Baghouse

Air pollution is the introduction into the atmosphere of chemicals, particulates, or biological matters that cause discomfort, disease, or death to humans, damage other living organisms such as food crops, or damage the natural environment or built environment.

Basic Concept

Dust laden air enters through the hopper by suction or positive pressure

The heavier dust particles fall immediately into the hopper, while the lighter ones deposit on the outer surface of filter bags

Dust deposited on bag surface is dislodged & bag is cleaned by pulse of high pressure compressed air.

Top-Down flowin filter housing

Insulation to avoidundershootingof dew point(hot gas version

Dust particles areretained on thesurface of the filtermedium and thecleaned air passesthrough the filtermedium and flowsinto the clean gaschamber or duct.

Penthousewith hoist

Dust collection hopper or tray with materialdischarge screw or scraper chain conveyor

Bagfilters : Classification based on how the fabric is cleaned

1. Shaking 2. Compressed Air 3. Reverse Air

Reverse Air

Types of Cleaning

In an industrial system of gas cleaning, the fabric is media made into either an envelope or a tube. These envelopes or tubes are called the bags and a housing of these is called Bag Filter or Bag House.

Bag Filter - Basics

Inlet dust load in gm/Nm3

Gas volume in Nm3/hr

Gas temperature

Nature of pollutant : Gaseous /

Particulate Properties of dust : Physical

(density / size fraction /temperature / ‘wettability’)

Properties of gas : Physical / Chemical (nature: acidic /alkaline, moisture content critical)

FACTORS GOVERNING SELECTION OF TYPE OF APC EQUIPMENT - 1

Nuisance value / Recovery value of both dust and gas

Outlet emission requirements / Efficiency required

Space availability Economics / Budget / Fund availability

/ Return on Investment

FACTORS GOVERNING SELECTION OF TYPE OF APC EQUIPMENT - 2

Air-to Cloth Ratio =

Total volume of gas (or air) handled by the Bag filter [m3/min] /Total filtration area provided in the Bag Filter [m2]

= [ m3/min-m2 = m/min, => velocity unit; hence also called filtration velocity, and is actually the velocity at which the dust

laden gases travel across the filter element ]

The more critical the dust { fine, light, sticky, non-agglomerating, abrasive, etc} or higher the dust loading, the larger is the filtration area provided, i.e. lower is the air-to-cloth ratio maintained.

Can Velocity =

Velocity at which the gas travels upwards across the cross section of the Bag filter =

Total volume of gas (or air) handled by the Bag filter [m3/min] /Cross sectional area of Bag Filter casing [m2]

This is an important aspect and has to be restricted especially for fine, light, and non-agglomerating dust (lime, carbon black are typical examples) as otherwise the dust may remain in a fluidised state in the bag filter and not get discharged from the unit at all.

Filter Fabric selection

Online type :-Cleaning is done on line ( chamber in

operation)

Off Line type :-Cleaning is done in the off line mode. i.e

cleaning of the chamber after isolating the flue gas entry .

This avoids re entrainment of dislodged dust

Used in case of fine dust

Bag Filter – Type-Online

Single module-hopper Entry

How it works – Normal Gas Flow

Bag Filter – Type-Offline

How it works – Reverse Gas Flow


In offline Pulse Jet Bag Filter which is a compartmentalized Bag Filter, one compartment is sequentially taken out for cleaning purpose. Rest all the compartments are under filtration process. Typically offline cleaning is employed for finer dust particle sizes which does not settle easily.

In Modular construction Pulse Jet Bag Filter which is Online in cleaning operation, one compartment can be taken out doe maintenance purpose if required.

• The cleaning in this type of filter is online i.e. filtration and cleaning simultaneously occurs in a compartment. These type of filters are usually designed for Process application which handle large gas volumes.

• In both the above types of Bag Filters outlet type poppet dampers pneumatically operated are required for isolation of compartments.

PJBF-Offline


Constant emission air pollution control (APC) equipment. Suspended particulate emission control using positive filtration. Possible to achieve lower outlet emission. Suitable upto gas temp. of 260 deg C. Can handle various types dust viz. explosive/non-explosive, abrasive,

hygroscopic, sticky, coarse/fine. Low initial set-up cost.

Pulse Jet: Pulse Valve

Pulse Jet Components - Diaphragm Valve

Pulse Jet Component – Air Manifold Tank

Pulse Jet Components – Tubesheet (Cell Plate)

Pulse Jet Components - Venturis

Pulse Jet Components - Bags

Pulse Jet Components – Bags

Pulse Jet Components - Cages

Pulse Jet Components – Cleaning system

Pulse Jet Components – Cleaning system

Pulse Jet Components – Timer or DP Based Control

Pulse Jet Cleaning Operation through Timer

6 Ways Dust Gets to Clean Air Plenum

Hole in Bag Snapband/Flange Top Welding Cracks Clean too soon (Over Cleaning) Not Cleaning (Under Cleaning) Air Leaks at Door Seal

Pulse Jet Component – Blowpipe

Enlarged Holes

Normal Holes

Pulse Jet– Blowpipe Misalignment Problemof Cage

of Blowpipe

Less than 1/4 inch(6.35 mm)

PROBLEM POSSIBLE CAUSE

SOLUTION

High DP Bad Gauge Check gauge by blowing into it. If needle does not move replace gauge

Leaking gauge pipe

Repair leaking gauge pipe

Choked gauge pipe

Clean / replace gauge pipe

Low header pressure

Minimum required pressure is 6.3kg/cm2g (90psi). Check supply pipe, drain valve for leaks. Check Diaphragm & solenoid operation


SOLUTION

High DP Static Charge on Filter

Static Electricity will interfere with the cleaning operation. Ground the filter

Water in Air Line

Remove water & clean the system. Check regularly the manual/Auto drain valve of Air Filter. Replace the defective one.

Bag Blinding or chocking

High moisture & condensation will cause dust cakes, which are difficult to remove & it blinds/chokes bags.

1)Preheat Bag Filter on start-up & use space heater ON for long shutdown. 2)Wash bags & use after drying.

3) Membrane bags – Permanent soln.


SOLUTION

High DP Wet Compressed Air

Humid compressed Air allows dust cake to stick to the bags. Ensure, clean & dry compressed air

Too high System Air Flow

Check for airflow figure. If it is very high the A/C Ratio will also be very high causing high DP as well as Re-entrainment

Dust Particles – Too fine

Ask customer for actual particle size analysis & compare with figures given in the order – Excessive fines will simply choke the pores on bag surface

Pulse pipe mis alignment

The pulse pipe nozzle should be concentric with the bag centre


SOLUTION

High DP Bag-Cage Pinch – not Okay

For normal felt bags the bag –cage pinch should be within 6mm ~ 12mm. Replace ‘Too tight’ bags, as well as ‘Too loose’ bags

Long Pulse Frequency

Adjust OFF Time by observing Bag Filter DP and set. Reduce OFF Time by 5seconds interval and watch till DP stabilize

Pulse ON Time

Pulse ON time should Typically in the range of 80~100ms. Some Fine dust application, it may require higher ON time, but that should be verified first

PROBLEM

POSSIBLE CAUSE

SOLUTION

High DP Sequential Controller Problem

Any malfunction can cause irregular pulsing, causing raise in DP across BF. Repair/replace card(s)

RAV Leakage

High Dust Load

If actual value is higher than design, check everything and then increase pulse frequency till 10sec interval time.

Else, advice customer to go for pre-filter

Failure of solenoid valve diaphragm


SOLUTION

Low DP Bad Gauge Check gauge by blowing into it. If needle does not move replace gauge

Leaking / choked gauge pipe

Repair leaking gauge pipe

Holes in Bags Replace worn bags

Low System air volume

Check duct systems for deposits & closed dampers – It causes work area problem for dedusting system

Wrong Bag installation

Look for dust on clean air plenum & blank /dummy the defective bags


SOLUTION

Emission Holes in bags, cut in snapbands

Replace damaged bags

Precoating / seeding not done for new bags

Carryout proper precoat/ seeding. If not possible, wait for sometime till the process stabilizes after start-up

Wrongly installed dummies

Check all dummies and ensure tight fit, else replace them

Chemical attack

Check whether bags are being torn just by hand pressure. If so, chemical attack is confirmed


SOLUTION

Poor Bag Life

Overcleaning Increase pulse frequency or OFF time duration

Abrasion Poor inlet design causing high inlet velocity and elbows at inlet can cause accelerated abrasion of bags –

Bent / corroded Cages

Replace bent / corroded cages

High Air Volumes

High A/C ratio shortens bag life.


SOLUTION

Poor Bag Life

Moisture in Comp air

Moisture in compressed air might cause acid mist in some application and weaken bags. Moisture also shrink some fabric materials. Take corrective action to control moisture

Thermal Shrinkage

Some Fabrics like PPS (Ryton) is having thermal shrinkage. Over exposure of high temperature might cause such shrinkage. Setting of temperature alarm is important


SOLUTION

Hopper Plugging

Cleaning malfunction

Check pulsing system as a whole and take corrective action

Dust disposal system – malfunction

Inform customer about mal functioning about RAV/Screw Conveyors/ chain conveyors

Wrong design of Dust disposal system

Establish thru’ data collection

Technology

Baghouse