Research On Turbulent Aggregation Of Fine Particles In Flue Gas

Because of its significant influences on environment and health, the fine particles,known as PM2.5, have become the focus of governments, as well as the public. It is thecoal power plants that proved to be a major source of PM2.5. Whereas, the diameter ofthe harmful particle is too minute to control its emission via traditional measures, suchas electrostatic precipitator (ESP) and bag filters. Consequently, given the simpleroperation, lower cost, what is so-called turbulent aggregation has turned to be a newdevelopment direction. It is a method could intensify the aggregation to obtain greaterparticulates by physical and chemical interactions, so efficient that dedusters can cleanthe aggregated particles easily.There are several mechanisms in the process of aggregation including Brownianaggregation, turbulent aggregation and Coulomb aggregation which only exists whencharges carrying electricity. The author defined an aggregation kernel function based onthe application ranges of three mechanisms and initial distribution of diameters, thenstudied the impact of the particle diameter and flue gas temperature on the kernelfunction. The results show that with increase in flue gas temperature and particlediameter, the kernel function fluctuated within a narrow range; for poly-disperse system,the greater the differences between particle diameters, the greater the aggregationkernels in size. But for mono-disperse system, Brownian aggregation has a badperformance; Coulomb aggregation’s effects represent a positive trend along with theincreasing of the particle diameter, instead of the differences between them.The thesis also analyzed two different turbulent aggregation devices and theirparameters working on effects and pressure drop. Results reveals that cylinders fordisturbing when parallels to the flow direction prove to be a better aggregateperformance, which would be enhanced by enlarge the distance between cylinders. Asfor vortex vanes in aggregating, pressure drop and the effects of cruciform structure, ingeneral, gradually decrease along with the expand of the line spaces. Take theaggregation and pressure drop into account, it is suggested that we set the line space as250mm and the row space as100mm to gain a better aggregation.A novel turbulent aggregation device combined the characters of cylindrical and vortex vanes are promoted by author. Through simulating with CFD, the studyinvestigated the new device’s behavior in aggregation and flue gas velocity’s influences.Results demonstrate that generated by the new turbulent aggregation, large scaleturbulence would accelerate the aggregation of minute particles(<1μm), small scaleturbulence also benefits the aggregation of greater particles(>1μm). In addition, theswifter the flue gas flow, the less effective will be the aggregate and the more will be thepressure drop at the same time.