Simulation And Analysis Of CO₂ Capture By Chemical Absorbent For Coal-Fired Power Plant

Nowadays, the global climate change has so obvious impact to humankind, and CO2 has undeniable mutual relationship with global climate change. CO2 mainly comes from fossil fuel combustion process, and fossil fuels are main energy for the power plant, so coal-fired power plant is a concentrated emissions source of CO2. To alleviate climate change, the control and reduction of CO2 emissions from power plant has an important significance.Chemical absorption has so many advantages, such as high efficiency, superior capture effect, large process load, stable process effect, that chemical absorption, especially organic amine-based solvent absorption is very suitable for the separation of CO2 in flue gas from coal-fired power plant. Therefore, the simulation of CO2 captured by amine has an important significance. The flue gas from power plant was taken as the research object. Chemical absorption with MEA was used to absorb CO2 in flue gas, and the process flow was introduced. CO2 capture system was simulated by ASPEN PLUS, the simulations in this research contain three parts:(1) absorption tower simulation; (2) desorption tower simulation; (3) simulation for integrated system of absorption tower and desorption tower. Some laws were obtained through simulations, and the characteristic analysis were conducted.(l)For the absorption process, the influences of parameters, including flow rate, concentration and temperature of absorption solution and flue gas on the absorption fraction were studied. The relationship between absorption solution flow and CO2 load, and also the conditions of CO2 load on each trays were researched. The results show that the effect of absorption solution temperature and flue gas temperature on absorption fraction is not obvious, an appropriate temperature for both is 40℃.10 bubble-cap tower trays are enough for absorption solution with concentration of 30%, and the best absorption solution flow is 110m3/hr.(2)For the desorption process, the influences of reboiler heat duty and reboiler pressure on the desorption fraction were mainly studied. The relationship between reboiler pressure and lean liquid outlet temperature, reboiler heat duty and gas temperatures of each desorption tower trays, were researched too. The results show that the optimizing reboiler heat duty is 6500kw; the optimal reboiler pressure is about 0.12 MPa; When reboiler heat duty is high, trays temperatures are high; but trays temperature drop smaller from underpart to upside. Outlet temperature for lean liquid increases linearly with the increment of reboiler heat duty. High temperature should be avoided, the temperature should be controlled at about 110℃.(3)For the integrated system of absorption tower and desorption tower, the influences of reboiler heat duty and lean liquid flow on the CO2 yield coefficient were studied. In specific heat duty, the conditions of the trays temperatures and gas flow rates in two towers were researched. The results showed that optimal concentration for MEA is about 15% (mass fraction); CO2 yield coefficient reaches the maximum (90%) when the absorption liquid flow is 140mr3/hr; the optimizing heat duty is 7500kw.In addition, with total cost of capture system as target, economic model for a CO2 capture system was established. Now it is possible to evaluate economy of a CO2 capture system. The energy consumption for desorption was calculated as 165.2KJ/molCO2, which is close to general value 176-220KJ/molCO2.