The iron and steel industry has a large amount of dust and soot emissions and its properties are diverse. The dust collectors used for dust and dust treatment include wet dust collectors, electrostatic precipitators and bag filter.
Because of the low dust removal efficiency, the wet dust collector has a large amount of water and generates secondary water pollution, and has basically been eliminated. The electrostatic precipitator has high efficiency, can reach 99.0%, temperature resistance is up to 350°C, resistance is small, about 200 Pa～300 Pa, and the processing air volume is large, reaching 106m3/h or more. It was used in steel industry, but due to its application ratio Resistance range 104 ~ 1010Ω.cm, due to changes in the physical and chemical properties of dust, and can not adapt to changes in process conditions and load. In the iron and steel industry, there are a large variety of dust and soot, with a large specific resistance change. Many specific resistances are beyond their applicable range, and some process conditions change greatly. As a result, their dust removal efficiency is unstable, often falling below 90%, resulting in frequent emission concentrations. Fluctuations, it is difficult to maintain the emission concentration of <100 mg/Nm3 for a long period of time under different working conditions. Therefore, it is rarely used so far.
The bag dust collector has high dust removal efficiency, can reach 99.9% to 99.99%, and it is stable in operation, independent of the specific resistance of dust, and is not influenced by dust type, concentration size (dust that can handle up to 1000g/Nm3), particle size The size limit can adapt to large changes in process conditions and load, and emission concentrations below 30 mg/Nm3 can even reach 5 mg/Nm/3. The range of processing air volume is large and flexible as small as 1000 m3/h, as large as 2×106 m3/h or more, and the area is relatively small. When maintenance and inspection are needed, when the filter bag is replaced, the filter can be filtered at any time without shutdown. The dedusting is highly efficient and stable, and large amounts of useful raw materials and other materials can be recovered, and limestone, dolomite, etc. can be sprayed into the dedusting system pipeline to adsorb the oil mist, asphalt, and tar in the flue gas, and then removed by the dust collector. The incompletely adsorbed dust deposited on the filter bag can also be further adsorbed and protect the filter bag from being adhered. The disadvantage of the bag filter is that the temperature resistance is restricted by the material of the filter material. At present, the temperature can only reach 260°C to 280°C (the stainless steel and ceramic fiber filter material under development can withstand more than 450°C), and the equipment resistance is relatively large (0.015 MPa). ), filter bag life can currently only reach 2 to 4 years.
The traditional view is that the electrostatic precipitator has low resistance and saves power. In fact, if the high-voltage rectifier and electric field power consumption of the electrostatic precipitator are taken into consideration, the energy consumption of the three-field electrostatic precipitator and the energy consumption of the bag filter are basically the same. If the emission concentration is less than 50mg/Nm3, the electrostatic precipitator is adopted. Above the three electric fields, the total energy consumption and investment of the equipment will exceed the bag filter.
Bag filter application
There are many types of bag filter, such as mechanical rapping type, back blowing type, pulse jet type, compound mechanism type and so on.
Because of its low dust removal efficiency, complex rapping structure and easy damage to filter bags, mechanical vibrating bag filter has been used in the early days and gradually eliminated. So far, only small-sized dust collectors have been used.
Anti-blow bag filter was once used in large quantities, but due to its poor cleaning ability, low filtration wind speed, large operating resistance, large maintenance workload, especially large amount of steel consumption, it has been rarely used.
Complex mechanism type bag filter currently has an electric bag compound dust collector, the former is the electric dust, the latter is the bag dust, has a small amount of application in the building materials industry.
Pulse bag filter is a powerful dust removal type, it has good cleaning effect, high filtration efficiency, and low equipment resistance. Its structure is unit module combination, can be flexibly arranged, and the operation and management automation control level is high, and the occupied area is small. , Low investment, after years of practice and improvement, has been widely used in the steel industry.
Pulse bag filter
There are many types of pulse bag filter, such as tube type, air box type or ring gap pulse dust collector, blast furnace gas dry method pulse dust collector.
Replace the filter dust collector with a plastic burning plate. Among them, the tubular pulse dust collector has the fastest development and the most extensive application.
The tube type pulse dust collector is a kind of bag type dust removal equipment which uses pulse jets to inject, and it is a kind of high energy and powerful pulse cleaning. The dust removal intensity is great, the effect is good, and the equipment resistance can be kept low. With different filter materials, the discharge concentration can reach 5mg/Nm3 ~ 50mg/Nm3. The structure of the equipment is simple, modular and sub-combination room combination is adopted, which can be flexible and adaptable to different site layouts. Bag length, small bag unit with 1.0 m length, mid-size unit with 2.0 m to 4.0 m length, and large long-pulse pulse dust collector with 5.0 m to 8.0 m length to accommodate different air volume requirements and maximum air flow rate Up to 2 million m3/h.
In recent years, in order to achieve a low emission concentration, reduce the resistance of the equipment, and extend the service life of the filter bag, the filtration speed is generally selected to be 1.0 m/min to 1.2 m/min, and also 1.5 m/min.
From the injection pressure classification, there are two types of high-pressure pulse (0.4 MPa ~ 0.7 MPa) dust collector and low-pressure pulse (0.15 MPa ~ 0.3 MPa) dust collector;
For high concentration dust and viscous dust, off-line cleaning is adopted. On-line cleaning is adopted for easy-to-clear dust. Operation and maintenance can be performed by off-line air-shutoff without stopping the machine.