Operating-line equation:
yb
Va ya La xa L y x V V
The operating-line must lies above the equilibrium line in order for absorption to take place, i.e., y 0 y •x and y represent the bulk compositions of the liquid and gas, respectively, in contact with each other at any given section through the column.
•For dilute mixtures, containing less than 10% of soluble gas, the effect of changes in total flow is usually ignored and the design is based on the average flow rates（当混合气体
Op era tin gl ine
y a ya xa ab x xa x
b
xb 11
cu rve
b y bb bb y b y
a b
Absorption Driving forces at an arbitrary section x-y:
中溶质浓度较低时，气液流量的变化可以 忽略）.
yb
yb yyb b
yb bb b b bb y b yy b y b yy a a yb aa a a a xxa y a x aa xxb b
b
Eq uil ibr ium
bb
b byb yb b b yb b b y a yb yba y xaa ya a xb a xa xaxb
(部分) (任意的) （ x-y 横截面）
Va y a Overall material-balance equations, Va Va y a La y a (18.4) a x Total material: La Vb Lb Va V ya La a V Component A: La xa Vb yb Lb xb VLya Va y a a (18 .5) aa La xa L V y Operating-line equation xaaa Vaa LyV Va x aa L VaL y L Va ya La xa L La a y aa xa a y x (18.6) y L V x V V V x La La a y a a V L La x a x y V xa xy a La a x xa L VLVb x y xV L V y LLa xa y L y Vb b V x y Vb Vxa L x L Vb V yb b x xy V y yb L Vb x xyb Lb b 9 y y xV L V
Packings Packings Packings Packings Packings Liquid plate Support plate Packing Support Packing Suppo Support Support plate Mist catcher tor Liquid redistribu Liquid redistribu to Liquid shelltor redistri Liquid redistribu tor Liquid Columnar redistribu she Columnar
Clamp plate Columnar shell shell Columnar shell she Columnar Columnar shell Columnar Gas
Packing restrainer 4VS Packings Z Packings Packing Support u Packing Suppo
6
Va y a Va (1)Material balances Va y a La V used •The types of equipment and designyconcepts a x ya La a a in distillation are similar to those used for y a La V a V L La xaa absorption and stripping. Here we choose packed V y La xaaa Va) as yV column(differential-contact plant V a a L the x a y a y a VaLa example. L x y a La V a x L Lower conc. end L L y a V x a xa a L a V La a x y V 稀端 xa xy a La a x xa L VLVb x y •Fig. 8.1-2 Material-balance xV L V y LLa xa y L y diagram for packed column. Vb b V x y Vb Vxa L x L Vb V yb b Higher conc. end x xL V y V xyb y L b xb yb 浓端 b V xV 7 y y L
2
Gas Liquid Mist catcher
Gas Gas Gas Liquid Liquid
Liquid Mist Mist catcher catcher Mist catcher Clamp plate plate Clamp Packing restrainer
Illustrative figure of packed column
Column diameter:
4VS DT u u (0.5 ~ 0.85)u F
VS-gas volume flow rate, m3/s, uF-velocity of liquid D
4 S flooding VS D
T T
1)U U min ;2)
T
d 填料
8(避免壁
u(2)Checking:0..85)u F )u F 适宜 (0.5 ~ 适宜 1)U U min ;2) min DT T
u适宜(1) D should be rounded up; 适宜 •Attention: T
(8 (Avoiding liquid flow 8 避免壁流现象)
[1.PACKINGS AND PACKED TOWER DESIGN]
[Refer to Chapter 4 4.2 Packed Columns in Chinese textbook] Reading materials: pp. 546~557
4
2.PRINCIPLES OF ABSORPTION
Gas u (0.5 ~ 0.V Liquid redistri Liquid F redistribu to 485)u S DT Liquid u DT 1)U U min ;2) 8(避免壁流现 Mist d 填料 Gas~ 0.85)catcher u (0.5 uF 3 Clamp plate Liquid
连续微分接触设备
Va y a Material balances for the portion Va the of Va y a La column above an arbitrary section x-y , ya Va x ya a (18LV a .2) Total material: La V L Va La Va y a aL La y Component A: La xa Vy Lx VaV a V x a (18 .3) x La a Vaaa yaa L yV xa V=molar flow rate of the gas y a y a VaLa L x y a La V a x L phase at x-y section V x La La a y a a V L La x a x y V L= molar flow rate of the liquid xa xy a La phase at x-y section a x xa L VLVb x y xV L V y LLa xa y L y Vb b V x y Vb Vxa L x L Vb V yb b x xy V y yb L Vb x xyb Lb b 8 y y xV L V
Chapter 8
Gas Absorption
1
Definition of Absorption:
•Absorption is a (column-type) process that separates components of a gas mixture by their solubility differences in the added solvent. •In absorption, solute(s) is transferred from the gas phase to the liquid phase. •Desorption/stripping: the reverse of gas absorption: recover valuable solute from the absorbing solution and regenerate the solvents.In stripping, the transfer is from the liquid to the gas phase.
along wall)
5
d packing 填料
Tower height ZT
(1)Calculation from HETP: ZT=HETP*NT. (2)Calculation from the number of transfer units: ZT=HOy*NOy; etc. •The height of the tower, and hence the total volume of packing, depends on the magnitude of the desired concentration changes and on the rate of mass transfer per unit of packed volume.