| The CO2concentration of the flue gas in the oxy-fuel combustion may reach up to more than90%and CO2can be liquefied and recycled directly without separation, avoiding the complicated separation process, so the oxy-fuel combustion is a promising new technology for CO2capture in power generation system. However, conventional atmospheric oxy-fuel combustion systems require substantial parasitic energy within the air separation and carbon dioxide purification and compression units. In order to overcome the significant improvement of electric consumption in the atmospheric oxy-fuel power plant, the integration and optimization of the pressurized oxy-coal combustion power generation integrated with CO2capture system were studied under the pressure of6-8MPa in this thesis.On the basis of oxy-fuel combustion and the fluidized bed combustion, the overall power generation of the pressurized oxy-fuel combustion integrated with CO2capture system was conducted. From the air separation, combustion, heat transfer to the CO2capture and sequestration, the whole process was completed under the pressure of6-8MPa. The vapor latent heat of the flue gas recovered by the high pressure flue gas condenser was used for heating feed water, decreasing the extracted steam and the output power of the steam turbine increased. Simultaneously, CO2can be liquefied and recycled at the normal temperature, then CO2liquefied process was simplified and the compression power consumption greatly reduced.The conventional enthalpy calculation method at the air combustion style based on the ideal gases is not applicable to the pressurized oxy-fuel combustion. In this thesis, the residual enthalpy equation of tri-atomic mixture gas at high temperatures and high pressures has been deduced based on the real gas virial equation. The enthalpy of flue gas was calculated by programming and compared with the results simulated by the business process simulation software, so the accuracy of the results was verified.Due to the flue gas recirculation, the water vapor content in the flue gas improved greatly. The condensation heat transfer film model of the mixture containing plenty of non-condensable gases under high pressure was established and modified based on the Nusselt condensation theory. The influence of the wall temperature, the mixture velocity, the water vapor fraction and the mixture pressure on the condensation heat transfer was calculated and analyzed. The vapor content balance in the flue gas was calculated and analyzed under different flue gas dehumidification and recirculation modes. The pros, cons and the economy of different flue gas recirculation modes were demonstrated and anlysed in detail.Taking a300MW coal-fired generating unit as the research object, comparing with the atmospheric oxy-fuel combustion, the saturation temperature of the water vapor increased to167～188℃with the pressure raised to6-8MPa. Due to the recirculation of the vapor latent heat, the extracted steam reduced and the turbine power generation output improved about6.3%. At the same time, CO2is cooled to liquid state by the normal temperature cooling water, then the compression power consumption decreased by two orders of magnitude. However, the power consumption of the air separation unit increased as the system pressure was raised. When the oxygen purity was100%, the net efficiency of the pressurized oxy-coal power integrated with CO2capture system achieved to30.1%-30.7%, increased by4.2-4.8percent than the atmospheric oxy-fuel combustion power generation.The largest power consumer within the pressurized oxy-fuel system is the air separation unit and the power requirement strongly depends upon the oxygen purity. Therefore, a sensitivity analysis has been done to study the impact of the oxygen purity on the thermodynamic performance of the system. The results showed that:the relatively air separation unit power requirement occurred at95%oxygen purity and the overall net efficiency achieved to30.8%in this case. |
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