selection of NH3 recierculation system/vessels

[SimonBrown]

Hi

I understand that there are so many considerations that go into selection and proper installation of a liquid recirculation system (Ammonia) . For example, how and where the pump suctions are arranged/fixed, votex breakers, placement of liquid/gas inlets/outlet etc., are all contributing issues to trouble free system operation.

In the selection of a recirculation system, with all those operational issues in mind, which recirculatior system; horizontal vessel with drop leg or vertical vessel with pump connected at bottom, is recommended by your experiences as the most trouble free system, suppose there is no issue with availability of machine room space

simon

[US Iceman]

Hi Simon,

There are several considerations to be sure. The two most important issues are:

Liquid separation
- in part based on sufficient surge volume to
hold liquid during defrost, and
- Sufficient velocity reduction for liquid separation

Sufficient NPSHA
- determined by pump NPSH required at the design
flow conditions and head requirements

Either vessel orientation works well, as long as it is properly designed. I think the same could be said for the pump connections also, although I prefer an individual drop leg for each pump suction.

There is an older thread on liquid overfeed systems that might be worthwhile for your review also.

[Vlada]

hi Simone.

I agree with Icemans pointş and only to add that vessel, being liquid separator, is also oil collector. Design must predict this and includ easy maintains and oil purging.

I prefer horizontal orientation with oil extension at a bottom and pumps drop leg slightly lifted inside vessel. This way oil is not going to the pumps suction.

Horizontal orientation give more accurate design control of liquid separation. With length or diameter you can easily calculate needed liquid velocity.

Very important is to put wet return and suction connections at far opposite ends of vessel.

[US Iceman]

I would also add the following to this topic, which could be separated into four distinct areas of problems:

1) How to design the vessel for liquid separation
2) How to design the vessel so that no problems are created for the refrigerant pumps
3) How to design the refrigerant pump installation for good operation
4) How to select refrigerant pumps to ensure they work as desired

These touch on two different areas; design of the vessel, and application of the components. Both have specific requirements, some of which Vlada pointed out quite well.