chemical & mechanical design

8/13/2019 Chemical & Mechanical Design

1/39

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.


2/39


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.


3/39


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.


4/39

PRODUCTION OF 100,000 TONNE PER ANNUM OF 2-ETHYLHEXYL ACRYLATEMECHANICAL AND CHEMICAL DESIGN 5-4

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.


5/39


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.


6/39


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).


7/39


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


8/39


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


9/39


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.


10/39


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


11/39


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


12/39


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


13/39


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


14/39


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


15/39


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


16/39


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


17/39


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


18/39


* +

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


19/39


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


20/39


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.


21/39


(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(


22/39


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 (


23/39


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



Nominal shell diameter, Ds= 444 mm


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


24/39


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




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


25/39


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


26/39


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)


27/39


(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).


28/39


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


29/39


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:



Density : 995.9 kg/m3


: 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:





: 41.895 mm

The nearest value for optimum duct diameter is nominal pipe 50 mm

Pipe size at outlet:





: 40.45 mm

The nearest value for optimum duct diameter is nominal pipe 50 mm


30/39


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.


31/39


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


32/39


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


33/39


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


34/39


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.


35/39


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


36/39


Table E2: Fouling factors (coefficients), typical values


37/39


Figure E1: Temperature correction factor: one shell pass; two or more even tubepasses


38/39


Table E3: Conductivity of metals

Figure E2: Tube-side heat-transfer factor


39/39


Figure E3: Shell-side heat-transfer factors, segmental baffles

chemical & mechanical design

Documents