should the compressor discharge pipe have riser?

[gwapa]

It is a good praxis to hook up the discharge compressor pipes to a manifold to the top of it. This manifold pipe normally rise few meter to a level equal or higher that the inlet connection s of the condensers.
During low load period the manifold could fill of ammonia liquid.
Question:
Should it have a riser? What will be the entrainment velocity?
regards
gwapa

[Segei]

It is a good praxis to hook up the discharge compressor pipes to a manifold to the top of it. This manifold pipe normally rise few meter to a level equal or higher that the inlet connection s of the condensers.
During low load period the manifold could fill of ammonia liquid.
Question:
Should it have a riser? What will be the entrainment velocity?
regards
gwapa

Why this manifold should be filled by ammonia liquid?

[Josip]

Why this manifold should be filled by ammonia liquid?

I would like to know also

Best regards, Josip

[RANGER1]

I think you should as some of the plants we work on fill up compressor vertical riser when compressor is off .

Sometimes a stop check is installed at top of riser as well to prevent this as duo steel/steel check valve we use pass some liquid into seperator .

[Josip]

Hi, Ranger1

It is a good praxis to hook up the discharge compressor pipes to a manifold to the top of it. This manifold pipe normally rise few meter to a level equal or higher that the inlet connection s of the condensers.
During low load period the manifold could fill of ammonia liquid.
Question:
Should it have a riser? What will be the entrainment velocity?
regards
gwapa

I think you should as some of the plants we work on fill up compressor vertical riser when compressor is off .

Sometimes a stop check is installed at top of riser as well to prevent this as duo steel/steel check valve we use pass some liquid into seperator .

you are right ... in some cases as you described we can have a problem with some liquid .... but


I think that was not a question

Best regards, Josip

[Paul J]

During the off cycle the discharge pipe can cool and condense liquid in it. Even if you have a riser the condensing liquid causes more vapour to be drawn into the pipe and this vapour condenses and so on and so on. Usually the comp set has a discharge check valve to prevent migration into the oil sep.

[charlie n]

With a recip. compressor, delay opening of the oil return solenoid for 15 minutes after compressor start. This allows the machine and the oil separator to warm up and evaporate any liquid that may have drained down the riser during the off cycle. Connect compressors to the top of the main discharge pipe (manifold. This helps to reduce any liquid drain back into the oil separator.

[simplygold]

Ah, we went through this problem this winter here! Make an upsidown p-trap that comes down into the header....

This way the Nh3 will not condense in the header (or condensor riser) when the pressure gets to low and slug the machine.

Walked into 3 Howdens this December off on low oil temp shutdown. Huh? I looked through the sight glass and saw the vessel FILLED to the brim with liquid, Icy! Close the economizer and try to warm up the vessel to boil the liquid off. Any way, these compressor have discharge checks but the discharge piping is plumbed directly into the header on a flat plane, no riser. Guess what? All discharge check valves will leak some over time!

[McFranklin]

I always like to take the discharge piping higher than the header and connect into the top of the header. The slang term is "candy cane" because it looks like a Christmas candy cane. Imagine the letter "J" upside down. We also do the same for the suction lines. It helps keep the liquids and contaminates in the pipe and not in the compressors. If you can lateral the discharge line into the header that is even better. And by that I mean the branch line enters the main at an angle, so the two flows merge together rather than meet at a 90 degree angle.

[alan wolf]

hello
have recently heard of some screw sets in dubai apparently with no hp check valves. nh3 migrates back into chiller if hp shut off not closed and a nightmare to get started again

aww

[gwapa]

I think that the discharge of the compressor should always be hook up to the top of the pipe (manifold). It reduces the risk of some contaminants coming from other compressors gets in the discharge pipe of the compressor in stand by operation.

From this main pipe or manifold you normally go to the condensers which are located higher level.

The question is how should we go a higher level?

Normally the main manifold is located in the compressor room but the end of the manifold, where it rises to a upper lever, is located outdoor.

The manifolds are designed at the installed capacity or pick load .But when you are running at low capacity the outdoor pipe could work as a condenser. The liquid formed can move downwards to the main manifold. Some liquid will vaporized and other will condense again. This liquid will disappear when the hi load came again.

I think that this effect of condense and vaporize will settled down some oil in the manifold. This oil should be drag to the condensers. Now the “Inverter Siphon” or riser comes, a place to catch the oil and drag to the condensers.

I don’t know if I’m right. Please I appreciate your very kind comments.
Gwapa

[Segei]

I think that the discharge of the compressor should always be hook up to the top of the pipe (manifold). It reduces the risk of some contaminants coming from other compressors gets in the discharge pipe of the compressor in stand by operation.

From this main pipe or manifold you normally go to the condensers which are located higher level.

The question is how should we go a higher level?

Normally the main manifold is located in the compressor room but the end of the manifold, where it rises to a upper lever, is located outdoor.

The manifolds are designed at the installed capacity or pick load .But when you are running at low capacity the outdoor pipe could work as a condenser. The liquid formed can move downwards to the main manifold. Some liquid will vaporized and other will condense again. This liquid will disappear when the hi load came again.

I think that this effect of condense and vaporize will settled down some oil in the manifold. This oil should be drag to the condensers. Now the “Inverter Siphon” or riser comes, a place to catch the oil and drag to the condensers.

I don’t know if I’m right. Please I appreciate your very kind comments.
Gwapa

I don't think that ammonia will condense in discharge line. It is not enough surface for condensation. To condense ammonia you should increase pressure. At very low load pressure will not increase because ammonia will condense inside of condensers. Some gases can condense inside discharge line(butane), but not ammonia.

[charlie n]

I think that both Gwapa and Sergei have good points. There is very little possibility of condensation in discharge pipe at low load but at no load, there will be some condensation. There may also be a little condensation at low load in northern locations in winter. There will also always be oil in this discharge pipe. A p-trap made from 3 elbows welded together is a simple addition to catch the oil & condensate which will be evaporated (condensate) and carried to the condenser (oil) at high load.