Equipment Design and Costs for Separating Homogeneous Mixtures
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Transcript of Equipment Design and Costs for Separating Homogeneous Mixtures
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Equipment Design and Costs for Separating Homogeneous Mixtures
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1. Distillation
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Design Procedures for Columns with Sieve Trays Designation of design bases
Composition and physical properties of feed and product
Special limitations: maximum temperature and pressure drop restrictions, presence of reactive materials or toxic components etc
Selection of design variables: operating pressure, reflux ratio, feed condition
Establishment of physical equilibria data data for binary pairs are combined with a model
(Wilson, NRTL and UNIQUAC) to predict multi-component behavior; UNIFAC model is used for prediction based on functional group
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Design Procedures for Columns with Sieve Trays (cont’d)
Determination of number of equilibrium stages Underwood equation for minimum reflux Minimum number of stages from Fenske equation
Number of equilibrium stages, N as a function of and (Gilliand equation)
minN
avHK/LK
BLK
HK
DHK
LK
min ln
x
x
x
xln
N
2/1
BHK/LKDHK/LKavHK/LK
minR
566.0
minmin
1175.0
1 R
RR
N
NN
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Design Procedures for Columns with Sieve Trays (cont’d)
Selection of column internals
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Design Procedures for Columns with Sieve Trays (cont’d)
Determination of column diameter
5.0
v
vL
2.0
sbnf 20CV
nfn V%9050V
n
"v
n V
mA
dnC AAA 2/1
cA4D
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Design Procedures for Columns with Sieve Trays (cont’d)
Efficiency:
Tray Spacing: 0.46 to 0.61 m (0.3 and 0.91 m are also used)
Column height
245.0
avHK/LKLo 492.0E
oact E
NN
HH1NH sactc
sH
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Design Procedures for Columns with Sieve Trays (cont’d)
Sieve Tray Geometry Hole dia: 0.005-0.025 m Fractional free area: 0.06-0.16 m2 Fractional downcomer area: 0.05-0.3 m2 Pitch/hole dia ratio: 2.5-4.0 Tray spacing: 0.305-0.915 m Weir height: 0.025-0.075 m
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Design Procedures for Columns with Random Packing
Determination of diameter Vapor velocity is 70 to 90 % of flooding velocity Recommended pressure drop
400 to 600 Pa/m for atmospheric and high-pressure separation
4 to 50 Pa/m for vacuum operations 200 to 400 Pa/m for absorption and stripping
column
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Design Procedures for Columns with Random Packing (cont’d)
Heights of columns HTU method
)NTU)(HTU(Z
ceG
"v
AaK
mHTU
1
2
y
y*yy
dyNTU
eL
L
ev
vLv ak
V
ak
VHTUHTUHTU
L
mV
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Design Procedures for Columns with Random Packing (cont’d)
HETP method
1
lnHTUHETP
NHETPZ
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Design Procedures for Columns with Structured Packing
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Design Procedures for Columns with Structured Packing (cont’d)
Diameter Height
HETP: Rule of thumb 10a
29.9HETP
p
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Other Distillation Processes
Batch distillation: Food, pharmaceuticals and biotechnolgy
industries Rayleigh equation
2i
1i
x
x ii
i
xy
dx
F
Wln
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Other Distillation Processes (cont’d)
Azeotropic distillation
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Cost Estimation
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Cost Estimation (cont’d)
Costs of distillation column
25 trays 50 trays
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Cost Estimation (cont’d)
Costs of sieve tray
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Cost Estimation (cont’d)
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Cost Estimation (cont’d)
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Cost Estimation (cont’d)
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Cost Estimation (cont’d)
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2. Absorption and Stripping
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Gas Treatment with Solvent Recovery
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Design Procedures
Column diameter: 70 to 90% of the flooding velocity, Larger of the top or bottom diameter is used
Number of equilibrium stages: Modified Kremser equation
1A
AA1N
i
i1N
i Solute fraction absorbed
1S
SS1N
i
i1N
i Solute fraction stripped
VK
LA
ii
L
VKS i
i
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Design Procedures (cont’d)
Stage efficiency and column height Overall efficiency
Column height: Tray spacing/HTU/HETP
Lo log8.572.19E
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3. Membrane Separation
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Selection of Membranes
Fabricated from natural and synthetic polymers
Membrane modules Plate and Frame ($250-400/m2) Spiral-wound ($25-100/m2) Hollow fiber ($10-20/m2) Tubular ($250-400/m2) Capillary ($25-100/m2) Ceramic ($1000-1600/m2)
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Concentration Profile across Membranes
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Design Parameter
Permeance: porosity, solubility or partition coefficient
Separation factor/selectivity Purity and yield
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Flow Patterns
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4. Adsorption
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Selection of Adsorbent
Activated Carbon Molecular Sieve Zeolites Silica gel Activated Alumina
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Basic Adsorption Cycles
Temperature Swing cycle Cycle time: few hours Capacity: 1 kg per 100 kg
of adsorbent
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Basic Adsorption Cycles (cont’d)
Inert Purge cycle Regeneration is done by purging inert
gas and lowering the partial pressure of the adsorbate
Cycle times are only a few minutes Capacity 1 to 2 kg adsorbate per 100 kg
adsorbent
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Basic Adsorption Cycles (cont’d)
Pressure Swing cycle Cycle time: few minutes Capacity: 1 to 2 kg per
100 kg adsorbent