system design

[davidlleida]

Hi everybody,
I have a project for freezing foods
this are the loads:
660 kW at -45 ºC evaporating temperature
600 kW at -28 ºC evaporating temperature
No load for -10 ºC
I was thinking first about two separate 2 stage systems with ammonia 4:1 (cold rooms).
But I was told that this could be afford with some screws and economizer, only one stage compressors? (If I remember).
I have seen some drawings in different threads (thank you Josip and US Iceman)
But I have problems to adapt them to my needs.
I know that cascade nh3/co2 could be a good option but I prefer think about it later.
My question is if someone could give some explanations or drawings for a system that could achieve this with good technical aspects (optimization, reduced electric consumption...) and without a too large initial cost
Thank you in advance!
There's so long way to come...

[Quality]

I think you need some advice from Andy he he is a moderator of this site and I know he knows his beans I am sure he will point you in the right direction

[davidlleida]

Thank you Quality,
I will wait for any comments that could help me.
Any opinion will be helpful.
I think that the different evaporation pressures are "too close" for a 2 stage "optimal" system.
I mean that high stage compressors have to carry out a great compression ratio.
But this will happen with all the different system options or not?.

[davidlleida]

I think i have understood the design system for this loads (-40-22 ºC) with just one stage screw compressors and economiser.
economiser vessel gives gas flow to the screw port at the same pressure as gas-liquid saturated of -28 in order to feed the room at this temperature.
The same vessel gives liquid flow to -28 rooms and receive it's gas-liquid sustion line, or is better to provide the system with another vessel in order to make this work (separately from economiser).
thank you all for your help (in the case this finally arrives

[TXiceman]

Optimal and low cost do not really go together.

Just as an initial look at this, I would us an intermediate duty compressor around -10 dC (You need to vary this level for the best equipment fit between 019 dC and 0 dC). Parallel operation of the -45dC and the -28dC load into the -10 dC inlet compressor.

I would keep it on all ammonia and notr bother with the CO2 cascade.

Ken

[davidlleida]

Thank you, TXiceman
I will work on that way

[Magoo]

At those refrig Kw verus temps., it will be not cheap, I can assure of that. Two stage cycle is efficient power wise.
magoo

[davidlleida]

Thank you Magoo!
I agree with you, we will wait for the customer's opinion!