Seventh International Seminar

Welcome

GEECO Enercon Pvt. Limited, Tiruchirapalli, India M Somasundaram

Technical Consultant for Boilers Former General Manager / BHEL +919443259553; [email protected] Major Job References – Technical Consultancy on Boilers of Thermal Power Plants:  RCA and damages Assessment of boiler explosion- Annupur Unit-2, 600 MW, MBPMPL  Review and RCA of boiler explosion- Unit-1, 300 MW at Bandhakhar, Korba  Analysis of sonic vibration in 3x67.5 MW boilers at Kalinga Nagar  Unburnt carbon and NOx level reduction optimisation in Units 2x500 MW boilers at Maithon  Tube failure analysis of 4x600 MW boilers at Vedanta Jharsuguda  Combustion optimisation for firing varying qualities of coal in 67.5 and 120 MW boilers at Jojobera  Indonesian coal firing in Unit-5, 500 MW and Unit-8, 250 MW, Tata Power Company, Trombay  Reheater Metal Temperature and Tube failure analysis of 2x500 MW boilers at Maithon  Tube failure presentations, discussions and analysis in the Workshop for O&M Personnel of various Utilities & CPPs held at Korba  Presentations, discussions and training of O&M personnel of Adani Power Limited on Boiler and Auxiliaries, Coal, Performance/Combustion Optimisation, Tube failures, Boiler emergencies, Emission control, Inspection, etc.  Tube failure analysis of 4x135 MW boilers at BALCO Korba  Boiler Performance analysis and recommendations for combustion optimisation of NTPC Farakka #2, 200 MW boiler  Boiler Tube Leak analysis of 3x660MW boilers at Talwandi Sabo Power Limited  Mill system performance analysis at 5x660MW Mundra Thermal Power Project  Combustion behaviour of boilers with different coals and upgradation to enhance efficiency of 2x90 T/hr boilers at DCM Shriram Kota Optimization of Performance, O&M issues of Boiler and Airheater Boiler

• In a thermal power plant boiler has the role of converting the Chemical energy available in Coal/fuel to Heat energy in steam.

• The heat energy in steam is converted to Electricity by a Turbo-generator Heat Balance for Steam Process

Energy Input Steam @ pressure Feed Water

Useful Energy Energy Input STEAM PROCESS Air &Fuel Output

Energy Loss - Energy Loss - Energy Loss - Flue Gas Blow Down Piping Friction, Water Equipment, etc. Energy Output = Energy Input - Losses Optimization Of Boiler Two Main Factors •Thermal Efficiency- The conversion of chemical heat in fuel to production of steam. oHigher thermal efficiency will reduce fuel cost.

•Auxiliary Power Consumption - by Fans, mills etc. oReduction in auxiliary power will lead to increase in net power available (NET POWER= power generated - house auxiliary power consumption). Boiler Efficiency – Indirect Method

• Efficiency= 100 - Losses in % Summary of losses in Boiler Controllable Dry gas Loss % 5.542 Combustible Loss % 1.453 Carbon Monoxide Loss % 0.065 Mill Reject Loss % 0.049 % 7.109 Un-Controllable Moisture Loss % 6.523 Radiation Loss % 0.270 Air Moisture Loss % 0.200 Sensible Heat Loss % 0.415 % 7.408 Total Losses % 14.517 Efficiency (100-Losses) % 85.483 Controllable losses effected by APH sizing & performance

• Dry gas loss - APH outlet flue gas temperature and leakage

• Unburnt carbon loss - Air temperature leaving APH

DRY GAS LOSS

This is the heat carried away by Flue gas at boiler outlet The Loss is directly proportional to • Flue Gas Temperature and • Flue Gas quantity High Flue Gas Temperature Every 20 deg C increase in exit gas temp. reduces the boiler efficiency

by. Improper 1% combustion air regime setting . Unclean heat transfer surfaces . Damaged / worn-out / corroded air heater elements . Air heater leakage more . Excessive entry of cold seal air, cooling air, etc.

DRY GAS LOSS - Flue Gas Temperature Reduction methods . Operate the boiler at correct excess air. (Usually 20 % for coal) . Cleanliness of boiler surfaces . Good combustion of fuel. . Reduction of tempering air to mill. . Reduction in air ingress . Addition of heat transfer surface in economizer / redesign of second pass . Cleaning of air heater surfaces and proper heating elements . Addition of heating elements in airheater – if space is available / future provision is made DRY GAS LOSS - Flue Gas Quantity Reduction Methods

•Operate with proper Excess Air •Avoid ingress of Air •Attend to Air Heater Leakages regularly

Carbon Loss Reduction • Good burner maintenance • Check coal property and tune combustion • Ensuring consistent mill fineness. Replace Worn-out mill parts – classifier vane, rolls/bull ring segments, classifier cone • Proper secondary air adjustment • Reducing primary air to the minimum most possible • Cut-out oil support at higher loads where coal flame is stable. • Keep boiler heat transfer surface clean • Air temperature leaving APH Auxiliary Power Consumption

The Major Auxiliaries consuming Power in Boilers are .Forced Draft Fans .Primary Air Fans .Induced Draft Fans .Pulverizing Mills Factors Affecting Auxiliary Power ID Fans PA Fans • AH Leak • AH Leakage • Gas Temperature • PA Header Pr. • Duct Leakages • Mill Air Flow • Excess Air • Pressure Loss • Load/ Plant Heat Rate o AH Choking • Draught Loss Mill o AH Choking • Coal Qty. FD Fans o GCV • AH Leak o Load/ Plant Heat Rate • Wind Box Pr. • Coal • Excess Air o Moisture • Load/ Plant Heat Rate o HGI • Pressure Loss • Coal Fineness o AH Choking • Mill Condition o SCAPH Choking

Auxiliary Power Consumption Major reasons for increase in auxiliary power consumption are

1. High excess air Operation 2. Air ingress in boiler 3. Air heater leakage / Choking 4. Higher PA fan outlet pressure 5. Coal pulverization too fine Capacity Reduction in a Boiler

Fuel input Draught system • Low CV coal • ID fan limitations • Milling capacity o Pressure drops high o Grinding capacity . AH choking o Drying capacity . Chimney back pressure o Carrying capacity high o Drive capacity o High volume . AH leakages Metal temperatures high . Duct leakages • High spray requirements . High gas temperatures • Fouling of surfaces • Worn out impellers Combustion optimization Combustion optimization

In a steam generator combustion optimization means well tuning of fuel and air distribution to get the best flame temperature. Combustion optimization

Objectives . Safety of personnel and equipment . To protect equipment from failures . To produce steam at the required parameters and quality . To achieve optimum efficiency and economy during operation Combustion Diagram Plane of Combustion Completion

Point at which combustion should be completed Flame Pattern

Unacceptable Combustion Basic requirements for optimizing . Coal feeder and millcombustion should be in good operating condition . Mill classifier should be free to operate with uniform opening of all vanes . Coal-air temperature, mill airflow and total airflow are accurately measured, and control systems should be in working condition . All the burner nozzle assemblies are in good condition and set properly to ensure equal movement in all elevations . SADC system in auto mode of operation . All the flame scanners are checked, tested and the flame scanning system should be in good working condition Secondary Air Damper Control System Auxiliary Air Damper 120 Fuel Air Damper Control 100 Control 80 to keep the flame front at a 120 to maintain wind box to furnace DP 60 desired distance 40 100

20 80 fuel air damper % damper air fuel 0 60 0 20 40 60 80 100 120

mmwc 40 fuel input, % maximum mill capacity 20

Furnace to W.Box DP, 0 Over Fire Air Damper Control 30 45 60 100 to control NOx Boiler load, %

Upper Lower 100

0 50 75 100

OFA damper opening % opening damper OFA Boiler load, % Optimized Combustion 1. Combustion process should be stable as indicated by minimum furnace draft fluctuation. 2. Flame scanner pickup with adequate flame intensity should be reached. 3. Unburnt levels in bottom ash and fly ash should be minimum. 4. Flame condition looked through furnace peepholes of each elevation/ corner to ensure proper anchoring of flame front. (about 300-500 mm from nozzle tip) 5. Look at the S panel for brightness, visibility, minimum falling of clinkers, etc. 6. Superheater and reheater spray levels should be within its limit. 7. Exit gas temperature should be within its desired limit (130 – 1400C), which depends on the boiler load.

8. Emission levels of SOx and NOx should be optimum. 9. Flame temperatures measured at various elevations / burner corners to be uniformly distributed across the elevations. Air Preheaters Air Preheaters Purpose: Recover heat from the hot flue gases that leave steam generating units – (the heat from the flue gas leaving the furnace is transferred to the incoming air supply from the FD fans and PA fans)

Thus

• Improving the boiler efficiency

• Also, Provide the drying and transporting medium for pulverised coal Other advantages of Air Preheaters

• Hot air improves stability of combustion • Intensified and improved combustion • Burning poor quality fuel efficiently • High heat transfer rate in the furnace • Less unburnt • Intensified combustion permits faster load variation Types of Air preheaters Recuperative Regenerative Tubular Air Preheater, Plate Type Air Ljungstrom Air Preheater and Preheater & Steam Coil Air Preheater Rothemuhle Air Preheater (SCAPH) Heat exchangers without storage Heat exchangers with storage Two fluids flow at different temperatures One heating surface is exposed at in a space separated by a solid partition certain intervals of time, first to a hot fluid and then to a cold one Heat is transferred by Convection & Surface of APH first removes heat Conduction through the separating wall from the hot fluid and is itself heated in the process, then the surface gives up this heat to the cold fluid Process of heat transfer - STEADY Process of heat transfer - TRANSIENT Bi-Sector Air preheater Tri-sector Air Preheater Tri-sector Air Preheater Regenerative Air Preheater

Heating Element Tubular Air Preheater Steam Coil Air preheater

To protect the Cold End Heating Elements / Components of an Air Preheater from Low Temperature Corrosion. Common Terms Used for Air Preheater Performance Exit-gas temperature with This is the measured average exit-gas leakage temperature and includes the dilution (also termed “corrected”) effect of leakage through airheater seals. Exit-gas temperature with no This is the average temperature at which leakage the gas would leave the preheater if (also termed “uncorrected”) there were no leakage in the heater.

This temperature cannot be measured directly, but it can be arrived at by a simple calculation accounting for the cooling effect of the leakage. Common Terms Used for Air Preheater Performance Exit gas temperature (Uncorrected) = {(% leak / 100) x (Cpa/Cpg) x (Exit gas temperature with leakage - Air inlet temperature)} + Exit gas temperature with leakage

Cpa/Cpg = 0.95 for coal; 0.93 for Oil; 0.90 for gas Common Terms Used for Air Preheater Performance Gas Temperature Temperature of Gas entering drop minus Temperature of Gas leaving (uncorrected-not including leakage).

Air rise Temperature of air leaving minus Temperature of air entering

Temperature head Temperature of the gas entering heater minus Temperature of the air entering heater.

Common Terms Used for Air Preheater Performance

(Gas Temperature Drop ) Gas side effectiveness,%= —————————————— × 100 (Temperature Head)

(0.63 to 0.67 for Trisector air preheaters)

(Indicator of the internal condition of the air preheater-conditions inside the air heater worsen - air heater baskets corroded /eroded /fouled)

A decrease in gas side efficiency • increases measured exit gas temperature and also • decreases air outlet temperature

Factors Affecting Air Heater Performance Entering A change in entering AIR /GAS temperature will cause AIR /GAS the exit gas temperature to change in the same Temperature direction.

Changes in entering AIR /GAS temperature result in a change in Temperature Head which directly affects the drop in gas temperature

e.g: If the entering air temperature increases by 10°C, the exit gas temperature increases by (10 x gas side efficiency) °C e.g: If the entering gas temperature increases by 10°C, the exit gas temperature increases by 10 x (1 — gas side efficiency) °C

Factors Affecting Air Heater Performance Gas An increase in gas mass flow rate results in Flow a higher exit-gas temperature.

Conversely, a lower exit-gas temperature results from a lower gas mass flow entering the unit. Factors Affecting Air Heater Performance HCR Heat-capacity ratio (HCR): or “X” ratio (mass flow of air x avg. specific heat of air) (is a measure HCR = —————————————————————— of the (mass flow of gas × avg. specific heat of gas) operating

conditions) (about 0.75 for A lower than design X-ratio leads to Trisector o higher than design gas outlet temperature airheaters) . A 10 to 12% change in this ratio may alter exit-gas temperature by as much as 15 to 20°C.

A lower than design X-ratio indicate o excessive gas weight through the air heater or o airflow is bypassing the air heater. o excessive tempering air to the mills or o excessive boiler infiltration o Air preheater bypass for cold-end protection. Factors Affecting Air Heater Performance Pressure . DP changes approximately in proportion Drop to the square of the air and gas weights through the heater.

. Higher the excess air higher the air preheater pressure drop

. A build-up of heating-element deposits will increase in pressure drop.

Factors Affecting Air Heater Performance Air . Variations in pressure levels between Preheater the high - and low-pressure sides Leakage o An increase in the pressure differential will increase the leakage, while a decrease in pressure differential will reduce the leakage.

. Improper settings of the heater radial and circumferential seals will also result in an increase in leakage. Air Preheater Leakage “Direct” leakage: • Air that pass into the gas stream between the radial and axial seals and sealing surfaces o Depends on static pressure differential between the air and gas streams.

“Entrained” leakage: • Air contained in the rotor as it passes from the air side to the gas side. o Depends on the rotor depth, rotor diameter, and rotor speed.

Total airheater leakage = Direct leakage + Entrained leakage

Air Preheater Leakage Increase in air heater leakage increases the station service power requirements of FD and ID fans

Air leakage rates (with proper seal clearances) • Bi-sector regenerative - 6% to 8% • Trisector air heaters - 10 to 13%

Possible causes of increased leakage: • axial and radial seal mechanical damage or wear • sector plate mechanical damage or warping • rotor eccentricity or excessive air to gas side differential pressure A significant increase in air heater leakage warrants a physical inspection of the air heater. Recuperative air heaters: should have zero leakage (but tube failures due to corrosion or erosion or mechanical damage can result in leakage) Air Preheater Leakage Airheater leakage, % Quantity leakage air = ——————————————————————————————————————————— x 100 Quantity of wet products of combustion entering airheater

Airheater leakage, % {(Kg of wet products of combustion leaving airheater / kg of fuel fired) - (Kg of wet products of combustion entering airheater / kg of fuel fired) = ———————————————————————————————————————————————————————— x 100 (Kg of wet products of combustion entering airheater / kg of fuel fired)}

Airheater leakage, % (% CO2 in gas entering airheater - % CO2 in gas leaving airheater) = —————————————————————————————————————————— x 90 % CO2 in gas leaving airheater

(CO2 % on volume basis) O & M Issues of Air Preheater Airpreheater element erosion Tubular Air preheater Erosion  Erosion of tube at the entry side • frequent cleaning of airheater and/or • Use replaceable inserts at the erosion prone areas.

Fouling, Plugging and Corrosion

. Deposits in air preheaters are initiated by condensation of acid or Moisture from flue gas on metal surface operating at temperature below dew point.

. Degree of fouling depends on airheater heating element metal surface.

. Minimum metal temperature occurs at the cold end, as a result most fouling and corrosion occur here.

Fouling, Plugging and Corrosion

Coal firing: As coal contains less sulphur, corrosion is not normally as much a problem as fouling and hence lower exit gas temperature to a level of 120 °C is permissible.

In oil firing: • Corrosion and plugging due to corrosive products of combustion are very common. • Operating the oil fired boiler at very low excess air reduces the acid formation and hence corrosion.

The gas outlet temperature and/or air inlet temperature has to be raised to restrict the corrosion to the permissible level.

Minimum Average Cold End Temperature - Coal

195

185

175

165

155 Temperature, Deg F Deg Temperature, 145 0 1.5 3.5 5 Sulphur Content of Coal (% As Fired) Minimum Average Cold End Temperature - Oil Firing 245

235 Material Specification Case-I Material Specification Carbon steel components, Case-II 225 Corrosion resistant, low- Corrosion Resistant, low alloy steel alloy steel cold end element intermediate element, Corrosion-resistant, low- alloy steel rotor to same level as enamelled element 215

205 Material Specification Case-III Enamelled cold-end element, Enamelled intermediate 195 element, Corrosion-resistant, low alloy steel rotor to some level as enamelled element 185

Minimum Average Cold End Temp, Deg F. Deg Temp, End Cold Average Minimum 175

165 0 1 2 3 4 5 6 Sulphur Content of Fuel, % S To combat Low flue gas temperature corrosion during starting and low loads

. Use low Sulphur oil . Bypass cold air so that the gas temperature is kept at higher level . Bypass gas so that acid condensation on airheater does not occur at all . Increase the air inlet temperature by using Steam Coil Air Preheater . Recirculate the hot air . Operation with Low excess air To Combat corrosion during normal operation

• Effective on-load blowing of airheaters with SUPERHEATED steam (about 150 °C superheat). An automated TDV is required. • Use of Corrosion resistant alloys for cold end. • Use of easily and economically replaceable cold end portion of airheater • Design the boiler for high flue gas exit temperature (with lesser efficiency of boiler) • Maintain the recommended cold end average temperature (Air inlet temperature is increased mostly by SCAPH) Blocking of Air preheater baskets due to ash deposit Blocking of Air preheater baskets due to ash deposit Points to be taken care during boiler operation:

o Maintain adequate Soot blowing steam pressure & temperature (14 kg/cm2 & 350 ˚C) o Maintain minimum Average Cold End Temperature o Keep Soot blower in continuous operation during oil firing and Maintain minimum ACET of 110˚C. o Ensure Soot blower frequency is adequate by monitoring DP across APH. o Increase Soot blowing frequency for large no. of boiler start ups and also during low load boiler operation. o Ensure proper Gas distribution among Air preheaters. o Ensure required gas velocity to avoid ash settling in heating elements. o Minimise the blending percentage of imported coal. Blending percentage is to be decided upon import coal quality & moisture content and also considering other boiler operating parameters. o Ensure proper functioning of Economiser ash evacuation system. o Ensure no carry over of ash/ dust/ leaking fan lub oil along with Secondary / Primary air to APH. o Monitor the cold end heating elements condition through Observation & port light assy. o Do not operate hot end soot blowers (if provided) when the hot end heating elements are in eroded/ thinned condition. o Ensure proper combustion in boiler to avoid unburnt carry over. Blocking of Air preheater baskets due to ash deposit Points to be taken care during boiler shutdown: . Water wash the heating elements during boiler shutdown when the gas inlet side temperature is around 100˚C. . Ensure proper drying of heating elements after water washing . Ensure complete cleaning of heating elements whenever water washing is done otherwise the left out ash would form into hardened cement and impossible to remove (inboard end baskets) . Analyse the ash deposit to identify the cause for plugging and do necessary corrective and preventive actions. . Ensure healthy condition of soot blower drive unit, nozzles & pipe lines . Ensure soot blower nozzles & pipe lines are clean and not choked . Ensure parking position of Soot blower nozzle near Rotor post to avoid erosion of nozzles. . Ensure the soot blower nozzle travel covers full heating elements . Ensure no leakage in water washing, deluge pipe lines and SCAPH . Ensure Econimiser ash evacuation system is in proper order . Ensure there is no passing/ leaking of Soot blower steam valve . Ensure boiler oil guns are in good condition . Control Air preheater leakages by proper seal setting and replacing eroded/ damaged components . Replace the eroded / corroded heating element baskets Boiler Emergencies

1 Furnace Bottom / Ash Hopper collapse

2 Boiler Explosion 3 Boiler Implosion 4 Windbox fire (external) 5 Expansion Joints failure 6 Boiler Tube Failure 7 Noise/Vibration in Boiler Second Pass 8 Airpreheater Fire 9 Pulveriser Fire 10 Ash accumulation in pent house Air preheater fires Air preheater fires are rare. . A fire may occur during cold start up on oil or start-up following hot stand-by because of poor combustion of the oil fuel. Reason: Not maintaining the correct oil viscosity at the burner tip Remedy: • Correct firing viscosity is 15 to 20 cst at the burner tip • Maintain correct oil temperature corresponding to this viscosity • Each batch of oil to be tested for Temperature Vs Viscosity • Even LDO needs checking these days. Fire Sensing Device Purpose:  to detect hot metal surfaces within the rotating heating element of the air preheater.

Requirement of a fire detector: • Rapid response time • Ability to detect small fires that are deep within the heating element pack. • High reliability • Ease of installation on existing as well as new Air preheaters • Simplicity of maintenance and servicing. • Ability to provide signal for operating personnel and ability to monitor the entire rotating structure. Fire Sensing Device

To detect the air preheater fire, • fire detecting thermocouples are provided • continuously monitor the abnormal increase in temperatures of gas leaving and air leaving the APH.

The milli-volt signals from these thermocouples are processed in DDCMIS to generate APH fire alarm.

Air preheater Fire Sensing - Thermocouples Locations

Thermocouples located at 1. Air Outlet and 2. Gas Outlet

• Chromel-Alumel • sense an undue temperature rise in the air and gas flow streams • Gives alarm if measured value is more than set point Adopt good operating practices to prevent air preheater fire • Reduce number of startups of boiler to a bare minimum. • Avoid operating boiler in low loads requiring oil support for a prolonged duration • It is a good practice to check oil viscosity characteristics on a periodic basis and whenever there is a change in supplier. • Clean oil gun tips and lap the internals to satisfy the design requirements. • Never restart the oil burners without purging during startup. • Boiler startup operation must be avoided when air pre-heater soot blowers are not available. • Always make it a practice to soot blow all the air pre-heaters, the non working air preheaters also must be soot blown by keeping the isolation damper marginally open to allow the soot to be blown out. • During startups, low load operation and shutting down, make it a practice to watch the trend of air and gas temperature leaving the air pre-heaters. • Operate air pre-heater soot blowers regularly • Fire detecting device has to be kept active and tested as and when possible. Factors affecting Availability of APH • Inadequate soot blowing during boiler start • Leads to air pre-heater fires • Long forced outage • Malfunctioning of oil burners • APH motor failure – Only for rotary type • High level of corrosion • High level of blockage – Increase auxiliary power consumption • Improper water washing O&M Points

Some O&M points . Cleaning of airheater to keep down the fouling

. Check Leakage in airheaters by analysing flue

gas for CO 2 drop across the airheater.

. Have a preventive maintenance programme, to check the drives, bearings, cleaning devices, oil circulation system for regenerative rotary airheaters Some O&M points • Evaluate the optimum seal setting • Ensure SCAPH online during each boiler start • Replace APH elements when undue increase in exit gas temperature or very high pressure drop • Avoid reuse of old baskets while changing • Adhere to all routine & preventive maintenance • Evacuate Eco ash hopper regularly as recommended • Regular optimization of boiler operation

Some O&M points Daily Walk-down Checks At the air preheater: . Inspect the upper and lower bearing assemblies. Check oil level and for oil leaks. . Check operation of the soot blowers and make sure that it is not leaking when the control valve has closed. . Inspect the cleanliness of the air side through observation doors. . Check for soot blower erosion of the air preheater basket elements. . Listen for any loud noise which might indicate problems with the seals. . Check the drive motor and gear reducer for signs of oil leakage Parameters for AH Performance Monitoring Parameters • Unit Load, MW • Feed water and / or Main Steam flow, T/hr • Total Air flow, T/hr • Coal Flow, T/hr • Mills in service, Nos. • Avg. Flue Gas O2 - AH Inlet, % • Avg. Flue Gas CO2 - AH Inlet, % • Avg. Flue Gas O2 - AH Out, % • Avg. Flue Gas CO2 - AH Out, % • Avg. Flue Gas Temp - AH In, C • Avg. Flue Gas Temp - AH Out, C • Avg. Primary Air to AH Temp In, C • Avg. Primary Air from AH Temp Out, C • Avg. Secondary Air to AH Temp In, C • Avg. Secondary Air from AH Temp Out, C • Pressure Drop across Flue gas path, mmwc • Pressure Drop across Primary air path, mmwc • Pressure Drop across Secondary air path, mmwc • Total Secondary Air Flow, T/hr • Total Primary Air Flow, T/hr • Design Ambient / Ref Air Temp, C • FD/ID/PA fan current, A Flue Gas O2 and Temperature measurement – Sampling Locations

Locating sampling locations is of prime importance: • For gas in and air in: close to the airheater • For gas outlet: as far away from the airheater - to take care of stratification effect caused by the direct and entrained leakages and enable the gas and air have a chance to mix before sampling • For Air outlet: far downstream from APH - to allow mixing of the flow to reduce the stratification Factors Affecting APH Thermal Performance • Air pre-heater leakage • Higher the leakage higher the loss • Low moisture coal than design • Need higher quantity of tempering air • This bypasses the APH – Increase exit gas temperature • High excess air • Blockage in air pre-heater • Corrosion of APH elements • Soot blowing frequency • High ambient temperature • Boiler operation with high overload • Slagging & fouling of boiler heat transfer surface • Low feed water temperature at boiler inlet Monitoring of Air Preheater Performance

Plot the values on a time line graph and compare with design/acceptance/PG test and historical values • Airheater gas side efficiency • Airheater leakage • Corrected exit gas temperature • Measured exit gas temperature • Gas side to air side differential pressure • Gas side pressure drop

Any unusual findings to be highlighted Conclusion

The common problems faced with air preheaters were taken into account during the design stage itself but planned maintenance and careful operation is essential to counteract the problems successfully so that total economy in steam generation can be achieved.