Ways to Improve Boiler Efficiency

SESSION OBJECTIVES AT THE END OF THE SESSION EACH PARTICIPANT WILL BE ABLE TO

List out different losses in a Boiler.

Understand the reasons / factors which influence efficient operation of Boiler.

MAJOR LOSSES IN A BOILER Stack lossLosses due to poor insulationLosses due to poor Boiler sealing.Losses due to leakages.Blow-down loss.Loss due to improper combustion. Losses due to poor heat transfer in heating surfaces.Losses due to part load operation.

COMMON BOILER OPERATIONAL PROBLEM IMPROPER FUEL STORAGE, HANDLING AND PREPARATION [Wet Coal, Size, Poor Pulveriser/ Classifier, Less inventory/ More Inventory]

OPERATION AT NON-OPTIMUM EXCESS AIR LEVELUnavailability of O2 AnalyserAir In-Leakage Upstream of the Plant O2 AnalyserIncorrect O2 Analyser CalibrationImproper Location of O2 Analyser

COMMON BOILER OPERATIONAL PROBLEM IMPROPER COMBUSTION CONTROL

Poor Control of Mixture of Fuel and AirExcessive Air-Rich Combustion for Safety and StabilityImproper Combustion Because Of Less Air i.e. Combustible LossBasic Ingredients [Change in Viscosity, Temperature, Pressure Or Calorific Value of Fuel ] and Ambient ConditionsWorned, Damaged and Dirty Burner.Soot deposits on Boiler Tubes.

COMMON BOILER OPERATIONAL PROBLEM LACK OF COMBUSTION UNIFORMITY Maladjustment of Air Dampers.Partially Plugged Air Heater.Poor Wind-box Design.Unsteady Coal Flow From the Pulveriser.Partially Plugged /Cracked Oil Gun Atomiser Tip.Broken / Poorly Positioned Oil Gun Diffuser.

Different common abnormality that requires maintenance Malfunctioning of steam TrapInadequate InsulationPoor sealing in APHErratic behaviour of combustion air fans Steam leakAbnormal power consumption by auxiliaries

Different common abnormality that requires maintenance

Combustion control:

Periodically check the combustion efficiency of a boiler with a combustion gas analyzer. Reduce the excess air if it is taking more air. If it is air starved, supply sufficient air for complete combustion. For small to medium boilers, recommended for portable combustion analyzer for a weekly to monthly check. Proper air / fuel ratio is a must and it is to be monitored /adjusted depending upon fuel quality, season and load. The analyzer should not only check excess air but also check carbon monoxide, because burner may become fouled even in the presence of proper air / fuel ratio.

CLEAN HEAT TRANSFER SURFACES TO REDUCE FOULING AND SCALE A higher stack temperature is generally an indication of fouling or scale on boiler heat transfer. Poor firing conditions at the burner is one of the major cause for gas side tube deposit. A loss of 1% efficiency is with the rise of 40 C in stack temperature. Poor feed water quality can cause scale on the water side heat transfer surface. A build up of 1/32 inch of normal scale composed of Ca and Mg salts or iron and silica decreases 2% or 7 % of efficiency respectively.

CLEAN HEAT TRANSFER SURFACES TO REDUCE FOULING AND SCALE Gas-Side Fouling: Solid deposits in the form of soot or slag on the gas side surfaces of boiler tubes reduces the heat transfer of the boiler water thereby reducing the efficiency of the boiler. The loss of boiler efficiency is approximately 1% for every 50 C increase in stack temperature above baseline conditions. Use of high pressure blast/ soot blowing will definitely improve the situation.

CLEAN HEAT TRANSFER SURFACES TO REDUCE FOULING AND SCALE

Water-Side Fouling: Chemical deposits or scaling on the water side retard the transfer of heat energy to boiler water making a significant loss in efficiency. As a result, a premature tube failure occurs due to increase in gas side metal temperature and operating problems like foaming and the consequent moisture carryover into the steam line causes fouling of downstream steam heating equipment. An active water treatment program can solve this and improves the efficiency.

STANDBY LOSSES:

It accounts to 1.5 - 2.0 % of the rated boiler fuel input. This loss is small when boilers operate at or near their rated capacity, but significant where boilers operate frequently at low loads. INSULATION: First inch of insulation reduces heat loss by 90 %. It is recommended that valves, flanges, steam traps and other fittings should be insulated more than regular pipe with removable insulation jackets because of the extended surface area on the fittings.

STEAM DISTRIBUTION SYSTEM LOSS STEAM LEAKS: A major threat to efficiency because of ; fuel loss, make up water loss, mechanical & chemical loss, more makeup water needs more blow down i.e. again wastage of more water, chemicals and energy. Arresting leaks have a short payback (two months or less) and preserve the life of surrounding insulation.STEAM TRAP: It is not a matter of "Will it fail ?" but it is a matter of "When will it fail?" Malfunction in steam traps are : stick open or closed. But from the energy manager's perspectives, traps designed to fail open are acceptable rather than closed. The identification of failed traps are : high amount of flash steam through vent lines of condensate and feed water tank. A routine schedule in an active preventive maintenance programme is required.

STEAM DISTRIBUTION SYSTEM LOSS INTERNAL STEAM LEAKS: Valves in bypass around steam trap are prime source for internal steam leak. If the bypass loss amounts to 500 pounds of steam per hour loss is around 1.9%.EXTERNAL STEAM LOSS: If the loss amounts to 700 pounds of steam per hour loss is around 2.7%TRAP FLASH LOSS: Steam Trap returning condensate to vent condenser, around 17% of condensate mass will flash to steam carrying away around 47% of the condensate remaining energy. Capture flash steam which is typically vented to the atmosphere and lost carrying away significant amount of energy.

CONDENSATE MANAGEMENT Return condensate saves a significant energy as compared to makeup water with higher conductivity and concentration of dissolved solids which also require more blow down means wastage of energy.

BLOWDOWN MANAGEMENT

BOTTOM BLOWDOWN [ for removing mud or sludge]SKIMMING BLOWDOWN [CBD] Removing top layer of water at steam/water interface to remove light particles, dissolved solids, particles that cause foaming and high conductivity. Use of frequent shot blow down is better than frequent long blow down. However, continuous blow down is even better if it allows for the use heat recovery devices.

WASTE HEAT ENERGY IN STACK GAS Heat carried away by the dry flue gases, moisture loss [latent and sensible heat in water vapor by combustion of hydrogen in fuel, humidity of combustion air and water content of the fuel]Because of :Operate with high stack gas temperature, not being operate with heat recovery equipment.No sophisticated combustion control, necessitates high excess air level [ 20 % to 60 %.No means to condense water vapor before flue gas leaves boiler.To avoid corrosion and sulfuric acid condensation.Soot deposits on heating elements of APH.Contamination around seal.

WASTE HEAT ENERGY IN STACK GAS ECONOMISER: Located in exhaust duct that absorbs heat energy from flue gas which would otherwise be wasted to provide additional heat to feed water reducing boiler firing rate. It is preferred over APH in retrofit addition because of low initial cost, lower draft loss and minimal auxiliary power requirement. An increase in feed water temperature of 10 C results a fuel saving approx. 1%. And a 30 decrease in flue gas temp. will rise the feed water temperature by 10. Heat transfer rate are highest when the temperature difference between flue gas and feed water is the highest.

WASTE HEAT ENERGY IN STACK GAS Oxygen Trim:Burner Setting.Burner air Resister Flap Position / OrientationOil Gun Tip Position.Oil Gun Diffuser Position.Fuel Oil Temperature & Pressure.Fuel Oil Atomising Pressure.Coal Particle Size.Installation of an on-line analysis device to automatically adjust the air/fuel ratio to minimize excess air while avoiding incomplete combustion.Retrofit of any boiler should also, consider burner change (which may be able to provide complete combustion at lower excess air level).

Efficiency Related Boiler Maintenance Procedure Performance degradation that resulted in an increase in stack gas temperature, excess air requirement, carbon monoxide / smoke or unburned carbon in ash, convection / radiation losses from the boiler exterior / ductwork and piping, auxiliary power consumption by fans / pumps or pulverisers need immediate preventive maintenance which would definitely lead a best achievable boiler efficiency.

Using a boiler room log book for evaluating & increasing boiler efficiency Performance monitoring through boiler logs help in identifying the deviations from desired performance and to take corrective measures to increase the boiler efficiency. By this, it is easy to determine when to:

Clean the boiler (fireside or waterside). Adjust the combustion regime.Repair or maintain the refractory or insulation works.Replace safety devices, fuel filters or gaskets.Ensure water treatment & quality as per design norm.Blow down quantity.

Efficiency Related Items That Need To Be Included In The Boiler Operators Log General data: Steam Flow, Pressure and Superheated Temperature, Feed water temperature.Firing System data: Fuel type, flow rate, temperature, oil / gas supply pressure, pressure at burners, burner damper settings, windbox to furnace air-pressure differential. Air Flow Indication Air preheater inlet & outlet gas O2, Stack gas O2, FD damper position / amperes as well as flow.

Efficiency Related Items That Need To Be Included In The Boiler Operators Log Flue Gas and Air Temperature Boiler outlet flue Gas, Economiser/Air Heater Inlet & Outlet gas, air temperature to Air heater (before & after).Unburned Combustible indication CO measurement, Stack appearance, Flame appearance & Flue gas analysis.Air and Flue Gas pressure FD discharge, Furnace, Boiler outlet, economiser differential, air heater air and gas side differential.Unusual Conditions Steam leak, abnormal vibration/noise, equipment malfunction and excessive makeup water demand.

Efficiency Related Items That Need To Be Included In The Boiler Operators Log Blow Down OperationSoot Blower Operation Reduces the fuel consumption by removing soot, non-combustible materials, mineral scales, and other deposits. Scale that is only 1/16 thick will cause the boiler to use 15% more fuel, 1/8 of scale requires 20% more fuel, and of scale increases fuel consumption by 39%. Soot blowing may preferably be done once in a day as per designers programmable sequences.Status of idle burners: In a multi-fuel firing boiler, ensure the smooth functioning of firing equipment which are not in service by taking them into service at least for a day in a month.

INCREASE BOILER EFFICIENCY Reduce excess air to boiler(s).Install low excess air burner(s).Replace or repair faulty burner(s).Replace natural draft burner(s) with force draft burner(s).Install condensing boiler / water heater.Clean boiler(s) through soot blowing to eliminate fouling on fire side.Ensure quality boiler water from water treatment Plant to reduce water side scaling.Blow down as per requirement.Improve feed water chemical treatment to reduce scaling.Optimize boiler loading when using multiple boilers.

WASTE HEAT RECOVERY Install economizer to preheat feed water (if economical).Install heat exchanger to preheat feed water.Install heat exchanger to preheat boiler makeup water.Install heat exchanger to recover blow down heat.Preheat combustion air with recuperator.Recover waste heat to supplement hot water demand.Recover heat from boiler flue gas to supplement building heat.Direct contact condensation heat recovery.Indirect contact condensation heat recovery.Repair steam and condensate leak(s).Repair failed steam trap(s) & eliminate steam leakages.

WASTE HEAT RECOVERY Return condensate to boiler.Shut off steam tracer during summer.Pressurize condensate return system.Replace On/Off control system with variable firing rate control system.

Other OpportunitiesInstall back pressure turbine for co-generation.Install variable frequency drives on feed water pump and combustion air fan.Install regenerative feed water heating system.Modify to combined cycle system.

Thank you