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Using Propane Refrigerant To Cool Itself Using Trim Cooler

propane refrigeration recycle trim cooler

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#1 TX-2

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Posted 17 December 2018 - 01:48 PM

I have simulated a propane refrigeration cycle in HYSYS that provides cooling service to a few heat exchangers. The propane is compressed using a compressor, it is then cooled using an air cooler to 66 C, followed by a trim cooler which cools it to 30 C. 
 
The refrigerant is then routed to throttling valves where pressure drop creates the desired cooling in two exchangers, Cooling Water Chiller and Dehydration Chiller require cooling of -16 C and one Hydrocarbon Chiller which requires -37 C, as such the throttling pressure drops vary. 
 
Now the sticking point, the trim cooler uses cooling water which is available at 20 C, this cooling is achieved using the same said refrigeration cycle. So basically the propane is air cooled, and then sent to trim cooler where it is cooled using chilled water. The chilled water is provided by the Water Cooler which uses propane refrigerant from above cycle. I tried simulating this configuration everything is fine until I connect the propane refrigerant line of the Water Cooler to the main propane refrigeration cycle. 
 
Please see the attached screenshot of my HYSYS simulation for the configuration of my cycle. 
 
When I connect stream 93 (Shell Side Inlet of Water Cooler) to TEE-100 (the Propane Supply Header) and stream 96 (Shell Side Outlet of Water Cooler) MIX-103 (Propane Return Header) the simulation goes in a loop and the flow rates of all streams in the cycle keep on increasing and eventually reach infinity (very high values). If I keep stream 93 and 96 as standalone, the simulation works fine. 
 
I feel that there is a thermodynamic limitation of using the connected configuration as I am using the same stream of propane refrigerant to eventually cool itself which causes progressive increase in loss of energy/entropy. 
 
Can you please advise if you have come across a similar connected system? Is the connected configuration actually a thermodynamic limitation or a simulation limitation? 
 
I will appreciate your inputs on this. Please let me know if you need more information. Thank you very much in advance.

 

Attached Files


Edited by TX-2, 19 December 2018 - 01:11 AM.


#2 Bobby Strain

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Posted 17 December 2018 - 03:37 PM

It's difficult to follow your simulation PFD. Maybe you can fix it up a bit. Maybe show two views. And remove all the unnecessary information.

 

Bobby



#3 shan

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Posted 17 December 2018 - 04:30 PM

You should add a dummy stream attached on TEE-100 because the flow summary of Streams 16, 100, 101 and 93 is not necessarily equal to flow of Stream 20. 



#4 TX-2

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Posted 19 December 2018 - 01:17 AM

Thanks everyone. As Bobby suggested, I have cleaned up my HYSYS simulation to show only the relevant information and added a hand drawing showing the configuration. What I am trying to determine is that is it possible to use the propane refrigerant from the cycle to eventually cool itself in the Trim Cooler, I have highlighted the line in yellow in my hand drawing. I feel that refrigerant/cooling duty to the Water Cooler needs to be supplied from outside this cycle not from the cycle. I will appreciate your help with this. Please let me know if you need additional information. 


Edited by TX-2, 19 December 2018 - 03:52 AM.


#5 Bobby Strain

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Posted 19 December 2018 - 11:02 AM

I believe that you should first remove the  water loop exchangers and replace them with propane heater/cooler until you get a solution. Furthermore, I would move the propane recycle controller to the compressor discharge. You must add a controller or multiple controllers to adjust propane flow to various loads. Once you accomplish this, then you can replace the heater/cooler with exchangers.

 

Bobby



#6 Technical Bard

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Posted 21 December 2018 - 09:20 AM

Look up a flowsheet for a two stage refrigeration compressor with economizer.    You must have an external cooling method (air or water) to reject the heat from the system.



#7 TX-2

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Posted 25 December 2018 - 04:31 PM

Thanks Bobby and Technical Bard. So basically what I understood is that the yellow highlighted configuration is not possible/feasible. I have setup my simulation such that the propane and cooling water flow rates are not fixed rather adjusted based on the cooling requirements.




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