Oil return in NH3 plants

[Sergei]

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.

[US Iceman]

Drained oil contains water, dirt, acids and etc.

Have you verified this with an oil analysis?

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?

[Sergei]

Have you verified this with an oil analysis?

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.

[US Iceman]

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.

And I agree. Let's step aside for the moment and look at this from a different perspective.

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.

[TXiceman]

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.

First and foremost, a properly operating plant should not have any dirt and acids in the refrigerant or oil.

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

[Sinke]

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.

...Ken, I now see that you live in the another planet....
...here, human life is worth nothing...
...so, that is the last care for the owner of factory...

[Sergei]

First and foremost, a properly operating plant should not have any dirt and acids in the refrigerant or oil.

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

Hi, Ken.
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.