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Electrostatic PrecipitatorElectrostatic Precipitator

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.

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

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

TYPES OF DUST COLLECTING EQUIPMENTS

Sl.NO.

Type of Dustcollectors

Pressuredrop

mmWc

Collectioneffieicny,

%Remarks

1. Gravity Settlingchamber

25-30 30 to 40 Less efficiency, morespace required andnot suitable for powerplant

2. Inertial Collectors Impact Centrifugal

(cyclones)

30 – 4060-80

30 – 4075 to 80

Not for power plant Were widely used in

power plants butcan not satisfy thepresent daypollution controlrequirement

Sl.NO.

Type of Dustcollectors

Pressuredrop

mmWc

Collectioneffieicny,

%Remarks

3. Scrubbers(wet) 50 to 60 80 to 90 Used mainly in processindustries and can notsatisfy the pollutioncontrol requirement

4. Electrostaticprecipitators

15-25 99.99 Can meet any efficiencyand mostly used in allpower plants.

5 Fabric Filter 125 to150

99.99 Can meet any efficiencyand used many powerplants abroad. Gainingmomentum in IndianPower plants also.

TYPES OF DUST COLLECTING EQUIPMENTS

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

ADVANTAGES OF ELECTROSTATIC PRECIPITATORS

• Very high collection efficiency

• Low pressure drop

• capacity to collect sub-micron particles

• Robust construction - Longer life

• Less maintenance

• Adaptability

ELECTROSTATIC PRECIPITATOR PRINCIPLE

ELECTROSTATIC PRECIPITATOR WORKING PRINCIPLE

The precipitation process involves 4 main functions

• Corona generation• Particle charging• Particle collection• Removal of particles

ESP - CORONA GENERATION

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

CORONA DISCHARGE IN SPIRAL ELECTRODE

ESP - PARTICLE CHARGING

• The -ve charges of ions and free electrons travel towards +ve electrode and 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 are electrically charged,

ESP - PARTICLE COLLECTION

ESP - REMOVAL OF PARTICLE

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 gas

flow rate of 1 m3/s.

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

DEFINITIONS

EFFECT OF VARIOUS PARAMETERS

Gas velocity

• velocity is decided by the gas flow and collection efficiency required

• Higher the gas velocity, higher the carryover of dust particles without collection - Re-entertainment

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

• optimum velocity depends upon the application will improve the performance.

EFFECT OF VARIOUS PARAMETERS

Aspect ratio

• During the rapping, the falling of dust particle take a trajectory form

• Lower the aspect ratio, the trajectory dust travel along with gas flow without falling in to hoppers - Leads to re-entrainment loss.

• Higher the ratio, performance will be good• optimum aspect ratio depends on allowable velocity, required

collection efficiency and available space.

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.

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 environmental improvement cost

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

ENVIRONMENTAL REGULATIONS – TODAY’S WORLD

World Bank’s ‘proposed guide lines’ • For new thermal power plants (TPP) for

capacities ≥ 50 MW• Pollution control at project formulation

level itself• Site specific emission guide line• Propose standard of 50 mg/Nm3• Aided projects are to abide by this• Further implication on technical,

economic & institutional

Emission of various pollutants under the business-as-usual scenario

Projection

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

COMPARISON OF PARTICULATE EMISSION NORMS IN OTHER COUNTRIES

150India

4356Sweden

194250Australia

3950Europian community

3950Germany

2836USA

ppmMg/Nm3Country

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

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

ESP DESIGN CONSIDERATIONSHIGH 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

EFFIC

IEN

CY

REQ

UIR

EM

EN

T -

%

20g/Nm3

40 g/Nm3

60 g/Nm3

80 g/Nm3

100 g/Nm3

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 - %

CO

MP

AR

AT

IVE E

SP

SIZ

E

BASE : ESP SIZE FOR 90% = 1

ELECTROSTATIC PRECIPITATOR

ELECTROSTATIC PRECIPITATOR