Esp Fundamentals

7/27/2019 Esp Fundamentals

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ELECTROSTATIC

PRECIPITATOR

AN

ENVIRONMENT

SAVIOUR


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SPECIFICATION

DESIGN CODE : FAA-6*45-78125-2

FLOW : 296M3/SEC.

TEMP. : 1290C

INLET DUST BURDE :73.83gm/m3(78.66T/HR)

TREATMENT TIME :35.37 SEC.

PRESSURE DROP :20 MMWCC.E RAPPING FREQ. :1.1RPM

E.E RAPPING FREQ. :2.5 RPM

HORIZONTAL FLOW STEEL CASING PYRAMIDAL HOPPER


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jai maan sharde!

CORONA EFFECT

COLLECTING ELECTRODEEMITTING ELECTRODE


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WHAT IS CORONA ?

CORONA is an electric discharge phenomenon in which gas molecules

are ionised by the collision of electron in the region of high strength electric

field.

The electron for CORONA initiation is supplied by random source such asnatural radioactivity or cosmic rays. Under the influence of high strength

electric field these free electrons are accelerated to terminal velocity. The

rapidly moving electrons collide with the orbital electron of gas molecule

and release it from the orbit. Hence the gas molecule assumes + VE charge

and more free electrons are released. The free electrons again collide withother gas molecules, forms +VE ions and releases more free electrons . This

process continues till the energy of free electrons reduces to the level that it

can not dislodge the orbital electron of gas molecule,hence these free

electrons are captured by the gas molecules and assumes -VE charge.Under

the influence of electric field ,these -Ve charged gas molecules movetowards collecting electrode and charge the dust particles. When dust

particle gets saturated electric field is exerted on it and move towards

collecting electrode where it gives up its charge and stick there due to

intermolecular cohesive/adhesive forces. More the intensity of electric field,

more fast and more the no. of free electrons, accordingly more ionisation&more efficiency of ESP.


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LINE DIAGRAM OF ESP EC-HVR CKT.

VE

VE

HVRC

SHR

ICE-C

FIRING CKT.

ACRHVR

HFC415 V

A.C.

THYRISTER

FILTER VOLTAGE

FILTER CURRENT

ACR-TO LIMIT THE P/CURRENT IN CASE OF FLASH OVER ON D.C.SIDE

SHR-SHUNT RESISTER,1V=FULL CURRENTHVRC=HIGH VOLTAGE RESISTER CKT.,400MICRO AMPS.

HFC-HIGH FREQ. CHOKE,PROTECTS HVR FROM SURGE OCCURING DURING SPARKING


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FACTORS AFFECTING ESP

PERFORMANCE

RESISTIVITY OF DUST PARTICLES

FLUE GAS VELOCITYPARTICLE SIZE & FIELD STRENGTH

RAPPING FREQUENCY

SPARKS RATE

HOPPER EVACUATION


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RESISTIVITY OF DUST PARTICLES

Resistivity of dust particles play major role in ESPperformance

A too high resistive dust does not readilycharge&give up its negative charge to collective electrode

whereas low resistive dust particle readily gives upits negative charge and assumes positive charge.

Inlet flue gas temp ,sulpher content & moisturecontent play major role in controlling resistivity of

flue gas.Low resistivity - 104-107 ohm-cm

Normal resistivity- 108-1010 ohm-cm

High resistivity - more than 1010

ohm-cm


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RESIST

IVITY(ohm-cm)


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FLUE GAS VELOCITY

There are two forces acting on the dust particles havingperpendicular to each other as shown in above diagram.

The first one is due to flow of gas and the second one isdue to electric force on the ionized dust particleperpendicular to the motion of gas.

The path followed by the dust particle will be resultantof two forces as shown above.

The efficiency of ESP decreases with increase in velocity& decrease in voltage.

C.E C.EE.E

ELECTRIC FORCEFORCE

DUE

TOV

EL.

A

BC


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PARTICLE SIZE & FIELD

STRENGTHThe efficiency of ESP is governed by DEUTSCH- ANDERSON equation :

Efficiency = 1-[e](-A/Q)

=Migrationvelocity= r E /2r =Radius of particle

E =Field strength

=Viscosity or frictional coefficient of flue gasA = Effective collecting area of ESP

Q = Gas flow through ESP

e = 2.718

RAPPING FREQUENCY


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RAPPING FREQUENCYRapping is also a complex phenomenon in ESP . If rapping

frequency is too high then it will not allow the dust todeposit on collecting electrode and hence the collection

/removal of dust will be difficult. Similarly, if rappingfrequency is too low then very thick layer of ash will

deposit on C.E. which will cause considerable voltage dropor can cause back corona if resistivity is very high .

C.E. RAPPING FREQ.FIELDNO.

START TIME REPEAT TIME RAPS/HR.

01 00,00 00,04 15

02 00,01 00,05 12

03 00,02 00,06 10

04 00,03 00,07 08

05 00,04 00,12 05

06 00,00 00,30 02


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SPARK RATERECOMMENDED :5-10 SPM

Field strength is adjusted in such a way

that limited sparks takes place. Withsome sparks/min. , we are able tocreate more strong field . The outagedue to spark is offset by achieving morestrong electric field with limited spark.However, if spark is too high thenfrequent collapse of field will reduce theefficiency and increase the erosion ofemitting electrode.


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ASH COLLECTION DATA PERPASS

FIELD STAGE% RAP./HR ASH

COLLECTION(KG/

RAP.)

ASH

COLLECTION(MT/

HR)

01 78.00 20 837 16.74

02 17.14 10 340 3.40

03 3.20 06 114 0.684

04 1.10 04 58 0.232

05 0.40 03 28 0.084

06 0.16 02 17 0.034

TOTAL=21.74MT/HR


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BACK CORONABack corona is the emission of +ve ions from collected dust

layer that occurs when voltage drop across the collected dust

layer exceeds the electrical breakdown strength of interstitialgases in the dust layer.

As the high resistive dust layer builds upon the collecting electrodes ,

the the dust layer and collecting electrode form a high strength

electric field. The surface of the dust layer is negatively charged ,the

interior is neutral and collecting electrode is grounded (+ ve) .Under

this condition all the ion current must pass through the dust layer to

reach the collecting electrode . This current creates an electric field

in the dust layer & when it becomes large enough the local electrical

breakdown of interstitial gases occurs. As this happens ,+ve ions aregenerated within the dust layer and are accelerated towards emitting

electrode .On the way it neutralizes the -ve charged particles and

reduces the ESP efficiency.This breakdown condn. is BACK

CORONA.The voltage reduces and current increases in thiscondition.. Resistivity 2*1011 ohm-cm


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CHARGING DURINGCOLD START UP

ESP fields should not be charged below 1000c asmoisture present will cause ash cake formation oncollecting electrode which is difficult to dislodge.

Also ESP temp.should be sufficiently higher thanthe acid dew point temp. (90-1000c)beforecharging to avoid stress corrosion cracking ofelectrodes.

Switch on the heaters 24 hrs. before BLU.Start rapping motors on intermittent mode justbefore BLU..


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CHARGING DURING OIL

FIRINGIt is recommended to charge ESP fieldsduring oil firing at ~ 50 mA.

In the charged condn., the electric fieldrepels the chloride vapour of the flue gaseswhich if comes in contact with E.E. causesbrittleness in E.E. and it may snap duringoperation.

The current during oil firing should be limitedbelow spark level as spark in oil firing maycause fire hazard.

ESP RETROFIT ACTIONS IN


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ESP RETROFIT ACTIONS INNTPC

Various ESP performance improvement programmes

have been followed in NTPC stations where SPMemissions were reported to be high.The modificationprogrammes followed are:

Additional ESPs have been retrofitted at BADARPUR TPSSt.-I, TALCHER TPS St-II & BALCO CPP (All four units).

EPMS have been installed at following stations :SINGRAULI STPS (St-I& II) , KORBA STPS (St I&II) ,RAMAGUNDAM STPS (St-I&II) , RIHAND STPS ,VINDHYACHAL STPS , FGUTPS & FARAKKA STPS (St I ).

Also dummy fields filling done at SINGRAULI (St I) andRAMAGUNDAM (St I) UNITS .

By providing EPMS in above seven stations , there hasbeen very high reduction in energy consumption (Up to70 %) and marginal reduction in SPM emission (Up to

22%).


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STACK SPM EMISSIONS BEFOREAND AFTER RETROFITTING

ADDITIONAL ESPs

SL.

NO.

STATION SPM BEFORE

RETROFITTING

SPM AFTER

RETROFITTING

1. Badarpur

(st I)

AROUND 5000 136-142

2. TALCHER TPS(St -II)

1400-1800 105-130

3. BALCO 1100-1500 160-290


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PERFORMANCE OF ESPsIn spite of retrofitting/renovation programmes , the SPM

emission of following stations are still exceeding thestatutory limit of 150mg/NM3 as per EP-AIR ACT 1981:

STATION DESIGN

SPM

PRESENT

SPM

DESIGN

EFFICIENCY

RIHAND I 100 200-350 99.81

BALCO 150 160-290 99.6

KORBA I 300 180-264 99.51

KORBA II 396 180-264 99.52

FARAKKA I 550 180-290 99.53


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REMEDIAL TECHNOLOGIESTO BE ADOPTED

STATION UNITS TECHNOLOGY

RIHAND 2*500 MW WF , FGC

KORBA 1*200 MW2*200 +3*500 MW

SCFGC

BALCO 4*67.5 MW FGC

FARAKKA 3*200 MW

2*500 MW

FGC

MODIFICATIONTHROUGH ANSALDO

LEGEND:WF :WATER FOGGING

FGC : FLUE GAS CONDITIONING

SC : SODIUM CONDITIONING

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