| Considering the situation that increasing attention has been paid on the CO2 emission control worldwide, China faces tremendous pressure because of the big CO2 emission amount and increasing CO2 emission rate. Oxy-combustion technology has been considered as a feasible choice to reduce the CO2 emission from the coal-fired power plants through adding a cryogenic air separation process (ASU) and a flue gas treatment process (FGU) to a conventional combustion process. High purity oxygen (greater than 95% by volume) from the ASU, instead of air, is used as the oxidizer in the oxy-combustion technology, and about 70～80% of the flue gas is recycled back to the furnace with the oxygen stream, then high purity CO2 could be obtained. In order to have a comprehensive understanding of the characteristics of the oxy-combustion technology, an analysis and evaluation work with consideration of thermodynamics, economics as well as environment was performed to a 600MWe supercritical oxy-combustion pulverized coal-fired power plant.A flexible oxy-combustion system simulation platform was firstly designed using the commercial flowsheet software Aspen Plus. And many important operation parameters (such as flue gas recycle ratio, oxygen concentration and oxygen excess factor, et al) in different cases were studied. The results show that the net efficiency of the oxy-combustion system is 10.84%(LHV) lower due to the ASU and FGU processes; however, high purity CO2 product can be obtained from the oxy-combustion system and the SOχand NOχcan be Co-captured. The preferred recycle ratios are 0.695-0.716 for the cold recycle cases, and the preferred recycle ratio for the hot recycle case is 0.613. All of these results will be helpful to the oxy-combustion system design and operation, and they are the basis for the following research works.To understand the techno-economic feasibility of the oxy-combustion technology in China, a detailed techno-economic evaluation study was performed on three typical power plants (2×300MW subcritical,2×600MW supercritical,2×1000MW ultra super-critical), as conventional air fired and oxy-combustion options in China, by utilizing the authoritative data published in 2010 for the design of coal-fired power plants. Techno-economic evaluation models were set up and costs of electricity generation, CO2 avoidance costs as well as CO2 capture costs, were calculated. Moreover, the effects of CO2 tax and CO2 sale price on the economic characteristics of oxy-combustion power plants were also considered. The results show that the electricity costs of the oxy-combustion plants are 1.39～1.42 times that of the corresponding conventional plants; the CO2 avoidance costs and the CO2 capture costs of the oxy-combustion plants are 160～184(?)/t and 115～128(?)/t, respectively. Because the oxy-combustion technique has advantages in thermal efficiency, desulfurization efficiency and denitration efficiency, oxy-combustion power plants will reach the economic properties of conventional air fired power plants if, (1) the CO2 emission is taxed and the high purity CO2 product can be sold, or (2) there are some policy preferences in financing and coal price for oxy-combustion power plants, or (3) the power consumption and cost of air separation units and flue gas treatment units can be reduced.Based on the system simulation results, a detailed exergy analysis was conducted to the 600MWe oxy-combustion PC system (divided into four models:boiler, turbines and feed water heaters (FWHs), ASU, and FGU) and the corresponding conventional PC system (includes boiler, turbines & FWHs models). The boiler model was decomposed in detail. The exergy (including physical exergy and chemical exergy for different phases) of each model and the whole system was obtained, showing the oxy-combustion boiler could reach higher exergy efficiency than the conventional combustion boiler because the combustion exergy efficiency in the oxy-combustion furnace is about 4% higher than that in the conventional furnace. In addition, the exergy destruction/loss calculation, the exergy efficiency calculation and the analysis of the energy quality were also carried out. The exergy analysis results of the boiler models reveal that the synthetical and cascade utilization of physical energy and chemical energy could be realized in the oxy-combustion technology; in each boiler model, water wall and air heater have lowest exergy efficiencies; the boiler model contributes most exergy destruction/loss in the oxy-combustion system, the exergy destruction of the turbines & FWHs model is just 9.01% of the total fuel exergy, and the corresponding value of ASU and FGU systems is 7.71%; the exergy efficiency of the oxy-combustion system is 37.13%, which is 4.08% lower than that of the conventional system.Combining the exergy analysis and the cost accounting, thermoeconomic cost models of the 600MW oxy-combustion system and the 600MW conventional system were established based on the "structure theory of thermoeconomics". In addition, an exergy cost decomposition methodology was established in this thesis and the unit exergy cost is divided into three parts:fuel, exergy destruction and negentropy. Furthermore, exergoenvironmental cost models for the two systems were also established by introducing the environmental costs to the thermoeconomic cost models. There are three models used to price the environment factor:capture cost, environment damage cost and tax. In this work, the oxy-combustion technology was analyzed with comprehensive consideration of thermodynamics, economics as well as environment. The results show that the unit exergy costs of units in the oxy-combustion system increase about 10% in comparison to those in the conventional system and the corresponding increase rate of unit thermoeconomic costs are about 22%, moreover, the internal relation between these two values are found. For unit exergy costs, the fuel part contributes the most, but the exergy destruction part affects the unit exergy costs of devices in the same model most. However, the capture of pollutants is necessary and beneficial if the environment impact is considered, the oxy-combustion technology is not only environment friendly, but also competitive in economy. Taxation is an effective tool for internalizing the externality of environment damage, and a proper CO2 emission tax 140￥/t was also proposed. In addition, the SOx and NOx emission tax values are much low in China.All the results obtained indicate that the thermal efficiency and exergy efficiency of the oxy-combustion boiler increase because the synthetical and cascade utilization of physical energy and chemical energy is realized in the oxy-combustion technology. However, because the ASU and FGU systems consume much power, so the thermal efficiency of the oxy-combustion system decreases a lot but the reduction of its exergy efficiency mitigates. The power consumption and investment addition increase the electricity cost of the oxy-combustion system and the calculation of the CO2 avoidance cost as well as CO2 capture cost further clearly indicates the economic barriers of the oxy-combustion technology. But if considering the CO2 emission taxation and the CO2 product sale, the oxy-combustion system is expected to reach the economic properties of the conventional combustion system and realize the large-scale CO2 emission control; at the same time, the results from the exergoenvironmental cost analysis reveal that the CO2 capture and sequestration is not only necessary and also beneficial if the environmental impact is considered, the oxy-combustion technology is not only environment friendly, but also competitive in economy.
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