Research On Fouling Of Collecting Electrode And Anti-scaling Of Coating On Collecting Electrode In Wet Electrostatic Precipitator

The substandard discharge of industrial dust exhaust gas seriously endangers the atmospheric environment and human health.As an advanced dust-containing gas treatment technology,wet electrostatic precipitator is widely used in various industries.The wet electrostatic precipitator transfers the dust,toxic gas and other substances in the dusty exhaust gas to the circulating water through the spraying device.The dusty exhaust gas is purified and discharged to the standard and various pollutants are continuously accumulated in the WESP system.After the device is running for a period of time,serious fouling occurs on the surface of the collecting electrode,which is a key component of the wet electrostatic precipitator.The fouling of collecting electrode causes a series of problems,such as low dust removal efficiency,corrosion of discharge electrode,safety hazard of the equipment and so on.In order to solve the fouling of the collecting electrode,this paper takes the circulating water in WESP system of a medium-density fiberboard manufacturer as the test water sample,and uses the self-made test device for simulating fouling of collecting electrode to explore the influencing factors,and investigate its scaling mechanism.At the same time,coating was prepared on the surface of stainless steel plate by electroplating process,and the anti-scaling performance in the above test device was studied.The main research contents are as follows:（1）In the self-made test device,the fouling cycle test is carried out with raw water of the factory as test water sample.According to the turbidity change of circulating water and the appearance of collecting electrode,it can be known that the scaling process is basically completed until the seventh day.Therefore,the single fouling test period is determined to be 7days.In addition,IR,XRD,SEM and EDS were used to test the scales on the surface of the collecting electrode,and determine that the main components are K₂Ca（SO₄）₂·H₂O crystals and wood fibers.（2）The effects of operating temperature,circulating water hardness,SS concentration,pH value and collecting electrode material on fouling were investigated.Under the test conditions of operating temperature of 50°C,circulating water hardness of 8.0 g/L,SS concentration of 980mg/L,pH of 6.0 and collecting electrode made of 304 stainless steel,it is found that the fouling induction period is 3 days.The amount of scales is 6.5068 g/m².Taking the above test conditions as a control group,the operating temperature is reduced to 30°C,the induction period is extended to the sixth day,and the amount of scales is reduced by 29.82%.As the hardness of the circulating water increases,the amount of scales increases.When the hardness of the circulating water was adjusted to a maximum of 12.0 g/L,the amount of scales is increased by 28.63%.With the increase of suspended solids concentration,the amount of scales increased first and then decreased.When the suspended solids concentration is 560 mg/L,the amount of scales is the least,which is only 0.3190 g/m².As the pH value of the circulating water increases,the amount of scales increases first and then decreases.Adjusting the pH value of circulating water to 7.0 and8.0 can prolong the induction period,and the amount of scales is reduced to 0.3625 g/m² and0.3297 g/m²,respectively.Comparing the fouling of the collecting electrode made of 304 and316 stainless steel materials,the surface roughness of the collecting electrode made of 316stainless steel is lower,which is not conducive to the adhesion of crystal nuclei,the induction period is prolonged,and the amount of scales is reduced by 66.38%.（3）IR,XRD,SEM and EDS were used to analyze the scale products under different operating conditions,and the influence of various factors on the fouling of the dust collector was explored.The research shows that the operating temperature,circulating water hardness,SS concentration,pH value and collecting electrode material will not change the crystal of the scales,but will affect the crystal form,size,crystallinity,composition.At a running temperature of30℃,a low crystallinity granular crystal attached to the surface of the fiber was found,and the content of the C element in the scales reached 39.61%.With the increase of hardness of circulating water,the crystallinity of crystals in the scales gradually increases,forming regular crystals such as columnar and fibrous with a length of up to 40μm.The content of C in the scales is within the range of 10-18%.With the increase of suspended solids concentration,the crystallinity of the crystal in the scales gradually decreased,and the content of C element gradually increased.When the suspended solids concentration is 560 mg/L,a small amount of fibers and flaky crystals are attached to the surface of the collecting electrode.The increase of pH value will result in the decrease or even disappearance of crystal in scales.When the pH value of the circulating water was adjusted to 7.0 and 8.0,a small amount of granular crystals were formed on the surface of the collecting electrode,the crystallinity was decreased,and the content of C element increased to more than 50%.The surface of the collecting electrode made of 316stainless steel forms a crystal grain of about 10μm,and the content of C element in the scales reaches 56.90%.（4）The circulating water containing high concentration of scaling ions and the"defects"on the surface of the dust collecting plate is the two basic conditions for fouling in the WESP system.The fouling of the collecting electrode is a complicated process,which is the result of the combination of surface crystallization and solution crystallization.The wood fibers in the circulating water play a crucial role in the fouling process.The regular crystals on the surface of the collecting electrode is hard and difficult to remove.The fibers deposited on the surface of the collecting electrode tend to"trap"the granular crystals in the solution,which are loosely structured and easily peeled off.（5）Zinc and chrome coatings with average crystal grain sizes of 21.36 nm,23.52 nm,13.56nm and 36.43 nm were successfully prepared on 304 and 316 stainless steel substrates by barrel galvanizing and hard chrome plating respectively.The coating masks the"gutter"structure of the304 stainless steel surface and the"microporous"structure of the 316 stainless steel surface.The zinc coating gives the surface of the stainless steel plate a protruding structure,which causes the surface roughness to increase.The chrome-plated 304 stainless steel surface was perfectly modified to reduce the surface roughness to 0.1802μm,and the chrome-plated 316 stainless steel surface roughness to 0.0127μm.（6）The order of the anti-scaling performance of each coating is as follows:chromium coating/316 stainless steel,316 stainless steel,chromium coating/304 stainless steel,304 stainless steel,zinc coating/316 stainless steel,zinc coating/304 stainless steel.The concentration of chloride ions is high,and the corrosion phenomenon of the zinc coating is accompanied by a serious fouling.It is necessary to add a corrosion inhibitor to the circulating water to reduce the corrosion phenomenon,thereby improving the scale inhibition effect of the zinc coating.Compared to the respective substrate materials,the chromium coating extended the induction period,and the amount of scales of chromium coating/304 stainless steel,chromium coating/316stainless steel was reduced to 43.62%and 75.31%of the matrix material,respectively.The effect of chromium coating on the induction period and the amount of scales is on the one hand the limitation of the surface roughness of the chromium coating and on the other hand the characteristics of the substrate material.Surface roughness is not the most critical factor in determining the degree of fouling.The combined effect of surface characteristics determines the degree of fouling.Considering the economic and practical conditions,adjusting the hardness of circulating water to 8.0 g/L,the SS concentration to 560 mg/L,and the pH value to 7.0 can alleviate the fouling on the collecting electrode,and significantly improve the operating efficiency and dust removal efficiency of the wet electrostatic precipitator.By reducing the surface roughness of the dust collecting plate,reducing the nucleation site and weakening the adhesion of the scales to the collecting plate,the purpose of alleviating the fouling of the collecting plate can also be achieved.