| The atmosphere is one of the natural environment that human beings live on.As China's total energy consumption grows and the atmospheric pollutant emission standards tightens,there is an urgent need to develop high-efficiency fine particle removal technologies.Electrostatic precipitation is the most widely used particle removal technology for coal-fired power plants.However,its collection efficiency of fine particles is not high enough.The key to reduce the emission of particulate matter is to further improving fine particle charge and their migration velocity in the electrostatic field.In this paper,fine particle charging mechanisms in electrostatic precipitators and charged particle agglomeration mechanisms were studied.The effects of corona discharging parameters,flue gas parameters and particle properties on corona discharge and particle charging were studied by experimental investigations.On the basis of the above-mentioned studies,the key influencing factors and strengthening mechanisms of charged particle agglomeration were studied.Promotion methods of particle charging,agglomeration and removal based on multi-field regulation including temperature,humidity control and ion concentration were achieved,which were demonstrated in a 330 MW unit.Firstly,the effects of discharge parameters(electric field intensity,ion density),particle properties(particle size,composition,etc.),flue gas parameters(flue gas temperature,humidity)on corona current and particle charge were studied.The electric field intensity and ion concentration in the electrostatic precipitator were effectively improved by optimizing the ion concentration in the discharge zone and adjusting the temperature and humidity.Therefore,the collision rate of ions and particles was increased.The effect of water droplet humidification on the charge capacity of particles was studied.The water layer on the surface of the particles could improve the polarization ability of the particles in the electrostatic field.Therefore,the average charge of particles larger than 0.5?m was increased by more than 35%with the water droplet concentration of 8.8g/m3.Secondly,an ionic-wind-assisted particle agglomeration experimental system was designed.The effects of applied voltages and pore-plate porosities in the pre-charger on electric agglomeration and the collection efficiency of electrostatic precipitator were studied.The optimized method of particle agglomeration was obtained.The particle count mean diameter was increased by 39%and fractionation collection efficiency was improved by more than 15%.What's more,the effects of liquid-bridge force on particle size distribution and fractionation collection efficiency were studied.The mechanism of the interaction between fine particles and the effects of adhesive force on agglomeration procedure was revealed,and an optimal operation parameters were obtained.With the aid of liquid bridge force,the count mean diameter of PM1.0 increased by 38.9%compared to the initial distribution and migration velocity was above 5cm/s.On the basis of experimental study,combined with fine particle force analysis and morphology analysis before and after agglomeration,agglomeration modes of charged particle were obtained.Thirdly,a new method of condensable particles testing based on the principle of dilution and condensation was developed to realize parallel sampling of the condensable particles and the filterable particles.The emission concentration and removal efficiency of condensable particles in an ultra-low emission coal_fired unit were obtainec.The removal efficiency by FGD+WESP of the filterable particles was 94.93%while the removal efficiency of the condensable particles was 65.37%.Condensable particulate matter was mostly PM2.5 and the average emission concentration was above 3 mg/Nm3.The inorganic components of condensable particulate matter were mainly Al,Ca,Na,Fe,Si,NH4+,SO42-,F,Cl,etc..Alkanes accounted for 82.89%and 79.77%of organic components peak area ratios of in FGD inlet samples and WESP export samples,respectively.Finally,to solve the problem of high particulate matter emission concentration of electrostatic precipitator of a 330MW unit,a reconstruction project was carried out to enforce particle charging and agglomeration.An temperature adjustment facility was added to the double-chamber five electric field electrostatic precipitator to improve particle removal efficiency by reducing the working temperature of electrostatic precipitator without changing its effective collecting area.Thereby,particle charge,agglomeration and migration velocities were improved.After the reconstruction,the average particle emission concentration of the electrostatic precipitator was 30.5mg/Nm3,which was reduced by 78.8%. |
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