Technical progress and application research of electric bag composite dust collector

1. The Origin and Development of Electric Bag Composite Dust Collector

1.1 Generation

As the country's requirements for pollution control continue to increase, especially the control of dust emission concentration is becoming more and more stringent, the technical requirements for environmentally friendly products are also getting higher and higher. The existing electrostatic precipitator technology cannot meet the requirements of low emissions, mainly because the dust removal efficiency is greatly affected by the dust properties (chemical composition and particle grading) and flue gas parameters (flue gas volume, flue gas temperature, flue gas chemical composition). Although the electrostatic precipitator is also constantly innovating and changing, and many new technologies have emerged, such as mobile electrode electrostatic precipitator technology, low-temperature electrostatic precipitator, and wet electrostatic precipitator, the actual application is not very ideal. There are problems such as high failure rate of mobile electrodes, easy pipe burst at low temperatures, large investment in wet electricity, easy corrosion, and inconvenient maintenance. Although the existing bag filter can be discharged without being affected by the flue gas working conditions and it is easier to obtain high dust removal efficiency, its disadvantages are large resistance, large corresponding power consumption, short filter bag life, and high maintenance costs. Most of its applications in the power industry have ended in failure, especially in large units.

Longjing took the lead in developing and researching electric bags. In early 2003, China's first industrial electric-bag combined dust collector was successfully used in the electrostatic precipitator renovation of the Shanghai Pudong Cement Plant, creating a precedent for my country's electric bag composite dust removal technology.

1.2 Three stages of development

1.2.1 The first stage: conventional electric bag composite dust collector

The first stage of the electric bag composite dust collector organically combines the characteristics of electrostatic dust removal and bag dust removal. It is a high-efficiency dust collector that uses the pre-dust collection and charging of the front-stage electric field and the filtering and dust removal of the back-stage filter bag area. It fully utilizes the high dust collection efficiency of the electric field in the front-stage electric area, greatly reduces the dust concentration entering the filter bag area, reduces the filter load of the filter bag, avoids the wear of the filter bag caused by coarse particles, and uses the charged dust filtration mechanism of the front-stage electrostatic precipitator area to improve the comprehensive performance of the equipment. The combination of the two has obtained new performance advantages. The overall reliability of the structure is high and the emission is stable. The dust emission concentration increases from 100mg/Nm3 to 50mg/Nm3 and then to 30mg/Nm3, which has greater economic and social benefits. At this stage, the electric bag composite dust collector is widely used in low-emission transformation projects.

1.2.2 The second stage: ultra-clean electric bag composite dust collector

With the in-depth implementation of the national energy conservation and consumption reduction policy, according to the "Coal Power Energy Conservation and Emission Reduction Upgrade and Renovation Action Plan (2014-2020)" issued by the National Development and Reform Commission, the Ministry of Environmental Protection, and the National Energy Administration, the Ministry of Environmental Protection's "Notice on the Preparation of the 13th Five-Year Plan for Ultra-low Emission Renovation of Coal-fired Power Plants", and the Ministry of Environmental Protection, the Development and Reform Commission and the National Energy Administration issued in December 2015 The "Full Implementation of Ultra-low Emission and Energy Conservation Renovation Work Plan for Coal-fired Power Plants" and other documents require coal-fired power plants to implement ultra-low emissions of smoke. In order to adapt to the ultra-low emission control standard of 5-10 mg/m3 of smoke, the development of electric bag technology has entered the second stage, namely the ultra-clean emission stage. This technology is further developed through technical innovation and upgrading on the basis of conventional electric bag composite dust removal technology. It has the advantages of low and stable export smoke concentration, long service life of the filter bag, low operating resistance, low operation and maintenance costs, and can ensure long-term efficient and stable operation.

1.2.3 The third stage: high temperature electric bag composite dust collector

The ultra-low emission transformation of coal-fired power plants has achieved remarkable results, and the flue gas treatment market in the non-electric industry, which accounts for half of the market, has also been gradually included in the ultra-low emission transformation. The flue gas in the acid, aluminum, ferroalloy, glass and other industries in the non-electric industry is mostly high-temperature flue gas. Therefore, in order to adapt to the ultra-low emission treatment of high-temperature flue gas in the non-electric industry, the electric bag dust collector technology has entered the third stage, that is, the high-temperature stage, and it has the characteristics of adapting to high-temperature flue gas.

2Technological progress of electric bag composite dust collector

The electric bag composite dust collector is an integrated structure, consisting of the front-stage electric dust removal area and the back-stage bag dust removal area. In the three development stages of the electric bag, its structure and technology have been continuously innovated.

2.1 Overall structure improvement and optimization

As shown in Figure 1, the electrostatic precipitator area and the bag filter area are arranged in the same shell. The flue gas first passes through the front-stage electrostatic precipitator area, and most of the smoke is collected by the electrostatic precipitator. The charged dust that is not captured then enters the back-stage bag filter area evenly. The clean air chamber on the upper part of the flower plate of the bag filter area is divided into several small chambers. Each small chamber is equipped with an outlet damper, which is connected to the top outlet smoke box. The outlet damper is controlled by a pneumatic lifting valve, and any chamber can be closed to perform offline cleaning without filtering. Reduce the number of openings of the inspection door, reduce the air leakage rate of the dust collector, and ensure the best combination of the comprehensive performance of the electric bag composite dust collector. This structure is a multi-chamber structure with central air intake and upper air outlet, which is the most typical structure of conventional electric bag composite dust collectors. The characteristics of this structure: easy equipment maintenance, safety, and good reliability: small footprint, low air leakage rate, for small units, because there is no independent air inlet valve, online maintenance at high load cannot be achieved, and the load needs to be reduced during maintenance. For large units, a wind shield door is set at the front of each channel entering the power area (that is, a multi-channel structure is set up), and any channel can be isolated through operation to facilitate maintenance.

Figure 1 Chamber structure

As the country's policy requirements for energy conservation and emission reduction for enterprises continue to increase, the requirements for electric bag composite dust collectors have been raised to a higher level, and the structural technology needs to be optimized and improved to meet new development needs. First of all, the multi-chamber structure is cancelled in the structure, that is, the clean air chamber is not divided into small chambers, the lifting valve structure at the outlet is cancelled, and the pneumatic lifting valve is cancelled. After the flue gas enters the clean air chamber, it is directly passed into the outlet smoke box, as shown in Figure 2. There is no lifting valve, which reduces the cylinder, lifting gas path, control, etc.: the multi-chamber is cancelled, the equipment is simple and easy to maintain. Ultra-low emission control prohibits flue gas from bypassing, so the lifting valve structure is cancelled, and the bypass valve structure is correspondingly cancelled. In order to adapt to the fuel flue gas in the start-up stage, the super-humid flue gas after the pipe burst, and the ultra-high temperature flue gas without the protection of the bypass valve for the filter bag, improvements are made in the structure and the treatment of the filter bag, such as adding a pre-ashing device, improving the oil and water resistance level of the filter bag, and using high-temperature filter bags. After optimization, the structure is a straight-through chamber structure with central air intake and upper air outlet.

Figure + straight-through chamber structure

2.2 Electric area improvement

In order to achieve ultra-clean emission of smoke at the outlet of the electric bag, technicians have studied the inlet concentration of the bag area, the air-to-cloth ratio, and the selection of the electric area [2]. Experiments show that when the inlet concentration of the bag area is less than 5g/m3, and a high-quality filter material is used, and the air-to-cloth ratio is about 1m/min, the outlet emission concentration can be less than 10mg/m3. Therefore, one of the most important technical measures for improving the second-stage ultra-clean electric bag is to reduce the inlet smoke concentration entering the bag area, that is, by improving the pole matching type of the electric area, using a pole matching type of the electric area with high discharge performance and high field strength, increasing the particle charge, and enhancing the particle coagulation effect, so as to improve the dust removal efficiency of the electric field area. In addition, the small-area power supply technology is used for the electric area to increase the average working voltage, and the particle charge is also increased accordingly, which plays an important role in the charging and electrocoagulation of fine particles. At the same time, the small-area power supply improves the reliability of the electric area. Even if one of the electric areas fails, the other electric area can still work.