Fluidized bed bag dust removal

Bag dust removal is a form of physical dust removal. A bag filter is a dry, high-efficiency dust collector that utilizes fiber-woven bags as components to remove solid particles from dusty gases before they can reach other parts of the system. Its working principle is that dust particles are intercepted as they pass around the fibers of the filter cloth due to inertial forces that cause them to collide with the fibers. Dust particles with a size of 1 micron or less have their movement direction continuously altered by impacts from gas molecules (Brownian motion); since the gaps between the fibers are smaller than the free path of Brownian motion, these dust particles collide with the fibers and are thus separated out. Filtering can be produced by the filter cloth itself, or by the dust cake accumulated on it. Due to the formation of dust cakes, the effects of entrainment (mainly interception and diffusion effects) are enhanced, allowing particles with diameters much smaller than those of the filter media pores to be collected as well. For a bag filter used in an entire boiler system, the filter bags are the core components; the quality of these bags and the appropriateness of their selection directly affect the efficiency and service life of the filter ； The quality of the filter bags and the appropriateness of their selection have a direct impact on the efficiency and service life of the dust collector ； There are many types of materials for filter bags, and there are significant differences in their performance and prices.

This post was last edited by chen-jun-1024 on 2010-10-19 at 11:23. Nowadays, electric bag filters are used in larger circulating fluidized bed boilers. I. Working principle of the electric bag combined dust collector 1. Definition of the electric bag combined dust collector: The electric bag combined dust collector is a high-efficiency combined dust collector that makes use of and integrates the advantages of electric dust collectors and bag dust collectors; it first captures a large amount of dust from the flue gas using an electric field, and then collects any remaining fine dust with the help of bags. It features dust removal, stability (≤50mg/Nm3), and excellent performance. 2. Working principle: Based on the working principles of electrostatic precipitators and bag filters, it combines the dust removal advantages of both: the pre-electric field removes more than 70–80% of the dust in the flue gas ； The subsequent bag filter captures and collects the remaining dust in the flue gas. Among them, the pre-dust removal and charging effects of the preceding electric field play an important role in improving the performance of electrobag dust collectors. 1) Electrostatic pre-dust removal effect 1: ① Pre-dust removal reduces the dust load on the filter bags, thereby lowering the rate of resistance increase. Electrostatic pre-dust removal effect 2: ② Pre-dust removal extends the cleaning cycle of the filter bags, reduces energy consumption for cleaning, and prolongs the service life of the filter bags. Electrostatic pre-dust removal effect 3: ③ Preventing wear on the filter bags by large particles in flue gas dust. After the large particles in flue gas dust are settled and pre-removed by the preceding electrostatic field, the dust particles that reach the subsequent filter bags are smaller, resulting in less wear on these filter bags. When the flue gas contains coarse particulate dust (such as that from circulating fluidized bed boilers), the use of electro-bag filters can completely prevent abnormal wear and damage to the filter bags. 2) Electric field charging effect 1: ① Improving the powder layer structure on the surface of the filter bags: After the flue gas dust is charged by the corona in the preceding electric field, the charged dust particles arrange themselves in an orderly manner among those deposited on the filter bags. The like-charged particles repel each other, resulting in a dust layer with high porosity and good air permeability, as well as easier removal. Electrostatic charging effect 2: ② can reduce the resistance of the filter bag. P: The resistance of the filter bag is equal to the resistance P1 of the dust layer ①, plus the resistance P2 of the surface treatment layer ②, plus the resistance P3 of the filter bag’s structural layer. II. Technical performance characteristics of the electro-bag combined dust collector: 1. Suitable for collecting dust with high specific resistance, offering high efficiency and stability in dust removal. The efficiency of electro-bag dust collectors is not affected by fine dust with high specific resistance, nor by the type of coal or the characteristics of soot; it is easy to keep the emission concentration below 50 mg/Nm3, with stable performance over the long term. 2. The operating resistance is 500 Pa lower than that of a pure bag filter, which can reduce the power consumption of the exhaust fan. The operating resistance is 500 Pa lower than that of a pure bag filter, and the power consumption of the exhaust fan can be reduced by 1.74 KW for every 10,000 m3/h of air flow. 3. Long dust cleaning cycle and low energy consumption for the air supply. Due to the low amount of dust collected by the filter bags, the resistance increases slowly; as a result, their cleaning cycle time is more than twice that of conventional bag filters, while the consumption of compressed air is less than 1/3 of that in conventional bag filters. 4. Extend the service life of the filter bags. U has low operating resistance, and the small differential pressure load on the filter bags prolongs their service life. The long dust cleaning cycle and few cleaning instances extend the service life of the filter bags. Under the same operating conditions, the service life of the electro-bag filter is 2 to 3 years longer than that of a pure bag filter. 5. The initial investment is low, and operating and maintenance costs are minimal. Increasing the filtration air velocity slightly can reduce the number of filter bags and valves, thereby lowering equipment costs. Low operating energy consumption and a long service life of the filter bags further reduce operating and maintenance expenses. In summary, the electro-bag composite dust collector addresses the three major problems commonly encountered in current dust collectors: namely, the emission issues of electrostatic dust collectors. The problem of high resistance in U-bag dust collectors. The problem of short service life of bags in U-type bag filters. III. Technical Performance Indicators and Application Scenarios 1. Main technical performance indicators of electro-bag filters: Exhaust emission concentration: ≤50mg/Nm3. Pressure difference before and after the w filter bag: ≤600Pa. w Dust collector inlet and outlet resistance: ≤1000Pa. The service life of the w filter bag is 2–3 years longer than that of conventional filter bags. 2. Application scenarios: Purification of dust with high specific resistance and special coal types, which are difficult to collect efficiently using electrostatic dust removal. It requires the purification of flue gas from coal-fired boilers to ensure emissions of ≤50mg/Nm3. It is particularly suitable for the efficiency improvement retrofit of old electrostatic precipitators. IV. Structure and Components of the Electrobag Combined Dust Collector 1. Inlet flare http://www.ynyf.cn/newEbiz1/871ynyfres/filerepository/images/c373e910a127636e8fffe2ff5f058f322. Ash hopper 3. Housing 4. Pre-stage electric field 5. Vibration device 6. Flow guiding device 7. Filter bags 8. Dust cleaning system 9. Clean air chamber 10. Lifting mechanism 11. Exhaust flue 12. Manhole The electrobag system can be functionally divided into: A. Pre-stage electric field dust removal, B. Post-stage bag dust removal, C. Detection function, D. Protection function, E. Electrical control. A. The composition of the pre-stage electric field dust removal section is the same as that of a conventional electric dust collector. The general selection principles are as follows: For renovation projects, the existing pre-stage electric field structure can be reused to reduce equipment costs. New project: A pre- and post-field partition structure is adopted to improve the operational reliability of the electric field. B. The posterior bag dust removal unit consists of filter bags, bag cages, a dust cleaning system, lift valves, and a compartmentalized housing structure. 1) Filter bag structure: external filtration type circular bag, with an elastic bag mouth that is tensioned and fixed to the grid plate for sealing. 2) Sack cage structure: upper and lower segmented structure. 3) Chambers: Divide the bag filter into several chambered structures. 4) Dust removal system: Pulse jet structure. 5) Lift valve: Up and down lifting structure. C. Detection device: Composed of pressure, differential pressure, and temperature detection. D. Protection devices: There are two types, namely filter bag surface protection and temperature protection, with the choice depending on the operating conditions. E. For electrical control, the electric field is managed by an advanced microcomputer-based voltage automatic controller, which offers constant current or constant voltage control functions. The U-bag utilizes Siemens PLCs and high-precision contactless pulse output control technology to ensure uniformity in the air volume delivered by each pulse valve. V. Structural Features of the Electrobag Combined Dust Collector 1. Structural features of the electrobag system: Pre-stage electrostatic dust removal and post-stage bag dust removal are arranged in series, sharing the same housing; a specially designed diversion and guiding device is used between these two dust removal stages. It has advantages such as clear area division, mature technology, and easy maintenance. 2. Structural features of the bag dust removal system in electro-bag filters: 1) A mature low-pressure long-bag structure. 2) Modular structure, allowing switching between offline and online dust cleaning, with online maintenance capabilities. 3) Top manhole: It is convenient and simple to replace the filter bag without having to enter the dust collector. 4) Submerged electromagnetic pulse valves are used to ensure efficient, stable, and reliable dust cleaning. 5) Pulse dust cleaning structure, with no resistance loss due to elbows in the pulse airflow. 6) It can prevent bag burning and oil fumes in conditions of high flue gas temperature and the presence of oil fumes. 3. Air flow distribution structure 1) Function: To ensure uniform distribution of flow velocity and air volume as the air flows through the electric field and the bag filters. 2) Structure: A unique patented technical structure. VI. Common filter media for coal-fired boilers 1. Names and characteristics of common filter media for coal-fired boilers – PPS needle-punched filter media; chemical name: polyphenylene sulfide. Operating temperature: ≤200–260°C. u has strong acid and alkali resistance. 2. Filter media treatment method: oil-resistant water treatment to improve dew resistance. The surface of u is treated with a PTFE coating; the pores in this coating range from 1 to 3 μm. This improves the filtering accuracy of the filter bags (ensuring compliance with the <20 mg/Nm3 emission standard), enhances their resistance to dew formation, improves their dust-cleaning performance, and reduces the resistance of the filter bags.

We do this often; for smaller fluidized beds, we mostly use bag filters, and the results are very good.