| Coal-bed methane (CBM) and coal gangue resources are rich in our country. However, exploitation and utilization of coal gangue and CBM resources are still in a low level. It is necessary to design a clean and high efficiency system for coal gangue and CBM industrial utilization. So that, the pollution can be prevented from source and goals of saving coal resources and reducing pollutions can be achieved.Co-combustion of low-calorific value fuels is one of hot topics in fluidized bed combustion field. At present, most research focused on solid fuels, and combustion stability and efficiency need to be improved. According to the combustion characteristics of coal gangue and CBM, a method for co-combustion coal gangue and CBM was put forward. The technologies for gas and solid fuel combustion were combined to improve combustion efficiency and stability. The research is significant in academic and has a good prospect for industrial utilization.Gas-gas-solid physical and mathematical model of multiphase flow and combustion about co-combustion of CBM and coal gangue in CFB were established for the first time. The major influence factors for co-combustion were investigated numerically and experimentally. Effects of low calorific gas fuel on flow, combustion and pollutants emission in fluidized bed were researched. The co-combustion characteristic of different phase-state fuels was acquired, which provide theoretical foundation for technology and device developments of co-combustion CBM and coal gangue in CFB.Firstly, a new combustion burner with high combustion efficiency for low calorific CBM was advanced. Based on numerical simulations and experimental study, distribution characteristics of its temperature field, velocity field and concentration field were researched, and the beat burner structure was obtained. The results show that mixing effect of air and gas is increased, when setting guide vanes in gas tube and using two air circle chambers with the way of wind for internal direct flow and rotational flow outside, as well as, a good jet rigid is maintained, which means that it is much more suitable for low calorific gas combustion. There is the optimal comprehensive property, when the guide vanes number is six and blade obliquity is 60°.Secondly, the landscape orientation jet characteristics and its effects on gas-solid flow characteristic in burner were analyzed with numerical simulation method. The particle velocity field, concentration distribution characteristics, and optimized coal gangue burner were gotten. Hot state numerical simulation was put forward to investigate mixing burning characteristic of low calorific gas in circulating fluidized bed and effects of different mixing ratio of coal methane and coal gangue CR and excess air factor?on mixing burning characteristic. The best working condition was proposed, according to temperature field, velocity field and component concentration distribution in different operating conditions. Research results show that: Firstly, when dislocation hedge is applied between the secondary wind and CBM combustion burner in CFB, the exit of secondary wind is in dense phase area, and CBM combustion burner is in the transition region between dense phase area and rare phase area, which means the mixing of gas and solid is full and the flow state is stable. All of these advantages are helpful of fire of CBM, and can avoid CBM contending with coal gangue for wind in combustion process. Secondly, compared with the conditions of combusting only coal gangue, when adding CBM, the temperature of dense phase area decreases slightly in furnace, but the temperature of rare phase area increases. Therefore, the nearby field of CBM nozzle formed an area with relatively high temperature, which benefits the combustion of unburned coal gangue particle and CBM. Thirdly, through appropriate increasing CR ratio, AR ratio and?, the flow field distribution will be improved, particle combustion will be strengthened, and the combustion stability will increase. When CR value is 2.8, AR value is 20~30%, and?is value 1.3, the optimal mixing condition exists.Thirdly, the cold state of coal bed methane and coal gangue co-combustion in CFB was researched by experimental study, which mainly focused on the air flow resistance characteristic, coal fluidized characteristic and the gas jet characteristic. Also, gas-solid flow characteristic under different jet height and jet strength of the furnace was investigated. The results show that:?the resistance characteristic curve of the air distribution plate is basically similar to a quadratic curve.?the boards structure is reasonable which has a better fluidization characteristic curve.?the mix and disturbance of the gases in the furnace are strengthened and the flow distribution is improved by the introduction of jet.?airflow velocity reduces at the following areas of mouth furnace expansion to jet mouth and the velocity gradient changes greatly as the jet position higher. Particle concentration in dense phase region reduces, the average particle concentration gradient decreases.?the greater the jet rate, the lower airflow velocity of the jet mouth following areas, and more change velocity gradient. Solid concentration slightly increases as the increasing of jet rate. Lastly, co-combustion of coal bed methane and coal gangue in CFB was investigated. Effects of co-combustion ratio, secondary air ratio, and excess air ratio on combustion and exhaust gas characteristics were studied. The results show that?With increase of CR, dense phase area temperature drops while dilute phase region temperature little increases. Compared with combustion of coal gangue, the furnace temperature tends to be uniform, and combustion efficiency increases when co-combustion of coal gangue and CBM is adopted.?With increase of AR, dense phase area temperature raises while dilute phase region temperature drops slightly. Furnace temperature distribution trends to be uniform and combustion efficiency increases and then decreases when AR value is added.?Dense phase area temperature drops with the increase of?. When?value varies with 1.2~1.35, temperature difference in dilute phase region was very small. Combustion efficiency first increases and then decreases.?A stable combustion situation with high efficiency and low NOx emission can be obtained when bed temperature is controlled reasonably and proper CR,?value were chosen.?The best operating condition with uniform furnace temperature distribution, high combustion efficiency, low NOx emission is achieved when CR=2:8,?=1.3 and AR varies with 20%~28%.The characteristics of flow, combustion, and pollutants during coal gangue and CBM co-combustion in CFB were studied systematically in this paper. The major influences for co-combustion were obtained. The research made the theoretical foundation for the optimization and industrial application of coal gangue and CBM co-combustion, and also provided a good way of comprehensive utilization for coal gangue and CBM. |
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