Experimental Study On Fine Particles Emission And Deposition Characteristics In A Pressurized Oxy-fuel Fluidized Bed

The fine particulate matter（PM）emitted from coal-fired power plants has caused serious harm to the ecological environment and human health,while that deposited on the surface of the heat exchange could deteriorate the heat transfer and threaten the safe and economic operation of the boiler.As a promising clean coal technology,fluidized bed pressurized oxy-fuel combustion technology can achieve efficient CO₂ capture while ensuring the efficiency of power plant.However,the study on the emission and deposition characteristics of PM under this technology was very limited.Therefore,this paper discussed the emission and deposition characteristics of PM from solid fuel combustion in a pressurized oxy-fuel fluidized bed.The specific research content and results are as follows:In the first part,relying on the continuous feeding pressurized fluidized bed,the influence of factors such as atmosphere,pressure,fuel type,co-firing on the emission characteristics of PM was explored.The results indicated that:in the range of 0.1～0.5MPa,the PM₁ concentration of oxy-fuel combustion was higher than that of air combustion,but this difference decreased with the increase of pressure,and the influence of combustion atmosphere on the concentration of PM_1-10 was not obvious.In oxy-fuel combustion,the increase in pressure suppressed the emission of PM₁ but increased the concentration of PM_1-10.Moreover,elevated pressures caused significant changes in the composition of PM₁,especially in its alkali and sulfur content,which increased significantly.In terms of ash base concentration,it appears that the effect of pressure on the vaporized yields of inlet elements Ca,Na,K,and S was not significant.The PM₁ yields of the elements Fe and Si appeared to be diminished at elevated pressure.The emission characteristics of PM of lignite,bituminous coal,petroleum coke and rice husk were compared at 0.5MPa.The results showed that the concentration of PM_0.4 and PM₁ of lignite was significantly higher than that of other fuels.If based on the inlet ash,petroleum coke had the strongest‘ability’to generate PM.In addition,although the composition of the PM produced by each fuel was different,the easily gasified elements were mostly distributed in PM₁,while the refractory elements were mostly distributed in PM₁₊.Co-firing lignite with rice husks at 0.5MPa showed that the concentrations of PM₁ and PM_2.5 were significantly reduced,which was presumably caused by the dilution effect and the interaction of fuel ash.In the second part,based on the experimental study of PM emission,typical experimental conditions were selected to explore the influence of factors such as atmosphere,pressure and co-firing on the characteristics of fouling.The results showed that:the combustion atmosphere had an effect on the morphology and composition of the inside deposits at 0.3 MPa.The inside deposits had more regular spheres and larger size under 30%O₂/70%CO₂（denoted Oxy30）condition than those from 21%O₂/79%N₂（denoted air）and 21%O₂/79%CO₂（denoted Oxy21）combustion,which was probably due to the intensive submicron particle coagulation.Furthermore,the particles contained in the inside deposits had higher Fe and Cl in Oxy30combustion compared with that in the other two combustion modes.However,the content of S in the deposits was the highest under Oxy21 condition,which may be attributed to the fact that high CO₂ partial pressure strengthens self-desulfurization ability of ash.Compared with the inside deposits generated in the range of 0.1～0.5MPa during oxy-fuel combustion,it is found that the deposits at elevated pressure contains not only more super-micron particles,but also higher contents of Ca,Na and S.Under 0.5MPa condition,the tendency of ash deposition was obviously alleviated by co-firing lignite with rice husk.On the one hand,the dense inside deposits layer was destroyed by the super-micron particles generated from rice husk.On the other hand,the interactive reaction caused by co-firing reduces the concentration of fouling precursors,that is,PM₁.In this paper,the effects of different factors on the emission and deposition characteristics of PM were investigated in a pressurized fluidized bed,which provides experimental data reference for the pressurized oxy-fuel combustion technology.