Liquid Recirculation-oil question?

[lana]

Hi everybody,

I would like to ask the experts in liquid recirculation about oil return when the refrigerant is not NH3. If for example R22 is used then how is the oil drained at different stages? Liquid R22 is heavier than oil and therefore, oil will be at the top of the liquid.

I am sure the experts know what I mean.

Thanks a lot.
Cheers

[US Iceman]

Hi lana.

You are correct about the oil. The prevailing specific gravity for the fluid(s) wins, therefore the heavier fluid sinks.

On R-22 recirculation systems the oil floats in a layer on top of the liquid R-22 in the vessel. However, this oil layer is not entirely distinct. It may have a greater concentration of liquid oil on the bottom of the layer, while on top the oil foam may be less dense.

What I have done in the past is to use three side connections on this vessel (close to the normal operating liquid level). These three connections are at slightly different elevations around this normal liquid level. The connections are then piped into the suction side of an eductor/venturi, which has a hot gas supply.

The high pressure hot gas provides the motive force for the venturi to suck the oil/liquid R-22 back to a location suitable for returning it to the compressor. Metring valves are used to adjust the hot gas flow volume and also on the side connections also. this way you can adjust flows to compensate for operation.

If the compressors are recip's we used to use a liquid/suction heat exchanger in the discharge line of the compressor to evaporate the liquid R-22, before the oil was returned to the crankcase.

If a screw was used...we just dumped the liquid and oil back into the compressor suction (another reason for the adjusting valves).

[smpsmp45]

Dear US ICeman,

I like the way you put up the things. Excellent reply

[Grizzly]

Lana and Iceman

Have either of you (Or anyone else) come across the
problem of replacement R22 Refrigerants.
Where because their densities are heavier, systems that had efficient oil recovery with R22 (Oil on top of refrigerant).
The oil recovery fails.
Basically because the oil sits at a different level the oil recovery ports are no longer in the correct place.

I am led to believe their is a large amount of Ice Rinks within the UK.
That will be closing because their equipment is economically un-viable, because of problems related to this.

So I am led to believe that the densities of the newer refrigerants and their relationships to their oils.
Is 1 of the main problems when looking at retrofitting a R22 system.
Has anyone else come across this issue?
Grizzly

[US Iceman]

The oil recovery fails.
Basically because the oil sits at a different level the oil recovery ports are no longer in the correct place.

Hi Grizzly. This explanation is going back in the old memory banks....

I don't think the problem is with the refrigerants themselves. My guess is this is happening because of the oils required for those refrigerants. The newer synthetic oils have different vapor pressures. So as the refrigerants are replaced, new oil types are also utilized. The oil still floats on the top of the refrigerant, but in different locations within the layer.

Where the oil rich layer forms is due to the operating evaporating pressure. The oil rich layer might be exactly on top of the liquid at one evaporating pressure while at a different evaporating pressure the oil rich layer may be slightly below the liquid refrigerant level (at the top).

So...what you need to know is the oil type and refrigerant and operating conditions. The oil supplier should be able to determine where this oil rich level will be so that the oil recovery locations may be modified.

That's cheaper than shutting down an otherwise profitable business.

[Grizzly]

Hi Grizzly. This explanation is going back in the old memory banks....

I don't think the problem is with the refrigerants themselves. My guess is this is happening because of the oils required for those refrigerants. The newer synthetic oils have different vapour pressures. So as the refrigerants are replaced, new oil types are also utilised. The oil still floats on the top of the refrigerant, but in different locations within the layer.

Where the oil rich layer forms is due to the operating evaporating pressure. The oil rich layer might be exactly on top of the liquid at one evaporating pressure while at a different evaporating pressure the oil rich layer may be slightly below the liquid refrigerant level (at the top).

So...what you need to know is the oil type and refrigerant and operating conditions. The oil supplier should be able to determine where this oil rich level will be so that the oil recovery locations may be modified.

That's cheaper than shutting down an otherwise profitable business.

Thanks for a knowledgeable reply Iceman.

The main problem that Colleagues have experienced as I understand it.
Is what Combination of refrigerant / Oil to use when replacing R22.
That allows the oil to be recovered without huge modifications.
Basically a lot of say Ice rinks in the UK are probably 20 + years old.
And although the plant is still fully operational and extremely reliable.
Once R22 is phased out, which is midnight December 31st 2009 in the U.K. These plants become
obsolete,(it would appear we are on a different schedule to your side of the water?)
I hope you understand my point?
Cheers Grizzly

[US Iceman]

I understand where you are coming from Grizzly. It is my understanding that you don't have to replace the system or refrigerant.

Perhaps Argus (or someone else) could provide some details on that point. He seems to have the pulse of the requirements there in the UK. I think the phasing out only relates to the manufacture of new equipment using R-22 and the supply of this refrigerant .

However, if a leak occurred then you could have some issues with finding R-22 of any suitable quality or quantity. At that point I think you are looking for a replacement refrigerant.

At the moment, I have been investigating this and am coming to the general conclusion that R-507 might be a decent selection. Of course that requires POE oil, so there are some issues to deal with on that point.

[lana]

Thanks everybody for replies.

Dear US Iceman,

What I learned about oil in the NH3 system is that the oil is directed to an oil sump and then drained manually.
What I understand from your explanation is that the oil is somehow returned to the suction side of the compressor automatically (for R22).

Is this correct?

As you know I am not an expert and therefore, I don't know about venturi or ....

Thanks a lot for your time.

Cheers

[US Iceman]

Hi lana,

You are correct. The R-22 liquid overfeed systems require an automatic oil return system. And for some strange reason I have not been able to get a good answer on, we always drain the oil from an ammonia system and discard it.

Seems to be a very strange topic which no one has been able to provide a good answer to...yet.

The venturis are simply used to provide a suction for scavenging the oil from the vessels by using a high pressure gas source. The really quite simple to use.

[lana]

Dear US Iceman,
Many thanks for the explanation.
Helpful as always.

Cheers

[squidward]

Hi lana,

You are correct. The R-22 liquid overfeed systems require an automatic oil return system. And for some strange reason I have not been able to get a good answer on, we always drain the oil from an ammonia system and discard it.

Seems to be a very strange topic which no one has been able to provide a good answer to...yet.

The venturis are simply used to provide a suction for scavenging the oil from the vessels by using a high pressure gas source. The really quite simple to use.

Hey Iceman, I had a guy tell me that oil in an nh3 system cleans out the passages- oil from harvester was very dark until we flooded the system with oil, now not so dark. Made sense to me, anyway didn't want to put dirty oil back in...

[Camille]

Hi Iana

On liquid recirculation system using a pump recirculator package, you can install oil skimmers on the vessel, starting with the refrigerant levels and 3 inches down for each oil skimmer, the oil skimmed with the refrigerant can be taken to an oil separator where heat [electric heater] is introduced to boil off the refrigerant and the oil is returned to the compressors by pressurizing the oil pot , see attached picture of the oil skimmers, hope this help
Regards
Camille Zabbal

[CHIEF DELPAC]

Hi squidward I agree with you. All our oil from the oil pots goes to the recycler.

[US Iceman]

...I had a guy tell me that oil in an nh3 system cleans out the passages...

It is not the oil which cleans up the system, it is the ammonia. The oil acts as a carrier for all of the junk as the ammonia moves through the system. The oil simply settles out in low velocity areas and collects there. That is why it has to be drained out or recovered. So it does not accumulate and cause problems with heat transfer.

[CHIEF DELPAC]

US Iceman When I started in refrigeration, the reclaimed oil was thought to be contaminated with carbon and wear metal from the compressors.The compressors were recips. with rotary boosters.

[US Iceman]

Hi Chief,

I think there is a lot of debris, particles, etc in this oil. It usually consists of welding slag (ground up very finely after some time), varnish, etc from the mill where the pipe was made, and other numerous collections of junk that finds it's way into the pipe during installation.

I have also heard the oil (somehow) changes viscosity due to some chemical reactions. I would love to hear a really good answer on this issue.

They way I look at is: If we want the compressors to last a long time we have to protect them (& bearings too). Oil filtration and high quality oil is one way of doing that.

I think (and I would like to hear counter opinions on this) if we used synthetic oil the viscosity is more stable to pressure and temperature changes. If we provide high quality filtration, the wear particles are reduced, hence a lower negative impact on bearings, etc.

Way back when in the old days when only mineral oil was used it became standard practice to drain oil from low areas and simply dump it or recover it as hazardous waste. That meant the oil levels had to be refilled in the compressors.

However, none of this happens in what I'll loosely call ***** systems. The oil circulates through the system (if designed properly) and we have all sorts of gadgets to recover oil on the high side and equalization methods for multiple compressors. I have seen the same thing on large ***** systems where steel pipe is used.

Unless their is a significant reaction that reduces the oil quality, I cannot see why we cannot recycle the oil from ammonia systems if it is filtered to remove the debris, particles, etc.

The two RE members I can think of who could shed some more light on this are: Johnny Rod & Milo & TXiceman too. Maybe they can add to this discussion...

[Grizzly]

An interesting topic this Iceman.
Of the many sites I have worked on there is only 1 (ammonia) that I can remember.
That recycled their oil (Clavus 68) and then they had a bespoke filtration system fitted.
Even so the state of the oil returning
was enough to make any engineer cringe.
I am sure sometimes you could of lapped valves with it!
Anyway they were adamant, that they were going to reuse it.
Despite mine or anyone Else's protests.
Something happens to the oil in an ammonia plant that doesn't in a ***** system?
I think we are on a vicious circle here aren't we?
Could it be anything to do with ammonia's ability to absorb and carry within it water?
Cheers Grizzly

[US Iceman]

Even so the state of the oil returning was enough to make any engineer cringe.

I am sure sometimes you could of lapped valves with it!

I don't doubt what you say Grizzly. What I would like to do, but have not yet is to get an oil sample from an oil pot and have an analysis ran to see how much the oil quality has changed.

If you could lap valves with the used oil, then I seriously think it should not be returned to the system. However, if it could be filtered to a like-new condition and the acid or water content were low enough to be acceptable and the viscosity was OK. Why not?

If I'm missing something, I am open to other thoughts also. At this point, I'm trying to use logic as best as I can, but my background does not cover the chemistry very well...

[Grizzly]

I don't doubt what you say Grizzly. What I would like to do, but have not yet is to get an oil sample from an oil pot and have an analysis ran to see how much the oil quality has changed.

If you could lap valves with the used oil, then I seriously think it should not be returned to the system. However, if it could be filtered to a like-new condition and the acid or water content were low enough to be acceptable and the viscosity was OK. Why not?

If I'm missing something, I am open to other thoughts also. At this point, I'm trying to use logic as best as I can, but my background does not cover the chemistry very well...

I might be able to help there?
If I remember correctly this particular site had us analyse their oil.
So I think there may well be a copy in the office.
Next time I am in I will ask and get back to you.
Suffice to say it was pretty contaminated, if I remember correctly!
Grizzly

[chillyblue]

Hi

I used to work on flooded R22 circ systems and i used to do it the same as Camiile it was done safely using a dead mans handle when returning to the compressors. Sometimes i just left the liquid to boil of naturally rather than the heater.

CB

CB

[US Iceman]

If I remember correctly this particular site had us analyse their oil.

That's great! The next thing we need is an analysis of the same oil in a new condition. Then you have the basis for a good comparison.

[CHIEF DELPAC]

Hi all The engine room that I broke in on had vertical oil seperators on the discharge line of the comps. This oil was returned to the comp. base through afloat valve. The oil that was drained from the oil pots went through an oil filter system. This system left to many fine particles in the oil so was abandoned. The next system to be used was a centrifugal seperator similar to what is used in marine engines ie a fuel polisher. This also did not clean the oil so it to was abandond. We then went back to using new oil.

[Grizzly]

That's great! The next thing we need is an analysis of the same oil in a new condition. Then you have the basis for a good comparison.

But Sir!
Are you never Happy?
Sadly I have never been asked to analyse new oil.
Grizzly

[CHIEF DELPAC]

Grizzly The oil testing lab here on the wet coast always request a sample of new oil to compare to comp. oil samples. 30

[US Iceman]

But Sir!
Are you never Happy?

That would be me...

Look at it like this. If you have an oil analysis of old oil, what do you compare it to? Everything like color, or it pours easier is subjective.

Once you have the data for the old and new samples you have a good direct comparison to make decisions.

[Grizzly]

Chief and Ice
Good Points well presented.
Sadly I can only bring to the table what I have got!
I'll be back.
Grizzly

[RANGER1]

A number of clients i work for collect their waste oil and have it "laundered " in house or proffesionally ( NH3 ) .

In all of these cases it is on screw comp plants with old type oil seperators and a lot of carryover .
It has been proven sucessful to use this oil . The oil would not have been as near as hot as recip plant .
Method used to clean is centifuge , filter and heated above 100 deg c
Plants with a lot of air for various reasons and empty liquid reciever tend to oxidize oil and better to just change it with new oil (mineral oil ) .
On more modern plants with very small oil carry over cant see why you would bother , just fill with new oil .
R22 overfeed we have used oil / refrigerant skimming off discharge of liquid pump successfully through liquid line or discharge line heat exchanger ,with tx valve. There is so much activety and mixing inside vessel it cant really seperate to differant layers as would a surge drum or shell and tube h/exchanger . Would say liquid overfeed is different to most other applications .