Draining Oil from Receiver

[Sleigher]

Hi All,
I know it is not generally a good idea to drain oil from the receiver but for some reason we have a couple of receivers (on the same system) that are getting a lot of oil build up.
We drain the LPR and the Intercooler regularly but we're not getting the oil out of the system.
I was thinking of running a charging hose from the bottom of the receiver to the intercooler and dumping the oil into the intercooler where we could more safely drain it out.
I have, long ago, drained directly from the receiver but I didn't like it. We may have pumped the receiver down before we did that. I don't really remember.
I'm interested in any thoughts on this.
Also, I'm thinking that maybe the reason we are seeing so much oil is due to our reduced head pressure.
While I like the head to run as low as possible it may be that the piping isn't conducive for the low head.
We installed a new condenser about 8 months ago and have since been running a much lower head pressure, about 120 where before that we were probably running at about 140-165.
Just a theory.
Thanks in advance for any thoughts on these topics.

Peter

[Tesla]

running at lo load will cause oil return probs like logging at lo and cold points of the system. Systems and pipe sizing is done on full load calcs but the systems only run at full load on less than 10% of the year. Increase the head pressure or resize pipes to accomidate lowered pressures. Reduced pressue decreases refrigerant velocity which inturn reduces oil return

[RANGER1]

Above comments would only be for ***** in my opinion .
Draining of oil from HP liquid reciever can be dangerous and better to avoid .
I would agree to transfer oil / some liquid to intercooler is good idea .
Obviously use appropriate type of hose for ammonia and a tee piece with valve so you can bleed off ammonia in hose to atmosphere or water .

To reduce oil drained you need to determine which compresser/s throw over oil .
What type of machinery do you have , recips screws ?

[Segei]

Hi All,
I know it is not generally a good idea to drain oil from the receiver but for some reason we have a couple of receivers (on the same system) that are getting a lot of oil build up.
We drain the LPR and the Intercooler regularly but we're not getting the oil out of the system.
I was thinking of running a charging hose from the bottom of the receiver to the intercooler and dumping the oil into the intercooler where we could more safely drain it out.
I have, long ago, drained directly from the receiver but I didn't like it. We may have pumped the receiver down before we did that. I don't really remember.
I'm interested in any thoughts on this.
Also, I'm thinking that maybe the reason we are seeing so much oil is due to our reduced head pressure.
While I like the head to run as low as possible it may be that the piping isn't conducive for the low head.
We installed a new condenser about 8 months ago and have since been running a much lower head pressure, about 120 where before that we were probably running at about 140-165.
Just a theory.
Thanks in advance for any thoughts on these topics.

Peter

How much oil do you drain from HPRs? 120 psig is typical pressure for many plants. I don't think that your plant was designed for 140-165 psig. It is safer to have quick closing valves for oil drain. How do know that it is time to drain?

[Sleigher]

"How much oil do you drain from HPRs? 120 psig is typical pressure for many plants. I don't think that your plant was designed for 140-165 psig. It is safer to have quick closing valves for oil drain. How do know that it is time to drain?"

Typically we don't drain oil from receivers. As far as 120 psig being "typical" I would have to disagree. While it may be a nice head pressure most plants are usually designed with a much higher head in mind due to initial cost. I have four different ammonia systems. The lowest head we can consistently maintain is 120. This is on a plant with three condensers. One of which I recently replaced with a unit twice the capacity of the original unit. I'm lucky I rarely have to justify what I want to install. The last total plant I installed runs a head of about 135-140. This plant is way over designed and runs real well most of the time.
The other two plants were designed on the cheap. During the summer we are lucky to keep it in the 160s.
As far as how do you know about the oil? We have the older style sight glass on these units. You can see the oil in the column. In the past I think we have had times where the oil seemed to be confined to the column and not through out the receiver.
We do have spring loaded valves on all of the locations where we regularly drain oil. They work well as long as you can keep your operators from propping them open or tying them open.

Compressor types: This is an older plant. We have a pair of VSA Yorks (1936) running on a single Synchronous motor. They pump some oil but they do have separators on them. We also have a number of Vilter V/W machines that also have separators and a pair of York V/W machines which we don't run much.
Before trying to move the oil around via hose, I'm going to dial back the fan horsepower and see if we can get it to flow on its own. I don't recall having much issue prior to installing the new condenser.
Thanks again.
I'll post our results.

Peter

[RANGER1]

Usually oil will not seperate in a liquid reciever due to its constant circulation back into the system .
Can't see how head pressure or new condenser can cause oil in HPLR .

If don't drain it from reciever it will eventually end up in low side anyway .

Maybe on low loads oil can accumulate in HPLR , of course oil in sight glass is a pain .

Are all your oil return floats definately working and water cooled heads getting good flow ?

[Segei]

"How much oil do you drain from HPRs? 120 psig is typical pressure for many plants. I don't think that your plant was designed for 140-165 psig. It is safer to have quick closing valves for oil drain. How do know that it is time to drain?"

Typically we don't drain oil from receivers. As far as 120 psig being "typical" I would have to disagree. While it may be a nice head pressure most plants are usually designed with a much higher head in mind due to initial cost. I have four different ammonia systems. The lowest head we can consistently maintain is 120. This is on a plant with three condensers. One of which I recently replaced with a unit twice the capacity of the original unit. I'm lucky I rarely have to justify what I want to install. The last total plant I installed runs a head of about 135-140. This plant is way over designed and runs real well most of the time.
The other two plants were designed on the cheap. During the summer we are lucky to keep it in the 160s.
As far as how do you know about the oil? We have the older style sight glass on these units. You can see the oil in the column. In the past I think we have had times where the oil seemed to be confined to the column and not through out the receiver.
We do have spring loaded valves on all of the locations where we regularly drain oil. They work well as long as you can keep your operators from propping them open or tying them open.

Compressor types: This is an older plant. We have a pair of VSA Yorks (1936) running on a single Synchronous motor. They pump some oil but they do have separators on them. We also have a number of Vilter V/W machines that also have separators and a pair of York V/W machines which we don't run much.
Before trying to move the oil around via hose, I'm going to dial back the fan horsepower and see if we can get it to flow on its own. I don't recall having much issue prior to installing the new condenser.
Thanks again.
I'll post our results.

Peter

Majority of refrigeration plants(in North America) designed for condensing pressures 150 -180psig. You can't design plant for 120psig. However, operating range of condensing pressures typically 120-180psig. Your maximum head pressure of 160-170psig isn't so bad. Your plant with bigger condenser operated at 120psig before you install this condenser. It happen during periods of cool weather. Did you have oil issue in that time?
I would install oil pot for HPR. However, it shouldn't run all the time. Drain oil+ammonia in this oil pot when you need it. Ammonia will evaporate and you can safely drain oil.

[nh3wizard]

Majority of refrigeration plants(in North America) designed for condensing pressures 150 -180psig. You can't design plant for 120psig. However, operating range of condensing pressures typically 120-180psig. Your maximum head pressure of 160-170psig isn't so bad. Your plant with bigger condenser operated at 120psig before you install this condenser. It happen during periods of cool weather. Did you have oil issue in that time?
I would install oil pot for HPR. However, it shouldn't run all the time. Drain oil+ammonia in this oil pot when you need it. Ammonia will evaporate and you can safely drain oil.

If you decide to do it this way just make sure your oil pot is rated for at least 300 psig, and of course with a relief valve.

[Sleigher]

We've been running head pressure at #150. for the last three days.
The level in the column has gone down about 8 inches and we are getting a good amount of oil out of the intercooler and LPR.
Of course the level could have gone down due to the increased pressure compressing the oil/ammonia solution but we will see how much we get out.
Prior to installing the new condenser which dramatically increased our capacity, we did not have issues with oil build up in the receiver.
We'll run with the higher head for a week or so and see what the effect is on oil return.
After that we will go back to the 120 set point and see if we start building oil again.
Thanks for the replies.

Peter

[Sandro Baptista]

Sleigher,

Is there any compressors in particular you notice that they loose oil more quickly than usual when you decrease the condensation pressure?

Sometimes when the oil separator is not really good a decrease of pressure could be an advantage, albeit the fact the discharge temperature also decreases.

Low pressures implicates less capability of the oil drops be coalescent and consequently fall by gravity.
Check the compressors that loose more oil and put they in the lasts capacities of the system...so they work less. This is my opinion/advice.

Regards

Baptista

[Sandro Baptista]

I'm sorry about the oil separator I meant a disadvantage with the decrease of pressure. I think however that you have understood anyway what I wanted to say.

[Magoo]

Hi Sleigher.
By changing condenser and lowering discharge pressure you increase system capacity and save on energy consumption. Every company accountants dream come ture, one-up capital expenditure and on-going savings and a pay back period. All good stuff. But the system suffers, as you said increase in capacity.
Lowers the compression ratio so consumes less power and a higher flow rates through compressors. The gas flow rate is possibly higher than the rated capacity of oil separators, so increased oil carry-over to system which is indicated in the receiver sight glass leg. Liquid sub-cooling adds to accumulating oil in HP receiver. So by raising system HPand reducing carry-over the oil level reduces and entrained back to system.
Ask for more money to replace oil separators to suit increased flow rates and add secondary coalesars as well.

[Segei]

As far as I understand this plant was operated at 120psig before big condenser was installed. It didn't happen in summer time, but during periods of cool weather this plant can be run at 120psig. If it is true, head pressure isn't issue.
I think that it is good practice to keep track of oil charging and oil draining. If something happen, you have information to compare.

[D.D.KORANNE]

Is it not the loss of oil is high that it passes further to receiver . At times we have had systems wherein atimer controlled solenoid fed back ( to the compressor crank-case) the separated oil in the separator on nh3 systems . Oil separator located away from compressor can help separate oil better for recovery as it has a cool down time before separation .

[sagittarius]

I agree increasing the discharge pressure and temperature would be better for oil separating from ammonia.And adding/changing the coalescer in the oil separater for screw compressor unit.

[Segei]

Probably, energy savings were the reason to install large condenser. To be successful in energy savings we should change our approach. New approach should be engineering. I mean engineering design and engineering operation.
Let's have a look at this plant. First we have to determine the real reason of this issue. The reasons can be low condensing pressure or compressors problem. Assume that we determined that low cond. pressure is the problem. Old approach to increase cond. pressure and statement that plant wasn't designed for so low condensing pressure.
New approach. Determine the factors influence on this issue. Increased volume flow is the reason of oil carry over. Capacity of compressors and suction pressure are major factors. Compressor can be unloaded and suction pressure can be reduced. Certainly this two factors will reduce efficiency of the compressors. However, lower condensing pressure will increase efficiency of compressors. We have two opposite factors. So we have to determine which factor the greater and what is the better for the system. Sometimes one step is good for the compressor but not good for system(plant). Higher suction pressure is always better for the compressors but not always better for the system. Refrigeration plant should be operated at optimum suction pressure. May be it sounds a bit complicated but this is way to go in energy savings. Optimization of refrigeration plant operation isn't simple issue. For this plant(and for many others) the best way to save energy will be lowering cond. pressure below 120psig during winter operation. However, you should be open minded to do that.

[Sandro Baptista]

As far as I understand this plant was operated at 120psig before big condenser was installed. It didn't happen in summer time, but during periods of cool weather this plant can be run at 120psig. If it is true, head pressure isn't issue.

Before the condenser was installed the system in the winter have lower cooling needs so the compressors work less.

Sleigher, which are the compressors that loose more oil?

[US Iceman]

Some general comments as I get caught up here...

The high pressure receiver will not normally hold very much oil because the dip tube scavenges the bottom of the receiver where the oil will lie.

Lower discharge pressure is good for energy savings however it also affects the oil separation. The oil separates better at lower temperatures and pressures.

[subb-zero]

Have you ever thought why you keep draining oil so often? What type of oil separator do you have? Oil does not mix with ammonia as oil is more dense and will collect in the low side of the system. Check the oil separator, if the oil is not returning it will travel in the system and land up in the low side you wont get oil in the Hp receiver.

[Sandro Baptista]

The oil separates better at lower temperatures and pressures.

US Iceman, I think you meant lower temperatures and high pressures, right?

[nh3wizard]

Iceman is right lower pressures and temperatures.

[Sandro Baptista]

Iceman is right lower pressures and temperatures.

I'm sorry I can't agreed with you. For the same discharge temperature High pressures are favourable to the formation of big drops of oil that will fall by gravity.

[Segei]

I'm sorry I can't agreed with you. For the same discharge temperature High pressures are favourable to the formation of big drops of oil that will fall by gravity.

US Iceman talked about the liquid not about the vapor.

[sagittarius]

Oil is less miscible in refrigerant at lower temperature and pressure

[nh3wizard]

Correct me if I am wrong; but in order to get a lower temperature dont you need a lower pressure?

[US Iceman]

Lower temperatures also help with separating oil from vapor. Some of the older members here (or should I say the more experienced members) might remember some of the old distillation devices used in compressor discharge lines.

They were essentially an intercooler installed in the discharge lines. The liquid ammonia at condensing pressure & temperature allowed the oil to fall out of the discharge gas. Then the oil could be drained out of the vessel (but very carefully or even better using an oil pot!).

Sometimes its helpful to be older.

[Sandro Baptista]

US Iceman talked about the liquid not about the vapor.

I'm sorry US iceman I haven't get that idea from your post.

Thanks Segei for your correction.

[subb-zero]

Is the oil problem sorted?

[RANGER1]

How can higher pressures help with less oil carry over of compessor ?

Higher pressure will have affect on compressor efficiency ( less efficient ) .
Higher discharge tempretures can contribute to more oil carry over due to viscosity ( oil is thinner ) .
If oil is vapourized no seperator will stop it .
Sleigher didn't answer if any particular compressor uses a lot of oil which is the only way oil can enter condeser or liquid reciever .
Possibilities oil return system not working or broken valve/s in compressor .
The system does'nt make oil it comes from a compressor initially which surely must be consuming more oil around time of condenser upgrade .

The only other possibility is , oil has been logged in condenser area and
changes have stirred things up IF compressers are not using oil .

[Sandro Baptista]

How can higher pressures help with less oil carry over of compessor ?

Higher pressure will have affect on compressor efficiency ( less efficient ) .
Higher discharge tempretures can contribute to more oil carry over due to viscosity ( oil is thinner ) .

RANGER1

The medium have more gas density which carry small oil drops so they can coalescence (I don't know exactly how that word is written in english but I mean that in that way they can joy and grow and the fall by gravity and centrifugal forces).

Never said that the higher pressure doesn't affect on compressor efficiency.

[Sleigher]

Thanks again for all the replies from all around the world.
It is interesting that the approach proposed by many doesn't always take into account the fact that our circumstances might be different than your own.
One poster stated something about the screw compressor not pushing much oil, others advised replacing the separators and so on.
This is an older plant. The 1936 Yorks have been recently "rebuilt" new bearings and valves along with whatever else we could scrounge up. There was, however, some substantial scarring in the cylinder walls that are no doubt contributing to our oil issue. We chose to live with the imperfect cylinders as the alternative (removing, replacing, resleeving?) was not cost effective. I'm sure some of you have had to work on an older machine with parts that are no longer available. Some of our parts came out of someones barn in Cleveland. We got lucky and found an oil pump hanging off a compressor that was stored in a parking lot next door. The parts we had made were not cheap. The main bearings cost $2000/set.
The machines were doing a pretty good job with only half the valves intact and the bearing in bad shape so with new rings, valves and bearings it's working much better. Draining oil on a regular basils is part of running an ammonia plant. They do have separators on them but they don't get it all.
As US ICEMAN posted, the oil isn't usually an issue in a HP receiver. We never did drain any oil from this receiver.
I posted earlier that the change in head pressure seemed to push the oil out. Seems like that is still the case. Unless the oil was only in the sight glass in which case it simply drained out of the glass back into the receiver but I cant see a reason why it would only build up in the glass.
As far as correcting the oil carryover- well that would be nice but almost everything we do now is kinda expensive. This particular engine room has a total of 14 compressors, none of which seems to be using much more oil than any of the rest of them.
We're not having any temperature issues and we recycle the oil that we pull out of the oil traps so economically it makes more sense to watch our oil logs/usage and continue on as we have been.
Thanks again for the replies.
Peter

[RANGER1]

It all depends on what type of oil seperaor and velocity .
If its a demister pad oil hits it and drops out .
If its cyclonic it would be gas velocity which does'nt work as well if compressor unloads for long periods .

Sleigher could have either of these who knows ?

Sorry Sandro Babtista I'm only generalizing on everyones comments

[US Iceman]

The 1936 Yorks have been recently "rebuilt" new bearings and valves along with whatever else we could scrounge up.

Have you tried Electro-Motion down in St. Louis? I bought some parts from them many years ago for some old York 6X6's.

[scuba]

We are currentaly having a problem with oil build-up in our receiver,our liquid injection lines to our compressors are filling up with oil and failing them on high temp. The receiver has not been drained in 20 years. The only solution we came up with is to hook up a temporary tank to our receiver boil off the liquid to low temp and drain the oil. Any other suggestions .
Thanks Scuba

[sterl]

Scuba:
This a once in 20-year exercise or have you got machines loosing oil? Are all your machines liquid injected or otherwise cooled by the refrigerant?

Had a customer with a similar problem though his plant may not have been similar to yours....We banked ice for a couple of days and rigged up a "diversion" on the pumped oil circuit on a booster to a handy PHE....Condensed the booster discharge with the ice, put all the liquid refrig directly to the intercooler and from there to the low side, kept the booster oil cool with the still cold water....Didn't need liquid injection or t-syphon. Pumped out the HPR via the liquid makeup to the low side vessel we were sucking from. None of the normal condensers were operating... Took about 2-hours for the receiver to go down to 10 inches; and what we removed nvolved a whole lot more than just oil.
The restart took longer....

[scuba]

Thanks for the reply Sterl,All the screws are liquid injection and this is the first time we had any problems. None of the screws seem to be losing oil.
We hooked up the temporary receiver and boiled of to low temp and drained the receiver,after two days of working on it the results were no good we only drained about 20 oz. of oil. The mystery remains,were else could the oil in our liquid injection lines be coming from. Thanks for the replys.

Scuba

[ammonia tec]

How much oil do you drain from HPRs? 120 psig is typical pressure for many plants. I don't think that your plant was designed for 140-165 psig. It is safer to have quick closing valves for oil drain. How do know that it is time to drain?

they call it a deadmans valve (spring return). i would put reg on main discharge header. or most cond. could be valved off in sections?in winter time that helps alot . suction check valve failure, make sure ur comp. shaft not back spin as it shuting down ? replace coalescer and clear strainners,inspect strainer on return oil pressure thats too close to head pressure? i would isolate and pump out 1 evap. more likely its laying on bottom. head pressure depeins on the tolen. of compressor. most fricks 150 151 models have been runing 150 160 psi discharge pressure. dont over fill with oil. hope this helps. too much typing,lol.

[ammonia tec]

Thanks for the reply Sterl,All the screws are liquid injection and this is the first time we had any problems. None of the screws seem to be losing oil.
We hooked up the temporary receiver and boiled of to low temp and drained the receiver,after two days of working on it the results were no good we only drained about 20 oz. of oil. The mystery remains,were else could the oil in our liquid injection lines be coming from. Thanks for the replys.

Scuba

some fricks have ecom. injection cooling those check valves are known when they go bad oil will leak by. as per mfg personnal

[ammonia tec]

its more likely his whole system is oil slugging back to hpr-1. he has oil coming and going from the compressor. maybe?more likley

[ref717]

I agree with Ranger1 and Sleigher,new Ammonia plant refrigeration systems(e.g. -5,-15,-27 temp.) condensing pressure should be operating at about 160-175 psi. Reducing this pressure would put more load on your condensers because the discharge pressure of th compressors are constant. I think the problem here is the compressor oil separator.,maybe you have a vertical oil separator and its filter is not working properly to separate the oil from the ammonia gas.

[Segei]

I agree with Ranger1 and Sleigher,new Ammonia plant refrigeration systems(e.g. -5,-15,-27 temp.) condensing pressure should be operating at about 160-175 psi. Reducing this pressure would put more load on your condensers because the discharge pressure of th compressors are constant. I think the problem here is the compressor oil separator.,maybe you have a vertical oil separator and its filter is not working properly to separate the oil from the ammonia gas.

Operating plant at 160-175 psig you will waste a lot of energy. Definitely the issue is oil separator. You can design oil separator to operate at condensing pressure below 100 psig.

[ref717]

Nowadays compressors have built-in oil separators along with the compressor unit.,I agree that operating on low condensing pressure will reduce energy consumption but then again it depends on the system design of the plant.

[Segei]

Nowadays compressors have built-in oil separators along with the compressor unit.,I agree that operating on low condensing pressure will reduce energy consumption but then again it depends on the system design of the plant.

For screw compressors, major reason of oil carry over is high velocity of discharge gas. When we reduce condensing pressure, density of discharge gas will be reduced as well. At relatively constant mass flow, reduced density will lead to increased velocity of discharge gas. To reduce velocity 2 actions can be done: increase size of oil separator or reduce gas mass flow. Mass flow can be reduced by unloading compressor or lowering suction pressure.

[piewie]

I would never advise taking refrigerant in a hose from the receiver to the intercooler or LPR that is as dangerous if not more than draining the oil directly from the receiver. Besides once the oil is in the Intercooler or LPR it is another ball game altogether as the oil is more easily entraned in the refrigerant due to the bubbling effect of the refrigerant and the fact that the refrigerant is in a constant state of change or near change. Try pumping down the receiver and then draining the oil.

[R717Kid]

My two cents worth....

In regards to most plants not being able to run lower head pressures, for whatever reason....during a recent project I was able to lower head pressure through system optimization. In the upper midwest I can run 110 psig on a 70 degree night with 60% relative humidity. Winter I can run 95 psig with fans only. In addition, lower head pressure does increase velocity of the gas through the system and it is the older compressors in need of servicing or oil seperators that need help that lend way to oil carryover. Recording everything while making systematic changes is paramount. Motor amperage at the compressors will be very notable when reducing head pressure. Knowing how much oil you are putting into and blowing through a compressor should be part of condition based monitoring. If you are troubleshooing without all the data, then you are playing a guessing game essentially.

Now, if you have operators proping self closing valves open or other bad habbits then you have operators deviating from safe work practices/procedures followed by management who doesn't hold people accountable for these actions and this is how ammonia gets a bad name and accidents happen.

[Segei]

My two cents worth....

In regards to most plants not being able to run lower head pressures, for whatever reason....during a recent project I was able to lower head pressure through system optimization. In the upper midwest I can run 110 psig on a 70 degree night with 60% relative humidity. Winter I can run 95 psig with fans only. In addition, lower head pressure does increase velocity of the gas through the system and it is the older compressors in need of servicing or oil seperators that need help that lend way to oil carryover. Recording everything while making systematic changes is paramount. Motor amperage at the compressors will be very notable when reducing head pressure. Knowing how much oil you are putting into and blowing through a compressor should be part of condition based monitoring. If you are troubleshooing without all the data, then you are playing a guessing game essentially.

Now, if you have operators proping self closing valves open or other bad habbits then you have operators deviating from safe work practices/procedures followed by management who doesn't hold people accountable for these actions and this is how ammonia gets a bad name and accidents happen.

You are focused on lowering head pressure. This approach will always save energy for the compressors , but not always for the system(plant). Sometimes reduction of head pressure from 120 psig to 110 psig will save you 20 HP of compressor power, but this step require additional 30 HP of condenser power. It means that plant is more efficient at 120 psig. During summer operation to minimize energy use condensing pressure should "float" up and down based on wet bulb temperature.
Oil carry over is a barrier to operate plant at low condensing pressure, but every barrier has a solution.