ACC Leak/Performance Issue – Air-Cooled Condenser ...

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• This topic has 33 replies, 18 voices, and was last updated 6 years, 9 months ago by .

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• • AmirParticipant

    Hello Users,

    We have a 1+1 configuration with 15 fans and we are having vacuum issues. The pressure does not go below 4.3 in even with the hogger running. The jets (with any configuration) can't bring the pressure any lower after the hogger comes off.

    We performed leak test using Helium and we didn't find anything noticeable. We hired a leak detection experts and they come by twice and they didn't find a noticeable leak either. Our pressure rises are so quick that the hogger comes on every 7 minutes at about 6 in and runs about 7 minutes until the pressure get to about 4.3 in.

    We leak tested all the piping and systems under vacuum: STG exhaust, steam seals, man ways, rupture discs, condensate removal system (even the isolation valves for back flow), drains, LP blow down tank, by-pass valves, condensate tank,expansion joints, ACC tubes, and '

    We have notices that some of our ACC tubes are cold and some hot and they are in a very close proximity. This usually is a sign of excessive leak.

    We are open to ideas and suggestion. Please share your experience.

    Regards,
    -Amir

  • Chris NannemannParticipant

    Hi Amir,
    Have you performed an inspection of the inlet header? Were you able to spray helium at the top of the tube bundles, right next to the inlet header?
    We have experienced leaks at our tube inlets. They are sometimes hard to find with helium leak testing if you cannot spray all the way at the top, or if it is windy, etc.

    Also, what chemistry program are you running, and what in what steam pH range do you operate?

    I ask this because we found that running too low of steam pH leads to excessive FAC in the STG exhaust header and the ACC inlet header. This was causing a lot of leaks and we had trouble maintaining vacuum for a long time.

    Regards,
    Chris

  • chriskarchParticipant

    Have you checked your hogger suction isolation valve. Your air leakage may be coming from your hogger exhaust piping leaking through the isolation valve. We had this issue. When we removed the valve for inspection we found that there was a failure in the valve seat. This failure caused damage to the valve disk. Further investigation revealed that the valve was not properly rated for vacuum.

  • huubhubregtseParticipant

    Hi Amir,
    helium leak detection is a difficult job.
    It took the Rye House power plant 6 weeks to find the leak. (Loose flange of a pressure test line)
    Helium leak detection is the best way to find leaks but sometimes it takes time to find it.
    we have experienced leaks in bellows as well, especially with multi layer bellows.
    Also the turbine exhaust area could give problems, such as near the gland steam or the casing.

    Huub

  • huubhubregtseParticipant

    Hi Amir,
    if you want to eliminate possible leaks of the hogger and or holder you keeep them in operation. during operation no air can flow into the condenser via this route.
    If al the ejectors are in operation and the vacuum drop is still unacceptable the leak is not in the extraction section.

    Huub

  • huubhubregtseParticipant

    HI

    the bellows are installed in the steam duct.
    they consist of a SS bellows welded to CS rings.
    Some of them are Multi ply where the inner sheet gives the sealing.
    the other sheets are mostly having holes to avoid pressure between the sheets.
    if the innner ring get a hole due to fatique there is a entrance for air into the ACC.
    We have seen this problem before

    Huub

  • mcepedaParticipant

    We had some issues on ACC performance and we found the next on different events:
    ' Condensed traps at holding ejectors were not working properly so the condensed were accumulated so quick up to the point where the ejectors were almost flooded and stopped working efficiently. At that time, we purge the condensed traps almost all days until we can perform a comprehensive maintenance.
    ' Other issue we experienced was on the Steam Turbine Seal system, we found and air leakage through other trap that occasionally empty the water column used to seal the steam extractors from the Steam Turbine seals.
    ' Have you have identified low temperatures on your ACC just at some cells? Or all your ACC is colder than normal? If there are just some cells colder, you can start looking there'
    ' Finally, as a comment, we have found air leakage by ultrasound, if you have this as part of your tools, is cheaper and easy to use; it just need be well calibrated in order to identify air leakages.

  • NickParticipant

    Have you checked upstream of the ACC for air ingress leaks with Helium? Often the ACC is thought to be the source of the leak, yet it is often something upstream of it where the air leak is. If you haven't done so already, think of helium testing upstream.

  • udhay61Participant

    Hi
    Hope you have taken all possible steps to locate the leaks , nice. One clarification is required whether checked the connecting pipe between the air evacuation header running in the top near the ST Exhaust duct . There will be minimum 2 to 4 connecting pipes for each module. Sometime found cracks in that causing vacuum drop. Also exactly in the ST exhaust penetrating portion sealing portion also gave problem. All syphon loops, vacuum breaker etc maybe checked. Thanks.Regards

  • Franco LizaParticipant

    Amir, Has the ST a dog bone expansion joint? If it has it, inspect dog bone (exhaust expansion joint of ST), we experienced dog bone leaks, we sealing external temporally, and during an outage we fixed by re-tightening. Other possibility is leak in valve of hogger (usually is a big valve), they could not be properly sealed.

  • AmirParticipant

    Hello All,

    The company is the world’s best air cooled condensing units exporter supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.

    We finally found the leak!!!

    We got a He hit on a drain from STG #1 Bearing Packing Head/LP Head drain. (see my comment on May 4, at 9:29 pm). The #1 bearing housing/head is located in the exhaust tunnel. We disassembled the housing/packing head and found all the joints were not sealed properly and the contractor didn't torque the bolts to the spec and not enough RTV applied to the surfaces. We found no damages to the steam seals. Note: Our combined cycle was commissioned about 18 month ago.

    After we started the combined cycle, our vacuum went to normal. This is a very hard place to find the leak cause there is a great chance there will be no hit on the drain. We believe the air got into the #1 bearing housing (which suppose to be under atmospheric pressure) from the oil lines cause we tested all the other connections. This is something for A14 users to look into in case they have vacuum leak.

    I greatly appropriated you all comments and feedback.

  • Andy MacqueenParticipant

    '

  • Rishi VelkarParticipant

    Hello all,

    We are having the same back pressure issue and are not able to find the leak. We have to start the hogger every two hours. We had CONCO (leak detection company) out 4 times so far yet had no success in locating the leak.

    The main problem is that even an artificial leak is created by opening a valve and spraying Helium over it is not being detected properly at the air ejector. The test shot takes about 2 mins to be detected a the air ejector further more it is very weak. Has anyone faced this issue before where you were not able to detect even the test leak?

    We checked the air ejector nozzles, the valves and the drains , everything is in good working condition. It just seems as though the helium gets diluted in the ACC since the leak is big. The hogger brings the DO from 700ppb to 200ppb for about thirty minutes and gradually goes back up.

    We have tested the Steam gland seals, drain tanks, by pass valves, DA/condensate tank and air hogger/ejector skid and haven't had any luck but doing testing without getting a good hit on the on the test leak is futile.

    Anyone have any ideas or suggestions as to why we wouldn't be able to get a good hit on the test shot? Can the Air leak dilute the Helium ?

    • This reply was modified 7 years, 5 months ago by Rishi Velkar.
  • vahidjohnParticipant

    Yes you will see a significant temperature difference on the IR camera

  • Marko LazarevicParticipant

    Hello everyone.

    I was wondering whether this is the most suitable topic to express our problem, but I ll give a try. Unit (300MW) is running for more than year and a half. ACC consists of 30 cells, 6 streets, we have 3 vacuum pumps (1 is in operation). During last outage we have made several modification related to boiler side, which is now affecting less steam flow coming to HP turbine. Consequently, more steam is coming to IP and LP turbine ending up in ACC. It is possible that slighty increased steam flow is affecting ACC performance which is slightly different (worse) comparing to previous summer. Actually, this summer, for the first time, we were forced to decrease unit load, so we could keep the unit in operation, as backpressure increased up to 400mbar. As per my understanding, ACC operation might be jeopardized by means of heat transfer decreased or in some cases extremely high ambient temperature which cannot be avoided. On a regular basis we are conducting vaccum leakage test by means of stopping vacuum pump operation, keeping the fans running at the same speed along with constant ambient air temperature (as much as possible). Test lasts for 15 minutes and results are always very good (backpressure increase less than 2mbar/min). So, my question is whether it is possible that dirty heat exchange surface area is biggest reason for ACC performance deterioration (comparing to last summer 30-40mbar higher backpressure in same conditions)?

    Marko

  • Maikol AiraParticipant

    Hello ACC Users,

    I am from Peru. We would like to improve ACC cooling System (water spray or fogging system) to increase Vacuum of Steam Turbine Exhaust and have better performance. We will appreciate if you share with us your experience about it.

    Best regards,
    -Maikol Aira

  • Dear Maikol,

    I represent a HP spray cooling system company and Galebreaker wind screens. We have a test facility to prove the benefits of spray cooling for an ACC. We combine wind screens with the spray cooling to best assure the spray goes into the fans it is intended for. I would be pleased to discuss with you further. You may contact me at

  • Hello Maikol,
    I am agree with Desmond and Ockert.

    If you observe a performance drop, my first advise would be to clean your fin tube with a good cleaning system if it's not already done.

    If during the year the performance is changing due to hot tempreature, fogging can be a good idea only if:
    ' relative humidity is low during your hot season (so you can vaporise a lot of water and get the adiabatic reaction which decrease air temperature)
    ' your hot season is short (it will consume a lot of water!).

    I can support you about this 2 subjects, at your disposal ' (ax-system.com).

    Contact us to discuss your requirements of air cooled condensing unit. Our experienced sales team can help you identify the options that best suit your needs.

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Hello,

I am in the process of trying to decide if our company should switch from: a 60 ton water cooled condenser to: a 60 ton air cooled condenser.

My problem is that I have been unable to get a firm answer on whether a 60 ton air cooled condenser will give the same cooling power as our current 60 ton water cooled????

This if for an apartment complex in the state of Kentucky, USA. Temps typically peak in the mid 90's, occasionally 100+ degrees F. Average yearly humidity is 58% @ 1:00 p.m. to 81% @ 7:00 a.m.

We have been able to maintain a 42 degree chiller water temp pretty consistently. If we could get into the 38 or 40 degree range though, that would be a nice bonus, but that is not critical.

The existing water cooled tower is corroding and must be replaced soon.

It seems that in the long run, an air cooled condenser would be cost beneficial as there would be no water consumption and treatment costs. That seems to offset the increased electrical usage of the air cooled type.

We are using a chiller with 2 reciprocating compressors located indoors and the condenser nearby outdoors.

Any advise on the cooling power of the same size water cooled vs. air cooled condensers would be greatly appreciated.

Thanks. SeeTwo

tonnage The answer is "it depends".

Condenser ratings are provide at specific conditions, and these conditions should be clearly stated by the manufacturer. The conditions include things like mass flow rates for the primary and secondary fluids, the entering and leaving temperatures for the primary and secondary fluids, pressure drop through the primary and secondary sides, etc.

Since you are considering going from water cooled to air cooled you cannot really make a direct comparison. You need to figure out what your actual capacity needs to be, and select a new condenser that will be able to provide that capacity at your location under whatever "design" conditions you elect to use.

SeeToo,

The flow and return condenser water temperatures from the cooling tower will always be lower than the ambient dry bulb temperature (I would estimate by 10 deg. F).

If you replaced the cooling tower with a dry cooler of equivalent duty, the flow and return condenser water temperatures would be approximately 10 deg. F higher than the ambient dry bulb temperature.

Consequently, the chiller will reduce in capacity by at least 15% (probably more), it will also be more prone to trip-out on high pressure during the hottest days.

Assuming your company does not wish to replace the existing chiller, I can suggest three options for your problem.

1. Replace the existing cooling tower with a new cooling tower - there will be no adverse affects on the chiller.

2. Replace the existing cooling tower with a dry cooler - the chiller will be derated and may trip-out more frequently on the hottest days.

3. Replace the existing cooling tower with an adiabatic cooler, this is a dry cooler with water spray fitted - It will give performance very similar to the cooling tower, but without the water treatment costs.

I hope this helps.

Cooky




I don't think you will be happy with the performance of an air cooled condenser unless you have capacity to spare. Water temps will be a good bit higher. But frankly considering you mention chill water temps below 40 and a reciprocating chiller I really think you need to consider a new chiller and some AHU coil replacement. There is no need to run that low of chill water temps. A new chiller would pay for itself in a very short time. It also sounds like you need a system that requires little maintenance. Tower Tech in OK. makes a virtually maintenance free tower that is all FRP so it won't rust. Nalco chemical sells a computer controlled water treatment system that can be remotely check via a modem. Often one can hook up with an energy management company who will finance the whole thing with money saved in power consumption and there will be no out of pocket costs. Air cooled units are noisy and need more space for condensers. They also require more power. Air cooled receip & screw = 1.20 to 1.40 Kw/ton (incl compressor, cond. fan & CHW pump). Water cooled would be about 1.05 to 1.1. The air cooled unit will require less maintenance. If you can provide the additional space for condensers locate them so noise is not a problem, then go air cooled. Note that in the 200 ton & larger size the water cooled system using centrifugal chillers can go down to about 0.8 kw/ton (includes compressor, cooling tower fan, condenser pump & chilled water pump.
CHW pump = 0.05 kw/Ton
Cond Pump = 0.10 kw/Ton
Cooling Tower Fan = 0.05 kw/Ton
Condenser Fan = 0.10 to 0.15 kw/Ton
Recip air Cooled Chiller Compressor = 1.05 Kw/Ton
Air cooled screw chiller 1.2 Kw/Ton
Rotary water cooled chiller compressor = .8 to .9 kw/ton
water cooled centril compressor (200 Tons 7 up) = 0.6 kw/ton First of all is the existing an evaporative condenser with refrigerant flowing through it or a water loop that cools water and pumps it inside to be used to condense refrigerant. If it is the latter I would not do it. I would replace the tower with a new one. I can tell you that with small condensing units a tube in tube water condenser can reject much more heat than a refigerant air condenser when changed out like for like(tonnage rating). If the air condenser is undersized you're beat, you can't control variables like water temperature and flow rates to squeeze more capacity out.

With an air condenser you have dirty coils to deal with and refrigerant leaks. Make sure the piping is done corectly to account for compressor capacity control or you could suddenly start losing compressors when you never did before.

Best would be a cooling tower to keep the refrigerant charge localized near the compressors. Don't trade short term savings for long term problems.

To: All,

Many thanks for all the advise from all the repliers!

I will monitor the water temps we are now experiencing and update this thread after I have enough data.

It sounds like going to the same size air cooled condenser on a water cooled system that is currently adequate, but barely so (not adequate on 100+ days*) would not be advisable because of the loss of cooling capacity.

* However, this spring we did some maintenance work on the coils in the apartments that were not cooling adequately in years past. We replaced isolating valves and flushed coils. So far, there has been much improvement.

So, chiller/tower capacity size is possibly okay. We need more time to test the system in the hottest weather.

To: Cooky,

You are correct that we do not want to replace the reciprocating chiller at this time. We recently re-built both compressors. However, at some point in the future we would consider upgrading to a modern scroll type chiller in our indoor boiler room and continue to have a outdoor condenser (either water or air cooled). I've heard they are less noisy and more efficient with fewer moving parts.

Re: your suggestion #3, wouldn't the evaporating water sprayed into an adiabatic cooler leave mineral deposits behind (and degrade performance in time)? That is why our current water cooled tower is set to bleed off water onto the ground isn't it (to drain off the minerals left by evaporating water)?


To: r22,

The condenser set up we use is the 2nd one you mentioned: A water cooled condenser tower with a water loop that is pumped inside to the chiller.