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RANGER1
28-04-2017, 08:10 AM
Interested in most successful method or methods for purging air out of multiple evaporative NH3 condensers.
Plant has no air purger at the moment.
Any feedback would be interesting.
I believe Segei knows the best way.

Tycho
28-04-2017, 05:47 PM
if you have a connection on top of the HP receiver, I would purge hard from there during standstill, because as you know, non condesibles will form a layer between the ammonia liquid and gas.

on systems where the choices for connection is limited there is usually always one on top of the condenser.
in these instances I would stop the system isolate the condenser and purge till I have 0/-10C pressure on the condenser, hoping that the evaporating gas had pulled most of the air with it, then fire up the system to see where we land on the pressure.

Segei
29-04-2017, 05:45 PM
I know one good method. I found it in one IIAR technical paper. You close hot gas inlet into evaporative condenser and continue to run water and fans. After a while whole condenser will be full of liquid ammonia and air will collect in the top part of the coil. This air can be purged. Definitely, you should have 2 or more condensers.

NH3LVR
29-04-2017, 09:28 PM
Always a problem with a system that runs in a vacuum and does not have a purger, depending on how tight the system is. I have seen such systems that had to be purged every day.
Usually I would approach the problem by turning off the compressor and leaving the water and fans on for a time. Note the head pressure when it is as low as it gets. Start purging slowly into water. When the head pressure has fallen and no longer drops you are done.
Some people try to evaluate the bubbles as they rise through the water. I have never found this to be accurate.
This does leave air in the receiver of course, but solves most of the problem.
I did have a issue at one plant with the condensers filling up, evidenced by the fact that the the liquid was leaving very sub cooled. There were four condensers and I purged them all. It did not solve the problem.
I purged a bit from the receiver and everything stared working again. I have no good explanation for that.
Sell them a purger if it runs in a vacuum! It will save them a lot of money and increase their capacity.

Segei
29-04-2017, 10:02 PM
Unfortunately, purgers not always solve the issue of air in ammonia system.

RANGER1
29-04-2017, 10:26 PM
I know one good method. I found it in one IIAR technical paper. You close hot gas inlet into evaporative condenser and continue to run water and fans. After a while whole condenser will be full of liquid ammonia and air will collect in the top part of the coil. This air can be purged. Definitely, you should have 2 or more condensers.

Thanks for responses,
Tried other methods with no result on this particular job (no bubbles in water)
Used above method of Segei & appeared to get lots of air out.(lots of bubbles)
We have been aware of it for about 5-6 year, before that never heard of it.
I guess you just add to the repertoire, makes sense if air is heavier than ammonia won't go to top as we have thought in the past.
I did not purge from liquid receiver, as ran out of time, it has thermosyphon oil cooling with 125mm balance line, thought it may not matter to much, might do it again.
Plant does not run in a vacuum, but did a lot of work on it over the last several months.

NH3LVR
29-04-2017, 11:33 PM
It gets a bit more complicated. The presence of moisture make the NH3 heavier than air. of course we will have some moisture if we have drawn in air. The only place I have been able to remove moisture reliably is draining it from a inter cooler.
What we are really trying to do is to remove non-condensables from the condenser. They cannot get out of the condenser readily through the liquid seal. I have never tried Segei's method. it might take a long time to perform, but I can see it could be effective.
Of course removing the water and the air is going to save operating costs.

Segei
30-04-2017, 03:41 PM
Air in ammonia system is very interesting but not completely understood issue.
This is my point of view. We should purge air from the points where it has the highest concentration. Where are these points? Definitely, you can isolate condenser, run water and fans to condensate ammonia and purge from top of condenser based on gravity. However, it is not the best way to purge. Purging should be done during operation from the area above the liquid in the liquid trap. During operation concentration of air at inlet of condenser will be close to 0% because it will blown by hot gas down to the liquid trap. On the surface of the trap gas velocity will be close to 0 and this is the point where air will be collected and it will have the highest concentration. These are the points where air purgers collect air-ammonia mixture for potential ammonia removal and air purging. I have one probably unusual question about systems with air purgers. How often do to you check tightness of solenoids for each purging point?

RANGER1
30-04-2017, 09:33 PM
Air in ammonia system is very interesting but not completely understood issue.
This is my point of view. We should purge air from the points where it has the highest concentration. Where are these points? Definitely, you can isolate condenser, run water and fans to condensate ammonia and purge from top of condenser based on gravity. However, it is not the best way to purge. Purging should be done during operation from the area above the liquid in the liquid trap. During operation concentration of air at inlet of condenser will be close to 0% because it will blown by hot gas down to the liquid trap. On the surface of the trap gas velocity will be close to 0 and this is the point where air will be collected and it will have the highest concentration. These are the points where air purgers collect air-ammonia mixture for potential ammonia removal and air purging. I have one probably unusual question about systems with air purgers. How often do to you check tightness of solenoids for each purging point?

Probably never unless there is a problem
The way they are normally piped up does not allow in most cases, unless you design pipework to be able to do it.
Have you had issues with that scenario?

Segei
01-05-2017, 11:28 PM
3 years ago I was asked to look at large ice cream production refrigeration plant. I was really surprised to find that this plant operate at 160-170 psig condensing pressure all year around. They told me that at condensing pressure below 150 psig liquid ammonia doesn't drain properly from evaporative condensers. This is very sensitive to this plant because some ice cream production machines were fed by ammonia from HPR. If HPR is empty, no production. They had this issue for 10-15 years. $1,000,000-2,000,000 were overspent only on additional energy. Contractor asked $1,000,000 to fix the problem. This plant has 6 big evaporative condensers and these condensers have shallow 2-3 feet liquid traps. Probably, contractor wanted to make these tarps deeper. I have done investigation and found that real reason is leaking purging solenoid. Every purging point should be purged separately because they have different pressure. Yes, difference can be a few psig but it can make a difference. For example, if solenoids are not tight, point with 153 psig pressure will overpressure and prevent purging from points with 150 psig, 151 psig, 152 psig. If condenser not purged, air will start collect and it will hold the liquid ammonia. So they replaced purging solenoids and issue was solved. Probably, they paid less than $10,000 to do that. I think that many refrigeration plant suffer from leaking purging solenoids.

RANGER1
02-05-2017, 08:31 AM
3 years ago I was asked to look at large ice cream production refrigeration plant. I was really surprised to find that this plant operate at 160-170 psig condensing pressure all year around. They told me that at condensing pressure below 150 psig liquid ammonia doesn't drain properly from evaporative condensers. This is very sensitive to this plant because some ice cream production machines were fed by ammonia from HPR. If HPR is empty, no production. They had this issue for 10-15 years. $1,000,000-2,000,000 were overspent only on additional energy. Contractor asked $1,000,000 to fix the problem. This plant has 6 big evaporative condensers and these condensers have shallow 2-3 feet liquid traps. Probably, contractor wanted to make these tarps deeper. I have done investigation and found that real reason is leaking purging solenoid. Every purging point should be purged separately because they have different pressure. Yes, difference can be a few psig but it can make a difference. For example, if solenoids are not tight, point with 153 psig pressure will overpressure and prevent purging from points with 150 psig, 151 psig, 152 psig. If condenser not purged, air will start collect and it will hold the liquid ammonia. So they replaced purging solenoids and issue was solved. Probably, they paid less than $10,000 to do that. I think that many refrigeration plant suffer from leaking purging solenoids.

Segei,
Very interesting point, as can't say have heard of it.
If not so honest you could be a much richer man $ wise!
Would certainly helped your reputation.
Would it be a possibility if different size or type of condenser has "X" pressure drop more than other condensers, it could also backfeed.
Might depend on brand & type of solenoid.
We use Danfoss or recommended Hansen valves.

Segei
03-05-2017, 03:03 AM
Unfortunately, since I gave my proposal about these solenoids management of this company has been changed twice. Current management is not convinced that I save them $1,000,000 of unnecessary investments. However, they replaced solenoids, lowered condensing pressure to 130 psig and plant work well. During winter operation they run 4 identical condensers. I found that this issue is not so severe when you have 1-2 condensers. When you have 3 and more condensers, it can be bad. I think that after 15-20 years of operation every solenoid can start leaking by. However, many people don't know about it until something significant happened.

sterl
04-05-2017, 08:30 PM
A well purged condenser will run at a lower outlet pressure than an identical condenser that contains a minor amount of non condensables; even if both have the same extent of fans and similar operating. Which is to say, on trapped parallel condensers, the well purged condenser will need to have the highest stack of liquid above the trap. With dissimilar condensers, the effect tends to be amplified. Compound that by the tendency to place the last condenser installed furthest from the discharge main: and you can have serious issues come up with the addition of the last condenser. Everything worked OK before, add one compressor and one condenser and the discharge main gets furthur from the manometric center: and all those 3-foot trapped condensate drains start flooding up.

Tycho
04-05-2017, 11:03 PM
Always a problem with a system that runs in a vacuum and does not have a purger, depending on how tight the system is. I have seen such systems that had to be purged every day.
Usually I would approach the problem by turning off the compressor and leaving the water and fans on for a time. Note the head pressure when it is as low as it gets. Start purging slowly into water. When the head pressure has fallen and no longer drops you are done.
Some people try to evaluate the bubbles as they rise through the water. I have never found this to be accurate.
This does leave air in the receiver of course, but solves most of the problem.
I did have a issue at one plant with the condensers filling up, evidenced by the fact that the the liquid was leaving very sub cooled. There were four condensers and I purged them all. It did not solve the problem.
I purged a bit from the receiver and everything stared working again. I have no good explanation for that.
Sell them a purger if it runs in a vacuum! It will save them a lot of money and increase their capacity.

THIS!

In my first post, i didn't take into consideration that there were multiple condensers, hence a liquid trap on the outlet.
I am mostly used to systems with a single condenser, because in Norway we have abundant access to cold water and cold air :) and most systems run on one single large condenser, be it seawater cooled or air cooled with water mist

When I read liquid trap here, at first I scrunched my nose a little, because I have been on a system where the system was expanded from 1 Howden WRV 255 to two howden WRV 255, and the the condenser was replaced by a much larger one and thermosyphon oil cooling was installed on the new compressor, while seawater cooling was maintained on the original one.

I was there for something completely different and the client was complaining that he was never able to maintain a steady level in the HP receiver, and because of that he never got a stable oil temperature on the new compressor.
The thermosyphon was rebuilt, and the "evaporative pipe" on the thermosyphon was pulled all the way to the top of the condenser, instead of just to the top of the HP receiver which should have been sufficient.

it was one large evaporative condenser, and on the liquid outlet of the condenser there was a liquid trap that went from the bottom of the condenser and up covering 1/4 of the total height of the condenser(yes there was an equalizing pipe from the HP receiver to the top of the condenser).
For this particular installation, what would happen was that the liquid would gather in the condenser until it overflowed the liquid trap, and then when the liquid started overflowing the liquid trap, the siphon effect would take place and it would suck the condenser dry and dump all the liquid into the HP receiver.

Any way, that is my experience with a liquid trap on a single evaporative condenser, the liquid trap was removed and the system had been running like a dream since :)

I also have to strongly agree with Sergei... When he says "the head pressure is as low as it gets" I'm reading that as when the pressure is slightly lower or equal to the pressure/temp of the air around the the condenser.

And also, when purging ammonia into water... don't judge by the bubbles as Sergei says, because if you are purging too "hard" and with the hose to shallow, or nor enough water, the ammonia will create gas bubbles that will not collapse before they reach the surface because there is too much coming out and the water around it won't absorb it....

Also, if you purge NH3 into water... Fit a non return valve on your purging hose....

somewhere between 1 - 2 bar NH3 gas pressure, something funny starts happening... instead of NH3 going out through the hose, water starts coming up the hose and into the system against the gas pressure, because NH3 is so hygroscopic it will suck water in even if it has the higher pressure.


I purged a bit from the receiver and everything stared working again. I have no good explanation for that.
The problem is partly what I mentioned earlier, Air is heavier than NH3 gas but lighter than NH3 liquid, like I said, Non condensibles like "air" (nitrogen/oxygen) in an NH3 system will eventually get trapped between the NH3 liquid and NH3 gas in the HP receiver, because that is where everything "calms down"
As we know, the level in the HP receiver is dependent on the equilibrium with the condenser, so from the top of every HP receiver there is an equalizing pipe to the top or bottom of the condenser, depending on if it is a Shell/tube, or phe, designers may choose to connect this equalizing pipe to the top or bottom as they see fit...

on a shell/tube, from experience, to connect the equalizing pipe to the condenser inlet makes for a very unstable pilot level, I had thought that the pressure drop across the condenser was non existent, but I have seen that even that negligible pressure drop was enough to push the level in the pilot receiver down and cause a very unstable pilot level. Therefore I always strive to use one of the side connections (connections on either end, not close to the discharge inlet) on a shell/tube condenser, to eliminate any influence from the discharge.

On A PHE condenser, because everyone knows that the pressure drop across a PHE is bad, I connect the equalizing pipe to the inlet and the outlet of the PHE, to make sure it can drain properly, without causing any "liquid hang"

I think the problems you had with the condensers filling up were because of "Air blockage"
There was so much non condensibles trapped in the HP receiver and when liquid trickled down from the condensers, the "air" would rise in the equalizing pipe and then block condensation in part of the the condenser until the LP receiver called for liquid and then again allowed flow through the HP side.

I've been using this one http://www.gea.com/docnav/Product%20Documents/Grasso%20Purger/0089293-IMMPURGER.pdf for 20 years now, and as long as it's installed correctly it works like a charm

shaaf
13-05-2017, 04:43 PM
During first start up of ammonia system . We closed one individual condenser inlet valve and run water pump and blower fan after half an hour open slightly vent valve which is installed after the inlet valve for 15 mintes.
Secondly purge air by vent valve on liquid receiver.