Chapter 7 shell tube heat exchanger

TEMA typesTEMA: Tubular Exchanger Manufacturers Association • Size of heat exchanger is represented by the inside diameter of shell or bundle diameter and the tube length in inches • Typ

CHAPTER

SHELL TUBE HEAT

EXCHANGERS

7

Fluid velocity

Low viscosity liquids (water, alcohol…) 0.5 ÷ 3.0

High viscosity liquids (oil, glycol, glycerine…) 0.2 ÷ 1.0

coefficient also, high pressure drop as well

Shell and Tube

Fluid in inner tube (1 pass)

Fluid in outer tube (1 pass)

Fluid in inner tube (1 pass)

Fluid in outer

tube (1 pass)

Double pipe heat exchanger

Shell-and-Tube Heat Exchangers

(1 pass)

Configuration

Large surface area in a small volume

For high pressure

Well–established fabrication techniques

A wide range of materials

Easily cleaned

Well–established design procedures

Shell-and-Tube Heat Exchangers

1-2 Fixed Head

1-2 Floating Head

One shell pass and two tube passes

Shell-and-Tube Heat Exchangers

1-2 U-tube

2-4 Floating Head

Quiz: Identify the following

Temperature-Driving Forces

The rate of heat transfer in an shell-and-tube exchanger is computed as:

Assuming (1) steady-state; (2) counter- or cocurrent

(parallel) flow; (3) constant overall heat transfer

coefficient; (4) no phase changes on either side; and (5) negligible heat losses:

Q = mC.(HC,out – HC ,in) = mH.(HH,out – HH, in)

Q = U.A.ΔT LM

Temperature-Driving Forces

Example

GENERAL DESIGN CONSIDERATIONS

Fluid allocation: shell or tubes

Where no phase change occurs, the following factors will determine the allocation

of the fluid streams to the shell or tubes.

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 placed in the tubes

Fluid temperatures reduce the shell surface temperatures, and hence the need for lagging to reduce heat loss, or for safety reasons.

Operating pressures The higher pressure stream should be allocated to the side.

tube-Pressure drop For the same pressure drop, higher heat-transfer coefficients will

be obtained on the tube-side than the shell-side, and fluid with the lowest

allowable pressure drop should be allocated to the tube-side.

Viscosity Generally, a higher heat-transfer coefficient will be obtained by

allocating the more viscous material to the shell-side, providing the flow is

turbulent

Stream flow-rates Allocating the fluids with the lowest flow-rate to the shell-side will normally give the most economical design

Fluid arrangment

Factors Tube side Shell side

Phase Gas / Vapor Liquid

Corrosion More Less

Hazardous More Less

Flammable High Low

For the fluid in shell side:

• Liquids with ⁄ < 61, along the tube (prefer to counter current flow)

• Liquids with ⁄ > 61, across the tube

• Gases with 4000 < < 40000, across the tube

Factors Tube side Shell side

Temperature Far from amb Close to amb.

TEMA types

TEMA: Tubular Exchanger Manufacturers Association

• Size of heat exchanger is represented by the inside diameter of shell (or bundle diameter) and the tube length in inches

• Type and name of a heat exchanger is designed by three letters (front header – shell – rear header)

• Front header (stationary header) is where the fluid enters the tube side of the exchanger

• Rear header is where the tube side fluid leaves the exchanger or is returned to the front header with multiple passes

• Bundle comprises the tubes, tube sheets, baffles and tie rods… to hold the bundle together

• Shell contains the tube bundle

TEMA types

AEM CEU SIZE 23–192 TYPE AESAEN DEU SIZE 23/37–192 TYPE CKTBEL SIZE 19–84 TYPE GBU

BEM

BEN

SIZE 33–96 TYPE AFM

SIZE 17–192 TYPE CEN

Front header types

• Easy to repair and replace

• Allow access to the tubes for cleaning or repair without having to disturb the pipeline

and header–end plate), risk of leakage

• Higher cost than B type

• Suitable to high pressure (only one seal)

• Access to the tubes requires disturbance to the pipeline in order to remove the header.

• Cheapest type

Front header types

• For high pressure applications > 100

• Allow access to the tube without disturbing the pipeline

• Difficult to repair and replace (the tube bundle is an integral part of the header)

• For very high pressures > 150

disturbing the pipeline

• Difficult to repair and replace (the tube bundle is an integral part of the header)

• This is the most expensive type

Front header types

disturbing the pipeline

header and tube sheet are an integral part

of the shell)

• Cheaper than an A type

Shell types

• Suitable for most duties and applications

• Pure countercurrent flow is required in a two tube side pass (two shells side passes by a longitudinal baffle)

• Thermal and hydraulic leakage across the baffle

Shell types

• For horizontal thermosyphon reboilers

• For applications requires the small shell side pressure drop

• Similar applications to G type but tends to be used when larger units are required

Shell types

pressure drop is exceeded in an E type, and tube vibration is a problem

• The divided flow on the shell side reduces the flow velocities over the tubes and hence reduces the pressure drop and the likelihood of tube vibration

• Two inlet and one outlet is referred to I type

Shell types

disengagement space in order to minimize shell side liquid carry over

• To be used as a chiller, cool the tube side fluid

by boiling a fluid on the shell side

• For shell side condensers and gas coolers (the maximum shell side pressure drop is exceeded

by all other shell and baffle type combinations)

Rear header types

• For fixed tube sheets only (the tube sheet is welded to the shell), so it’s impossible to access

to the outside of the tubes is not possible

• Allow access to the inside of the tubes without having to remove any pipeline and the bundle

to shell clearances are small

• Small thermal expansions and this limits the operating temperature and pressure

Rear header types

• Similar to the L type but it is slightly cheaper

• The header has to be removed to gain access to the inside of the tubes

• Small thermal expansions and this limits the operating temperature and pressure

• Allow access the tubes without disturbing the pipeline

• Difficult to maintain and replace (the header and tube sheet are an integral part of the shell)

Rear header types

• Allows access to the inside of the tubes for cleaning and also allows the bundle to be removed for cleaning

• Large bundle to shell clearances required in order to pull the bundle

• For low pressure nonhazardous fluids (the shell side fluid may leak via the packing rings) Design

is 316℃

• Small thermal expansions, not low cost design

Rear header types

• Allow the bundle to be removed

• Unlimited thermal expansion

• Smaller shell to bundle clearances than the other floating head types Difficult to dismantle for bundle pulling and the shell diameter and bundle to shell clearances are larger than for fixed head type exchangers

• Most expensive

Rear header types

• Cheaper and easier to remove the bundle than with the S type

• Unlimited thermal expansion

• Largest bundle to shell clearance

• More expensive than fixed header and U–tube types

Rear header types

expansion, not pure counter flow unless an F type shell is used, limited to even numbers of tube passes

• Allows the bundle to be removed to clean the outside of the tubes, the tightest bundle to shell clearances

• Design pressure is up to 64 , temperature is 450℃

• Cheapest of all removable bundle designs, but slightly more expensive than a fixed tube sheet design at low pressures

Rear header types

• Unlimited thermal expansion, allows the tube bundle to be removed for cleaning

• The large bundle to shell clearances required to pull the bundle, the shell and tube side fluids can mixed if leakage occurs

• Limitation to low pressure nonhazardous fluids (both the fluids may leak via the packing rings).

• Cheapest of the floating head designs

1 Stationary Head–Channel 21 Floating Head Cover – External

2 Stationary Head–Bonnet 22 Floating Tubesheet Skirt

3 Stationary Head Flange–Channel or Bonnet 23 Packing Box Flange

4 Channel Cover 24 Packing

5 Stationary Head Nozzle 25 Packing Gland

6 Stationary Tube sheet 26 Lantern Ring

7 Tubes 27 Tie Rods and Spacers

8 Shell 28 Transverse Baffles or Support Plates

9 Shell cover 29 Impingement Plate

10 Shell Flange–Stationary Head End 30 Longitudinal Baffle

11 Shell Flange–Rear Head End 31 Pass Partition

12 Shell Nozzle 32 Vent Connection

13 Shell Cover Flange 33 Drain Connection

14 Expansion Joint 34 Instrument Connection

15 Floating Tubesheet 35 Support Saddle

16 Floating Head Cover 36 Lifting Lug

17 Floating Head Cover Flange 37 Support Bracket

18 Floating Head Backing Device 38 Weir

19 Split Shear Ring 39 Liquid Level Connection

20 Slip-on Backing Flange 40 Floating Head Support

9 15 16

33 17 13 11 34

12 35

35 10

3 34

5

1

36

• Floating head backing (longitudinal baffle)

• Packed floating tubesheet & lantern ring (AJW)

Construction

Construction

• Pull through floating head (BET)

Floating head exchangers

Packing materials producelimits on design pressure andtemperature More expensive(typically of order of 25% forcarbon steel construction)than the equivalent fixedtubesheet exchanger

Allows differential thermal expansion between theshell and the tube bundle Both the tube bundleand the shell side can be inspected and cleanedmechanically

Tubes can not expandindependently so that hugethermal sock applicationsshould be avoided

A floating head exchanger is suitable for therigorous duties associated with high temperaturesand pressures

The floating head cover is bolt

to the tube sheet, so itrequires the use of space

Construction

Fixed tube sheet exchangers

Provides for single and multiple tubepasses to assure proper velocity

No provision to allow for differentialthermal expansion developed betweenthe tube and the shell side This can betaken care by providing expansion join onthe shell side

Less costly then removable bundledesigns

Design pressure is up to 40 bars(below 1000mm diameter), and 25bars (above 1200mm diameter)

Design temperature is up to 350oC

Construction

Construction

as for individual tubes

Because of U–bend, some tubes are omitted at thecentre of the tube bundle, tubes can be cleaned only

by chemical methods (difficult for mechanicalcleaning), so tube side fluids should be clean

Due to U–nesting, individual tube is difficult to replaceBoth the tube bundle and

the shell side can beinspected and cleanedmechanically

Mixed counter and parallel flow

Tube wall thickness at the U–bend is thinner than atstraight portion of the tubes

Less costly than floating head

or packed floating headdesigns

Draining of tube circuit is difficult when positionedwith the vertical position with the head side upward

• Kettle floating head reboiler (AKT)

• Kettle floating head reboiler (AKT)

Construction

Construction

Packed lantern ring floating head

Internal floating head (split backing ring)

Outside–

packed floating head

Pull– through floating head

Rear head type L, M, N U W S P T

Relative cost from A

Individual tubes free

to expand Floating head

Floating head

Floating head

Floating head

Removable bundle No Yes Yes Yes Yes Yes

Replacement bundle

possible No Yes Yes Yes Yes Yes

Individual tubes

replaceable Yes Only those in outside

Tube cleaning by

chemicals inside and

outside

Interior tube cleaning

mechanically Yes Special tools required Yes Yes Yes Yes

Packed lantern ring floating head

Internal floating head (split backing ring)

Outside–

packed floating head

Pull– through floating head

Exterior tube cleaning

No Yes

No Yes

No Yes

No Yes Hydraulic–jet

cleaning:

Tube interior

Tube exterior

Yes No

Special tools required

Yes

Yes Yes

Yes Yes

Yes Yes

Yes Yes Double tube sheet

Number of tube

passes

No practical limitations

Any even number possible

Limited to one

or two passes

No practical limitations

No practical limitations

No practical limitations Internal gaskets

for fouling fluids

• Standard tube lengths: 6; 8; 10; 12; 16; 20; 24 The long tubes reduce the shell diameter and capital cost (especially high pressure)

• Liquid velocity in tube

• : bundle outside diameter

• : tube outside diameter

• : number of tube

• : tube pitch

• : bundle outside diameter

• : tube outside diameter

• : number of tube

• : tube pitch

For mechanical cleaning

Standard tube dimensions

(in) (in)

Thickness (in)

Internal area (in 2 )

External surface (ft 2 /ft)

Internal surface (ft 2 /ft)

Weight, low carbon steel, 0,2836 lb/in 3

(lb/ft)

1

4

0,194 0,028 0,0296 0,0654 0,0508 0,066 460,206 0,022 0,0333 0,0654 0,0539 0,054 520,214 0,018 0,0360 0,0654 0,0560 0,045 560,218 0,016 0,0373 0,0654 0,0571 0,040 58

3

8

0,277 0,049 0,0603 0,0982 0,0725 0,171 940,305 0,035 0,0731 0,0982 0,0798 0,127 1140,319 0,028 0,0799 0,0982 0,0835 0,104 1250,331 0,022 0,0860 0,0982 0,0867 0,083 134

1

2

0,370 0,065 0,1075 0,1309 0,0969 0,302 1680,402 0,049 0,1269 0,1309 0,1052 0,236 1980,430 0,035 0,1452 0,1309 0,1126 0,174 2270,444 0,028 0,1548 0,1309 0,1162 0,141 241

Standard tube dimensions

(in) (in)

Thickness (in)

Internal area (in 2 )

External surface (ft 2 /ft)

Internal surface (ft 2 /ft)

Weight, low carbon steel, 0,2836 lb/in 3

(lb/ft)

5

8

0,407 0,109 0,1301 0,1636 0,1066 0,601 2030,435 0,095 0,1486 0,1636 0,1139 0,538 2320,459 0,083 0,1655 0,1636 0,1202 0,481 2580,481 0,072 0,1817 0,1636 0,1259 0,426 2830,495 0,065 0,1924 0,1636 0,1296 0,389 3000,509 0,058 0,2035 0,1636 0,1333 0,352 3170,527 0,049 0,2181 0,1636 0,1380 0,302 3400,541 0,042 0,2299 0,1636 0,1416 0,262 3590,555 0,035 0,2419 0,1636 0,1453 0,221 377

Standard tube dimensions

(in) (in)

Thickness (in)

Internal area (in 2 )

External surface (ft 2 /ft)

Internal surface (ft 2 /ft)

Weight, low carbon steel, 0,2836 lb/in 3

(lb/ft)

3

4

0,482 0,134 0,1825 0,1963 0,1262 0,833 2850,510 0,120 0,2043 0,1963 0,1335 0,808 3190,532 0,109 0,2223 0,1963 0,1393 0,747 3470,560 0,095 0,2463 0,1963 0,1466 0,665 3840,584 0,083 0,2679 0,1963 0,1529 0,592 4180,606 0,072 0,2884 0,1963 0,1587 0,522 4500,620 0,065 0,3019 0,1963 0,1623 0,476 4710,634 0,058 0,3157 0,1963 0,1660 0,429 4920,652 0,049 0,3339 0,1963 0,1707 0,367 5210,680 0,035 0,3632 0,1963 0,1780 0,268 567

Standard tube dimensions

(in) (in)

Thickness (in)

Internal area (in 2 )

External surface (ft 2 /ft)

Internal surface (ft 2 /ft)

Weight, low carbon steel, 0,2836 lb/in 3

(lb/ft)

7

8

0,607 0,134 0,2894 0,2291 0,1589 1,062 4510,635 0,120 0,3167 0,2291 0,1662 0,969 4940,657 0,109 0,3390 0,2291 0,1720 0,893 5290,685 0,095 0,3685 0,2291 0,1793 0,792 5750,709 0,083 0,3948 0,2291 0,1856 0,703 6160,731 0,072 0,4197 0,2291 0,1914 0,618 6550,745 0,065 0,4359 0,2291 0,1950 0,563 6800,759 0,058 0,4525 0,2291 0,1987 0,507 7060,777 0,049 0,4742 0,2291 0,2034 0,433 7400,805 0,035 0,5090 0,2291 0,2107 0,314 794

Standard tube dimensions

(in) (in)

Thickness (in)

Internal area (in 2 )

External surface (ft 2 /ft)

Internal surface (ft 2 /ft)

Weight, low carbon steel, 0,2836 lb/in 3

(lb/ft)

1

0,670 0,165 0,3526 0,2618 0,1754 1,473 5500,732 0,134 0,4208 0,2618 0,1916 1,241 6560,760 0,120 0,4536 0,2618 0,1990 1,129 7080,782 0,109 0,4803 0,2618 0,2047 1,038 7490,810 0,095 0,5153 0,2618 0,2121 0,919 8040,834 0,083 0,5463 0,2618 0,2183 0,814 8520,856 0,072 0,5755 0,2618 0,2241 0,714 8980,870 0,065 0,5945 0,2618 0,2278 0,650 9270,902 0,049 0,6390 0,2618 0,2361 0,498 9970,930 0,035 0,6793 0,2618 0,2435 0,361 1060