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Bag filter operation pradeep kumar
- 1. Basics of dedusting (nuisance) filter WELCOME TO ALL PRADEEP KUMAR Sr GM OPERATION KARIKKALI WORKS CHETTINAD CEMENT WORKS
- 3. The Myth The filter bags filter the dust The fact is the cake formed on the filter bag surface does the filtering job. Permanent cake on the filter Protects the filter from impingement and erosion Of the dust laden gases.
- 4. General principles of dedusting To prevent equipment from generating the dust and to achieve trouble Free operation of dedusting plant certain conditions must be met. Some of these conditions are described in the following sections Dedusting plants may be divided into the following components A. Equipments to be dedusted B. Dedusting pipes and valves C. Filter D. Fan and motor E. Insulation
- 5. General theoretical design guidelines Filtration velocity The maximum allowed filtration velocity depends on the flow resistance of the bag pulse filter cake and the cleaning ability of the filter bag and of course on the cleaning method. the pressure difference (∆p) across the filter bags increases: the higher the filtration velocity the thicker the filter cake (residual dust layer after cleaning) and the quicker it builds up (dust load time/cleaning interval) the higher the Blaine value of the dust (the finer the dust) the more compressible or sticky the dust (important for AFR usage) the older the bags (due to penetration of fine dust particles into the fabric) false air ingress via the worn out rotary air lock , worn out filter body ( this causes dust entrainment also)
- 6. Mode of operation . Identify the equipment to be dedusted .max.6 dedusting points . should be connected to one common filter . Calculate the dedusting airflow for each dedusting point and duct . Calculate the air flow for the complete dedustiong pipe system . Determine the pipe sizes from the air flows . Choose the auxiliary equipment- throttle valves,ventilation flaps , filter, fan and insulation-,based on the dedusting air volumes and other data such as Barometric pressure , temperature and humidity
- 7. Dust collecting system design guidelines Amount of dust sources to vent No more than six (6) to eight (8) dust sources to vent should be connected to one dust collector. Venting air volume The true required venting air volume that the ventilation system has to handle must be determined first. Therefore, it has to be determined how much vent air is required at each dust point. The recommended standard volumetric requirements for the venting of typical applications in ambient air are shown in table. The air flow for the remaining venting pipes before the filter should be the sum of the presented values as shown in mentioned appendix.
- 8. Deviations from the above guide lines may be possible depending on the practical Experience ,esp depending on the characteristics of the material like Abrasion, moisture, size and explosive nature etc;also on the equipment type like open or closed. At least the following equipments are considered ‘open’ - Apron conveyor or feeder - bucket conveyor - crushers - Weigh feeders - Belt conveyors The following equipments are closed - Drag Chain - Pneumatic transport system - silos - screw conveyor - air lift - bucket conveyor
- 9. Can velocity The can velocity is the theoretically calculated raw gas velocity between the filter bags at the bag bottom area. This is valid independently of raw gas inlet design. The maximum allowed velocity depends on the gas flow direction between the bags and the terminal velocity of particle collectives/agglomerates that have to fall into the hopper by gravity. From experience, we know that the vertical upward vector of the gas flow velocity should be lower than 1.0 or maximum 1.3 m/s
- 10. Insulation In cases where the relative humidity of the dedusting air is so high that condensation may arise as aresult of heat emitted by the dedusting pipe and the filter bottomh hopper should in rare situations be equipped with heating elements Concentration of dust The type dust concentration in the dedusting air from the transport equipment, silos, stores etc is between 20 and 50 g/ cuM of the dedusting air.This concentration is valid if the equipment and the pipe Connections are designed in conformity with the design of the supplier.
- 11. Hooding and material Discharge Chute height
- 12. 1.3 m/s 10 to 20 m/s 10 to 20 m/s 10 m/s for non explosive abrasive dust Like clinker , slag and fly ash 20m/s for explosive dust Like coal. For lignite bends must strictly be avoided Dust concentration 20- 50 g/cum < 45 microns 2 M At material discharge chute, drop height must be not more than 2M. If it is more than 2 M, Baffle plates are provided Discharge chute
- 14. 2 M Drop height must be Not more than 2M. If it is more than 2 M Baffle plates are provided Discharge chute
- 17. Elephant and feather theory
- 18. 10-20m/s Air drag 100 mic 75 mic 60 mic 45 mic 1.4 m/s
- 19. < 1.3 m/s
- 39. Cement silo CFI q4 air for intervening air slides q5 aeration foe tank below CFI silo 4 m3/min q6 displacement air in tank
- 62. Dedusting of Q20 m3/min from the top plate of the Screen or Q m3 /min through the subsequent equipment. Q20 = Q m3 /min rounded up to the air flow for an air velocity Of 20 m/s in the dedusting pipe line Q= necessary dedusting air flow m3 /min =16 m3/min* screen area in m2
- 78. Filter bags ( filter media)
- 79. Selection criteria The filter medium is the all-important central feature of any dust collector operating on the filtration principle. With the correct or incorrect choice of the filter material, the whole dust collection operation will stand or fall in actual practice. Important selection criteria are: filter type, particularly cleaning principle moisture level,gas temperature (average and peaks) composition and chemical properties of the gas raw gas dust load, particle size particulate abrasiveness allowed dust load in the clean gas physical and chemical properties of the dust
- 80. Air-to-cloth ratio (A/C ratio) The air-to-cloth ratio (A/C ratio) is simply a mathematical expression used to measure the amount of filtering cloth area available to filter a given volume of air at a given flow rate. There are standard air-to-cloth ratios based on cleaning mechanism styles, and this ratio is used to determine the operating limits of the bag house. The guide ratios for collectors with pulse-jet cleaning are as a function of the bulk material to handle for auxiliary Equipment venting as follows: 1.2 m3 /m2 x min for slag, coal and clinker dust 1.5 m3 /m2 x min for limestone and cement dust
- 82. a, b:manual or mechanical, by rapping or shaking c: mechanical, by vibrating d:pneumatic, by reverse air flow (often combined with shaking or vibrating) e:pneumatic, by compressed air (pulse-jet) Vibrator (a) (b) (c) (d) (e)
- 83. Selection criteria The filter medium is all –important central feature of any dust collector operating n the filtration principle. With correct or incorrect choice of the filter material,The whole dust collection operation will stand fall in actual practice Important selection criteria are • Filter type, particular cleaning principle • Moisture • Gas temperature ( average and peak) • Compostion and chemical properties of the gas • Raw gas dust load, particle size • Particle abrasiveness • Allowed dust load in the clean gas, emission level , mg/M3 • Physical and chemical properties of the dust Further more, the filter medium must satisfy the following conditions • High air permeability ( low pressure loss) • Good mechanical strength • Good thermal stability at operational temperature • Good dimensional stability at operational temperature
- 84. Furthermore, the filter medium must satisfy the following conditions: high air permeability (low pressure losses) good mechanical strength good thermal stability at operational temperature good dimensional stability at operational temperature Without membrane
- 109. Thank you for your kind attention K.P.PRADEEP KUMAR Sr G M Operation Karikkali Works Chettinad cements LTD