need help with sizing LPR separator ammonia

[aphun]

Hi
I need help about the size of my LPR separator (horizontal 2200 mm L x 600 mm dia), liquid (bubbles) goes to the suction line when run 2 compressor at 100% capacity.
some people told me is small and need to change.
Thanks
aphun

[US Iceman]

If this is a new system, you should ask the firm who provided the equipment to give you a new vessel sized correctly. If the contractor did this, then he should provide the new vessel.

Another issue to be aware of is; the vessel could be sized properly now and the system is not being operated correctly also.

Sizing vessels requires more information than just the refrigeration capacity and operating temperatures. If the system starts too fast and the capacity is quickly increased it may not matter how big the vessel is. It can still flood back liquid!

And one last comment. Please do not post the same message in multiple locations. Someone will answer when they can, and if they can. Multiple posts will not get a response any faster. Sometimes, no one may answer and the multiple posts occupy space.

Thanks for your cooperation.

[aphun]

Oh Im sorry, dont know and thanks Mr Iceman for response,
It is not new, we get running in another location and move on like we found, pipes, tanks, commps, etc.
aphun

[US Iceman]

You have to be very careful with this. Vessel sizing and selection charts are usually based on what we call steady-state operation. This means operating at normal suction pressures without sudden or drastic changes.

If the suction pressure is rapidly reduced, the liquid can suddenly boil very quickly and leave the vessel!:eek:

[aphun]

Hi Mr Iceman,
The contractor told me, put an acumulator tank before the compressors, with a heater inside like the oil compressor in order to remove the level of liquid by evaporation; does it increase the suction temp and afect the performance if i want -35ºC in the tunnel? could be work?
The horizontal separator that we have had inside demister wire before the suction oulet, also I read sometimes it doesnt help when the level is low in the tank because some drops of liquid get inside the pad.
Thanks.

aphun

[US Iceman]

Using heaters on vessels collecting liquid ammonia is not a good idea. The latent heat of ammonia is so high that a very, very large heater(s) would be required.

Demister pads are supposed to collect the liquid droplets traveling with the vapor. The droplets collect on the pad and then accumulate into larger droplets. These then fall into the vessel (if it was designed properly).

Vessels with demisters are usually much smaller than vessels without demisters, so don't let this scare you.

Here is a link to a vessel brochure. The units are in inch-pound so you may to convert some of your numbers. Look at page 14 for capacity & evaporating temperatures.

http://www.evapco.com/media/pdf/asme-pressure.pdf

These capacities are based on steady-state, as I said before. When you tunnel starts up it may be warm. This means the evaporating temperature will be very high, which will provide high suction pressures. At this condition the compressor capacity will be much greater than the normal condition. So, you wan to start the compressors at minimum capacity until the suction pressure is reduced to the normal pressure range.

Looking at the chart on page 14 you can see the capacity at -40°F & -30°F. Look for a capacity that is equal to your total compressor capacity. Then look at larger diameters. Vessels are very cheap when compared to any other part. If it is too large, it will not hurt anything. If it is too small, then you see problems like you are having.