VFD Feed pump without control valve

[Raai2015]

thread407-150339 : Refering to this thread and my subject, I have two queries.
1. In a case , if i just operate the VFD pump without control valve Option for drum Level control , Will it have enough pressure for attemperatoration? Have anybody used this option (pressure drop i have is Economiser & Primary or 1st superheater and ofcourse static head is same is both)
2. We have the fixed pressure Boiler for all case. Is it good idea to install the VFD without control valve Option? & what is the life time of VFD , becasue if i calculate the payback period it should be within the lifetime.

 

[LittleInch]

It's note easy to answer this and your other question without understanding the range of pressures and flows your boiler package requires.

It's been said in this forum a few times that things like boiler feed and other situations where the static head/pressure is a large part of the pump discharge requirement that VFDs are not the best solution as the frequency range to go from no flow to max flow is actually quite low and creates a problem in controllability and starting of the VFD.

you ask if it will have enough pressure? How are we supposed to know / guess??

Ditto lifetime of VFD?

To get some better response you need to provide data.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Raai2015]

Ok, this is for small 50 bar EfW Boiler.
between 70-100% BMCR , without Operation of controlValve (Eco&PSH&Flowmeasure & some frictionalpressure drop)only with VFD , possible to control the Drum Level, But during the part load not the same case i see in my calcualtion. I m thinking of using the Control valve or orifice. But just want to know from power plant Operators , is it the case or do they come across different situation.
secondly, regarding the Price, if it is operated(PLF 90%, 90%BMCR) for a year it saves around 25,000 Pounds as per my calcualtion. Not sure it is low or high . so i just thought i will calculate the pay back period and see if it is within the lifetime of VFD. But please note i am new to Pump Operation with VFD. I have come across only constant Speed and variable Speed pump.

Baskar

 

[Raai2015]

Variable Speed in the sense hydraulic coupling

 

[Raai2015]

Hello all, I have some results.
Just a little background.
1. Fixed pressure boiler in the EFW facility.
2. Feed pump - Centrifugal pump with VFD
3. Drum control as customer specification: By VFD with three element control
4. Attemperator : Variable type
Activity :
1. Check the Drum level is possible to control with Only VFD as required by customer or do we need Control valve operation as well?
Process Observation on drum control:
1.Feed pump : Is designed with 110% Flow and 115% Pressure as per code requirement
2. During Normal operation (100% Load) : DP across Economiser and PSH is calculated as less than 2.5 bar . But variable nozzle attemperator supplier needs minimum , 3 to 5 bar above the steam line.
3. Even at full load case it will be difficult for the pump control and we may need Main control valve to creat some DP (back pressure).
4. If customer is very strict on Drum control to VFD only option, We may need to use other types of attemperator like venturi type (DP need is +,5 bar) . But the disadvantage is lesser turndown and Not good spray as compared with variable area.
5. Now it is between full load operation drum control with VFD + CV (full load with atleast 5 bar DP) and attemperation with Variable nozzle Valve OR drum control with VFD + CV (zero DP at full load & Some DP at part load) and attemperation with Variable nozzle . Customer to decide.
General :
1. In my calculation with Fixed pressure operation boiler , VFD doesnt seems to cost effective as cost saving per year is 25,000 Euro. Not sure of VFD maintenace cost. If anybody has thump rule idea (some basis ofcourse) would be fair enough to evavluate.