Design of Pollution Control Equipment

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Design of Pollution Control Equipment

Project and Presentation byMs. Kakoli Shaw

Mr. R.C.DOHARE


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Introduction

Workplace environment has direct impact on a employeeshealth.

Particulate matter is a major air pollutant in the industrial

workplace environment.

Major harmful effects of Respirable Suspended ParticulateMatter (RSPM) are bronchitis, red eyes, respiratory

symptoms and aggravated asthma.

De-dusting systems are used for abatement of such

potential health hazard as a part of industrial hygiene.

Design of a more efficient and effective de-dusting system

as compared to the existing one has been done using

ACGIH guidelines for Industrial Ventilation.


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Limit Values of Dust (TWA/8 hrs)


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Related Research Work

S.M.T.K Samarakoon and S.Thiruchelvam (2006) showedin their research results that about 41% and 12% of thetotal population living within 500 m and 1000 m distancefrom the lime kiln area, respectively were experiencinghigh health costs due to exposure to lime dust.

Ali B.A, Ballal S.G,Alba A.A et al (1998) showed in theirepidemiological study that particulate matter like cementdust causes increased risk of respiratory diseases.

A case study in alumina industry by P.K.Pattajoshi (2006)

revealed that permissible limit values exceeded in locationslike lime plant bunker area and recommendation of a gooddust extraction was given.


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Related Research Work (contd)

C.M.Hammond (1980) stressed the importance of further

research in design of local exhaust ventilation hoods.

Krieger,Dames and Moore(1995) showed in their risk

assessment project that fugitive emissions of a lime factorycontributed to air pollution.

Many such studies have been cited in project which show

that particulate matter is an occupational health hazard and

emphasize on the use of dust captive systems for effectivemanagement of occupational health in any industry.


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Site Visit Findings

With focus on status of work zone area, following observations

were made

Dust generation during handling and transfer of powdered

raw material, material unloading and vehicle movement.

Fugitive emissions generation due to dust leakage from

conveyors and conveyor transfer points.

Too much dust in ambience

Dust control being done by dry cyclone based dust extraction

systems.


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Problems in Existing Dust Control System

Low cleaning efficiency Higher dust emission from stack

Ducts get frequently choked

Inadequate suction at the hoods

Puffing taking place at suction points

Work zone is dusty

Dust deposited on floor of work place

Loss of precious material Adverse effects on workers health

Breakdowns and repetitive problems for long duration


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Site Pollutant Characteristics

Reacts with water to form Ca (OH) 2and lots of heat

Reacts with CO2to form CaCO3

Exposure causes severe eye irritation, burning, skin irritation and

respiratory irritation.

Concentration Limits

Components Common name OSHA PEL ACGIH TLV

Calcium oxide Quick Lime 5 mg/m3 2 mg/m3

Calcium

carbonate

Limestone 15 mg/m3 10 mg/m3

Magnesium

oxide

Periclase 10 mg/m3 10 mg/m3

Dolomite Dolomite 15 mg/m3 10 mg/m3


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Basics of Industrial Ventilation

Industrial ventilation is a method of controlling workerexposure to airborne toxic chemicals or flammable vapors

by exhausting contaminated air away from the work area

and replacing it with clean air.

Local exhaust ventilation is used in industries to capturedusts.

Components

Hood

Ductwork

Air cleaning device

Fan

Stack


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Selection criteria for appropriate dust

collection equipment

Following factors are considered Contaminant concentration

Gas stream characteristics

Contaminant characteristics

Energy consideration Dust disposal

Efficiency required

Comparing all the factors for various dust collectors, bag filter was

selected for the proposed dust extraction system.


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Design of Bag Filter Based Dust Extraction System

Dust is generated in work zone area during materialtransfer by conveyor belt.

As compared to the present dust control system, a better

and more efficient dust extraction system is designed for

conveyor belt ventilation. Changes made

Review of suction air quantity based on ACGIH norms

Designing a number of suction hoods and their location

Designing a bag house filter

Designing a stack of suitable height


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Design Philosophy

Several empirical formulae are available for calculationsand design. Amongst them, the design guidelines and

criteria given by the American Conference of

Governmental Industrial Hygienists (ACGIH) in

Industrial Ventilation A Manual of Recommended

Practice are most widely followed by engineers to design

local ventilation systems.

The ACGIH ventilation manual contains dozens of design

plates of ventilation systems for specific industrial

applications that have been used to control emissions. Thenext slide is the ACGIH design plate for conveyor belt

ventilation.


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Design Calculations

DATA OF EXISTING SYSTEM FOR ONE JUNCTION HOUSE BELT CONVEYOR

BELT WIDTH: 1.2 metre

BELT SPEED: 1.5 m/sec

HEIGHT OF FALL: 3 metre

MATERIAL: LIMESTONE (~ 50 mm size) LIME (less than 3 mm) Calculation of suction velocity

According to ACGIH Design Norms for conveyor belt ventilation; Suction airquantity Q is greater than or equal to 2800 m3/hr/m belt width for belt speeds over1 m/sec. Considering 20 % design cushion for leakage air entrance from either sideof the hood, the total volume of air to be considered for designing the componentsof the dust extraction system may be

Air Quantity Q = 2800 m3

/ hr x 1.2 = 3360 m3

/ hr However as the material is lime powder, which is very dry and dusty, a material

factor of 2 is considered.

Suction Air Quantity Q = 3360 x 2 m3 / hr = 6720 m3/ hr


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Design Calculations (contd)

Since the height of fall is more than 1 metre, we add an extra exhaust air of

1700 m3/ hr at the other end. It is proposed to install three suction hoods as

shown.


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Air quantity from hood H1= air quantity from hood H2

Thus, the air quantity to be sucked from hood H3= 1700 m3/ hr

The total Suction Air Quantity Q to be considered for further designing of components of

dust extraction system = Q1 + Q2 + Q3 = 6720 + 6720 + 1700 = 15140 m3/ hr

HOOD DESIGN FOR HOOD 1 AND 2

The suction hood is fabricated from MS plates. The capture velocity of a hood ranges

from 0.8 m/sec for fine powder to 2.5 m/sec for grains and 3 m/sec for lumps.

Air Quantity = 6720 m3/ hr = 1.87 m3/ sec

Now, air quantity Q = area A x capture velocity

Taking capture velocity of hood to be 1 m/sec1.87 m3 / sec = A x 1 m / sec

Area of hood = 1.87 m2


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For a square section, Area = Side2Hood size = 1.87 m x 1 m

Selecting a canopy hood and considering the belt width, the dimensions are

obtained as shown.

1.87 m

1m


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DUCT DESIGN

Duct velocity is in the range of 18 to 22 m/sec for horizontal ducts and 14

to 18 m/sec for vertical ducts. The inspection and cleaning doors are to be

provided at suitable locations in the ducting layout. The duct shall be of

circular cross section.

Suction Air Quantity = 6720 m3/ hr = 1.87 m3/ sec

Q = x velocity

where D is the diameter of duct.

Taking duct velocity to be 22 m/sec

Q = x 22

D = 328 mm

A duct of size 325 mm is selected.

4

2D

4

2D


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HOOD DESIGN FOR HOOD 3


Now, air quantity Q = area A x capture velocity

0.472 m3/ sec = A x 1 m / sec

Area of hood = 0.472 m2

A square canopy hood of 0.7 side is considered.

DUCT DESIGN


Diameter comes out to be 165 mm. A duct of size 165 mm is selected.

SYSTEM CAPACITY

Considering 20 % design cushion for leakage, ageing, etc

System Capacity = 15140 m3/ hr x 1.2 = 18000 m3/ hr


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BAG FILTER SYSTEM

Inlet dust load as measured = 10 gm / Nm3

As per latest CPCB norms, Stack norms = 150 mg / Nm3

Designing shall be done for a lower value of 100 mg/Nm3

Bag filter efficiency =

Bag filter efficiency = 99%Air to cloth ratio is generally taken as 90 m/hr.

Air quantity coming to the bag filter system = 18000 m3 / hr

Cloth area = = 200 m2

Selecting bags of diameter 160 mm and height 3.6 m as per standard bags

available in the market;Cloth area / bag = = x 0.16 m x 3.6 m = 1.8 m2

Number of bags required = = 111 or say 112.

%100

10000

100100010

ratioclothtoAir

QuantityAir

LD

8.1

200


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DESIGN OF ID FAN

The type of fan for dust extraction application shall be centrifugal type with provision ofdirect type. The impeller of the fan shall be backward curved radial type. Noise level at

1 m distance from fan and motor assembly shall be limited to 85 db. For this purpose,

the noise silencer shall be provided at the fan outlet side.

Capacity required = 18000 m3 / hr

Static Pressure = 300 mm WC

Rating of motor =

Air Quantity = 18000 m3 / hr

H = 300 mm of water column

Assuming Fan efficiency = 0.8 Motor efficiency = 0.95 Derating Factor is 0.9 for 50 C

Rating of motor = = 23.64 kW

Motors available in market are of standard horsepower. Thus the rating of electric motor

shall be 30 kW and speed 1500 rpm.

factorderatingefficiencymotorefficiencyfanHQ

36001021.1

9.095.08.03600102300180001.1


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STACK DESIGN

Norms are that the stack height should be at least 30 m or 15 m above the nearest

tallest building in the immediate surrounding area of the stack. The building

nearest to the place of proposed stack is 35 m in height.

Thus stack height will be 50 metre

Air Quantity = 18000 m3 / hr = 5 m3 / hr

Air Quantity = x efflux velocity of stack

Efflux velocity of stack is taken to be 15 m/ sec for effective dispersion of dust

emissions from the stack

5 m3 / hr = x 15 m/sec

D = 650 mm

4

2D

4

2D


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INSTRUMENTATION AND ELECTRICS

An electrical panel and the power will be made available by a suitable feeder up to the

motor control center (MCC). The following instruments also need to installed

1. Flow measurement of fan

2. Temperature measurements of incoming air in duct, inlet of bag filter

3. Differential pressure measurements across bag filter

SAFETY ASPECTSThe following safety aspects need to be kept in mind during the design and operation of

the dust extraction system.

1. Bag filter casing design shall withstand shut off head of fan

2. The fan and bag filter shall be interlocked with the belt conveyor system so that

the fan will suck air only when the belt conveyor is running.

3. The hopper below the bag filter shall have minimum 8 hrs of storage capacity.4. Lightning arrester, orange and white stripes and aviation lamps shall be installed

on the stack.

5. Port holes, ladder and platform for stack monitoring shall be provided with all the

stacks and be maintained in good condition.


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UTILITY REQUIREMENTS

The following utilities are needed to be set up alone with the dust extraction system.

1. All electrical supplies and works including wiring, cabling etc and power facility

at 40 kW 3 phase connection, 415 V 50 Hz

2. Compressed air facility of 20 m3/hr at pressure 6-8 kg/cm2 is required for bag

cleaning

3. Industrial water facility

4. Fire Fighting water facility

5. Drinking water facility

6. Handling and hosting facilities- moonbeam with electric hoist shall be provided

for motor and fan maintenance

7. Screw conveyors to remove captured dust from the bottom of the hoppers underthe fabric filter and (if used) mechanical collector. Alternatively, air conveying

(pneumatic) systems and direct dumping into containers can be used for dust removal

from the hoppers.


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Conclusion and Recommendations

This project was commenced to design an appropriate de-dusting system for dustextraction during material transfer in an industry. This project addresses the basicnecessity of a healthy work zone area i.e. occupational hygiene for greater productivity.

CONCLUSIONS

1. Bag filter based de-dusting system has been suggested with cleaning efficiency of99%. Latest CPCB norms of 100 mg / Nm3 (stack emissions) has been considered in

line with latest industrial trends following Air Act, CREP etc2. The total dust extraction system for the junction house consists of 3 suctionhoods, ductwork, butterfly dampers at appropriate locations, a modular casing entry, off-line, pulse-jet bag filter, a centrifugal ID fan and a self supported stack.

3. Proper dust conveying velocities have been selected to avoid dust settling in ducts.

4. Sufficient cushion has been kept in the air volume calculations to maintain proper

suction at hoods.5. The designed dust extraction system not only keeps the work atmosphere freefrom air pollution but also aids in precious material (lime) being recovered, which canbe ploughed back into the process.


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RECOMMENDATIONS

In addition to the more efficient de-dusting system designed for air pollution control in

work zone, the following steps are recommended to be brought into practice in the Lime

Shop as routine job.

1. Provision should be made to spray water on the feeders before charging the raw

material into shaft kilns in Lime Shop. This would ultimately result in less dust

generation, healthy environment for the workers and stack emissions inside the norms.

2. Stationary and mobile super suckers or industrial vacuum cleaners should be

utilized regularly as per requirements in various areas and floors for better

housekeeping.

3. In house training program on pollution control systems at the Shop and feedback

clarification should be done for the workers.

4. Scheduled and routine maintenance of the pollution control systems should be

carried out.

5. Handling of lime, a sticky and hygroscopic material, is an operationally difficult

task. Special moisture repellant polypropylene filter bags can be used.


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6. Hopper heaters, zero speed switches, level switches and DP switches

which ensure the smooth and trouble free operation of the system can be

used.

7. Dust masks meeting the NIOSH N95 rating should be made compulsory

for workers.

8. Full clothing to cover arms and legs, gloves, safety glasses or face shield

should be provided to workers handling lime.9. Eye wash and shower station should be readily available.

10. Offline cleaning should be preferred as high level particulate emission

takes place during on-line cleaning process.


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THANKS

Documents

Design of Pollution Control Equipment