Soot is one of the main factors causing air pollution. The fundamental measure to reduce air pollution is to reduce the emission of harmful substances into the atmosphere. At present, the national environmental protection standards tend to be strict, and the fees and requirements for the discharge of pollutants are also increasing. In the past, as long as the standard was met, the sewage charges could be exempted, and the emission standards were relatively low. It was relatively easy for the power plant to achieve the discharge standards. Now that the emission standards have increased, it is relatively difficult to meet the standards with electrostatic precipitators, and even if the standards are met, the emission charges will be imposed on the pollutants. Therefore, coal-fired power plant in the choice of boiler flue gas cleaning equipment these objective factors must be considered. When choosing a dust removal technology, the effects of economy, availability, applicability and sociality should be fully considered. The determination of dust removal technology is influenced by various factors such as local conditions, site conditions, characteristics of burning coal, emission standards and dust removal efficiency to be achieved. In view of the current environmental protection requirements, the collection of pollutant discharge costs, and the difference in performance between electrostatic precipitators and baghouses, and the actual application in various industries, the basic performance of the two types of dust collectors in practical applications is simple. Objective comparison.
First, dust removal efficiency
As we all know, bag filter has a higher collection efficiency than the electrostatic precipitator, in particular, have a serious impact on the human body of heavy metal particles and submicron dust particles capture more effective. Generally, the dust removal efficiency can reach more than 99.99%, and the emission dust concentration can be stable below 50mg/Nm3, even up to 10 mg/Nm3, and almost zero emissions. From the current application of coal-fired boilers in the power industry, the discharge of bag filters can be guaranteed to be below 30 mg/Nm3. The boiler flue gas purification of the two 200 MW units of Hohhot Power Plant uses a bag filter. The results of the long-term automatic monitoring of the CEMS system and the results of the manual sampling test by the testers of the authoritative testing unit indicate that the emission concentrations are all below 27 mg/Nm3. With the further improvement of national environmental standards and the increasing use of low-sulfur coal in power plants (or high-efficiency desulfurization), it is becoming more and more difficult for ESPs to meet standards. The efficient filtration mechanism of the bag filter determines that it is not affected by the changes in the physical properties of the burning coal, and has a stable dust removal efficiency. In view of the current national environmental protection emission standards and the collection of emission costs, the economic benefits brought by the bag filter are obvious.
Second, the impact of system changes on the dust collector
The coal type of a coal-fired power plant is relatively stable, but it cannot avoid the occurrence of changes in coal type or coal quality. The boiler system is a system that constantly changes and adjusts, so the physicochemical properties of smoke from the boiler, soot concentration, Parameters such as temperature are not guaranteed to change. This series of changes can cause significantly different changes for different precipitators. The following is a comparison of the main aspects:
1. The air volume of the air blower and the air blower are unchanged. The change of the dust concentration at the exit of the boiler is on the bag filter: the change of the soot concentration only causes the load of the filter bag of the bag filter, which leads to the change of the cleaning frequency (automatic adjustment). The soot concentration on the high filter bag is fast, the corresponding cleaning frequency is high, and the cleaning frequency is low, and the discharge concentration does not change. For electrostatic precipitators: the change of soot concentration directly affects the dust charge, so it also directly affects the dust removal efficiency of the electrostatic precipitator, and ultimately reflects the change in discharge concentration. Generally, the dust concentration increases and the dust removal efficiency increases, and the discharge concentration increases accordingly; the dust concentration decreases and the dust removal efficiency decreases, and the discharge concentration decreases accordingly.
2. The amount of boiler soot is constant, and the air volume of the air blower and the air blower changes to the bag filter: the change of the air volume directly causes the change of the filter wind speed, which causes the change of the resistance of the equipment, and has no effect on the dust removal efficiency. When the air volume is increased, the resistance of the equipment is increased, and the output of the induced draft fan is increased; otherwise, the output of the induced draft fan is reduced. For electrostatic precipitators: The change in air volume does not have much impact on the equipment, but the dust removal efficiency of electrostatic precipitators varies significantly with the amount of wind. If the air volume increases, the electric field wind speed of the electrostatic precipitator increases, and the dwell time of the dust in the electric field is shortened. Although the electric field wind disturbance enhances the effective driving speed of the charged dust, it is insufficient to compensate the dust caused by the high wind speed in the electric field. The negative effect of shortening the retention time and intensifying the secondary dusting, so the dust removal efficiency is very obvious; on the contrary, the dust removal efficiency has increased, but the increase is not large.
3, the temperature changes to the bag filter: the flue gas temperature is too low, condensation may cause "battery bag" and shell corrosion, the flue gas temperature is too high, the filter material allows the temperature to easily "burn bag" and damage the filter bag. However, if the temperature change is within the temperature range of the filter material, the dust removal efficiency will not be affected. The temperature that causes adverse consequences is at extreme temperatures (accident/abnormal conditions), so effective protection against extreme temperature control must be provided for the baghouse. For electrostatic precipitators: the flue gas temperature is too low, condensation will cause shell corrosion or high voltage creepage, but it is good for dust removal efficiency; flue gas temperature rise, dust ratio resistance is not conducive to dust removal. Therefore, the flue gas temperature directly affects the dust removal efficiency, and the impact is more obvious.
4. Changes in the composition of the flue gas (or burning coal) to the bag filter: The physicochemical composition of the flue gas has no effect on the dust removal efficiency of the bag filter. However, if the flue gas contains components that are corrosive to all filter materials, it will directly affect the service life of the filter media. For the electrostatic precipitator: the physicochemical components of the flue gas directly cause changes in the dust specific resistance, thereby affecting the dust removal efficiency, and the impact is great. The most direct influence is the content of sulfur oxides in the flue gas. Generally, the higher the content of sulfur oxides, the lower the specific resistance of the dust, the easier the dust is to be trapped, and the dust removal efficiency is high; on the contrary, the dust removal efficiency is low. In addition, changes in the chemical composition of the soot (such as silicon, aluminum , potassium, sodium, etc.) will also cause significant changes in dust removal efficiency.
5. Air distribution to the bag filter: The dust removal efficiency is not directly related to the air distribution, that is, the air distribution does not affect the dust removal efficiency. However, the local airflow distribution inside the dust collector should be as uniform as possible, and the deviation should not be too large. Otherwise, the local bag may be broken due to uneven local load or jet wear, which affects the normal service life of the dust filter bag. For electrostatic precipitators: Electrostatic precipitators are very sensitive to the distribution of airflow in an electric field. The distribution of airflow directly affects the level of dust removal efficiency. In the performance evaluation of electrostatic precipitators, the root mean square index of airflow distribution is usually one of the important indicators for evaluating the quality of an electrostatic precipitator.
6. Air preheater and system piping leakage to the bag filter: For the filter material with poor oxygen resistance, it will affect the bag life, such as: RYTON filter material, but the dust removal efficiency is not affected. The system resistance increases due to the increased air volume mixed into the cold air system. For electrostatic precipitators: there is no significant change in equipment resistance, but the increase in system air volume increases the influence of electric field wind speed on dust removal efficiency.
Third, operation and management
Bag dust collectors and electrostatic precipitators are two completely different types of dust removal equipment . There are also great differences in operation and management. Here are some comparisons for some basic problems:
1. Operation and management of the bag filter: stable operation, simple control, no high-voltage equipment, good safety, less interference factors to dust removal efficiency, and stable emissions. Since the filter bag is the core component of the bag filter and is the heart of the bag filter, it is relatively fragile and vulnerable, so the equipment management requirements are strict. For electrostatic precipitators: there are many interference factors to the dust removal efficiency during operation, and the emission is unstable; the control is relatively complicated, and the safety protection requirements of high-voltage equipment are high. Since the electrostatic precipitators are all steel structures, they are not easily damaged. Compared with the bag filter, the equipment management requirements are not strict.
2, stop and start the bag filter: convenient, but long-term outage needs to do the protection of the filter bag. For electrostatic precipitators: convenient, can be stopped at any time.
3, maintenance and maintenance of the bag filter: can achieve non-stop maintenance, that is, online maintenance. For electrostatic precipitators: stop when servicing
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