1 Introduction
With the rapid development of the national economy, the increase in pollutant emissions has had a great impact on the atmospheric environment. In recent years, the increase in domestic smog weather has caused the general public to pay attention to the environment. In order to implement the country's scientific development concept and energy conservation and emission reduction requirements, the newly promulgated air pollutant emission standard for thermal power plants (GB13223-2011) was officially implemented on January 1, 2012, requiring new construction from January 1, 2012. The soot, sulfur dioxide and nitrogen oxides of thermal power boilers and gas turbines must meet the limits specified in this standard; since July 1, 2014, the existing thermal power boilers and gas turbines have soot, sulfur dioxide and nitrogen oxides. The limits specified in this standard shall be met. Although thermal power plants have been actively improving production processes to improve emission control measures for atmospheric pollutants, the original processes and traditional emission control measures are still unable to meet current national standards, and there is an urgent need to adopt more efficient and environmentally friendly environmental technologies. The wide application of wet electrostatic precipitators in engineering provides important technical support for thermal power plants to implement national standards.
2 Working principle and equipment type of wet electrostatic precipitator
2.1 Working principle of wet electrostatic precipitator
The main working principle of the wet electrostatic precipitator is basically the same as that of the dry electric dedusting. That is, the dust-containing gas is ionized by the high-voltage electric field, and the dust-grain charge is moved to the dust collecting pole by the electric field force and is adsorbed on the dust collecting pole. Unlike dry electric dust removal, the gray dust on the pole plate is dropped to the ash bucket by the rapping. The wet electrostatic precipitator uses the plate flushing method to discharge the collected dust on the electrode plate with water because there is no rapping pole. The secondary dust generated by the board, the wet electrostatic precipitator can achieve a very low emission concentration.
2.2 Types of wet electrostatic precipitators
The wet electrostatic precipitator is installed in the absorption tower, and before the chimney, the flue gas after desulfurization is further removed, and the gypsum rain, PM2.5, SO3, etc. have good removal effects. Currently wet electrostatic precipitator divided by the anode plate material, the plate has a flexible, electrically conductive glass, steel, three types of the metal plate. According to the arrangement position, it can be divided into two types: tower type and tower exterior type. According to the arrangement, it can be divided into vertical type and horizontal type.
3 Introduction of existing wet electrostatic precipitators
3.1 Flexible plate wet electrostatic precipitator
The flexible electrodes using new wet ESP acid corrosion anode material excellent flexibility, coal combustion to achieve cleaner emissions in the flue gas desulfurization near zero water consumption, zero alkali consumption conditions. This technology is the only wet electrostatic precipitator technology with complete independent intellectual property rights in China. The core material of the device has excellent temperature and corrosion resistance and fully meets long-term operation in a saturated wet flue gas environment.
Technical characteristics of flexible plate wet electrostatic precipitator:
(1) The dust removal efficiency can reach more than 85%, and it can effectively remove pollutants such as PM2.5, SO3 acid mist, NH3 aerosol, water mist and heavy metal particles, and the comprehensive removal efficiency is over 80%.
(2) The flexible anode material is organic synthetic fiber, which has excellent corrosion resistance and fully meets the long-term operation in saturated wet flue gas environment. By utilizing the capillary phenomenon of the fiber structure, the plate can form a "full surface" uniform water film during operation, avoiding the phenomenon of "channeling" and greatly reducing the risk of the structure of the anode. The special structural design ensures the tension and installation accuracy of the flexible plates, and the single piece replacement of the anode can be realized.
(3) No continuous neutral flushing water protection, indirect flushing during operation, close to “zero water consumptionâ€. No continuous rinse water is added to ensure that the outlet droplet content is less than 15mg/Nm3. There is no circulating water, wastewater treatment system, no lye facilities, the system is simple and reliable, and the operation and maintenance workload is small and the cost is low.
(4) Modular design and flexible layout. The tower type, the tower type, the horizontal type or the vertical type can be arranged accordingly.
3.2 Conductive FRP wet electrostatic precipitator
Conductive FRP wet electric dust removal (demisting) technology was originally used in China's metallurgical and chemical industries. The material of the wet type electrostatic precipitator is made of conductive glass fiber reinforced plastic FRP. The structure of the dust collecting plate is tubular, and has a circular shape, a square shape, a regular polygon, etc., and the polygonal plate is mostly composed of a tubular structure and a vertical arrangement.
Technical characteristics of conductive FRP wet electrostatic precipitator:
(1) The dust removal efficiency can reach more than 80%, and it can effectively remove pollutants such as PM2.5, SO3 acid mist, NH3 aerosol, water mist, heavy metal particles, etc. The flue gas flow rate applied in the chemical industry is low, mainly relying on flue gas. The selection of the flow rate and the adjustment of the plate length to achieve the dust removal efficiency requirements.
(2) The plate is made of conductive FRP, and the conductive glass tube bundle module is mostly processed in the factory, and the site can be directly hoisted and installed. The field anode installation work is small, but the single block replacement of the anode plate cannot be achieved.
(3) No continuous neutral flushing water protection, indirect flushing during operation. In order to prevent scale fouling, it needs to be washed regularly, and the flushing frequency is higher than that of the flexible plate wet electrostatic precipitator. The system is simple and reliable, and the operation and maintenance workload is small.
(4) The plates are tubular structures, so they are mostly vertical.
3.3 rigid plate wet electrostatic precipitator
The technology was originally used by Japanese and European companies (such as Mitsubishi, Hitachi, B&W, SIEMENS). After being introduced into China, it was absorbed and developed by domestic companies. The plate material is mostly 316L stainless steel. Its structure type and conventional dry electrostatic precipitator are basically The same, the anode plate adopts the flat plate structure, the water spray is ash, the dust collector is mostly horizontal arrangement, the flue gas is flat and flat, and it is necessary to ensure sufficient installation space, the dust removal efficiency can guarantee 70% (an electric field) ~ 85% ( Two electric fields), each family is slightly different. Because the plate is made of 316L stainless steel, the corrosion resistance is low, especially for the chlorine-containing flue gas. Therefore, the protection plate is not corroded. The surface of the metal plate needs to be adjusted with the alkaline additive to adjust the flushing water continuously. . An alkali addition system is required outside the dust collector.
Technical characteristics of rigid plate wet electrostatic precipitator:
(1) The dust removal efficiency can reach more than 80%, and it can effectively remove pollutants such as PM2.5, SO3 acid mist, NH3 aerosol, water mist and heavy metal particles.
(2) The plate is made of 316L stainless steel plate with high mechanical strength and good rigidity. However, in order to ensure that the plate is not corroded, it needs to be sprayed continuously with the washing water with alkaline additive to protect it.
(3) The formation of a stable water film on the surface of the metal plate is the key to dust removal. It is necessary to add sodium hydroxide in the rinse water to adjust the pH value to neutralize the acid solution formed by the condensation of acid mist in the flue gas to avoid serious corrosion on the plate. In order to protect the plates, the alkaline washing agent is used to adjust the flushing water for continuous washing, and the whole process is flushed during the running process, the water consumption is large, the alkali consumption is large, and the power consumption is large. A separate alkali system is required. The collected acid is diluted with alkali and neutralized. After filtration, a small portion enters the desulfurization and hydration, and most of it returns to the spray system. Because of the continuous rinsing, the influence of the droplet size on the outlet is large, and the defogger needs to be added in the outlet flue, and the system resistance increases. The system is more complicated, and the operation and maintenance workload is more.
(4) Horizontal arrangement, the flue gas is flat and flat, and it must be ensured that there is enough installation space, so the installation position is high.
4 Conclusion
With the development of society, people pay more and more attention to the quality of life and their own health, and they are paying more and more attention to air quality. However, in the process of production and life, various types of pollutants are emitted into the atmosphere for many years, causing serious pollution to the atmosphere. The pollution of dust particles in air pollutants plays an important part, so it is an urgent task to prevent dust pollution and protect the atmosphere. In order to meet the emission control requirements of the new thermal power plant air pollutant emission standard (GB13223-2011) for soot, sulfur dioxide and nitrogen oxides, the existing thermal power plants are urgently required to adopt the wet electrostatic precipitator technology. Wet electrostatic precipitators have great value for the protection of the environment and the long-term development of thermal power plants. As the last level of air pollution control, wet dust collector is an important equipment in environmental protection engineering. Whether the design of the wet dust collector is excellent, whether the application and maintenance are properly affected directly affects the investment cost, the dust removal effect, and the operating operation rate. Therefore, mastering the working mechanism of the wet dust collector and carefully designing, manufacturing and maintaining the wet dust collector are of great significance for doing a good job in environmental protection. At present, the application of domestic technology and equipment has gradually matured and stabilized, and it is fully capable of meeting environmental emission requirements.
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