Flooded evaporators

[ACR502]

Hi all
Im new to this forum, ya just have to thank Mr Gates for starting all this. Its awsome.
I have an R-22 system with flooded evaps running 45 degress. Would like to know if any what are my options for automatic oil return. Currently have a drain off the bottom that drains back to a low side oil resovoir with a hand valve and solinoid valve. The valve just closes for pump down. Also read with R-22 the best place is not the bottom of the evap but off the top. Also thinking of changing the system to 134 with POE oil. Holds about 600 lbs. Thanks

[GXMPLX]

I think it is weird to use R22 in flooded evaps. Are you positive this is what you have?

If it is, it can be done.

R22 and oil mix so you have to program a pumpdown cycle but leave enough pressure in the evap to return the oil left and as little liquid refrigerant as possible.

Then open the evap drain, take out the oil, and refill the evap with refrigerant.

I don't see the point though because in the moment you refill, oil will come in together with the R22.

You need to have where to store the refrigerant during the pumpdown. Probably the high pressure receiver.

If you use R134a to replace R22 you'll loose capacity. I wouldn't use R404 for this but R507 could be if the system can withstand higher pressures.

[US Iceman]

It does not do any good to have the oil drain connections on the bottom of vessels for R-22. The oil floats on top of the liquid R-22. If the vessel and coil are pumped down, you might get some oil out that way, but this has to be slightly irregular way of doing things.

I would look at using R-507 instead of R-134a.

What are you using flooded evaporators on with R-22 at 45°F? That's kind of high for anything short of air conditioning. Are these coils used on a penthouse unit for cooling a process area?

By the way...welcome!

[NH3LVR]

R-22 is quite common here in flooded evaps. The oil return is taken off the top as that is where the mixture is oil-rich.
If you have a compressor or compressors that puts little oil in the system you can get away with the pumpdown method very well. I have done it with a spiral freezer with no problems. Of course if you have a cold storage coil you might not want to pump it down overnight.

[GXMPLX]

The oil floats on top of the liquid R-22.

No it doesn't. What you get is an oil-R22 liquid mixture which is less dense than pure R22 liquid.

So you don't just take oil out but liquid R22 too.

You do want to separate oil from R22 and the best way is evaporating it.

[US Iceman]

Oh Boy, here we go again.:)

As NH3LVR mentioned the layer of oil (mixed with liquid refrigerant) floats in the upper portion of the liquid pool. As the evaporating pressure changes at different temperatures (lower or higher) the depth of the oil-rich layer can be in different locations. At a specific pressure the oil layer may be right at the top of the liquid. At a lower specific pressure the oil layer may be lower (or slightly under the top liquid level).

In either event, you can safely say the oil-rich layer floats in the upper portion of the liquid refrigerant pool. It it's not exactly at the top, it will be close.

Scavenging systems using an eductor/venturi have been used for many years to suck off a small volume of this oil-rich layer and return it to some device for distillation of the liquid refrigerant and the oil (before the oil is returned to the compressor). This is only one method, but the one I'm most familiar with.

You have the same problem with liquid overfeed systems, or flooded shell & tube chillers, or gravity flooded air-cooling coils, etc. using R-22 also.

[GXMPLX]

Exactly, if you do a pump down you don't need to worry on mix, you get OIL!

The only problem is geting enough pressure to get it out. You could do a short cycle with hot gas.

Clean, less trouble.

[GXMPLX]

... it'll take the oil out in few seconds+pumpdown time, ... and after the oil will come back in few seconds with liquid R22!

[monkey spanners]

Gxmplx,

Are you saying that the oil will get returned through the suction during pumpdown? or that it will be left behind in the evaporator and drain to the bottom when you can open the existing oil drain solenoid and 'puff' it back to where you want it? (note the use of technical term :D) or most likely a bit of both.

Jon

[US Iceman]

I think what's going on is: In the need to recover oil from a vessel containing R-22, the vessel is pumped down on a somewhat regular basis. As the refrigerant boils off, the oil is left behind and then drained down to a oil pot. Then the oil can be recovered/transferred back to the compressor(s).

I can't say I have seen this done before but it would work. The only issues is it sounds like a manual process and any time you make a process manual it leaves some opportunity for things to go wrong by human error.

Other than that, it will work...

[keepitcool]

One thing I have seen is 4 or 5 oil return lines at different elevations (near the top) of the surge drum with solenoids feeding an oil pot with a heater, automatic shut off valves and hot gas to return the oil. It takes some extra controls but is pretty effective.

[US Iceman]

One thing I have seen is 4 or 5 oil return lines at different elevations (near the top) of the surge drum with solenoids feeding an oil pot with a heater, automatic shut off valves and hot gas to return the oil. It takes some extra controls but is pretty effective.

That sounds like the type of oil recovery I am familiar with. On the specific one I'm thinking of we use several small lines from the acumulator/surge drum/etc, which return to a common line which is in the suction of an eductor. The eductor is powered by a hot gas source and provides the power to transport the oil back to the compressor.

[GXMPLX]

Gxmplx,

Are you saying that the oil will get returned through the suction during pumpdown? or that it will be left behind in the evaporator and drain to the bottom when you can open the existing oil drain solenoid and 'puff' it back to where you want it? (note the use of technical term :D) or most likely a bit of both.

Jon

The second is correct like US_Iceman said.

I would't use R22 in flooded evaps, it is good enough with DX and you wouldn't have all this trouble.

The oil gets picked from under like usually after the pumpdown, the problem it is cold and viscous so you need pressure to get it out and that would be with hot gas and direct the oil to an oil receiver, not the compressor because the amount of oil left could be high plus you could get hot gas (unless you have additional control to check if there is oil).

You need a ventilation valve in the oil reservoir and a signal of low oil could start the pumpdown cycle.

I don't like the idea of picking it up from above not that it wouldn't work but you also get liquid R22 or not even oil if the boiling inside is high.

I'd use R717 much easier for flooded evaps and now a days you can controll it automatically too.

[Tycho]

Hi all
Im new to this forum, ya just have to thank Mr Gates for starting all this. Its awsome.
I have an R-22 system with flooded evaps running 45 degress. Would like to know if any what are my options for automatic oil return. Currently have a drain off the bottom that drains back to a low side oil resovoir with a hand valve and solinoid valve. The valve just closes for pump down. Also read with R-22 the best place is not the bottom of the evap but off the top. Also thinking of changing the system to 134 with POE oil. Holds about 600 lbs. Thanks

What kind of valves are you using in your system to control the overheat in the evap? is it a regular thermo expansion valve with a bulb fitted to the outlet of the evap or is it a modulating solenoidvalve (the term for these kinds of valves escapes me at the moment)

[ACR502]

Thanks for all your replies. Basically it is an exsisting process system I happen to get involved on. Oil return is a problem because the evap drains and surge drum drains are only on the bottom. The outher issue is the high pressure. The medium they are cooling enters at 120 degress and if the compressor stops, the evaporator relief will pop at 150psi ( not good). My thought was 134 and a higher releif valve setting after I find out what pressure the evaps can take. Capacity is not a problem because the compressor is oversized and runs fully unloaded at 1/3 rd capacity all the time. The evap temp is controlled by an epr valve that is connected to a pneumatic thermostat. The evap temp runs 85 to 100 psi during production and 70 to 80 at the compressor. We are currenty working on a chilled water system for them, but they expressed that they would like to keep this system as a back up. There is a very large oil seperator on the system which helps. The compressor is an open drive Carrier. Basically you have to baby sit the the unit and pump it down to try to get the oil back. Currenty we leave the evap drain cracked and it feeds back to a heated remote oil sump that is piped off the crankcase. The system is about 12 years old and really should be riped out. Problem is they spent a fortune on it by outhers. It has a sporlan feed valve on the surge tank that has a heater on the bulb. If anything maybe a new surge tank with a float valve and maybe a sight glass to see where the liquid level is. Does any now if poe oil will sink with 134? Hoping for a lower presure replacement gas if we keep it as a back up for them. Again thanks for all your input

[US Iceman]

It has a sporlan feed valve on the surge tank that has a heater on the bulb.


This is called a Level-Master valve. It's a cheap way to control the liquid level.



If anything maybe a new surge tank with a float valve and maybe a sight glass to see where the liquid level is.


Why not a new compressor and condenser while you're at it?:confused: I don't mean to be saracastic but if they keep thowing money at the problem they will never get rid of it. This is a case of bad engineering gone even worse.

[GXMPLX]

And while you do what US_Iceman says get an dry cooler, air to whatever-your-media-is as a first stage and the evaporator as second.

Pressures would so much easier to handle, improving reliability.

[Josip]

Hi, ACR502 :)

welcome to RE forums...


Thanks for all your replies. Basically it is an exsisting process system I happen to get involved on. Oil return is a problem because the evap drains and surge drum drains are only on the bottom. The outher issue is the high pressure. The medium they are cooling enters at 120 degress and if the compressor stops, the evaporator relief will pop at 150psi ( not good). My thought was 134 and a higher releif valve setting after I find out what pressure the evaps can take. Capacity is not a problem because the compressor is oversized and runs fully unloaded at 1/3 rd capacity all the time. The evap temp is controlled by an epr valve that is connected to a pneumatic thermostat. The evap temp runs 85 to 100 psi during production and 70 to 80 at the compressor. We are currenty working on a chilled water system for them, but they expressed that they would like to keep this system as a back up. There is a very large oil seperator on the system which helps. The compressor is an open drive Carrier. Basically you have to baby sit the the unit and pump it down to try to get the oil back. Currenty we leave the evap drain cracked and it feeds back to a heated remote oil sump that is piped off the crankcase. The system is about 12 years old and really should be riped out. Problem is they spent a fortune on it by outhers. It has a sporlan feed valve on the surge tank that has a heater on the bulb. If anything maybe a new surge tank with a float valve and maybe a sight glass to see where the liquid level is. Does any now if poe oil will sink with 134? Hoping for a lower presure replacement gas if we keep it as a back up for them. Again thanks for all your input

.... why not install one ammonia packaged chiller (PAC) and forget about all problems with *****, oil, etc .... lower the energy bills ... be friend to the mother nature ...

http://www.sabroe.com/products/standard-package-solutions/pac-chillers-recip.html

http://www.sabroe.com/fileadmin/filer/pdf/Brochurer/Chillers/PAC_chillers_with_recips_09.10.06.pdf

http://www.sabroe.com/fileadmin/filer/pdf/Brochurer/Chillers/PAC_chillers_with_screws_09.10.06.pdf



Best regards, Josip :)

[GXMPLX]

...
.... why not install one ammonia packaged chiller (PAC) and forget about all problems with *****, oil, etc .... lower the energy bills ... be friend to the mother nature ...


No, I don't agree you would spend more energy than with a dry cooler and whatever-you-want as second stage!

The first stage cooling would almost be free except for some fans.

[JERRYCOOL]

[QUOTE=Josip;113294]Hi, ACR502 :)

welcome to RE forums...



.... why not install one ammonia packaged chiller (PAC) and forget about all problems with *****, oil, etc .... lower the energy bills ... be friend to the mother nature ...


If it is a Chemical plant, use ammonia implies to use all explosion proof equipment.

[Josip]

Hi, GXMPLX :)


No, I don't agree you would spend more energy than with a dry cooler and whatever-you-want as second stage!

The first stage cooling would almost be free except for some fans.

.... and maybe some pumps to run water around... or!?!

.... agree with you.... if we are speaking about .....
.......The medium they are cooling enters at 120 degress......, but I was thinking only about standard (around 20*C/68*F) one stage water chiller (I miss info about 120 degrees, my mistake;))

...... I should use ammonia in a second stage .... definitely ;)

Best regards, Josip :)

[Josip]

Hi, JERRYCOOL :)


[quote=Josip;113294]Hi, ACR502 :)

welcome to RE forums...



.... why not install one ammonia packaged chiller (PAC) and forget about all problems with *****, oil, etc .... lower the energy bills ... be friend to the mother nature ...


If it is a Chemical plant, use ammonia implies to use all explosion proof equipment.

:confused: .... can you explain this a little more, please ....

even when we use R404A for refrigeration systems within chemical plants (Ex equipment) is a mandatory

... don't see what is extra special with use of ammonia... or maybe there it is....

Best regards, Josip :)

[JERRYCOOL]

Hi Josip,
Ammonia is IIA gas in IEC.
If the area in the chemical plant is originally hazadous area, it will be no problem to use ammonia.But if not and you still want to use ammonia, the area will be updated to hazadous area, adn all equipment should use explosion proof equipment. This will cause big cost impact for the owner.

thanks
Jerrycool

[JERRYCOOL]

Normally ***** itself will not cause the area be a hazardous area. The area classification depends on the whole plant design.

[Magoo]

Going back to original question of oil in evaporators. Has anyone thought about eliminating the oil carry-over from compressor, screw or recip, oil temps, injection rates, oil separation, pul down rates, coelesars etc etc., if you stop carry over the problem won't occur.
magoo