| The main reason of acid precipitation in China is the emission of large quantities of sulfur dioxide. As coal is the main energy resource in our country, sulfur dioxide emission by power plants accounts for a certain proportion in the total emission of sulfur dioxide of the country. To improve the atmospheric environment, it is of great significance to control sulfur dioxide emission caused by burning coal in our country. Comparing to traditional lime-gypsum process for desulphurization, circulating fluidized bed desulfurization technology has such features as simple system, low engineering investment, maintenance and operation cost, and small floor area, which is suitable for retrofit of existing power plants and industrial boilers. But in the process of actual operation, there is a big difference between desulfurization efficiency and the designed value, as the result of the poor mixing effect of flue gas, water spray, and desulfurizer in the circulating fluidized bed. Based on the actual problems in circulating fluidized bed desulfurization technology and targeted to improving the mixture of gas, liquid and solid in desulfurization tower, this paper is designed to find a method to improve mixture of gas, liquid, and solid through experiment and numerical simulation, so as to guide the design of circulating fluidized bed desulfurization.Taken the gas desulfurization system of Jilin Songhua River Power Plant as the prototype, we designed and built flue gas circulating fluidized bed cold state experiment table. Particle Image Velocimetry (PIV) was chosen to research gas-solid mixture under different feeding ways in the tower. We find that the condition of feeding before the guide plate has a bigger impact on the right side of the wall; the extent of the impact on the wall of solid particles in the tower under unilateral feeding condition is the biggest, which is the most dangerous condition; the extent of the impact on the wall of solid particles in the tower under bilateral feeding condition is the smallest, which is beneficial to reduce scaling of the desulfurated ash on wall and the ash clogging in feeding entrance.Then we conducted cold state experiments on the flow of gas and liquid inside the desulfurization tower based on the layout of nozzles in different angles and different layers. It showed that when single nozzle was arranged, the atomized water stayed for a long time in the tower, which was better to increase reaction time of desulfurization. When we decorated the nozzle and radial direction into-45°in the straight section, the axial velocity was relatively small and there was no obvious wall-scouring. And when we decorate them both into-45°, it is good for mixing as the result of big turbulence intensity and vorticity. Comparing single arrangement and double arrangement in the diffuser section, it was better to use double arrangement. Especially when we decorated the nozzle and radial direction into45°in the straight section and-45°in the diffuser section, the mutual interference of the atomized water moving up and down led to the bigger turbulence energy and vorticity, which was helpful for mixing. While comparing the two conditions, the nozzle and radial direction with-45°in the straight section and the double-layer arrangement, the former was better with higher turbulence intensity and bigger axial velocity.Further study was conducted to research the gas-liquid mixing at different nozzle angles, with numerical simulation method and considering the impact of tower temperature as well. We compared from three aspects, velocity, temperature and turbulent kinetic energy. Desulfurization mass transfer model was built to study the impact of spray quantities and calcium to sulfur ratio on the desulfurization efficiency. The study found that, when nozzle in the diffuser section was arranged45°, the left wall of desulfurization tower was eroded more seriously, and the turbulence intensity of the left wall appeared to be higher than that of the right side wall, and changed irregularly. When nozzle was disposed-45°in straight section, gas flowing into the desulfurization tower tended to offset to the left side of the wall without serious wall-scouring. Velocity field changed moderately. The turbulence intensity is very high in the bottom of the desulfurization tower, and turbulence intensity tended to accelerate following the increase of desulfurization tower height, and then slightly downward which helped the mixing of gas and liquid. When nozzle was fixed radial45°in the diffuser section, there was a big gap between inlet and outlet temperature of the desulfurization tower. The outlet temperature is higher. When the nozzle is fixed radial-45°in the straight section, there was a satisfied temperature difference between the inlet and outlet with lower outlet temperature. The temperature was distributed in the trend of high middle and low around, which can protect the wall very well. The proposed model for mass-transfer was applied to simulate the tower outlet flue gas moisture content and Ca/S molar ratio on the desulfurization efficiency. The results showed that under the conditions of the tower outlet flue gas moisture content range of0.059kg/kg and the Ca/S range of1.3, the desulphurization efficiency is expected to be improved to85%. The model would be helpful for the desulfurization system of the power plant. |
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