| Due to the rising concentration of CO2, a greenhouse effect gas, the global warming has become an increasingly prominent problem. The increasing CO2concentration in atmosphere is mainly caused by the burning of fossil fuels such as coal, oil and gas. It is estimated that1/3of the world’s total CO2emission is from the exhaust gas of coal-fired power plants. Since the most popular way of CO2reduction is carbon capture and storage technology (CCS), starting a study on CO2released by the power plants with this technology is of great importance.This paper, firstly, uses Aspen Plus software to study the combustion process of pulverized coal in a300MW power plant, and obtains the amount of each component of flue gas in coal-fired processes with air and rich oxygen (O2/CO2), respectively. Then, this paper goes on to find out the difference between the two process models and analyses the influence of temperature, excess oxygen coefficient and mole fraction of O2/CO2on the proportions of different components of flue gas. The paper also uses MEA chemical solution to absorb CO2in flue gas which is produced in conventional process, so as to obtain the results of lean solution stream recycled on the basis of separate absorption and regeneration process. In addition, some factors are also studied including the influence of the MEA mass fraction of lean solution, the CO2load of lean solution and CO2absorption rate on the mass flow of lean solution and the reboiler’s thermal load of regeneration tower. At last, by compressing the flues gas produced in the Air-fuel and the Oxy-fuel processes to the same critical state, the paper compares the production of CO2and the energy consumption in these two processes, and provides an economic analysis on main components, too.Through detailed study in this paper, the following results are obtained. Firstly, given the same amount of O2, the flame temperature in the Oxy-fuel process is206℃lower than that in Air-fuel process. The amount of flue gas produced decreases intensively, too, leading to an immense drop in heat losses. The amount of NOX produced in the Oxy-fuel process decreases a lot inferring more nitrogen atoms tend to generate N2. The amount of SO2remains the same, while there is2.03times more SO3in fuel gas. The CO production is significantly reduced, and the mass fraction of CO2has increased to81%from21%in the Air-fuel. Secondly, through sensitivity analysis, the curves between the changes of temperature, excess oxygen coefficient and mole fraction of O2/CO2and that of the proportions of main components of flue gas are obtained. By absorbing CO2in conventional fuel gas with30wt%MEA solution, the mass fraction of CO2from the regeneration tower is found to be89.4%, which proves to be effective in emission reduction. Besides, the curves between the MEA mass fraction of lean solution, CO2load of lean solution, CO2absorption rate, pressure of the regeneration process and the mass flow of lean solution, the reboiler’s thermal load have been obtained through sensitivity analysis. The results show that given the CO2load of lean solution to be0.20, the reboiler’s thermal load reaches its minimum load of387.1MW. Finally, through a comparative study of flue gas decarbonization, the energy consumption of compression in the Air-fuel process and Oxy-fuel process are found to be22.8MW and44.5MW, and the operating costs are found to be37764.8RMB/h and45253.9RMB/h, respectively. The fraction of CO2capture in the Air-fuel process is76.3%, the fraction of air separation in Oxy-fuel process is70.5%. Although the operating cost of Oxy-fuel process is higher than that of Air-fuel process, the decarbonization effect is much better.The results provide some basis for the further economic analysis of Air-fuel and Oxy-fuel processes, and also important and meaningful reference for CO2capture and compression of the flue gas from power plants. |
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