PRESENTATION

ON

ELECTROSTATIC PRECIPITATOR

PRESENTED BY:-Sh. RAMESH BABU VSh.

B.CHAKRABORTYSh. S. NASKARMs. NIBEDITA PADHY

OUTLINE OF PRESENTATION

BASIC PRINCIPLE ,CONSTRUCTION DETAILS & OPERATING SYSTEM OF ESP

ESP PERFORMANCE & FACTORS AFFECTING THE PERFORMANCE

ESP PERFORMANCE IMPROVEMENT PLAN

NEW MEASURES/TECHNOLOGY BEING TAKEN TO REDUCE ESP EMISSION

NEED OF ESP

MECHANICAL & ELECTRICAL PROBLEMS

NEED OF ESPNEED OF ESP

ASH CONTENT IN INDIAN COAL IS HIGH (30~45)%.

20% OF ASH COLLECTED IN (BAH), REMAINING 80% IS

CARRIED ALONG WITH THE FLUE GAS.

CREATES AIR POLLUTION RESULTING IN HEALTH HAZARDS.

DUST COLLECTION IS NECESSARY THROUGH ESP IN THE

BOILER.

ESP EFFICIENCY IS OF THE ORDER OF 99.9%.

WEAR OF ID FAN BLADES ARE REDUCED DUE TO DUST

RESULTING IN REDUCED MAINTENANCE WORK IN ID FANS

BOILER CIRCUIT WITH PRECIPITATOR

ADVANTAGESADVANTAGES

• COLLECTS ALL TYPES OF DUST.

• LARGE VOLUME HANDLING CAPACITY .

• OPERATES OVER A WIDE RANGE OF INLET

CONDITIONS .

• LOW PRESSURE DROP (RARELY CROSSES 10–15mm of WC)

• LESS MAINTENANCE

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,

A

G

COLLECTING ELECTRODE EMITTING ELECTRODE

70 KV DC

e - A +

G -

PRINCIPLE OF PRECIPITATION

e -e -

Ge -

G -G -

G -

G -

ESP - PARTICLE COLLECTION

ESP - REMOVAL OF PARTICLE

ESP PROCESS

COLLECTING ELECTRODE,GROUNDED

RAPPING MECHANISMDISCHARGE ELECTRODE WITH-ve HIGH TENSION (20-60KV)

4

DUST LAYER

1

1.ELECTRON EMISSION

2

2.DUST PARTICLE CHARGING

3

3.MIGRATION

4.DUST COLLECTION

5

5.RAPPING

-ve

-ve

GD SCREENS

COLLECTIVE AND DISCHARGE ELECTRODES

RAPPING MOTORS

SHAFT & SUPPORT INSULATORS

HOPPER & INSULATOR HEATERS.

RECTIFORMERS.

ESP CONSTRUCTION DETAILSESP CONSTRUCTION DETAILS

UNIFORM GAS DISTRIBUTION IS

IMPORTANT FOR PROPER

FUNCTIONING OF ESP.

GAS DISTRIBUTION SCREENS AND

DEFLECTION PLATES ARE

PROVIDED TO ENSURE THIS.

ANEMOMETER READINGS ARE

TAKEN ACROSS THE CROSS

SECTION OF THE ESP DURING

COMMISSIONING & GD TEST

GAS DISTRIBUTION SCREENGAS DISTRIBUTION SCREEN

GAS FLOW

COLLECTING ELECTRODE

COLLECTING ELECTRODE

EMMITTINGELECTRODE

Flue gas flow Flue gas flow

SCHEMATIC DIAGRAM

ELECTRONICCONTROLLER

HIGH VOLTAGE RECTIFIER TRANSFORMER

415 V , 1 ØSUPPLY

ELECTROSTATIC PRECIPITATOR

EC C E C

POWER CIRCUIT

S F C O/L L

TH

RFC

E

C

HVRC

TR

RECTIFIER

SH

STAGE II SUPPORT INSULATOR

ESP ROOF TOP MANHOLE

ASH LEVEL INDICATOR (ALI)

INTEGRATED OPERATING SYSTEM

MICROPROCESSOR BASED CONTROL & MONITORING TECHNOLOGY.

FEATURES:- OPERATES THE FIELDS IN CHARGE RATIO MODE.

MINIMUM POWER CONSUMPTION WITH CHARGE RATIO OPTIMISATION.

AUTOMATIC ESP START UP AND SHUTDOWN FROM UCB.

BAPCON

INTERMITTENT CHARGING TECHNIQUE.

AUTOMATIC SELECTION OF CHARGE RATIO BASED ON V-I

CURVES.

REMOTE CONTROL FACILITY.

ANNUNCIATION OF WARNING & TRIP ALARM.

BASE CHARGE SETTING AND MEASUREMENT.

RAPCON

CONTROL & SURVEILLANCE OF OPERATION OF RAPPING MOTORS.

STARTING ,REPEAT & RUN TIME CONTROL.

COMCON

ST#I (200)

ST#II(500)

1. GAS FLOW RATE (m3/sec) 358.4 1030

2. APH OUTLET TEMPERATURE 136 ºC 140 ºC

3. I/L DUST CONCENTRATION (GM/NM3) 60.7

82.56

4. O/L DUST CONCENTRATION (MG/NM3) 300 396

5. PRECIPITATOR TYPE 2FAA -7 X 3211190-2 FAA -

6x45- 4x48125 -2

6. NO. OF PRECIPITATORS PER BOILER 1 1

7. PERFORATED GD SCREENS 2(INLET) 2/1

(IL/OL)

8. NO. OF FIELDS IN EACH GAS PASS 7 12

9.EFFICIENCY 99.49 % 99.52%

10. PRESSURE DROP (IN mmWC) 15 18

11. VELOCITY OF GAS AT ELECTRODE(m/s) 0.869 1

12. TREATMENT TIME IN SECONDS 24.975 27

13. ASH RESISTIVITY 2.5*10 @13

2.5*10 @13

ESP SPECIFICATIONSESP SPECIFICATIONS

ST# 1 ST#2

NO. OF ROWS OF COLLECTING ELECTRODES PER FIELD 38

65

NO. OF COLLECTING PLATES PER FIELD 304

390

TOTAL NUMBER OF COLLECTING PLATES PER BOILER 8512

9360

NOMINAL HEIGHT OF COLLECTING PLATES IN METERS 9

12.5

NOMINAL LENGTH OF THE COLLECTING PLATE (MM 400 750

SPECIFIC COLLECTING AREA (M2/M3/S) 166.5

167

COLLECTOR SYSTEMCOLLECTOR SYSTEM

EMITTING SYSTEMEMITTING SYSTEM

ST#1 ST#2

• TYPE OF EMITTING ELECTRODES SPIRAL

WITH HOOK

• SIZE (DIAMETER IN mm) 2.7 2.7

• NO. OF ELECTRODES IN FRAME 32

36

FORMING ONE ROW

• NO. OF ELECTRODES IN EACH FIELD 1184 1728

• TOTAL NO. OF ELECTRODES PER BOILER 33152

82944

• PLATE TO WIRE SPACING (mm) 150 150

PARAMETER VARIATION EFFECT ON ESP PERFORMANCE

SL NO

ESP PARAMETER VARIATION ESP PERFORMANCE REMARKS

1 GAS FLOW RATE

2 GAS TEMPERATURE

3 ESP I/L CONCENTRATION

4 FLY ASH RESISTIVITY

5 SULPHER IN COAL

6 MOISTURE IN GAS

7 FLY ASH ALKALI CONTENT

8 FLY ASH UNBURNT

PARAMETER VARIATION EFFECT ON ESP PERFORMANCE

SL .NO.

ESP PARAMETER VARIATION

ESP PERFORMANCE

REMARK

9 FLY ASH PARTICLE SIZE

10 GAS VELOCITY

11 ASPECT RATIO

12 TREATMENT TIME

13 GAS SNEAKAGE

14 GAS DISTRIBUTION POOR

15 REENTRAINMENT

PARAMETERS THAT CAN BE CONTROLLED DURING RUNNING

EXTERNAL FACTORS AFFECTING ESP PERFORMANCE

BOILER OVERLOAD.

IMPROPER ASH EVACUATION FROM ESP HOPPERS.

INADEQUATE MAINTENANCE/MAINTENANCE PRACTICES.

UNHEALTHINESS OF TRANSFORMER RECTIFIER UNIT.

ELECTRIC HEATERS NOT FUNCTIONING.

SUDDEN STOPPAGE OF MILLS.

MECHANICAL PROBLEMS

POOR ELECTRODE ALIGNMENT DISTORTED/SKEWED COLLECTING PLATE VIBRATING DISCHARGING ELECTRODE DAMAGED DISTRIBUTION SCREEN SHOCK BAR BENT EXCESSIVE ASH DEPOSIT ON EMITTING/COLL ELECTRODE EROSION OF GRIP COUPLING RAPPING SHAFT DAMAGE FALLING/HANGING HOPPER DEFLECTION PLATES

COLLECTING ELECTRODE DAMAGED PORTION ST-II

CRM SHAFT DAMAGED PORTION

SHOCK BAR DAMAGED

ELECTRICAL PROBLEMS

UNSTABLE ELECTRICAL CONTROLS

RAPPING MOTORS/HEATERS NOT IN SERVICE

HEAVY ARCING/SPARKING

TRANSFORMER TRIPPING

INSULATOR CRACK

DAMAGED SHAFT & SUPPORT INSULATOR

PIN BROKEN

SUPPORT INSULATOR CRACK

BACK CORONABACK CORONA

++

++

--

-

-

-

-

-

+

+

+

+

+

ASH

LAYER

INTERMITTENT CHARGING INTERMITTENT CHARGING WITH BASE CHARGING

ESP PERFORMANCE AND

IMPROVEMENT PLAN

OBJECTIVES

ESP PERFORMANCE MONITORING

ESP PERFORMANCE OPTIMISATION

ENSURE MAXIMUM FIELD AVAILABILITY

PREPARATION OF DAILY EXCEPTION REPORT & WEEKLY REVIEW

POG RECOMMENDATIONS

DURING UNIT OPERATION DURING OIL FIRING DURING OVERHAULING

ROUTINE CHECKS

MONITORING OF ESP PARAMETERS.

HEALTHINESS OF HOPPER HEATERS .

HEALTHINESS OF ASH LEVEL INDICATOR.

HEALTHINESS OF RAPPING MOTORS.

MONITORING OF ASH FLOW IN HOPPERS.

AIR INGRESS IN ESP AREAS (FLUE GAS DUCT,

APH HOPPER, ESP HOPPER AREA & ESP ITSELF)

CLEANLINESS OF ESP ROOF AND EQUIPMENTS.

DURING OIL FIRING

ONLY TWO PASS IN SERVICE THAT TOO WITHOUT CHARGE RAPPING FREQUENCY MORE

HOPPER CHOKING MONITORING HEATERS IN SERVICE

WORKS CARRIED OUT DURING UNIT O/H

MECHANICAL:

WATER WASHING

INTERNAL REPAIR

REPLACEMENT / REPAIR OF EQUIPMENTS.

REPLACEMENT & ALIGNMENT OF RAPPING SHAFTS.

INSPECTION FOR POSITION OF RAPPING HAMMER SEQUENCE .

INSPECTION OF SPRING BACK ON EMITTING ELECTRODES AND

REPLACEMENT AS PER REQUIREMENT .

ALIGNMENT OF THE ELECTRODES AND RECTIFICATION OF HITTING

POINT.

REPLACEMENT / REPAIR OF THE COLLECTING ELECTRODES AND G.D

SCREENS .

INSPECTION OF ESP CASING AND HOPPERS FOR WEAR AND PATCHING

AT

ERODED PORTION .

SERVICING OF THE RAPPING GEAR BOXES AND ALIGNMENT .

REPLACEMENT OF BROKEN SUPPORT AND SHAFT INSULATOR.

DISMANTLING OF THE FLUSHING APPARATUS AND REPAIR.

REPLACEMENT OF EXPANSION BELLOWS.

REPAIR / REPLACEMENT AND CLEARING OF NOZZLES, HOLDERS, TIPS

AS

PER REQUIREMENT .

SERVICING OF HP/LP V/VS.

WORKS CARRIED OUT DURING UNIT O/H (cont.)

ELECTRICAL:-

CLEANING/CHECKING OF SHAFT/SUPPORT INSULATOR AND HOPPER

HEATERS.

CLEANING OF HVR,EC PANELS,MOTOR & HEATER MODULES.

REPAIR OF CRM,ERM & GDRM AND REPLACEMENT OF OIL SEALS.

REPLACEMENT OF SILICA GEL IN HVR.

CHECKING /REPAIRING OF DISCONNECTING SWITCH .

ATTENDING HVR OIL LEAKAGE.

CLEANING / REPLACEMENT OF ALI PROBES AND CARDS.

MEGGERING & RESISTANCE MEASUREMENT OF ALL INSULATOR &

HOPPER

HEATERS.

RELUGGING OF ALL BURNT CABLES.

TRIAL RUN OF ALL MOTORS AND HEATERS.

AIR LOAD TEST .

WORKS CARRIED OUT DURING UNIT O/H

NEW MEASURES/TECHNOLOGIES BEING TAKEN TO REDUCE EMISSION

FLUE GAS CONDITIONING

AMMONIA DOSING SYSTEM HAS BEEN INSTALLED IN BOTH 200 MW & 500MW UNITS BEFORE ESP INLET

PERFORMANCE TEST IS CARRIED OUT BY M/S SGS (India) Pvt. Ltd- Environment services-

Kolkata ON 08.01.2008-22.01.2008.

THERE IS A HIGH COST OF INSTALLATION AND RECURRING RUNNING COST

Effect of NH3 on SPM emission in 200 MW unit

0.020.040.060.080.0

100.0120.0140.0160.0

NH3 05Kg/hr NH3 10Kg/hr NH3 15Kg/hr NH3 25Kg/hr NH3 35Kg/hr

Rate of NH3 injection

Em

issi

on

co

nce

ntr

atio

n

Emission (mg/NM3)

•The emission was less than 50 mg/Nm3 at ammonia dosage rate of 10 Kg/hr. ( I.D.Fan-A O/L- 49.80 & I.D.Fan-B O/L – 23)•The emissions were less than 100 mg/Nm3 even after 5 hours of stopping of dosing.

THE EMISSION WAS LESS THAN 100mg/Nm3 at AMMONIA

DOSAGE RATE OF 20Kg/hr .

(ID FAN –A O/L:- 62.25 & ID FAN-C O/L :- 74.81)

Effect of NH3 on SPM Emission of 500MW

117.3

68.562.8 59.0 55.7

77.5

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

NH3 12 Kg/Hr NH3 20 Kg/Hr NH3 30 Kg/Hr NH3 40 Kg/Hr NH3 50 Kg/Hr NH3 30 Kg/Hr2FO

Rate of NH3 injection

Co

nce

ntr

atio

nEmission ( mg/NM3)

GD TESTS IN UNITS

GAS DISTRIBUTION TESTS ARE BEING CONDUCTED IN ALL THE UNITS ON A REGULAR BASIS TO IMPROVE ESP EFFICIENCY

UP-GRADATION OF ESP

• TO MEET REVISED EMISSION REQUIREMENT

• TO AVOID UNFORESEEN OUTAGES

• TO OPTIMIZE INSPECTION AND MAINTENANCE

SCHEDULE

• UP-RATING / CHANGE IN PLANT CAPACITY

• CHANGE IN FUEL OR RAW MATERIAL

CHARACTERISTICS

• CHANGE IN OPERATING CONDITION OF BOILER

• CORROSION OR EROSION OF MECHANICAL

COMPONENTS

• DETERIORATION IN PERFORMANCE DUE TO AGING

UPGRADING ESP

OPTION 1 OPTION 2

ADDITION OF ESP FIELD IN EACH PASS IN PARALLEL OR IN SERIES AS PER SPACE AVAILABILITY.

OPTION 3 :

OPENING SCREEN

HIGHLY RELIABLE DISPLAYS IN %LOCAL & REMOTE OPERATIONCR MODEWARNING & TRIP ALARMS

BHEL’s Advanced Precipitator CONtroller (BAPCON)

67

VARIOUS DISPLAYS IN BAPCON

- Precipitator current 5 U.V. LimitE Precipitator voltage 6 C.R.H Sparks per minute 7 Pulse current

limitO Im limit 8 Repeat time 1 Is limit 9 Address2 S control Peak & valley

voltage3 Time control P Base charge4 Stabilization time L Base charge

current

70

ALARMS IN BAPCON

o TRIP ALARMS:

o E1 - Safety chain broken.

o E2 - Eprom faulty.

o E3 - Power supply failure.

o E4 - Over voltage

o E5 - Ash level very high (for 10 min.)

o E6 - T/R temp very high / TH. Ovld.

o E7 - Bucholtz bottom float.

o WARNING ALARMS:

o T/R temp high.

o Bucholtz top float.

o Ash level high.

o Under voltage.

PARAMETERS IN RAPCON CONTROLLED BY IOS - P.C.

RAPPING FACTOR. PROGRAM SET NO. AUTO ON/OFF. MANUAL ON/OFF. SET REAL TIME. SET RAPPING TIME. GET RAPPING TIME. RESET ALARM.

RAPCON DISPLAY

IF ALIGNMENT IS NOT PROPER, LEAD TO UNEVEN CORONA GENERATION.

CORONA DISCHARGE WILL BE CONCENTRATED IN THE AREAS WHERE THE

ELECTRODES ARE CLOSER.

THIS UNEVEN CORONA LEADS TO UNEVEN PARTICLE CHARGING AND LOSS OF

EFFICIENCY.

THE SPARK-OVER VOLTAGE DEPENDS ON THE MAXIMUM CLEARANCE BETWEEN

THE ELECTRODES IN A FIELD.

IN CASE THIS CLEARANCE IS LESS, EVEN AT ONE PLACE IN THE ENTIRE FIELD,

THEN THE ENTIRE SECTION VOLTAGE COMES DOWN AND THE EFFICIENCY

REDUCES.

ELECTRODE ALIGNMENT

THE T/R CONTROL PANELS SHOULD BE ADJUSTED TO FEED THE MAXIMUM USABLE POWER TO THE RESPECTIVE FIELDS.

THE POWER REQUIREMENT VARIES CONTINUOUSLY WITH THE CHANGE IN PROCESS PARAMETERS WHICH IS TAKEN CARE BY AUTOMATIC CONTROLS.

POWER INPUT TO ESP FIELDS

DURING 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.

ASPECT RATIO

Aspect ratio = Effective length of ESP Collecting electrode height

IT IS THE TIME AVAILABLE FOR CAPTURING THE DUST PARTICLE.

MORE TREATMENT TIME AT REASONABLE VELOCITY IMPROVES

THE COLLECTION EFFICIENCY.

PROBABILITY OF CAPTURING THE RE-ENTRAINED PARTICLES

IMPROVES WITH TIME.

TREATMENT TIME

Treatment time, sec = Effective length of ESP in m Flue gas velocity in m/s

EXCESSIVE SPARKING REDUCES THE OPERATING VOLTAGE, EFFECT EFFICIENCY,

THUS REDUCING LIFE OF THE ELECTRODES.

FIELD STRENGTH IS ADJUSTED IN SUCH A WAY THAT LIMITED

SPARKS TAKES PLACE.

WITH SOME SPARKS/MIN. , MORE STRONG FIELD IS OBTAINED.

IF SPARK IS TOO HIGH : FREQUENT COLLAPSE OF FIELD WILL REDUCE THE

EFFICIENCY AND INCREASE THE EROSION OF EMITTING ELECTRODE.

SPARK RATE SHOULD BE KEPT WITHIN THE DESIRABLE LIMIT BASED ON

ELECTRODE LIFE, OPERATING VOLTAGE, PARTICLE RE-ENTRAINMENT AND

EXPLOSIBILITY LIMIT OF THE PROCESS GAS. BY ADJUSTING THE T/R CONTROLS.

SPARK RATE

ESP GAS FLOW DISTRIBUTION PATTERN THROUGHOUT THE

CROSS SECTION OF THE ESP SHOULD BE UNIFORM.

IF IT IS NOT WITHIN THE SPECIFIED LIMITS, THE

EFFICIENCY WOULD BE AFFECTED.

GAS DISTRIBUTION INSIDE

IF RAPPING FREQUENCY IS TOO HIGH : NOT ALLOW THE DUST TO

DEPOSIT ON COLLECTING ELECTRODE,THUS RE ENTRAINMENT

OF THE COLLECTED DUST.

IF RAPPING FREQUENCY IS TOO LOW : VERY THICK LAYER OF

ASH WILL DEPOSIT ON C.E. WHICH WILL CAUSE CONSIDERABLE

VOLTAGE DROP OR CAN CAUSE BACK CORONA IF RESISTIVITY IS

VERY HIGH .

INADEQUATE RAPPING CAUSES EXCESSIVE SPARKING, REDUCES

THE POWER INPUT TO THE ESP AND REDUCES THE EFFICIENCY .

RAPPING SYSTEM

• GAS VOLUME

• PARTICLE SIZE DISTRIBUTION

• GAS TEMPERATURE

• GAS VELOCITY

• RESISTIVITY

EFFECT OF PROCESS PARAMETERS ON ESP PERFORMANCE

IN CASE OF HIGHER GAS VOLUME, WHICH MAY OCCUR

FROM A CHANGE IN FLUE IN THE BOILER, THE GAS

VELOCITY IN THE ESP EXCEEDS AND THE TREATMENT

TIME REDUCES.

THIS CAUSES PARTICLES TO ESCAPE THE ESP FIELDS

WITHOUT COLLECTION THEREBY REDUCING THE

EFFICIENCY.

LOW GAS VOLUME USUALLY DO NOT REDUCE THE

EFFICIENCY.

GAS VOLUME

DECIDED BY COAL QUALITY, THE COAL MILL SETTINGS AND

BURNER DESIGN A PRECIPITATOR COLLECTS PARTICLES MOST

EASILY WHEN THE PARTICLE SIZE IS COARSE.

THE GENERATION OF THE CHARGING CORONA IN THE INLET

FIELD MAY BE SUPPRESSED IF THE GAS STREAM HAS TOO

MANY SMALL PARTICLES (LESS THAN 1 ΜM).

VERY SMALL PARTICLES (0.2 - 0.4ΜM) ARE THE MOST

DIFFICULT TO COLLECT BECAUSE THE FUNDAMENTAL FIELD-

CHARGING MECHANISM IS OVERWHELMED BY DIFFUSION

CHARGING DUE TO RANDOM COLLISIONS WITH FREE IONS

PARTICLE SIZE DISTRIBUTION

IN CASE OF DEVIATION IN GAS TEMPERATURE FROM THE

DESIGNED VALUE, THE RESISTIVITY OF THE DUST PARTICLE

CHANGES AND IF IT EXCEEDS THE CRITICAL VALUE OF

RESISTIVITY THEN THE EFFICIENCY COMES DOWN.

IF GAS TEMPERATURE DROPS BELOW THE ACID DEW POINT

TEMPERATURE, THEN THERE IS A DANGER TO THE ESP

INTERNALS AS THEY MAY GET CORRODED

GAS TEMPERATURE

VARIATION OF ESP EMISSION W.R.T. GAS TEMPERATURE IS NOT

LINEAR.

FOR 20 DEG. C (15 %) INCREASE OF GAS TEMPERATURE,

EMISSION SHOOTS UP BY ABOUT 2 TIMES.

VELOCITY IS DECIDED BY THE GAS FLOW AND COLLECTION EFFICIENCY

REQUIRED.

THERE ARE TWO FORCES ACTING ON THE DUST PARTICLES HAVING

PERPENDICULAR

TO EACH OTHER AS SHOWN IN DIAGRAM.

HIGHER THE GAS VELOCITY, HIGHER THE

CARRYOVER OF DUST PARTICLES WITHOUT

COLLECTION –HENCE REENTERTAINMENT .

VERY POOR VELOCITY ALTERS THE FLOW

DISTRIBUTION AND EFFECTS SETTLING

OF DUST PARTICLES.

GAS VELOCITY

FO

RC

E D

UE

T

O V

EL

OC

ITY

.ELECTRIC FORCE

RESULT

ANT F

ORCE

GRAPH SHOWS THE EFFECT ON ESP EMISSION, DUE TO INCREASE OF GAS FLOW ONLY, WITHOUT CONSIDERING VARIATION IN GAS TEMP. & DUST LOAD.

VARIATION OF ESP EMISSION W.R.T. GAS FLOW IS NOT LINEAR. FOR 25 % INCREASE OF GAS FLOW, EMISSION SHOOTS UP BY

ABOUT 5 TIMES.

IT IS DEFINED AS THE ABILITY OF THE COLLECTED PARTICULATE MATTER TO ACCEPT OR RELEASE AN ELECTRIC CHARGE.

LOW RESISTIVITY : PARTICLES GIVE UP THEIR CHARGE TOO EASILY AND BECOME RE-ENTRAINED IN THE GAS

TOO HIGH RESISTIVE DUST DOES NOT READILY CHARGE& GIVE UP ITS NEGATIVE CHARGE TO COLLECTIVE ELECTRODE .

RESISTIVITY DEPENDS ON: - GAS TEMP., GAS MOISTURE,

SULPHUR CONTENT IN COAL,

ASH COMPOSITION (SiO2,

Na2O3 ,CaO etc)

CARBON CONTENT IN ASH

PARTICLE SIZE OF DUST.

LOW RESISTIVITY - 104-107 OHM-CM NORMAL RESISTIVITY - 108-1010 OHM-CM HIGH RESISTIVITY - MORE THAN 1010 OHM-CM

RESISTIVITY

RE

SIS

TIV

ITY

(oh

m-

cm

)

HOT-END ESP

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