| Slather using of the fossil fuel makes the greenhouse effect increasing greatly. The research and demonstration project of the carbon capture and storage (CCS) have become a very important task in the field of thermal power generation. Oxy-fuel combustion technology is also known as O2/CO2 combustion technology, or air separation/flue gas recycling technology, which can trap high concentration CO2 directly without separation and control pollutant emission comprehensively. It is a new generation of clean coal power generation technology.In terms of energy balance, a 300MW boiler was taken as the research object for the conceptual design under oxy-fuel combustion on the aspects such as furnace radiation, convection heating surfaces, back-end surfaces, coal pulverizing system and so on. The designed coal was lignite with high moisture and low sulfur. This system recycled the system energy in the courses of generating oxygen by air separation and compressing CO2. An improved wide-band correlated-κdistribution model was developed to calculate the radiation characteristics of the triatomic gases with high concentrations under oxy-fuel combustion. The influence rule of the initial oxygen concentration to NOx emission and burn-out rate were revealed by numerical simulation. From the view of the basic theory of heat transfer, the convective heat transfer characteristic of flue gas under oxy-fuel combustion was analyzed. The whole economy of the oxy-coal fired boiler system was analyzed. By comprehensive consideration of heating surface investment, an index was proposed to evaluate the economy of the boiler convective heating surfaces, defined as the total cost per unit quantity of heat transferred. Variation of the total cost per unit quantity of heat transferred at different gas velocity was obtained. The reasonable arrangement of the boiler heating surfaces under oxy-fuel combustion was determined.Compared with air combustion, the radiative heat transfer in the furnace increased by about 7% in 30%O2/70%CO2 atmosphere, among which the contribution of triatomic gases to radiative heat transfer increased from 24% to 40% approximately. The convective heat transfer decreased by 9% compared with air combustion. The operation resistance of flue gas side decreases largely. With the gradual rising of the pressure in the furnace, the radiation intensity and emissivity of triatomic gases increase, but the increasing range deduce.Under oxy-fuel combustion, the existence of CO2 with high concentration increase the formation of CO, which promotes the reductive degradation of NO. The furnace outlet NO concentration is about 480mg/m3 under the 30%O2/70%CO2 operating condition, decreased by about 38% compared with air atmosphere.Compared with air combustion, the wall surface heat transfer coefficient increased under oxy-fuel combustion. As the gas velocity increasing, the total cost per unit quantity of heat transferred decreases first and then increases. The total cost per unit quantity of heat transferred is regarded as the objective function to exercise optimization design. As a result, boiler body size is reduced and part of the superheaters should be moved to the upper part of the furnace. Simulation results show that the carbon in fly ash increases slightly under this smaller cavity operation compared with that of primary size, which is still lower than the operating data of air combustion with primary boiler size.Under our country's present market economy condition, on the basis of the present coal price, the cost of CO2 removal under oxy-fuel combustion decresed by about 80% compared with MEA chemical absorption. When the system energy utilization in the courses of generating oxygen and compressing CO2 is taken into account, the cost of CO2 removal can be reduced by about 23% further under oxy-fuel combustion. |
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