temperature rises gradually. At the same oxygen concentration, combustion temperature under O2/CO2 atmosphere were higher than the combustion temperature under O2/N2 atmosphere. As the main component of fuel, the maximum methane concentration appeared in the outlet of the burner, gradually decreases along the flow. At Two atmosphere, the methane concentration distribution is little difference. The higher the oxygen concentration, the longer the combustion region at the same combustion atmosphere, natural gas burn longer distance, axial methane concentration decrease slowly.According to the variation laws of characteristics with combustion atmosphere, this paper focus on the influence of combustion-supporting gas temperature and peroxy coefficient on combustion characteristics of natural gas in power plant boiler at O2/CO2 atmosphere. The research results shows, as the combustion-supporting gas temperature rises, combustion efficiency has improved, temperature distributed better, and the flue gas temperature rising rate decreases. In the flue gas, methane concentration decreased with increased preheating temperature, the opposite way round of NOx concentration. When the preheat temperature is about 420K, each parameters is conducive to industrial production. With the increase of peroxide coefficient, the flue gas velocity decreases, the flame temperature increases gradually, and the methane concentration in the flue gas decreases, while NOx content increases from stable speed to rapid. When the peroxide coefficient is 1.13-1.5, each parameters is conducive to industrial production.Through comprehensive analysis of simulation results, and take the industrial applicability and economic benefits into account, a optimization scheme of natural gas power plant boiler O2/CO2 combustion has been proposed:preheating combustion-supporting gas to 420K, and keeping the peroxy coefficient as 1.13-1.15. This scheme can improve the efficiency of combustion and CO2 enrichment, and minimize pollutant emission. The results offer a reference for the process design and operation for flue gas recirculation and waste heat recovery of actual boiler. |
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