Analysis of Factors Affecting the Performance of Electrostatic Precipitators in Coal Fired Power Plants
Abstract: There are many factors affecting the performance of electrostatic precipitators in coal-fired power plants and can be summarized into the following three conditions: Operating conditions: the composition of coal, the composition of fly ash, the physical characteristics of fly ash and the flue gas conditions. Flue gas conditions include the type of flue gas, humidity, temperature, composition, pressure, and flow rate; dust properties mainly include dust density, dust resistance, dust dispersion, dust viscosity and concentration. Technical conditions: Electrostatic precipitator plate and limit configuration; Electric field classification; Electric field structure characteristics; Air flow distribution uniformity; Vibration mode setting and the size of the rapping force; Electrical control characteristics. Operating conditions: Including the first and second voltage, the first and second current, the situation of dust, rapping effect, rapping cycle, air leakage and secondary dust situation.
1 coal composition
In the composition of coal, sulfur, moisture, and ash have the greatest impact on electrostatic precipitator performance. Higher sulfur content in coal gas contains more SO2, SO2 can generate SO3 under certain conditions, SO3 easily attached to the surface of dust particles. On the high-sulfur coal, sulfur content on the electrostatic precipitator performance plays a leading role; low-sulfur coal, sulfur is relatively small. The effect of moisture is obvious, when the moisture contained in the coal is high, the humidity of the flue gas increases, the surface conductivity of the dust is good, and the specific resistance is lower. The level of ash in coal directly determines the dust concentration in the flue gas. When the dust concentration exceeds the scope of the electrostatic precipitator, the corona current will be increased with the concentration of dust quickly reduced; when the dust concentration reaches a certain limit, it is easy to form a strong space charge, the corona Current shielded, in serious cases will cause the current through the electric field space approaches zero, that corona closed.
2 fly ash composition
Fly ash mainly includes Na2O, Fe2O3, K2O, SO3, AI2O3, SiO2, CaO, MgO, P2O5, MnO2, etc., and ash and combustibles. Which SAr, Na2O, Fe2O3, AI2O3, SiO2 on the electrostatic precipitator performance relatively large. The content of combustibles in fly ash is related to the combustion status of the boiler. Combustible materials mainly include carbon black and coke. Fly ash in the combustible content of 1% 8%, but the fly ash decreased resistance, as a favorable factor; more than 8%, easy to cause secondary flying, unfavorable factors.
3 dust than resistance
Dust ratio resistance is equal to the unit area of ​​dust in the unit thickness of the resistance. It is an important indicator of dust conductivity. It has a particularly large impact on ESP performance. The specific resistance of the dust determines the current limit of the electrical breakdown of the high resistivity dust layer. When the specific resistance is below 104 Ω · cm, the dust deposition is neutralized in the moment of the dust collecting pole, it is easy to get out of the dust collecting pole and re-enter the airflow, reducing the efficiency of the dust precipitator; when the specific resistance is between 105 and 1011Ω. cm, when the dust is deposited on the dust collecting pole, it can form a layer of dust on the polar plate. When the polar plate vibrates, the dust layer falls like a sheet, the dust collector efficiency is higher, and the actual measurement shows that the dust is most suitable for the working of the electrostatic precipitator Specific resistance is 105 ~ 1011Ω.cm. When the specific resistance of the dust is higher than 1011 Ω · cm, the dust is hard to be neutralized when it is deposited on the dust collecting electrode, and a negative electric field is formed on the deposited particle layer, so that an anti-corona phenomenon occurs and the efficiency of the electrostatic precipitator is greatly reduced.
4 flue gas temperature
Electric dust collector flue gas temperature on the dust resistance is very large. Conduction of dust can be divided into surface conduction and volume conduction. When the flue gas temperature is low, the surface is mainly conductive, and the specific resistance mainly depends on the flue gas temperature and SO3 content. When the flue gas temperature rises, the surface conductivity decreases gradually and the metal ions in the dust become more active waves. In this case, the specific resistance Mainly depends on the volume of conductive. The main effect of flue gas temperature on ESP performance is the effect of temperature on gas viscosity.
5 flue gas humidity
The influence of flue gas humidity on electrostatic precipitator mainly affects the performance of electrostatic precipitator by changing the specific resistance of dust. Humidity is usually measured by the flue gas dew point temperature. The higher the dew point temperature of the flue gas, the greater the humidity of the flue gas, so that the more moisture the surface of the dust absorbs or condenses, the better the conductivity. Therefore, raising the water content in the flue gas can solve the problem of low dust removal efficiency of the electrostatic precipitator and the like. The effect of flue gas moisture content on the volt-ampere characteristics of electrostatic precipitators proves that the flue gas moisture content is proportional to the breakdown voltage and inversely proportional to the corona current. Increasing flue gas humidity can improve ESP performance.
6 flue gas composition
The effect of flue gas composition on ESP is mainly reflected in the negative corona discharge characteristics have a great impact, when the composition of the flue gas is different, in the corona discharge charge dust effective mobility will be different. Flue gas N2, H2 electron attachment rate is zero, does not produce a negative corona, and CL2 and SO2 molecules can produce a strong negative corona. They adsorb on the surface of the dust, increasing the surface conductivity of the dust, thereby reducing the specific resistance and improving the performance of the electrostatic precipitator. SO2 and other gases have a particularly stable high-impedance corona characteristics, can form a wide range of negative corona.
7 Smoke density and pressure
Smoke density is a function of flue gas pressure and temperature. Smoke density has a great influence on the corona electric field of the corona voltage, corona surface electric field intensity, space charge density and ion mobility. Thus having great influence on the discharge characteristics and dust removal performance of the electrostatic precipitator.
The energy required to produce an ionized collision in a given gas must be provided by the corona electric field strength. This depends mainly on the ionization potential of the gas and the average free path per collision. Under the same polar distance, the pressure is reduced and the corona voltage drops. The pressure of high pressure blast furnace gas is 1.5 times of atmospheric blast furnace gas, so under other conditions, the electrostatic precipitator purifying high pressure gas is higher than the pressure of purifying atmospheric pressure gas and the dust removal efficiency will also increase.
8 dust concentration
ESP have certain requirements on the concentration of dust must be within the scope of adaptation, beyond the scope of adaptation, the current will decrease with the increase of dust concentration.
When the concentration of dust in the flue gas is higher, the more the amount of soot ions, the less the space charge that can be formed and the decrease of the electric field current. When the dust concentration close to or exceed the concentration range of adaptation, the electric field current close to zero, corona occlusion occurs, the dust removal efficiency will be significantly reduced.
9 dust particle size
Charged dust velocity and dust particle size have a great relationship, in the multi-level electric field ESP, after the electric field dust particle size is small, the former electric field dust particle size larger. The moving speed of the charged dust toward the dust collecting electrode is proportional to the radius of the dust particle diameter. The dust particle size affects the space charge and the electric charge field of the dust particle, thereby affecting the change of the charged amount of dust and the moving speed. When the small particle dust is more, the influence of space charge increases, the current decreases, and the time of the first electric field dust particle nuclear power lengthens. When the dust concentration is relatively high, if the fine dust particles are more prone to corona occlusion. Dust particle size also affect the electrical conditions, such as secondary dust.
10 Dust density
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