Introduced the current domestic coal-fired boiler flue gas dust removal technology, including electrostatic dust removal, bag dust removal and electric bag composite dust removal. The principles and research status of the new technology of flue gas dust removal developed in recent years at home and abroad are reviewed. The development prospect and technical direction of the dust removal technology of coal-fired boilers in China are forecasted. The SK-600-PM10 dust concentration detector is used for pipeline dust detection, and the laser reflection method is used to detect the dust with high accuracy and long life. Can work at 200 ℃, output 4-20mA signal can be connected with PLC.
China is a large coal consumer, consuming about 2.15 billion tons of raw coal each year, of which about 70% is used for coal-fired power plants. China's energy structure determines the coal-based thermal power generation model. Coal combustion will produce a large number of dust particles, among which fine dust PM2.5 will not only cause cardiopulmonary and respiratory diseases, but also cause haze weather, leading to reduced atmospheric visibility.
In 2011, the Ministry of Environmental Protection promulgated the "Emission Standards for Air Pollutants of Thermal Power Plants" (GB13223-2011), which stipulated that the maximum emission concentration of smoke from thermal power boilers was 30mg / m3, and the maximum emission concentration of smoke from key areas was 20mg / m3. The Ministry of Environmental Protection issued GB3095-2012 "Ambient Air Quality Standards", in which PM2.5 is included in national standards and included in the compulsory monitoring scope of provinces and cities; in 2013, the State Council issued "Atmosphere". The Pollution Control Action Plan specifies specific tasks and proposes ten specific measures. With the introduction of various documents, the field of coal-fired boiler dust removal is facing unprecedented pressures and challenges. Only through conventional modification of existing dust collectors can new smoke and dust emission standards be met. Especially PM2.5 emission control has become an urgent problem for coal-fired power plants.
Status of Flue Gas Dust Removal Technology in China 1
At present, the production scale and usage of China's electrostatic precipitator rank first in the world, and the technology of electrostatic precipitator is close to the world advanced level. The core of the technology of the bag filter is filter media. With the continuous progress of materials science and technology, bag dust removal technology has been widely used. The electric bag composite dust removal technology is a new type of dust removal technology developed on the basis of two mature dust removal theories of electrostatic dust removal and bag dust removal. It has been successfully applied in many power plants in recent years.
1.1 Electrostatic Precipitator Technology The main working principle of an electrostatic precipitator (ESP) is to connect a high-voltage DC corona with a dust collector to form a strong electric field, ionize the gas, and positively charge the dust. The negative ion dust particles move to the corona electrode and the dust collector, respectively, and are deposited on the electrode plate, so that the ash and slag fall into the ash and slag barrel through the vibration device.
Since the electrostatic precipitator is based on a charged dedusting mechanism, the electrostatic precipitator is very sensitive to the characteristics of the fly ash (composition, particle size, density, specific resistance, adhesion, etc.), especially it is difficult to collect high specific resistance dust and fine smoke, and changes in operating conditions It also has a great impact on dust removal efficiency. In addition, it cannot capture harmful gases and requires a high level of manufacturing, installation and operation.
There are three feasible methods to improve the efficiency of existing electrostatic precipitators: improving electrostatic precipitators (including expanding electrostatic precipitators, adopting new electrostatic precipitator technology and integration of various new technologies), electric bag composite electrostatic precipitator technology, and wet electrostatic precipitators器 技术。 Device technology.
1.2 Bag-type Dust Removal Technology The main working principle of bag-type dust collector includes two parts: filtering and dust removal. Filtration is the result of inertia collision, gravity deposition, diffusion, interception, and electrostatic action of dust in dust gas. Bag filter dust collection uses filter materials for surface filtration and internal deep filtration. Dust removal means that when the dust accumulation on the surface of the filter bag reaches the set resistance value, the dust removal mechanism will remove the dust on the surface of the filter bag, so that the filter maintains the continuity of filtering and dust removal work.
The biggest disadvantage of the bag filter is that it is limited by the material of the filter bag. In high temperature, high humidity, and highly corrosive gas environments, the adaptability of the bag filter is poor. The running resistance is large, the average running resistance is about 1500Pa, and some filter bag resistance will exceed 2500Pa shortly after operation. In addition, the filter bag is easy to break and fall off, and the old bag is difficult to effectively recycle.
The US Environmental Protection Agency (EPA) Environmental Technology Certification (ETV) project tested the performance of ePTFE-coated filter media and found that the filter media coating can control PM2.5 within a certain range and eliminate harmful gases. This project has a good guiding role for the development of bag dust removal technology. The improved bag filter can be further studied from the aspects of filter film cover, filter material improvement and innovation, and effective recycling of old bags.
1.3 Electric bag composite dust removal technology The working process of the electric bag composite dust collector is to charge 70% -80% of the soot into the electric field, and the remaining 20% -30% of the soot is collected through the filter bag. The electric bag composite dust collector is compatible with the advantages of electrostatic dust collector and bag dust collector. It makes up for the shortcomings of the two, and the dust removal mechanism is scientific and reasonable.
The main disadvantages of the electric bag composite filter are ozone corrosion, high working resistance, large investment and large area. The filter bag has a short life and the cost of replacing the filter bag is still an important issue.
The improvement of the electric bag filter composite dust collector includes three aspects: optimizing the long-term synergy and related structural arrangement of the electric bag filter unit and the bag filter unit, eliminating the ozone generated by the electric bag filter unit, and the technical transformation of the filter material.
2 New technologies for flue gas dust removal Due to the influence of various practical factors, the above three types of dust collectors are difficult to meet the new flue gas dust removal standards, especially PM2.5 emission control. In recent years, scholars at home and abroad have conducted a large number of theoretical studies and experimental demonstrations on new dust removal technologies such as coalescence technology, wet dust removal technology, rotating electrode technology, high frequency power supply technology, and flue gas conditioning technology. Many technologies have made breakthrough progress and initial applications, but still need to be improved and improved.
2.1 Coalescing technology Cohesion refers to the process by which fine dusts contact and collide with each other through physical or chemical methods to form larger particles. After the fine carbon soot is aggregated into larger particles, it is easier to be captured by the dust collector, which improves the dust removal efficiency of the fine soot. At present, the main fusion technologies researched at home and abroad are: electric condensation, turbulent condensation, acoustic condensation, vapor phase fusion and merging, chemical merging and optical merging.
Electrocoagulation is the most practical and effective method of various condensation technologies. Electrocoagulation is the process of charging small particles, causing them to attract, collide, and agglomerate with each other, and agglomerate into large particles.