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Transcript of Chemical & Mechanical Design
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PRODUCTION OF 100,000 TONNE PER ANNUM OF 2-ETHYLHEXYL ACRYLATEMECHANICAL AND CHEMICAL DESIGN 5
CHAPTER 5
HEAT EXCHANGER
5.1 INTRODUCTION
Heat exchangers are found in most chemical system. Sinnot (1999) reported that heat
exchanger is a device that is used to transfer thermal energy between two or more fluids at
different temperatures and in thermal contact (Sinnot, 1999).
Some of more common applications are found in heating, cooling, evaporation or
condensation, control process liquid and etc. Direct and indirect transfers are two ways of
heat being transferred by heat exchanger. In direct contact type of heat exchanger or
recuperators, the fluid does not mix because it was separated by the walls. It contrasts with
indirect contact of heat exchanger or simply regenerator where heat exchange is done via
energy storage and rejection trough the exchanger surface. In designing heat exchanger,
there are several criteria that to be taking into consideration. The details such as the type of
fluid and phase will be the major factor in choosing the type of heat exchanger.
5.1.1 Types of heat exchangers
The term of exchanger absolutely applies to all types of equipment in which heat
exchange specifically to donate equipment in which heat is exchanged between two
process streams. For example if exchanger in which a process fluid is heated or cooled by
a plant service stream is referred to as heaters and coolers, if the process stream is
vaporize, the exchanger is called vaporizers.
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The types of heat exchanger used in chemical process and allied industry are listed below:
Table 5.1: Heat exchanger type
No. Types Functions
1. Double pipe heat exchanger The simplest type. Use for heating and cooling.
2. Shell and tube heat exchanger Used for all application.
3. Plate exchanger Use for heating and cooling.
4. Plate-fin exchanger Use for heating and cooling.
5. Spiral heat exchanger Use for heating and cooling.
6. Air cooled Cooler and condenser.
7. Direct contact Cooling and quenching.
8. Agitated vessels Use for heating and cooling.
9. Fired heaters Use for heating and cooling.
(Sinnot, 1999)
5.1.2 Shell and Tube exchangers: Construction details
The shell and tube exchanger is the most common type of heat transfer equipment used in
chemical and allied industries. The advantages of this type are:
I. The configuration gives a large surface area in a small volume
II. Good mechanical layout: a good shape for pressure operation
III. Uses well-established fabrication techniques
IV. Can be constructed from a wide range of materials
V. Easily cleaned
VI. Well established design procedures.
In manufacturing industry, the application of heat exchanger is used for the process of
system to derive the final product. The selection of heat exchanger is very important in
order to achieve 3Ps which are people, profit and planet. The safety of people or workers,
safe environment and earn profit with recycle back waste of heat in the process. In order to
select an appropriate heat exchanger, one would firstly consider the design limitations for
each heat exchanger type. Although cost is often the first criterion evaluated.
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The simplest and cheapest heat exchanger is the fixed tube sheet design. The main
advantages are the bundle cannot be removed for cleaning and there is no provision for
differential expansion of shell and tubes. The U-tube requires only one tube sheet and is
cheaper than the floating-head types. This type is widely used but limited in use to relative
cleans fluids as the tube and budles are difficult to clean.
The exchanger with floating head is more versatile than fixed head and U-tube
exchangers. They are suitable for high temperature differentials and easier to clean and
also can be used for fouling liquids.
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Table 5.2: Selection of heat exchanger
Type designation Significant feature Application best suited limitations
Fixed tube sheet Both tube sheets fixed to shell Condenser; liquid-liquid; gas-
gas; liquid-gas, cooling and
heating, horizontal or vertical,
reboiling.
Temperature difference at
extremes of about 200F
Floating head or tubesheet (removable and
nonremovable bundles)
One tube sheet floats inshell or with shell, tube bundle
may or may not be removable
from shell, but back cover can
be removed to expose tube
ends.
High temperature differentials,above about 200F. Extremes;
dirty fluids requiring cleaning of
inside as well as outside of shell,
horizontal or vertical.
Internal gaskets offer dangerof leaking. Corrosiveness of
fluids on shell side floating
parts. Usually confined to
horizontal units.
u-tube, u-bundle Only one tube sheet required.
Tubes bent in U-shape.
Bundle is removable.
High temperature differentials
which might require provision for
expansion in fixed tube units.
Clean service or easily cleaned
conditions
on both tube side and shell side.
Horizontal or vertical
Bends must be carefully
made or mechanical damage
and danger of rupture can
result. Tube side velocities
can cause erosion of inside
of bends. Fluid should be
free of suspended particles.
Kettle Tube bundle removable as U-
type or floating head. Shell
enlarged to allow boiling and
vapor disengaging.
Boiling fluid on shell side, as
refrigerant, or process fluid being
vaporized. Chilling or cooling of
tube side fluid in refrigerant
evaporation on shell side.
For horizontal installation.
Physically large for other
applications.
Source: Rules of Thumbs for chemical engineer, Carl Branan, 2002.
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5.2 BASIC DESIGN PROCEDURES
5.2.1 Design Criteria for process heat exchanger
The criteria that a process heat exchanger must satisfy are easily enough stated
if we confine ourselves to a certain process. The criteria include:
1) The heat exchanger must meet the process requirements. This means
that it must effect the desired change in thermal condition of the process
stream within the allowable pressure drops. At the same time, it must
continue doing this until the next scheduled shut down for maintenance.
2) The heat exchanger must withstand the service conditions of the
environment of the plant which includes the mechanical stresses of
installation, start-up, shutdown, normal operation, emergencies and
maintenance. Besides, the heat exchanger must also resist corrosion by
the environment, processes and streams. This is mainly a matter of
choosing materials of construction, but mechanical design does have
some effect.
3) The heat exchanger must be maintainable, which usually implies
choosing a configuration that permits cleaning and replacement. In order
to do this, the limitations is the positioning the exchanger and providing
clear space around it. Replacement usually involves tubes and other
components that may be especially vulnerable to corrosion, erosion, or
vibration.
4) The cost of the heat exchanger should be consistent with requirements.
Meaning of the cost here implement to the cost of installation. Operation
cost and cost of lost production due to exchanger malfunction or
unavailable should be considered earlier in the design.
5) The limitations of the heat exchanger. Limitations are on length,
diameter, weight and tube specifications due to plant requirements and
process flow.
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Figure 5.1 shows the general outlines of the design procedures.
Step 1
Specification
define duty
Step 2
Collect physical
properties
Step 3
Assume value of
overall coefficient
Uo, ass
Step 4Decide no of shell
and tube passes
calculate Tlm,
correction factor
and Tm
Step 5
Determine heat
transfer area
required
Step 6
Decide tube, tube
size, material
assign fluid to shell
or tube side
Step 7
Calculate no of
tubes
Step 8
Calculate shell
diameter
Step 9
Estimate tube-side
heat transfer
coefficient
Step 10
Decide baffle
spacing and
estimate shell-side
heat transfer
coeffcient
Step 11
Calculate overall
heat transfer
coefficient
including fouling
0 < Uo, cal Uo, ass < 30%
Uo, ass
Set Uo, ass = Uo,
calc
Step 12
Estimate tube and
shell side pressure
drops
Pressure drop within
specification ?
If yes
Step 13
Estimation cost of
heat exchanger
Can design be
optimized to reduce
cost ??
If yes
Accpet design
If No
Figure 5.1: Design procedure of heat exchanger (Sinnot, 1999).
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5.2.2 Fluid allocation factor
Table 5.3: Fluid allocation
Factor Fluid allocation
Corrosion The more corrosive fluid should be allocated to the tube side
Fouling The fluid that has the greatest tendency to foul the heat transfer
surfaces should be place in tube
Fluid temperature If the temperature is high enough to require the use of special
alloy, placing the higher temperature fluid in the tubes
Operating pressure The higher pressure stream should be allocated to the tube
side
Viscosity A higher heat-transfer coefficient will be obtained by allocating
the more viscous material to the shell side.
(Sinnot, 1999)
5.3 CHEMICAL DESIGN OF HEAT EXCHANGER
5.3.1 Step 1: Specification
The product, 2 ethylhexyl acrylate 12430 kg/hr, leaves at top of distillation column at
119.7C and is to be cooled to 30C by exchange with water at 20C.
Chilled
water inlet,
20C
water
outlet, 35C
2-ethylhexyl
acrylate at inlet,
119.7 C
2-ethylhexyl
acrylate at outlet,
30CE-107
S25S24
The heat load was 2.989 x 106kJ/hr or 830.278 kW
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Cooling water balance
Table 5.4: Fouling factor
Fluid Coefficient (W/m2.C) Factor (resistance)
(m2C/W)
Cooling water (towers) 3000 - 60000 0.00030.00017
Organic liquids 5000 0.0002
(Sinnot, 1999)
5.3.2 Step 2: Physical properties
Table 5.5: Properties at tube side (Chilled water)
Properties Inlet Mean Outlet Unit
Temperature 20 27.5 35 C
spec heat 4.044 4.0415 4.039 kJ/kgC
thermal conductivity 0.611 0.6213 0.6315 W/mC
density 1007 1001.45 995.9 kg/m3
viscosity 0.8904 0.7719 0.6514 cP
Flow rate 49320 49320 49320 kg/hr
Table 5.6: Properties at shell side (2-ethylhexylacrylate)
Inlet Mean Outlet Unit
Temperature 119.7 74.85 30 C
spec heat 2.966 2.8335 2.701 kJ/kg C
thermal conductivity 9.903 x 10-2 0.1069 0.1147 W/m C
density 792.7 833.55 871.4 kg/m3
viscosity 0.394 0.8565 1.319 cP
Flow rate 12430 12430 12430 kg/hr
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5.3.3 Step 3: Overall coefficient
According to typical overall coefficient as shown in Table 5.7, the overall coefficient will
be in the range 250 to 750 W/m2C. So, first trial starts with 500 W/m2C.
Table 5.7: Typical overall coefficient
Shell and Tube heat exchangers
Hot fluid Cold fluid U (W/m2C)
Coolers
Organic Water 250 - 750
Light oils Water 350 - 900
Heavy oils Water 60 - 300
Gases Water 20 - 300
Organic Brine 150 - 500
(Sinnot, 1999)
5.3.4 Step 4: Exchanger Type and Dimensions
An even number of tube passes is usually the preferred arrangement, at these positions
the inlet and outlets nozzles at the same end of heat exchanger which simplifies the
pipe work.
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Figure 5.2: Heat exchanger
Start with one shell pass and two tube passes.
Where
Assumptions:
I. No change in specific heat
II. The overall heat transfer coefficient is constant
III. No heat losses
Shell
Tubes
T2
T1
t2
t1
Temperature
Heat transfer
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True temperature difference by applying correction factor to allow for the departure from
counter current flow:
Where Ftis temperature correction factor
Two dimensionless temperature ratios:
R = equal to the shell-side fluid flow rate times the fluid mean specific heat devided by
the tube side fluid flow rate times the tube-side fluid specific heat.
S = measure of the temperature efficiency of the exchanger
Based on figure 12.19 0.98An economic exchanger design cannot normally achieved if the correction factor falls
below about 0.75
5.3.5 Step 5: Heat transfer area
5.3.6 Step 6: Layout and Tube size
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A shell-and-tube type heat exchanger is recommended because it is a versatile
exchanger often used in similar applications. The main factors prompting this decision
are the large surface area provided in a small volume, a good shape for higher
pressure operations, and the ease of cleaning. The final factor is that design and
fabrication methods are well established. This enables the design specification to be as
close to the optimum as is practical.
A floating head-type shell-and-tube heat exchanger is recommended for this
application because of the need to provide capacity for thermal expansion of the tube
bundle. The floating head also enables easy withdrawal of the tube bundle for cleaning
purposes. This factor may be very advantageous, not because the streams are
subjected to fouling, but because of the possibility high boiling residues carryover from
the reactor will be deposited on the walls of the tubes.
Finally, a split-ring heat exchanger is selected. This split-flange design reduces
the large clearances for efficiency and ease of cleaning.
Table 5.8: Design specification
Material Stainless Steel
Length of tube, Lt(m) 4.2672
Outer diameter, Dto, (m) 0.01905
Inner diameter, Dti, (m) 0.01575
Material thermal conductivity,(W/m.K) 16
Pitch, Pt =1.25Dto(m) 0.02381
(Christie, 1993)
5.3.7 Step 7: Number of Tubes
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Equation 5.11
5.3.8 Step 8: Bundle and Shell Diameter
Where
Db= bundle diameter
Dto= tube outside diameter
Table 5.9: Constant for use in equation 5.14
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Triangular pitch, pt= 1.25 Dto
number of passes 1 2 4 6 8
K1 0.319 0.249 0.175 0.0743 0.0365
n1 2.142 2.207 2.285 2.499 2.675(Sinnot, 1999)
Tube pinch = 1.25Dto
Shell bundle clearance, Figure 12.12 is 58 mm
The shell inside diameter, Ds= Db+ 58
Ds= 386 + 58Ds= 444 mm = 0.44m
5.3.9 Step 9: Tube side heat transfer coefficient
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5.3.10 Step 10: Shell side heat transfer coefficient
0.249 2.207 Shell bundle clearance, Figure 12.12 is 58 mm, (Sinnott and Towler 2009).
The shell inside diameter, Ds= Db+ 58
Ds= 386 + 58
Ds= 444 mm = 0.444m
As a first trial, take baffle spacing = Ds/2, this spacing should give good heat transfer
without too high a pressure drop.
Baffle spacing Lb= 222
Number of baffle = Nb +1 = L/Lb
Nb = 18 baffles
Cross flow Asfor the hypothetical row of tubes at the shell equator:
Where
Pt= tube pitch
lb= baffle spacing
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Calculate the shell side equivalent diameter (hydraulic diameter)
Use baffle with a 25% cut which should give a reasonable heat transfer coefficient
without too large pressure drop.
From figure 12.29, By neglecting viscosity correction, 5.3.11 Step 11: Overall Coefficient
Where
Uo= Overall Coefficient, W/m2C
hs = Shell side coefficient, W/m2C
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hi= tube side coefficient, W/m2C
hod = shell fouling factor, W/m2C
hid= tube fouling factor, W/m2C
kw= thermal conductivity of the tube wall material, W/m2C
Percent error:
The value falls within the range, thus it is acceptable
5.3.12 Step 12: Pressure Drop
5.3.12.1Tube-side pressure drop
* +
Where
Np= number of tube-side passes
Ut= tube-side velocity, m/s
L = length of tube.
Jf = tube side friction factor, figure 12.24 = 2.7 x 10-3
Neglect viscosity correction
[ ] 5.3.12.2Shell-side pressure drop
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* +
Jf = shell side friction factor, figure 12.30 = 6 x 10-2
Neglect viscosity correction
[ ]
5.4 MECHANICAL DESIGN FOR HEAT EXCHANGER
In the mechanical design for heat exchanger subject to internal pressure, several steps
need to be taken into consideration, the steps involve are:
1. Design pressure and design temperatures
2. Material of construction
3. Design stress
4. Wall thicknesses
5. Head and closure thickness
6. Channel cover thickness
7. Dead weight load
8. Vessel support
9. Nozzle diameter
10. Baffle heat exchanger
5.4.1 Design pressure and temperature
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For vessel under internal pressure, the design pressure is taken as the pressure at
which 5 to 10% above the normal operating pressure in order to prevent from spurious
operation of relief valve during minor upsets.
The strengths of materials decrease with increasing temperature, thus themaximum allowable stress will depend on the material of construction. Under the ASME
BPV Code, the maximum working temperature at which the maximum allowable stress
is evaluated should be taken as the maximum working temperature. Take a safety
factor as 10%.
For tube side,
Operating temperature : 30 C
Design temperature : 30 x 1.1 = 33 C
For shell side
Operating temperature : 119.5 C
Design temperature : 119.5 x 1.1 = 131.45 C
Table 5.10: Design pressure and temperature for heat exchanger
Operating Design
Shell side Tube side Shell side Tube side
Temperature , C 119.5 35 131.45 38.5
Take design pressure of 3 bars for both shell and tube heat exchanger because of for
safety reason and leakage inspection purpose (BASF).
5.4.2 Material of construction
Selection of suitable material must take into account the suitability of the material for
fabrication as well as compatibility of the material with the process environment. A few
factors that should be considered while choosing the material of construction are:
Corrosion Resistance
Operating conditions
Economic feasibility
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Suitability for fabrication
Process safety
Table 5.11: Material of construction
Material Advantage Disadvantage
Carbon Steel Low cost, easy to fabricate, abundant,most common material. Resists mostalkaline environments well.
Very poor resistance to acids andstronger alkaline streams. Morebrittle than other materials,especially at low temperatures.
Stainless Steel Relatively low cost, still easy tofabricate. Resist a wider variety ofenvironments than carbon steel.
Available is many different types.
No resistance to chlorides andresistance decreases significantlyat higher temperatures.
254 SMO (Avesta) Moderate cost, still easy to fabricate.Resistance is better over a widerrange of concentrations andtemperatures compared to stainlesssteel.
Little resistance to chlorides andresistance at higher temperaturescould be improved.
Titanium Very good resistance to chlorides(widely used in seawaterapplications). Strength allows it to befabricated at smaller thicknesses.
While the material is moderatelyexpensive, fabrication is difficult.Much of cost will be in weldinglabor.
Pd stabilizedTitanium
Superior resistance to chlorides, evenat higher temperatures. Is often usedon sea water application whereTitanium's resistance may not beacceptable.
Very expensive material andfabrication is again difficult andexpensive.
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(Source: http://www.cheresources.com/exprules.shtml)
Vessel and pipes should be made of stainless steel or aluminium. Although 2-ethylhexyl
acrylate does not corrode carbon steel, there is a risk of contamination if corrosion does
occur (http://www2.basf.us).
Table 5.12: Types and characteristics of stainless steel
Type Characteristics
304(18/8) Generally used.
Contains minimum Cr and Ni that give Stable
austenitic structure.
Carbon content is low enough for heat treatment
not to be normally needed with thin sections to
prevent weld decay.
304L low carbon version of type 304(
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sulfuric acid.
From criteria selection above, it can be concluded that Stainless Steel 316 is the
best material to be used in designing heat exchanger. Weld decay is the intergranular
corrosion in chemical plant. This is caused by the precipitation of chromium carbides at
the grain boundaries in a zone adjacent to the weld. Weld decay can be avoided by
using low carbon grades (
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Inner pressure, Pi= 0.3 N/mm2
Allowable stress, S = 137.6891 N/mm2
Inner diameter, Di= 15.75 mm
Joint efficiency, E = 0.85
0.02 mmCorrosion allowance = 3mmMinimum thickness, t = 3.02 mm, 4.22 mm has chosen as tube thickness (Standard
size).
5.4.4.2 Minimum thickness of shell wall
Where
Inner pressure, Pi= 0.3 N/mm2
Allowable stress, S = 112.3163 N/mm2
Nominal shell diameter, Ds= 444 mm
Joint efficiency, E = 0.85
0.7 mmCorrosion allowance = 4mm
Minimum thickness, t = 4.7 mm, minimum thickness of 5 mm is chosen (Sinnot, 1999).
5.4.5 Head and closure thickness
Table 5.13: Choice of closure
Flat plates and formed
head
Cover for manways
Channel cover for heat exchanger
Cheapest type
Limited to low pressure and small- diameter
vessel
Torispherical head Most commonly used
For vessel up to operating pressure of 15 bar
Ellipsoidal head Most economical closure for pressure above 15
bar
Hemispherical head The strongest shape
For high pressure
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Price higher than Torispherical head
From Table 5.13 types of closures, by conducting the process condition and diameter of
vessel, the most suitable head of closure are Torispherical head.
5.4.5.1 Torispherical head
t uat
Rc= crown radius = 444 mm
Inner pressure, Pi= 0.3 N/mm2
Allowable stress, S = 112.3163 N/mm2
Joint efficiency, E = 0.85
5.4.6 Channel cover thickness
Flat plates are used as the closure of heat exchangers. The minimum thickness of the
channel cover required is calculated as follows:
t e
uatBolted cover with a full face gasket, take Cp = 0.4 and D equal to the bolt circle
diameter. De = Ds
t
t= 9.1787mm + 4 mm = 13.1787mm
5.4.7 Dead weight load
5.4.7.1 Weight of vessel
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The calculations weight of a cylindrical vessel with domed ends, and uniform wall
thickness, can be estimated from the following equation:
v vmmv mt
uatWv= total weight of shell
Cv= 1.08 for vessel with few internal fittings
Hv= length of cylindrical section = 4.2672m
g = 9.81m/s2
t = wall thickness, mm = 5 mm
Dm= mean diameter = (Ds+ t x 10-3), m = (444 + 5) x 10-3= 0.449 m
m= density of vessel material, kg/m3
, stainless steel = 8300 kg/m3
v ( )
5.4.7.2 Weight of tubes
t t( )m uatNt= number of tubes = 190
Do= outer diameter = 0.01950 m
Di= inner diameter = 0.01575 m
m= density of material = 8300 kg/m3
t
(
)
5.4.7.3 Weight of insulation
Mineral wool density = 130 kg/m3
Thickness of insulation = 75 mm
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Density of insulation = 130 x 2 = 260 kg/m3
Approximate volume of insulation
te
uat
uat
V = 0.45 m3
W = Vg
W = (130) (9.81) (0.45)
W = 573.8850 N
Total weight = vessel weight + tube weight + insulation weight
Total Weight = + + 573.8850 = 29015.44 N = 27.26 kN
5.4.8 Vessel support
The support vessel will depend on the size, shape and weight of the vessel; the design
temperature and pressure; the vessel location and arrangement and the external and
internal fittings and attachments. Horizontal vessel normally mounted on two saddle
support.
Saddles must be designed to withstand the load impose by the weight of the vessel and
contents. The dimension of typical standard saddle designed are given in table
Table 5.14: Standard steel saddles (adapted from Bhattacharyya, 1976)
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(Sinnot, 1999)
Table 5.15: Saddle support for heat exchanger
Vesseldiameter
m
Weight
kN
Dimension , m mm
V Y C E J G t2 t1 boltdiameter
boltholes
0.45 m 27.26 0.37 0.11 0.42 0.18 0.15 0.07 4.6 3.9 15.43 19.29(Sinnot, 1999)
Figure 5.3: The diagram for saddle support and its dimensions (Sinnot, 1999).
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5.4.9 Nozzle diameter
Designing tube side and shell side nozzles heat exchanger is based on TEMA heat
exchanger standard.
For carbon steel : Dopt= 293G0.52-0.37 Equation 5.33
For stainless steel : Dopt= 260G0.52-0.37 Equation 5.34
Figure 5.4: Typical standard flange design, (BS 4504) (All dimensions mm)
(Sinnot, 1999)
5.4.9.1 Tube side nozzle
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Pipe size at inlet:
Material of construction : Stainless steel
Flow rate : 13.7 kg/s
Density : 1007 kg/m3
Optimum duct diameter : 260G0.52-0. 37
: 78.5 mm
The nearest value for optimum duct diameter is nominal pipe 80mm:
Pipe size at outlet:
Material of construction : Stainless steel
Flow rate : 13.7 kg/s
Density : 995.9 kg/m3
Optimum duct diameter : 260G0.52-0. 37
: 78.84 mm
The nearest value for optimum duct diameter is nominal pipe 80mm
5.4.9.2 Shell side nozzle
Pipe size at inlet:
Material of construction : Stainless steel
Flow rate : 3.453 kg/s
Density : 792.7 kg/m3
Optimum duct diameter : 260G0.52-0. 37
: 41.895 mm
The nearest value for optimum duct diameter is nominal pipe 50 mm
Pipe size at outlet:
Material of construction : Stainless steel
Flow rate : 3.453 kg/s
Density : 871.4 kg/m3
Optimum duct diameter : 260G0.52-0. 37
: 40.45 mm
The nearest value for optimum duct diameter is nominal pipe 50 mm
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5.4.10 Baffle heat exchanger
From chemical design calculation:
Tube outside diameter , Dto : 0.01905m
Pitch, Pt : 0.02375m
Number of tubes : 190
Bundle diameter, Db : 0.386m
Shell inside diameter, Ds : 0.444m
Baffle spacing, Ib : 0.222m
HC= baffle cut height = Dsx Bc, where Bcis the baffle cut as a fraction, Bc= 0.25
Hb, = height from the baffle chord to the top of the tube bundle,
Bb= "bundle cut" = Hb/Db,
b = angle subtended by the baffle chord, rads,
Db= bundle diameter.
Height from the baffle chord to the top of the tube bundle
uat
mBundle cut
uat
m
From Figure 5.5, Ra (ratio of the bundle cross-sectional area in the window zone to thetotal bundle cross-sectional area) = 0.15 and b (angle subtended by the baffle chord)
1.9 rad = 108.86.
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Figure 5.5: Baffle geometry factor (Sinnot, 1999)
Number of tubes in window zone Nw= Ntx Ra Equation 5.37
Nw= 190 x 0.15 = 28.5 = 29 tubes
For equilateral triangular pitch, pt= 0.87pt
Pt= 0.87(0.02375) = 0.02066m
Number of tube rows in window zone, Nwv
wv pt uat
Nwv= 3.97 = 4 rows
Number of tubes in cross flow zone, Nc= Nt2Nw Equation 5.39
Nc= 132 tubes
Ratio number of tubes in window zone to total number, Rw
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w wt
uatRw= 0.3
Window zone area: Aw
w
a wt
uat
w
Aw= 0.015m
2
Number of tube rows in cross flow zone area: Ncv
b Hb
t
Ncv= 10.74 = 11 rows
Baffle cut height, Hc
Hc= Dsx Bc Equation 5.43
Hc= 0.444 x 0.25 = 0.111 m
Assume tube to baffle clearance, Ct= 0.8 mm and baffle to shell clearance, Cs= 1.6mm
Tube to baffle clearance area, Atb
Atb= 0.00385 m
2
Baffle to shell clearance area, Abs
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Abs= 0.00156m2
Baffle cut area, Ab= Ib(DsDb)
Ab= 0.222(0.4440.386) = 0.0129 m2
Figure 5.6: Baffle and tube geometry (Sinnot,1999).
Bundle diameter, Db : 0.386m
Shell inside diameter, Ds : 0.444m
Hc = 0.111 m
b= 108.86
5.4.11 Summary of mechanical design
Table 5.16: Mechanical design sheet for heat exchanger
Heat Exchanger Specification SheetEquipment No
Description Heat ExchangeDesigned by : Abdul JalilSheet No 1/1
OPERATING DATASize (m) Type Shell and tube No of Units 1
Shells per unit 1 HORIZONTAL CONNECTED IN (parallel/series) Parallel
Surface per Unit 1 Surface per shell 1 No of passes 2
PERFORMANCE OF ONE UNIT
SHELL SIDE TUBE SIDE
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Fluid circulating Stream 25stream 26 Chilled water
Total fluid entering IN OUT IN OUT
Vapor (kg/h) n/a n/a n/a n/a
Liquid (kg/h) 12430 12430 49320 49320
Density (kg/m3) 833.55 1001.45
Viscosity liquid (cP) 0.8565 0.7719
Specific Heat (kJ/kg K) 2.447 4.0415
Thermal conductivity (W/mK) 0.1253 0.6213
Temperature (C) 119.7 30 20 35
Pressure (kPa) 121 489
Velocity (m/s) 0.72 0.21
No of passes 1 2
Fouling resistance (W/m2C) 784.48 3335.296
Pressure drop, kPa 5.4 8.4
Heat exchange (kJ/hr) 2.989 x 106
Material Stainless steel 316
Insulation Mineral wool 75mm
Design Pressure (N/mm2) 0.3 0.3
Design Temperature (C) 131.45 38.5O.D (mm) 449 19.05
I.D (mm) 444 14.83
Minimum thickness (mm) 5 4.22
Length (m) 4.2672
Pitch (mm) 23.81
Vessel cover Torispherical head, 5.2393 mm
Channel cover thickness, mm 13.1787
Dead weight of vessel (N) 2869.3284
Weight of tube (N) 23817
Weight of insulation (N) 573.8850
Weight of heat exchanger(kN) 27.26No of baffles 18
Baffle cut 25%
REFERENCES
Branan, C. 2002. Rules of Thumb for Chemical Engineer.USA: Elsevier.
Christie, J. G. 1993. Transport Process and Unit Operations.New York: Prentice Hall.
Don, W. G. and Perry, R. H. 1997. Perrys Chemical Engineers Handbook . US:
McGrawHill
Incropera & Dewitt. 2007. Fundamental of Heat and Mass Transfer. US: McGrawHill
Publication.
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Sinnot, R. K. 1999. Chemical Engineering Design. Great Britain: Butterworth
Heinemann.
Thakore, S. B. and Bhatt, B. I. 2007. Introduction to Process Engineering and Design.
India: McGrawHill Publication.
APPENDIX E
Table E1: Typical overall coefficient
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Table E2: Fouling factors (coefficients), typical values
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Figure E1: Temperature correction factor: one shell pass; two or more even tubepasses
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Table E3: Conductivity of metals
Figure E2: Tube-side heat-transfer factor
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Figure E3: Shell-side heat-transfer factors, segmental baffles