AT Two Stage Vacuum Pump

Welcome to CR4. The first thing to check is that there is negligible inward leakage to the condenser as there is nothing better to make a fluid mover run hot than giving it some work to do. Some information on flowrates across the range of plants would be an interesting addition to this thread.

That a Nash delegate has been called in is good, although this individual clearly needs to be there prior to the plant outage and a second call encouraging 'digital extraction' is a vital step.

Do advise developments here.

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Thanks for the Welcome PW,

As far as inward leakage is concerned, they do have 3, in what we would call large leaks. Of course we cant quantify the size of these leaks, but basing them on hit time, time to offscale, and clear out time, we estimated they are the large leaks. The turbine generator and governor end seals are both leaking. The third is a leak on the expansion joint which they have tried sealing with a type of blue tar but of course did not solve the issue. They do have some other minor leaks as well.

Flowrates we would obtain from the Rotometers attached to the vacuum pumps, but sadly, these are not functional at any of the plant sites. While we have requested stations to repair/replace, our requests have been denied.

That's where the problems lie. Stop the leaks and repair the instrumentation. Good luck. <unsubscribes>

One other thing to note, these leaks have been there for years, +5 at least. I know when they have their major outage next year, the governor and generator leaks on the turbine will be fixed when they take the turbine apart.

You don't have a large leak, you have a massive leak, and I doubt that the pump packing is the problem. If it's at a particular station with two identical units then I suspect those pumps are the fine vacuum pumps and they're overheated because they're doing hogging, not fine vacuum duty.

You already know there are back-pressure issues; are there high makeup water levels and poor water chemistry issues as well? If so then I would be looking at the condenser water side leaking into the hotwell, probably leaky rolled tube ends at the tube sheet. I wonder why they don't want to run the ejectors/hoggers to assist the fine pumps.

Let us know what you find.

I agree with the majority of what you have written, but there is a small piece that seems amiss.

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If water is being drawn into the condenser hotwell, while poor chemistry will indeed be an indicator, makeup water requirements won't be high....exactly the opposite. Water sucked into the condenser will yield high water level in the condenser eventually.

"...makeup water requirements won't be high....exactly the opposite...". Correct, that's why I used the word "level" not "requirement" since somewhere in the makeup water system loop an alarm is going to sound about excess water in the system (probably in the deaerator tank, flooded hotwells are usually caused by a burst tube or a failed condensate pumping system).

Okay. It all makes sense now, my misunderstanding.

When there is an answer that is reasonable and gets all the minutia correct except one thing that appears exactly 180 degrees out of whack, it gets to me more than those answers that are obviously completely off base. Thanks for the reminder to check my assumptions.

I'm with RAMconsult on the immediate need for some backing for the vacuum pumps.

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Your question is focused on the vacuum pumps, and the life of those pumps is almost certainly being used up more quickly running hot all the time.

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On the basis of where is the largest hole sucking money out of the plant though, it is unlikely to be in vacuum pump rebuild replacement....

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I don't have to ask, chemistry is problematic, chemical additions have been more frequent, larger. The increase in dissolved gasses has also impacted cleanliness factor, so heat transfer across the tubes is degrading.

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There is money gushing out the door....reduced power from backpressure caused by non condensable gasses and decreased heat transfer, more money for chemicals, money related to increased corrosion and efforts to regain cleanliness, and increased likelihood of equipment failure/repair/replacement. It isn't smart to delay corrections for conditions that create high dissolved gasses alone. sufficient capacity for removing noncondensable gasses sufficient for maintaining decent condenser vacuum needs to be a priority.

Coolant leaking into the vaccum side (into the condenser tubes), depending on the leak rate, will cause a high load of non-condensible gases, but also may wreck havoc on a number of other things including the turbine (high silica loading in steam), boiler corrosion issues, etc. The Nash pumps may not be set up correctly in the first place. If not a large enough leak to account for the heat level of the vacuum pumps, you need to get data from their logs about the back-pressure, and condensate temperature, since temperature goes up with back-pressure.

I suggest a thorough interview with the engineering staff at GD Nash to discuss what is missing. It seems the seals maybe should be wetted to reduce friction?? Another point to bring out, is that even if the basic install steps included most everything, and motor-pump alignment is off, there could be another source of heat, but you did not mention a big vibration problem, so let's let that go for now.

I understand that your vacuum pumps have gland packing and not mechanical seals.

There could be many reasons for pump stuffing box running hot. The indication that there is no visible leak as drops (one drop per second as suggested by OEM) gives dome lead.

Unlike hydraulic pumps (restricting liquid leaking out), the duty of packing in stuffing box of a vacuum pump is to prevent air getting into vacuum pump. This is done by three actions, one: by reducing area of leakage, two: by proving a water seal around the sealing area and last, not the least is to cool. The assurance of water to seal at right place is very important and the proper placement of 'lantern ring' has to take care of this. It is advisable to shutdown the machine and ensure:

1. No objectionable scoring under the packing area on the shaft or sleeve.

2. Clean the water injection port and ensure the availability of water.

3. Clean the lantern ring from sealing.

4. Repack with right sized ropes, the right numbers and positions.

5. Ensure sealing water gets in and comes out, with excess drips at gland to start with.

6. After starting the pump, gently tight the gland till the leak reduces to one drop per second.

7. Try not use (They both have an extra hose attached delivering city water to help them stay cool) external cooling, since bearing area is very close by sealing area and water may engross/mitigate into bearing.