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Subcooling And Vapor Refrigerant Condensation

compressor refrigeration ethylene plant

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#1 panagiotis

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Posted 19 November 2023 - 06:20 PM

Hi all, I am asking again a similar question.

When you have a subcooler in a refrigeration cycle (for example propane refrigeration in ethylene plants) this subcooling has effect on COP or on compresdor power? Subcooling increases COP or reduces the power of compressor. Or the compressor power remains the same?

In some ethylene plants, propane vapor refrigerant is used to heat up the bottom stream of a distillation column (for example ethylene fractiomator). The propane vapor is condensed in the refrigeration section. This affects the COP of the cycle or the power of the compressor?

#2 Bobby Strain

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Posted 19 November 2023 - 09:06 PM

My guess is that you have a process simulator. You should check it out. If not, use a Mollier diagram.

 

Bobby



#3 shvet1

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Posted 19 November 2023 - 10:55 PM

What does COP mean?

Everything has effect on compressore power as compressor is the only source of energy.



#4 panagiotis

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Posted 20 November 2023 - 03:45 PM

If you add a subcooler in a refrigeration loop what is the effect on the compressor power??

#5 shvet1

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Posted 20 November 2023 - 11:04 PM

In theory compressor consumption decreases. This may become true or opposite depending on local conditions. Comprehensive modelling is required.


Edited by shvet1, 21 November 2023 - 12:59 AM.


#6 breizh

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Posted 21 November 2023 - 01:57 AM

Hi,

Google search:

"An increase in sub-cooling effectiveness reduces the compressors work input and increases the system refrigeration capacity. Also, an increase in the degree of sub-cooling, reduces the pressure ratio, and increases both the refrigerant mass flow rate and coefficient of performance (COP) of the system"

 

https://www.scienced...140700714003016

 

Breizh 



#7 Bobby Strain

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Posted 21 November 2023 - 07:00 PM

You can find a spreadsheet by Ankur on this forum. You can change the duty on the subcooler and see the effect on compressor power.

 

Bobby



#8 panagiotis

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Posted 22 November 2023 - 02:25 AM

Thanks Bobby!!

#9 panagiotis

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Posted 22 November 2023 - 07:22 PM

Bobby, I looked at the excel prepared by Ankur. But, I think the inlet temp is missing from the formula of polytropic power calculation.

#10 Bobby Strain

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Posted 22 November 2023 - 09:19 PM

I am not surprised. Do you have HYSYS or other simulator?

 

Bobby



#11 breizh

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Posted 22 November 2023 - 09:57 PM

Hi,

Nothing wrong with the calculation, just pay attention to the formula and units!  The mass flowrate W was replaced by the volumetric flowrate Q with the appropriate change to convert W to Q , no more T and appearance of P (inlet condition).

reference Perry chapter 10-39 if needed.

 

 

Breizh 



#12 panagiotis

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Posted 23 November 2023 - 03:43 AM

Hi Breizh,

I will have a better look at it.




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