Fabric filter/Bag House

I have tried to make it as simple as i can.

1. M.Junaid Khan D-17-CH-12 FABRIC FILTERS FOR PARTICULATE MATTER

2. Fabric filter is an air pollution control device and dust collector that removes particulates or gas released from commercial processes out of the air.

3. Working Principle The gas entering the inlet pipe strikes a b affle plate, which causes larger particles to fall into a hopper due to gravity. The carrier gas then flows upward into the tubes and outward through the fabric leaving the particulate matter as a "cake" on the insides of the bags.

4. mechanism Inertial collection – Dust particles strike the fibers placed perpendicular to the gas-flow direction instead of changing direction with the gas stream. Interception – Particles that do not cross the fluid streamlines come in contact with fibers because of the fiber size. Brownian movement – Submicrometre particles are diffused, increasing the probability of contact between the particles and collecting surfaces. Electrostatic forces – The presence of an electrostatic charge on the particles and the filter can increase dust capture. A combination of these mechanisms results in formation of the dust cake on the filter, which eventually increases the resistance to gas flow.

5. Filter Media Woven filters are used with low energy cleaning methods such as shaking and reverse air. Felted fabrics are usually used with high energy cleaning systems such as pulse jet cleaning.

6. While selecting the filter medium for bag houses, the characteristics and properties of the carrier gas and dust particles should be considered. The properties to be noted include: Carrier gas temperature Carrier gas composition Gas flow rate Size and shape of dust particles and its concentration

7. TYPES OF FABRIC FILTER

8. Baghouses are classified by the cleaning method used. The three most common types of baghouses are mechanical shakers, reverse gas, and pulse jet.

9. mECHAnical shaker baghouse In mechanical-shaker baghouses, tubular filter bags are fastened onto a cell plate at the bottom of the baghouse and suspended from horizontal beams at the top. Dirty gas enters the bottom of the baghouse and passes through the filter, and the dust collects on the inside surface of the bags. Cleaning a mechanical-shaker baghouse is accomplished by shaking the top horizontal bar from which the bags are suspended. Vibration produced by a motor-driven shaft and cam creates waves in the bags to shake off the dust cake. Note: The air-to-cloth ratio for shaker baghouses is relatively low, hence the space requirements are quite high. However, because of the simplicity of design, they are popular in the minerals processing industry.

10. Reverse Air baghouse A reverse air baghouse cleans at a lower pressure than a pulse-jet baghouse. No cages are supporting the bags so as the dust cake cuts off the inflow of dirty air, it uses the reverse flow of clean air to remove the dust. The bags partially collapse and remove the dust

11. Reverse Pulse Jet baghouse In reverse pulse-jet baghouses, individual bags are supported by a metal cage (filter cage), which is fastened onto a cell plate at the top of the baghouse. Dirty gas enters from the bottom of the baghouse and flows from outside to inside the bags. The metal cage prevents collapse of the bag. Bags are cleaned by a short burst of compressed air injected through a common manifold over a row of bags. The compressed air is accelerated by a venturi nozzle mounted at the reverse-jet baghouse top of the bag. Since the duration of the compressed-air burst is short (about 0.1 seconds), it acts as a rapidly, traveling through the entire length of the bag and causing the bag surfaces to flex. This flexing of the bags breaks the dust cake, and the dislodged dust falls into a storage hopper below. Reverse pulse-jet dust collectors can be operated continuously and cleaned without interruption of flow because the burst of compressed air is very small compared with the total volume of dusty air through the collector. (Pulse valves control the release of air pulses during the cleaning cycle. When the baghouse control board or timer board initiates a cleaning cycle it sends an electrical signal to the solenoids, when then activate the pulse valve. Inside the pulse valve, a rubber diaphragm opens and closes to release the compressed air stored in the air header tank)

12. Design A baghouse consists of numerous vertical hanging, tabular bags, 12-40 cm in diameter and 2 – 10 m long. They are suspended with their open ends attached to manifold. The number of bags may vary from few hundreds to thousands, depending upon the size of baghouse. The bags are housed in a shell made of rigid metal material in a single or double compartment.

13. Design 1. Air-to-Cloth Ratio :- The volume of gas flow passed per unit area of the bag i.e. Air to cloth = Volume of gas flow (Q)/ Area (A) of bag ratio (Typical value 0.010 to 0.020 m/sec-for shaker type) 2. Net area of bags of bags = Q/Air to cloth ratio 3. Area of one bag = Π x D x L L=length of bag D= Dia of bag 4. No of bags = Net area / area of one bag

14. Design 1. Air-to-Cloth Ratio :- The volume of gas flow passed per unit area of the bag i.e. Air to cloth = Volume of gas flow (Q)/ Area (A) of bag ratio (Typical value 0.010 to 0.020 m/sec-for shaker type) 2. Net area of bags of bags = Q/Air to cloth ratio 3. Area of one bag = Π x D x L L=length of bag D= Dia of bag 4. No of bags = Net area / area of one bag

15. Operating Problems Cleaning - At intervals the bags get clogged up with a covering of dust particles that the gas can no longer pass through them. At that point, the bags have to be cleaned by rapping, shaking or by reverse air flow by a pulse jet. Rupture of the cloth -The greatest problem inherent in cloth filters is the rupture of cloth, which results from shaking. It is often difficult to locate ruptures and when they’re found the replacement time is often considerable. Gas Temperature -Fabrics are designed to operate within a certain temperature range. Fluctuation outside of these limits, even for a small period of time, can weaken, damage, or ruin the bags. Bleeding -This is the penetration of the fabric by fine particles, which is common in fabric filtration. It can occur if the weave is too open or the filter ratio is very high. The solution is touse a double layer material or a thick woven fabric. Humidity -This is a common and important problem, especially if the dust is hygroscopic. It would therefore be advisable to maintain moisture free conditions within the bag house, as a precautionary measure. Chemical attack -This is another problem associated with fabric filters. The possibility of chemical attack due to corrosive chemicals present in theeffluent. A proper choice of fabric filter will avoid this problem.

16. advantages High collection efficiencies is for all particle sizes, especially smaller than 10 micron in diameter. Simple construction and operation Normal Power consumption Dry disposal of collected material

17. Disadvantages Operating limits are imposed by high carrier gas temperatures, high humidity and other parameters. Reactive gases and chemical particles attack the filter media Fine particles penetrate through fabric and cause rupture of cloth, which may be difficult to locate, repair or replace High maintenance and fabric replacement cost Large size of equipment

18. APPLICATIONS Fabric filters find extensive application in the following industries and operations: Metallurgical industry Foundries Cement industry Chalk and lime plants Ceramic industry Flour mills

19. THANK YOU ANY QUESTION?