Process Simulation And Optimization Of Semidry Circulating Fluidized Bed Flue Gas Desulfurization Process Based On CFD

In China,SO₂ concentration in air pollutants is too high due to the coal-based energy structure,so how to effectively reduce the SO₂ concentration in flue gas has become an important issue.Semi-dry desulfurization has the advantages of wet desulfurization with high desulfurization efficiency and dry desulfurization with low corrosiveness.Hence,our study used semi-dry circulating fluidized bed flue gas desulfurization?CFB-FGD?technology to remove SO₂ in flue gas.Some hydrodynamics and reaction characteristics in CFB are more difficult to be reflect through experiments.However,computational fluid dynamics?CFD?simulation technology can more clearly and comprehensively reflect the internal CFB hydrodynamics and reaction characteristics with the development of computer technology,which can further provide more effective information in order to better control and stabilize operation.Based on this,this work mainly from the two aspects of flow field optimization and reaction optimization to improve desulfurization efficiency:?1?This study used the particle dispersion degree C_v value as a standard to evaluate the uniformity of particle distribution in the CFB riser by calculating the C_v values at14 heights of H=1.4-2.7m.The smaller the C_v value,the more uniform the particle distribution in the riser.Based on this,a comparative study with or without internal structures in CFB was done.The results indicated that the C_v value decreased from10.670 to 7.520 after the internal components were added,demonstrating that the uneven distribution of particles in the CFB riser has been well improved and the flow field optimized.Then,by studying the influences of initial installation height of internal structures,space distance of internal structures and width of internal structures on the C_v value,the optimal internal structure installation conditions are obtained as following:the initial installation height is 1.6m,the installation space distance is 0.076m and the width of internal structures is 0.051m.?2?Based on the two-film theory,a desulfurization model suitable for Euler-Euler model was developed to predict the desulfurization efficiency of CFB-FGD process.The model assumed that there is only one particle in a droplet,and considered the mass transfer process and the dissolution and diffusion processes of the desulfurizer particles in droplets.Comparing the simulated data with experimental data,it was found that the relative error does not exceed 25%,indicating that the desulfurization model can predict the desulfurization efficiency accurately.The results showed that the desulfurization efficiency decreased with inlet SO₂ concentration and inlet gas velocity increasing.As the circulating solid mass flow rate increased,the desulfurization efficiency increased first and then decreased.The desulfurization efficiency increased with the increment of jet water flow rate.?3?The response surface method was used to systematically study the main effects of four operating conditions-inlet SO₂ concentration,inlet gas velocity,circulating solid mass flow rate and jet water flow rate-and their interaction effects on the desulfurization efficiency.The results demonstrated that the order of effects of various operating conditions on desulfurization efficiency is:jet water flow rate>inlet flue gas velocity>inlet SO₂ concentration>circulating solid mass flow rate.The interaction effect of circulating solid mass flow rate and jet water flow rate has the most significant effects on desulfurization efficiency among interaction effects.Meanwhile,the optimal operation conditions were obtained:the inlet SO₂ concentration is 875mg/m³,the inlet flue gas velocity 5.8m/s,the circulating solid mass flow rate 0.22kg/s and the jet water flow rate 3.4L/h,and the desulfurization efficiency under this condition is 99.686%.Then,the effects of internal structures on desulfurization efficiency under normal operating conditions and optimal operating conditions were studied.It was found that the addition of internal structures can effectively increase the desulfurization efficiency by 5%-10%under normal operating conditions.Under optimal operating conditions,the addition of internal structure can only increase the desulfurization efficiency by about 1%.