| Electrostatic precipitator(EP),as the main dust removal equipment of flue gas from coal-fired power plant,has a removal efficiency of more than 99.5%for larger particles.However,due to the low ion concentration and driving speed,the charging,collision and collection efficiency of fine particles(PM2.5)are low.The VEP can improve the ion concentration and the smoke retention time of discharge field,and help to solve the problem of low charge and electricity of particles,but the removal efficiency of fine particles is generally lower than 80%;The electrostatic agglomeration is an effective method to improve the removal efficiency of fine particles.In this paper,the charge coagulation effect of fine particles and submicron particles was enhanced by combining charged coagulation with VEP technology and by placing the electric charge coagulation device in the flue.The advantages of large momentum of gas in the flue were fully utilized without enlarging the volume of the dust collector.The high-speed fine particles collide with high concentration ions,condense and increase into large particles in alternating electric field,which can effectively solve the problem of low removal efficiency of VEP.The main results were as follows:(1)The mechanism of the electrospinning and strengthening the VEP was studied.The particle charge models of DC and pulse electric fields were established,respectively,and the theoretical values of the particle charge in the flue were obtained;The main factors influencing the amplitude of particles were charged,AC voltage and AC frequency by using the established oscillation equation of particle in AC electric field;The model of the unipolar charge and the coefficient of the two pole charge coagulation was used to get that the velocity difference between the particles is more favorable to collisional coagulation;According to the structure of VEP,the drive velocity equation in VEP was derived.The results provided a theoretical basis for the application of the electrospinning and strengthening the VEP.(2)The numerical simulation of VEP was studied by electrostatic agglomeration and enhancement.The simulation of particle motion in electric field and flow field by fluent 18.0 showed the evolution law of coagulation collision in charge coagulation device and VEP.The results showed that the particle size was the main factor that affects the charge and oscillation amplitude of the particles when the electric field parameters of the device were the same.The movement of particles in VEP was analyzed.Because of its small pressure loss,large ion momentum and long residence time,the effect of particle charge electrostatic agglomeration and removal was greatly improved.(3)The experimental study on the charge characteristics of fine particles was carried out.The discharge characteristics of DC corona and pulse corona were studied.The results showed that the best charge effect was when the electric field was close to breakdown,and the optimal charge voltage of positive high voltage DC,negative high voltage DC and positive high voltage pulse was 10.5 k V,-11.5 k V and 7 k V(9 KHz),respectively;In view of the four charging modes of positive high voltage DC,negative high voltage DC,bipolar high voltage DC and positive high voltage pulse,the single factor ion concentration test was carried out by adjusting the charge voltage and the average wind speed of flue.The ion concentration of four modes reached peak value under the condition of optimum charge voltage and wind speed of 5 m/s,and the positive ion concentration of unipolar positive DC,bipolar DC and positive pulse charge was 2.0×10~8/cm~3,1.5×10~8/cm~3and 2.4×10~9/cm~3,respectively;The negative ion concentration of unipolar negative DC,bipolar DC and positive pulse charge was3.4×10~8/cm~3,2.7×10~8/cm~3and 8.6×10~7/cm~3.The change of particle charge in four charging modes was studied by adjusting the charge voltage and the particle size.The results showed that the particle charge increases with the increase of voltage and particle size.The total charge of particles was the largest in the positive high voltage pulse when the median particle size was 1μm;The total charge of particles is the largest in negative HVDC when the median particle size was 2.5μm and 5μm;The lower charge value of bipolar DC charging was due to Coulomb condensation and charge neutralization,and the median particle size increases to 1.5,2.8 and 5.2μm,respectively.(4)The charge and electrostatic agglomeration of fine particles were studied.The experiment of grading efficiency is carried out by adjusting the charge voltage.The results showed that the efficiency of classification increases with the increase of the charge voltage.The classification efficiency of PM2.5 and PM1 in the unipolar positive DC,unipolar negative DC,bipolar DC and positive pulse mode was 38.2%and 23.7%,43%and 35.7%,46.9%and 39.9%,45%and 41.8%,respectively.At the same time,the effect of AC voltage and frequency on the coagulation effect of particles was tested.The results showed that the penetration rate of particles decreases with the decrease of AC voltage,the agglomeration ratio was positively related to AC voltage,and negatively related to AC frequency.The best AC electric field parameters are voltage 20 k V and frequency 100 Hz;Under the optimal electric field parameters,the efficiency of the four charging modes was 39.8%,45.3%,47.4%and49%,respectively.(5)The experimental study on the removal of fine particles by electrostatic agglomeration and enhanced VEP was carried out.The results showed that the dust removal performance was the best when the working voltage of VEP was-16 k V,and the quantity collection efficiency of PM2.5 and PM1 was 77.4%and 58.8%.When the charging and coagulation device was opened,the dust removal efficiency of unipolar positive DC,unipolar negative DC,bipolar DC and positive pulse charging mode was90.6%,92.6%,94%,95%,respectively.The removal efficiency of VEP PM2.5 was up to 92.6%,94.4%,95.1%and 95.5%,and the removal efficiency of PM1 is higher than 90%.According to the change of particle mass concentration,the mass collection efficiency and mass enhancement efficiency were calculated.The results showed that bipolar charging was better than unipolar charging,and unipolar negative DC charging was better than positive DC charging.High voltage pulse charging for 0.5μm,the efficiency of mass enhancement was 93.51%;The mass enhancement efficiencies of PM2.5 and PM1 were 35.37%and 91.26%,respectively. |
