Skip to main content

Why does vacuum in steam condenser reduce or drop??

  1-High exhaust temperature: Vacuum drops or maintains at lower side due to high exhaust steam temperature flow into steam condenser. This high exhaust temperature is mainly due to 1-Operation of Turbine at lower loads 2-More clearance in labyrinth seals 3-Not operating exhaust hood sprays 4-More load on condenser 5-Breaking of ejector U loop 2-Low circulating cooling water flow Vacuum in condenser reduces due to inadequate cooling water flow through steam condenser. This is mainly due to; 1-Problems associated with pumps 2-Air pockets in pipe line 3-Leakages in cooling water line 4-Stuck of discharge valve of pump 3-High cooling water temperature at condenser inlet Higher cooling water temperature at condenser inlet results into reduction of vacuum due to poor heat transfer from steam to water 4-Poor heat transfer in condenser Very less or poor heat transfer in steam condenser reduces vacuum to very low level resulting into high exhaust temperature &am

Opportunities for energy conservation in power plants

Energy conservation in Boilers:
  • Control excess air in combustion which can lead to huge dry flue gas loss. Install online O2 analyzer for better controlling of excess air.
  • Control Air pre-heater (APH) out let flue gas temperature, it is said that on every 22 °C rise in boiler outlet flue gas temperature leads to decrease in boiler efficiency by 1%.
  • Optimize fuel moisture, which can lead to loss due to moisture.
  • Installation of fuel (bagasse) driers for recovering potential heat from chimney inlet flue gas.
  • Control unburnt in bed ash and fly ash, which can lead heat and fuel loss.
  • Maintain maximum possible feed water inlet temperature at economizer inlet. On 6–7 °C rise in temperature of feed water at economizer inlet leads to 1% fuel saving. And 15 °C rise can lead to increase in overall thermal efficiency by 3%.
  • Utilize unburnt from Economiser, bank zones by incorporating Cinder reinjection (CR) system
  • Optimize boiler continuous blow down to reduce heat loss with hot water
  • Create the ideas for utilizing blow down water for heating of combustion air, or feed water and even boiler blow down water can be used for cooling tower make up by reducing its temperature
  • Utilize blow down flash steam for heating feed water in deaerator. Continuous blow down (CBD) from steam drum operating at 115 kg/cm2 releases 42–45% flash steam.
  • Reduce boiler pressure if permissible, for process, boiler pressure can be maintained as per process requirement. This is the most effective way of fuel saving.
  • Incorporate VFD to all boiler auxiliaries like fans and fuel feeding systems.
  • Instead of throttling discharge air dampers ,provide inlet guide vanes to fans to control the air flow.
  • Arrest all boiler steam, flue gas and water leakages.
  • Operate boiler on optimum loads, boilers give more efficiency at 65–85% of full load.
  • Inspect air distribution nozzles, dampers regularly.
  • Try to get maximum temperature of combustion air by incorporating Steam coil air preheaters (SCAPH).It is said that on every 20 °C rise in combustion air temperature leads to increase in boiler efficiency by 1%.
  • 10–12% of hot air recirculation into FD fan suction can maintain rated APH inlet air temperature, which can lead to elimination of SCPAH thereby reducing LP steam consumption.
  • Utilize DG exhaust flue gas temperatures for heating systems like combustion air, feed water etc.
  • Operate the soot blowers regularly to remove soot formed on heating surfaces. It is estimated that 2.5% of fuel consumption will increase on deposition of 3 mm soot on heating surfaces of pressure parts.
  • Operate boiler feed pumps at rated or maximum possible suction pressure to reduce auxiliary power consumption.
  • Incorporate VFD to boiler feed pumps and reduce speed whenever possible
  • Operate feed water control valve at maximum opening i.e. control valves should open 70–80% for normal operation. It will reduce the pressure drop in control valves and hence load on boiler feed pumps.
  • Attend the the leakage of Boiler feed pumps ARC valves.
  • Use Neutra pit water or ETP treated water for ash quenching and other services.
  • Use Neutra pit water or ETP treated water for ash quenching and other services.
  • Operate the pneumatic ash handling system in probe mode instead of timer mode to save the compressor power.If run in timer mode optimise ash conveying time & cycle time.
  • Use high temperature coatings for valves, lines etc. o reduce heat loss.
  • Optimize deaerator steam vent line and orifice size to avoid excess steam vent or utlise this vent out steam for heating combustion air.Deaerator steam vent loss is around 0.1 % of Boiler steam generation.
  • Remove air from indirect steam using equipments, as 0.25 mm thick air offers the same resistance to heat transfer as a 330 mm thick copper wall.
  • Maintain water quality to avoid boiler scaling. A 1 mm thick scale deposit in the water side could increase fuel consumption by 5–8%.
  • Insulate all hot water storage tanks.
Energy conservation in Fuel handling & storage system:
  • Always store fuel in fuel shed to avoid wetting and excess drying of fuel in rainy and summer seasons respectively.
  • Store fuel on PCC (Plain cement concrete) bed to avoid carpet loss of fuel.
  • Cover fuel yard and storage shed by trees (bamboo) to reduce handling and feeding loss of fuels during high wind speed.
  • Conveyors should have seal proof hood covers to avoid flying/escaping of fuel during high wind speed.
Energy conservation in Turbine and its auxiliary system:
  • Maintain maximum rated pressure at Turbine inlet to achieve less SSC.
  • Maintain maximum possible vacuum to reduce SSC.
  • Maintain optimum cooling water inlet and outlet temperatures for all heat exchangers like steam condensers, oil coolers and Generator air coolers
  • Optimize cooling tower blade angles, more the angle more the power consumption.
  • Reduce the clearance between CT fan blade and concrete hood or fiber hood; generally it should be up to 25–30 mm.
  • Provide VFDs to cooling tower fans and Main cooling water pumps to control speed as per requirement.
  • Replace all aluminum blades by energy efficient FRP blades.
  • Clean cooling tower water spray nozzles regularly.
  • Arrange drift eliminators and fills properly for uniform spreading of air and water.
  • Clean condenser and ejector tubes yearly to achieve proper heat transfer
  • Keep cooling tower surrounding free from structures, building, trees to enable free air movement.
  • Ensure cooling water pump top casing crub level is below the normal operating level of cooling tower toavoid carrying of air in water or it may lead to cavitation.
  • Make a provision for online backwash systems for surface condenser and oil coolers to improve heat transfer.
  • Clean oil pumps filters regularly.
  • Incorporate VFD to Condensate extraction pumps (CEPs).
  • Install condensate recovery system from all process line drains and traps.
  • Use CEP discharge water instead of BFP discharge water for desuperheating of low pressure process steam.
  • Select optimum head condensate extraction pumps. If Deaerator working pressure is 2.75 kg/cm2A CEP of 80 meter discharge head considering all losses is sufficient.
  • Try to get maximum percentage of condensate from processes.
Energy conservation in other balance of plant (BOP) areas:
  • Replace all globe valves by ball valves of instrument pressurized air.
  • Clean suction air filters of compressors regularly as 250 mmwc pressure drop in suction filter will lead to the reduction of compressor efficiency by 2%.
  • Opening of air filters should be sufficient to suck enough air.
  • Locate compressors at lower level as at higher elevation compressors consume more power.
  • Install compressors in well ventilated areas.
  • Ensure cool water and air for compressors air cooling system. At every 4 °C rise in inlet cooling water temperature will increase power consumption by 1%.
  • Clean after and inter coolers regularly to get better heat transfer.
  • Install auto moisture drains for air lines.
  • Avoid unnecessary use of compressed air for applications like cleaning, washing, pneumatic tools etc.
  • Optimize discharge air pressure of compressor, on reduction of 1 kg/cm2 discharge air pressure leads to input power saving by 6–10% And on reduction of discharge air pressure by 1 kg/cm2 will reduce air leakage by 10%.
  • Carryout periodic air leakages test.
  • Prefer two stage reciprocating air compressors over single stage for same FAD and pressure as single stage compressors consume much power than multi stage.
  • In centrifugal fans (ID, FD and SA fans) Maintain optimum cone clearance and overlap gap to reduce power consumption.
  • Provide optimum height  silencers for high speed centrifugal fans and take care the silencer is free from all obstacles.
  • Modify ducting system by removing all obstacles to avoid pressure drop.
  • Incorporate VFDs to ventilation blowers to control speed during low temperature season (Winter and rainy seasons).
  • Provide VFDs to all possible pumps.
  • Replace all loose V belts as loose and damaged V belts conribute in more power consumption
  • Timely checking of equipment vibrations and alignment to avoid unnecessary power consumption and machine failure.
  • Avoid over greasing of bearings to reduce churning effect and energy consumption.
  • Replace higher rated capacity pumps with rated to avoid running of higher capacity pumps under load.
  • Replace all worn out wear rings of impellers and casing, as more clearance between wear ring and pump suction will contribute in more power consumption to maintain required flow.
  • Instead of controlling discharge valve, impeller trimming is the best way to control flow and power consumption.
  • Use booster pumps for small loads requiring higher pressure.
  • Provide all measuring instruments like flow, pressures for pumps to monitor their performance regularly.
  • Avoid bends and U seal pattern for suction line of pumps.
  • Use mechanical seals over gland packings.
  • Avoid connecting small size pump discharge line to higher size header, the ratio of header and discharge line should be in the range of 1.3 to 1.6 only. For higher size ratio power consumption will be more.
  • Replace all conventional gear boxes like worm-worm wheel and helical by more efficient planetary gear box.
  • Replace DOL starter motors of heavy equipments like chain conveyors with soft starters.
  • Modify the chain conveyor system to reduce unwanted dead loads like slat weights, link size etc.
  • Incorporate timers of street and plant lighting system.
  • Replace all the plant lighting bulbs by high efficient LED bulbs.
  • Maintain higher power factor at all the load ends by installing capacitor banks to reduce excess reactive power.
  • Provide forced cooling system for higher capacity power transformers to reduce losses.
  • Provide proper ventilation to the motors. For every 10 °C increase in motor operating 
  • temperatures over recommended peak, the motor life is estimated to be halved.
  • Synchronous motors are more suitable to improve power factor.
  • Balance the three phase power supply, an unbalanced voltage can increase motor input power by 3–5%.
  • Ensure the motor proper rewinding, an improper rewinding could lead to efficiency reduction.
  • Ensure proper alignment between motor and load ends (fans, pump, gear box, blower etc.) to avoid more power consumption and failures.
  • Optimize the quantity of lubricants in bearings and gearboxes to reduce unwanted load due to excessive lubricants.
  • Provide an alternate arrangement for connecting river water directly into clarifier; it will save power consumption for lifting water from reservoir to clarifier.
  • Prefer gravity make up system for condenser hot well make up, it will save pump power for hot well


Frequently visited posts

Boiler feed pumps (BFP) questions & answers for interview

Boiler feed pumps (BFP) questions & answers for interview: 1-What is the function of Boiler feed pumps (BFP) in power plant? Functions: To supply the feed water to boilers To conduct the Boiler hydraulic tests To supply the desuperheating & attemperator water required for process steam lines & boilers respectively TOP-6 BEST POWER PLANT O&M BOOKS Boiler calculations for Boiler operation engineer (BOE) exam Viva Questions & answers for preparation of BOE exam & interview  2- What are the type of prime movers (drives) used for BFPs? Prime movers: LT drive (415 V) HT drive (11 KV) Turbo drive (Steam driven) 3-What are the auxiliaries associated with BFP? BFP auxiliaries Cooling water pump & lines Lube oil system ARC valve Mechanical seal flushing system Balance leak off line & its PRV 4-What are the various pipe lines connected to BFP? Questions & Answers on AFBC Boilers Suction pipe line D

Basic things you must know about nut bolts & spanners

A Bolt is a mechanical device which has head on one end of a body and a thread on the other end designed for fastening of two parts. Bolt is inserted into holes in assembly parts, it is mated with a tapped nut. Tension is normally induced in the bolt to compress the assembly by rotating the nut. This may also be done by rotation of the bolt head. A Screw is a headed and threaded bolt used without a nut. It is inserted into an internally tapped hole and tension is induced by rotation of the screw head. A Stud is a fastener with no head but it has threads at both ends of the shank. It, like a screw, has one end those screws into a tapped hole. A nut is used on the other end to create tension. Major diameter – largest diameter of thread (D) Minor diameter – smallest diameter of thread Pitch – distance between adjacent threads.       Boiler calculations for Boiler operation engineer (BOE) exam TOP-6 BEST POWER PLANT O&M BOOKS Types of nut bolts & Washer

Calculation of heat rate & efficiency of the power plant

Heat rate  is the amount of energy used by an electrical generator/power plant to generate one kilo Watt-hour (kWh) of electricity Heat rate (HR) = Heat input / Power generation =Kcal / Kwh Boiler calculations for Boiler operation engineer (BOE) exam Viva Questions & answers for preparation of BOE exam & interview Total heat input: The chemical energy available in the fuel (coal, biomass, oil, gas etc) is converted into heat energy in Boilers, this process is called as oxidation. The heat available in the fuel is measured in terms of Kcal/kg, KJ/kg or BTU units. The part of this fuel is used as useful heat and rest is lost as dry flue gas loss, moisture loss, un  burnt loss, radiation/convection losses etc.Based on Boiler efficiency this heat energy from the fuel is utilised, generally fuel heat utilisation is in the range of 60 to 90%. This heat generated in the boilers due to oxidation of fuel is used to generate high pressure & temperature steam. Thus genera


A steam condenser is device or an appliance in which steam condenses and heat released by steam is absorbed by water. Heat is basically shell & tube type heat exchanger, where cooling water passes through tubes & steam condenses in shell. The functions of the condensers are: It condenses the steam exhausted from Turbine last stage Increase the thermal efficiency of the plant reducing the exhaust pressure and thereby reducing the exhaust temperature It maintains a very low back pressure on the exhaust side of the Turbine Supplies feed water to Boiler through deaerator TOP-6 BEST POWER PLANT O&M BOOKS Condenser related components: Hot well Cooling water inlet & outlet system Cooling tower Support springs or expansion neck Air Ejector system Condensate extraction system Cooling water tubes & tube sheet Vacuum breaker valve Safety valve or rapture disc Water box Air & water vent lines Types of steam condensers: Surface Co

22-Most likely Question Answer Guide for Boilers troubleshooting

TOP-6 BEST POWER PLANT O&M BOOKS 1.What are the emergencies that are expected to happen in boiler operation? Emergencies that can happen in boilers operation are: Boilers tubes leakage Failure of feed water control station Unbalanced draft in furnace Furnace explosion Blow down valve failure Feed water pumps failure Secondary combustion in super heaters and ESP Also read 16-Perfect reasons for increasing the fuel consumption of Boilers 2.List out the potential reasons for boiler tubes failure. Reasons for boiler tubes failure: Failure due to overheating Failure due to internal scales Failure due to aging Failure due to uneven expansion Failure due to ash and flue gas erosion Failure due to material defects Failure due to internal and external tube corrosion Improper or effected circulation due to opening/passing of low point drains 3.List down the sequential action taken after boiler tube leakage to restore the boiler. Following activities ar

Questions answers & calculation on Boiler draught & Chimney

1-What do you mean by the term draught? It is the pressure difference, which causes flow of gases to take places. 2-What is the function of draught in Boiler? To supply the combustion air required for proper combustion To evacuate the combustion products from the furnace or combustion chamber To evacuate the combustion products to the atmosphere So draught is the pressure difference between the inside the boiler and outside air. Inside the boiler pressure is due to combustion products (Flue gas) & outside pressure is due to fresh atmospheric air. 3-What are the different types of draughts used in power plant boilers? There are mainly two types of draughts. Natural draught & artificial draught Natural draught is generally obtained by Chimney Artificial draughts have main two types Steam jet: It is again classified into Induced & forced draught Mechanical draught: This is classified into Induced draught, forced draught & Natural draught

Boiler calculations for Boiler operation Engineer Exam (BOE)

  1-Oxygen percentage in Boiler outlet flue gas is 4.9%, then what will be the percentage of excess air? We have excess air EA = O2 X 100 / (21-O2)                                    EA = 4.7 X 100 / (20-4.7)                                    EA = 30.71% 2-Calculate the Oxygen level (O2) in flue gas, if excess air is 25% We have Excess air EA = O2 X 100 / (21-O2)                                    25 = O2 X 100 / (21-O2)                                    O2 = 4.2% 3-A Boiler’s combustion system requires 5.5 kg of air for burning 1 kg of fuel, then calculate the total air required for complete combustion if its flue gas has 4.1% of O2 We have, Total air = (1 + EA/100) X Theoretical air EA = O2 X 100 / (21-O2) EA = 4.1 X 100 / (20-4.1) = 25.78% Therefore Total air = (1 + 25.78/100) X 5.5 = 6.92 kg of air per kg of fuel burnt 4-A Coal fired boiler having total heating surface area 5200 M2 produces 18 kg of steam per square meter per hour of heating surface, then calculate the Boiler cap