VFD application on Pump

[icecool]

Hello Everyone,

Can anybody suggest me whether it is useful of adding VFD in Boiler feed pump in a power plant.

I gone through the details. I understand the advantages of VFD but not sure about the overall burden of VFD on O&M cost.

The overall cost of VFD is almost equal to the cost of Motor itself. 1t increase the overall budget cost. Therefore, it is important to understand the Energy saving, ROI, and O&M difficulties.

Please suggest the VFD effect on the above mention parameters.

The plant detail is as follows

BFP motor rating : 900kW

Frequency : 50Hz

Please note that the plant is Solar thermal and it has cycling operation means pump will start every morning and shutdown in the evening.

 

[LittleInch]

Although you don't say it I can only assume that your BFW pump has quite a variable flow? i.e. as the sun comes up the amount of heat energy collected gradually increases to a peak and then slowly winds down? Can you confirm or provide the range of flow?

Hence your issue is how to do this change of flow rate effectively. More (3 or 4) smaller flow fixed speed pumps would be better on a BFW supply than a single VFD unit as they don't work well on fixed head variable flow duty. This would also reduce your starting current and only be using power when you need to.

If your flow is somehow fairly constant, then size your pump or pumps correctly and get the highest efficiency you can and forget about a VFD on BFW pumps. If starting current is your issue there are other ways to soft start large motors without using a VFD

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[BigInch]

Where they build these things, sun is normally on or off (day or night). When sun is on, the parabolic nature of the collectors focuses the available energy efficiently at relatively wide incidence angles. It should be able to generate full power from at least 9 am to 6 pm and otherwise most likely be off. The heat transfer medium will quickly heat up, then they will go for full flow. The more heat going to the generator, the better. Solar driven turbines are relatively small when compared to conventional turbine generators, so they tend to be day time peaking units, run either on or off, full or nothing. See the load profile in the link, not much more than a 1 hour ramp up/down,

http://www.volker-quaschning.de/articles/fundamentals2/index_e.php

Learn from the mistakes of others. You don't have time to make them all yourself.

 

[BigInch]

Reminds me of the compound housing in Saudi Arabia. The water tank was on the roof. If you didn't take a shower by 8 am, you couldn't take another one until 1am the next morning, after it had cooled down enough that you could tolerate the temperature again.

Learn from the mistakes of others. You don't have time to make them all yourself.

 

[LittleInch]

Fair enough - I was just speculating as to why he though a VFD was required. "Cold" water supply can be a bit of an interesting concept in many places. We used to hang the washing out at night in KSA otherwise it would get dried to a crisp and no amount of ironing would take the creases out....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[BigInch]

Like most, he probably believed the usual misconception that you can (always) save energy with VFD, or maybe he just wanted to soft start and didn't know that there are soft starters available separately, without the excess baggage of a VFD.

What many eventually find out, is that they spend 5 to 10% more energy when using a VFD, because they add them into a system that had a control valve before and then run them where the control valve would have served just fine by itself, and/or they forget that the VFD gives off heat into a space that they then have to cool. Electrical losses + HVAC load....



Learn from the mistakes of others. You don't have time to make them all yourself.

 

[ScottyUK]

There are many good applications for a VFD where savings can be realised, but BFW pumps aren't one of them. Any technology can give a bad result if badly applied.

 

[dcasto]

If the system needs less flow, ie less boiler feed water, then pinch the discharge and back the pump up the curve and lower the horsepower. In my area we have to use vfds only because we can't soft start or worse yet across the line start. Then again, the motors are under 200 hp so vfds are not that expensive.

 

[icecool]

Thanks all for your valuable input.