Session-2
Shell and Tube
Exchangers
Ugrasen Yadav
Group Leader (Process & Heat Transfer)
August 13, 2009
SINGLE PHASE SHELL AND TUBE HEAT
EXCHANGERS
X Overview
z
z
z
Overall aims of thermal design
Brief description of various exchanger types
Optimising tubeside design
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
– Stepwise calculations for viscous liquids.
z
Optimising shellside design
–
–
–
–
–
z
Shell style and baffling
Shellside stream analysis and temperature profile distortion
How to minimise penalty due to temperature profile distortion
Minimisation of shellside pressure drop
The use of multiple shells in series/parallel
Allocation of sides: shellside and tubeside
2
Overall aims of thermal design
X 1. Achieve the specified duty at minimum overall cost
X 2. Overall cost = initial cost + operating cost
X 3. Operating cost = pumping cost + maintenance cost.
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X 4. To minimise initial cost, achieve highest htc within allowable
pressure drops.
X 5. Allowable pressure drops should be assigned judiciously.
3
TEMA Standards
X TEMA (Tubular Exchanger
Manufacturers
Association)
X Devised a standard
nomenclature to describe
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
exchanger with 3 letter
designation for Front head,
Shell and Rear head
4
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
TEMA BEM Type
5
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
TEMA AEM Type
6
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
TEMA AES Type
7
Front Head Types
A Type (Channel and removable cover)
X Bolted to tubesheet at one end & flat cover plate at
the other end.
X Cleaning of insides of tubes is possible without
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
removing the whole channel or associated piping.
X Relatively high cost due to two flanged joints.
X Very widely used used, especially in petroleum
refineries
8
Front Head Types
B Type (Bonnet)
Flanged joint at one end of channel.
Welded head at other end of channel.
Cheaper & lighter than A type.
Not recommended for exchangers requiring
frequent tube side cleaning.
X For mechanical cleaning of tubes, bonnet &
associated piping must be removed.
X Used for cleaner tube side fluids.
X For large diameter bonnets, manway may be
provided to provide access without removing
bonnet and associated piping.
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X
X
X
X
9
Front Head Types
C Type (Channel integral with tube sheet)
X Similar to A type, except that the channel is welded
X
X
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X
X
directly to tubesheet.
Tubesheet extended & bolted to shell.
Shell is removable, channel & tube bundle left in
place.
Suitable for hazardous tube side fluids & heavy,
high pressure tube bundles.
Suitable for exchangers requiring more frequent
cleaning on shell side.
10
Front Head Types
N Type (Channel integral with tube sheet)
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X Similar to C type, except tubesheet is welded to shell.
X Only applicable for fixed tube sheet exchangers.
X Tubes can be internally cleaned without removing the
channel or the associated piping.
X Can be used for hazardous services.
X Shell side cleaning is not possible.
X Requires larger shell diameter.
11
Front Head Types
D Type (Special high pressure closure)
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X Specially designed closure for high pressures on
tube side.
X Tube sheet and channel are integral (drum tube
sheet).
X Very large bolt sizes for channel cover requiring
use of hydraulic bolt tensioners.
X Several designs available (some patented) to
reduce cost. Breechlock type is one such
proprietary design.
12
Rear Head Types
Can be broadly classified as
X Fixed tubesheet type
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X Floating head type
X U-tube type
13
Rear Head Types
Fixed tube sheet
X No access to outside of tube bundle.
X Used with clean, non-corrosive shell side fluids which do not require
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
mechanical cleaning of shell side of tube bundle.
X Relatively cheap.
X Large differential thermal expansion between shell & tubes can lead to
overstressing of tubes or damage to tube-to-tubesheet joints.
X Requires expansion joints or expansion bellows on shell to overcome
problem of differential expansion.
14
Rear Head Types
Floating Head
X Tube bundle is removable.
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X Relatively more expensive.
X Used when mechanical cleaning of shell side of tube bundle is required.
X Requires larger clearance between OTL and shell ID. resulting large fluid
bypass and leading to larger shell ID.
15
Rear Head Types
U-tubes
X Commonly used for high pressure applications.
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X Relatively cheapest (eliminates one tubesheet, channel).
X Removable tube bundle. Can be mechanically cleaned on shell side.
X Cannot be mechanically cleaned in U-bend region. Hence, used with clean
fluids on tube side.
X Can handle large thermal differential expansion between shell and tubes.
16
Rear Head Types
L Type
X Fixed tube sheet arrangement.
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X Corresponds to A type front head.
X Generally used with single or odd
no. of tube pass exchangers
X Cleaning of insides of tubes is
possible without removing the
channel.
17
Rear Head Types
M Type
X Fixed tube sheet arrangement.
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X Corresponds to B type front head.
X Generally used with even no. of tube pass
exchangers
18
Rear Head Types
N Type
X Fixed tube sheet arrangement.
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X Corresponds to N type front head.
X Generally used with single or odd
no. of tube pass exchangers
X Cleaning of insides of tubes is
possible without removing the
channel.
19
Rear Head Types
P Type:
X In this the gap between the shell and the
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
floating tube sheet is sealed by
compressing packing material.
X This is not suitable for hazardous and high
pressure applications.
20
Rear Head Types
S Type ( Floating head with backing device)
X Also called as split ring floating head (SRFH).
X Floating head is bolted to backing device.
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X Backing ring is split (made in two halves).
X Commonly used with A type front end head.
X AES is most common type in refinery services.
21
Rear Head Types
T Type (Pull through floating head)
X Rear end can be pulled through without removing
the floating head.
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X Requires larger shell diameter than S type.
X Relatively costlier than S type.
X Easier to dismantle than S type.
X Commonly used in Kettle type heat exchangers.
X Preferred when there is large pressure differential
between shell & tube sides.
22
Rear Head Types
U-Type (U tube bundle)
X Bundle is easily removable for external
cleaning.
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X No problems of differential thermal expansion.
X Extensively used for clean tube side services
like steam, gases, BFW.
X Used for two-phase mixtures on tube side to
prevent phase separation.
X When used with D type front head, gives very
economical design by eliminating tube sheet
and channel at rear end.
23
Rear Head Types
W Type (Externally sealed floating tubesheet)
X Also called as O-ring or lantern ring type
X Uses lantern ring seals between the floating tube
sheet, shell & channel.
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X Possibility of leaks at packed joints.
X Suitable for low pressure, non-hazardous fluids on
both shell and tube side.
X Used for water, steam, air, lube oil.
X Design temperature should not exceed 191°C;
limitations on design pressure.
24
Shell Types
E Type
X One pass on shell side.
X Mostly common type – industry standard.
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X If two or more tube passes are used, then
temperature cross may be a problem.
X Temperature cross can be avoided by using
multiple shells in series.
25
Shell Types
F Type
X Two passes on shell side.
X Mostly used with two tube side
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
passes to ensure true countercurrent
flow.
X Possibility of fluid leakage through
longitudinal baffle from first pass to
second pass.
X Leakage can be controlled by using
lamiflex type seals or by welding the
longitudinal baffle to the shell.
26
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
The ‘F’ shell
27
Shell Types
G Type
X Also known as split flow shell.
X Low shell side pressure drop can be
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
achieved.
X Has higher temperature efficiency than E
type.
X Mostly used as thermosyphon Reboiler.
X Full support plate provided at centre of
shell inlet / outlet nozzles.
28
Shell Types
H Type
X Also known as double split flow type.
X Similar in principle to G type.
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X Pressure drop is very low (almost one-
eighth of E type).
X Mostly used as thermosyphon Reboiler.
X Full support plate provided at centre of
shell inlet / outlet nozzles and at centre of
the shell.
29
Shell Types
J Type
X Also known as divided flow type.
X One shell inlet and two shell outlet
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
nozzles; variant with two inlet and one
outlet nozzles.
X Since half the fluid is flowing through half
the length of the shell, shell side pressure
drop is very low.
X Commonly used for low pressure
condensers and other services with low
allowable pressure drop
30
Shell Types
K Type
X Also known as Kettle type.
X Exclusively used for vaporizing services.
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X Tube bundle submerged in pool of liquid.
X Liquid level maintained above tube bundle.
X Vapor disengagement space provided
above tube bundle.
X Full tube support plates provided.
31
Shell Types
X Type
X Also known as crossflow type.
X Lowest pressure drop of all shell types.
X Used when the shell side volumetric flow rate
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
is very high and /or allowable pressure drop
is very low.
X Mostly used in vacuum condensers.
X Full tube support plates are provided.
X Proper design to avoid mal-distribution at
shell inlet.
X Multiple inlet & outlet nozzles / distributor
plates provided.
32
TEMA Types Summary
AEU /
BEU
AEW /
BEW
AEP /
BEP
AES /
BES
AET /
BET
CEU
3
6
7
8
9
Removable Bundle
Yes
Yes
Yes
Yes
Replaceable Bundle
Yes
Yes
Yes
Yes
Yes
No
Type of Design
Relative Cost(1 is
lowest, 9 is highest)
Removable Bonnets/
Channel
Individual Tube
Replacement
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Tubeside Cleaning
Shellside Cleaning
Double Tubesheet
Design
Number of Tubeside
Passes
Provision for Thermal
Expansion
NEU
AEM
BEM AEL
NEN
2
1
5
4
Yes
Yes
No
No
No
Yes
Yes
Yes(1)
Yes(2)
No
No
Yes
Yes
Yes
Yes
No
Yes
No
Yes
Yes
Yes
Yes
No
No
Yes
Yes
Chemical
Chemical &
Mechanical
Chemical &
Mechanical
Chemical &
Mechanical
Chemical &
Mechanical
Chemical
Chemical
Chemical &
Mechanical
Chemical &
Mechanical
Chemical &
Mechanical
Chemical &
Mechanical
Chemical &
Mechanical
Chemical &
Mechanical
Chemical &
Mechanical
Chemical &
Mechanical
Chemical
Chemical
Chemical
Available
No
Available
No
No
Available
Available
Available
Available
1-2
Any
Any even
number
Any even
number
Floating
Tubesheet
Floating
Tubesheet
Floating
Head
Floating
Head
Any even
number
Each tube
expands
freely
Any even
number
Each tube
expands
freely
Any
Expansion
Joint when
Applicable
Any
Expansion
Joint when
Applicable
Any even
number
Each tube
expands
freely
33
Basic Correlations for Thermal Design
Q = U * A * MTD
Q = heat transferred, kcal/h
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
U = Overall heat transfer coefficient, kcal/h m2 C
A = Heat transfer area, m2
MTD = Mean temperature difference, deg C
34
Design Data
X Total heat duty
X Stream flow rates and inlet/outlet temperatures
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X Operating pressure
X Allowable pressure drop
X Physical properties
X Fouling resistance
35
Design Data – contd.
X Design pressure and temperature
X Heat exchanger type
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X Materials of construction and corrosion allowance
X Size or space limitations
36
Optimising tubeside design
X Relatively straightforward
X Physical variables: tube diameter, tube length and number of tube
passes
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X Heat transfer Nu = 0.027 (Re)0.8 (Pr)0.33
X Pressure drop: G, Re, density, tube ID, tube length, and no. of tube
passes
X Velocity affects pressure drop more strongly than it affects heat
transfer coefficient.
37
Some fundamental correlations
Nu = 0.027 (Re)0.8 (Pr)0.33
hD/k = 0.027 (DG/µ)0.8 (cµ/k)0.33
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
h = 0.027 (DG/µ)0.8 (cµ/k)0.33 (k/D)
(a) h~ G0.8
(b) h~ µ-0.47
(c) h~ k0.67
(d) h~ c0.33
Question: Why are gas htc’s low?
38
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Stepwise calculations for viscous liquids
Case study: The problem
Shellside
Tubeside
Fluid
BFW/Steam
VGO
Flow rate, kg/h
23,000 (fully vaporised)
130,000
Temp. in/out, C
154/154
300/165
All. pr. drop, kg/cm2
Neg.
1.4
Fouling resistance, h m2 C/kcal
0.0002
0.0006
Viscosity in/out, cp
-
1.6/6.4
Heat duty, MM kcal/h
11.2
39
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Design without stepwise calculations
No. of kettles
2 (in parallel)
Kettle/port ID, mm
1825/1225
Tubes per kettle
790 nos. of SS316, 25 mm OD x 2 mm thk x 9000 mm
long
No. of tube passes
12
Tube pitch, mm
32 square
Baffling
Only full support plates
Heat transfer area, m2
2 x 552 = 1104
40
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Design with stepwise calculations
Single-point
Stepwise
Tubeside HTC, kcal/h m2 C
348
229
Tubeside pr. drop, kg/cm2
1.28
1.35
Overdesign, %
24.0
-9.1
X Re 9813 -> 2851, MTD 138.5 C -> 17.04 C
X First zone 2.325 m, last zone 45 m for the same heat duty
X Pr. drop variation small, tubeside entirely in transition zone.
41
Optimising shellside design
X Far more complex than tubeside
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X More parameters
¾
Shell style
¾
Baffle type, spacing and cut
¾
Tube layout pattern
¾
Tube pitch
42
Shell style
X Already discussed in the Shell Types
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
E shell
F shell
H shell
G shell
J shell
43
Types of baffles
X Single segmental
X Double segmental
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X No-tube-in-window (NTIW)
X Disc and doughnut
X Helical baffles (will be discussed in “Advances in Heat transfer”)
X RODbaffles (will be discussed in “Advances in Heat transfer”)
X EM baffles (will be discussed in “Advances in Heat transfer”)
44
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Types of baffles
45
Single segmental baffles
X Most common type of baffle.
X Also known as segmental baffles.
X Baffle cut defined as % of shell ID (Ds).
X Baffle cut: 15% to 45%.
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X Baffle spacing: 0.2 Ds to Ds.
X For a given shell side pressure drop,
fewer baffles are required.
X Flow-induced vibration problems may
occur because of larger baffle spacing.
46
Double segmental baffles
X Alternating arrangement of single piece
& two piece baffle segments.
X Baffle cut: 15% to 25%.
X Baffle spacing: 0.2 Ds to Ds.
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X Much lower pressure drop can be
achieved compared to segmental type.
X Consequently, baffle spacing can be
reduced.
X Lower potential for flow-induced
vibrations.
47
No-tube-in-window baffles (NTIW)
X Segmental baffles having no tubes in
baffle window region.
X Every tube is supported at every baffle.
X Eliminates flow-induced vibration
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
problems.
X Intermediate tube supports can be
provided.
X Since all tubes are in cross flow, higher
heat transfer coefficients are achieved.
X Higher shell diameters are required.
48
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Baffle design
X Optimize baffle design: spacing and cut
49
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Use of DS baffles
Case study: the problem
Shellside
Tubeside
Fluid
Nitrogen
CW
Flow rate, kg/h
80,000
379,200
Temp. in/out, C
135/40
35/40
Heat duty, MM kcal/h
1.89
Op. pr., kg/cm2 abs.
29.2
5.0
All. pr. drop, kg/cm2
0.15
1.0
Fouling resistance, h m2 C/kcal
0.0002
0.0004
Material of construction
CS
CS
50
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Use of DS baffles
Case study: the results
Single-segm
Double-segm
Shell ID, mm
1100
1100
No. of tubes x NTP
1156 x 4
1156 x 4
Baffle sp. mm x cut, %
600 x 35
390 x 2 rows overlap
Cross/window vel, m/s
4.96/4.41
3.82/3.15
Shellside pr. drop, kg/cm2
0.2
0.13
HTC ss/ts/ov, kcal/h m2 C
423/5799/304.2
300/5799/235
Overdesign, %
57.9
16.1
51
Tube Layout Patterns
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X Tube layout patterns
z
Triangular (30°)
z
Rotated triangular (60°)
z
Square (90°)
z
Rotated Square (45°)
X Square and rot. square layouts used in exchangers requiring mechanical
cleaning on shell side.
X For square & rot. square layouts, min. cleaning lane of 6.35 mm to be
provided as per TEMA Standards; tube layout required to be aligned.
52
Tube Layout Patterns
X Rotated square layout gives higher heat transfer compared to square
layout when shell side flow is laminar.
X Rotated square layout may require larger shell diameter compared to
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
square layout because of alignment of tubes.
X Triangular layout gives higher heat transfer and pressure drop than rot.
triangular layout for a given baffle spacing.
53
Tube Layout Patterns
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Flow direction
Horizontal cut with 30° layout
Flow direction
Horizontal cut with 60° layout
54
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Tube Layout Patterns
Flow
direction
Flow
direction
Vertical cut with 30° layout
Vertical cut with 60° layout
55
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Stream analysis
F Seal rods
Seal strip
A -> tube-to-baffle hole leakage
B -> main crossflow
C -> bundle-to-shell bypass
E -> baffle-to-shell leakage
F -> pass-partition bypass
56
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Temperature profile distortion
57
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Case study: the problem
Shellside
Tubeside
Fluid
Light HC
CW
Flow rate, kg/h
9840
65,600
In/out temp., C
114/40
33/40
Heat duty, MM kcal/h
0.46
All. pr. drop, kg/cm2
0.7
0.7
Fouling res. (met)
0.0002
0.0004
58
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Case study: principal parameters
Shell ID, mm
500
Tubes
188 nos., 20 mm OD x 2 mm thk x 6000 mm
long
No. of tube passes
2
Tube pitch, mm
26 sq.
Baffling
Single seg, 140 mm sp, 21% cut on dia.
Connections
3” shellside, 6” tubeside
Heat transfer area, m2
70
59
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Case study: the results
bs = 140
bs = 160
bs = 175
bs = 190
‘A’ stream
0.189
0.173
0.163
0.154
‘B’ stream
0.463
0.489
0.506
0.521
‘C’ stream
0.109
0.113
0.116
0.118
‘E’ stream
0.24
0.225
0.215
0.207
Delta factor
0.6
0.692
0.735
0.766
s/s htc, kcal/h m2 C
614
570
562
550
OHTC, kcal/h m2 C
380
362
359
354
Pr. drop, kg/cm2
0.034
0.029
0.027
0.026
MTD, C
13.73
15.9
16.87
17.58
Overdesign, %
-21.1
-12.8
-8.26
-5.73
60
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Minimising shellside pressure drop
X
Single-pass shell and single segm. Baffles
X
Single-pass shell and double segm. Baffles
X
Divided-flow shell and single-segm. Baffles
X
Divided-flow shell and double-segm. Baffles
X
No-tubes-in-window segmental baffles
X
Cross-flow shell
61
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Use of Multiple shells
X
Multiple shells in parallel
X
Multiple shells in series
- Handle temperature cross
- Increase velocity and HTC
- Reduce penalty due to temp. profile distortion
X
Multiple shells in series/parallel
62
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
How to determine no. of shells in series for a temp. cross
application
63
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Case study: Multiple shells in series: the problem
Single shell
2S
Shell ID
1000
550
Total HTA, m2
287
2 x 80 = 160
No. of tubes/shell x NTP
620 x 6
172 x 2
Baffle sp, mm x cut, %
318 x 20
290 x 25
S/s vel, m/s x pr. drop, kg/cm2
0.23 x 0.07
0.54 x 0.28
Shell/Ov HTC, kcal/h m2 C
671/392
1167/528
Ft x delta
0.8 x 0.905
0.954 x 0.954
MTD, C
21.1
28
Total empty wt, tons
11.6
3.9 x 2 = 7.8
64
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Case study: Multiple shells in series: the
results
Single shell
2S
Shell ID
1000
550
Total HTA, m2
287
2 x 80 = 160
No. of tubes/shell x NTP
620 x 6
172 x 2
Baffle sp, mm x cut, %
318 x 20
290 x 25
S/s vel, m/s x pr. drop, kg/cm2
0.23 x 0.07
0.54 x 0.28
Shell/Ov HTC, kcal/h m2 C
671/392
1167/528
Ft x delta
0.8 x 0.905
0.954 x 0.954
MTD, C
21.1
28
Total empty wt, tons
11.6
3.9 x 2 = 7.8
65
Allocation of Shellside and Tubeside
X
Specialized facet of heat exchanger design: experience
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
particularly useful
X
Straightforward for many services, e.g., light hydrocarbon
condenser
X
However, if the process stream is corrosive, no longer so.
66
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Allocation of Shellside and Tubeside Parameters
X
Temperature
X
Pressure
X
Pressure drop
X
Viscosity
X
Fouling and cleaning
X
Corrosion
X
Flow rate
X
Temperature range
X
Very often, these parameters place contradictory demands.
X
Case study follows after discussion of individual parameters.
67
Temperature and pressure
X
High temperature stream-> costlier MOC’s:
preferable on tubeside as fewer components on tubeside.
High pressure stream favoured on tubeside:
(a) fewer components on tubeside ,
(b) tubes can withstand much higher internal pressure.
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X
68
Pressure drop
X
Pressure drop higher on tubeside for the same HTC, especially for
viscous liquids. Thus viscous liquids are better handled on the
shellside.
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X
Gas pr. drop often lower on tubeside if a single tube pass can be
used, e.g., FTS exch’s. However, if tube diameter has to be
increased, not worthwhile.
69
Viscosity
Viscous liquids far better handled on shellside: much higher HTC
for same pr. drop.
X
The greater the viscosity, the greater the difference between the
HTC’s.
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X
70
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Fouling and cleaning
X
Dirtier fluid preferably routed tubeside: shellside more susceptible
to fouling, also more difficult to clean.
X
Unfortunately, the dirtier stream is invariably more viscous.
X
There is thus a direct contradictory demand between viscosity
and fouling.
X
Final selection depends on overall economics: which allocation
produces the cheaper overall cost, initial + operating.
X
Very common problem in crude preheat trains
71
Corrosion
If more corrosive stream is on tubeside, costlier MOC for tubes,
channel and channel cover, floating-head cover and tubeside
tubesheet face.
X
On the shellside, shell, shell cover, tubes, floating-head cover and
shellside tubesheet face have to be of costlier metallurgy.
X
Hence, better to route more corrosive fluid through tubeside.
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X
72
Flow rate
Low flow rate streams better handled on tubeside: number of tube
passes can be increased
X
On the shellside, baffle spacing and cut can be reduced only to a
certain extent. Thereafter, multiple shells in series are required:
costly.
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
X
73
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Temperature range
X
Not very apparent to many designers.
X
With 2 tube passes, stream with large temp. range (>100-110 C)
better routed through shellside: avoid differential expansion and
leakage at channel-tubesheet girth flange.
X
More than 2 passes may be tolerable.
X
Single pass will have no such problem
74
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Case study – the problem
Crude oil
HVGO
Flow rate, kg/h
476,000
112,000
Temp. in/out, C
229/243
298/240
Viscosity in/out, cp
0.26/0.24
0.69/1.12
Fouling res. kcal/h m2 C
0.0006
0.0008
Heat duty, MM kcal/h
4.49
Design pr., kg/cm2 g
44.0
22.0
MOC
5Cr1/2Mo
SS410
75
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Case study – side allocation considerations
Preferred allocation of Crude
Reason
Viscosity
Tubeside
HVGO more viscous
Corrosiveness
Shellside
HVGO requires superior MOC
Fouling nature
Shellside
HVGO dirtier
Pressure
Tubeside
Crude design pressure much higher
Flow rate
Shellside
HVGO flow rate much lower
Temp. range
No preference
Temp. range of neither stream is excessive
76
Case study – the solution
No. of shells in series
Design 1: Crude on shellside
Design: Crude on tubeside
2
2
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
Tube OD x thk x length, mm
25 x 2.5 x 6000
Shell ID, mm
1060
1120
No. of tubes per shell x NTP
670 x 8
810 x 2
Baffle spacing, mm x cut, %
450 x 25
330 x 20
Pr. drop crude/HVGO, kg/cm2
1.05/1.43
0.29/0.32
HTC crude/HVGO, kcal/h m2 C
2327/1043
1492/732
Overall HTC, kcal/h m2 C
306
255
Heat transfer area, m2
2 x 304 = 608
2 x 367 = 734
77
Impingement Protection
X
Provided to prevent or minimize erosion of tube bundle
components at entrance and exit areas.
X
An impingement plate or other means of protection is shall be
provided when entrance line values of ρV2 exceed the following:
Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009
–
–
–
X
For non-abrasive, single phase fluids 2232 kg/m-sec2 (1500
lb/ft-sec2).
All other liquids, including a liquid at its boiling point 744 kg/msec2 (500 lb/ft-sec2).
For all other gases and vapors, including nominally saturated
vapors, and for liquid vapor mixtures, impingement protection is
required.
Shell or bundle entrance and exit ρV2 should not exceed 5953
kg/m-sec2 (4000 lb/ft-sec2)
78
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Shell & Tube Exchanger By Ugrasen Yadav, August 13, 2009