Question

SELECT ALL THAT OCCURS WHEN THE REFLUX RATE IS INCREASED.

A) THE OVERHEADS DISTILLATE RATE IS INCREASED;

B) THE OVERHEADS DISTILLATE PURITY IS INCREASED;

C) THE COLUMN TEMPERATURE IS INCREASED;

D) THE NUMBER OF THEORETICAL PLATES INCREASES IN A PACKED COLUMN;

Answer 1

Ans

We will analyze all the given options.

Option A

On increasing the Reflux rate,

It means the distillate product is not obtained, it is being more recycled than withdrawing as a final product. Thus it decreases the overhead distillate rate.

Option A is incorrect.

Option B

On increasing the Reflux rate,

It increases the contact between the vapor and the liquid, due to it more volatile component is more transferred and the efficiency of separation enhances. Thus, the purity of the overhead distillate increases.

Option B is correct.

Option C

On increasing the Reflux rate,

Reflux stream has a lower temperature than the vapor temperature in which both contacts inside the column. The column temperature is decreased due to heat transfer takes place from vapor to reflux liquid. To maintain the temperature heat duty of the boiler is increased at high reflux conditions.

Option C is incorrect.

Option D

On increasing the Reflux rate,

From the ROL equation

y = Rx/(R+1) + xd / (R+1)

It will increase the term R/(R+1) i.e. slope of the rectifying line. It will close to the 45° line in the McCabe-Thiele diagram and will have the less number of stages than before.

Option D is incorrect.