ACC Leak/Performance Issue

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

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.

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

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

Hello Amir,

Do you have cooled water temperature monitoring and non condensable temperature? Look for big difference between those temperature each street since air leakage will decrease non condensible temperature even more than usual. As a rule of thumb, gap should be around 5 C. After locating the street in trouble, shutdown the fan and monitor with an IR camera how the cold area stars increasing, if there are one. It could help you to find the leakage.

Best,
Manuel

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

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.

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.

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

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.

🙂

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 6 years, 11 months ago by Rishi Velkar.

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

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

Marko:
Contamination of the heat transfer surface can indeed influence the efficiency of the system, I assume by the fact you are asking you have doubts about the cleanliness of the system.

Also external factors such as ambient air temperature and wind can influence ACC performance. Warmer air will of course cool less, due to lower temperature differential and lower density. Also wind draws extra load on the fans decreasing static pressure output of the fans into the ACC.

You could consider having your bundles cleaned as this is typically good practice, I know many sights prefer the spring for this to be ready for hot summer weather, also it could be a good idea to have your fan peformance evaluated to see if your ACC is receiving sufficient air flow, or if more air flow is required to meet this new cooling capacity requirement.

Please feel free to send me a PM (desmond_DOT_dehaan@Howden_DOT_com) if you need any local references that we may be able to provide assistance for you.

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 gmirsky@galebreaker.com

Makoi,

Key is to understand how much cooling capacity increase you are looking for.
Are you trying to improve peak performance on hot and windy days only, or do you need to increase your performance in all situations?
Spray systems were recently discussed in a CTI paper (TP18-02 Efficient Water Use to Boost the Air-Cooled Condenser Performance) a very good document to understand the concepts better. Downloads available here:
CTI Thermal Performace papers

You can also increase performance by improving the air flow through the ACC by mitigating wind influences to increase uniformity, cleaning your bundles and of course optimizing your fan system.

Spray systems, especially aftermarket, should be used sparingly as the ACC was probably not designed for high humidity or even wet conditions inside the ACC.
A hybrid cooling system with cooling towers to address peak cooling loads such as at Commanche can have dramatic performance effects, but are of a different investment level than the above options.

Hi Maikol. I agree with Desmond. Are you trying to get back past performance or are you trying to increase performance relative to design?

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).