Experimental Study On Removal Of CO₂ In Coal-Fired Flue Gas By Ammonia

The global warming has become a global environmental problem. It is mainly due to the enhanced greenhouse effect produced by greenhouse gas emission into the atmosphere as a result of fossil fuels combustion and the forests cutting down in the land. Coal-fired power plant contributes more to the CO₂ emission and is a concentrative CO₂ emission source. Improving power generating efficiency, accelerating the fuel substitution and capturing CO₂ directly from the flue gas of the power plant can be taken into account to control and reduce CO₂ emission to the atmosphere, with the last being the most important method to control CO₂ emission nowadays.In this paper, flow chart, characteristic, fields of utilization, the state of the art and the economics of chemical absorption, physical absorption, physical adsorption, cryogenic distillation and membrane separation technologies et al. are analyzed and compared with each other. It indicates that chemical absorption is the most effective CO₂ capture technology and ammonia is a new reasonable absorbent.A set of experimental equipment was designed to remove CO₂ from coal-fired flue gas by ammonia spraying, and experimental study of CO₂ continuous removal was also completed by this experimental equipment which has a cascade mini ring(CMR) packed column as the reactor. In the experiment, the diluent ammonia solution was sprayed from the top of the absorption column, fully mixing and reacting with the simulative flue gas from the bottom. The volume concentration of CO₂ in the flue gas was continuously detected by Coal-Gas Analyzer, and then the curve of CO₂ removal efficiency changing in time was obtained.In this paper, the effect of several factors to CO₂ removal efficiency was studied respectively, such as ammonia concentration, CO₂ concentration and temperature. The absorption capacity of ammonia was studied by bubble absorption and acid hydrolysis. The reaction production was also analyzed by FTIR. The results demonstrate: the method of ammonia spraying excels the traditional ones for it can reach a high remonval efficiency (higher than 85%) and a rapid removal rate under a proper reaction condition. Increasing ammonia concentration or decreasing CO₂ concentration may enhance CO₂ removal efficiency. The effect of temperature to CO₂ removal efficiency is obvious, and the highest CO₂ removal efficiency appears at about 40℃. The absorption capacity of ammonia is 0.86mol CO₂/mol NH3 or 2.22 kg CO₂/kg NH3, which is higher than that of MEA. The reaction product is proved by FTIR to be NH4HCO3, which is a kind of nitrogenous fertilizer widely used in agriculture in China and has business value.The research in this paper has some guiding significance of industrial application of removing CO₂ from coal-fired flue gas by ammonia spraying.