The Experimental And Theory Study Of Characteristics About Desurfulrization And NO Release Under O₂/CO₂ Coal Combustion

Combustion of coal is a main means to provide energy which is the foundation to our living. The use of coal combustion is increasing steadily to meet the need of economy development. And the pollutants from coal combustion influence reversely on environment, among them CO2 is greenhouse gas , while SO2 and NOx is the cause of acid rain. At present, how to harmonize the relation between economy development and environment protection become the focus internationally. Developing a technology with high efficiency and low pollution is imperative under the situation.Recently the technology of O2/CO2 recycled combustion is gradually paid attention internationally, and many organizations have ploughed into it. In the process air is replaced by pure oxygen, and flue gas is recycled. The heat loss resulted from N2 release is cut down, so the combustion efficiency is improved greatly. At the same time the CO2 concentration in the flue gas is increased to 95% and it will be easy to capture. Therefore, much research is necessary for a better understanding.In the work the characteristics of coal combustion in O2/CO2, the direct sulfation of CaCO3-SO2 and NOx emission were studied and the coal combustion numerical simulation carried out. The job consists of aspects as followings:1. Combustion characteristics of the pulverized coal was studied by thermogravime-tric analysis under the O2/CO2 atmosphere and the results were compared with traditional air conditions. The ignition temperature and burnout temperature of the pulverized coal are significantly lowered under O2/CO2 conditions, so the burning characteristics are improved greatly. The conclusion is confirmed by dynamic analysis. It is shown that calcium-based desulfurization efficiency increases in O2/CO2 atmosphere.2. Sulfation process under moderate and high different temperature in both atmosphere of air- O2/CO2 was studied by thermogravimetric analysis and one dimension drop-tube experiment. The influence of temperature,O2 and SO2 concentration, and grain diameter on desulfurization efficiency was investigated by thermogravimetric analysis. The effect of temperature,Ca/S,CO2 volume percent, residual time, excessive air coefficient and coal species on sulfation process was studied under one dimension drop-tube.3. The thermodynamics characteristics of CaSO4 decomposition was obtained by establishing the relation between Gibbs Free Energy and T, and the decomposition pressure of SO2 and T. CaSO4 decomposition in O2/CO2 is prevented compare to air. The influence of the concentration of CO2, SO2 and O2 on CaSO4 decomposition was evaluated, and the activation energy was obtained.The results from experiment andcalculation consistent with the thermodynamic conclusion.4. The effect on pore structure and direct sulfation of CaCCb added by K2CO3 A12(SO4)3 and Cs2CO3 was studied by Pore Master and SEM analysis. The results show that by adding Na2CO3,K2CO3 or Al2(SO4)3, the pore structure of CaCO3 was optimized, and sulfation effect is improved. The other way round is in CS2CO3. Ash melting point is not lowered by adding of Na2CO3.5. The characteristics of NOx release in O2/CO2 atmosphere was studied and compared with air, the law was summed up by analyzing the effect of coal species, temperature, excessive air coefficient et al on it. The effect of fuel-N, recycled-N and the combination of them on characteristics of NOx release was investigated.6. The coal combustion process and characteristics of NOx release in O2/CO2-air was simulated with the Fluent software, the temperature field, heat exchange characteristics and NOx concentration field were obtained and the results were consistent with experiment.7. Discussed the membrane separation process and the principle to produce oxygen, and believed that the technology of coal combustion in O2/CO2 will be applied widely to industry with improving of producing oxygen by membrane separation process.