Ammonia Transfer System

[gwapa]

Dear Friends
I am working to disign a Refrigeration System for an Ice Cream Plant. The system will have 3 sucction temperature -45°C,-35°C and -10°C and will work in two stage . All the three sucction will be provided with an acumulator and pumps to feed the evaporators with a 4:1 flow.

The question is : Each acumularor must have an ammonia tranfer unit to empty the accumulator in case of very hight level ???? or it is imposible to reach at a very hight level

[US Iceman]

Hi gwapa,

I can't remember the last time I saw a liquid overfeed package with a transfer system.

Tranfer systems are normally used on DX systems or flooded systems when you have a suction accummulator back in the engine room.

In considering the design criteria for each vessel (-40C, -35C, & -10C) you need to provide sufficient reserve volume in theses vessels for such things as: the volume of liquid returning to the vessel during evaporator defrost or volume of liquid needed to re-fill the evaporators after defrost.

If the vessels are selected with sufficient volume for the normal operational requirements, the use of a liquid transfer system would not be necassary.

Another consideration would be the additional capacity that might be required in the future, if extra evaporators could be installed. It is easier to add capacity to a new vessel, rather than to add a new vessel at a later date. This is somewhat based on guesses and not very exact, but it might be worth considering.

One last thought to consider... If the compressors start or can load up when the liquid level is high in the vessels you coul dsee some liquid carry-over form the vessels back to the compressors.

The control system should provide for slow loading to prevent the liquid in the vessel from boiling to violently, when high liquid levels are encountered (such as after the evaporators defrost).

One thing I like to do is use a mechanical float switch as a primary protection to shut the compressor down when high liquid levels occur.

A capacitance probe could provide the normal level controls; low level pump shut off, normal operating liquid level, and high level alarm.

The mechanical float switches are very reliable and not prone to problems with radio frequencies, grounding, or other electrical problems that can be found with capacitance probes.

[Josip]

Hi,

Dear Friends
I am working to disign a Refrigeration System for an Ice Cream Plant. The system will have 3 sucction temperature -45°C,-35°C and -10°C and will work in two stage . All the three sucction will be provided with an acumulator and pumps to feed the evaporators with a 4:1 flow.

The question is : Each acumularor must have an ammonia tranfer unit to empty the accumulator in case of very hight level ???? or it is imposible to reach at a very hight level

In considering the design criteria for each vessel (-40C, -35C, & -10C) you need to provide sufficient reserve volume in theses vessels for such things as: the volume of liquid returning to the vessel during evaporator defrost or volume of liquid needed to re-fill the evaporators after defrost.

If the vessels are selected with sufficient volume for the normal operational requirements, the use of a liquid transfer system would not be necassary.

As US Iceman said, you can use any level control, but you must calculate size of separators (surge drums) according to capacities separately for system -45/-35/-10C. If you have too small vessels, it is the same (useless) which level control you use - it will trip Very big vessels are too expensive, so...

If you give us capacities for each system maybe someone can find (as rule of thumb) vessel size

Best regards, Josip

[US Iceman]

Very big vessels are too expensive, so...

This is worth remembering. If a transfer system is considered, look at the cost of the transfer system plus the installation of it.

If you add this cost to making the accumulator (with refrigerant pumps for an overfeed system) a larger diameter or longer length, you may get more benefits for the same total amount of money.

You also have less stuff to work on if a transfer system is not used.

[Samarjit Sen]

I am involved in exactly a similar project. In my case the evap temp are 2 ie, -45 Deg C and - 35 Deg. C. The load for the -45 deg. C is 48 kw and that for the - 35 Deg. C is 35 kw. What type of compressor would you advice. Should I install Screw Compressor or a Recip.

Sorry for forcing myself into this thread, but as the project was similar I thought I would seek your opinion.

[bruceboldy]

Hi

we use to do the design you mentioned recir vessel with transfer on several jobs i did, multiple levels and pressures.
I do not think we ever actually used the transfer much but it was there if needed

It is simple to do, just put in a connection high on the side of the vessel. if liquid gets to that level it will flow over to a batch transfer tank next to the accumulator

Use a level control on the batch tank, vent it (three way valve or two solonoids )to the place you want the liquid to go and use pressure and a small transfer pump, viking etc to move the liquid A Small relay and a timing relay can run the whole thing.

Not very expensive and if you have undersized vessels and a lot of defrost surge, it works very well.

I will send a dwg if you need it
best to you

Bruceboldy

[Josip]

Hi, Bruceboldy

I would like to see that drawing, please. I'll send you PM with email address.

Best regards, Josip

[Peter_1]

I'm interested too.
Suppose a hypothetical case where they do not run the -45°C and the -35°C ssytem and only the -10°C, is there then no change that the vessels will be overfilled?

What about using a compound system - hope this is the right expression - where the HP of the '-45°C section' and the '-35°C section' goes straight into the receiver of -10°C?
We service such a NH3 system.