Experimental Study On Submicron Particles Humidifying Agglomeration From Coal Combustion

The pollution caused by submicron particles in coal-fired fumes is serious in China,which is hazard to the atmospheric environment and people's health.Urgent to control the submicron particles has aroused a world-wide attention.However, conventional dedusting equipments are unable to limit pollutant discharge effectively. The separation efficiency of submicron particle is low,and a mass of them are escaping with the fume.The pretreatment of fume to agglomerate submicron particles before conventional dedusting equipments can make the size of particles big enough for separation.This will increase the separation efficiency of submicron particles effectively.There is no need to change operating conditions of electric power plants and conventional dedusting equipments.So,pre-agglomeration is a promising technology on trapping submicron particles.On the basis of previous researches,we founded a new method of spray humidification to agglomerate particles in the fluidized bed.Systematic experiments and theoretical studies had been studied in this paper.Characteristics of gas-solid, gas-liquid flow and submicron particles microscopic characteristics were studied on different fluidized conditions in a fluidized bed.Afterwards,we founded a model to describe spray humidification to agglomerate particles,and studied influences of different factors on particle agglomeration.Firstly,the gas-solid and gas-liquid flow characteristics and the microscopic characteristics of submicron particles in different flow conditions were investigated on the fluidized bed bench.The axial and tangential velocity distribution of solid phase particles and the gas-solid slip velocity and changes in turbulent kinetic energy in the swirling flow conditions in fluidized bed were studied,which combined with the analysis of the influence to particles agglomeration.The concentration,speed and size distribution of liquid droplets were discussed,which aimed to obtain the characteristics of droplet field in the fluidized bed.The particle size and morphology characteristics of fly ash were studied and the effect of particles agglomeration to desulphurization and dust removal system were analyzed.Secondly,drawing on the theory of colloidal flocculation and aerosol coagulation, a model of submicron particles humidifying agglomeration in the fluidized bed during the spray process was developed.The impact of humidification mode including spray water and spray agglomerant solutions to particles agglomeration were studied.The factors such as spray volume,particle diameter,droplet diameter,dust concentration, flue-gas volume and residence time of particles were analyzed.It exists spray humidifying and evaporation drying area in the fluidized bed and force analysis models in these two areas were established.In the end,at the basis of theoretical analysis on characteristics of the swirling flow and the agglomeration of the particles,a simulation model of particles agglomeration had been established under the condition of swirling flow and straight flow in fluidized bed.The following characteristics of particles and droplets under the conditions of the swirling/straight fluidization were calculated and analyzed,and then the effects of the droplet diameter,particle diameter,water volume and droplet velocity on the particle agglomeration were studied.The tower can be divided into local high-performance capture zone,smooth capture zone and low-performance capture zone by the collection efficiency along with the tower.The humidifying agglomeration of particles in the fluidized bed can effectively achieve the growing of submicron particles in order to meet the removal requirements of the conventional dedusting equipments,realizing the effective removal of particulate matter.Therefore,humidifying agglomeration of submicron particles in the fluidized bed provides a new approach and way of reforming and upgrading conventional dedusting technology.