Venturi for oil recovery in flooded system

[Friobernal]

Hi;

I´ve heard about the use of a venturi in ammonia flooded sytem for oil recovery....

Can anybody explain me how it works?

Regards

[Sir Josiah Sodd]

I haven’t thought of this one in years…….. Never used it on ammonia, but we used it on R11 chillers

Carrier used a modification to correct oil logging on their hermetic centrifugal chillers.
The chillers ran on R11 and low load conditions would leave some of the oil stranded in the evaporator. In this case the oil floated on the refrigerant. As well as lube problems, the film of oil inhibited evaporation.

As I recall, and this was some 25 or more years ago, it was a field mod that required some precision drilling on the unishell.
The bulletin may still be available.

What you did was to obtain a Venturi or eductor from Carrier and this was equipped with a ¾ gas thread. You then measure carefully to a point on the outside of the shell corresponding with a critical level where the oil was supposed to collect, drilled and tapped the metal and fitted the Venturi.
The idea was to get the intake of Venturi exactly at the oil level.

The cross tees were connected to the condenser and the oil pump respectively.
Discharge pressure was usually about 10psi, enough to develop a pressure differential across the eductor and induce oil into the cross member and then off to the pump. If I recall further it had a solenoid energised by oil level or pressure…..

That was the theory……. Never used it since and I can’t claim that it was a huge success then.


Is this what you had in mind?

[Sir Josiah Sodd]

I haven’t thought of this one in years…….. Never used it on ammonia, but we used it on R11 chillers

Carrier used a modification to correct oil logging on their hermetic centrifugal chillers.
The chillers ran on R11 and low load conditions would leave some of the oil stranded in the evaporator. In this case the oil floated on the refrigerant. As well as lube problems, the film of oil inhibited evaporation.

As I recall, and this was some 25 or more years ago, it was a field mod that required some precision drilling on the unishell.
The bulletin may still be available.

What you did was to obtain a Venturi or eductor from Carrier and this was equipped with a ¾ gas thread. You then measure carefully to a point on the outside of the shell corresponding with a critical level where the oil was supposed to collect, drilled and tapped the metal and fitted the Venturi.
The idea was to get the intake of Venturi exactly at the oil level.

The cross tees were connected to the condenser and the oil pump respectively.
Discharge pressure was usually about 10psi, enough to develop a pressure differential across the eductor and induce oil into the cross member and then off to the pump. If I recall further it had a solenoid energised by oil level or pressure…..

That was the theory……. Never used it since and I can’t claim that it was a huge success then.


Is this what you had in mind?

[US Iceman]

Here is a link to an excellent explanation of venturi's (or sometimes called jet pumps).

http://www.penberthy-online.com/faq/...itive_Jets.pdf

I have used these for halocarbon, ammonia, and propane refrigeration systems.

My experience with these was for the purpose of oil recovery off of flooded chillers or other vessels.

The first part is to recognize where the oil will be present in the vessel. On ammonia systems, the oil will settle to the bottom of the vessel which makes the oil recovery much easier.

On halocarbons systems, the oil floats in a layer at the top of the liquid level. The actual depth of the oil layer is dependent on the refrigerant pressure and temperature. This is a function of the oil solubility and miscibility with the refrigerant. For halocarbon system I normally used three taps off of the vessel. These were located around the intended liquid level. One high, one lower, and one in the middle. All of these were spaced about 2 inches apart in a vertical axis.

The venturi suction connnection (low pressure port) was connected to a common line from these three taps. A high-pressure gas source was controlled by a solenoid valve into the venturi inlet. I also used a metering valve in this high-pressure inlet to regulate the gas flow.

When the high-pressure gas source is applied to the venturi, a low-pressure area is created on the low-pressure port by the venturi effect. This suction will move an oil/refrigerant mixture out of the vessel and pump it out the discharge port of the venturi.

At this point you have to have a distillation process to evaporate the refrigerant from the oil mixture before it is returned to the compressor. If the distillation process is arranged so that gravity can drain the oil back into the compressor, a pump is eliminated.

These devices will pump a lot of oil/refrigerant mixture. The other item to remember is that you are using a hiigh-pressure gas source for pumping. All of the high-pressure gas is being vented to the suction side of the refrigeration system, so this has some negative impact on compressor capacity.

I have had very good results with these. I would recommend using a very small venturi, since the oil recovery process could be set up to run continuously.

[Friobernal]

Thanks for answering,

I have clear the theory, but it would be great if somebody could attach a picture. (I have to see more installations)

Thanks again Iceman; i have a lot of questions and y see that you have good answers

[Friobernal]

Hi Iceman;

I´m attaching 2 files about venturi, where i can see clearly what is happening, but unfortunately i don´t understand your expanation without a drawing (i´m not very clever )

Anyway, when you talk about a vessel: Is it the liquid separator that feeds the evaporators?

When you talk about high pressuregas; are discharge gas from the compressor?

I´m a little bit confused

Regards

[US Iceman]

Hi Friobernal,

I have seen the venturi used for two purposes; one shown in your attachement, and the other for oil recovery.

(ejector/jet pump/eductor/etc. Again we see different names to describe the same item)

The diagram you gave shows a venturi used to circulate cold liquid refrigerant from a liquid separator to a plate heat exchanger. This improves the circulation and turbulence through the heat exchanger only. Better heat transfer.

Here is a link that gives more detail on this type of use.

http://www.haphillips.com/products.html?pc=68&pid=34

The oil recovery arrangement has been poorly documented since these were developed by manufacturers for specific purposes.

As a previous person said, he has seen these on Carrier chillers. I have also seen them on Dunham-Bush flooded shell and tube chillers (R-22) used with screw compressors.

The version I created during my time with a manufacturer was used for oil recovery on flooded chillers and liquid separators of different types (intercoolers, pumped recirculation vessels, etc.).

I'll try to answer your questions...

The high-pressure gas source I mentioned is the discharge pressure of the refrigeration system. This provides the power source to make the venturi operate.

The vessel can be any liquid separator that operates at a pressure lower than the discharge pressure of the refrigeration system. This is important, since the suction port on the venturi must be at a lower pressure than the gas supply pressure.

A picture is worth a thousand words right?

I will have to see if I have something here in the office.

I will attempt to describe this arrangement.

Imagine a tee fitting (the venturi) with the bottom port down. This is the low-pressure or suction port. This port is connected to the three oil taps on the vessel (where the oil level will be in the vessel).

The port on the right is the high-pressure supply connection (discharge gas). This is where I use a solenoid valve and metering valve to control the flow of the discharge gas into the venturi. The solenoid was controlled by a timer. The timer was set to energize the solenoid for 5 minutes every hour. An adjustable timer is preferred.

The port on the left is the medium pressure outlet. This is where the mixture of oil and refrigerant discharge back to the distillation device (commonly called an oil still. These can have electric heaters or other heat sources to evaporate the liquid refrigerant.).

The venturi should be located above the oil tap connections. This prevents the venturi from flooding with liquid refrigerant during the off cycle.

During operation, the high-pressure gas supply creates the suction on the low-pressure port (the bottom port). The liquid and oil mixture are sucked into the venturi. The discharge is through the venturi outlet at a pressure slightly greater than the vessel pressure. The vessel is where we are recovering oil.

You should be careful with the oil return method back to the compressor. If you have a screw compressor, the oil/refrigerant mixture can be directed to the compressor suction line before the suction stop valve. But, the flow must be controlled.

For reciprocating compressors, I always warm the oil with some device before returning it to the crankcase.

We do not want any liquid refrigerant returning to a crankcase on a recip. compressor!

If you have multiple compressors then you have to equalize the oil level between the compressors with some method. This helps to maintain a constant oil level in all of the compressors.

Most of this was developed by following good practices for refrigeration systems and worked very well in all cases.

I hope this helps to explain the operating principles we used.

Best Regards,

US Iceman

[botrous]

Sir Josiah Sodd . . .
you posted the same post twice , and it's a big one , be nice and delete one of them . . . no offence but the forum is already slow . . . i know i have no right to ask you to do that , that's the moderators job . . . i allowed myself to ask you as fellows ...
best regards