Evaporation Of Desulfurization Wastewater In High Temperature Flue Gas And Adhesive Agglomeration Of Fine Particles

Flue spray evaporation technology can effectively treat the desulphurization wastewater from wet desulphurization process.In addition,the addition of polymeric agglomerating agent to desulphurization wastewater will make the fine particles in flue gas pre-agglomerate into larger particles at the same time of evaporation,which is easy to be removed by subsequent electrostatic precipitator.In this paper,the evaporation characteristics of waste water droplets in the flue and the trapping characteristics of droplets on fine particles are studied.The specific contents are as follows:Firstly,based on the theory of heat and mass transfer,a mathematical model of heat and mass transfer of desulfurization wastewater droplet evaporation in high-temperature flue was established,and the calculation was carried out by USING C programming language.The effects of flue gas temperature,droplet size and other parameters on droplet evaporation characteristics of desulfurization wastewater were investigated.The results show that the larger the droplet size is,the longer the complete evaporation time is;The high flue gas temperature will decrease the complete evaporation time of droplet and increase the evaporation rate and surface temperature of droplet in steady evaporation stage.The increase of flue gas temperature also helps to reduce the influence of relative humidity on droplet evaporation.With the increase of flue gas velocity,the droplet complete evaporation time and equilibrium temperature decrease respectively.When the velocity of flue gas increases to a certain speed,the effect of increasing the velocity of flue gas on droplet evaporation is no longer obvious.Secondly,the droplet evaporation model established above was modified in order to explore the effect of adding agglomerants on the evaporation characteristics of desulfurization wastewater droplets in high temperature flue.The results show that the addition of agglomerants can significantly increase the informal time and steady-state evaporation time of droplet,but has little effect on the complete evaporation time of droplet.The increasing rate of droplet surface temperature in unsteady evaporation stage and the droplet surface temperature in steady evaporation stage were decreased by adding agglomerating agent.In the unsteady evaporation stage,the agglomerant can significantly reduce the droplet evaporation rate,and the effect decreases gradually with the evaporation process.Then,based on computational fluid dynamics and discrete element method（CFD-DEM）,the motion characteristics of droplets in high temperature flue were simulated,and the variation rules of droplet motion trajectory and other parameters were analyzed.The results show that the droplet will first move in the opposite direction of the flue gas flow for some distance after entering the high-temperature flue gas.Under the action of drag force,its velocity gradually decreases to 0,and then accelerates along the direction of smoke flow.The drag force of droplet in flue gas increases with the increase of droplet size and the relative velocity between droplet and flue gas.The maximum distance of droplet movement in flue gas will increase with the increase of droplet size and initial velocity.Then,on the basis of the model established above,an API with the function of discrete droplet method was loaded into EDEM,and the number of collisions between a single droplet and fine particles in a high-temperature flue was simulated to study the variation of the number of collisions between droplets and fine particles in the statistical area over time,so as to explore the trapping characteristics of droplets on fine particles in flue gas.The results show that the collisions between droplets and fine particles mainly occur in the inertia zone,and the number of collisions between droplets and fine particles increases with the increase of droplet size,initial droplet velocity and wastewater flow rate.The peak value of the collision times distribution curve between single droplet and fine particles shifts to the right with the increase of droplet size and initial droplet velocity.But an increase in wastewater flow would shift the peak to the left.Finally,the whole dynamic evolution process between droplets and fine particles in high temperature flue is described by establishing group equilibrium equation,and the group equilibrium equation is solved by using partition method.The effects of droplet on the capture efficiency of fine particles,the change of fine particle number concentration and the distribution of fine particle size were calculated under the condition of changing flue gas velocity and droplet size.The following conclusions can be drawn:the turbulent collision nuclei will increase with the increase of the relative velocity between droplet and flue gas,droplet size and other parameters,and the collision efficiency will also increase.The concentration of fine particles will decrease rapidly within 10^-3s.The rate of decline then leveled off.The decrease of fine particle number concentration will increase with the increase of flue gas velocity,droplet size and initial droplet velocity.The larger the particle size of fine particles,the stronger the efficiency of droplet to capture them.