Screw discharge cooling

[Volnei]

Hi guys,

Somebody told me about cooling the booster screw discharge with liquid injection directly into the discharge pipe eliminating the intercooler, thus the booster discharge would be the high stage suction and we can save money eliminating the intercooler besides the pressure discharge to be smaller than those with intercooler.

Does anybody has any experience about this?

Best regards,

Volnei

[Andy]

Hi, Volnei, this is a common design on two stage NH3 systems at present. I first seen this concept on Grasso screws, with the low stage compressor discharging directly into the high stage suction, both compressors are fitted on the same base plate. There is another connection at the interstage this is a suction or economiser feed, usually from an open flash economiser, this is what makes the cycle efficient with the subcooling of the liquid using the intermediate pressure.
Regards. Andy.

[lldelfin67]

Hi,
If these is one is one booster to high stage can be I also seen these system use on the CO2 recovery system from a brewery but for multiple booster compressor and multiple high stage compressor it is not applicable the volume of gas is big and can't be taken by just one high stage compressor

[HallsEngineer]

I have seen it used on a freeze drier to good effect and the pipe between the single machines was around 3 feet long.

[TXiceman]

On this type system, the high stage compressor generally does not have any injection oil fed to it. It gets enough oil from the booster. If they are short coupled and no side load at the intercooler level, they are generally started at the same time.

Ken

[HallsEngineer]

correct, we had a solenoid on the oil feed to high stage to shut it off when the booster starts. but we now try to reccomend the danfoss akv to cool delivery on liquid injection. using the EKC 319A.

[Magoo]

all good in theory, but similar to a hand grenade with a loose pin. Good luck. Magoo

[Josip]

Hi, Magoo

all good in theory, but similar to a hand grenade with a loose pin. Good luck. Magoo

agree with you...but original post is from 2002....

I made a similar one cold store installation in the year 1984 (4 screws buster (-35*C/-45*C) + 4 screws high stage (-10*C/35*C).....good Sabroe design..., but with a lot of small adjustments to start up the plant.....

Best regards, Josip

[hendry]

Hi, Magoo



agree with you...but original post is from 2002....

I made a similar one cold store installation in the year 1984 (4 screws buster (-35*C/-45*C) + 4 screws high stage (-10*C/35*C).....good Sabroe design..., but with a lot of small adjustments to start up the plant.....

Best regards, Josip

yeah ... talking about date/time ...
some of our fellow "speakers" do not have their time/date displayed 'correctly' ... i wonder why?

i've seen such installation in compound compressors [2-stage compressor] but then some still insist shell & tube intercooler prior to connection to high side suction.

in my opinion, intermediate HE still preferable to eliminate nuisance in ctrls.

[Josip]

Hi, Hendry

yeah ... talking about date/time ...
some of our fellow "speakers" do not have their time/date displayed 'correctly' ... i wonder why?

???

i've seen such installation in compound compressors [2-stage compressor] but then some still insist shell & tube intercooler prior to connection to high side suction.

in my opinion, intermediate HE still preferable to eliminate nuisance in ctrls.

agree with you....


Best regards, Josip

[Core4 Guy]

Directly injecting liquid into the discharge Vs. an intercooler in a two stage system. The question was about energy savings. I will comment on one thing. A BTU is a BTU. If it takes the same amount of refrigerant to cool the discharge gas from the low side machine to the high side machine the only penality of a systems intercooler would be pressure drop. Does this make sense? There have been practicianers of both designs for 30+ years.

Hussmann refrigeration used to make the TD System (designed by Cap Blake) 40 years ago that used liquid injection with R-502. I was a neat peice of two stage design.

Ammonia system designers used intercoolers so they could control the exchange with more safety.

I believe that a single stage is more efficient with less parasitic losses if the comression ratio allows...

[hendry]

Directly injecting liquid into the discharge Vs. an intercooler in a two stage system. The question was about energy savings. I will comment on one thing. A BTU is a BTU. If it takes the same amount of refrigerant to cool the discharge gas from the low side machine to the high side machine the only penality of a systems intercooler would be pressure drop. Does this make sense? There have been practicianers of both designs for 30+ years.

Hussmann refrigeration used to make the TD System (designed by Cap Blake) 40 years ago that used liquid injection with R-502. I was a neat peice of two stage design.

Ammonia system designers used intercoolers so they could control the exchange with more safety.

I believe that a single stage is more efficient with less parasitic losses if the comression ratio allows...

hola!
sometimes it is a bit hard to draw a line between which is correct/better than the other. i feel it depends on whom you kick start your experiences with.
anyway, the most important is still the design must works.

[Magoo]

Well done all the picky picky ones, I joined 07 and did note the original posting date. Now you are all full of comment.
Well there ya go.
magooooo

[HallsEngineer]

as soon as you take the compressor compression ratio up you are doing more work - higher kW used simple. There is a limit where single stage just stops being a good decision but i have commissioned too many plant with a COP less than one due to the fact "the compressor can do it." Two compressors doing the duty is often more efficient than a single stage just look at COP achievable with two stage two tmp cooling plants i have on working at a COP of 7. Its much better for loads to two stage plants but customers are shortsighted with plant install costs and then question the electric bill at the end of the month. Two stages is a good simple idea which works very efficiently with oil cooling instead of liquid injection for compressor cooling. It is one of my biggest problems when customers "prefer" single stage because they don't understand a little extra money now will save a fortune over time.

Sorry rant over.