4 replies to this topic

[garych]

Hi, I am stucked in the propene refrigerant loop simulation.

 

Initially, I was given :

1. Operating condition at stream 1

2. Pressure at stream 3 (Since it has to be at bubble point, hysys can calculate the temperature)

3. Unknown chiller duty 

 

Based on my understanding, the evaporation step in a refrigerant loop should be of constant pressure and temperature, which means that the stream 2 and stream 3 operating condition has to be same. (But it is not so in my simulation.... ) 

Correct me if I am wrong.

 

So, how should i adjust the chiller duty (on what basis) to achieve the above condition?...

Attached Files

•  DSC_0134.JPG   117.48KB   2 downloads

Edited by garych, 01 June 2014 - 02:12 AM.

[PingPong]

Stream 3 is not at bubble point, normally it is at dew point.

 

Pressures at (2) and (3) are not the same, so temperatures will not be the same either.

Edited by PingPong, 01 June 2014 - 04:01 AM.

[Dacs]

I assume that you're using propane as your refrigerant. In this case, it can be treated as a single component stream and there's no dew and bubble points to deal with.

 

That said, I assume that VLV-100 is your letdown valve and stream 2 would be 2 phase.

 

From what I can tell, your heater duty (Heater Q) exceeds the heat required to bring all the liquid in stream 2 to vapor. In short, you have superheat in stream 3.

 

What you can do is to delete Heater Q duty, and modify stream 3 vapor fraction to 1. This will back-calculate the heat required to bring stream 3 at saturated vapor. By the way, looks like you have some pressure loss across your exchanger, so don't expect to have matching conditions between 2 and 3.

 

Hope this helps

[ColinR33]

This is the way I set mine up:

 

Stream 1 - Leaving the condenser - this will be set with a vapour fraction = 0, your condensing temperature and your composition.  This combine with a specified pressure drop in the condenser (typically 1-3 psi) then sets your compressor discharge pressure.

Stream 3 - Leaving your evaporator, this will have a vapour fraction = 1 and will be set at some temperature below the desired process temperature you want to obtain in you evaporator.  For propane systems I typically use a 5°F approach - ie. if you want 0°F process temperature, then your evaporator operates at -5°F).  Pressure drop in the evaporator is minimal, less than 0.5 psi (often <0.2).

 

You do these steps, everything else will fall into place.  Note that the larger the pressure drop across the chiller the larger the difference in your refrigerant inlet and outlet conditions.  They will never match completely.

 

Cheers

[RockDock]

I do it exactly the same way as ColinR33