Rating of Liquid Vapour Separator

[rize1159]

Can any one know how to check the rating of low side vapour liquid separator from a P&ID in a single stage system?
For how many KW of refrigeration this vessel is going to work while planning for expansion of old system?

[gesi]

rize1159, redefine your question

[RANGER1]

Can any one know how to check the rating of low side vapour liquid separator from a P&ID in a single stage system?
For how many KW of refrigeration this vessel is going to work while planning for expansion of old system?

This could give you some idea, as I have no idea.

https://www.haphillips.com/uploads/files/Vessel_Book_WP-18E-01.pdf

[NH3LVR]

This is a calculation I do not know precisely how to make. I always had a Design Engineer make the calculations.
It is simple to use a catalog with smaller systems, but larger systems require a bit more knowledge.
The factors involved (among others) are the density of the gas, how much liquid is in the return, and vessel design. Basically you are trying to slow down the velocity of the Refrigerant so that any liquid will fall out in the vessel before going to the compressor. The design of the vessel is also important. For instance you can increase the effective size of a vessel by introducing the flow from both ends.
Wish I could be of more help.

[cricri]

Rize 1159,

in summary
you have to know on what side of the system is accepted the volume expansion (LP vessel or HP liquid receiver)
if it's in LP vessel; 3 volumes are calculated:
- minimum level to prime the pumps. min 200mm depend if there is a pot at the bottom and an ''anti-vortex''.
- expansion volume above minimum volume. include coils volume, headers, condensers, all return liquid....
this will set the high level switch position on the vessel at design + a safety margin.
- separation volume above the max level
- in this volume you have to calculate the gaz speed at design capacity (incude flash gaz from expansion device).
This speed must comply with the maximum separation speed acceptable. Depend of shape (vertical/horizontal), number and position of return header and suction header, separation height, evaporation temperature.

This is the old method of calculation, of course today there are sofwares :o.
there are still tables and curves for the old calculation....
beware, new LP vessel can be fitted with ''devices'' to improve liquid and gaz separation.=>smaler vessels.

Brain storming:
of course when all liquid is back in the expansion vessel (HP or LP). there is no possibillity to get the maximum capacity from evaporators....After long standstill you can.....

[rize1159]

This could give you some idea, as I have no idea.

https://www.haphillips.com/uploads/files/Vessel_Book_WP-18E-01.pdf

Thanks Ranger1

[rize1159]

This is a LP side vessel.
We can assume 50%level max. as a rule of thumb.
It has only one suction line for vapours to compressors.
It is horizontal vessel with one return line from evaporator and one liquid inlet from expansion valve.
Problem: We have 03 parallel compressors operating from this vessel and quite OK. We want to add 02 more. This will increase vapour flow rate. But would we be having good separation effeciency?
Diameter of vessel 1200mm and length is 3500mm. It is horizontal. Currently operating at 1800KW/-4C ammonia. Want to increase to 3000KW/-4C.
Some are saying its OK and others are noding in negative. Quite confused

[RANGER1]

This is a LP side vessel.
We can assume 50%level max. as a rule of thumb.
It has only one suction line for vapours to compressors.
It is horizontal vessel with one return line from evaporator and one liquid inlet from expansion valve.
Problem: We have 03 parallel compressors operating from this vessel and quite OK. We want to add 02 more. This will increase vapour flow rate. But would we be having good separation effeciency?
Diameter of vessel 1200mm and length is 3500mm. It is horizontal. Currently operating at 1800KW/-4C ammonia. Want to increase to 3000KW/-4C.
Some are saying its OK and others are noding in negative. Quite confused

Rize1159,
Can you advise pipe sizes on dry suction back to compressors
Also high pressure liquid line.

I am a guesser in this area, but this is what I come up with, also using Danfoss Coolselector for valves.
Best get an engineer, as looks suspect.
If you get any liquid carry over, high levels etc, very big chance of compressor damage & problems.
As a minimum could also install suction slop pot, but if going to that trouble best off install new surge drum for new evaporators with new or upgraded suction & liquid lines.

From H.A.PHILLIPS your vessel is to small
1800kw = 512 tons 1371mm diameter x 3860 long suction line 250nb liquid line makeup 50nb

3000kw= 853 tons 1828mm diameter x 4100mm long 300mm suction line liquid makeup line size 65nb

[cricri]

Rize1159,
after calculation, 1800 kw ;-4°C / (supposed +35°C); level 600 mm in LP vessel D1200 x 3500 mm / NH3.
calculated separation speed is 0,81 m/s.
This value is matching exactly with the maximum speed allowed.

you cannot imagine 3000 kW.

[rize1159]

Sorry guys, there is one mistake. I got confused with other vessel.
Dia of vessel is 2000mm not 1200mm and length is 3000mm.
Liquid make up after expansion valve is 65mm but compressor suction is 200mm.
+35C condensing temperature is right assumption.


after calculation, 1800 kw ;-4°C / (supposed +35°C); level 600 mm in LP vessel D1200 x 3500 mm / NH3.
calculated separation speed is 0,81 m/s.
This value is matching exactly with the maximum speed allowed.

I am little confused. with a minimum height of liquid 600mm, how 1.2m diameter of vessel will be justified for horizontal vessel. Shouldn't horizontal vessel be maximum half filled? In my calculation, it should be 3.7m dia for 1800KW.

[rize1159]

Rize1159,
Can you advise pipe sizes on dry suction back to compressors
Also high pressure liquid line.

I am a guesser in this area, but this is what I come up with, also using Danfoss Coolselector for valves.
Best get an engineer, as looks suspect.
If you get any liquid carry over, high levels etc, very big chance of compressor damage & problems.
As a minimum could also install suction slop pot, but if going to that trouble best off install new surge drum for new evaporators with new or upgraded suction & liquid lines.

From H.A.PHILLIPS your vessel is to small
1800kw = 512 tons 1371mm diameter x 3860 long suction line 250nb liquid line makeup 50nb

3000kw= 853 tons 1828mm diameter x 4100mm long 300mm suction line liquid makeup line size 65nb

Can you explain it. I cant get you selection

[cricri]

Please check the position of your hight level safty switch, this is important for any further calculation.
No, I cannot share a soft with you.
diam 2000x lg 3000 is a strange size for a vessel....

[GrantD]

Hi Bud,

For 1800KW @ -4/+35 NH3 vessel sizes as follows:

1.) Single separation horizontal vessel = your size must be minimum 2,55m long x 1,850mm wide. High level @ 925mm from bottom.

2.) Double separation horizontal vessel = your size must be minimum 3,06mm long x 1,46mm wide. High level @ 730mm from bottom.

I am conservative on allowable velocities but have not had any machines break.

The above calculations assume that there is sufficient surge volume between minimum level and high level from defrosting of coils, etc.

Calculations based on high level @ 1/2 way on vessel for quick check. More detail of plant and share P&ID can add more value to your query.

[rize1159]

[QUOTE]Please check the position of your hight level safty switch, this is important for any further calculation.
it is mid way i.e 1000mm.

No, I cannot share a soft with you. I am asking name of software for purchasing option.

[rize1159]

1.) Single separation horizontal vessel = your size must be minimum 2,55m long x 1,850mm wide. High level @ 925mm from bottom.

2.) Double separation horizontal vessel = your size must be minimum 3,06mm long x 1,46mm wide. High level @ 730mm from bottom.

I am conservative on allowable velocities but have not had any machines break.

I think you are using 0.5m/s velocity for height calculation. For length, can you explain a little more.


The above calculations assume that there is sufficient surge volume between minimum level and high level from defrosting of coils, etc.
I have question on it that how we are going to maintain separation height without consideration surge volume and max liquid level in vessel all the time. Should not calculation of dia of vessel be as below
Separation height + max level allowed in vessel + surge volume height


Calculations based on high level @ 1/2 way on vessel for quick check. More detail of plant and share P&ID can add more value to your query.[/QUOTE]

Attached P&ID

15784

[cricri]

3000 kw ;-4°C / (supposed +35°C);1 return / 1 suction; level approx 1000 mm in LP vessel D2000 x 3000 mm / NH3.
15785

calculation tool Not availlable on the market

[rize1159]

Thanks cricri,
As per calculation system seems ok for 3000KW?

[cricri]

Yes but it's with your inputs.
I entered 4032lt return liquid to match with half level in the vessel.
I entered also 1 return (worst situation), but from your PID it could be 2.

[GrantD]

I think you are using 0.5m/s velocity for height calculation. For length, can you explain a little more.

The minimum length is based on the velocity used x number of passes x staying time of 3 seconds. The rule that we use states if you double the stating time then you can multiply the velocity x 1.7 times. Velocity used @ 3 seconds @ -4 deg. C SST is 0,25m/s

I have question on it that how we are going to maintain separation height without consideration surge volume and max liquid level in vessel all the time. Should not calculation of dia of vessel be as belowSeparation height + max level allowed in vessel + surge volume height

If this is a critical charge plant then you maintain separation height by the charge of the plant. Possibly the vessel is not sized for the full charge required?

If this plant has a receiver and some form of liquid make control to the vessel then you set the "working level" in the vessel but I don't know what your surge volume is - meaning how much liquid must the vessel handle when loads switch off / go on defrost, etc.