Question

FRACTIONAL DISTILLATION COLUMN

Q1: Energy efficiency of the unit operation

One of the latest industry trends is the drive towards more energy efficient processes.

a. Identify TWO areas of energy consumption for the unit operation

b. Propose strategies to optimize the unit operation to achieve better energy efficiency.

Answer 1

Ans. (a) The Two most important areas are reboiler & condensor. Other minor part is pumps & preheater.

(b) Few of the Strategies to achieve better energy efficiency are as follows:-

1. Better & Improved control leads to of process reduces variability in distillate composition which in return reduces overall energy usage.
2. Reducing pressure saves energy. Even reduction of just 10 psi saves $240,000/year in energy cost. One concern is that lowering pressure could cause flooding. However, the molar vapor flowrate reduces with reduction in energy input at constant product composition. This offset the volumetric increase. But this strategy should be first run as a tray-to-tray simulation.
3. Condenser with a lower temperature medium, like using water condenser additionally to existing air condenser.
4. Feed location. Always look into this. A feed in less-than-optimum position in the distillation column negatively affects energy use and, thus, capacity. Feed location might have been appropriate initially but, as time has passed and feed or product specifications have changed, may require repositioning. A small change in feed location can save on large reboiler duties.
5. Operating distillation with adsorption also lead to improved energy efficiency.
6. Always remember above strategies should be first run as simulation to find the best sequence of strategies.