Air in NH3 plants

[Sinke]

...Hi all..
...How to solve that problem...
...and not to loose to many ammonia...
...thanks...

[US Iceman]

You need to use a refrigerated non-condensable gas purger. By refrigerating the ammonia and non-condensable gas, you force the ammonia to condense. The air and other gases are vented to a water bubbler to absorb any residual ammonia.

The colder the purger is, the better it works, and the less ammonia you loose through the bubbler.

[TXiceman]

I like the Hansen Auto Purger. Works great. Something older and more mechanical is the Armstrong Purger.

Ken

[Frankthefridge]

I've been badgered towards making my first post, so here goes, hoping of course that it may prove useful.

I too am biased towards a Hanson Multipoint Auto Non Condensible Gas Purger as it is the best. Chuck Hanson likewise. However this and any other type of purger must be connected to the correct points in the NH3 system for it to do the job. To remove air whilst the plant is operating on say a BAC/Evapco type evaporative condenser, one must always purge from ideally the top of each common liquid outlet manifold (inside the casing and with a valved connection usually specified when new). However it will work almost as well when taken off the top of the liquid outlet pipe as close to the condenser as possible - hoping that any reducer is eccentric and mounted the right way up!

I attended an IIR conference in Montreal in the early 90's and listened to a paper by one of Hansen's design engineers outlining essentially the above. In my naivety I had up to then believed that when a plant is in operation the air would remain near the top of the condenser. But of course Hansen showed it is carried down to the outlet manifold/piping, where it accumulates in it's attempt to rise back through the serpentine, and that is the place to get it out.

I would also take a connection to the top of the high pressure receiver. Generally one only gets air here when the system has not been purged for a long time.

It is also usual to fit a blow off connection at the highest point of the hot gas entry to the condenser. This can be useful if for whatever reason there is a lot air in the plant and you want to get it out reasonably quickly. Of course you have to stop the plant and run the water over the coils for an hour plus before doing so. I strongly recommend any engineer interested in purging ammonia plants to contact BAC as they have admirable literature on the subject.

[US Iceman]

I would say you did a nice job for your first post to the RE forums. Glad to have you here.

A couple of comments if I may.

However it will work almost as well when taken off the top of the liquid outlet pipe as close to the condenser as possible...

I have had one conversation with a sales rep who mentioned his manufacturer is starting to offer purge connections on top of the liquid outlet connections as "options". I should confirm this, but it seems obvious as to the need and I cannot understand why these should be optional???

...hoping that any reducer is eccentric and mounted the right way up!

Pipe diameter reductions before the coil isolation valve should be eccentric reducers with the flat side on the bottom.

Or, you can use a full size valve and then reduce on the downstream side of the valve using a concentric reducer (in the vertical axis).

If it were up to me I would recommend using full size valves and piping all the way to the main drain line.

This is a gravity drain line and is not sized the same way as a high-pressure liquid line feeding evaporators.

I see this all too often and it creates problems with draining condensers and liquid stacking up in the coils. The equalizer lines are also often very undersized, which is a critical mistake in my opinion.


PS. Why did you have to be badgered to make your first post?

[Frankthefridge]

Agree with all you say, especially your implication that said connections should be standard and not options.

Thanks for the nice words on my maiden post.

Well let's drop 'badgered' and say 'eased towards' Anyhow I will spend a bit more time reading posts and probably enjoy the odd contribution and sometimes responses.

[US Iceman]

Feel free to jump in whenever the urge strikes you.

[Peter_1]

FrantheFridge, welcome and as Us Iceman said, this was a very helpful post, at least it was for me.
I allways thought purging on the highest point of the condensor.
I will look once more on the website of Hansen when I have some time.

[TXiceman]

Purging is part science and part art. Depending on the location of the receiver and the condenser drain piping, you can get the non-condensibles in the receiver. You will need to purge from multiple points and the Hansen is set up to purge from multiple points.

Condenser outlet piping is critical to being able to get the air out.

Ken

[Sergei]

Air purgers usually design to purge air during operation of refrigeration plant. In this case air collect above liquid surface(liquid condenser outlet, high pressure receiver, termosiphon receiver). Hot gas condenser inlet can be used when condenser isolated or refrigeration plant is off. In that case air will collect at top point. During operation air will be blow to liquid surface by hot gas flow.

[US Iceman]

Purging off of the top does work, but it wastes a lot of ammonia as opposed to the refrigerated purgers.

[Sergei]

Usually, refrigeration plants with positive suction pressures don't have air purgers. Sometimes(not so often) we have to purger non-condensible gases from these plants from top point. Certainly, air purger is necessity for a plant with negative suction pressure.

[US Iceman]

I have been recommending the use of refrigerated purgers for plants operating with above atmospheric suction pressures also.

The systems get serviced all the time and eventually some air finds it's way into the system. Sometimes during charging too.

If the system doesn't have a refrigerated purger then the only way to purge it is via the top of the condenser (if someone thought to put a valve in).

[Ponca Dave]

I've been badgered towards making my first post, so here goes, hoping of course that it may prove useful.

I too am biased towards a Hanson Multipoint Auto Non Condensible Gas Purger as it is the best. Chuck Hanson likewise. However this and any other type of purger must be connected to the correct points in the NH3 system for it to do the job. To remove air whilst the plant is operating on say a BAC/Evapco type evaporative condenser, one must always purge from ideally the top of each common liquid outlet manifold (inside the casing and with a valved connection usually specified when new). However it will work almost as well when taken off the top of the liquid outlet pipe as close to the condenser as possible - hoping that any reducer is eccentric and mounted the right way up!

I attended an IIR conference in Montreal in the early 90's and listened to a paper by one of Hansen's design engineers outlining essentially the above. In my naivety I had up to then believed that when a plant is in operation the air would remain near the top of the condenser. But of course Hansen showed it is carried down to the outlet manifold/piping, where it accumulates in it's attempt to rise back through the serpentine, and that is the place to get it out.

I would also take a connection to the top of the high pressure receiver. Generally one only gets air here when the system has not been purged for a long time.

It is also usual to fit a blow off connection at the highest point of the hot gas entry to the condenser. This can be useful if for whatever reason there is a lot air in the plant and you want to get it out reasonably quickly. Of course you have to stop the plant and run the water over the coils for an hour plus before doing so. I strongly recommend any engineer interested in purging ammonia plants to contact BAC as they have admirable literature on the subject.

Is that you John? and by the way Joan likes Charles over Chuck.

[Ponca Dave]

I've been badgered towards making my first post, so here goes, hoping of course that it may prove useful.

I too am biased towards a Hanson Multipoint Auto Non Condensible Gas Purger as it is the best. Chuck Hanson likewise. However this and any other type of purger must be connected to the correct points in the NH3 system for it to do the job. To remove air whilst the plant is operating on say a BAC/Evapco type evaporative condenser, one must always purge from ideally the top of each common liquid outlet manifold (inside the casing and with a valved connection usually specified when new). However it will work almost as well when taken off the top of the liquid outlet pipe as close to the condenser as possible - hoping that any reducer is eccentric and mounted the right way up!

I attended an IIR conference in Montreal in the early 90's and listened to a paper by one of Hansen's design engineers outlining essentially the above. In my naivety I had up to then believed that when a plant is in operation the air would remain near the top of the condenser. But of course Hansen showed it is carried down to the outlet manifold/piping, where it accumulates in it's attempt to rise back through the serpentine, and that is the place to get it out.

I would also take a connection to the top of the high pressure receiver. Generally one only gets air here when the system has not been purged for a long time.

It is also usual to fit a blow off connection at the highest point of the hot gas entry to the condenser. This can be useful if for whatever reason there is a lot air in the plant and you want to get it out reasonably quickly. Of course you have to stop the plant and run the water over the coils for an hour plus before doing so. I strongly recommend any engineer interested in purging ammonia plants to contact BAC as they have admirable literature on the subject.

Is that you John? and by the way Joan likes Charles over Chuck. better behave.

[IceMan_4000]

Hansen purgers are great. if you are in a vacum make sure you get the auto purger plus. We always worry about air with plants running in a vacum but seem to forget about the other products inside air. WATER this needs to be removed as well.

http://www.hantech.com/documents/PDF/PDS_APPlus.pdf

Water in the ammonia just means you will need to drop that suction pressure to meet refrigeration requirements. It sure takes alot of horses the deeper your vacum

IceMan_4000

[Oregon Jim]

Hello Everyone. This is my first post on this site. I am happy to find a site with ammonia people to chat with.

I operate a small ammonia system for a local food processor, and we use Hansen AutoPurgers in all of the ammonia systems at our facilities. We purge from the top of the condensers and the tops top of our high pressure receivers. In addition to just improving the overall efficiency of our systems, the purge counters have been wonderful early indicators of cracks and leaks in our evaporator coils.

[NH3LVR]

Oregon Jim;
Welcome to RE.
It is nice to see another US NH3 guy on the board. I was going to send you a PM, but it seems that you have elected not to receive such.
Again, welcome to the forum

[Josip]

Hi, Oregon Jim

welcome to RE forums....hope you will enjoy here with us..

Hello Everyone. This is my first post on this site. I am happy to find a site with ammonia people to chat with.

I operate a small ammonia system for a local food processor, and we use Hansen AutoPurgers in all of the ammonia systems at our facilities. We purge from the top of the condensers and the tops top of our high pressure receivers. In addition to just improving the overall efficiency of our systems, the purge counters have been wonderful early indicators of cracks and leaks in our evaporator coils.

Hi, NH3LVR you can download Oregon Jim's vCard

Best regards, Josip

[NH3LVR]

Hi, NH3LVR you can download Oregon Jim's vCard

Of course I can. silly of me to forget. Old age popping up I guess. Wish I was younger and knew everything again.

[josef]

Hi, NH3LVR, when you was younger was to have been such experience as today?

[TXiceman]

Glad to have another USA NH3 sniffer among the group. I LOVE NH3.

Ken

[NH3LVR]

Hi, NH3LVR, when you was younger was to have been such experience as today?

No, I just thought I knew it all.
Really got fooled a couple of days ago by a strange control sytem for a ***** 22 critical charge system. Glad I do not have do do this stuff anymore. (Except when I do)

[US Iceman]

Welcome to the RE forums Jim.

It's always nice to have another ammonia person with us here. I do have one question for you though at this early date...

We purge from the top of the condensers...

Form the top of the condenser coils or from the top of the condenser coil drain lines?

[benji]

Hey ice-man i installed one of those air purges at the market where i had worked. they called NEAP non electrical air purger they work quiet well though and you can actually set each condenser to purge one after the other gr8 hey.. i think the made by hansen control valves in chicargo illinois.

[aawood1]

Hi, Still at work now after a call out thanks to some air in one of the refrigeration systems we have for a Frigo freezer. When the call came in from the tech. on shift to say he could not keep the system running and it cut out on high pressure the frist thing I asked the tech. on site, "Was the air purger switched on and working" Yes was his reply. Informed him on how to purge the air off from the top of the condenser with the plant stopped and call me back if this did not work. The next call he said this did not work so could I come in and see what I could do. When I got in to work only to find him trying to remove the air from the top of the condenser inlet pipe's with the plant running and he said that he plant would for 10 min. before it cut out each time. I let him go home and stopped the plant and purged the air off. As I checked around the system I found that someone had valved off the gas line's from the condenser to the purger. Now all opened up and the system running but what away to spend the bank holiday.
Arthur.

[kelvin_27_84]

simple, just find your highest point in your plant and do manual purging - cheapest.

How to know whether you will lose any NH3, simple put your nose there, the starting will be just air, purge till u smell the toilet smell and there you get it.

Next is like what most mention, air purger, expensive, alot of work involve (engineering & piping)

[nh3wizard]

simple, just find your highest point in your plant and do manual purging - cheapest.

How to know whether you will lose any NH3, simple put your nose there, the starting will be just air, purge till u smell the toilet smell and there you get it.

Next is like what most mention, air purger, expensive, alot of work involve (engineering & piping)

I do not think I would be putting my nose near it, and what toilet smell are you referring to? I have purged lots of ammonia systems but they never smelled like a toilet.

[US Iceman]

...simple put your nose there, the starting will be just air, purge till u smell the toilet smell and there you get it.

Absolutely not! Never put your nose down to something like this. Smelling for small leaks is one thing, but this is not something I would recommend.

Refrigerated purgers do not require a lot of engineering at all. I don't know why you would even say that.

[Josip]

Hi, kelvin_27_84

simple, just find your highest point in your plant and do manual purging - cheapest.

How to know whether you will lose any NH3, simple put your nose there, the starting will be just air, purge till u smell the toilet smell and there you get it.

Next is like what most mention, air purger, expensive, alot of work involve (engineering & piping)

I must slightly disagree and put my 2 cents on...

.... the highest point is ok .. what about receiver...

.... manual purging is not the cheapest solution.... because

.... a lot of ammonia is going out together with air (wasting of refrigerant), we can smell "toilet smell" almost immediately, but the best way is then to put the hose into water and observe air bubbles...

.... manual purging cannot totally eliminate air

.... manual purging will take a lot of time to do it properly

.... may be illegal to release ammonia into environment

.... for manual purging we have to stop complete plant and wait sometime to separate non-condensible gases (NCG) from ammonia

.... the best solution (for me) is air purger either manual or automatic one ... of course it is not cheap and request some engineering works like design and piping, but having an ammonia plant running for years with a very little air within will cost a fortune in power consumption... see attached pdf document

considering all that finally seems a good air purger is free or even energy saving i.e. best buy at least on all ammonia plants working under atmospheric pressure where we have more chance to get air into plant

Best regards, Josip

[Sergei]

Hi, kelvin_27_84



I must slightly disagree and put my 2 cents on...

.... the highest point is ok .. what about receiver...

.... manual purging is not the cheapest solution.... because

.... a lot of ammonia is going out together with air (wasting of refrigerant), we can smell "toilet smell" almost immediately, but the best way is then to put the hose into water and observe air bubbles...

.... manual purging cannot totally eliminate air

.... manual purging will take a lot of time to do it properly

.... may be illegal to release ammonia into environment

.... for manual purging we have to stop complete plant and wait sometime to separate non-condensible gases (NCG) from ammonia

.... the best solution (for me) is air purger either manual or automatic one ... of course it is not cheap and request some engineering works like design and piping, but having an ammonia plant running for years with a very little air within will cost a fortune in power consumption... see attached pdf document

considering all that finally seems a good air purger is free or even energy saving i.e. best buy at least on all ammonia plants working under atmospheric pressure where we have more chance to get air into plant

Best regards, Josip

Hi, Josip.
I agree about the purger. Every plant operating at suction pressure lower that atmospheric should have a purger.
I don't agree...
Air in the receiver don't influence the condensing pressure.
For refrigeration plants with 2 or more condensers. Air purging can be done during operation. Close the discharge valve before condenser(water pump and fans ON). Wait 10-15 min. Refrigerant will condense and liquid will fill the condenser. Air can be purge in the water from the top point.

[kelvin_27_84]

ok guys, In Indonesia where I have a few plants that require to purge, we usually do that. It is not illegal but irritating. All I can say is that, manual purging is a cheaper solution. It is true there are risk involve in such ways that I described. And yes a better way of manual purging is of course in water. I forgotten about that. Please forgive me. .

[Josip]

Hi, Sergei

Hi, Josip.
I agree about the purger. Every plant operating at suction pressure lower that atmospheric should have a purger.
I don't agree...
Air in the receiver don't influence the condensing pressure.
For refrigeration plants with 2 or more condensers. Air purging can be done during operation. Close the discharge valve before condenser(water pump and fans ON). Wait 10-15 min. Refrigerant will condense and liquid will fill the condenser. Air can be purge in the water from the top point.

yes recently they found the best position is to purge air on the top of liquid outlet pipe from condensers...

... of course no need to agree ..... what about those installations.... and they are working fine...

ok guys, In Indonesia where I have a few plants that require to purge, we usually do that. It is not illegal but irritating. All I can say is that, manual purging is a cheaper solution. It is true there are risk involve in such ways that I described. And yes a better way of manual purging is of course in water. I forgotten about that. Please forgive me. .

Hi, kelvin_27_84

all is ok, we are here just to make a good discussion how to do something in the best possible way hopefully to make our world better and cleaner....

Best regards, Josip

[Cold Down Under]

I have just engineered a couple of shell and tube purgers for large ammonia production plants. They have a continual NC load into their system as part of the ammonia production process. Essentially what I discovered (after a whole heap of mucking around with partial pressures and stuff) was that there was an optimal balance between the concentration of NC and the additional running power of the plant to get rid of them from the vapour space of the vessel and condenser drain. The power penalty of the NC on absorbed power would find a balance point on the power penalty for additional refrigeration to condense the ammonia in the NC stream, in this case we were using the economiser port on the screw to do the purger condensing. Basically in order to maintain a fixed level of NC in the system a certain amount of vapour from the receiver needed to be treated through the S&T. As the target concn of NC decreased more vapour needed to be treated to continue to maintain the lower NC concentration so more cooling was required - hence more compressor power - offset by the reduction in compressor power due to lower discharge pressures. A fair old balancing act. May not have as much of an impact in theoretically "closed" systems, but may be interesting in large low temp plants with continual small leakages.

[US Iceman]

It would be interesting to see what you can up with. I'm surprised you actually had to do this as most purgers are very small cooling loads in respect to the main loads.

[RANGER1]

In the process of actually making ammonia a lot of other unwanted gases other than air ,are purged off and applied to other processes with a very large purger hooked up to economizer port.
A large storage tank held at 0 to 3 PSI is used for storing and adding ammonia from the process plant.
This new ammonia has to be continually purified of NC.
If only used for storage there is very little NC.

[US Iceman]

Thanks Ranger1. I have not been invovled in an ammonia production process so that makes perfectly good sense.

Learned something new today.

[TXiceman]

I have design some rather large non-condensible purgers for ammonia production, storage systems and terminals. The largest was a full 20 TR (240,000 BTUH) load on the compressor. Some were single drum and some dual drum systems. A single drum system would have a shell and coil vertical vessel tat was 12 to 18" in diameter and about 6' high (seam to seam). The controls on these can get to be real interesting.


Ken

[Sergei]

I have just engineered a couple of shell and tube purgers for large ammonia production plants. They have a continual NC load into their system as part of the ammonia production process. Essentially what I discovered (after a whole heap of mucking around with partial pressures and stuff) was that there was an optimal balance between the concentration of NC and the additional running power of the plant to get rid of them from the vapour space of the vessel and condenser drain. The power penalty of the NC on absorbed power would find a balance point on the power penalty for additional refrigeration to condense the ammonia in the NC stream, in this case we were using the economiser port on the screw to do the purger condensing. Basically in order to maintain a fixed level of NC in the system a certain amount of vapour from the receiver needed to be treated through the S&T. As the target concn of NC decreased more vapour needed to be treated to continue to maintain the lower NC concentration so more cooling was required - hence more compressor power - offset by the reduction in compressor power due to lower discharge pressures. A fair old balancing act. May not have as much of an impact in theoretically "closed" systems, but may be interesting in large low temp plants with continual small leakages.

Sometimes you can bypass NC to the suction.

[Cold Down Under]

See attached chart for the effect of NC in an ammonia production / storage refrigeration plant.

The compressor is a screw compressor with a 900 kW motor.

There are effectively two competing issues at play:

1. Effect of NC on head pressure increasing absorbed power.

2. Effect of additional mass flow to economiser port increasing absorbed power.

Increasing 2 decreases 1, increasing 1 decreases 2 - where is the optuimum condition?

The optimum quantity of NC in the system is the point where the power consumption penalty of the increased head pressure is minimised without increasing the power consumption penalty from additional side load. This occurs at approximately 0.2 - 0.3 bar partial pressure of air in the ammonia system.

All really convenient - 777 bkW / 0.95 (manufacturer's tolerance on absorbed power figures *1.1 (manufacturer's minimum driver power above full load) = 900 kW. This is called optimising engineering after the motor has been ordered - phew.

[Sergei]

See attached chart for the effect of NC in an ammonia production / storage refrigeration plant.

The compressor is a screw compressor with a 900 kW motor.

There are effectively two competing issues at play:

1. Effect of NC on head pressure increasing absorbed power.

2. Effect of additional mass flow to economiser port increasing absorbed power.

Increasing 2 decreases 1, increasing 1 decreases 2 - where is the optuimum condition?

The optimum quantity of NC in the system is the point where the power consumption penalty of the increased head pressure is minimised without increasing the power consumption penalty from additional side load. This occurs at approximately 0.2 - 0.3 bar partial pressure of air in the ammonia system.

All really convenient - 777 bkW / 0.95 (manufacturer's tolerance on absorbed power figures *1.1 (manufacturer's minimum driver power above full load) = 900 kW. This is called optimising engineering after the motor has been ordered - phew.

Do you have evaporative condensers?
What is the set point of head pressure?
Do you change this set point?

[Cold Down Under]

The system has a plate condenser using cooling water from site so not a great deal of scope to vary the head pressure setpoint. From memory the head pressure is around 39 SCT + 0.3 kPa for non-condensables. And hope like hell that the heat exchanger supplier is correct that the nc will pass through the HX to the receiver.



If the NC gets out of control and we need more capacity on the purger we will bypass some load to the LT suction.

[US Iceman]

The NC gases will flow through the condenser into the receiver, however it depends on the actual piping and operation.

If the condenser outlet (drain line) is trapped the liquid seal created by the trap can cause the NC gases to stay on top of the liquid seal. So... the NC gases stay in the condenser. This is why evaporative condensers have purge connections on the bottom coil connection.

On the other hand, if the drain line from the condenser is not trapped (flowing by gravity drainage) the liquid and NC gases simply flow down into the receiver.