| The serious environmental problems associated with fossil fuel combustion have motivated a decades-long pursuit of clean combustion technologies with higher efficiencies and near-zero emissions. Oxyfuel combustion technology is currently one of the most effective clean combustion technologies. In order to achieve efficient low-carbon energy conversion, Oxy-Coal Combustion Steam System of Near-zero Emissions was proposed. This process involves gasification of raw coal or demineralization of coal to generate syngas or super-clean coal. The produced fuel is combusted in pure oxygen. Recycled water is injected into the combustion chamber in steps to form high temperature, high pressure, high water vapor and high oxygen concentration environment. The produced high temperature and high pressure mixture of CO2/H2O（about 90%H2O 10%CO2） drives the turbine to work. Emitted gas experiences condensation, generating high concentration CO2 to realize low investment capture of CO2. Based on the conceptual Oxy-Coal Combustion Steam System of Near-zero Emissions, the dissertation studies the laminar flame characteristics and detailed chemical reaction mechanisms for the CO/H2 combustion in O2/H2 O atmosphere. Some key important characteristic parameters such as laminar flame speed and flame structure under different equivalence ratio, H2 content, preheating temperature, H2 O content and pressure are obtained. Combustion of CO/H2 and elemental reactions under different conditions are unveiled. Detailed elemental reaction mechanisms under O2/H2 O conditions are constructed. The basic data of laminar flame characteristics under high concentration of water vapor provides theoretical guidance to the high efficiency clean combustion of coal-based fuel under high concentration of water vapor. The results fill the gap in the basic data of oxyfuel combustion under high concentration of H2 O.First, the principles and advantages for Oxy-Coal Combustion Steam System of Near-zero Emissions are analyzed. The efficiency of power generation considering the capture of CO2 is higher than 50%. The processes of releasing and converting chemical energy of fuel are studied to understand the characteristics of direct conversion from chemical energy of coal-based fuel to enthalpy of media. Combustion of syngas and super clean coal is studied to verify the feasibility of O2/H2 O combustion technology. It is found that characteristics of CO/H2 combustion in O2/H2 O and reaction mechanism are the key scientific problems.A laser diagnostic test bed（PLIF） in lab scale for testing high pressure flame characteristics are constructed. The OH-PLIF method is able to measure flame speed and flame structure. The laminar flame speed based on Benson area is employed. The difference between OH-PLIF and OH* methods is within 2%. The laminar flame speed of CO/H2/Air was measured and compared with the data in literature to confirm the accuracy of the experimental system and method. Calibration of OH was conducted in OH-PLIF system using flat flame burner to obtain OH concentration of calibration flame and the scale factor of intensity of fluorescence.Previous chemical mechanisms of CO/H2 combustion in a O2/H2 O atmosphere diverge significantly. They were based on air combustion and can’t be directly used to predict combustion flame characteristics of CO/H2 in O2/H2 O, and the combustion mechanisms in a O2/H2 O atmosphere is lacking. The relative sensitive elemental reactions in O2/H2 O atmosphere were obtained by sensitivity analysis Based on the latest kinetic studies on several single elemental reactions reported in separate papers, especially the reaction kinetic parameters related to H2 O which is the third body in the three body reactions, the chemical reaction mechanisms under suitable high water vapor condition is developed. Under different equivalence ratio, H2 content preheating temperature, H2 O content and pressure, the results are consistent, which verify the accuracy of the established mechanism.The existing of laminar flame speed data of CO/H2/air humidified combustion can’t be directly used to the O2/H2 O atmosphere because the steam content is low, the CO/H2 laminar flame speed data are still lacking. The laminar flame speeds of CO/H2 in the 47% of H2 O, with different H2 content（0 to 50%）, equivalence ratio（0.6 to 2.0）, and pre-heating temperature（400K to 573K） were studied. The temperature and OH concentration distribution in Benson flame are measured by OH-PLIF method.With increasing equivalence ratio, the laminar flame speed firstly increases and then decreases, peaking at the equivalence ratio of 1.3. The peak value does not change with H2 content;the concentration of OH in Benson flame decreases gradually, while the flame temperature increases firstly and then decreases.With increasing H2 content, the flame speed increases slowly, and then increases rapidly, showing a nonlinear increasing trend; the Benson flame height decreases gradually, and the concentration of OH radicals increase gradually（from 0.160 mole/m3 at 0% increased to 0.175 mole/m3 at 50% H2）.Under low H2 content, the addition of H2 O accelerates the reaction of O+H2O=2OH, which promotes the combustion of CO/H2. Under high H2 content, reactions of O+H2O=2OH and O+H2=H+OH compete on obtaining O radical, thus the reaction of CO/H2 is prevented. With increasing pre-heating temperature, the laminar flame speed increases exponentially, and radicals of OH, H and O in the flame increases gradually.Laminar flame speed at different ratios of H2/CO varying from 0 to 60% are studied. With increasing H2 O content, when H2 content is relative low, flame temperature decreases from 2900 K to 2500 K, and the concentration of OH in the flame increases firstly and then decreases. as well as the laminar flame speed. When the content of H2 is higher than 15%, the laminar flame speed decreases gradually. The laminar flame speed under different CO/H2 ratios at H2 O content of 47% and pressure of 5atm and 10 atm were measured. With increasing pressure, the concentration of radicals of H, O and OH decrease, the concentration of HO2 radicals increase, and the laminar flame bulk speed decreases. |
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