2 replies to this topic

[weliketorave]

Hi, I was hoping I could get some help or guidance setting up the mass and energy balance for this column below. I havent had too much practice with columns so just trying to get a good work flow going.

 

Also, Im getting confused by the utility wording for steam and chilled water. If anyone has experience with condensers and thermosyphon reboilers.

 

Steam Utility: Steam at 130 psig supply, reduced by owner to 40 psig

Chilled Water: Chilled water supply at 40F with a 10F temperature rise, 45 psig supply pressure (I interpreted this as the chilled water supply at 40F with the return at 50F)

 

 2-Figure1-1.png   43.07KB   2 downloads

 

Thank you for your help! 

[breizh]

Hi,

Don't duplicate the posts.

Share with us your work (balances), we may be able to comment. Data are missing to perform complete balances (purities of bottom and top or impurities), same for temperatures.

Separation Processes, Second Edition (escholarship.org)

A google search : nmp water separation

 

Good luck

Breizh 

Attached Files

•  Chiller principle.xls   850KB   10 downloads
•  The_Design_and_Layout_of_Vertical_Thermosyphon_Reboilers.pdf   1.15MB   6 downloads
•  Thermosiphon lecture .pdf   671.01KB   5 downloads
•  thermosiphon reboilers.pdf   235.23KB   4 downloads

[Pilesar]

Your interpretation of utilities sounds correct. The reason the steam pressure is reduced is to keep the steam condensing temperature low enough so that the NMP does not excessively degrade in the reboiler. You can calculate the distillate flow from the overall material balance envelope. Because the bottoms flow rate is so small, I assume its composition will calculate to be essentially pure heavy component. If you know the bottoms flowrate and composition, the distillate composition can be determined by material balance of the individual components. You can calculate the condenser duty from the cooling water energy balance. So how will the reflux flow be determined? I think this will be an iterative calculation. The problem does not state the temperature or pressure of the product streams. We know that the bottoms stream will boil at a lower temperature than the steam condensing temperature. The overhead vapor will condense at a temperature somewhere above 50 F. This information will set some boundaries on the possible column pressures when considering the product compositions. Assuming a pressure, you can calculate boilup from the duty and bottoms flow rate using the heat of vaporization of the calculated bottoms composition. Assuming a condensing pressure will similarly allow calculating the amount condensed based on the condenser duty, distillate flow, and heat of vaporization of the overhead composition. The heat of vaporization may change significantly in the possible range of pressures. Because the column traffic has to make sense, you can adjust the pressure assumptions so that a consistent result is obtained.