Exercise

Using the problem definition given in Figure 5.3, calculate n-C₄ flow rate in the distillate product, if the debutanizer column has 18 (actual) plates.

Constraint:

The concentration of i- C₅ should be <1 mole% of total C₄’s and lighter compounds in the distillate product.

Given:

Column efficiency =75%, Reflux correction factor =1.5

Mean tower conditions: 210°F and 110 psig

Select appropriate light and heavy keys, and use the K values for the corresponding key compounds using the chart given in Figure 5.4 at the mean tower conditions.

Instructions for Submitting Your Answers:

Once you have calculated your answer, post it in the Exercises Dropbox inside the Lesson 5 folder in Canvas.

If possible, submit a Microsoft Word, or Excel document, showing all the steps in your calculations, indicate the K values you read from the nomograms, and assumptions, if any. You may submit scanned images or clear handwritten pages as a pdf that is less than 2 MB in size.

Figure 5.3. Debutanizing full-range naphtha.

Click here for text description of Figure 5.3.

Application of Fenske Equation

Image shows a debutanizer unit which splits full-range naphtha (gas – 390*) into C4 & lighter (with small amounts of i-C5) and debutanized naphtha (and a small amount of n-C4)

It also notes that the mid-boiling point is 382*F and that the total is 805.1

 

Table from Figure 5.3

Feed	Mole Fraction	Moles/h
C2	0.008	6.4
C3	0.054	43.5
i-C4	0.021	16.9
C4	0.084	67.6
i-C5	0.1	80.5
C5	0.043	-
C6	-	-
C7	-	-

 

Credit: Dr. Semih Eser © Penn State is licensed under CC BY-NC-SA 4.0

Figure 5.4a. K values for light hydrocarbons at low temperatures (DePriester Chart).

Figure 5.4b. K values for light hydrocarbons at high temperatures (DePriester Chart).