| The flue gas produced by coal-fired boilers contains high concentrations of sulfur dioxide,which seriously endangers human health.Therefore,a reasonable desulfurization technology must be used to purify the flue gas.Compared with dry and wet desulfurization technology,semi-dry desulfurization technology has the advantages of low operating cost,no secondary environmental pollution,and relatively high desulfurization efficiency.The circulating fluidized bed flue gas desulfurization tower adopts a typical semi-dry desulfurization technology,and the equipment has been widely used at home and abroad.At present,the circulating fluidized bed desulfurization tower still has problems such as unstable flow field in the tower and low desulfurization efficiency during operation.Thus,it is necessary to fully study the gas-solid two-phase flow process and chemical reaction in the circulating fluidized bed desulfurization tower to optimize the operating conditions and desulfurization efficiency in the desulfurization tower.In this paper,the Barracuda software based on the CPFD method is used to simulate the gas-solid flow process and the desulfurization reaction in the circulating fluidized bed desulfurization tower.The research results can provide theoretical reference value for the manufacture and operation of the desulfurization tower.A physical model of a circulating fluidized bed desulfurization tower is established based on the actual industrial size in this paper.The movement process of gas and particles in the desulfurization tower is described by Euler-Lagrangian method.The continuous phase is calculated by the Navier-Stokes equation and the discrete phase is calculated by the multiphase particle in-cell（MP-PIC）method.The chemical reaction process in the desulfurization tower is realized by the droplet evaporation rate and SO2 absorption rate equation.First of all,the corresponding physical model of desulfurization reactor is established according to the test bench parameters in the literature in this paper.The desulfurization tower is simulated under the same operating conditions as in the experiment.The results of simulation and the experimental results in the literature show that the simulation data is in good agreement with the experimental data.It is proved that the mathematical model used is highly reliable for simulating the multiphase flow and chemical reaction in the circulating fluidized bed desulfurization tower.This paper studies the gas-solid two-phase flow and chemical reaction of the desulfurization tower under the influence of different working conditions based on the experimental verification.In addition,the verified mathematical model is used to simulate the gas-solid flow process in the desulfurization tower.The effects of the desulfurization tower on the gas velocity field,temperature field,pressure field,water vapor distribution,particle velocity and particle residence time distribution characteristics in the tower under different operating conditions and physical structures have been deeply studied.The research results show that the increase of the flue gas inlet velocity of the desulfurization tower leads to the increase of the pressure drop at the inlet and outlet of the tower.With the increase of the flue gas inlet velocity and particle radius,the residence time of the particles in the tower decreases.The flue gas inlet temperature has a great influence on the distribution of water vapor in the bed.When the flue gas inlet velocity and temperature are15m/s and 393K,respectively,the gas-solid distribution in the desulfurization tower is more uniform than other working conditions.The bed diameter of the desulfurization tower has a greater influence on the gas-solid two-phase distribution than the height of the desulfurization tower bed.The gas-solid distribution in the tower is relatively uniform when the ratio of the bed height of the desulfurization tower to the diameter of the desulfurization tower is 3.33.The distribution of gas and particles in the tower can be adjusted by adding a baffle at the bottom of the desulfurization tower,reducing the wear on the right wall surface of the desulfurization tower,and promoting the improvement of desulfurization efficiency.After comparative analysis,it is found that the optimization effect of adding four straight baffles at the bottom of the desulfurization tower is the best.Finally,the desulfurization characteristics under different influencing factors are studied according to the obtained gas-solid two-phase distribution characteristics in the circulating fluidized bed desulfurization tower.The influence of factors such as flue gas inlet velocity,flue gas inlet temperature,SO2 inlet concentration,Ca/S,the amount of Ca（OH）2 in the lime slurry droplets,and the lime slurry droplet size on the desulfurization efficiency is quantitatively analyzed.The research results show that the SO2 mass fraction in the bed decreases as the axial height of the desulfurization tower increases.Three desulfurization process zones can be proposed according to the distribution characteristics of the SO2 mass fraction in the bed,namely,the initial mixing process zone,the high-efficiency desulfurization process zone and the low-efficiency desulfurization process zone.The desulfurization efficiency decreases with the increase of the flue gas inlet velocity,the bed diameter of the desulfurization tower,the SO2 inlet concentration and the size of the lime slurry droplets.The desulfurization efficiency increases with the increase of the bed height of the desulfurization tower,the amount of Ca（OH）2 in the lime slurry droplets,and the increase of Ca/S.When the SO2 inlet concentration is less than 2000mg/m3,the lime slurry droplet size is less than 50μm,and the Ca/S is greater than 2,the desulfurization efficiency is the best.The increase of the flue gas inlet temperature has a positive effect on the improvement of the desulfurization efficiency,but the desulfurization efficiency will decrease when the flue gas inlet temperature is greater than 413K.Compared with the many influencing factors studied in this paper,the size of lime slurry droplets has the greatest impact on the desulfurization efficiency,and the flue gas inlet temperature has the least impact on the desulfurization efficiency.The initial contact position of lime slurry droplet and flue gas at the lower end of the bed is better than that in the middle of the bed. |
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