Bag filter operation pradeep kumar

Basics of dedusting(nuisance) filter

WELCOME TO ALL

PRADEEP KUMAR Sr GM OPERATIONKARIKKALI WORKSCHETTINAD CEMENT WORKS

Nuisance filter

The MythThe filter bags filter the dust

The fact is the cake formed on the filter bag surface does the filtering job. Permanent cake on the filterProtects the filter from impingement and erosion Of the dust laden gases.

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 dedustedB. Dedusting pipes and valvesC. FilterD. Fan and motor E. Insulation

General theoretical design guidelines

Filtration velocity

The maximum allowed filtration velocity depends on the flowresistance of the bag pulse filter cake and the cleaning abilityof the filter bag and of course on the cleaning method.

the pressure difference (∆p) across the filter bags increases:

the higher the filtration velocitythe 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)

Mode of operation

1. Identify the equipment to be dedusted .max.6 dedusting points 2. should be connected to one common filter3. Calculate the dedusting airflow for each dedusting point and duct

4. Calculate the air flow for the complete dedustiong pipe system

5. Determine the pipe sizes from the air flows

6. 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 , temperatureand humidity

Dust collecting system design guidelines

Amount of dust sources to ventNo more than six (6) to eight (8) dust sources to vent should beconnected to one dust collector.

Venting air volume

The true required venting air volume that the ventilation system hasto handle must be determined first. Therefore, it has to be determined how much vent air is requiredat each dust point. The recommended standard volumetric requirements for the venting of typical applications in ambient airare 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 mentionedappendix.

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

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 particlecollectives/agglomerates that have to fall into the hopper by gravity. From experience, we know that the vertical upward vector of the gasflow velocity should be lower than 1.0 or maximum 1.3 m/s

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 withheating elements

Concentration of dust

The type dust concentration in the dedusting air from the transportequipment, 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.

Hooding and material Discharge Chute height

1.3 m/s

10 to 20

m/s

10 to 20 m/s10 m/s for non explosive abrasive dust Like clinker , slag and fly ash20m/s for explosive

dust Like coal. For lignite bends must strictly be avoidedDust concentration20- 50 g/cum< 45 microns

2 M

At material discharge chute, drop height must benot more than 2M.If it is more than2 M, Baffle plates

are provided

Discharge chute

2 M

Drop height must beNot more than 2M.If it is more than 2 MBaffle plates are provided

Discharge chute

Elephant and feather theory

10-20m/s

Air drag

100 mic75 mic

60 mic45 mic

1.4 m/s

< 1.3 m/s

Cement silo CFI

q4 air for intervening air slidesq5 aeration foe tank below CFI silo 4 m3/min q6 displacement air in tank

Belt weigh feeder

Dedusting of Q20 m3/min from the top plate of theScreen or Q m3/min through the subsequent equipment.Q20 = Q m3/min rounded up to the air flow for an air velocityOf 20 m/s in the dedusting pipe line

Q= necessary dedusting airflow m3/min =16 m3/min* screen area in m2

Filter bags ( filter media)

Selection criteria

The filter medium is the all-important central featureof 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 principlemoisture level,gas temperature (average and peaks)composition and chemical properties of the gasraw gas dust load, particle size particulate abrasivenessallowed dust load in the clean gas physical and chemical properties of the dust

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 givenflow rate. There are standard air-to-cloth ratios based on cleaning mechanism styles, and thisratio 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 dust1.5 m3/m2 x min for limestone and cement dust

Filtering surface

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)

Selection criteria

The filter medium is all –important central feature of any dust collectoroperating n the filtration principle. With correct or incorrect choice ofthe 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

Furthermore, the filter medium must satisfy thefollowing conditions:high air permeability (low pressure losses)good mechanical strengthgood thermal stability at operational temperaturegood dimensional stability at operational temperature

Without membrane

Thank you for your kind attention

K.P.PRADEEP KUMAR Sr G M OperationKarikkali Works

Chettinad cements LTD