Study On Characteristics Of Gas-liquid Two-phase Flow In Cfb Boiler Rear Pass With Deep Flue Gas Desulphurization By Spraying Ammonia

CFB(Circulating Fluidized Bed) boiler with the advantages of low pollutant emissions, wide coal adaptability and ash and slag comprehensive utilization, etc., is widely respected in the industry. However, with the continuous improvement of the national SO2 emission standards for coal-fired power plants, CFB boiler only relying on the furnace desulphurization is difficult to meet the new standards. So on the basis of the furnace desulphurization by inputting limestone, installation deep flue gas desulphurization by spraying ammonia in the rear pass is one of CFB boiler developing direction. This issue aims at the deep desulphurization design of a 300 MW CFB coal gangue power plant in Shanxi Province, which considering its own reality. Its design combines desulphurization methods of furnace desulphurization by inputting limestone and deep flue gas humidification activated desulphurization by spraying ammonia in the rear pass. And study the nozzle properties and the characteristics of gas-liquid two-phase flow in this device.This paper first study the atomization characteristics experiment of the desulphurization atomizing nozzle, which is the key equipment of desulphurization device. Use high speed camera to measure droplet size, and the relationship between the different fluid pressure and the flow fluid, atomizing angle, range and the sector flow distribution. Then install a deep flue gas desulphurization in the rear pass of a 300 MW CFB coal gangue boiler, and conduct desulphurization experiment in the site. By changing the amount of inputting limestone, the amount of ammonia, ammonia concentration and the number of spray nozzles, observe the change of the concentration of SO2 and the content of CaO in the fly ash before and after injection desulphurization agent. The experiment results show that, on the basis of the furnace desulphurization by inputting limestone, after ammonia is injected into the flue, the content of CaO in the fly ash and the concentration of SO2 in the fuel gas are significantly reduce, which verifies the feasibility of this desulphurization method. The desulphurization effect is obvious. It has a good popularization value.Last use rear pass with deep flue gas desulphurization by spraying ammonia for the study, establish gas-liquid two-phase flow three-dimensional mathematic model, and use Fluent to simulate the gas-liquid two-phase flow field of the flue after spraying desulphurization agent. Numerical simulate the drawing of flue gas flow field, the desulphurization agent track and the concentration distribution of desulphurization agent in the flow field, after desulphurization agent sprayed into the flow field. On this basis, simulate and optimize the effect of the nozzle position and injection angle. Determine the option mixing effect of the flue gas and desulphurization agent in the different flow of the nozzle. The simulation result is fit well with the experimental result. This result can provide scientific reference for the same kind CFB boilers with deep desulphurization technology device.