Lecture Notes On Equipment Sizing
Lecture Notes On Equipment Sizing
Lecture Notes On Equipment Sizing
Sizing
(second
part)
ARCaparanga
Separation Tower
Design
Distillation, Absorption,
Extraction, and Adsorption
Sizing Problems
No. of stages
Type of column
Height, diameter, cost
Shell thickness and weight
Utility requirements and operating cost
Type of Equipment
liquid
vapor
vapor
liquid
6
5
4
3
2
1
vapor
liquid
liquid
vapor
PLATE COLUMNS
PACKED COLUMNS
(Finite-stage Contactors)
(Continuous Contactors)
PLATE COLUMNS
Sieve trays
Bubble cap
Valve trays
Downcomer
PACKED
COLUMNS
Packing type
Liquid redistributer
Packed Tower
versus Plate Tower
Packed Tower
Diameter < 4 ft
Cannot handle dispersed solids in feed
No inter-stage cooling
Limited operating range
Not suitable for large temperature variations
Cheaper to construct
Design database is poor
Cheaper if corrosive fluids are involved
Pressure drop is smaller (good in vacuum operation)
xf
x
xd
xD yF
L
L
R
V D L yD xF R 1
x
y
1 1 x
Rmin
xD yF
yD xF
R
L
V 1 R
Incr. BP.
[Assume
light key
E
F
heavy key
99%]
Most of D goes
overhead
Most of E goes in
bottoms
x
HK
D x LK
log LK HK
i x Fi
4. Underwood equation:1 q
i i
L
min
1
i
i x Di
i
5. Column diameter
L+D
TYPICAL VELOCITIES
OF VAPOR FLOW
Atmospheric 3 ft/s
Vacuum 6 8 ft/s
F
(L+F)
L+D
F-D
Pressure 1 ft/s
6. Utility requirements
reflux
coolant in
feed
condenser
3
reflux drum
reboiler
reflux pump
distil ate
reboiler pump
bottoms
condensate
L
1.4 typical
mG
y = mx
Solvent + solute
yin
xout
Heat Exchanger
Sizing
Problem
Given: flow rate and inlet and outlet
temperature of the stream to be heated or
cooled
Compute: type and area of heat exchanger,
utility requirements, pressure drop
References: Peters and Timmerhaus, pp. 528573
Perrys handbook
Corrosive fluids
Fluid with greater fouling tendency
Fluid at higher pressure
Less viscous fluid
Utility Selection
Cooling medium cooling better
Heating medium
Low pressure steam: 0 15 psig, 250 ~
275oF
Medium pressure steam: 15 150 psig,
360oF
High-pressure steam < 500 psig, 450oF
Downtherm < 750oF
Fused salt < 1100oF
Direct fire > 450oF
Countercurrent flow
in OD tubes, 8 ft length
< 10,000 sq.ft. area per exchanger
Assume 15-20oF min approach temperature
If necessary optimize area by adjusting outlet
temperature of utility.
Use tables and graphs for U.
Keep U/A < 12,000 Btu / h-ft 2 in reboilers.
For coolers use maximum water outlet temp
permissible
For air-coolers use 20 hp per 1000 sq.ft of area. Air
inlet at 90oF. Temperature approach 40 at outlet
Pumps
Centrifugal pumps
15 ~ 5000 gpm
500 ft maximum head
Axial Pumps
20 ~ 100,000 gpm
40 ft head
Rotary pumps
1500 gpm
50,000 gpm
Reciprocating pumps
10 ~ 10,000 gpm
1,000,000 ft head
NPSH: 1~m of head (Pin - Pvap)
Fans
Compressors
Chemical Reactors
Specify
i)
ii)
iii)
iv)
v)
Volume of reactor
geometry
heat transfer
agitation
material of construction
3. Hetero liquid/gas
- stirred vessels with baffles/agitation
- use gas velocity
0.2 ft/sec if gas is mostly absorbed
0.1 ft/sec if gas is 50% absorbed
0.05 ft/sec if gas is mostly not absorbed
4. Liquid/Solid
- well-stirred CSTR
- slurry reactors
5. Solid/gas
- packed types (solid not consumed)
- fluidized bed
- spouted bed
Materials of
Construction
Carbon steel
most commonly used
Not suitable for dilute acids or alkaline solutions
Brine, salts will cause corrosion
Not suitable at high or cryogenic temperatures
Stainless Steel
Type 302, 304, 316 common
Corrosion resistance
High temperature strength
Copper
Good for alkalis
Ni-clad steels
Good for caustic materials
Glass-lined steels
Good for caustic materials
Plastics
Moderate temperatures < 400oF and pressures
Teflon
Low temperature
Liquid polypropylene
ss
Liquid ethylene
LNG (methane)
LNG (nitrogen)
-53oF
-154oF
-258oF
-320oF
201
9% Ni steel
9% Ni steel
304 ss
Cost Factors
Material
Relativ
e Cost
Comments
Carbon steel
Acids
304 s.s.
High T
applications
Corrosion
Resistant
316 s.s.
10
High T
applications
Corrosion
Resistant
Inconel
13
Chlorides
Hastelloy c
40
Plastics
Low Temp
Applications
Low Structural
Strength
Ceramics
High Temp.
Glass
Lab systems,
Murphy's law
To estimate the time it takes to do a task,
estimate the time you think it should take,
multiply by two, and change the unit of
measure to the next higher unit.
Corollary:
"There are occasions when we must be sloppy
or imprecise in our calculations, and there are
times when we must be precise. The essence
of engineering is to be only as complicated as
you have to be, but you must also be able to get
as complicated as the problem demands".