NH3 system for minus 40 deg c brine temperature

[meg]

Hello everybody,

This is my first mail on such a informative web site.

Has anybody designed ammonia system for minus 40 deg C brine temperature? Please clarify following doubts:-

1) apart from oil seperator what are the necessary arrangements to be provided for avoiding oil entering in to the evaporator. kindly mentioned the recovery system too.

waiting for positive reply.

[Peter_1]

I haven't designed such a systems but for a brine of -40°C (= -40°F) or evaporating at -46°C (-50.8°F) is a low pressure below atmospheric pressure when using NH3

[Josip]

Hi, Meg

Welcome to RE

Hello everybody,

This is my first mail on such a informative web site.

Has anybody designed ammonia system for minus 40 deg C brine temperature? Please clarify following doubts:-

1) apart from oil seperator what are the necessary arrangements to be provided for avoiding oil entering in to the evaporator. kindly mentioned the recovery system too.

waiting for positive reply.

Tell us, please, what is your system for?

Best regards, Josip

[meg]

Dear Mr.Peter,

Your suggestion will not solve the problem.

[Peter_1]

Was that a suggestion I've made?
I haven't read you had a problem, only a doubt.

You may install the best oil separtor, there will allways oil passing through it.
So necessary arrangements will have to be a system removing the oil out of teh NH3/oil solution.

You haven't even mentioned what kind and size of evaporator you will use.

Sorry if I didn't give you the answer you expected.

[US Iceman]

what are the necessary arrangements to be provided for avoiding oil entering in to the evaporator

Absolutely none. Oil will enter the evaporator no matter what you do. The only way to prevent this is to use an dry compressor (no oil in circulation).

The oil recovery system is a simple small vessel which allows oil to drain into it by gravity from the bottom of the chiller. They are called "oil pots".

I'm assuming the chiller is a flooded shell & tube. You did not mention sufficient details for a lengthy answer. Sorry.

[kasperDK]

hi

i think the use of gammonia for this, only will give you problems, try a caskad system NH3/CO2 R717/R744 or R717/R1150 ammonia/ethylen

[Peter_1]

Kasper, Meg doesn't want suggestions,

[refsystem]

we can use ammonia for this type of application. Of course the pressures are lower than ambient and need to provide only welded joints. The oil throw from compressor alongwith gas can be minimised with larger oil separtor/coaliscer element. Also you can provide some special automatic oil draining system to collect the oil from receiver and charge back to the compressor after heating. I hope this would help you. Any oil reached the chiller can be drained only after the siwtching off the compressor as the chiller is under negative pressure during operation.

[Peter_1]

Any oil reached the chiller can be drained only after the siwtching off the compressor as the chiller is under negative pressure during operation.

Unless you use a pump, just a suggestion.

[kasperDK]

dear Mr Peter_1

Sorry my fault :-)

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For a olie return system from the evap. , i´l use enjektor or pump drum using hotgas

what Olietype will/or are you using?

i do not think i will want the olie form the evap returning to the compressor/s it may be damage
------------

-but you still have th the problem with Air that will enter the system

[luzhang]

Good oil separator design will help reduce the oil amount enter in the evaporator.the oil recovery system is necessary.It is better to design an auto air purger to remove the non-condensing foul gas.

[refteach]

You may want to look at using a PAO oil, it is a full synthetic which will give you around a -55 C pour point. Instead of a mineral based oil.

This way if any oil makes it through the separator, it will still remain fluid at the temperatures you are running.

[tinglehand]

Hello.

I believe someone answer this question in this same thread some time ago. It is almost impossible to prevent the oil going into the evaporator. I worked some time with system at -30 and -42 deg C (screw compressors). All this will depend of your compressors and the oil separator that they have. Also how good is the oil separation after the condenser. As Iceman said use oil pots in you evaporator, maybe you will not need defrost but it will be really difficult to take the oil out of your evaporator at such temperature of the brine (hot gas could help you a lot) and of course there is the issue of the pressure.

I will not recommend oil recovery in the evaporator or condensers due to the cost and the quality of the oil there that will depend of the discharge compressor temperature and ammonia quality (water presence).

[tinglehand]

Good point refteach

[TXiceman]

Absolutely none. Oil will enter the evaporator no matter what you do. The only way to prevent this is to use an dry compressor (no oil in circulation).

The oil recovery system is a simple small vessel which allows oil to drain into it by gravity from the bottom of the chiller. They are called "oil pots".

I'm assuming the chiller is a flooded shell & tube. You did not mention sufficient details for a lengthy answer. Sorry.

Right on US Iceman.

I sure hope it is flooded as DX just will not work at these levels on NH3. As for the comment made to not recover the oil in the evaporator or condenser, I do not know the reasoning behind this. We as a standard build flooded ammonia chillers to the temperature levels discussed her. They all get a settling leg on the chiller and a heated oil pot connected to the leg. Oil has a SG of 0.9 to slightylu over 1 in some cases and ammonia is closer to 0.6. Even at lower temperatures, in a still area, th eoil drops to the bottom and migrates to the oil pot. Avery few days, turn off the drain to the pot, leave the vent line open and turn on the electric heater. The ammonia boils off, the oil remains behind and is warm enough to pressurize or pump back to the compressor.

Also, need a very tight piping systems, seal-cap valves and good purger to remove the inerts. I'd suggest the Hansen Auto Purger Plus.


US, were you at the RETA Convention in Arlington, Texas last week?

Ken

[US Iceman]

Hi Ken,

US, were you at the RETA Convention in Arlington, Texas last week?

No, I had to miss it. For the last several months I have been fighting a loosing battle with alligators in my effort to drain the swamps. (If you know what I mean )

I really did want to go, but no such luck. I'm going to try for the IIAR convention early next year. As we get a little closer to this date we should touch base and see if we can meet up.

[Ponca Dave]

If your chilling a brine I assume it is not mixed with the NH3 so your suction pressure is at least 11.7"
the oil comes from the compressor and should be at the bottom of the intercooler and if your vessel is designed properly the oil shouldn't get to the pumps.
Unless I am missing something you have a severe design flaw.