| Nowadays, energy shortage and environmental pollution are the two major problems that human are facing to, and efficient utilization of low-grade fuels has been highlighted for more special attention. The ignition and combustion mechanisms, combustion characteristics and pollution emission of multi-generation-semicoke and stone coal in CFB combustor were investigated systematically and intensively in the thesis. Furthermore, the characteristics of fly ash recycle in CFB combustor was also studied, which could play a guidancing role in industrial operation.The investigation on physicochemical characteristics of semi-coke was conducted with employing Scanning Electron Microscope (SEM), nitrogen adsorption, mercury porosimetry, infrared spectroscopy. And the results demonstrate that compared with parent coal, semi-coke has the following conspicuous changes:pore structure has been developed strongly, and the amount of pores increases significantly, especially for small-scale large pores. Many functional groups, such as OH, NH, CH, CH2 and CH3, reduce. Moreover, the contents of some chemical compounds, including saturated polyesters, aldehydes, ketones, alkenes, aromatic rings, heterocycles oxo-compounds, are all decreased too. CH3 to CH2 mole ratio increases, while the content ratio of oxygen-containing groups to aromaticity decreases.Atmospheric and pressurized thermogravimetry were employed to study the pyrolysis-ignition-combustion mechanisms of different semi-cokes, and the results show:With the increased gasification temperature or heating rate, ignition temperature (Ti) is increased, volatile release index (r) is decreased, combustion stability (Rw) is reduced, burnout performance (Cb) is enhanced, and activation energy (Ea) of semicoke is decreased. With the increased reaction pressure, Tt drops, r increases, Rw improves, Cb drops down after increasing, Ea rises after falling. When reaction pressure at 0.8MPa, burnout temperature is maximized, and Ea is minimized. With the increased average diameter of semi-coke particles, Ti and r increase, Rw fall after rising, Cb changes non-monotonically, Ea increases non-monotonically. With the increased char-to-coal ratio, Ti increases after falling, r and Rw decrease, Cb improves, Ea increases. Besides, calculation results from Distributed Activation Energy Model (DAEM) show that activation energy of semi-coke decreases with the increased mass loss rate. Experiments were carried out in a bench scale CFB combustor to investigate the combustion and pollution emission characteristics of semi-coke. It was found that the emission concentrations of SO2, NO and N2O would be decreased with the increased char to coal mass ratio. With the increased temperature from 850℃to 940℃, the emission concentration of NO is raised while that of N2O is cut down. With the increased excess air coefficient or the decreased secondary air rate, the emission concentrations of SO2, NO and N2O would be increased. With the increased superficial gas velocity, NO emission concentration decreases, while N2O emission concentration increases.At present, high carbon content of fly ash and low utilization ratio of limestone are the two main problems existing in some CFB boilers. The combustion of recycled fly ash could not only reduce the carbon content, but also increase the utilization ratio of limestone. Experiments on the combustion of the recycled fly ash, obtained from Guizhou Thermal Power Plant burning local anthracite coal, were conducted in a bench-scale CFB combustor. Effects of ash to coal mass ratio (Ca/S. molar ratio), furnace temperature, reactivation mode of fly ash, solid circulation rate and superficial gas velocity on the desulfurization efficiency and carbon content of fly ash were investigated to find the reasonable operation parameters, which could guide the industrial operation.Based on many chievements of other preivious study, a general mathematical model has been developed to simulate CFB combustion with the consideration of fly ash recycle. The characteristics of hydrodynamic of CFB, coal-char combustion, pollutions emission combustion are considered extremely as well. The simulation results show a good agreement with the experimental results, and the model could reasonably simulate semi-coke combustion in CFB boiler with fly ash recycling, which would play a significant role in guiding industrial operation to reflect the operating characteristics of CFB system.Finally, a preliminary test was performed in a bench scale fluidized bed combustor to study the roasting characteristics of several kinds of stone coal pellets, focusing on the effects of roasting temperature, roasting time, superficial gas velocity and various additives on the pellet-remaining ratio after roasting. Fly ash, bottom ash and bed material were collected. V2O5 was extracted from the fly ash and bottom ash by deionized water, acid solutions of 2% Na2CO3, 6% H2SO4 and 10% H2SO4, while the effects of roasting temperature, roasting time, leaching mode on leaching rate were analyzed. The test results showed that with cement as additive, temperature at 900℃and roasting time-90 minutes, the excellent pellet-remaining ratio after roasting and leaching rate were obtained, and the vanadium recovery rate was as high as 55.1%.
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