Study On Internally Circulating And Multistage Spouting Fluidized Desulfurization Technology

Air pollution is an increasingly important issue throughout the word。The SO2 emission can't measure up to standard that percentage composition SO2 of air pollution from coal combustion is decreasing 10% planed at the during of the fifteen plan,while the number is larger 27% than the original. Our country request that the SO2 emission is 10% less than the standard number required by the fifteen plan at the end of 2010。It is crucial to control the SO2 emission, and fifty percent of the total emission quantity is produced by the thermal power units. The circulating fluidized bed flue gas desulfurization technique (CFB-FGD)has drawn increasing interest and popularized in our country. The CFB- FGD technique is projected to have lower capital and operating costing than the conventional wet FGD techniques. Further more, the waste products hasn't secondary drain water. Due to the advantage of moderate SO2 removal efficiency, the technique has been widely used for boilers. With these factors in mind, current technologies of CFB-FGD are reviewed while focus on the removal efficiency and utilization of calcium-based sorbents. In order to resolve the problem of the poor sorbents utilization, removal efficiency and the tower maladjustment, one new style internally circulating multistage spouting tower is presented in this paper. The process features the variable cross-section area and internal structural unit. The advantages include rapid mixing of sorbent, as well as very high heat- and mass-transfer rates between the gas and sorbent. And the technique is the stable flow field and improving the sorbents utilization. Due to the variable cross-section area in tower, the operating flue gas velocity in the level one tower exceeds the value in the second-order. The variable amplitude is lower than single-stage tower on the operating flue gas velocity when load is changed. The capability of adequate variability is improving.The variable cross-section area has an influence on the concentration distribution in different tower. The results show that the particle concentrations are low in the level one tower and high in the level two tower. According to the characters of multistage spouted tower, the paper has adopted to sector SO2 removal. The gas-liquid contacting and mass-transfer transport processes mainly occur in the level one tower, while reaction in the second-order is between the flue gas and aqueous particles. Firstly, this paper is devoted to understanding the heterogeneity gas-solid two-phase flow in tower by means of the phase doppler particle analyzer (PDA) measurements and bed collapse test. Cross-sectional profiles of mean and fluctuation particle velocities in axial and lateral directions, particle number density, particle size and its distribution, as well as the local temporal evolutions of particle velocity and particle size are measured by PDA. The heterogeneous flow structures in gas-particle flows are obvious in the venturi inlet and at joints two-level tower and tower outlet. The particle internal recycling is stable and homogeneous in multistage spouted tower, and particle concentrations are dilute in lower and dense in upper. The ratio of concentration level two to level one is 4 or larger than 4. Varity of cross-section has good effect on improving the slip velocity between gas and particle. The distance between the top tower and the level outlet is favorable to gas-solid separation and improve particle concentration. The rain cape guide device can reinforce internal particle circulation. Particle fluctuate velocities in axial direction exists peak value in local zone near the wall of level one tower. The more the particle fluctuate is large near the wall, the more particle flushing the tower wall is intense. The probability of deposition is decreasing because of the mass-transfer reaction of gas-liquid in the level one tower.A hot-state experiment study has been performed. The influence of operation parameters on SO2 removal has been investigated. Its key component-atomizer has been researched in detail. The facts effected SO2 removal efficiency that the distribution characteristic of droplet size in space at different deepness of lime slurry and the quality rate of gas and liquid have been studied. The distributions of concentration and velocity and temperature of particle and SO2 have been measured by the on-line admeasurement devices and home-made thermojunction of sandwich structure thermocouple with air pump. The influence of powder concentration inlet and the quantity of lime slurry in the different tower level and components-atomizer installation position are investigated.The dynamic behavior of gas-solid flow is predicted based on the theory of gas-solid two-phase flow and the kinetic theory of granular flows and considered the interaction particle and particle. The effects of the time step and coefficient of restitution on the fluidization in tower are investigated. Simulation results show that the ratio of large particle velocity and small particle is different in the two-level tower. The results can be obtained small size particle velocity is high in the acceleration zone venturi inlet and in level two tower, and is low in the level one tower. The velocity distribution of large size particle is different from the small size particle and contrary completely. It is improving to gas-solid mass-transfer rate because the strengh particle fluctuate velocity and slip velocity between different size particles.The time-averaged particle concentration and velocities reflect heterogeneous flow structure in agreement with experiment measurement were predicted by PDA.Aqueous particle drying model is presented in two-stage tower considered the effect of heat transfer vapor and the product mole. The mechanisms responsible for improvements in performance with the use of additives were investigated and discussed. The paper has compiled program coupled with drying model and gas-solid two phase flow model by compiler interface. Simulation results show that the method is to allow predictions of the mass transfer coefficients and to model the SO2 removal.On the basis of experimental and simulated study, the internally circulating and multistage spouting fluidized desulfurization has been applied to a 20t/h grate-fired boiler. Control and processing schemes were designed, the governing standards were also given. Auxiliary equipments design calculation and Selection for he demonstration plant were carried out. The potential problems and treatment process were considered particularly. It was forecasted that SO2 removal of 83% and sorbents utilization of 69.2% were achieved at the condition of Ca/S=1.2, by the condition of numerical simulation work condition.