Simulation And Optimization Of CO₂ Capture From Flue Gas By Ammonia Scrubbing

The reduction of CO2 emissions from flue gas of fossil fuel-fired especially coal-fired power plants is essential to mitigate climate change. However, the cost of CO2 capture is so large that the current research priority is to find new solvents. Former studies have shown the effectiveness and advantages of ammonia. This study simulated the ammonia absorption system and integrated it with steam cycle. The factors affecting absorption, regeneration, CO2 compression were analyzed respectively. The steam cycle of power plant was simulated; the effects of the steam extraction on electricity output were studied. At last, the capture system was integrated with steam cycle and the power plant efficiency reduction caused by CO2 capture was researched.The ways how the parameters affect absorption and regeneration were studied via the simulation of absorber and stripper. The decrease of flow rate and the increase of CO2 concentration in solvent are good for reducing reboiler duty. Large amount of energy would be saved if the absorption goes at atmospheric pressure without being compressed. The optimal values of temperature, ammonia concentration and CO2 concentration in solvent can be decided through their influences on flow rate of solvent, ammonia losses and water losses. The molar ratio of CO2 in the gas outlet of stripper is significant to reboiler duty. A molar ratio of 70% is suitable for ammonia losses, water losses and the separation before compression of CO2. The temperature of reboiler and reboiler duty are decided by regeneration pressure. Both regeneration ratio of CO2 and reboiler duty decreases with the increase of CO2 concentration in solvent. With the increase of stripper pressure, the CO2 pressure of output increases and the losses of ammonia and water decrease.The steam cycle model of a 300MW power plant was set up and the relationship between extraction of steam and temperature of feed water with the load of power plant was found. The comparison of simulated data with actual data validated of the model.The integration of CO2 capture system with steam cycle shows the cost of CO2 capture: the output of power plant reduces because that steam is extracted to heat the reboiler and electricity is needed to compress flue gas and CO2 to increase the pressure of solvent. CO2 concentration in solvent and the pressure of stripper are the two key factors. The reduction of efficiency of power plant would be decreased if proper concentration and pressure are chosen. Furthermore, the position where to extract steam decides the flow rate of steam extracted and the power output.At last, the comparison with other ammonia studies and MEA methods show that the ammonia capture system is better than MEA system, and the optimal conditions chosen in this study are appropriate.