Thermal Power Plant

Efficiency & PerformanceEnhancement

Fundamentals

Evaluation Methods

Corrective Actions

Fai

lure

Rat

e

No of Years

Bath Tub curve

Need For E & P Enhancement

Present Performance Conditions

Boiler Eff Unit Heat Rate RemarksUnit # 1 89.39% 2637 Both HPH not in serviceUnit # 2 87.80% 2656Unit # 3 88.48% 2497Unit # 4 87.60% 2590

APH LMTDUnit # 1 87.70Unit # 2 79.50Unit # 3 97.35Unit # 4 98.86

Equipment

§ Boiler

§ Air Heater

§ Mills

Equipment

§ Boiler

§ Air Heater

§ Mills

AREAS CONTRIBUTING TO VARIOUS LOSSES IN A BOILER

‡ COMBUSTION IN BOILER

‡ AIR HEATER PERFORMANCE

‡ MILL PLANT PERFORMANCE

‡ FANS

‡ WATER LOSSES

FACTORS AFFECTING PERFORMANCE OF COMBUSTION

¤ SURFACE CONTACT AREA OF FUEL WITH AIR

¤ AIR-FUEL RATIO

¤ RETENTION TIME

¤ COMBUSTION CHAMBER TEMPERATURE

¤ TURBULANCE IN COMBUSTION CHAMBER

¤ REMOVAL OF PRODUCTS OF COMBUSTION

LOSSES IN BOILER

• CONTROLLABLE# COMBUSTIBLE IN ASH LOSS# DRY GAS LOSS# CO IN FLUE GAS# MILL REJECTS LOSS

• UN CONTROLLABLE# MOISTURE IN FUEL# HYDROGEN IN FUEL# AIR MOISTURE# SENSIBLE HEAT IN ASH

# RADIATION AND UNACCOUNTED

COMBUSTION

• TIME

– SUFFICIENT RETENTION TIME MUST BE ALLOWED FOR THE FUEL TO STAY INSIDE THE FURNACE TO COMPLETE COMBUSTION

– TIME REQUIRED/AVAILABLE DEPENDS• FUEL TYPE,QUALITY,SIZE

• FURNACE SIZE

• VELOCITY– DRAUGHT

COMBUSTION

• TEMPERATURE

– EFFECTS THERMAL DIFFUSION OF REACTING MOLECULES DUE TO INCREASED VELOCITY OF MOLECULES WITH INCREASE IN TEMPERATURE

– INFLUENCE THE RATE OF REACTION

• FACTORS AFFECTING TEMPERATURE

– HEAT ABSORBED BY FURNACE– HEAT ABSORBED BY REACTANTS TO BRING THEM TO

IGNITION TEMPERATURE– HEAT ABSORBED BY NITROGEN IN AIR

COMBUSTION

• TURBULANCE

– MECHANICAL AGITATION OF REACTANTS TO BRING THEM INTO PHYSICAL CONTACT

– REQUIREMENT IS MORE AT FINAL STAGE OF COMBUSTION

– LESSER THE TURBULANCE MORE CARBON LOSS– DEPENDS

• WIND BOX TO FURNACE DIFF.PR.IN CORNER FIRED BOILERS

• TERTIARY AIR IN WALL FIRED BOILERS

CARBON LOSS

• HEAT LOSS DUE TO UNBURNT CARBON LEAVING THE BOILER ALONG WITH EITHER BOTTOM ASH OR FLY ASH

COMBUSTIBLE IN ASH

1 AIR DISTRIBUTION– DISTRIBUTION– EXCESS AIR

2 PARTICLE SIZE– MILL FINENESS -200 mesh– MILL FINENESS + 75%

3 COAL QUALITY– VOLATILE MATTER

4 COMBUSTION– TIME– TEMPERATURE– TURBULANCE

FACTORS AFFECTING

AIR DISTRIBUTION

• EXCESS AIR

– AIR SUPPLIED IN ADDITION TO STOCHIOMETRIC AIR FOR COMPLETE COMBUSTION OF FUEL

• OPTIMUM EXCESS AIR DEPENDS ON

– FUEL QUALITY

– FIRING SYSTEM DESIGN

• EXCESS AIR LESS THAN OPTIMUM RESULTS

– INCREASED CARBON IN ASH

PARTICLE SIZE

† COARSER THE FUEL PARTICLE MORE THE CARBON LOSS

† MAINTAIN OPTIMUM FUEL SIZE BY PERIODICALLY MONITORING P.F.SIZE

† OPTIMUM FINENESS FOR H.V.SUB BITUMINOUS COAL

† 100% THROUGH 50 MESH

† 90% THROUGH 100 MESH

† 70% THROUGH 200 MESH

VOLATILE MATTER

« LOWER THAN DESIGNED VALUE NEEDS MORE TIME FOR COMPLETE COMBUSTION WHICH FURNACE CAN NOT PROVIDE

« LEADS TO INCREASED COMBUSTIBLES IN ASH

« REMEDY« BLENDING OF COAL

DRY FLUE GAS LOSS

• HEAT CARRIED AWAY BY THE DRY CONSTITUENTS OF FLUE GAS THROUGH THE CHIMNEY

DRY FLUE GAS LOSS

HEAT CARRIED AWAY BY DRY FLUE GAS SHD = WD*CP*(TG - TA) Kcal/Kgf WHERE WD WEIGHT OF DRY FLUE GAS Kgm/Kgf CP SPECIFIC HEAT OF DRY FLUE GAS Kcal/Kgm0C TG GAS TEMPERATURE AT AIR HEATER OUTLET 0C TA AMBIENT TEMPERATURE 0C DRY FLUEGAS LOSS = (SHD/C.V.)*100 % WHERE SHD - HEAT CARRIED AWAY BY DRY FLUE GAS Kcal/Kgf C.V. - CALORIFIC VALUE OF FUEL Kcal/Kgf

O2 MEASUREMENT

• DRY BASIS– MEASURED THROUGH ORSAT APPARATUS

• WET BASIS– WET MEASURED THROUGH ONLINE

ANALYSERS LIKE ZIRCONIA PROBE

• DIFFERENCE BETWEEN WET AND DRY O2% IN FLUE GAS

COAL FIRED BOILERS - 0.2%

FACTORS AFFECTING DRY FLUEGAS LOSS

• COAL QUALITY– MOISTURE– CARBON– CALORIFIC VALUE

• AIR INLET TEMPERTATURE– AMBIENT TEMPERTURE

• FLUE GAS QUANTITY– EXCESS AIR– AH LEAKAGE

Equipment

§Boiler

§Air Pre Heater

§Mills

AIR HEATER PERFORMANCE

• GAS OUTLET TEMPERATURE LOWER THAN OPTIMUM

– LEADS TO COLD END CORROSION

• LOSS OF HEAT TRANSFER ELEMENTS

• The optimum temp is 146 C

• GAS OUTLET TEMPERATURE HIGHER THAN OPTIMUM

– MORE DRY GAS LOSS

– RISE OF 22 deg C ABOVE OPTIMUM REDUCE BOILER EFFICIENCY BY 1%

– 20 C RISE ABOVE OPTIMUM RESULTS LOSS OF 600Kcal (approx.) HEAT IN 1 TONNE OF F.G.

FACTORS AFFECTING A.H. GAS OUTLET TEMPERATURE

• FLUE GAS O/L TEMPERATURE LOWER THAN OPTIMUM– LIGHTING AND FIRING COLD BOILER

• USE SCAPH

– AIR LEAKAGE• SEALS CONDITON• DIFF. PR. BETWEEN AIR AND F.G

• FLUE GAS O/L TEMPERATURE HIGHER THAN OPTIMUM– QTY. OF AIR PASSING THROUGH A.H.

• TEMPERING AIR ( cold air to mill)

– TEMP.OF GAS ENTERING A.H• DEPOSITS ON BOILER HEAT TRANSFER AREAS• DELAYED/SY.COMBUSTION• FEED WATER TEMP

– FOULED / CORRODED ELEMENTS– DEFECTIVE BAFFLES– QTY.OF GAS PASSING THROUGH A.H.

AIR HEATER PERFORMANCE TESTS

• PERFORMANCE ITEMS DETERMINED

– GAS SIDE EFFICIENCY– AIR LEAKAGE– X-RATIO

ARRANGEMENT OF AIR PRE HEATER

AIR HEATER CALCULATIONS

GAS SIDE EFFICIENCY

G =

F.G I/L to APH – F.G. O/L to APH with no leakage

F.G I/L to APH – Air I/L to APH

100

Air Heater Gas Efficiency

• Current Plant Performance

RIGHT LEFT RIGHT LEFTUnit # 1 59.85% 59.55% 57.90% 57.64%Unit # 2 61.25% 60.33% 59.20% 58.11%Unit # 3 64.05% 63.56% 62.08% 61.63%Unit # 4 63.82% 62.43% 61.72% 60.44%

GAS EFFICIENCY(wrt PA Temp.) GAS EFFICIENCY(wrt SA Temp.)Unit

EFFECTS OF TRAMP AIR TO BOILER

• DOES NOT CONTRIBUTE TO COMBUSTION

• OFTEN IT IS COLD

• INCREASE GAS VELOCITY THROUGH E.S.P

• INCREASES DRY FLUE GAS LOSS

SOURCES OF AIR INGRESS

• ASH HOPPER SEALS

• ASH HOPPER DOOR LEFT OPEN

• DEFECTIVE EXPANSION JOINTS

• DUCT OPENINGS (MANHOLES) UNCOVERED

• BOILER ROOF DEFECTIVE

• COLD AIR DAMPERS PASSING

Determining (X RATIO)

HEAT CAPACITY OF AIR PASSING THROUGH A.H.X RATIO = -------------------------------------------------------------------------- HEAT CAPACITY OF GAS PASSING THROUGH A.H.

WA9*CpA

X RATIO = ------------- = WG14*CpG

CpA / CpG = 0.95

F.G I/L to APH –

F.G. O/L to APH with no leakage

Air O/L to APH – Air I/L to APH

100

X Ratio

• Present Plant Performance

RIGHT LEFT RIGHT LEFTUnit # 1 85.35% 81.46% 70.92% 69.10%Unit # 2 84.34% 82.64% 68.53% 65.81%Unit # 3 91.95% 86.98% 70.14% 73.08%Unit # 4 84.77% 82.93% 72.12% 70.26%

GAS EFFICIENCY(wrt PA Temp.) GAS EFFICIENCY(wrt SA Temp.)Unit

Equipment

§Boiler

§Air Pre Heater

§Mills

MILL PERFORMANCE FACTORS

• P.F. FINENESS

– CARBON LOSS– MILL POWER CONSUMPTION

• COAL-AIR RATIO

• MILL REJECTS

EFFECTS OF P.F.FINENESS

• TOO COARSE– WEAR IN COAL PIPE– SLOWER IGNITION– POOR FIREBALL MIXING– UNSTABLE FLAME FRONT AT LOW LOADS– HIGH CARBON LOSS

• TOO FINE– INCREASED WEAR OF PULVERISER– DECREASED PULVERISER OUTPUT( INCREASE IN MILL

RECIRCULATION)– INCREASED POWER CONSUMPTION

• 1% CHANGE IN FINENESS EQUALS APPROXIMATELY 1.5% IN CAPACITY

COAL PROCEDURE FOR CHECKING FINENESS

• PERIODICAL COLLECTION OF COAL SAMPLE FROM ALL PIPE LINES OF A MILL IN TWO PLANES USING STANDARD PROBE

• BEFORE COLLECTING SAMPLE ENSURE

– MILL IS RUNNING AT MORE THAN 75% LOAD

– MILL IS RUNNING AT A STEADY LOAD FOR 30 MINUTES

– NO LOAD CHANGE TAKES PLACE DURING SAMPLE COLLECTION

£ MIX ALL THE SAMPLES COLLECTED FROM A MILL HOMOGENEOUSLY

£ TAKE REQUIRED MASS OF SAMPLE BY CONING AND QUARTERING

£ CONDUCT SIEVE ANALYSIS ON THE SAMPLE

£ OPTIMUM FINENESS£ 100% THROUGH 50 MESH£ 90% THROUGH 100 MESH£ 70% THROUGH 200 MESH

EFFECTS OF COAL AIR RATIO

• HIGH AIR FLOW¿ AFFECTS COAL CLASSIFICATION¿ REDUCES DISCHARGE OF PYRITES¿ INCREASES COAL PIPE EROSION ¿ AFFECTS IGNITION POINT¿ MORE P.A. FAN POWER CONSUMPTION

• LOW AIR FLOW¿ INCREASES COAL PIPE SPILLAGE ¿ CAUSES DRIFTING IN COAL PIPE AND ULTIMATE

COAL PIPE CHOKING

CLEAN AIR FLOW TEST

• DETERMINES– WHETHER THERE IS ENOUGH AIR TO TRANSPORT

THE COAL– AIR FLOW DISTRIBUTION IN COAL PIPES– COAL PIPE OBSTRUCTION

• METHOD

P IS MEASURED BY PITOT TUBE IN COAL PIPE AT 0.935R, 0.791R, 0.612R, AND 0.354R WHERE 'R' IS THE RADIUS OF PIPE IN INCHES

CLEAN AIR FLOW TEST

PV 0.5 AIR VELOCITY = 18.275 [ ----------------------------- ] Ft/s 1.326 Pb +0.0735 PS { ------------------} 460+T WHERE PV - PITOT TUBE DIFF.PR.IN INCHES OF WC. Pb - BAROMETRIC PRESSURE IN INCHES OF Hg. PS - STATIC PRESSURE IN INCHES OF WC. T - TEMPERATURE IN 0F

PV 0.5 AIR VELOCITY = 5.5702 [ ---------------------------------------- ] M/s 18.7113 Pb / 25.4 + PS /345.34 ( -------------------------- ) 273.3 + T WHERE PV - PITOT TUBE DIFF.PR.IN mm. OF WC. Pb - BAROMETRIC PRESSURE IN mm OF Hg. PS - STATIC PRESSURE IN mm OF WC. T - TEMPERATURE IN 0C

CLEAN AIR FLOW TEST

AIR FLOW = 0.32725*D2*V* lbs/min D - DIA. OF PIPE IN INCHES V - AIR VELOCITY ft/s -AIR DENSITY

DESIRED RESULTS

MEASURED AIR FLOW BETWEEN 135% AND 160% OFSTANDARD AIR FLOW

MEASURED AIR VELOCITIES ARE WITHIN 5% OFAVERAGE VELOCITIES

CAUSES OF MILL REJECTS

• LOW AIR VELOCITYλ LOW AIR FLOWλ AIR BYPASSING

• HIGH RE CIRCULATION RATIOλ WEAR OF GRINDING ELEMENTSλ IMPROPER SETTING OF GRINDING ELEMENTSλ OPERATING MILL WITH HIGHER FINENESSλ HIGH MOISTURE COAL/LOW MILL OUTLET

TEMPERATURE

Factors affecting Fan Performance

• Higher ambient temperatures result in less stack draft.

• ID fan capacity limitation may result in load reduction or inability to maintain desired excess air levels.

• Low excess air due to fan capacity limitation can result in– Increased slagging and fouling – High Flyash Loss On Ignition– Superheater and Reheater tube overheating– High boiler exit gas temperature

Causes for Poor Performance

Conditions causing Poor Performance of Boiler

• Non-Optimum Reheat or Superheat steam temperatures.

• Higher than design economizer exit gas temperature or

furnace exit gas temperature caused by poor combustion.

• Higher than design Re heater or Super heater De-Superheating spray flows.

• Fly ash Unburned Carbon or Loss on Ignition greater than 5% for Bituminous Coals

• High Bottom Ash Loss on Ignition.

Conditions causing Poor Performance of Boiler

• Non-Optimum utilization or distribution of primary air, secondary air

• Increased auxiliary power consumption by coal pulverizers and fans

• Reductions in capacity factors due to excessive furnace or convection pass slagging or fouling.

• Excessive boiler setting air in-leakage.

• Excessive air heater leakage.

• Increased cycle losses with increased sootblowing due to non-optimum combustion.

Conditions causing Poor Performance of Boiler

• Reductions in capacity factors due to pulverizer or fan capacity limitations.

• Reductions in capacity factors due to Superheater or

Reheater tube overheating and/or coal-ash corrosion.

Requirements for achieving Optimum operating Conditions

Requirements For Achieving Optimum Conditions

• Furnace exit must be oxidizing, preferably 3% excess O2.

• Minimal air in-leakage between the furnace exit and economizer exit.

• Pulverizer fineness of >75% passing 200 Mesh and <0.3% remaining on 50 Mesh.

• Secondary (combustion) air balanced to within ±5% between burners

• Optimum windbox to furnace differential, typically 100 mm w.c. at full load.

• Optimum Pulverizer Primary Air to Fuel Ratio. In most cases, air to fuel ratio of 1.8 to 1.

Requirements For Achieving Optimum Conditions

• Fuel balanced between each pulverizers fuel lines to within ±10% deviation from the mean.

• Pulverized coal line dirty airflow balanced between each pulverizers fuel lines within ±5%.

• Pulverized coal line clean air velocities balanced to ±2% of the mean.

• Burner mechanical tolerances with burner buckets stroked and synchronized to within ±2° (tangentially fired).

• Primary airflow metered and controlled to ±3% accuracy.

Snapshot of PHD Report

Thank You