
2/20

To find nin for inlet:

i) Ethylene

= 259.103 x

= 9.237

ii) 1-Hexene

= 139.517x

= 1.6577

To find nout for outlet:

i) Ethylene

= 394.63 x = 14.068

ii) 1-Hexene

= 3.986x

= 0.04736


3/20

To find out for outlet stream

i) Ethylene

Ethylene:Ethyelene (60 C, g) Ethyelene(30 C, g)

Q-W = H + KE + PE

* no work input, so W: 0

* no kinetic & Potential energy, so KE & PE: 0

out = =

= + + +

=

+

+

+

= -1.225 + 0.051615 + + = (- 1.17026

x

)

= -1170.26

ii) 1-Hexene

1-Hexene:1-Hexene (60 C, l) 1-Hexene(30 C, l)

Q-W = H + KE + PE

* no work input, so W: 0

* no kinetic & Potential energy, so KE & PE: 0

out = = =


4/20

=

= (5.499

x

)

= 5499

To calculate final energy balance for heat exchanger

= [-1170.26

x 14.068

] + [5499

x 0.04736

][(0 x 9.237

) + (0

x 1.6577

)]

= - 16202.79


5/20

Mechanical Design

Heat exchanger

The transfer of heat to and from process fluids is an essential part of most chemical

processes. The most commonly used type of heat-transfer equipment is the ubiquitous shell and

tube heat exchanger; the design of which is the main subject of this report. The word

exchanger really applies to all types of equipment in which heat is exchanged but is often used

specifically to denote equipment in which heat is exchanged between two process streams.

Exchangers in which a process fluid is heated or cooled by a plant service stream are referred to

as heaters and coolers.

If the process stream is vaporized the exchanger is called a vaporizer if the stream is

essentially completely vaporized; a reboiler if associated with a distillation column; and an

evaporator if used to concentrate a solution.The term fired exchanger is used for exchangers

heated by combustion gases, such as boilers; other exchangers are referred to as unfired

exchangers.

The principal types of heat exchanger used in the chemical process and allied industries,

1. Double-pipe exchanger: the simplest type, used for cooling and heating.

2. Shell and tube exchangers: used for all applications.

3. Plate and frame exchangers (plate heat exchangers): used for heating and cooling.

4. Plate-fin exchangers.

5. Spiral heat exchangers.

6. Air cooled: coolers and condensers.

7. Direct contact: cooling and quenching.

8. Agitated vessels.

9. Fired heaters.


6/20

Heat Exchanger Type

Heat transfer equipment is usually specified both by type of construction and by service.

A heat exchanger is a specialized device that assists in the transfer of heat from one fluid to the

other. In some cases, a solid wall may separate the fluids and prevent them from mixing. In other

designs, the fluids may be in direct contact with each other. In the most efficient heat

exchangers, the surface area of the wall between the fluids is maximized while simultaneously

minimizing the fluid flow resistance. Fins or corrugations are sometimes used with the wall in

order to increase the surface area and to induce turbulence.

In heat exchanger design, there are three types of flow arrangements: counter-flow,

parallelflow, and cross-flow. In the counter-flow heat exchanger, both fluids entered the

exchanger from opposite sides. In the parallel-flow heat exchanger, the fluids come in from the

same end and move parallel to each other as they flow to the other side. The cross-flow heat

exchanger moves the fluids in a perpendicular fashion. Compare to other flow arrangements

counterflow is the most efficient design because it transfers the greatest amount of heat.

There are two major different designs of heat exchangers: shell and tube, and plate heat

exchanger. The most typical type of heat exchanger is the shell and tube design. This heat

exchanger can be design with bare tube or finned tubes. One of the fluids runs through the tubes

while the other fluid runs over them, causing it to be heated or cooled. In the plate heat

exchanger, the fluid flows through baffles. This causes the fluids to be separated by plates with a

large surface area. This type of heat exchanger is typically more efficient than the shell and tube

design.

Shell & Tube Exchanger

A shell and tube heat exchanger is a class of heat exchanger designs. It is the most

common type of heat exchanger in oil refineries and other large chemical processes, and is suited

for higher-pressure applications. It consists of a tube bundle enclosed in a cylindrical casing


7/20

called a shell. One fluid runs through the tubes, and another fluid flows over the tubes (through

the shell) to transfer heat between the two fluids.

Two fluids, of different starting temperatures, flow through the heat exchanger. One

flows through the tubes (the tube side) and the other flows outside the tubes but inside the shell

(the shell side). Heat is transferred from one fluid to the other through the tube walls, either from

tube side to shell side or vice versa. The fluids can be either liquids or gases on either the shell or

the tube side. In order to transfer heat efficiently, a large heat transfer area should be used, so

there are many tubes. In this way, waste heat can be put to use. This is a great way to conserve

energy.

Typically, the ends of each tube are connected to plenums through holes in tube sheets.

The tubes may be straight or bent in the shape of a U, called U-tubes. Most shell-and-tube heat

exchangers are 1, 2, or 4 pass designs on the tube side. This refers to the number of times the

fluid in the tubes passes through the fluid in the shell. In a single pass heat exchanger, the fluid

goes in one end of each tube and out the other.

There are two basic types of shell-and-tube exchangers. The first is the fixed tube sheet

unit, in which both tube sheets are fastened to the shell and the tube bundle is not removable. The

second type of shell-and-tube unit has one restrained tube sheet, called the stationary tube sheet,

located at the channel end. Differential expansion problems are avoided by use of a freely riding

floating tube sheet at the other end or the use of U tubes. This design may be used for single or

multiple pass exchangers. The tube bundle is removable from the channel end, for maintenance

and mechanical cleaning. There are often baffles directing flow through the shell side so the fluid

does not take a short cut through the shell side leaving ineffective low flow volumes. Counter

current heat exchangers are most efficient because they allow the highest log mean temperature

difference between the hot and cold streams. Many companies however do not use single pass

heat exchangers because they can break easily in addition to being more expensive to build.

Often multiple heat exchangers can be used to simulate the counter current flow of a single large

exchanger.


8/20

U tube heat exchanger was been used to cooling down the organic liquid in fluid. It is far

the cheapest and easy to operate. Moreover, many industrial plant used this heat exchanger for

their plant. The tube on the heat exchanger will be flowing Ethylene and 1-Hexene while the

shell will be used to flow raw water.

An even number of tube passes is usually the preferred arrangement, as this position the

inlet and outlet nozzles at the same end of the exchanger, which simplifies the piping. HE- 01

will be designed with one shell and 2 tube passes. The tube has outer diameter of 19.05 mm,

inner diameter of 14.83 mm and length of 10 meter placed on a triangular 23.81 mm pitch (pitch

diameter = 1.25). The shell and tube heat exchangers provide large amounts of heat transfer area

up to 5000 ft2 in relatively small space. It was available in standard sizes specified by TEMA

(Tubular Exchanger Manufacturers Association). The tube length available in multiple of 4 ft,

for example, 8ft, 12ft, 16ft, and 20ft.

TUBE

The tubes are the basic component of the shell and tube heat exchanger, providing the

heat transfer surface between one fluid flowing inside the tube and other fluid flowing across the

outside of the tubes. The tube may be seamless or welded and most commonly made of copper or

steel alloys. Other alloys of nickel, titanium, or aluminum may also be used for specific

applications. The tube may be either bare or extended surface on the outside. Extended or

enhanced surface tube s are used when one fluid has a substantially lower heat transfer

coefficient then the other fluid .doubly enhanced tubes that is , with enhancement both inside and


9/20

outside are available that can reduce the size and cost of the exchanger. Extended surfaces

(finned tubes) provide two to four times as much heat transfer area on the outside as the

corresponding bare tube, and this area helps to offset a lower outside heat transfer coefficient.

Tubes should be able to withstand the following

1. Operating temperature and pressure on both sides

2. Thermal stresses due to the differential thermal expansion between the shell and the tube

bundle

3. Corrosive nature of both the shell-side and the tube-side fluids

Area of one tubes of the heat exchanger.

Area of tube:

A= x D x L

D: Diameter of outer diameter of tube

L: Length of tube

A= x (19.05 x 10-3

) x 5 m

A = 0.3 m2

Temp. : 30C (Tco)

Temp. : 95 C (Tho)

Temp. : 60C (Tcin)

Temp. : 55C (Thi)


10/20

Since this heat exchanger used a counter flow, the calculation for Tm was

Tm = ()

However, Tm varies with position in the HEX whether it is in parallel flow or counter-flow

HEX.

The simplest type of heat exchanger consists of two concentric pipes of different diameters, as

shown in Figure, called the double-pipe heat exchanger. In parallel flow, both the hot and cold

fluids enter the heat exchanger at the same end and move in the same direction. In counter flow,

on the other hand, the hot and cold fluids enter the heat exchanger at opposite ends and flow inopposite directions.

a) 1:Thi - Tco

: 5530

: 25 C

b) 2:Tho - Tci

: 9560


11/20

: 35 C

Tm:()

:

Tm : 29.76 C

To find the area, heat exchanger used a Newtons Law of cooling. Theoretically it stated

that states that the rate of temperature of the body is proportional to the difference between the

temperature of the body and that of the surrounding medium. This statement leads to the classic

equation of exponential decline over time which can be applied to many phenomena in science

and engineering, including the discharge of a capacitor and the decay in radioactivity. Newton's

Law of Cooling is useful for studying water heating because it can tell us how fast the hot water

in pipes cools off.

Newtons Law of Cooling:

Where,

Q = total heat transfer

U = overall heat transfer coefficient

A = total heat transfer area

Tm = Log mean temperature difference

To find Q,

Q : m x cp x T

Where,

m = mass flowrate

Cp = specific heat

T = temperature difference

To find m (mass flowrate)

Where m is the flowrate of inlet and oulet, thus,

mTUAQ )(


12/20

: 797.240

: 797240

To find Cp,

Cp of the water was get by using the properties of saturated water table where for the temperature

of 55 C and 95 C was,

Temperature, C Specific heat cp, J/kg.k

55 4183

95 4212

Heat Exchanger



Tout: 30 C

Pout: 40 Bar



Tin: 60 C

Pin: 40 Bar

Stream 12, Top

A = 398.62 kg/hr

Stream 13

B = 398.62 kg/hr


13/20

Convert to J/g.C,

= 8395 = 0.03052 T = 9555

= 40 C

Thus,

Q : 797240

x 0.03052

x 40 C

Q : 973 270.592

To find the area of the heat exchanger,

This heat exchanger is cooler using cooling water to cool organic fluids. U is preferably between

250 to 750 W/m2 C.

We may select 500 W/m2 C as an initial guess.

973 270.592

= 500

x A x Tm

A = 65.40 m2

* Area of one tube,

A = x (19.05 x 10-3

) x 5 m

A = 0.3 m2

Number of tubes,

=

=

=218 tubes

So, for 2 passes heat exchanger, the tubes per passes were 109 tubes.

Tube side velocity

mTUAQ )(


14/20

Tube cross sectional area

= (14.83 x 10-3)2

= 0.0001727 m2

So, the area per pass was,= 109 x 0.0001727 m

2

= 0.0188243 m2

Volumetric flowrate

=

= 0.187

Tube side velocity

=

= 9.93

Bundle and shell diameter

According tables in Chem. Eng. Design by Sinott, R.K for 2 tubes passes was,

K1 = 0.249

N1= 2.207

So the Db(bundle diameter) was

= 19.05 mm x (

^ = 409.95 mm (0.40 m)

For a U-tube heat exchanger with a bundle diameter of 0.40 m, the typical shell clearance was 33

mm

Ds= 409.95 mm + 33 mm

= 442.95 mm


15/20

Shell thickness

The nominal diameter (outside diameter in millimeters rounded is to the nearest integer)

of the heat exchanger in case of shells manufactured from flat sheet. The following diameters (in

mm) should be preferably used in the case of cylindrical pipe shell: 159, 219, 267, 324, 368, 419,

457, 508, 558.8, 609.6, 660.4, 711.2,762, 812.8, 863.6, 914.4 and 1016. Design pressure of a

heat exchanger is the gage pressure at the top of the vessel. This pressure is used to determine the

minimum wall thickness of the various pressure parts. The design pressure should at least 5%

greater than the maximum allowable working pressure. Usually a 10% higher value is used. The

maximum allowable working pressure is the gage pressure for a specified operating temperature

that is permitted for the service of the exchanger units.

The shell thickness () can be calculated from the equation below based on themaximum allowable stress and corrected for joint efficiency:

ts=

=shell thickness= design pressure (10% of 40 bar, = 44 bar)= Shell ID (0.44 m or 440 mm)=Maximum allowable stress of the material of construction (150 N/m for stainless steel)=Joint efficiency (usually varies from 0.7 to 0.9)

ts=

= 218.36 mm

The minimum shell thicknesses should be decided in compliance with the nominal shell

diameter including the corrosion allowance. Usually the minimum shell thicknesses are in order

for various materials for the same service: Cast iron> Carbon steel Al and Al-alloys (up to

700C)> Cu and Cu-alloys Ni Austenitic stainless steel.


16/20

Shell cover

There are different types shell covers used in shell and tube heat exchangers: flat,

torispherical, hemispherical, conical and ellipsoidal. Out of various types of head covers,

torispherical head is the most widely used in chemical industries for operating pressure up to

200psi.The thickness of formed head is smaller than the flat for the same service .The minimum

thickness of the shell cover should be at least equal to the thickness of the shell.

The required thickness of a torispherical head ( Th) can be determined by:

Th =

W = * +

= Crown radius = Shell ID = 440 mm=Knucle radius = 6% of Dsis taken = 9.54 mm

=corrosion allowance = 0 for stainless steel.

W = =

W= 1.77

Th =

[ ] =

Th= 170.31 mm


17/20

Nozzles and branch pipes

The wall thickness of nozzles and other connections shall be not less than that defined for the

applicable loadings, namely, pressure temperature, bending and static loads. But in no case, the

wall thickness of ferrous piping, excluding the corrosion allowance shall be less than (0.04+2.5) mm, where is the outside diameter of the connection. The typical nozzle size with shellID is provided in Table

Shell ID, inch Nozzle ID, inch

39 10

Based on the table above, by calculate the shell diameter, the shell diameter was 17 inch, thus,

the perfect nozzle diameter would be 3 inch.

Nozzle thickness ()

Tn =

Use stainless steel for the nozzle (same material)

Considering diameter of nozzle ( ) to be 76.2 mm (3 inch); =0.7=corrosion allowance = 0 for stainless steel

Tn=

= 22.19 mm


18/20

EQUIPMENT SPECIFICATION SHEET

Equipment Type: Heat Exchanger

Equipment Name: HE-01

Function: Cool Down temperature of Ethylene and 1-Hexene

By: Noor Zarif B. Noor Khizan

Main Stream flow (kg/hr) 398.62

Exchanger types U tube heat exhanger, 1 shell + 2 tube. Organic fluid in

tube, cooling water in shell

Tube OD (mm) 19.05

Tube ID (mm) 14.53

Tube length (m) 5

Number of tubes 218

Design Pressure 44 bar ( 10% above operating pressure)

Material Construction 304 stainless steel

Bundle Diameter (m) 0.40

Shell Diameter (m) 0.44

Shell Thickness (m) 0.21836

Shell cover (m) 0.17031

Nozzle ID (inch) 3

Nozzle Thickness (mm) 22.19


19/20

Schematic Diagram of Heat Exchanger

T = 368 K


20/20

the tube has outer diameter of 19

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