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Thread: Oil separation
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22-06-2006, 06:40 PM #1
Oil separation
Hi Everybody. Please receive a big hello from Argentina, South America.
I need some help with a chiller from sabroe (2SAB 163 and 1 SAB128).
the evaporator is a PHE from Alfa Laval MK15 with 70 cassettes. The performance of the PHE is reduced by oil on the evaporator. We are purging an average of 1.5lts of oil per day every week.
To do this we have to stop the chiller for a minimum of 5 hours to let the oil set down.
The recirculation pipe for liquid ammonia is 4in, and as collecting pot it has a T leg of the same 4in diameter.
My impression is that this is to small to separate the oil from the ammonia. Recirculation of ammonia is 3500 kg/h according to PHE calculation.
Suction temperature is -7°C it should be -3°C, discharge 13 bar
Does anybody knows a safe separation velocity for a liquid ammonia to oil separator?
Oil is PAO 68 from york
thank you
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22-06-2006, 08:11 PM #2
Re: Oil separation
Originally Posted by marianom
seems you are experiencing a common fault with the SAB 163 Units (high oil carryover).
There is probably a fault in the refrigeration system, check for the following.
1/ liquid carryover (low suction superheats and low discharge temperatures)
2/ Compressor running for long periods of time at part load on the slide.
3/lower than normal condensing temperatures (increased volume flow through the oil separator, beyond normal design)
If you can post a log of the following we can probably tell you what is wrong.
Saturated suction pressure (in deg c)
suction temperature
Saturated discharge pressure (in deg c)
discharge temperature
liquid temperature off condenser
pressure at condenser outlet (not necessary but helpfull)
oil temperature
Chiller fluid in
Chiller fluid out
Looking forward to you post
Kind Regards AndyIf you can't fix it leave it that no one else will:rolleyes:
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22-06-2006, 08:15 PM #3
Re: Oil separation
Originally Posted by marianom
Normally Sabroe on their chillers have a pot that can be hot gased to return the oil to the compressors.
Kind Regards AndyIf you can't fix it leave it that no one else will:rolleyes:
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22-06-2006, 09:17 PM #4
Re: Oil separation
Andy:
We do have a return system, with the pot you describe. the problem is that the oil does not settle down while any compressor is running. So we have to stop the refrigeration plant to collect the oil and pump it back to the compresors,now manually because the compressors are off.
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22-06-2006, 09:23 PM #5
Re: Oil separation
Thank you for your advice andy!!
I need to go to the compressor in order to read these values.
The main oil separator is a standard coaleser filter from Sabroe.
the oil carry fordward is 25 ppm for these coalesers and calculating this figure on oil is very aproximately the 1.5 liter/day we are pumping out of oil.
So it is possible that the oil separation pot on the liquid recirculation pipe of the evaporator to be to small?
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23-06-2006, 07:47 PM #6
Re: Oil separation
Originally Posted by marianom
What about automatic oil return, why drain when a well designed oil return system will return the oil to the compressors without wasting it
Kind Regards AndyIf you can't fix it leave it that no one else will:rolleyes:
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23-06-2006, 07:51 PM #7
Re: Oil separation
Originally Posted by marianom
Oil rectification systems return oil and liquid refrigerant, boiling off the refrigerant and returning the oil. Movement in the system should not effect the rectification of oil, the oil will still go to the bottom. Check the system operation, I am sure thre is a problem with the rectification or it's sequencing.
Kind Regards AndyIf you can't fix it leave it that no one else will:rolleyes:
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29-06-2006, 01:55 PM #8
Re: Oil separation
is there a chance that you could sketch for
your system, compressors with the discharge oil separators, chillers etc, so I could comments on your oil problems
Regards
Camille
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29-06-2006, 02:54 PM #9
Re: Oil separation
Had similar problem.
Changed the oil with POE 32, and problem is now solved.
If you want to stick with POE 68, then use ICI which is less miscible than Castrol and similar.
Remember that 68cSt is the kinematic viscosity of oil at 40°C.
The same oil at -10°C becomes a molasse with a viscosity of over 1500cSt.
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29-06-2006, 04:26 PM #10
Re: Oil separation
This are the condition of the main compressor working at 100%
Suction:
pressure:……………2.7 bar equi -3.6°C
Temperature:…... – 1.8 °C.
superheating temp:….1.8 °C.
Discharge:
Pressure:……………10.7 bar equiv 30.3°C
Temperature:……...64.1 °C.
superheating temp:....34.2 °C.
Glycol:
Temperature out:…….. 0.5 °C
Temp in: ....................4°C
Oil Pao 68:
Pressure:…………….6.5 bar.
Diferencial:………...0.2 bar.
Temperature:……...39.9 °C
Compressor capacity:................100 %.
Motor Current:…..224 A (50HZ 380 v)
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29-06-2006, 04:28 PM #11
Re: Oil separation
HI marianom,
Have you checked the oil return line from the separator(s) back to the compressor(s)?
Is the oil returning through these lines?
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29-06-2006, 04:53 PM #12
Re: Oil separation
Nonickname:
The Oil we use is PAO 68, would you please clarify what POE means?
Regarding the viscosity of the oil at low temperature, I agree with you that at low temperature the viscosity high, but i don´t know what to install to separate the oil before without a big investment.
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29-06-2006, 05:15 PM #13
Re: Oil separation
Poly Ester Oil = POE, why that order no idea but technicly it aut to be PEO
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29-06-2006, 05:18 PM #14
Re: Oil separation
Yes Iceman, We did.
the problen is not the oil return system, is that the oil is not setling down on the separation pot, while the compressors are running. There is a level indicator for oil on the pot, and is only activated if when the compressor is off (we know it works, because when there is a lot of oil on the evaporators activates the level whith the compresor running)
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29-06-2006, 05:24 PM #15
Re: Oil separation
Yes Iceman, the oil returns,the problem is that when the oil pot on the evaporator fills up, the system returns that oil to the compressor, but if inmediately you stop the compressor and let it rest for 4 to 5 hous you may purge up more than 30 liters from a PHE
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29-06-2006, 06:08 PM #16
Re: Oil separation
Originally Posted by marianom
If on site I would try the following.
1/ lower the liquid level in the surge vessel above the PHE
2/ Increase the condensing pressure
But not both at the same time. Your compressor amps seem low for a Sab163, but I suppose the condensing pressure would account for that.
With ammonia DO NOT use POE oil, ammonia carries water around with it POE oil absorbs water
You could also try taking the oil/refrigerant mixture for the oil rectifer off at a slightly higher point. But try rasing the condensing pressure
Kind Regards AndyIf you can't fix it leave it that no one else will:rolleyes:
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29-06-2006, 06:32 PM #17
Re: Oil separation
Originally Posted by The MG Pony
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29-06-2006, 08:14 PM #18
Re: Oil separation
Thank you Andy.
we have tried the first, and the heat exchanged drops dramatically with just a reduction of 1 inch from the recomended level on operation.
the second, happends naturally due to the condensing temperature depends on the fouling of the condenser river side (CIP washed every 4 weeks)
We can not see any significant difference.
We are looking to introduce a modification on the installation to collect the oil.
do you recomend a second coalecent filter or a oil to liquid separator on high pressure side?
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29-06-2006, 10:21 PM #19
Re: Oil separation
Originally Posted by marianom
Oil wash systems, I have no experience with, but what little I know is(or have heard) is they can be problematic to set up, and expensive to maintain
One common Coalecent separator will be enough, with a level switch to open a valve into each compressor on lower than normal oil level
Kind Regards AndyIf you can't fix it leave it that no one else will:rolleyes:
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29-06-2006, 10:45 PM #20
Re: Oil separation
Hi, marianom
Originally Posted by US Iceman
Originally Posted by marianom
I do not know but I think that you have two oil return systems. One from oil separator and another one from PHE.
Your problem is with the first one. Return of oil from oil separator to the chamber with shaft seal. There you have (I think) one unit with small regulating valve and sight glass (see picture). Inside of that unit under plug you have also a small filter which must be checked.
Hope this will help
BTW, how old is your plant and when you faced those problem?
Best regards,
Josip
It's impossible to make anything foolproof because fools are so ingenious...
Don't ever underestimate the power of stupid people when they are in large groups.
Please, don't teach me how to be stupid....
No job is as important as to jeopardize the safety of you or those that you work with.
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30-06-2006, 01:47 AM #21
Re: Oil separation
Originally Posted by marianom
That would indicate the coalescing element is leaking somehow (elements not seated properly in separator, or element itself is bad).
In another post you mentioned this;
the oil carry forward is 25 ppm for these coalescers and calculating this figure on oil is very approximately the 1.5 liter/day we are pumping out of oil.
Another question, which I'm not sure of the answer is... Is the oil separator designed to operate at 10 bar discharge pressure? If not, the velocity through the separator can be too high and cause oil carryover also, even if the elements are new and seated properly.
The more I think about this it seems to an oil separator problem, not oil recovery.
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30-06-2006, 10:46 AM #22
Re: Oil separation
Originally Posted by US Iceman
The manual takes about a fine element, but not coalecent
I may be wrong but I assumed that these units were not fitted with coalecent filters, mainly through experience, they all use oil at a higher rate than units with coalecent secondaries
This filter may simply be that a fine mesh filter.
Kind Regards AndyIf you can't fix it leave it that no one else will:rolleyes:
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30-06-2006, 02:23 PM #23
Re: Oil separation
Hi Andy,
You are right. The manual Josip posted does describe a "fine filter element". In the drawings it is installed in the separator in a similar manner as a coalescing element.
The demister pads normally do a very good job of removing a large volume of the liquids (oil in this case), so it would appear the "fine filter element" is being used as a final separation method.
I guess I would like to see some pictures or technical descriptions of the "fine filter element". As you say, the oil carryover rate would be higher than a separator with coalescing elements.
Originally Posted by from manual Josip posted
Your suggestion about raising the discharge pressure would help to see if the oil carryover rate decreases.Last edited by US Iceman; 06-07-2006 at 02:08 AM. Reason: text editing
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05-07-2006, 11:21 PM #24
Re: Oil separation
Josip:
we review these valve adjustment, to adjust it according to the manual long time ago. Always as the manual say, told an old Master.
It seems the filter element ( if not a coalecer) is not giving us good results
the plant is 4 years old. I get in touch with it last year. they told me this problem is from the start up.
The York Service are very reticent to give us good support on these because the are afraid of claim or what ever, but this is the case, the support from them is really bad.
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05-07-2006, 11:27 PM #25
Re: Oil separation
We have replaced the filter element, twice (a part from York) but up to now could get no technichal description of it.
one of them was damage because a faulty check valve imploding it (back flow)
The second time was a suggestion of the York service to improve oil recovery, but note no difference after the change.
Best regards
Mariano
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05-07-2006, 11:28 PM #26
Re: Oil separation
It is clear that this oil pot is on the low pressure side , no?
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06-07-2006, 10:04 AM #27
Re: Oil separation
Originally Posted by marianom
Yes the pot is on the low side, but will be pressurised with hot gas to push the oil back to the compressors
Kind Regards AndyIf you can't fix it leave it that no one else will:rolleyes:
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07-07-2006, 03:44 PM #28
Re: Oil separation
On the attached file, you can see a drawing of the installation on the PHE side. There are four PHE, the two on the right are the evaporators. (on red the oil pot we were talking about)
You may see also that there is no oil separation on the high pressure side. There is no liquid receiver, liquid condensates on the plate heat exchanger and is fed to the low pressure side trough a level control located on the outlet of the condenser PHE.
The 2 on the left are part of the condensation system. (we use river water to condensate, but trough an intermediate PHE) to avoid the risk of river water contamination.
Also the condenser PHE have the refrigeration oil PHE.
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24-07-2006, 04:46 PM #29
Hai Everybody
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