Experimental Study On CO₂ Capture From Coal-Fired Flue Gas By Thermo-regeneration Ammonia Absorption Process

Global climate change has recently become a major environmental problem in the world. The emission of CO2 from fossil fuel combustion is the main cause of this change, amongst of which, the coal burning accounts for a large proportion of CO2 emission. The absorption of CO2 by ammonia solution with the advantages of high efficiency and low regeneration energy has recently become a hotspot in the area of CO2 reduction. This paper studied the CO2 absorption and regeneration processes using ammonia solution under simulated flue gas conditions and evaluated the economy of this technology, providing some experimental and theoretical guildlines for future industrial application.Firstly, the paper studied the CO2 absorption efficiency by using 5 wt% ammonia solution, proving that its efficiency was better than that of conventional CO2 absorbents. Thereafter, this paper investigated the effects of different operating conditions on the absorption efficiency, including ammonia mass fractions, absorption temperatures, absorbent flow rates, gas flow rates and inlet SO2 concentrations. Experimental results revealed that at high CO2 loadings (0.4-0.6), the efficiency was very difficult to be improved even further increasing the content of ammonia in the solution. Therefore, additives, e.g. piperazine (PZ) and sodium phosphate, were used to improve the efficiency.Then, the paper studied a regeneration process with regards to the effects of ammonium bicarbonate concentrations, CO2 loadings, flow rates of rich solution, heating oil temperatures and the temperatures of rich solution into the regeneration column on reboiler energy consumption, CO2 regeneration efficiency and ammonia leakage rate. Experimental results revealed that the optimal conditions for the regeneration process was that the concentration of rich solution and CO2 loading should be closed to the saturated concentration of ammonium bicarbonate and 1, respectively and the temperature of heating oil should be lower than 120℃.Finally, the paper used operating and technical parameters of CO2 capture process (MEA method) employed in Huaneng Power plant and the obtained optimal operating conditions in this study to evaluate the operating cost of decarburization process by ammonia-based solution. It was determined that the reboiler energy consumpt and the operation cost were about 55.0% and 77.9%of the MEA method respectively even with 5% higher CO2 removal effeiciency, revealing a good economic viability of CO2 reduction process by thermo-regeneration ammonia absorption method.