A type of electrostatic precipitator converted into an electric bag combination dust collector

With the sustained high-speed development of China's economy, urbanization and industrialization processes are accelerating, and various air pollutants are rapidly increasing. The atmospheric environmental problems that have continuously emerged in developed countries over the past century are now concentrated in China. Fine particulate matter floating in the atmosphere is the main pollutant affecting urban air quality nationwide.

At present, conventional dust removal techniques are difficult to effectively control primary fine particles with a particle size of 0.1-0.2 pm and secondary fine particles converted from gas particles. These fine particles reduce the contrast between objects and the background by scattering and absorbing visible light, thereby lowering visibility. What's even more serious is that these fine particles have strong adsorption capacity and serve as "carriers" and catalysts for various pollutants. Sometimes, they can become aggregates of multiple pollutants and are the main culprits causing various diseases.

PM2.5 pollution has become a prominent atmospheric environmental problem, attracting high attention from countries around the world (such as electrostatic precipitators). They have successively researched and developed PM2.5 detection equipment, testing systems, and control technologies. Although China started relatively late, with the promotion of the government and environmental protection enterprises, corresponding basic work has also been done. In terms of control technology, on the one hand, strict emission standards for dust removal equipment have been implemented, and on the other hand, new technological approaches have been sought or developed. Recently, the Ministry of Environmental Protection has tightened the emission concentration limits for air pollutants and included PM2.5 in the environmental air quality monitoring project.

The significant reduction of emission concentration is the basis for effectively controlling atmospheric particulate matter composite pollution. With the increasingly prominent problem of fine particle pollution, it poses a challenge to whether the existing high-efficiency dust collectors can effectively control PM2.5. It is necessary to seek new ideas for the development and promotion of relevant control technologies (electric bag combined dust collectors).

Conventional high-efficiency dust removal equipment such as electrostatic precipitators and bag filters cannot effectively capture fine particles with a particle size of 0.1-0.2pm. The electrostatic precipitator has a very high dust removal efficiency for particles larger than 10pm, but when the particle diameter is less than 2pm, the dust removal efficiency significantly decreases, and the dust collection efficiency will be lower than 90%. In extreme cases, the efficiency will also drop below 50%. The most emitted particles from the electrostatic precipitator are fine particles of 0.2-2pm.

The bag filter is also like this, no matter how efficient it is, most of the emitted particulate matter is less than 2.5pm. Therefore, in the absence of new efficient technologies for collecting PM2.5, reducing PM2.5 emissions will inevitably come at a high cost (based on further improving the efficiency of existing dust collectors and correspondingly reducing the emission of fine particles). Due to the difficulty in charging fine particles and their strong penetration, especially during high-temperature combustion and smelting processes, PM2.5 and particles formed by the vaporization and condensation of sulfur or nitrogen oxides and metals are difficult to collect with existing high-efficiency dust collectors.

The electrostatic precipitator has the following limitations: ① The electrostatic precipitator (electrostatic precipitator converted to electric bag combination dust collector) has limited ability to capture ultrafine particles (such as PM2.5), mainly because ultrafine particles are difficult to charge, and secondary dust generated by electrode vibration makes it easier for the captured fine particles to escape. ② The dust removal efficiency of electrostatic precipitators is affected by many factors, such as smoke temperature, flue gas flow rate, fly ash characteristics, sulfur content, etc., and fluctuates greatly, which has a great impact on the stable and efficient operation of electrostatic precipitators The country strengthens the control of sulfur dioxide emissions, and the decrease in sulfur dioxide concentration in flue gas leads to an increase in the specific resistance of smoke particles, resulting in an increase in the back corona of electrostatic precipitators and a decrease in dust removal efficiency (electric bag hybrid dust collectors).

The limitations of bag dust collectors include not only high operating resistance, but also issues with the service life of filter bags (such as sticking bags, burning bags, leaking bags, and corrosion and wear all affect the service life of filter bags). How to extend the service life of filter bags, reduce the frequency of bag replacement, and minimize daily maintenance costs is currently a hot research topic.

Although appropriate filter materials can be selected during the design phase of bag dust removal based on the properties of the flue gas to be treated to avoid bag sticking and burning (some large bag dust collectors have added some auxiliary facilities such as bypass flue and emergency heating and cooling to improve their safety factor), the dust cake attached to the bag must be removed before the bag filter can be regenerated (electrostatic precipitators are replaced with electrostatic bag combination dust collectors). Therefore, the cleaning of the filter bag is essential, and the more thorough the cleaning, the better, which is more conducive to the stable and continuous operation of the dust collector. However, the vibration of the filter bag that produces noise during dust cleaning, as well as the wind speed and dust particles during filtration, have a significant impact on the service life of the filter bag.

The first form has been successfully applied in China for many years. Practice has proved that after dust enters the electric field, most of the dust in the flue gas is first removed, and the remaining dust is charged and enters the bag dust removal area. This creates a new working condition for bag dust removal, that is, after charged dust enters the bag dust removal area, most of the negatively charged dust is adsorbed onto the surface of the filter bag. Due to the fact that most of the charged dust is negatively charged, dust with the same charge repel each other, thus forming an orderly arrangement (electric dust collector changed to electric bag dust collector) and a loose dust layer on the surface of the filter bag.

In addition, dust containing opposite charges in the electric field undergoes electrocoagulation to form large particles. Due to the effect of high-voltage electric field, the properties of the dust layer formed by the charging of dust entering the filter bag area have undergone significant changes, which not only change the size of the dust particles, but also change the state of dust accumulation. Compared with the dust layer formed by uncharged particles on the surface of the filter bag in conventional bag dust removal, the permeability of the dust layer is better and the cleaning effect is better.

However, once the charged dust leaves the electric field, the recombination speed of electrons is also very fast. After the combination of positive and negative electrons, the dust loses its charge and cannot produce electrostatic effects in the filter bag area. Because the resistance of the dust layer in the filter bag accounts for about 70% of the overall resistance of the electrostatic precipitator, and the resistance of the filter bag is mainly generated by the dust layer deposited on the surface of the filter bag. Observing the dust collected from the front and back bags, the dust layer on the surface of the filter bag near the electric field is arranged in an orderly manner, with a loose structure and high porosity. But on the surface of the filter bag that is far away from the electric field (from the electrostatic precipitator to the electrostatic bag filter), the dust layer is very dense, similar to the collection form of a pure bag filter.

To solve the difference in the degree of charge of dust collected on the surface of the filter bag far away from the electric field, the second form of electric bag dust collector alternately arranges the electrostatic part and the filter bag. This type of dust collector places electrostatic precipitator and bag filter in the same chamber, which can interact well with each other during particle collection and dust transfer to the ash hopper, with good results. However, by transforming the electric field of the electrostatic precipitator into an electrostatic precipitator with alternating electric bags, the dust collection electrode, corona electrode, cathode frame, and anode frame in the original electric field are interlocked and cannot be reused. Basically, all components in the electric field will be discarded, resulting in a high cost (electric to bag combination dust collector).

The electric bag dust collectors currently used in the market are actually electric dust collectors in the front and bag dust collectors in the back, which are connected in series, equivalent to two-stage dust removal. About 80% of the dust is collected by electric dust collectors first, and the remaining dust enters bag pressure purification. Due to the large concentration of dust, the reduction of filter bag resistance will be reduced, and the cleaning time will also be extended. However, the positive factors of charged dust are not reflected (electric to bag dust collectors).

In addition, at the end of the world, the United States developed an electric bag composite dust collector called Max9, which is equivalent to setting a corona wire in the middle of four filter bags, and achieved ideal results in small-scale experiments.

At present, there are two main forms of electric bag dust collectors both domestically and internationally. One is the front electric bag and back bag method, where the front stage consists of one or two electric fields and the back stage consists of filter bag dust collectors. The other is the arrangement of electrostatic parts (i.e. discharge electrodes and dust collection electrodes) and filter bags alternately arranged (electric bag composite dust collector).

Our company has designed an improved electrostatic precipitator, which has good dust removal effect and is easy to retrofit on the basis of existing electrostatic precipitators, with low cost.

Comprising a closed shell, alternating arrangement of filter bag parts and electric field parts located inside the shell, characterized in that: the filter bag part is composed of parallel arranged filter bags and a baffle outside the filter bag at the inlet of the electrostatic bag filter; The electric field part consists of two rows of corona electrodes arranged parallel to the filter bag part and a row of dust collection plates, with the dust collection plates located between the two rows of corona electrodes (electric to bag composite dust collector).

As is well known, the electric bag filter with alternating arrangement of electric bags is equipped with porous plates or perforated plates on both sides of the filter bag. The reason is that the filter bag is supported by a skeleton made of steel. In the absence of protection for the filter bag in the electric field, corona discharge, flashover, and even arcing may damage the filter bag. To protect the filter bag from burning and perforation, a protective baffle (such as a porous plate) must be installed on the filter bag near the electric field edge.

The present utility model utilizes the structure of the original electric field, removing part of the installed filter bag and forming an independent electric field in the other part. The corona wire is either closer to the dust collection plate (relative to the filter bag) or the discharge needle tip is facing the dust collection plate, effectively avoiding the damage that corona discharge may cause to the filter bag (replacing the electrostatic precipitator with an electrostatic bag composite dust collector).

The layout scheme of placing the electric field and filter bag in the same room using the original structure of the electrostatic precipitator greatly optimizes the product structure and improves economic benefits. Due to the fact that the dust is charged by the electric field before entering the filter bag area, the gas to cloth ratio is doubled, and the capture rate of fine particulate dust is also improved. As the components of the original equipment continue to be utilized, the investment and construction period of the renovated equipment are reduced, and the economic benefits are outstanding.