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

Thumb rules for power plant

  • Boiler heating surface (M2) = Boiler capacity in kg/hr/(17–18)..Ex: 115 TPH boiler will have heating surface = (115 X 1000/17 or 18) = 6390 to 6750 M2 (Appx.)......
  • Boiler flue gas ducting size (M2) = Boiler capacity in TPH/15.
  • No. of open tubes in steam drum for water recirculation = 30–31% of total no. of tubes present.
  • Deaerator steam venting capacity = Deaeration capacity X 0.1%.
  • Super heater safety valve relieving capacity at full open condition in TPH = Boiler MCR X 36–38%.......Ex: 125 TPH Boiler has SH safety valve of relieving capacity = (125 X 36/100) = 45 TPH.
  • Drum safety valve (1 no.) relieving capacity at full open condition in TPH = Boiler MCR X 46–48%.
  • All boiler safety valves (super heater and drum safety valves) relieving capacity at full open condition= Boiler MCR X 125–130%.
  • Safety valves pop up pressure = Operating pressure X 106–107%.Ex: A boiler operating pressure of 110 kg/cm2 has safety valve set at 110 X 106/100 =116.6 kg/cm2.
  • Boiler start up vent steam blow capacity 30–35% of boiler MCR on full open condition.
  • Boiler CBD water flow is 0.8 to 2% of steam generating capacity of the boiler.
  • Drum man hole door size 410 mm X 310 mm (Elliptical).
  • Boiler drum hold up capacity is 2–4 minutes at MCR operation.
  • Feed water velocity in Economiser coils 0.6 to 1 meter/sec.
  • Pressure drop in Economiser coils 0.5 to 1 kg/cm2.
  • Flue gas Pressure drop in ESP 25 to 30 mmwc.
  • A travelling grate Boiler ID fans motor rated capacity in KW = Boiler capacity TPH X 200%.....Ex: A boiler of capacity 75 TPH requires ID fan motor of rated KW = 75 X 200/100 = 150 KW each
  • A travelling grate Boiler ID fans (2 Nos) capacity (m3/sec.) with 25% extra margin = Boiler Capacity(TPH) X 95%.....Ex: A 100 TPH boiler has two ID fans of each capacity =100 X 95/(100 X 2) = 47.5 m3/sec.
  • Mass of flue gas generated = Mass of air per kg of fuel to be burned + 1.
  • Boiler fans power consumption = Total plant auxiliary consumption X 35–38%.
  • Boiler feed pumps power consumption = Total plant auxiliary consumption X 35–38%.
  • Turbine auxiliary power consumption = Total plant auxiliary consumption X 10–12%.
  • Fuel handling power consumption = Total plant auxiliary consumption X 4%.
  • For every 1% increase in bagasse moisture, boiler efficiency reduces by 0.27% and vice versa.
  • For every 5% increase in excess air for bagasse, boiler efficiency decreases by 0.18% and vice versa.
  • For every 100 kcal/kg increase in bagasse GCV, boiler efficiency increases by 1.2% and vice versa.
  • For every 0.5% increase of Hydrogen in bagasse, boiler efficiency decreases by 0.8–1% and vice versa.
  • For every 10 °C increase in flue gas temperature, boiler efficiency decreases by 0.45% and vice versa.
  • For every 100 kcal/kg increase in GCV of coal, boiler (TG) efficiency increases by 0.36% and vice versa.
  • Boiler peak load = Boiler MCR X 110%.
  • Minimum possible duration of boiler peak load is 30 minutes/shift.
  • Minimum stable operating load on the boiler is around 30% of boiler MCR.
  • Total dissolved solids = Conductivity X 06.

  • Control oil pump capacity = AOP/MOP capacity X 10%.
  • Emergency oil pump capacity = AOP/MOP capacity X 25%.
  • Lube oil required for gear box = Total lube oil circulating X 60–65%.
  • Lube oil required for generator = Total lube oil circulating X 8–10%.
  • Lube oil required for turbine = Total lube oil circulating X 20–25%.
  • Lube oil outlet temperature = Lube oil inlet temperature + 15–20 °C.
  • Cooling tower evaporation loss = Turbine exhaust steam to condenser X 80–90%.

  • Minimum allowable bearing clearance in mm = 0.00185 X bearing ID
  • Maximum allowable bearing clearance in mm = 0.00254 X bearing ID.
  • Bearing grease top up quantity = 0.05 X b X d, b = bearing width in mm, d = bearing OD in mm.
  • Hub size = 2 X Shaft diameter.
  • Shaft Key size, width = (d/4) + 2, thickness = d/6, (d = diameter of shaft).
  • Minimum span for pipe line supporting in meter = (7√d)/3, where d = pipe OD in inches.
  • Threading length of half threaded bolt = 2d + 6 mm (if bolt length l <150 mm) and 2d + 12 mm (if bolt length l >150 mm).
  • Spanner size = Bolt major diameter (mm) X 1.5.
  • Nut thickness = 0.9 X d, d = nut size.
  • Bolt head thickness = 0.8 X d, d = major diameter of bolt.
  • Washer Internal diameter = D + 1…mm.
  • Washer outer diameter = 2D + 3……mm.
  • Washer thickness = D/8, where D is OD of washer.
  • Diameter of bolt head across the flat ends = 1.5 X d + 3 mm.
  • Welding current required for welding (Amps) = Welding rod size (mm) X 40 +/- 20.
  • Pipe weight/foot = (dt − t2) X, (pipe OD in inches & t is thickness of pipe in inch).
  • Pipe line spacing = Flange size of maximum diameter pipe + Smallest pipe size + Insulation thickness + 25 mm.
  • Preheating of steel is done if %C + %Mn/4 is >0.58.
  • Boiler platform loading capacity 500 kg/m2.
  • Boiler fire man floor platform loading capacity 1000 kg/m2.
  • Brinnel hardness number (BHN) = Rockwell hardness number X 10.8.
  • Bearing, grease or lip seals have a design life of less than 2000 hours. In a constantly running pump this would be only 83 days.
  • Tail pulley, bend pulley and take up pulley Outer diameter = Head pulley OD X 80%.
  • Snub pulley OD = Head pulley OD X 60%.
  • PCS (Pull Chord Switch) are placed at every 15 meters along the length of conveyor.
  • BSS (Belt Sway Switch) are placed at every 30 meter along the length of conveyor.
  • Carrying and return self aligning transoms are placed at every 20 meters along the length of the belt.
  • Horizontal chain conveyor motor capacity = Chain span X Fuel handling capacity / 80
Example: A chain conveyor of capacity 100 TPH & having centre to center distance 30 meters requires motor of capacity 100 X 30 / 80 =37.5 KW to drive the conveyor safely
  • Pump shutoff head = Design head X 1.07.
  • Pump efficiency with cold water is less than pump efficiency with hot water
  • Safe operating speed of boiler feed pumps is 55–60% of rated speed.
  • Boiler feed pumps suction strainer pressure drop should be 0.04 to 0.06 kg/cm2.
  • The pumps best efficiency point (B.E.P.) is between 80% and 85% of the shut off head.
  • A double suction pump can run with less N.P.S.H. or at faster speed without cavitating.
  • Multistage pumps reduce efficiency 2% to 4%.
  • 1% capacity of pump will reduce on every 0.025 mm increase in wear ring clearance.
  • Suction piping should be at least one size larger than the suction flange of the pump.
  • Pumps piped in series must have the same capacity (impeller width and speed).
  • Pumps piped in parallel must have the same head (impeller diameter and speed). 
  • A centrifugal pump can handle 0.5% air by volume. At 6% it will probably become air bound and stop pumping. Cavitation can occur with any amount of air.
  • A Vortex pump is 10% to 15% less efficient than a comparable size end suction centrifugal pump.
  • There should be at least 10 diameters of pipe between the suction of the pump and the first elbow.
  • Rating current of motor = 1.36 X hp or 1.79 3 KW.
  • Starting current of a single phase motor (1 to 10 HP) = 3 X Motor full load current.
  • Starting current of a three phase motor (up to 15 HP) = 2 X Motor full load current.
  • Starting current of a three phase motor (>15 HP) = 1.5 X Motor full load current.
  • Current carrying capacity of copper cable: 2 amps/mm2.
  • Earthling resistance for single pit is <2 ohm.
  • Voltage between neutral and earth <2 V.
  • Resistance between neutral and earth <1 ohm.
Motor body earthing strip size:
  • 85 SWG GI Wire for motors <5.5 KW.
  • 25 X 6 mm GI Strip for motors 5.5 to 22 KW and Lighting and control panels.
  • 40 X 6 mm GI Strip for motors 5.5 to 22 KW.
  • 50 X 6 mm GI Strip for motors >55 KW and D.G and Exciter Panel.
  • Motor insulation resistance = (20 X voltage)/(1000 + 2 X motor KW).
  • Single phase motor draws 7 amps current per HP.
  • Three phase motor draws 1.25 to 1.36 amps current per HP.
  • No load current of three phase motor is 30 to 40% of full load current of motor.
  • Submersible pump takes 0.4 KWH of extra energy at 1 meter drop of Water.
  • Creepage Distance 5 18 to 22 mm/KV for moderate polluted air and 25 to 30 mm/KV for highly polluted air.
  • Minimum Bending Radius for LT Power Cable is 12 X diameter of Cable.
  • Minimum Bending Radius for HT Power Cable is 20 X diameter of Cable.
  • Minimum Bending Radius for Control Cable is 10 X diameter of Cable.
  • Insulation Resistance Value for Panel = 2 X KV rating of the panel.
  • Test Voltage (AC for Meggering = (2 X Name Plate Voltage) + 1000.
  • Test Voltage (DC for Meggering = (2 X Name Plate Voltage).
  • Current Rating of Transformer = KVA X 1.4.
  • No load current of Transformer = <2% of Transformer rated current.
  • There are 4 Nos. of earth pits per transformer (2 No. for body and 2 No. for neutral earthing).
  • Diesel generator set produces 3 to 3.5 KWH/liter of diesel.
  • DG less than or equal to 1000 KVA must be in a canopy.
  • DG greater than 1000 KVA can either be in a canopy or skid mounted in an acoustically treated room.
  • DG fuel storage tanks should be a maximum of 990 Litter. Storage tanks above this level will trigger more stringent explosion protection provision.
Available @ Flipcart/Amazon/Notion press


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