Boiler Feed Pump Curve

The function of Boiler Feed Pump is delivery water from feed water tank to steam drum, supply spray water to control of temperature of super-heater, re-heater and auxiliary steam. Boiler Feed Pump is design with two stages of pressure, 1st stage called booster pump is the cheap one and 2nd stage called main pump is the expensive one. Booster pump is location at the up stream side and it is very risk to get water cavitation when feed water tank get lost of pressure. If the de-aerator or feed water tank can not be located high enough above boiler feed pump to develop a high enough NPSH, other method must be used by injecting cold water into the pump.

Boiler feed pump is controlling steam drum level by single element and three elements. Single element is controlling the level only read the change of steam drum by discharge control valve, the pump rotating speed is not change due drum pressure or main steam pressure is not change too. Rotating speed of pump maintain pump discharge pressure 10 Bar above steam drum pressure.

Three elements control is controlling the level by read feed water flow, main steam flow and the level of steam drum by speed of pump, it adjusted by fluid coupling. After power station already synchronized, drum pressure and main steam pressure will be increase proportional with the load. That is the right time to change single element control to three element controls by open main discharge and shut discharge control valve, and then adjusted flow of the pump by speed and maintain pump discharge pressure 10 Bar above steam drum pressure.



How to get performance of Boiler Feed Pump with several of speed?
Predict the performed of BFP when operating at speeds other than that at which tested can be used the basic relationship.
Capacity is proportional to the speed and head is proportional to speed square [1]
Effect of water temperature, can decreased of pump performance as a density change [2]



The Pump is tested at Suction temperature: 18 deg C, density 998 kg/m3
The Pump is operated at Suction temperature: 175 deg C, density 892 kg/m3

Convert Head to Pressure at 5730RPM Boiler Feed Pump with various speeds chart.
251.92= ((998*9.8*2920)/101325)*(892/998)

Covert 5730 RPM to 5900 RPM at Boiler Feed Pump with various speeds chart.
Flow
183.69=((5900/5730)*200)*(998/1000)*(892/998)
Pressure
263.43=((5900/5730)^2)*248.47




[1] Austin H Church CENTRIFUGAL PUMP AND BLOWER Huntington New York 1972 Page 68

[2] Allan B Gill POWER PLANT PERFORMANCE Butterworths London 1984 Page 130

click here for cavitation & NPSH theory

Click here for animation fluid coupling (voith turbo)

Information about Steam Drum Level Control, click below this...
http://idpowerstation.blogspot.com/2009/08/drum-level-control.html