| The energy structure of China will still be coal-based in a long period of time. Therefore the technical development of coal clean efficient utilization is a key issue related with our country’s energy security and development. The staged utilization of coal combined with oxy-fuel combustion is a novel coal clean utilization technology, and is one of the possible ways to achieve CO2emission reduction.This thesis based on the coal staged utilization combined with oxy-fuel combustion system, investigated the combustion characteristics of pulverized coal, the devolatilization characteristics of coal pyrolysis, and semi-coke oxy-fuel combustion characteristics, in according with research ideas of "thermogravimetric analyse of pulverzied coal oxy-fuel combustion—pulverized coal devolatilization characteristics of pyrolysis—semi-coke oxy-fuel combustion characteristics and comprehensive application—pulverized coal oxy-fuel combustion in horizontal tube furnace—pulverized coal oxy-fuel combustion in drop tube furnace—petroleum coke powder oxy-fuel burner test with2MW horizontal furnace."Investigated the pulverized coal oxy-fuel combustion characteristics by the thermogravimetric experiments. It is found that CO2in oxy-fuel combustion atmosphere has more apparent inhibition to low rank coal. When the oxygen concentration is lower than60%, the effection of oxygen concentration to the combustion characteristics is more obvious. The maximum reaction rate of anthracite increased to8.1times faster, and the maximum reaction rates of lignite and bituminous coal are also5.5times faster, when the oxygen concentration is increased from21%to100%. It will significantly reduce the reaction time of the pulverized coal oxy-fuel combustion, and will decrease the burnout temperature. Investigated three different ways of kinetics calculation, and found that the model-free methods are not suitable for the oxy-fuel combustion. Then retrofit a model-fitting method and improve the linear fit of the kinetic calculation for oxy-fuel combustion. The kinetic analysis found that the CO2and oxygen concentration effection is mainly reflected in the pre-exponential factor. Using the kinetic compensation effect calculation method to check the kinetic calculation results, and the calculation results showed that the retrofitting model-fitting method calculation result were reliable.Investigated the pulverized coal pyrolysis process with the fast pyrolyzer under a controllable heating rate over5000℃/s. Discovered that the H2production increased significantly when the pyrolysis temperature is higher than800℃. And High rank coal pyrolysis will produce more CH4. In addition, the extension of pyrolysis time has less effection on CO2production. The pyrolysis macromolecular product of high coal rank bituminous has more types and larger production than the low coal rank lignite. But the lightweight volatiles products such as H2, CO and CO2is less than the low coal rank lignite.According to the semi-coke oxy-fuel combustion thermogravimetric experiment results, the semi-coke combustion characteristics is close to the air combustion condition when the oxygen concentration in the combustion atmosphere is over40%and the burnout temperature and the maximum reaction rate are better than the air combustion condition. It is also found that the ignition temperature was less affected by the oxygen concentration. The absorption experiments of semi-coke results showed that the pore volume of test lignite semi-coke in800℃is76.3%of the coconut shell activated carbon, and the specific surface area is66.7%of the coconut shell activated carbon. Compared with the absorbent using by the garbage power plants, the adsorption characteristic parameters is nearly the same. Based on the huge price difference between lignite and the adsorbent, using the lignite semi-coke as the adsorbent raw material has a very broad market prospects.According to the pulverized coal oxy-fuel combustion in horizontal tube furnace experiment results, it is found that the oxygen concentration effection to high coal rank char burnout process is more obvious. The high oxygen concentration will increase the reaction rate, and reduce the reaction time. When the furnace temperature is900℃, and the oxygen concentration increased from5%to10%, the amount of CO in flue reduced quickly. And when the oxygen concentration increased from10%to60%, the CO amount decreasing speed slow down. When O2concentration is over60%, the CO amount decreasing speed slowed down further.Simulate oxy-fuel combustion process of pulverized coal on drop tube furnace. The CO2in oxy-fuel combustion atmosphere increase the flame resistance of anthracite with low oxygen concentration conditions. This is because the diffusion rate of O2in CO2is slower than in N2. When the excess oxygen coefficient increased from1.05to1.3, the CO concentration of anthracite oxy-fuel combustion flue gas is decreased from3.63%to0.97%. When oxygen concentration increased from21%to50%, the ignition distance from the burner decreased from30mm to10mm. The CO concentration of flue gas increased from0.08%to0.81%, when the furnace temperature rised from900℃to1300℃At last, a burner ignition test of petroleum coke powder was carried out on the2MW horizontal furnace. The flame temperature distribution of the petroleum coke powder was obtained in different oxygen ratio conditions. The maximum temperature of the best organized burning condition was1474℃, and the normal combustion condition highest temperature of the flame is around1320℃. According to the burner test results, some suggestions for oxy-fuel combustion burner design of pulverized coal and semi-coke were obtained:When the oxygen is not preheated, injecting fuel with large amount of cold oxygen will decrease the flow temperature, and obstruct the ignition process. Other oxygen nozzles should be arranged homogenized around the powder delivery flow nozzle. If the oxygen flow rate is too high or too low will delay the ignition postion and not conducive to the combustion stability. |
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