Showing posts with label pumps/compressors/fans. Show all posts
Showing posts with label pumps/compressors/fans. Show all posts

Boiler feed pumps start up & shutdown procedure


                 Start-up Pre-check lists

  • Ensure Boiler feed pump is not in permit for maintenance works
  • Ensure all the maintenance activities on pumps are completed
  • Ensure equipment are normalized from electrical & mechanical side
  • Ensure Boiler feed pump is free from obstacles
  • Ensure enough lighting or illumination is available there
  • Ensure pump coupling is well guarded by robust coupling guard
  • Ensure Pumps local field instruments like pressure gauges, switches, vibration sensors, DP gauges are healthy
  • Ensure coupling is free to rotate

Starting procedure:

Start permissive (interlocks)

  • Ensure deaerator level is normal
  • Ensure feed pumps suction valves is open
  • Ensure cooling water line & outlet valves to bearings & mechanical seals are open and also water is circulating through the lines.
  • Ensure bearing temperatures are normal
  • Ensure bearing vibration showing DCS is zero
  • Ensure there is no alarm exists for strainer DP (differential pressure)
  • Ensure suction pressure is normal
  • Ensure discharge valve of the pump is closed
  • Ensure minimum recirculation valve or ARC valve is in open condition
  • Ensure balance leak off line valve to deaerator is open (In some valves are not provided to balance leak off line)

Start-up sequence

  • Take clearance from electrical & field person to start the pump
  • After getting the clearance from both the team, start the pump by giving minimum set point 80% if it is VFD driven.
  • Once the pump started, ensure pump will attain minimum 40% RPM in just 10 seconds (in case of journal bearing pumps).For non-journal bearing pumps speed ramp up time is not recommended specifically.
  • During speed ramp up check bearing vibrations & temperatures are normal.
  • Ensure pressure in the discharge pressure gauge is increasing slowly & has reached rated pressure at rated speed.
  • Then check the vibration, bearing temperatures & sound from pump.
  • Check & ensure the correctness of balance leak off line pressure
  • Wait for stabilization of the pump, once the pump attained rated parameters, check the motor current, temperature & vibrations & ensure they are within permissive limit.

Also recheck pump bearings vibration, temperatures & any abnormal sound from pump.

Pump normal shutdown procedure

  • For VFD driven pumps reduce the pump speed to 80% (for start delta driven pumps speed cannot be reduced)
  • Close the pump’s discharge valve
  • Then stop the pump

Do not’s for Boiler feed pumps

  • Do not rotate the pump in reverse direction, reverse direction leads the seize of pump
  • Don not run the pump if its suction water temperature is more than design/required
  • Do not operate the pump at less than 80<% load for long time to avoid damage to the bearings
  • Do not close the auto recirculation line valve
  • Do not close the balance leak off line valve (if provided)
  • Do not stop the pump with discharge valve open
  • Do not throttle the suction valve of the pump at lower load, can throttle discharge valve


 For related articles read

powerplant & calculations






32-differences between centrifugal pumps and reciprocating pumps


Sl No.

Centrifugal pump

Reciprocating pump


It is dynamic type pump

It is a positive displacement pump


It produces more flow

It produces lesser flow


It produces less head (pressure) for same size of pump

It produces more head (pressure) for the same size of pump


Work is done by rotating the impeller

Work is done by back & forth movement of piston or plunger or diaphragm


Simple construction

Complex construction


Simple operation

Complicated operation


Smoother operation no vibrations

Due to reciprocating movement vibrations are always there


Continuous supply of fluid

No continuous supply of fluid


Pressure increases by decreasing the flow

Flow is independent on pressure


High viscosity fluid cannot be pumped easily

High viscosity fluids can be p[umped very easily


Low viscosity fluids can be pumped very easily

Cannot be pumped very easily


Centrifugal pumps are low costlier

More costlier than centrifugal pumps


Maintenance is easy

Maintenance is difficult


Less maintenance cost

More maintenance cost as there are more rotating & moving parts in pump


Grease & oil lubricated

Most of the pumps are oil lubricated only


Cab ne installed easily

Complicated installation


Require less space for same size pump

Require more space for same size pump


Less accurate in flow measurement

More accurate for flow measurement


Not suitable for small quantity dosing system like chemical plants or water treatment plants

Best for small & accurate quantity dosage like in water treatment plants to maintain desired water parameters


Priming is required for centrifugal pumps

Priming is not required


Pumps can be started with discharge valve closed condition

Pumps cannot be started with discharge valve closed condition


In consists of impeller to create head & flow

In consists of plunger, pistons & diaphragms to create head & flow


Centrifugal pumps might be of positive as well as negative suction

Most of the reciprocating pumps are of positive suction


PRV is not required

PRV is required to protect the pump during discharge line blockage


Minimum recirculation system is there to protect pump at lower discharge flow

Recirculation line is not required as head is independent of flow


Pump major internal parts are impeller, wear ring, shaft sleeve, stuffing box, lantern ring, balance & counter balance disc  etc

Pump major internal parts are, connecting rod, crank, piston, plunger, diaphragm, gears etc


Reverse rotation of the pump affects pump performance & capacity

Reverse rotation of the pump does not affect much


Pipe lines have fittings like eccentric & concentric reducer

Eccentric & concentric reducers are not used


Generally air vessels are not used in reciprocating pumps

Air vessels are used in reciprocating pumps


Thrust balancing is required in high pressure centrifugal pumps

Thrust balancing is not required


Cavitation can damage pump internals & related piping system

Cavitation does not affect much


For same flow foundation required  is not much robust & strong

Strong & robust foundation is required

Reference books for power plant O&M

Reciprocating pumps

Reciprocating pumps parts

For related articles read

Read QnA on air compressors

How do you calculate the efficiency of pumps

 Power plant and calculations

Questions & Answers on Boiler feed pumps design , operation & maintenance



 Design data from site:

Ø  Type of liquid handled and its maximum & minimum temperatures

Ø  Water qualities like pH & Hardness

Ø  Water Kinematic Viscosity (cst)

Ø  Specific gravity of water at operating temperature

Ø  Net positive suction head required (NPSHR)& available (NPSHA)

Ø  Boiler capacity & operating pressure

Ø  Maximum & operating blow down rate of Boiler

Ø  Height of Steam drum

Ø  Height of Deaerator (Water inlet source)

Ø  Pressure drop in Economiser

Ø  No.of valves used in feed water discharge line & corresponding pressure drop as per standard.

Ø  Maximum & minimum suction pressure available at pump suction

Ø  Type of cooling water & its maximum flow available for bearings cooling

 Pump Design Data:

Ø  Rated flow (M3/hr)

Ø  Rated head (meters)

Ø  Nominal speed & Effective speed (RPM) (NS > ES)

Ø  NPSHR (meter)

Ø  Pump & Motor efficiency

Ø  No.of stages of pump

Ø  Motor rating

Ø  Pump suction & discharge nozzles sizes

Ø  Vapour pressure (kg/cm2)

Ø  Pump’s shut off head (meter)

Ø  Pump minimum flow (25 to 30% depends on pump operating head & flow)

Ø  Cooling water pressure



Other considerations:

Ø  Balance leak off water flow source (generally balance leak off water is diverted to Deaerator)

Ø  Pump Rotation direction (Clock wise viewed from drive end)

Ø  Cooling water flow rate (LPM)

Ø  Pump’s suction & discharge elements hydro. Test pressures

Ø  Material of constructions (MOC) of all pump internals

Ø  Type of coupling used between pump & motor shaft

Ø  Type of Shaft seal used (Mechanical seal)

Ø  Protections given for pump (Protections like, bearing vibration sensors, bearing temperature sensors, pressure relief valve for balance leak off line, phase sequence relay for direction of rotation, cooling water pressure, pump over load etc)

Calculate the boiler feed pump and motor size required for a boiler of capacity 90 TPH has steam drum working pressure 88 kg/cm2. The height of the drum is 35 meter from boiler feed pump Centre. And the suction water to pump is taken from Deaerator which is situated 15 meter above the pump centre.

Given that,

Boiler capacity: 90 TPH = 90 M3/hr

Steam drum operating pressure = 88 kg/cm2

Steam drum height from pump centre = 35 meter

Height of Deaerator tank from pump centre =15 meter


Boiler blow down 1%

Deaerator operating level from floor: 2.5 meter

Pressure drop in Boiler economizer: 2.5 kg/cm2

Pressure drop in feed water control station: 5 kg/cm2

Pressure drop in line, gate and globe valves and bends of feed water line: 5 Kg/cm2

Pump operating temperature: 110 °C

Economizer out let feed water temperature: 275 °C

Pump and motor efficiency: 65% and 95% respectively.

Total required discharge head for pump = (Drum operating pressure + Drum height (m) + Economiser pressure drop + Control valve pressure drop + Pressure drop in line, gate and globe valves and bends) X 1.10 (Take 10–15% extra margin)

= (88 kg/cm2 + 35 meter + 2.5 kg/cm2 + 5 kg/cm2 + 5 kg/cm2) X 1.1

Convert all the pressure head into gravity head in meter from formula P = Density X g X H…by taking the densities of fluids (water) at operating temperatures.

 P = Desnity X g X H


Then, we have,

Total discharge head = (1248 m + 35 m + 33 m + 52.5 m + 52.5 m) X 1.1 = 1563 meter

Pump rated flow = (Boiler MCR + Blow down %) X 1.25 (Take 25–30% extra margin)

                           = (90 + (90 X 1/100)) X 1.25

                    = 113.625= 115 M3/hr

The Capacity of flow seems more, it is better to consider 3 pumps 2 running & 1 stand by


Select 2 Nos of pumps 1 working & 1 standby (1W+1S)

For motor power, we have

Pump hydraulic power Ph = (Flow (m3/sec.) X Total head (Hd - Hs) X g (m/sec2) X density of feed water at 110 °C)/1000

                                          = 0.0319 X (1563 - 15 - 2.5) X 9.81 X 951/1000

                                          = 459.94 KW

Pump shaft power Ps = Pump hydraulic power X 100/Pump efficiency

                                   = 459.94 X 100/65 = 707.60 KW

Motor input power = (Pump shaft power X 100/Motor efficiency) X 1.10

                       = (707.60 X 100/95) X 1.10

                       =819.32 KW

From motor selection chart select Standard sized motor that is 825 KW


Select 3 Nos of pumps, 2 Working & 1 stand by (2W+1S)

Then, capacity of the one pump = 115/2 = 57.5 M3/hr (May take 58 m3/hr round figure)

For motor power, we have

Pump hydraulic power Ph = (Flow (m3/sec.) X Total head (Hd - Hs) X g (m/sec2) X density of feed water at 110 °C)/1000

                                    = 0.01611 X (1563 - 15 - 2.5) X 9.81 X 951/1000

                                    = 232.28 KW

Pump shaft power Ps = Pump hydraulic power X 100/Pump efficiency

                             = 232.28 X 100/65 = 357.35 KW

Motor input power = (Pump shaft power X 100/Motor efficiency) X 1.10

                       = (357.35 X 100/95) X 1.10

                       = 376.16 KW

From motor selection chart select Standard sized motor that is 375 KW


Comparing Case-1 & II

Total Installation capacity of Boiler feed pumps for case-1 = 825 X 2 = 1650 KW

Total Operation power = 825 X 85% = 701.25 KW


Total Installation capacity of Boiler feed pumps for case-II = 375 X 3 = 1125 KW

Total Operation power = 375 X 2 X 85% = 637.5 KW


In view of energy conservation considering Case-II is feasible. But in view of installation & maintenance cost Case-I is feasible.

General Questions & Answers on BFPS

1-What is the function of Boiler feed pumps (BFP) in power plant?


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

  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?

  • Suction pipe line
  • Discharge pipe line
  • Bearing cooling water lines
  • Jacket cooling water lines
  • Mechanical seal flushing line
  • ARC line (Minimum re circulation line)
  • Impulse lines for instrumentation measurements (Suction pressure, discharge pressure, Differential pressure, balance leak off pressure)
  • Balance leak off line

5-What is the size of suction strainer of a BFP

It is generally 30 to 40 mesh, that is 30 or 40 hole openings in 1 linear inch on strainer.

A SS 30 wire mesh is generally wrapped on SS mesh having hole openings around 3 to 4 mm

6-What are the different protection devices given for boiler feed pumps?

  • Pressure relief valve
  • Balance leak off line
  • Auto re circulation valve

7-What is the function minimum re circulation line or Automatic re circulation valve (ARC VALVE?)

Minimum re circulation line is provided mainly for centrifugal pump with constant speed drive based on the system and vendor information. There are two types of minimum continuous flow required by the pump (Stable and Thermal). Pump is designed to operate at the flow greater than this flow rate. If pump is operated at less flow than the minimum continuous stable flow, it will damage bearing and internals and may abnormal vibration occur. Below the minimum continuous thermal flow, temperature of fluid will rise at faster rate. To avoid these problems, minimum re circulation line is provided. If the demand of the fluid is decreased below minimum continuous flow, then the auto re circulation valve of the pump will open and maintains the required flow and if flow increased more than minimum flow then auto re circulation valve closes. Generally for higher head flow like 1500 meter head pump the minimum circulation will be 20–25% of total capacity.

8-What is the function of balance leak off line?

Balance leak off line is used to balance the centrifugal pump shaft from axial thrust. During centrifugal pump operation, especially in multistage centrifugal, suction side will have relatively very less pressure as compared to the discharge side. Because of this, there are lot of possibilities that impeller along with the shaft and bearing will be pushed from discharge end to suction end which is also known as axial thrust. Balance line is used to balance the centrifugal pump shaft from axial thrust. Due to the axial thrust, pump bearings and internals will get damaged. To nullify this effect, a tapping from discharge end (between balancing & counter balancing disc) is connected to a balancing drum.

9-Why the balance leak off line water is not connected to suction line to save the pump hydraulic power instead of directing it into Deaerator?

 Balance leak off water temperature is little bit higher than pump operating temperature which may lead cavitations if it mixes with suction water. For some pumps where there is no risk of cavitations, in such cases this line is connected to suction side of the pump.

10-What is the operating pressure of balance leak off line ?

It is just 0.5 to 1 kg/cm2 more than pump’s suction pressure

10a-What is the standard  gap maintained between balance & counter balance discs?

It is around 0.8 to 1.2mm


11-What does it indicate if balance pressure is increasing gradually?

It indicates the wear out of balance or counter balance disc. That is gap or clearance between these two discs has increased

12-How do you calculate the maximum allowable balance leak off pressure?

Maximum allowable balance leak off pressure = 0.03X (Shut off pressure-Suction pressure)+ Suction pressure.

13-What is the velocity of water in the balance leak off line?

It should not exceed 5 m/sec on any account

14-Why the BFP discharge water & balance leak off temperature is slightly more than that of suction water temperature?

15-Due to the compression action of water inside the pump, the water pressure rises around 2 to 3 deg C more than the suction water. Water is an in compressible fluid

15-What do you mean by the shut off pressure in centrifugal pumps?

Shut-off head is a condition, when a centrifugal pump runs with discharge valve closed. It is the maximum head generated by a centrifugal pump with zero flow and relatively less power.

16-How do cavitations occur? What are the abnormal effects of cavitations?

Pump cavitation occurs when the pressure in the pump inlet drops below the vapour pressure of the liquid. Vapour bubbles form at the inlet of the pump and are moved to the discharge of the pump where they collapse and make high sound and vibrations often taking small pieces of the pump with them.







Cavitation is often characterized by:

Loud noise often described as a grinding or “marbles” in the pump.

Loss of capacity (bubbles are now taking up space where liquid should be).

Pitting damage to parts as material is removed by the collapsing bubbles.
17-What do you mean by NPSHA & NPSHR in BFPs?

NPSHA: Net positive suction head available is the absolute pressure at the suction port of the pump.

 NPSHR: Net positive suction head required is the minimum pressure required at the suction port of the pump to prevent the pump from cavitations.

NPSHA should be always greater than NPSHR (NPSHA >  NPSHR)

18-What is the significance of NPSH in BFPS?

If BFPs do not have required NPSH, then there will be more chances for formation of cavitations.

How the pump speed is related to NPSH

NPSHR varies approximately with the square of pump speed.


19-How do you calculate the NPSHA ?

NPSHA = Absolute pressure in

NPSHa = Ha +- HZ - Hf + Hv - Hvp

Where, Ha is the absolute pressure on the surface of the liquid in the supply tank.

HZ is vertical distance between the surface of the liquid in the supply tank and the center line of the pump.

Hf is friction losses in the suction piping.

Hv is Velocity head at the pump suction port.

Hvp Absolute vapour pressure of the liquid at the pumping temperature of the pump, it could lead to cavitations of pump.


20-What is the significance of vortex breakers in pumps?

A vortex breaker is a device/arrangement in pumps to stop the formation of a vortex when a fluid (liquid or gas) enters into pump suction. The formation of vortices can entrain vapour in the liquid stream, leading to poor separation in process steps such as distillation or excessive pressure drop, or causing cavitations.

21-What are the reasons for Vortexing in pumps?

Vortexing can occur if any of the following conditions are present:

  • Low liquid levels.
  • Liquid level falling greater than 1 Meter/sec.
  • There is a large concentration of dissolved gases in the liquid.
  • High outlet velocities in pipes leaving vessels. Generally greater than 3 meters/sec.
  • Liquids near their vapour point.
  • High circulation caused by asymmetrical inlet or outlet conditions.
  • Inlet piping too close to the wall or bottom of the tank.

22-What are the protection interlocks given for BFPs.

Protection interlocks: That is BFP will trip/stop on following conditions

  • Low Deaerator level
  • High bearing vibrations
  • High bearing temperature
  • Low cooling water pressure
  • More differential pressure of suction strainer
  • High load
  • Higher balance leak off pressure
  • Low speed (<40% of rated speed)

23-Write down the BFP start permissive interlocks

  • Start permissive interlocks
  • Deaerator level normal
  • Bearing temperature normal
  • Bearings vibrations normal
  • Cooling water pressure normal
  • Motor bearing temperature, winding temperatures normal
  • Discharge valve close
  • Suction valve open
  • Suction pressure normal
  • Differential pressure normal
  • Arc Valve open

24-How do you start the BFP?

BFP start up  sequence

  • Ensure all the start permissive are healthy
  • Ensure no maintenance activities are going on BFP & pump is ready to start with all respect
  • Start the pump from DCS by giving >80% command to VFD
  • Observe the bearing temperature, vibration & speed ramp rate
  • Ensure pump has reached its 50% speed within 10-15 seconds
  • If all parameters (discharge pressure, bearing temperature & vibrations, motor current, winding temperatures etc) are normal
  • Then open the discharge valve slowly
  • After 100% opening of discharge valve rise the speed as per your requirement
  • Note: Ensure all the parameters are normal on every operation on BFP

25-Why it is not allowed to run the BFPS at speed lesser than 50% of rated speed?

For journal bearing BFPS at speed < 50%  the oil splash rings will not flash oil in bearings, leading to the damage to the bearings due to low lubricating oil.

26-What will happen if BFPs run in reverse direction?

If pump runs in reverse direction for more than 5 seconds, there will be the more chances of pumps to seize

27-How do you stop the BFP?

  • Pump stop sequences:
  • Reduce the pump speed slowly up to 60% of rated
  • Close the discharge valve
  • Shut down the pump

28-What is the recommended minimum head for BFP operation?

Should not be less than 10% of its rated head except in start-up & shutdown conditions?

29-What will happen if pump is started and stopped with discharge valve open?

  • Pump may trip due to sudden motor over load
  • Alignment may get disturb
  • Shaft coupling may damage
  • May harm to bearings of pumps and motor
  • Piping supports may get disturbed
  • Pump foundation fasteners may get loose
  • So it is always recommended to start and stop the pump with discharge valve close.

29-What are the reasons for pump to seize?

Following conditions can cause pump to seize:

  • No suction or less liquid flow to suction
  • Operating pump continuously at lesser NPSH
  • Reverse direction rotation of pump
  • Damaged strainer
  • Foreign materials in impellers
  • Uneven thermal expansion of pump internals

30-What is the recommended acceptable value for a BFP shaft run out?

 It is around 0.03 mm (Max. 0.05 mm)


31-When should one can carry out alignment on BFP

Alignment on BFP shall be done when the temperature of the pump is <50 Deg C or in atmospheric temperature.

32-Why do you use 2 dial gauges for axial alignment of BFP?

 BFP has more axial float that is 8 to 9 mm without bearings & seal & 0.8 to 1 mm with bearings & seal, so in order to get accurate readings 2 dial gauges are used for angular alignment & 1 dial gauge for parallel alignment. Refer above figure

 33-What are the shutdown preservation methods for BFP?

 Shutdown preservation method

  • Depressurize the pump
  • Drain all the water
  • Fill the pump with 1:2 or 1:1  Glycol water mixture.
  • Rotate the pump shaft twice in a week

34-What is the recommended bearing temperature for BFPs?

It should be less than 75 deg C (Max 90 deg c)

35-What are the recommended bearing vibrations for BFPs?

It should be less than 3 mm/sec (Max 5 mm/sec)

36-What is the allowable leakage drops for BFP mechanical seal

15 drops/minute

37-What should be allowable the DP across strainer

38-What is the filter mesh size for BFP oil replacement

Mesh size is 30 micro meters

39-What preventive maintenance activities that you are going to carryout on BFPS?

Preventive maintenance activities:

  • Pump cleaning
  • Oil level checking & top up if required
  • Alignment correction
  • Suction strainer cleaning
  • Cooling water lines flushing
  • Foundation bolts tightness checking

40-What is the acceptable impeller & wear ring clearance in BFP

0.1 to 0.3 mm max.

 Boiler feed pumps start up & shut down procedure

15-Emergencies in power plant operation

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