5 replies to this topic

[hello785230]

I'm working on condensers for my ethylene production plant in my design project. The temperature of the cooling water supply line (assigned by the professor) is not low enough to cool my product, so I am using a refrigerant to cool my water.

I need to size my condensers, but I don't know the operating temperatures of my refrigerant.

I used propylene as my refrigerant. For my condenser, I have one that is cooling my product from 190F to 95F . What temperature should my refrigerant be? Where could I find information about this?

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The heat exchanger minimum approach temperature is 15F when the temperatures are in normal ranges and 5F when refrigerant are used.
My cooling water supply is at 90F and the cooling water return is at a maximum of 120F.

Edited by hello785230, 29 November 2011 - 11:49 AM.

[pavanayi]

hello785230,

Read on a term called 'Minimum Approach Temperature' used along with heat exchangers/heat exchanger networks.

This might be a starting point
http://www.cheresour...ach-for-design/

Edited by pavanayi, 29 November 2011 - 07:03 AM.

[srfish]

What are the operating temperatures of the cooling water?

[hello785230]

The cooling water supply temperature is at 305K and the cooling water return has to be at 322K.

[pavanayi]

hello785230,
Reading your edited entry,

You need product to be cooled to 95°F. Your approach temperature for refrigerant exchanger is 5°F, which means your refrigerant temperature can be up to a maximum temperature of 95-5 = 90°F

Since your refrigerant is pure (propylene), the refrigerant temperature will be constant for that particular level. The refrigerant will evaporate from liquid to vapour phase in the shell side of an exchanger (at 90°F) and thereby cool the product to a temperature of up to 95°F. The vapour generated in the evaporator will then go to the suction of the refrigeration compressor.

The above is considering only the particular product stream that you mentioned. In practise, when there are several exchangers that need refrigerant supply (as is normal in an ethylene production plant), There will be up to five different levels of propylene refrigerant and upto four levels of ethylene refrigerant (assuming pure refrigerants). The levels are determined based on optimising the total power required for the refrigeration. Pinch Analysis can be a tool used for this purpose. Since I am not aware of the scope of your project, my response can be limiting.

Edited by pavanayi, 29 November 2011 - 01:37 PM.

[hello785230]

I didn't know what minimum approach temperature meant at first. Now, I get it.Thank you!

Edited by hello785230, 02 December 2011 - 12:47 PM.