第二章吸收小结ABSsummary.ppt
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V, Y1 L, X1
Number of transfer units (NTU) & Height of a transfer unit(HTU)
V, Y2 L, X2 H Y, X, dH
V HOG = ΩKY a NOG = ∫
Y1 Y2
dY Y −Y *
V, Y1
L, X1
KYa: overall volumetric mass transfer coefficient based on gas component
Velocity of gas
Height of packed tower(1)
• limiting gas/liquid ratio • operating line and equilibrium line
With the decrease of L…. Y Y1
Y2
L=1.1-2 Lmin
• Diameter of packed tower
– Superficial gas velocity – flooding velocity
How to determine flooding velocity
L2 L1 B A A slope : 1.8 Loading point and flooding point B L=0 ? Continous phase and dispersed phase ? Counter current flow and cocurrent flow Pressure drop Pressure drop of gas
Regeneration process ie. Stripping or desorption
solute
Strong liquid
Part 1: how to conduct an absorption process?(2)
• • • • Distributor and redistributor packings packing support packing cover
Summary: Absorption
Knowledge:
Three main parts: Part 1: how to achieve an absorption process? Part 2 : how to determine the basic parameters of a packed column? Part 3: how to enhance an absorption process?
Part 1: how to conduct an absorption process?(3)
• packings
– dumped packings – stacked packings – constructed packings
• porosity: 60-90%
Part 2 : how to determine the basic parameters of a packed column (Diameter and Height)?
Part 3: how to enhance an absorption process?
• • • • Mechanism of mass transfer between phases How to reduce resistence How to enlarge driving force How to improve apparatus
transfer driving N A = area × × coefficien t force = K G A( p A − p A *)
Mechanism of mass transfer between phases: Two film theory
pA pAi cAi cA
• diffusion in each boundary layer • convection outside the layer • equilibrium at the interface
Part 1: how to conduct an absorption process?(1)
Dilute or lean gas absorption Rich gas (solute gas and inert gas) Weak or fresh liquid
Plate column packed column
interface
How to reduce resistance
J = − DAB dc A dz
1 1 1 = + KG kG Hk
N = kG ( pA − pAi) N = KG ( pA − pA*)
pAi=cAi/H
L
•Diffusivity (diffusion coefficient) •individual mass transfer coefficient •overall mass transfer coefficient •Henry’s Law •resistance
How to enlarge driving force
• solvent • temperature • absorption with chemical reaction(eg fast and irreversible )
Y OL EL1
EL2
EL3 X
How to improve apparatus
Summary: Absorption
• Methodology
– Differential contact vs stage contact – D, k, K
Sh L = C1 Re L
0.67 -0.8
Sc L Ga
0.33
0.33
来自百度文库
• new packings
– porosity and area – flow condition
• membrane absorption
– area (area per volume of apparatus) – flooding: flow condition
Membrane absorption
X2
X1
X
Height of packed tower(2)
V, Y2 L, X2 H
−VdY = NA = (ΩdHa)KY (Y − Y*) V dY dH = − ΩKY a Y − Y * V dY H =∫ Y 2 ΩK a Y − Y * Y
Y1
Y, X, dH
V Y1 dY = ΩKY a ∫Y 2 Y − Y *
Number of transfer units (NTU) & Height of a transfer unit(HTU)
V, Y2 L, X2 H Y, X, dH
V HOG = ΩKY a NOG = ∫
Y1 Y2
dY Y −Y *
V, Y1
L, X1
KYa: overall volumetric mass transfer coefficient based on gas component
Velocity of gas
Height of packed tower(1)
• limiting gas/liquid ratio • operating line and equilibrium line
With the decrease of L…. Y Y1
Y2
L=1.1-2 Lmin
• Diameter of packed tower
– Superficial gas velocity – flooding velocity
How to determine flooding velocity
L2 L1 B A A slope : 1.8 Loading point and flooding point B L=0 ? Continous phase and dispersed phase ? Counter current flow and cocurrent flow Pressure drop Pressure drop of gas
Regeneration process ie. Stripping or desorption
solute
Strong liquid
Part 1: how to conduct an absorption process?(2)
• • • • Distributor and redistributor packings packing support packing cover
Summary: Absorption
Knowledge:
Three main parts: Part 1: how to achieve an absorption process? Part 2 : how to determine the basic parameters of a packed column? Part 3: how to enhance an absorption process?
Part 1: how to conduct an absorption process?(3)
• packings
– dumped packings – stacked packings – constructed packings
• porosity: 60-90%
Part 2 : how to determine the basic parameters of a packed column (Diameter and Height)?
Part 3: how to enhance an absorption process?
• • • • Mechanism of mass transfer between phases How to reduce resistence How to enlarge driving force How to improve apparatus
transfer driving N A = area × × coefficien t force = K G A( p A − p A *)
Mechanism of mass transfer between phases: Two film theory
pA pAi cAi cA
• diffusion in each boundary layer • convection outside the layer • equilibrium at the interface
Part 1: how to conduct an absorption process?(1)
Dilute or lean gas absorption Rich gas (solute gas and inert gas) Weak or fresh liquid
Plate column packed column
interface
How to reduce resistance
J = − DAB dc A dz
1 1 1 = + KG kG Hk
N = kG ( pA − pAi) N = KG ( pA − pA*)
pAi=cAi/H
L
•Diffusivity (diffusion coefficient) •individual mass transfer coefficient •overall mass transfer coefficient •Henry’s Law •resistance
How to enlarge driving force
• solvent • temperature • absorption with chemical reaction(eg fast and irreversible )
Y OL EL1
EL2
EL3 X
How to improve apparatus
Summary: Absorption
• Methodology
– Differential contact vs stage contact – D, k, K
Sh L = C1 Re L
0.67 -0.8
Sc L Ga
0.33
0.33
来自百度文库
• new packings
– porosity and area – flow condition
• membrane absorption
– area (area per volume of apparatus) – flooding: flow condition
Membrane absorption
X2
X1
X
Height of packed tower(2)
V, Y2 L, X2 H
−VdY = NA = (ΩdHa)KY (Y − Y*) V dY dH = − ΩKY a Y − Y * V dY H =∫ Y 2 ΩK a Y − Y * Y
Y1
Y, X, dH
V Y1 dY = ΩKY a ∫Y 2 Y − Y *