Can anyone please explain what is scoop control for boiler feed pumps? Principle of operation and reason would be AWESOME :)
A quick internet search didn't help much
Very many thanks in advance
Scoop controller is a hydraulic device (which i have seen in my FD fans) which regulates the FD fan speed depending upon the signal from DCS. It consists of a hydraulic I/P converter coupled with a cylinder which opens or closes based on signal from DCS. There is always a start up interlock which requires scoop to be in minimum position. If you have any doubts please feel free to contact.
As I have seen in thermal plant operation:
For scoop control, the operator has to give the Set point for DP across the Feed Station Control Valve. To achieve this set point value of DP, Scoop controller PID maintains speed of Hydraulic coupled Pump operated by constant speed motor.
For Drum Level Control, Operator gives Set point for Drum Level Value. To achieve this set point value of Drum Level, 3 or 1 - element controller will maintains the Feed Station Control Valve position.
Purpose of scoop control -
1.This will reduce the throttling loss occurs due to high & fluctuating DP across control valve.
The Valve operates in better controllability position.
2. By the way, what is DP value you are maintain across Feed Control Station?
It seems you are interested to know the working principle of scook control system.Apart from explanation of other users about control here is some mechanical explanation.
Scoop control is a type of flexible coupling in between driver & Driven. Normally there are wheels (Primary on driver & Secondary on driven)filled with oil. Secondary wheel oil level can be control by inserting/withdrawal of scoop. Scoop tube inserted as far as possible in the scoop chamber of coupling, minimum oil ring, minimum output speed.
Power of driving machine is transmitted through the primary wheel on to the working oil, the working oil is accelerated in the primary wheel and the mechanical energy is converted into kinetic energy. The secondary wheel absorbs the kinetic energy and converts it back into mechanical energy. This energy is transmitted to the driven machine.
Rise in secondary wheel (driven shaft) will be steplessly.
Speed of secondary wheel is smaller than the primary wheel which is known as slip.There will be temperature rise due to slip, so cooler is required to cool the oil.
Control of scoop depends on the control system for Feed water header pressure control system.