Experimental Study And Numerical Simulation Of Agglomerated Fine Particles By Foam Method

Foaming agglomeration is one kind of chemical agglomeration of fine ash particles(FAP)methods.Various agglomeration agents are mainly used to agglomerate FAP into large particles by chemical reactions or chemical bond action.Foam method is different from droplet method and is making the agglomeration by the addition of foam agent and foam stabilizer when they are atomized into a large number of bubbles and droplets by the atomization nozzle.The foam increases the specific surface area of the agglomeration liquid to contact with the FAP stream.The bubbles get broken when FAP are constantly colliding and adhering to the bubbles.As a result,FAP are promoted to adhere into large size clusters.Firstly,the bubble conditions required for adhesion of FAP was studied in this paper.The foam bubble size and capability of particulate matter aggregate were estimated.By CCD,the finely atomized liquid foam sprayed from nozzles was recorded.The atomization bubble size and density(The number of bubbles and droplets in the section)were obtained by using MATLAB to manipulate images.Results showed that the addition of the foaming agent(sodium dodecylbenzene sulfonate)and foam stabilizer(coco acid diethanolamide)in solution enhanced the formation of bubbles while reduced the droplets amount.The bubble size of PAM(non-ionic polyacrylamide)agglomeration was small,and the atomized droplet and bubble density was big.Most the bubble size was less than 200? m.While the bubble size of the XTG(xanthan gum)agglomeration solution was large,the bubble size of CMC(sodium carboxy methyl cellulose)agglomeration solution was uniform and in between PAM and XTG,and the density of the bubbles and droplets was also great.At 25 cm distance from the spout in the axial direction,the bubble crush and aggregation tends to stabilized.When the spout diameter was 0.5mm,the mostly bubble sizes were in the range of 100 to 300?m,suitable to the bubble conditions for reunion of PM2.5.As the solution temperature increased,the number of atomized bubbles of 0 to 300?m increased significantly.Then experimental studies were conducted by self-developed platform.The effects of foam agglomeration agent types,concentration,temperature,number of spray layers and number of defogger layer on FAP removal efficiency were analyzed.It was found that the foam agglomerates were able to effectively reunite FAP to large particle cluster.Among the PAM,CMC and XTG three kinds of agglomeration solutions,the agglomeration effect of XTG solution was best.When 0.1% XTG agglomeration solution sprayed,the concentration of particulate matter after the agglomeration and the orifice plate demister decreased to 10.6 mg / m3 through.At 80?,the XTG agglomeration solution with two layers orifice defoggers,had the best removal effect and the concentration of particulate matter was 9.4 mg/m3.Increasing the number of spray layers could effectively reduce the emission concentration of FAP.Only increasing the layers of orifice defogger had little effect on agglomeration.Finally,according to the import and export parameters in the experiment,the PBM model in Fluent software was used as the agglomeration model for numerical simulation.Only the spray section and a downstream section were simulated.The model and its parameters were adjusted to obtain the flow simulation in accordance with the experimental results.Then the mechanism of the FAP agglomerating in foam was deduced.The FAP aggregation size increased with the bubble-liquid ratio increases,and the more bubbles played a major role in FAP agglomeration.The increasing viscosity of the spraying solution contributed to the FAP agglomeration,but the too large viscosity had negative influence on agglomeration for the greater flow resistance to cause worse atomizing.Under the required bubble conditions,the agglomeration mechanism in this study was that FAP was constantly immersed in bubble surface,and the bubbles got broken when the gravity and surface tension balance destroyed and to prompt the adhered FAP into large size clusters,ash particle phase size increased.The large size clusters can be removed by defogger or dust collector.