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Does anyone have any experience with oil return from the low side of the plant and back to the compressor?
I've been "raised" on not using oilreturn on NH3 plants, but I've heard some are installing automatic "purging" from the oil boiler on the low side and back to the compressor suction.
Anyone have any input on why or why not?
I have done this on ammonia and R-22 systems and have also seen others do it also.:cool:
Here are my thoughts...
The oil that escapes the oil separator always finds it's way to a low velocity area, where the oil separates. The oil in the crankcase (recip.'s) or oil separator (screw's) is this same oil. That oil when it is in the crankcase or oil separator is OK to use for the compressors (either type).
Therefore, the only difference between the oil is the location it is found. By this I mean, the oil is the same whether it is in the compressors or in the low-side of the system.
It's the same oil. The only difference is where you find it.
If you recover oil from an oil still, warm it up so it is easy to pump, then filter it using a similar oil filter as used on screw compressors (8-12 micron filter rating) you effectively have the same oil quality as it left the compressor.
I have always thought this oil draining was something invented by the people selling oil. If you perform periodic oil analysis this will tell you the oil quality and when it should be changed.
The only thing more important than using a high quality oil is; high quality oil filters to reduce the particle sizes and particle count to provide long equipment life.
This is especially important for new equipment to prevent premature damage to bearing surfaces. Once the bearing damage occurs, you are only prolonging the inevitable failure.
I have seen many situations where the oil has been returned, through one method or another, back to the compressor,
and only one situation where the oil was drained off.
the system where the oil was being drained was a large ammonia system. They drained the oil, and discarded it for years, and only recently started re-using the drained oil. They are now regularly testing the oil, (for viscosity and acidity). They drain the oil into pails, in the engine rooms, where the ammonia gasses off, then hand pour it into drums, (stinky job), and then pump it through filters before re-using it.
Earlier we used to design chillers ( flooded type) with holes on the shell & that too in inclined direction to collect the oil floating on Liquid amonia. Since the levels used to vary from time to time, the holes were in an inclined plane. But that oil was never used in the system & was drained off. But I am talking about 20 years back. After more efficient oil separators, that design is not used now a days
For most ***** systems, I have seen this occur as described above.Quote:
Originally Posted by smpsmp45
However, for ammonia systems this should be the other way around. Liquid ammonia floats on top of the oil.
There might be some cases where the oil could be collected from the liquid, if the liquid and oil are agitated though. And this might certainly be true in a flooded chiller as there are very high circulation potentials due to boiling.
Even with better oil separators, none of them are 100% efficient. The oil accumulation in the system just takes longer now.
Quote:
Originally Posted by US Iceman
We have a oilseperator on our chillers and liquidseperators that are fed from low points on the vessels.
Oil collects and on regular intervals is drained. You can shut of all valves leading to the seperator and turn on a 1 kw heater to heat up the mix, the ammonia is returned to the low pressure side via a 5 bar OFV valve.
What I'm wondering is this:
After having drained the oilseperator, let's say 10 times, to get out impurities from the installation, why not have the option to lead the oil back to the compressor via a solenoid valve?
-Close solenoids leading oil to the seperator
-Start heating element (shuts off at a set temperature)
-5 bar OFV opens to let boiled off ammonia return to the low side.
-temperature is reached, heater shuts off, 5 bar valve closes.
-open solenoid leading from bottom of seperator back to compressor suction.
-5 bar pressure diff to push the oil back to the compressor (may need a reg valve so you don't drown the compressor) via a filter/strainer.
Why is this not done?
I've heard arguments like:
-The oil is contaminated and should not be re-used.
-Only the lighter elements of the oil is thrown out by the compressor and thus does not have the correct viscosity (well then neither does the remaining oil DUH)
-Due to the HT temp on some compressors the oil is so degraded it's not recomendable to run it through the compressor again.
-Oil return on a NH3 plant? HA HA HA that's not possible! (followed by a shake of head)
------------------------
I don't see why this isnt used, we return the oil in ***** plants, often with a high percentage of ***** in the mix...
with what I mentioned above, you will have as close to pure oil as you can get from within the system, as you boil of the ammonia to get the increase in pressure.
any thoughts?
That will work and I have done something similar or variations of that.Quote:
Originally Posted by Tycho
I think if you get too many people that say NO, then no one thinks they can.:DQuote:
Originally Posted by Tycho
I have returned oil from the low side of ammonia, ***** and hydrocarbon systems for years without a problem. Since most of the screw compressors use a synethetic oil which is expensive, it should be recovered and reused.
The normal method to reclaim oil with ammonia systems is to let the oil settle to an oil pot and generally not heated during the settling cycle. Based on a time clock, you close the liquid feed solenoid, leaving the vent line open to the suction. When the oil reaches about 100 dF, you close the vent line as the ammonia has boiled off at this point. Next, pressurize the oil pot with discharge gas and open a solenoid to the compresor suction and meter the oil back over a several minute period. After this times out, close the return and pressurization solenoids and open the feed and vent to let more oil settle to the pot.
With ***** and hydrocarbon refrigerants you have to run a heated still and cycle the feed. Pressurize and return like an ammonia still.
I like the pressure feed method as it eliminates a pump.
Another way to retrun oil is to use an eductor and "pump" oil back to the compressor with a small stream of hih pressure gas. This method will take back a small bit of liquid and puts a small false load on the compressor.
Ken
The only time I have used a pump is when the oil is ran through a filter canister to collect debris before I dump it back into the compressor (especially a recip. system).
I have used both the eductor and the pressure differential method and both work quite well.
Used all the time, on the plant I've worked on. Either a oil pot at the bottom of the surge drum and use hot gas to blow it back in to the dry suction, or a oil return line on a "Star" LPR. This has a orificae in the return line which goes back in to the dry suction and as long as you have the correct charge in the system oil returns. Used on both NH3 and R22.
...I never heard for that innovation...Quote:
Originally Posted by Tycho
...When oil left compressors and mixed in pipes with ammonia and dirty from corossion...
...and you that dirty oil put in your new machine...
...best regards...
A properly maintained refrigeration system, ***** or Ammonia, should be fairly clean, so there should be no corrosion in the pipes.Quote:
Originally Posted by Sinke
I have reclaimed and returned the oil on hundreds of systems on *****, ammonia and hydrocarbons with out any problem. As a minimum, the oil needs to be run through a 100 mesh strainer before it is returned to the compressor.
Ken
Same for me. The filter/strainer mentioned IS important, so don't forget that!:oQuote:
Originally Posted by TXiceman
...you are right,but for new plants....Quote:
Originally Posted by TXiceman
...I work in Serbia(that country is close to Africa),and that plant is from 1978 year....
...so the corrosion in pipes is part of my life...
....when I got new plant I will think on return oil in my old compressors....
...until then....
The oil that leaves the compressor is the same oil that is out in the system. If you can filter the oil so that it is clean, you should not notice any difference.
...OK,but in the compressors I have two different oil...Quote:
Originally Posted by US Iceman
...in first stage one and in the second another tipe of oil....
Are both sets of compressor on one system or are there two independent circuits?Quote:
Originally Posted by Sinke
If both the low-stage and high-stage compressors are on the same circuit and using two different types of oil I would question that.
If both compressors are on the same refrigerant loop, you MUST use the same oil in the two compressors. your oill will get mixed as the low stage will carry oil to the high stage.
if the refrigerant loops are independent, then you can use tow different oils.
On a closed loop system, there is no reason not to collect and reuse the oil.
Ken
Modern refrigeration compressors have good oil separators. Usually, we have to drain just 1-2 gallons of oil per month or half a barrel per year. It cost us just a few hundred dollars per year. What is the reason to reclaim this oil? Drained oil contains water, dirt, acids and etc.
Have you verified this with an oil analysis?Quote:
Originally Posted by Sergei
If the oil in the system has acid and water in it, don't you think the oil in the compressors or oil separators will have the same tendencies?
I remember that recently Andy P. gave good link to information about water and acids in ammonia systems. I think that concentrations of water and acids are higher in low pressure side of refrigeration plant.Quote:
Originally Posted by US Iceman
And I agree. Let's step aside for the moment and look at this from a different perspective.Quote:
Originally Posted by Sergei
If the system is contaminated because it has acid in it from a high water content, then we need to look at removing the water first (as the potential source for the acid formation).
Then after the system is clean and dry again, begin to investigate the use of oil return.
I'm not recommending putting dirty oil into a compressor. I looking at this from a viewpoint that the system is properly maintained and designed and acid/water free (which it should be). Then oil return back to the compressors should not be a problem.
This is a lot like system analysis... we have to look for the root cause then fix it. Then proceed to the next step.
First and foremost, a properly operating plant should not have any dirt and acids in the refrigerant or oil.Quote:
Originally Posted by Sergei
Next ALL refrigeration systems use some oil on a continued basis. With the modern oils and modern coalescing oil separators, this carry over has been mostly minimized.
I totally disagree about not putting an oil reclaim system on all but the smallest of systems and even then prefer to have at least a manual oil recovery system. It is false economy to no install an oil recovery system. It is a minimal cost to install a non-heated gravity feed oil pot with a few hand valves and a strainer in the oil return line.
The other issues are convenience for the operation and safety. I have seen several ammonia/oil spills due to poor operator performance when attempting to manually drain oil. Also at issue here is the proper disposal of the used oil.
Attempting to drain oil manually can also lead to poor system performance if the oil is not kept drained on a regular basis.
For all of the positives of an oil recovery system, I can not see skimping a few $$$ and depending on manual oil draining from the evaporator.
A simple method to collect the oil and manually transfer is to install a non-heated oil pot below the pumper drum of suction side vessel. The pot has 3 connections, one for the oil in, two is the vent line and 3 is the oil return to suction. The drain and vent lines are left open for the oil to collect in the oil pot since oil readily separates from ammonia and goes to the bottom. On a once per week or two week schedule, you close the oil feed line and let the pot vent off through the vent line. After the oil has warmed a bit and boiled off the liquid ammonia, close the vent line and crack open the return line. As the oil warms, the pressure will push the ol to the suction.
I prefer to heat the oil a with an electric heater and push it back to the compressor with a 4th line which is connected to discharge pressure.
A typical compressor will use some where between 0.3 and 1 gallon of oil per 100 (4.1667 days) hours of operation as a maximum. If you have a plant with say 6 larger screws you could be putting as much as 6 gallons of oil out of the system every 10 hours of operation or 43.2 gallons per month of operation. This is a lot of oil to be removing manually and discarding at the price of synthetic oils ($20.00 per U.S. gallon) or over $10,000 per year.
Ken
...They are on one system...Quote:
Originally Posted by US Iceman
...it's easy you to say,when u have new plants and compressors...
...when you will be in my skin and work for my salary,then we talk about new innovations in old NH3 plants...
...thanks for suggestions....
...Ken, I now see that you live in the another planet....Quote:
Originally Posted by TXiceman
...here, human life is worth nothing...
...so, that is the last care for the owner of factory...
You reach a point on an older system that you should question whether you keep throwing good money into it rather than step back and decide on a plan for proper repairs to get the operating cost down time within reason.
I know the accountants just look at the bottom line, but the bottom line is effected by how efficiently the refrigeration system runs. The accountants do not like to see large capital expenditures as they have to capitalize these over a period of time to write them off. If they can push it into maintenance, it is usually written off in the year of the expense. Problem is over a 5 or 10 year period they will spend a lot more trying keep an old system running rather than spend the money and fix it right.
So old plants can be made to run right, but it will cost some money. If corrosion is a problem, the pipes and vessels need to have ultrasonic testing done for wall thickness to insure that you have a plant that is safe to operate. The last thing you want is a massive failure and a large refrigerant release.
I have seen plants that I refused to work in because of the equipment conditions. I wold not subject our workers to such dangerous conditions.
I am afraid that we all live on the same planet and I value all life...no matter where you are located.
Sorry to get on the soap box, but it really upsets me when an owner will not spend the $$$ to maintain a safely operating system (and the owner is riding around in a new Mercedes).
Ken
...Ken I perfectly understand you and I agree with you...Quote:
Originally Posted by TXiceman
...but I write about practice here in Serbia(country near to Africa)....
...he refuse to bye new mask for operators ....
...but that is another topic...
...thanks for concern...
These are all too common conditions, even here in the US. I think one of the main issues is the owner does not understand refrigeration, he simply knows it costs him money and he does not like that.Quote:
Originally Posted by TXiceman
Somehow the people working on the systems (or managing them) need to figure out a way to sell ideas for improvements that will make the owner money. This they do understand.
It's not easy, and it is very frustrating but... someone has to take the first step. All owners know how to do is save money and operate their business. For most of them, refrigeration is a "black box" that produces "cold" and costs them money.
I suspect there are more ammonia releases and accidents caused by manual oil draining that just about anything else. That's not good!:(
Hi, Ken.Quote:
Originally Posted by TXiceman
If you believe that refrigeration system is clean inside, you are wrong. Probably, you never drain oil yourself. Very often this oil is absolutely black. I would not recommend to put it back even after filtering.
Manual draining is not a problem, if you do it right. In our days quick closing valves prevent ammonia spill.
My experience(practical) have shown that 1000 Hp refrigeration plant usually loses around 1 gallon of oil per month. I believe that NH3Lover will agree with me, because he mentioned similar number.
Manual oil draining doesn't lead to poor performance of refrigeration plant, if you do it right. Usually, when bottom of oil pot start melting, it is time to drain oil.
For most of them, refrigeration is a "black box" that produces "cold" and costs them money.......
And a non-operating refrigeration system will cost them even more money...
I now it is fight to get the owners to do things the right way at times...but look at it as a challenge.
Ken
Hi Sergei,
All of these points you raise are valid.
Old refrigeration systems are a mess to clean up. There is so much junk in the system it is not funny. All of this contributes to the oil color, metal particles, etc.Quote:
If you believe that refrigeration system is clean inside...
Very often this oil is absolutely black.
This problem is also made worse everytime someone switches to different oils. I think it is safe to say in general... oils should not be assumed to be compatible, there is too much difference in chemistry. All of this contributes to what you are describing and makes the oil return suggestion for difficult to implement.
With a properly installed new system there is absolutley no reason to not return the oil.
Older systems take more work, but personally I believe it is possible and a worthwhile consideration.
My guess is TXiceman has probably drained a few gallons of oil also.;)
More oil than i care to have drained.....
Your point on mixing oils is dead on....not a good idea even if the rep says/NO PROBLEM.
I have seen a lot of problems mixing oils which were supposedly compatible, especially mineral base and synthetics. If you star having oil problems, the best thing to do is dump all of the oil, drain every low point and charge with fresh oil. Run for about two weeks on the new oil and dump all of the oil collected in the oil puts. Now dump this oil and recharge again. Continue dumping the recovered oil until it starts to come back clean. I have seen plants where we had to dump the oil three times to get it cleaned up.
If you stay on top of the maintenance, and keep the system tight and clean...oil should not be a problem.
The two places I see the system getting contaminated is :
1. sloppy oil charging. Leaving a opened barrel of oil out with water on top of it and not sealing the oil charging hoses.
2. Sloppy refrigerant charging. Same thing, not keeping the hose sealed or cleaning it before it is used.
My personal hoses and gauge set have the hoses closed all of the time. I open them and clear with some dry nitrogen or refrigerant if any question.
I have seen system operating over 20 years and the oil system is still clean. The oil is one of if not the most critical things in the system. Poor oil system and you will have compressor problems.
So if you have a dirty system, drain the recovered oil and dispose of it until you can do a proper oil change and flush.
I have seen some systems so bad that we had to do a chemical flush on the piping and then you have the problem of drying the system from the water in the neutralizing flush.
You let a system get in bad shape and it is a major head ache to clean it up. Trying to limp along with patches and adding any old oil will finally come back to bite you in the rear big time. It is just a matter of time.
I preach maintenance...maintenance....maintenance.
Ken
That's usually the first sign of a problem developing. I always try to reinforce this by telling the system people; it's your system, not the oil supplier. If a problem develops, who has to deal with it?Quote:
Originally Posted by TXiceman
That's it right there.Quote:
Originally Posted by TXiceman
Let's all say this together!;)
I found that several stages of oil separation(additional to oil separator) in ammonia system.
Stage 1. High pressure receiver and termosiphon. This is slow process, but oil is clean.
Stage 2. Intermediate pressure receiver. Drain oil once a month. Oil dirtier than in stage 1.
Stage 3. High suction temperature receiver. Drain oil every 2-3 months. Oil dirtier than in stage 2.
Stage 4. Low suction temperature receiver. drain oil every 4-5 months. Oil is absolutely black.
This plant has original charge of ammonia. Oil barrels kept sealed. However, some moisture go into the system with air(negative suction pressure).
...I support Sergej opinion....
oil in ammonia systems will go black almost imediately due to carbon left in the oil at manufacturing it is not too detremental. especially if its shell. The newish oil on the block that doesnt go black is petrochem reflo 68a it amazing but a bit more expensive. the company triple treats it to remove all carbon. The other thing to watch in old systems is water due to older engineers not being too bothered about moisture ingress on NH3. I would feel safe putting oil from any part of the system back into the compressor if an oil test has been done by a laboratory and returned without a problem.
...Good thinking...Quote:
Originally Posted by HallsEngineer
...I see you are on the ground and not in the clouds....