Experimental Study On Acoustic Agglomeration Of Coal-fired Fly Ash Particles

Burning coal will not only produce the greenhouse gas carbon dioxide,but also a large amount of dust.Among them,PM_2.5 is easy to enter the human body due to its small particle size,which causes respiratory diseases and cardiovascular diseases.At present,the widely used electrostatic precipitator in power plants has a poor catching effect on PM_2.5 particles.This is because the efficiency of electrostatic precipitator decreases with decreasing particle size.Therefore,there is still a large amount of fine particles entering the atmosphere.In order to improve the dust removal effect,it is necessary to use pretreatment technology to treat small particles into large particles.At present,acoustic agglomeration technology is one of the most widely studied technologies in pretreatment technology.Acoustic agglomeration refers to a technology that uses high-intensity acoustic waves on fly ash particles to cause agglomeration between the fly ash particles,thereby increasing the average particle size of the fly ash particle group.At present,researchers have proposed a number of particle agglomeration mechanisms to explain acoustic agglomeration,the most important of which is the orthokinetic agglomeration mechanism and hydrodynamic interaction mechanism.The hydrodynamic interaction mechanism is mainly divided into the mutual radiation pressure interaction and the acoustic wake effect.However,the current research work mainly focuses on the experimental research of acoustic reunion and have different opinions on the optimal parameters of acoustic agglomeration,and there is no certain conclusion.In view of the above problems,this paper mainly starts from the particle agglomeration mechanism analysis,experimental research on acoustic agglomeration of coal-fired fly ash particles,experimental research on acoustic agglomeration of a power plant pilot platform,and preliminary plans for power plant engineering applications.Firstly,this paper analyzes the force of the particles in the flow field,and calculates the orthokinetic agglomeration mechanism,mutual radiation pressure interaction and acoustic wake effect,and analyzes the influence of parameters such as particle size,acoustic frequency and sound pressure level on agglomeration kernel function and uses the collision efficiency to modify the agglomeration kernel function.It is found that the optimal frequency makes the orthokinetic agglomeration kernel function maximum,and at the same time when the acoustic wave frequency is between1000 Hz and 2000 Hz,the value of the orthokinetic agglomeration kernel function is basically close to the maximum value;the hydrodynamic agglomeration kernel function increases with increasing frequency.However,there is a frequency threshold.When it exceeds this value,the function value basically does not change with frequency;the correction of agglomeration efficiency caused by particle flow should be considered.Then,on the self-built acoustic agglomeration test platform,the coal-fired fly ash was used as the experimental object,and the influence of various acoustic wave parameters on the coal-fired fly ash particle agglomeration effect was studied.At the same time,the promotion effect of spray on acoustic agglomeration was also investigated.In experiments,we found that there is an optimal frequency of 1400 Hz,and the effect of acoustic agglomeration increases with the increase of sound pressure level,agglomeration time,and initial concentration.After adding the spray,the acoustic agglomeration effect is greatly improved,and even at a low sound pressure level can reach or exceed the agglomeration efficiency at high sound pressure levels.In the experiment,the agglomeration efficiency of the spray combined with acoustic wave reached a maximum of 70.7%,but the partial spray fine particles were not completely evaporated,resulting in the efficiency being lower than the actual efficiency.Next,we tested the agglomeration effect of acoustic agglomeration on fly ash particles in a large flow of smoke on a pilot platform.It was found that the experimental results were similar to those on a self-built small test platform.Acoustic agglomeration achieved a good effect at 1400 Hz,and it increased with the increase of sound pressure level,reaching a maximum aggolomeration efficiency of more than 25%.At the same time,it is found that the agglomerates are broken in the flue,which will reduce the actual agglomeration effect.The addition of water spray or chemical sspray can better promote particle agglomeration.In addition,the experimental results also show that the acoustic agglomeration combined water spray or chemical spray can greatly improve the capture efficiency of the electrostatic precipitator for fine particles.Finally,combined with the research on the agglomeration mechanism,the experimental research on acoustic agglomeration,and the experimental research on acoustic agglomeration on the pilot platform,we propose a preliminary plan for power plant applications.From the perspective of feasibility and energy saving,the acoustic coupled with desulfurization tower spray is more suitable for power plants.