Condensation Experiment Of Pressurized Oxy-coal Flue Gas And Heating Surface Design

Carbon dioxide produced by thermal power generation is the main source which causes greenhouse effect. The capture and storage of carbon dioxide from coal-fired power plants is an important way to reduce carbon dioxide emission. And the pressurized oxy-coal power generation technology based on oxy-coal combustion is a new generation of clean power generation technology which can achieve zero emission of carbon dioxide from coal-fired power plants.In the pressurized oxy-coal combustion system, the high pressure exhaust condenser with latent heat recovery is one of the key equipments. In order to provide the basis of designing the condenser, the article studies the thermodynamic properties of high pressure flue gas and the condensation heat transfer characteristic of vapor in the gas. In order to explore the influence of changes in the combustion mode and pressure on heating surface of boiler, the article also investigates the heat transfer, optimized design, and erosion of the heating surface.The flue gas produced by pressurized oxy-coal combustion is high-pressure, wet and mixed triatomic gases. The existing calculation methods of thermodynamic properties based on the ideal gas are no longer applicable. The article establishes the calculation model of thermodynamic properties of high-pressure gas mixture based on the actual gas, and the model is verified by software. To explore the condensation heat transfer of high-pressure flue gas, the experiment rigs of condensation heat transfer of wet flue gas inside a horizontal pipe and across a tube bundle are built respectively. The mathematical model of condensation heat transfer inside tube with iterative method based on energy balance on the gas-liquid interface is established. Through the combination of theoretical study and experimental research, the condensation heat transfer characteristic of wet gas mixture is analyzed. Based on exergy economic analysis, taking the total cost of heat exchanger of unit heat as the objective function, the article designs and optimizes the heating surface of pressurized oxy-coal combustion boiler applying genetic algorithm method. By comparison with the existing experiment results, the appropriate erosion model is chosen, the factors influencing erosion loss are analyzed. Embedding the erosion model into the FLUENT software, the article also investigates the flow of fly ash particles and the heating surface wear properties in atmospheric air combustion boiler and pressurized oxy-coal combustion boiler through numerical simulation.Comparing with atmospheric air combustion, the density of flue gas increases almost80times, while the specific heat at constant pressure, dynamic viscosity and thermal conductivity of flue gas change a little under oxy-coal combustion at6MPa. When the heating surface structure is unchanged, the flue gas velocity will reduce by2orders of magnitude, but the convective heat transfer coefficient will increase slightly. In the horizontal pipe, the heat transfer coefficient of wet gas mixture with condensation is1order of magnitude larger than that without condensation, and the heat transfer coefficient increases as the pressure rises. But the higher the pressure, the smaller the increment. Outside the bundle, the occurrence of condensation enhances heat transfer, the condensation heat transfer of gas mixture is in the same order of magnitude with single-phase convective heat transfer, and the heat transfer coefficient will rather diminish as the pressure increases. Besides, the condensation heat transfer coefficient increases with the larger of the Reynolds number and the content of water vapor no matter in or outside the tube. Compared to the conventional air combustion boiler, the optimized heating surface of pressurized oxy-coal combustion boiler is in a more compact structure, smaller size, stronger heat transfer capability and a little larger flow resistance of flue gas. The erosion loss of the wall increases with the rises of the particle impact velocity and particle size and the decrease of the hardness of wall material. The erosion loss first increases and then decreases with increasing particle incident angle. The location of maximum wear has also changed, and the erosion loss of each tube row is smaller, the erosion rate is more evenly distributed.