21 1. distillation

인하대 , 화공과

Chap. 21 Distillation

(1) Continuous steady-state distillation process

(flash distillation)

(2) Design and performance of sieve-tray distillation column

(rectification)

(3) Batch distillation


- Flash distillation


Chap. 21 Distillation공급원료는 pump 로부터 heater 를 지나고 valve 에 의해서 감압된다 . 증기와 액체의 혼합물은 vapor separator 로 들어가서 충분한 시간 동안 머문 후 증기와 액체로 나누어 진다 .

Basis: 1 mole of a binary mixture

mole fraction of a low boiler (more volatile)

f = mole fraction of the feed as vapor

1-f = mole fraction of the feed as liquid

mole fraction of vapor of a low boiler

mole fraction of liquid of a low boiler인하대 , 화공과


Material balance



EL 과 OL 의 교점

Vapor separator 에서 material balance 를 만족하면서 평형에 도달하는 point

the chart



System : benzene (b.p: 80.1 oC), toluene (b.p: 110.6 oC)



① f 의 결정

②

③ 의 교점

④ ②, ③ 에서 의 reading from EL

⑤ 로부터 temperature reading

from boiling-point diagram



System : Benzene 80.1 oC, toluene 110.6 oC, (0.5, 0.5)

At

f 0 0.2 0.4 0.6 0.8 1.0slope ∞ -4.00 -1.50 -0.67 -0.25 0




Temperature

y

x

T

0 1

Chap. 21 DistillationContinuous distillation with reflux (rectification)



Continuous distillation with reflux

Equilibrium stage

평형이라는 것은 물질전달에 대한 평형 뿐만 아니라

열적평형 이 되어야 함을 알 수 있다 .



- A 의 일부는 액체로부터 증발 (b.p 가 낮은 A 성분이 먼저

더 많이 증발 ) 되어 액체의 농도가 에서 으로 감소

- B 의 일부는 증기로부터 응축하여 증기의 농도가 에서

으로 증가



L phase V phase

뜨거운 증기와 만남 차가운 액체와 만남Boiling point 낮은 A 가

증발 (L→V)

Boiling point 높은 B 가 응축 (V→L)

온도 증가 온도 감소

증가 감소



Since the liquid streams are at their bubble points and

gas streams at their dew points, the heat necessary to

vaporize component A must be supplied by the heat in

the condensation of component B.



Material balance

Total MB

F=D+B

Component MB

=



n: rectifying section

Condenser : , plate n:

m: stripping section

Reboiler : plate m:



OL (1) Rectifying section

(2) Stripping section



Constant molal overflow

“high boiler 1mole 의 증기가 응축하면서 low boiler 1mole 의

액체를 기화시킬 수 있기 때문에 vapor 와 liquid 의 molal

flow rate 는 거의 일정” ← n, m 무시 → (straight OL), no need

for EB



Reflux ratio

to be controlled

at a point at the upper end of OL

The OL for the rectifying section intersects the di-

agonal at point

( , ).


Chap. 21 DistillationCondenserAssumptions - The condenser removes latent heat only. The condensate is liquid at its bubble point

① single total condenser



② partial and final condenser

Partial C : for reflux partial condenser; additional

theoretical plate

Final C : for overhead prod-uct 인하대 , 화공과


Bottom plate and reboiler



Stripping section 마지막에서

Diagonal point (



xB , y r :𝑒𝑞𝑢𝑖𝑙𝑖𝑏𝑟𝑖𝑢𝑚𝑝𝑜𝑖𝑛𝑡



Feed plate


Chap. 21 Distillationq: the moles of liquid flow in the stripping section

from the introduction of one mole of feed

Total flow rate of liquid in the SS

Total flow rate of vapor in the RS

Constant molal overflow

To locate the points where the two OLs intersect




at x = xF , y =− q xF + xF

1− q= xF


Construction of OL

① locating the feed line

② calculating the intercept of the rectifying line and

plotting the line with the intercept (

③ draw the stripping line through the point ( and the

intersection of the rectifying line with the feed line



Feed line slope:

RS: intercept

(

SS: (

인하대 , 화공과x

y

x F0 1

1

( xD , xD )

x D

RD

1+ RD

( xB , xB )superheated

cold


Feed plate location; The feed plate is always represented by

the triangle that has one corner on the rectifying line and one

on the stripping line.



in a diagonal line

If total reflux, D→0, →∞


Minimum number of plates


a f b: total reflux

ae, eb: actual operation

at minimum reflux ad, db



Minimum Reflux,


Chap. 21 DistillationOptimum reflux ratio



Reflux ratio ↑ plate no. ↓, fixed cost ↓

manufacturing cost for reboiler and condenser ↑

Optimum reflux ratio

- 1.1~1.5 times the minimum reflux ratio


21 1. distillation

Documents

21 distillationcontinuous distillation

reflux

21 distillation

21 distillation

rectification

heat

chap

reboiler