esp_abc

ABC of

E.S.P.

ROOF

RECTIFIER TRANSFORMER

COLLECTING ELECTRODE

CERM

DISCHARGE ELECTRODE

GAS DIST.PLATE

SUPPORT INSULATOR

DERM

PRECIPITATION PROCESS

• HIGH VOLTAGE ELECTROSTATIC FIELD OF DISCHARGE ELECTRODE

CREATES CORONA

• CORONA LEADS TO IONISATION OF GAS AND IMPARTES A NEGATIVE

CHARGE TO

THE ASH PARTICLES.

• THE NEGATIVELY CHARGED ASH PARTICLE GET ATTRACTED TOWARDS

POSITIVELY

CHARGED COLECTING PLATE AND GET COLLECTED.

FACTORS AFFECTING ESP PERFORMANCE

1. Gas distribution into the treatment zone

2. Discharge electrode

3. Collecting electrode

4. Rapping mechanism

5. Gas volume

6. Fly ash property – ‘Resistivity’

7. Hopper levels

8. Electrical conditions

1) GAS DISTRIBUTION INTO THE TREATMENT ZONE

Optimum use of collecting area can be ensured if the flow is

uniformly distributed across the ESP.

Otherwise non uniform flow will result in higher velocity in some

sections.This results in lower collection efficiency.

The actual measured velocity should lie with in 25 % of the

average velocity.

Electrostatic attraction

Gas velocityResultant velocity

2) DISCHARGE ELECTRODES

Discharge electrodes produces corona discharge.

The inlet fields can have aggressive electrodes i.e. electrodes should have more no of spikes

To overcome above problem :

• Avoid spark erosion

• Enable peak finder in the controller

• Divide total cross-section into electrical sub zones to provides a partial

solution to the breakdown of total field

• Take care during erection to avoid excessive mechanical stress on the

electrodes wires and dynamic alignment has to perfect

Slacking and breaking of discharge electrodes leads to breakdown

of whole field.

3) COLLECTING ELECTRODES

REQUIREMENTS TO BE SATISFIED BY COLLECTING PLATES :

• Rigid and yet good oscillation behavior so that rapping produces

high acc.

• Surfaces to be as smooth as possible to permit high flashover

limits.

• Freedom of thermal movement for CE to cope with sudden temp

change.BOWING OF COLLECTING ELECTRODES ARE BIGGEST THREAT

WARPED PLATES ARE THREAT TO ELECTRICAL EFFICIENCY

Plate distortion reduces the clearance from wire to plate.

Sparkover voltage ( hence power to the entire field ) is

limited by a single wire which is closest to the plate.

WARPED PLATES ARE A THREAT TO ESP’s AVAILABILITY.

Sparks will be concentrated at those points of closest

separation rather than random distribution. This often leads to

broken wires which may ground it as well.

WARPED PLATES DONOT RAP PROPERLY

A warped plate may dampen rapper forces and fail to

uniformly release dust from the surface.

• Very low frequency of rapping leads to more accumulation of

dust on

plates leading to lower efficiency.

• Very high frequency of rapping re-entrainment of dust into the

flue gas

• Lowering the input voltage/power to the electrodes at time of

rapping

gives better performance Field No

Ash collection in %

Rapping frequency

Time of rapping

1 79 20 32 18 10 63 2.4 4 154 0.44 2 30

4) RAPPING MECHANISM – FREQUENCY & DURATION

If the gas volume is high the velocity of ash will increases

resulting in

lower treatment time. This lead to lower collection effeciency.

High gas volume occurs because of :

• High mass flow due to excess ingress of air in air heater /

system

• High gas temperature because of soot deposition on the heat

transfer areas.

5) GAS VOLUME

I:I: Ion Current Ion Current DensityDensity

E: E: Electric FieldElectric Field

R:R: Dust Layer Dust Layer ResistivityResistivityCollecting Collecting

PlatePlate

E = R x IE = R x I

Ohm’s Law:Ohm’s Law:

Resistivity

Resistivity

Flue Gas Temperature

Flue Gas Composition

Moisture Content

SO3 Content

Fly Ash Mineral Composition

Sulfur

Sodium Oxide

Dust Resistivity

Surface Conduction <290° F

Ion Conduction is over surface of dust layer

1/4” Dust Layer(typical) Collecting Plate

Volume Conduction >440° F

Ion Conduction is through dust layer

1/4” Dust Layer( typical ) Collecting Plate

Resistivity

Flue Gas Temperature

Flue Gas Composition

Moisture Content

SO3 Content

Fly Ash Mineral Composition

Sulfur

Sodium Oxide

Resistivity,Resistivity,ohm-cmohm-cm

Temperature, F°Temperature, F°

200200 300300 400400 500500 600600 700700

Dry Air6.6% H20by Volume

13.5% H20

10101010

101099

10101111

10101212

Moisture Conditioning of Cement Kiln Dust

20% H20

IMPACT OF ASH RESISTIVITY - BACK CORONAIMPACT OF ASH RESISTIVITY - BACK CORONA

• In a high resistive dust a potential gradient is created within the

dust

layers which causes the occurrence of local sparks in the dust

layer.

• This spurious discharges are called “back corona” which

opposes the

positive corona.

• These local sparks in the accumulated dust layer causes the

particle to

be re-entrained into the gas flow.

BACK CORONABACK CORONA

3. Electric Wind Brings Dust

Laden Gas In

4. Crater Starts To Fill With Dust

1. Crater Forms

2. Positive Corona Flows

From Bottom Of Crater

To overcome back corona, field controller is operated in CHARGE To overcome back corona, field controller is operated in CHARGE

RATIO MODE / BACK CORONA MODE / PULSE ENERGIZATION RATIO MODE / BACK CORONA MODE / PULSE ENERGIZATION

MODEMODE

Ash Resistivity Vs Temperature Vs SulphurAsh Resistivity Vs Temperature Vs Sulphur

1. Modify gas temperature1. Modify gas temperature

2. Introduce humidity2. Introduce humidity

3. Condition with sulfur trioxide, ammonia or 3. Condition with sulfur trioxide, ammonia or

sodium compounds sodium compounds

4. Pulse energization or intermittent energization4. Pulse energization or intermittent energization

5. Increase ESP size5. Increase ESP size

Coping with High ResistivityCoping with High Resistivity

Resistivity,Resistivity,ohm-cmohm-cm

Temperature, F°Temperature, F°

200200 300300 400400 500500 600600 700700

Dry Air6.6% H20by Volume

13.5% H20

10101010

101099

10101111

10101212

Moisture Conditioning of Cement Kiln Dust

20% H20

SO3 Conditioning

SO3 Injection Nozzles

S Parameters Before NH3

dosingAfter NH3dosing

NH3 andControllerOptimization

1 Flue gas temperature 0C

155 155 155

2 Flue gas flow Nm3/sec 48.61 48.61 48.61

3 Flue gas humidity(volume %)

6.4 6.4 7.0

4 Steam generation te/hr

199 199 199

6 Ammonia flow kg/hr 0 15 15

7 SPM in the flue gas mg/Nm3

720 160 70

AMMONIA INJECTION – A CASE STUDY

Normal Full Wave Waveforms

00

00

KV waveform

mA waveform

KVPEAK KVMIN

1 Half Cycle

8.33 mSec

1 Full Cycle1/60th Sec.

Intermittent Energization

00

00

KV

mA

KVPEAK KVMIN

OFF

1 Half Cycle

ON

Full Cycle

OFF

ON

Voltage decays but does not go to zero during

off time

( + ) ( – ) ( + ) ( – )

Precipitator current (mA) drops to zero

when SCRs are gated off at zero crossing

Energization Method -vs- Electrical Conditions

• Energization KVEnergization KVAVGAVG KV KVPKPK KV KVMINMIN Current Current

DensityDensity• Full Power 32.7 41.0 25.2 32.0

• Knee of Curve 30.1 34.4 27.0 7.0

• Intermittent 24.5 48.4 20.3 6.6 Energization

V = PPTR Voltage KV

T = PPTRCurrent

Milliamps

1100

900

700

500

300

100

0

0 10 20 30 40 50

Moderate BackModerate BackCorona Corona

Severe BackSevere BackCorona Corona

MisalignmentMisalignment

Moderately HighModerately HighAsh Resistivity Ash Resistivity

Dust Deposits onDust Deposits onHigh Voltage Electrode High Voltage Electrode

SPARKSPARK

SPARKSPARK SPARKSPARK

Grounded HighGrounded HighVoltage Electrode Voltage Electrode

Abnormal Precipitator Current Voltage Abnormal Precipitator Current Voltage CurvesCurves

ELECTRICAL PARAMETERSELECTRICAL PARAMETERS

Different components in the electrical circuit are :

• Electronic panel :- Provides regulated AC voltage

• Linear reactor :- To limit S/C current during sparking

• HF choke circuit :- To protect the Trf. From surges

• Rectifier transformer :- Convert regulated AC to HV DC

• ESP controller :- Regulate,Monitor and optimize the input

Power

• Bus support insulator

OPTIMZED SETTINGS OF THE CONTROLLEROPTIMZED SETTINGS OF THE CONTROLLER

Even if the sparking voltage fluctuates continuously, AVC must

maintain operating voltage of ESP as close to the spark-over

voltage as possible to get max dust efficiency.

Arcing must quickly be detected and current quickly be cut.

After the spark, favorable conditions must be restored in shortest

time.

Optimizing the performance

Step

Im

Is

80% Is

mA

DC KV

Slope

SPARKS PER MINUTE = 1000 / ( STEP % x SLOPE % )

Spark Regulation in Normal operationSpark Regulation in Normal operation

When a spark occurs, current is reduced by a value of I setback

depending of type of spark. For a low intensity spark detected by

digital sensing, current is reduced in steps till favorable medium

is restored.

For high intensity sparks current is reduced to zero. After a

predefined time of T Quench (deionisation time)current is

increased through fast ramp to a step value in time T recovery

followed by a normal slope to a value which is just below the

spark over voltage.

This control action differentiates between normal flashover

and follow up flashover((Flashover which occur within a

predefined period of time after detection of a normal flashover)FRC CONTROLFRC CONTROL

The fast ramp control quickly reestablishes the current to a limiting value much faster than the normal rate of rise. This comes into action when many sparks may occur with in a short period of time reduce the current to a lower average.

Resistivity ohm-cmResistivity ohm-cm

SCA RequiredSCA Requiredforfor

99.95%99.95%EfficiencyEfficiency

15001500

10001000

500500

10101010 10101111 10101212

Dust Resistivity FactorDust Resistivity Factor

Origin

al

Add-On Original

Add-On

Frequently Asked Questions on ESPFrequently Asked Questions on ESP

WHY IS CYCLIC RAPPING ADVISABLE ?WHY IS CYCLIC RAPPING ADVISABLE ?

To reduce possible entertainment of the collected dust. This allows dust after deposition to build up into a layer like a cake and fall during rapping.

HOW CAN THE BEST OUT OF CONTROLLER BE EXTRACTED ?HOW CAN THE BEST OUT OF CONTROLLER BE EXTRACTED ?

By maximizing precipitator current, by correct setting of slope and step ( which govern spark rate ), by enabling the FRC control , and by enabling peak finder option. Charge Ratio can save energy.

WHY IS CLEARANCE BETWEEN CE & DE IS SO IMPORTANT ?WHY IS CLEARANCE BETWEEN CE & DE IS SO IMPORTANT ?

This clearance decides the spark-over voltage. Spark will occur even if clearance is OK at all the places throughout the field, but at one place the clearance is less.

WHY IS A REACTOR PROVIDED AT THE TRANSFORMER ?

It reduces the damage to the field by limiting the current when a galvanic short occurs between CE and DE.

WHAT DOES SPARK RATE INDICATE ? DOES IT DEPEND ON SPARK OVER VOLTAGE OR CURRENT ?

Suppose slope is set at 20%. Normally, 99% = 9.9 minute. So 20% = 2 minute.

If step = 100% (I.e. slope starts from zero ), then 2 minute is the time taken by the rectifier to reach the rated current.

If step is set at 5%, time between spark = 5% of 2 minute = 6 sec. In other words, sparks per minute = 1000 / ( S% x T% ) = 1000 / 20x5.

Spark Rate indicates how well an ESP is operating. A higher spark rate means considerable wear & tear and reduced mean field strength, i.e. eff.

PERFORMANCE OF ESP - INDAL’S EXPERIENCE

Are electrical readings normal

ELECTRODE SYS. RAPPING MECH. ELECTRICAL SYS.

GAS DISTRIBUTION

Does ESP perform satisfactorily ?END

Undersized ESP

Unknown process factor

NO

YES

OK OK OK

YES NO

.

Is alignment within tolerance

Are DE wires freeof sagging

Are DE top framescorrect, leveled

Are Collecting platesStraight, plumb

Is field free of broken wires

Straighten / Replace

sagging wires.

Adjust at support points.

Check forwarpage.

Straighten / replace / cut.Jammed at

Bottom Guide ?

Cut out brokenwires / removeforeign object

NO

NO

NO

NO

YES

YES

YES

NOYES

ELECTRODE SYSTEM

.

Are DE & CE areclean (<5 mm)

Is stack emissionfree of puffing

Check for drive / cam failure.

Check if DERM pin insulator has broken or out of place.

Adjust rapping frequency.

Check for misaligned / fallen hammers.

Adjust Collecting Electrode rapping frequency.

Check whether gas velocity is within design limit.

YES

NO

RAPPING MECHANISM

YES

NO

.

Is Controllerfunctioning

properly

Are insulators freeof dust build-up

Check the Step and Slope settings.

Check the spark sensitivity setting.

Check the firing-circuit of the SCRs.

Clean insulators & Corona Shield.

Think of purge air.

Replace broken insulator.

Check the heater operation.

YES

NO

ELECTRICAL SYSTEM

YES

NO

THANK YOU

Proactive Maintenance = More Effectiveness @ Less Cost

Mech

an

ical A

vailab

ilit

y

Maintenance Cost Expenditures

Data/Condition Based

Planned

Breakdown

(Efficiency)

(Eff

ecti

ven

ess)

Reliability / Risk Based

A

B

A1

A2

Proactive Maintenance Strategy Benefits

Key Ingredients of Complex Change

Will toChange

Vision DESIREDCHANGE

+ +Resources + SkillsAction

Plan+ =

Incomplete Change

Will toChange

Vision NO START


Plan+ =

Incomplete Change

Will toChange

VisionCONFUSION+ +

Resources + SkillsActionPlan

+ =

Incomplete Change

Will toChange

Vision FALSE START


Plan+ =

Incomplete Change

Will toChange

Vision FRUSTRATION+ +Resources + SkillsAction

Plan+ =

Incomplete Change

Will toChange

Vision ANXIETY+ +Resources + SkillsAction

Plan+ =

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