esp principle and design1 bac

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Welcome to

Electrostatic Precipitator

Plant services

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EFFECTS OF AIR POLLUTION

•GENERAL– VISIBILITY REDUCTION DUE TO SCATTERING OF LIGHT

FROM SURFACES OF AIR BORNE PARTICLES

–

MATERIAL DAMAGE– AGRICULTURAL DAMAGE DUE TO ASH DEPOSITION

• LOSS AND REDUCTION OF GREEN PLANT PIGMENT

CALLED CHLOROPHYLL RESULTING IN YELLOWING AND

EVEN DROPPING OF LEAVES.

– DAMAGE TO BUILDINGS, MONUMENTS OF MARBLE

ETC.

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EFFECTS OF AIR POLLUTION

• HUMAN HEALTH

– OCCUPATIONAL SKIN DECEASE

– AFFECTS LUNGS - SILICOSIS FOR FOUNDRY WORKMEN

– RESPIRATORY CONDITION DUE TO TOXIC AGENTS

• ACUTE CONJUNCTIONS DUE TO CHEMICAL DUSTS, FUMES

AND GASES

– DISORDER DUE TO PHYSICAL AGENTS - ENVIRONMENTAL

HEAT OR LOW TEMPERATURE

– EYE IRRITATION, COUGH AND BREATHLESSNESS

– FORMATION OF CARBOXYL HEMOGLOBIN WHICH

PREVENTS O2 CARRIAGE BY BLOOD

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GROWTH OF PROBLEMS OF AIR POLLUTION

• Rapid economic growth

•

Rapid industrialization and urbanization• Increased industrial production

• Population explosion

• Growth in demand for power

• Increase in requirement for thermal power plants

• More number of old coal based power plants

designed for high emission & low ash content coal

• High ash content or deterioration in quality of coal

reserve

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TYPES OF DUST COLLECTING EQUIPMENTS

Sl.NO. Type of Dustcollectors

Pressure

dropmmWc

Collection

effieicny,%

Remarks

1. Gravity Settling

chamber

25-30 30 to 40 Less efficiency, more

space required andnot suitable for powerplant

2. Inertial Collectors  Impact 

Centrifugal(cyclones)

30 – 40

60-80

30 – 40

75 to 80

  Not for power plant 

Were widely used inpower plants butcan not satisfy thepresent daypollution controlrequirement

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Sl.NO.

Type of Dustcollectors

Pressuredrop

mmWc

Collectioneffieicny,

%

Remarks

3. Scrubbers(wet) 50 to 60 80 to 90 Used mainly in procesindustries and can not

satisfy the pollutioncontrol requirement

4. Electrostaticprecipitators

15-25 99.99 Can meet any efficiencand mostly used in all

power plants.5 Fabric Filter 125 to150

99.99 Can meet any efficiencand used many poweplants abroad. Gainingmomentum in Indian

Power plants also.

TYPES OF DUST COLLECTING EQUIPMENTS

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PURPOSE OF POLLUTION CONTROL EQUIPMENT

•Recovery of material for economic reasons –  Pulp and Paper Industries (Sodium Sulphate)

• Removal of abrasive material in the dust to

reduce wear and tear of the Fan components

• Removal of objectionable matter in the dust

 –  NO2 and SO2

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ADVANTAGES OF ELECTROSTATIC PRECIPITATORS

•

Very high collection efficiency• Low pressure drop

• capacity to collect sub-micron particles

• Robust construction - Longer life

• Less maintenance

•

Adaptability

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ELECTROSTATIC PRECIPITATOR PRINCIPLE

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ELECTROSTATIC PRECIPITATOR WORKING PRINCIPLE

The precipitation process involves 4 main functions

• Corona generation

• Particle charging

• Particle collection

• Removal of particles

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ESP - CORONA GENERATION

• Due to the ionisation of gas molecules, + ve ions, -ve ions and freeelectrons are generated.

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CORONA DISCHARGE IN SPIRAL ELECTRODE

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ESP - PARTICLE CHARGING

• The -ve charges of ions and free electrons travel towards +ve electrodeand the +ve charges of ions travel towards -ve electrodes.

• When -ve ions travel towards +ve electrodes, the -ve charges get

attached to the dust particles and thus the dust particles areelectrically charged,

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ESP - PARTICLE COLLECTION

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ESP - REMOVAL OF PARTICLE

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ESP SIZING THEORY

DEUTSCH - ANDERSON EQUATION

Collection Efficiency = 1 - e - w. SCA

where,

w = Migration velocity

SCA = Specific Collecting Area

• Migration Velocity –  The velocity which the dust particle travel towards the collecting electrode

under the influence of electric field.

• Specific collecting area

 –  Amount of collecting area required to be provided to collect dust in gasflow rate of 1 m3/s.

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DEFINITIONS

• Flue gas velocity, m/s = Flue gas flow in m3

ESP effective cross section m2

• Aspect ratio = Effective length of ESP

Collecting electrode height

• Treatment time, sec = Effective length of ESP in m

Flue gas velocity in m/s

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DEFINITIONS

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EFFECT OF VARIOUS PARAMETERS

Gas velocity

• velocity is decided by the gas flow and collection efficiencyrequired

•

Higher the gas velocity, higher the carryover of dustparticles without collection - Re-entertainment

• Very poor velocity alters the flow distribution and effectssettling of dust particles

•

optimum velocity depends upon the application willimprove the performance.

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EFFECT OF VARIOUS PARAMETERS

Aspect ratio

• During the rapping, the falling of dust particle take a trajectoryform

•

Lower the aspect ratio, the trajectory dust travel along with gasflow without falling in to hoppers - Leads to re-entrainmentloss.

• Higher the ratio, performance will be good

•

optimum aspect ratio depends on allowable velocity, requiredcollection efficiency and available space.

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EFFECT OF VARIOUS PARAMETERS

Treatment time

• Time available for capturing the dust particle

• more treatment time at reasonable velocity improves the

collection efficiency• Probability of capturing the re-entrained partilces improves

with time.

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ENVIRONMENTAL REGULATIONS IN INDIA

Prior to 1984

• 1974 – water act• 1977 – water cess act

• 1981 – air act

The cost of compliance was more than that of non-compliance:

• 1986 – Environmental Protection Act

comprehensive act with ‘command & control’ 

• Future trend is to internalize the environmentalimprovement cost

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REVISED EMISSION STANDARD(GAZETTE NOTIFICATION BY MINISTRY OF E&F DATED 19 05 93)

• SUSPENDED PARTICULATE MATTER (SPM) : < 150 mg/Nm3

•

STANDARD ALSO STATES THAT• FOR POWER PLANTS

•CAPACITY LESS THAN 62.5 MW AND

COMMISSIONED BEFORE 01 01 1982 : 350 mg/Nm3

• FOR CEMENT PLANTS (TOTAL EMISSIONS)

• CAPACITY LESS THAN 200 TPD : 400 mg/Nm3

• CAPACITY MORE THAN 200 TPD : 250 mg/Nm3

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ENVIRONMENTAL REGULATIONS

 – TODAY’S WORLD

World Bank’s ‘proposed guide lines’ 

• For new thermal power plants (TPP) forcapacities ≥ 50 MW

• Pollution control at project formulation levelitself 

• Site specific emission guide line

• Propose standard of 50 mg/Nm3•  Aided projects are to abide by this

• Further implication on technical, economic & 

institutional

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Emission of various pollutants under the

business-as-usual scenarioProjection

0.1582.82434.022.0736.22011

0.1252.19338.019.6605.52006

0.0891.75259.117.9511.02001

0.0491.340.3016.162428.01996

SOXNOXSPMCOCO2

POLLUTANTS (MT)YEAR

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COMPARISON OF PARTICULATE EMISSION

NORMS IN OTHER COUNTRIES

150India

4356Sweden

194250Australia

3950Europian community3950Germany

2836USA

ppmMg/Nm3Country

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DESIGN DATA REQUIRED FOR ESP

• Application

• Process data

• Gas composition• Gas pressure

• Gas moisture

• Dust composition

• Particle size distribution

• Basic design data

• Gas flow rate

•

Gas temperature• Inlet dust concentration

• Environmental data

• Outlet emission

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FACTORSW CONSIDERED FOR ESP SELECTION

• Gas flow

• Gas temperature

• Inlet dust concentration

•Required outlet emission

• Required collection efficiency

• Moisture in gas

• Sulphur content in coal

• Ash resisitivity• Particle size distribution

• No. of ESPs per boiler

• Minimum number of fields required

• Minimum Specific collecting area• Maximum gas velocity

• Minimum aspect ratio

• Maximum area connected to one TR set

• Collecting electrode spacing

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ESP DESIGN CONSIDERATIONS

HIGH INLET DUST REQUIRES LARGER ESP

EMISSION VS ESP EFFICIENCY FOR

DIFFERENT DUST BURDEN

99.25

99.5

99.75

100

25 50 75 100 125 150

EMISSION REQUIREMENT-

mg/Nm3

   E   F   F

   I   C   I   E   N   C   Y   R   E   Q   U   I   R   E   M

   E   N   T -

20g/Nm3

40 g/Nm3

60 g/Nm3

80 g/Nm3

100 g/Nm3

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ESP DESIGN CONSIDERATIONS

ESP COLLECTION EFFICIENCY VS SIZE

0

1

2

3

4

5

6

7

8

9

90 91 92 93 94 95 96 97 98 99 100

COLLECTION EFFICIENCY - %

   C

   O   M   P   A   R   A   T   I   V   E   E

   S   P   S   I   Z 

BASE : ESP SIZE FOR 90% = 1

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ELECTROSTATIC PRECIPITATOR

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ELECTROSTATIC PRECIPITATOR