Removing scale from evaporative condensor by freezing

Hi all...
I have been sort of put in a position of looking into the cause of excessively high head pressures at our plant after a downsizing caught our refrigeration engineer and put him out the door.
What I have discovered is an extreme buildup of scale on the condenser tubes and a water treatment program that is ineffective. I would estimate at least 65% of the tube surface is covered and in many places the scale has actually bridged the gaps in the tube bundle. First - the provider of the water treatment service is being changed. Second - I need a stop gap solution to help out with the high head pressures until I can get a justification and condenser replacement worked in.

Mechanical cleaning has met with limited success, I am not yet ready to dive into a chemical cleaning and have heard you can freeze the condenser coils to cause the scale to crack and loosen its grip on the tubes. I understand the basics behind task, but would like some input on how best to accomplish.
Does anyone have a particular method they have used and had decent success?

thanks
Travis

Travis, as I read it you are not a Refrigeration Engineer.
Proposing to freeze the condenser coils is madness.
If you can create enough thermal movement to crack of the lime scale build-up.
What do you think it will do to your condenser tubes?
Get a decent chemical company in and seek someone who knows about refrigeration systems.
Tell the accountants that they have caused the huge expense you are about to incur and to increase the budget available.
By getting rid of their competent person.
Personally I hope it all goes wrong and you let us know!
Because then someone may realize that a pen does need a spanner sometimes.

If I have read your summary wrong and you are an engineer that has walked into this situation.
Then someone may help from this forum.
With the way I read it at this moment, it's not me!
Grizzly

Travis,
You do not need to replace the coil, chemical cleaning is the solution. If you are not prepared to take this on then find a contractor who will, paying someone now will save you a lot of money and headache's later. Look up a product called rydlyme.

several points....
Right! i am not a refrigeration engineer, neither was the individual that was previously in that job. Even though they called him one. He was the one that didn't keep an eye on the water treatment firm.
I am schooled in commercial refrigeration..... I realize there are significant differences.
The composition of the scale is roughly 1/2 and 1/2 calcium carbonate and silicate. The silicate will be the problem.
Just how different is the construction of the condensor coil from that of an evaporator coil to be so violently opposed to the freezing of the condensor coil? I hope that the scale will shrink at a different enough rate to loosen up its grip on the coil.
When has pointing out the obvouis ever worked with an accountant? :)
Is there a real purpose in hoping it all goes wrong?

thanks
t.

Yours is a good reply Travis.
If your company get you the assistance you need then you will prevail.
Grizzly

Hi Travis,
evapcondensers by there nature evaporate huge amounts of water to acheive the result, therefore all the soluable minerals concentrate in the basin, and so will separate out on the hottest bit, the tubes. You need to shock dose system with chemicals, next problem will be all the water strainers will clogg up with scale.
There will be no real short cut solution to your problem, heat transfer is restricted by calcium build up, you could concider flooding basin to waste and take advantage of colder ground water temps, but I would pick the spray nozzles are also half blocked with gunge build up compounding the whole situation
ps , accountants look at down time and costs envolved, get the system sorted with a over spec'd budget, if you recover situation under budget, he will love you long time

Hi Travis
Chemical cleaning is the way to go but make sure the company doing the the job are aware the coils are galvanized. They will have to use a chemical that will not damage the galvanizing. I have seen people use acid to remove the scale and id did but also removed the galvanizing.
I would talk to your new water treatment company they should be able to help.
Regards
Paul

Mix 40% water with 60% vinegar, [ the simple type you get in food shops] fill up the condenser, heat it up to 50C, let it stand for one hour, wash it with clean water and repeat if necesary.

Quote:

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Originally Posted by chemi-cool

Mix 40% water with 60% vinegar, [ the simple type you get in food shops] fill up the condenser, heat it up to 50C, let it stand for one hour, wash it with clean water and repeat if necesary.

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Chemi is short for Chemist then eh?

Does that actually work?
Grizzly

Grizzly my friend, I am totaly serious, I use it for so many things around the house and at work.

http://odyb.net/food-cooking/62-litt...es-of-vinegar/
http://ezinearticles.com/?How-to-Rem...cale&id=127981

and there is a lot more.

I think i will probably just get a batch of inhibited sulfamic acid and run that overnight until the calcium carbonate is at least gone. I am afraid i dont have a large enough suction port near enough to the condenser to get adequate flow to freeze the unit.

thanks
travis

Been added to my favourites page.
Thanks Chemi.
Grizzly

Some chemical companies have additives that can gradually remove scale. This approach will not damage the galvanized layer and scale will be release as sand.

Right first off you say you have a high discharge or head pressure problems. There is no quick or cheap method of curing the calcium build up. A good idea would be to have a piece of it analysed to see what it is then make some more enquiries. If it is scale build up from a high calcium count or hardness in the make up water then you need to attend to that by softening and in fact over softening will slowly start to disitegrate the build up and it will fall off and be removed by your filtration plant or as part of the process when you clean and disinfect the condensers. This is a long term process and requires diligent testing and maintenance of softners etc.

However your head pressure problem could be something else. Does any part of your plant run in Vacuum. Have you checked the system for non condensables? Do you have a purger? Is it working? I would start here first. The build up on the condenser is something that has been happening for a while it will not have effected the head pressure all of a sudden. Calcium build up is quite rapid but the effects take a while to be felt.

I am aware of the acid in vinegar and other household products that have excelent descaling and anti oxidisng properties, and I am impressed that they've been mentioned here. Where chemicals can cause a problem with corroding or compromising their agressiveness and taking longer to acheive descaling. Ozone generating systems are an option to reduce limescale, I found this out whilst reinstating ozone systems on laundy equipment. A site that I attend hadn't had their system in use for some time, and after about a month I reinstated it they were getting problems with the drain valve blocking.

This turned out to be a sludgy putty like substance that caked up the drainage system on several occasions, then eventually cleared up. Over the period of about a year the ozone system developed other faults due to its age and condition, then was off line for a few month, then after when it was repaired the same problem would occur. Nobody could put there finger on what this putty sludgy like substance was, then the penny dropped due to the coincidnece of the problem only occurring after the repair of the ozone generator. This was a site out in Hull which has the hardest water in the UK, but when I do any work on the machine now, the tub is so bright it looks brand new. The ozone will also keep all bacteria level down well below its marginal level. They do go wrong but are quite simple to fix once you have worked with them for a while, and some of the parts can be replaced with other off the shelf parts designed for other plant. As the specialised supplier parts can somewhat be over priced.

this topic is of special interest to me, since we also plan to purchase an evaporative condenser, and scale buildup is a concern, based on some plant operators i have talked to. our water source also has many minerals which may aggravate scale buildup. i will post later some information i obtained when i attended a water convention . maybe, some of you may have heard of them and would appreciate your comment also.

We used formic acid, a naturally product made by ants in almost an exactly equal situation in a BAC NH3 evaporative condenser. There was in a 800 kW machine more than 2 tons (metric) scale in it.
But it will take long to remove this. Filters and floats will clog and needs daily checkup.
If your machine is 25 years old or more, replace it, tubes will be affected also.

a quick soloution to yr high discharge pressure is to reduce the size of your evaporator or load you reduce its size the head will drop as its an equal equasion have done it many times on supermarket plant :) turn off 3 or 4 evaps plant works all comes down to temp turn them back on at 30 min intervals :)

chemi am likeing the vinegar approach the fire service use white vinegar on there hoses to clean them and remove lime scale and no thats not a rude joke before someone jumps on it have also heard of magnets being used to reduce limescale but have not seen if its effective

We used the inline permanent magnet on the water supplies to the humiditanks on the Deltaclima and Isovel units back in the eighties. They said it kept it down to a minimum but didn't stop it altogether, they still got caked. Somebody suggested flushing the tanks on a regular basis??? but couldn't see they were making the problem worse. Eventually sometime after till I was blue in the face suggesting it, they agreed to modify the condensate tray and use the condensed water from the trays fed with fresh water to top up the tanks. They tried this and it brought the scaling down to an even lower value almost solving the problem.

A time to time (several times/day) drain of the sump water is also needed, otherwise you will end with highly concentrated water.
We do it every hour for +/- 20 seconds.

Quote:

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Originally Posted by Peter_1

A time to time (several times/day) drain of the sump water is also needed, otherwise you will end with highly concentrated water.
We do it every hour for +/- 20 seconds.

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Peter seems like you would either be draining when you don't need to (therefore using water unnecessarily) or not draining often enough. we use a conductivity meter to determine when to "blow down the system"

emmet, since you did mention that you first check for conductivity before draining, what value of conductivity do you use as reference. our daily routine is to dump 1 drum (approx 180 liters) from each cooling tower. what about value of the tds ?

I just want to know is there any reaction of Sulfamic on galvanising or not.Kindly advise as I want to apply this application to my system.

Regards

Asheesh

Quote:

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Originally Posted by trsimmons7

I think i will probably just get a batch of inhibited sulfamic acid and run that overnight until the calcium carbonate is at least gone. I am afraid i dont have a large enough suction port near enough to the condenser to get adequate flow to freeze the unit.

thanks
travis

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The conductivity you will use for your "bleed setpoint" will be determined by the amount of calcium and alkalinity in your make-up (feed) water. Your water treatment service technician should be able to show you how he calculates this. As an example:

If your feed water contains 120 ppm Ca, 140 ppm M-Alk, and 420 umhos Conductivity:

at 2 cycles, it will have 240 ppm Ca, 280 ppm M-Alk, and 840 umhos Conductivity.

at 3 cycles, it will have 360 ppm Ca, 420 ppm M-Alk, and 1260 umhos Conductivity.

at 4 cycles, it will have 480 ppm Ca, 560 ppm M-Alk, and 1680 umhos Conductivity.

A very rough "rule-of-thumb" would be that a phosphonate-based scale inhibitor will keep minerals in solution until (ppm Ca) x (ppm M-Alk) > 200,000. I usually lower my setpoint to ~160,000 for added safety.

In the example above, the water at 3 cycles has 360 ppm Ca, and 420 ppm M-Alk. (360x420 = 151,200) So I would use 1250 umhos as my bleed setpoint, allowing the controller to bleed the tower water down to 1150 umhos before closing the bleed valve and cycling the water back up.

There is no "magic" in water treatment, only math. If your water treatment salesman is not able to show you the calculations he is using and tell you why they are valid -- find someone else. Or consider purchasing a feed/bleed/chem delivery system that is fully automated. The chemicals are relatively inexpensive - the real cost is the technician servicing them.

Asheesh,

Remember that you will need 2 pounds of Sulfamic acid to neutralize every 1 pound of Calcium Carbonate.

You can purchase blends of Sulfamic acid from water treatment providers that have metal inhibitors (usually borates and triazoles) to prevent corrosion. The biggest problem is that any acid treatment removes the passivation (oxide coating) from the galvanized surfaces, allowing zinc oxide formation (white rust) when the tower is put back in service. You must re-passivate the galvanized metals by running high-phosphate or high-alkalinity conditions for a period of time, until the metal regains it's protective oxide (passivated) coating.

Each tower manufacturer has their own recommendations for a passivation process.

Good Luck,

thanks for the advise, adk mike. i have tried to have our condensers de scaled, and had chemical added (daily dose, as recommended by supplier). unfortunately, the treatment only aggravated the scale formation. i gave the supplier two more chances to correct , but it still did not work out. i am looking for other reliable dscaler suppliers here. by the way, has any of you heard of "VAF filtration systems" ? I will ,again try to scan their brochure and attach it later (had no luck , attaching pics on previous occasions here ). their website is www.valveandfilter.com . it is an american company, i think, since the address of its application engineer is in Arvada, Co 80002 (colorado ?).

Thanks a lot Mike for your valuable advise.
Regards

fellow members, i attached the brochure from VAF. They are offering filtering system for cooling tower/evaporative condenser. Has anyone of you used their equipments ? How did you find the equipment , in temrs of removing scale buildup /sedimentation from cooling tower/evaporative condenser. For sure, we do not have the budget for purchase of the complete sysetm they are offering. But purchase of , just the "cylindircal equipment", where the filtering occurs, is being looked into.

Attachment 7993

hello again, fellow members. i attached a brohure of "LAKOS". I think working principle of this is quite similar to the VAF , which i also sent. has any of you used this system ?Attachment 7994

You certainly can crack the scale off an evap condenser by freezing it. And I would not even try to write a procedure for a site/circuit I did not know. But the IIAR site has an article from a tech presentation on it. Its the expansion of the ice that cracks the scale; nothing to do with the change in temperature shrinking the tubes.

And someone said the magic words as it applied to chemical shocking: Dilution, time, passivation. Apply all three with an understanding of where your circulating water is at....And consider: It is best applied to each condenser, independently; those with a common or remote sump are going to have a different management topic than those able to work "one sump at a time".

I personally advocate some "field effected" desuperheating when targeting condenser scale with chemicals on an operating evaporative. Otherwise: the leading end of the tubes gets relatively high dose of chemical, the tubes being so much hotter, and will tend to be more prone to disruption of the galvanic coating as a result. Also tends to be the heaviest layer of scale there.

I've also done both at the same time....but not with the conventional condenser pump. That kind of happened by accident the first time, but it is highly effective.