Replacing 2 pump with 1 bigger pump and combining 2 suction lines to a suction header 5

[DediRMM]

Hi all. I got an idea about replacing 2 pumps with 1 bigger pump by combining 2 suction lines to a suction header. Suction line is from cooling tower. I would like to hear some advice. Thanks.

 

[Artisi]

Would suggest just a little more technical detail might help, but don't over do, we just love dragging out all the relevant details as we go along.
A good start might be flow and head involved, existing pump details, proposed pump detail, an installation schematic.

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]

Seems like a good idea. You just need to design it properly and consider NPSH.

If the total flow is the same the shouldn't be any big issues but you don't give us any details so impossible to comment.

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

 

[1503-44]

Are you sure? Two pumps, even if they are smaller, have better reliability. If one stops working, you would still have the option to run the cooling tower at 50%. If that sounds good, then don't do it.

Statements above are the result of works performed solely by my AI providers.
I take no responsibility for any damages or injuries of any kind that may result.

 

[Artisi]

Using the same analogy, 3 x 50% installed pumps is even better.

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.)

 

[DediRMM]

There are 4 units of circulating water pumps (BB1 type) of same size. They operate at 1500m3/h with head of 30m each. I think there are 2 standby pumps. New pump will be operated at 3000m3/h with head of 30m. The plant is 2x7MW (CFPP). Please see drawing from the link.

I do not have data about outcomes from the cooling tower. It seems to me that combining 2 suction line for 1 pump is not a bad idea for this case right? Thanks.

 

[LittleInch]

Ok, there's a few things going on here which you need to consider.

1) what you're now doing is turning four separate units (the cooling towers) into two. Hence your turn down is now 2:1 not 4:1. if that's ok then you can consider it. You now won't be able to operate 3 units, only 2 or 4. only you can decide if this is a good thing or not.

2) To connect just the outlet of the tower pump inlet lines risks the two towers operating at different depths. Things are rarely exactly equal and any flow disturbance could result in one tower overflowing and the other almost dry. So if you're going to do this you need to bash a hole in the wall between the two and create a single sump area.

3) your bigger pump may be less power than your two smaller units, but you need to confirm by looking a the data sheets. but if they are the same power, why are you bothering?

4) Replacing two smaller units with one bigger one means: bigger cable all the way back to your MCC. A bigger MCC. A bigger breaker. A bigger volt drop when you turn it on. Don't neglect the electrical side of this. It could cost more than replacing the pump.

5) A bigger pump is bigger - Do you have the space to install it?

6) what's the upside?

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

 

[1503-44]

Little Inch is absolutely correct. There could be a lot of dominoes holding that present configuration up, besides the reliability issues. This is not something that should be done on a "sounds good, looks good" basis. It needs to be throughly studied to understand total impact. It is probably not going to be worth a messily 5 to 10% savings on power cost. You would really have to have some terribly inefficient units to make it worth the trouble and in fact, if that were the case, you should probably just replace them with new more efficient units of the same size. You may be just looking at the tip of the iceberg.[pre][/pre]

Statements above are the result of works performed solely by my AI providers.
I take no responsibility for any damages or injuries of any kind that may result.

 

[DediRMM]

Hi Littleinch, 1503-44 and Artisi. Thank you for your time and for the advice, highly appreciate them. This is my first thread as new comer to this forum and I feel so lucky to have your good advice gentlemen.

I never had a chance to visit the power plant, nor get adequate information from them so far. It becomes more difficult to arrange a visit during the covid pandemic. Hope to get more details from the plant engineer soon.

Yes, Little inch is absolutely correct. I need to check available space for bigger pump.

Forgive my english,about "the upside" that Littleich is asking. Does it mean advantage of doing the replacement? If so, I need to study thoroughly as said by 1503-44.

 

[LittleInch]

Yes. Upside means what is the benefit or advantage of doing this?

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

 

[1503-44]

Yes, it means the long list of advantages you will need to sell that idea.

I suspect, since you now mention this is a power plant, that reliability will be an extremely critical issue that will have contractual consequences in addition to lost sales opportunity, if the plant cannot generate the agreed amount of electricity when the large pump is down for maintenance, or repairs.

Statements above are the result of works performed solely by my AI providers.
I take no responsibility for any damages or injuries of any kind that may result.

 

[horacio Torres]

The use for several small pums is a matter of reliability..

For utilities reliability is set  the n + 1 units criterium just to have always one ready for start up when the running pum trip.

Clients ask for n+2 in cases when their experience shows that cooling water pumps maintenance are  longer compared to normal centrifugal pumps. Also we recommended it for the cooling towers and  steam power generation process than support utilities  refineries or petrochemicals plants.
Horacio