Boiler Feedwater VFD

[haze10]

Looking at an energy conservation measure. Want to install a VFD on the boiler feedwater pump to maintain a constant pressure regardless of flow rate. Understand that I need a pressure discharge 3% higher than the steam relief valve.

Has anyone done this, any literature or links?

The other idea is to reduce the amount of recirc back to the deairator tank. I can do the thermal calcs to determine min flow to stay below flash point, but does anyone know if there are code minimums, or safety factors I should consider.

 

[JimCasey]

Valtek makes a control system called a Starpak that integrates into their valve body. It has upstream and downstream pressure transducers,Temperature sensor, and the digital controller mounts directly to the valve. It can be programmed to control almost any variable. Control is near-instantaneous since everything is all in one spot-not strung all over the plant. You might consult with your local Valtek rep with your process parameters so that they can select the appropriate valve to match your system needs.

 

[haze10]

I've used VFD on many pumping applications and thing this should be resonably easy. Boiler steam relief valve setting is 250psi. ASME states feeder pump discharge is to be 3% higher plus piping head loss at full flow. So this would be 257.5 plus another 20 for a set pressure of say 280psi. This is what the pump puts out at full flow, but at low flow pressure rides up the curve to about 330psi. Reducing the pressure to 280 psi at low flow would save 10HP according to the curves. The control stratergy would be as original, same recirc orifice plate, same flow control valve. All I would be doing is installing the pressure transducer on the discharge before the control valve, and tie that directly to a VFD, the AB VFD has built in PI control. As long as the accel time is set low, pump should be able to respond quite easily. I don't understand why others are so skeptical and find this so complicate. I have seen designs that tried to control flow with the VFD or do on/off control and that I would think would need a lot more design.

 

[ozmosis]

haze10
you may wish to have a read through this similar thread:
thread407-150339