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.

 

[MortenA]

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

 

[Artisi]

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.)

 

[LittleInch]

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

 

[BigInch]

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.

 

[Pumpsonly]

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

 

[Artisi]

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.)

 

[BigInch]

"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.

 

[ScottyUK]

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.

 

[LittleInch]

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

 

[ScottyUK]

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.

 

[Artisi]

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.)

 

[icecool]

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.

 

[Artisi]

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.)

 

[Artisi]

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.)

 

[icecool]

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.

 

[Artisi]

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.)

 

[BigInch]

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.

 

[icecool]

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.

 

[Pumpsonly]

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.