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Changing to a larger horsepower pump
2

Changing to a larger horsepower pump

Changing to a larger horsepower pump

(OP)
I work at a power plant that uses river water for cooling. The water is brought in by (8)1000hp pumps. At all times at least 6 of these pumps must run. The problem is is that if one of the electrical feeders goes out - it takes out at least two of the critical 6 pumps. It has been suggested to replace the existing pumps with larger ones...like one 2000 Hp to replace (2) 1000 Hp.

What is the essential data required to determine if this is a feasible idea? I'm obviously not a mechanical engineer.

RE: Changing to a larger horsepower pump

You need to get a mechanical guy to look at the overall mechanical design.  There may be limitations elsewhere in the system that might make such a switchout ineffective.

TTFN

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RE: Changing to a larger horsepower pump

2
1 Cost of larger pumps
2 Cost of probably increasing the pipe diameters between pumps and headers (both suction and discharge) and header diameter.
3 I would guess, since I assume you're not changing system flowrates, only consolidating pairs of pumps into 1 unit, the delivery piping won't need major changing, but I sure can't tell from here.
4 Shutting down and ripping up the old foundations, putting in new ones, or can you build a new pump area with new piping power delivery feeders to that area?  If shutdown is prohibited for one reason or another, you're probably better off looking at a new facility in a nearby area.
5 Will the new pumps & pipe arrangements fit into the space available?  
6 Higher power requirements might affect your wire diameters
7 A larger pump starting may affect current drawdowns
8 A larger pump may affect transient pressures in the piping.
9 Soil must be suitable for foundations carrying higher loads without adverse settlements.  Check underground for clearance for new fdtns.  Replace any underground services that are affected.
10 Can you get the larger pump into the space available and still have access and lift out parts for maintenance?
11 Don't forget the auxiliary equipment may be larger too.
12 valve and fitting costs in any pipe segment that requires a new diameter.
13. watch the space required for making piping turns with the new diameters
14. pipe support elevations may need changing
15. pipe stress may need to be checked
That should get you started.
What makes you think that 2 big ones won't go down?

http://virtualpipeline.spaces.msn.com

"We can't solve problems by using the same kind of thinking we used when we created them." -Albert Einstein

RE: Changing to a larger horsepower pump

and a new pump area may require a special geotechnical study.  Best to have at least one test hole under each pump, although if close together, you may be able to cut the number of test holes.  One thing about geo, the more test holes the better, especially if the land use before your facility was an industrial area where knowledge of previous use may be lost.  I've found old telephone poles, oil barrels, scrap steel, concrete rubble, misc. trash, even oil lenses.

http://virtualpipeline.spaces.msn.com

"We can't solve problems by using the same kind of thinking we used when we created them." -Albert Einstein

RE: Changing to a larger horsepower pump

What is the difference between 2 x 1000 hp and 1 x 2000hp pump going off-line?
If it were me with this problem I would be investigating modifying electrics and not replacing pumps which is probably cheaper by a huge margin and will give you better pump coverage.

RE: Changing to a larger horsepower pump

If the pumps are electrically driven this could impact the electrical systems too.  Physically the size of the medium voltage starter may not change.  The starter could require a contactor with higher ampacity.  The motor conductors from the starter likely increase.  This may require larger conduit.  Being a power generation facility the inrush from "start" until the pump is up to speed might be no problem.  If the pump is remotely located the voltage drop during starting must be reviewed.  Also, the frequency of starts and duration between starts could change due to the increased current.

RE: Changing to a larger horsepower pump

(OP)
From strictly an electrical reliability point of view, this idea makes some sense because you could have totally redundant systems. In other words we could have 4 pumps on one switchgear, 3 running and one spare. And the same thing on the other switchgear.

Actually the plan will likely be to modify the electrical - as in installing (3) lineups of switchgear, 3 pumps each gear all installed from a different feeder. It's still going to be expensive but as the responses show...probably not as much as replacing the pumps.

RE: Changing to a larger horsepower pump

Makes sense to me- why change out good pumping equipment already installed and proven when the problem is with the electrics.

RE: Changing to a larger horsepower pump

Where do you get cooling water for a black start?
Don't you have a couple of big Diesel pumps?

Mike Halloran
Pembroke Pines, FL, USA

RE: Changing to a larger horsepower pump

Maybe it is not black start.  Very few are.

rmw

RE: Changing to a larger horsepower pump

bdn2004..

Have you seriously considered adding a  couple of emergency diesel driven pumps as mentioned above ?

Presumably, your electical problems will not last too long and the diesels can buy you a few hours/days worth of repair time.

There are some used diesel driven fire pumps on the martket in the size range that you require.

-MJC

  

RE: Changing to a larger horsepower pump

(OP)
MJCronin,

The new electrical system we are proposing has 3 different feeders, each capable of running the minimum (6) requied pumps at once.  In normal operation each feeder would assume 1/3 of the load, and auto switch if it lost power to another feeder.

I'm not following why you think adding a couple of deisel driven pumps would be more reliable.  Please explain. Thanks.

RE: Changing to a larger horsepower pump

It would most likely be cheaper to study your electrical system and modify to eliminate any "single points of vulnerability" as it's called at our plant.  For example, if you determine that there is one single relay that could fail and take out one set of switchgear, modify the circuitry so that there are two redundant relays and both must sense the actuating condition before the feeder is tripped, etc.

Adding the diesel-driven pumps will not increase the reliability of your system but instead will provide you with backup to take over if there is a failure that takes out more than two pumps.

RE: Changing to a larger horsepower pump

Backups increase system reliability.

Say the probability of failure of any given unit is 0.1
and you must have 1 unit running to operate the system.
 
If you have 1 unit, the probability of system failure = 0.1
Reliability_1 (Probability of running) is 1-.1 = 0.9

If you have 2 independent units, the probability of both failing is 0.1 * 0.1 = .01, thus System Reliability (needing only one operating is) = 1 - 0.01  = 0.99

System Reliability has been increased.  

http://virtualpipeline.spaces.msn.com

"We can't solve problems by using the same kind of thinking we used when we created them." -Albert Einstein

RE: Changing to a larger horsepower pump

I have nothing to solve the OP's problem but I'm just curious was a black start is?

RE: Changing to a larger horsepower pump

Starting something when the electrical power is off.  Usually its a diesel generator somewhere that can deliver enough power so the plant can at least go on standby in a ready state and wait until normal power returns.

http://virtualpipeline.spaces.msn.com

"We can't solve problems by using the same kind of thinking we used when we created them." -Albert Einstein

RE: Changing to a larger horsepower pump

If you have two spares now and room to put the new switchgear without removing the existing swichgear ( all at once that is .  You may be able to do all the elctrical work without any downtime. It's a matter of scheduling and co-ordination.
I wouldn't worry about diesels to run the pumps, if you loose power you have probably lost power to run other essential equipment in the plant ( like hot well pumps, closed cooling water, seal water etc. etc. )
A Black start is starting the plant with all external power lines de-eneggized. The plant is isolated from the grid.

RE: Changing to a larger horsepower pump

Two comments;

Pumps are not apples.  One two thousand HP pump doesn't necessarily equal two one thousand horse power pumps so unless you just happened to have some pump choices that were made in heaven halving the pumps might not be the answer.

Second, even if there were some perfect selections in the pump catalog that would offer you that solution, the infrastructure - the piping, foundations, suction pits, and lots of etcetra would have to change with the pumps so it would be major major surgery.

You are trying to solve a symptom of the problem.  The symptom is that you lose two critical pumps when you lose a circuit.  Solve the problem of losing the circuit and the pumps you have will do just fine.

Now an added comment.  I'll bet any plants in South Florida that had black start capability this afternoon were danged glad to have it (and probably used it to get back up.)

rmw

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