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VFD application on Pump

VFD application on Pump

VFD application on Pump

(OP)
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.

RE: VFD application on Pump

Its way too complicated to give a specific recommendation here - and its not a free consultancy!

In general i believe that a boiler feed might be a suited application - but then again: Some system uses constant flow and som constant temperature - only for the latter VFD is suited.

Best regards, Morten

RE: VFD application on Pump

This this is part of the OP's other thread and seems that advice given is a bit of a waste of time anyway, so this is just more spinning of wheels anyway , we are supposedly talking about 900 kW so this is not a toy and needs someone competent undertaking the project.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

RE: VFD application on Pump

If the system is designed correctly and the motor is suitable for VFD service and you put your VFD unit somewhere where it and any transformers can be kept reasonably cool, then there should be no specific O & M costs other different than you would perform for any other system.

Any "saving" on energy needs an alternative to compare it to 9usually this is a fixed speed drive which then needs throttling to prevent pump over run and hence "lost" potential energy of the fluid turning into heat. VFD is not always less energy - there are some significant extra losses in the VFD units and your pump may not be operating close to the BEP. However VFD in your case may be the only way to maximise your head / flow and stay within the limits of your system and VFDs are good at that.

Far too many variables for a forum like this to advise.

My motto: Learn something new every day

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

RE: VFD application on Pump

VFD on a boiler feed pump?? Probably not the best idea. BFW pumps usually have a high head at all times, at low or high flowrates. VFDs will not generate high heads at lower speed. In fact at 50% of rated flow, they will produce roughly 0.5^2 = 25% of their rated head. Note that 25% head probably represents a much lower pressure than you would need to get into the boiler.

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

RE: VFD application on Pump

I had came across pump specification prepared by a world re-known engineering company asking for VFD for a centrifugal pump rated for 25 meter head with a 5.5kW motor ponder

RE: VFD application on Pump

Can trump that, once had a large axial flow unit rejected because the overall efficiency exceeded the guaranteed efficiency by 1.5%. After we stopped laughing and realised he was serious decided we should point out what a w anchor
he was.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

RE: VFD application on Pump

"world-renowned" can be due to many reasons, these days excellence is most likely the least of them.

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

RE: VFD application on Pump

Agree with BigInch:

VFD's on BFW pumps are almost always a waste of money. Most of the energy goes into producing head, not producing flow. The control range from full flow to no flow will be a few percent of the operating speed, so your control is lousy. Use the money to buy a decent control valve and actuator.

Artisi - really? Wow.

RE: VFD application on Pump

Gents,

look at the OP other very recent posts, This is not a standard boiler feed water pump...., but a solar array

My motto: Learn something new every day

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

RE: VFD application on Pump

OK, I totally miseed that.

what operating pressure does a solar boiler operate at? It's obviously a decent size boiler to require a 900kW BFW pump.

RE: VFD application on Pump

Plus it's all wheel-spin at the moment, as it seems the OP hasn't ever established if the pump can operate at 3600RPM.
No pump data has been posted - so we are all crystal ball gazing and who would know what the answer is likely to be.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

RE: VFD application on Pump

(OP)
The Pressure in Steam Generator is 110 bar(a)

Its 3000 RPM (please see the 1st post Frequency is mention as 50Hz). Does it matter whether its 50Hz or 60Hz frequency?

The pump flow rate is 150 m3/hr. it's a BB5 pump.

Let me know if any more details needed.

RE: VFD application on Pump

Brand, model, pump curve, wouldn't hurt, plus contacting the manufacturer to establish if it can in fact operate in the region you want wouldn't hurt you.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

RE: VFD application on Pump

icecool, please explain what you are doing, your first post on the other matter was 1100m3/h with 900kw - now this post is 150m3/h with 900kw.
It's all far too confusing for my elderly brain - how about sitting down and putting something together that is meaningful to all interested parties.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

RE: VFD application on Pump

(OP)
Artisi,

You are combining 2 different posts..

This VFD is for Boiler Feed Pump while the other pump was HTF (High Temp Fluid) pump..So both are independent and flowing different liquid in different circuit.

RE: VFD application on Pump

I am not combining the 2 different systems, your initial post in this thread said 900 kW 50 hz.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

RE: VFD application on Pump

Of several types of solar thermal power plants, the largest MW are of this type. I assumed the pump he was talking about was the one feeding the steam generator.

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

RE: VFD application on Pump

(OP)
Its a coincidence that both are 900kW. But they are different.

Thanks BigInch, Yes you are correct.

There are 2 streams

Stream 1: Heat Transfer Fluid : HTF Pumps it through solar field, get some heat, and then passes through the Steam Generator and transfer energy to Water/Steam

Stream 2: Water : BFP pumps water to Steam Generator.

Steam Generator is the heat exchanger which transfer energy from HTF fluid to Water..

From VFD point.. Both pumps (HTF Pump and BFP) are big pump with consuming huge MW and both have to start/stop everyday..That is the reason I wanted to know the consequences of using VFD.

RE: VFD application on Pump

The HTF pump may able to benefit from VFD because it is mostly friction head.
But for the BFP, as BigInch explained, it is mostly static head (pressure),It is a relatively flat system curve.
You need to maintain the pump discharge pressure at 110 Bar + piping friction loss at what ever flow. You can not reduce the speed much to have meaningful power saving. Bear in mind the VFD has power loss also and can be costly to maintain.
If you are concern about the daily start stop use a soft starter instead.

RE: VFD application on Pump

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

RE: VFD application on Pump

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/fundament...

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

RE: VFD application on Pump

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.

RE: VFD application on Pump

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

RE: VFD application on Pump

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.

RE: VFD application on Pump

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. smile

RE: VFD application on Pump

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.

RE: VFD application on Pump

(OP)
Thanks all for your valuable input.

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