SHELL AND TUBE HEAT EXCHANGER DESIGN
In Partial Fulfillment of the Requirements for the Course Heat and Mass Transfer for Chemical Engineering
Submitted by: Benito, Angelica Joyce Cabaddu, Quennie
ABSTRACT
In designing a suitable heat exchanger for cooling a gas oil from 200°C to 40°C the parameters are cautiously followed. In this paper a suitable design for cooling a gas oil is presented, the most suitable design is a 4-pass divided flow, shell and tube type heat exchanger with a 25 percent cut baffles and a pull through floating head. The thermal design and mechanical design computation is carried out to demonstrate the requirements and dimensions needed to yield an optimized design suitable for cooling a gas oil. In presenting the proposed design of the heat exchanger, Computer aided drafting CAD ® and Sketch Up ® is used.
ABSTRACT
In designing a suitable heat exchanger for cooling a gas oil from 200°C to 40°C the parameters are cautiously followed. In this paper a suitable design for cooling a gas oil is presented, the most suitable design is a 4-pass divided flow, shell and tube type heat exchanger with a 25 percent cut baffles and a pull through floating head. The thermal design and mechanical design computation is carried out to demonstrate the requirements and dimensions needed to yield an optimized design suitable for cooling a gas oil. In presenting the proposed design of the heat exchanger, Computer aided drafting CAD ® and Sketch Up ® is used.
TABLE OF CONTENTS CONTENTS ABSTRACT .............................................................................................................................................................
NOMENCLATURE FOR THERMAL AND MECHANICAL DESIGN .................................................................. 1 I.
INTRODUCTION ......................................................................................................................................... 5
II. OBJECTIVE ................................................................................................................................................... 5 III. SHELL AND TUBE HEAT EXCHANGER ................................................................................................ 5
A. DEFINITION........................................................................................................................................................
5
........................................................... ................................................................. .................................. 5 B. THEORY ...........................................................
C. APPLICATIONS .................................................................................................................................................... 6 D. CLASSIFICATIONS ........................................................ ................................................................. ....................... 6 .............................................................................................................................. 6 1. Fixed tube-sheet heat exchanger ..............................................................................................................................
2. U-tube heat exchanger .......................................................................................................................................... .......................................................................................................................................... 6 3. Floating head heat exchanger ....................................................... ................................................................. ............ 6 IV. STEPS FOR DESIGN OF HEAT EXCHANGER ........................................................................................ 7 V. PROBLEM STATEMENT .......................................................................................................................... 17
Figure 1 : 4- Pass Divided Flow type Shell and tube Heat Exchanger schematic diagram .... 17 Figure 2: Parts to consider on mechanical design ........................................... ................................................................ ..................... 27 Figure 3: 3-D design of heat exchanger ........................................... .................................................................. .................................... .............41 ................................................................. ............................................ ................................ .......... 42 Figure 4: Tubes and Baffles ...........................................
Table 1: Conductivity Conductivity of Metals ............................................ .................................................................. ............................................ ........................... ..... 7 Table 2: Typical Overall Overall Coefficients ............................................ ................................................................... ....................................... ................ 10 Table 3: Constants in calculating tube pitch pitch and the bundle diameter .................................. .................................. 12 Table 4: Properties Properties of Water and and Gas oil ......................................... ............................................................... .................................... .............. 17
NOMENCLATURE FOR THERMAL AND MECHANICAL DESIGN Tube diameter
(D 0 )
Tube diameter
(Di )
Tube length
(L)
BWG number
Tube pattern
Triangular Pitch
Fouling factor for cooling water
1 h id
Fouling factor for gas oil
1 h
Temperatur e correction factor
( F t )
Mean tempe rature difference
(Tm )
Overall heat trans fer coefficient
(U o )
Provisional area
(A)
Number of tubes
(N t )
Tube pitch
(Pt )
Bundle diameter
(Db)
Bundle diameter clearance
(BDC)
Pressure drop in the shell
(Ps )
Number of tubes per pass
(Nt pp )
Tube - side mass velocity
(Gm )
Tube - side velocity
( ν t )
Tube - side Reynold' s number
(Re)
Tube - side Prandtl' s number
(Pr)
Tube - side heat trans fer coefficient
(hi )
Overall heat trans fer factor
(U ) o
Design of Gaskets
( D OG )
Gasket Width
(N)
Mean Gasket Diameter
(G)
Basic Gasket Starting Width
(Bo )
Effective gasket seating width
(b)
Bolts
( Wm1 )
The bolt load under tight pressure
( Wm2 )
The minimum bolt cross-sectional area(
( f a = f b ) ( A m )
both material is carbon steel)
I. INTRODUCTION
In the process industries the transfer of heat between two fluids is generally done in heat exchangers. Heat exchanger is used to transfer heat between a solid object and a fluid, or between two or more fluids. It is one in which the hot fluid and the cold fluid don not come into direct contact with each other but are separated by a tube wall or a flat or curved surface. The most common type of heat exchanger is the shell and tube heat exchanger. It is used in oil refineries and other large chemical processes, and is suited for higher-pressure application. This type of heat exchanger consists of a shell with a bundle of tubes inside it. One fluid runs through the tubes, and another fluid flows over the tubes to transfer heat between the two fluids. II. OBJECTIVE
The main purpose of this paper is to present effectively a suitable, efficient and a fully optimized design of heat exchanger for cooling a gas oil from 200°C to 40°C. III.SHELL AND TUBE HEAT EXCHANGER
C. Applications
The simple design of a shell and tube heat exchanger makes it an ideal cooling solution for a wide variety of applications. One of the most common applications is the cooling of hydraulic fluid and oil in engines, transmissions and hydraulic power packs. With the right choice of materials, they can also be used to cool or heat other mediums, such as charge air. One of the big advantages of using shell and tube heat exchanger is that they are often easy to service, particularly with models where a floating tube bundle is available. D. Classifications 1. Fixed tube-sheet heat exchanger
A fixed tube sheet heat exchanger has straight tubes that are secured at both ends to tube sheets welded to the shell. The principle advantage of fixed tube sheet construction is its low cost because of its simple construction. In fact, the fixed tube sheet is the least expensive construction type, as long as no expansion joint is required. Other advantages are the tubes can be cleaned mechanically after removal of the channel cover or bonnet, and the leakage of the shell-side fluid is minimized since there are no flanged joints. A disadvantage of this design is that since the bundle is fixed to the shell and cannot
IV. STEPS FOR DESIGN OF HEAT EXCHANGER Note:
all information including figures and charts were obtained from Colson &
Richardson, Chemical Engineering, volume 6)
1. Assume tube diameter and BWG, Assume tube length, L 2. Assume fouling factor based on inside and outside tubes, h di and hdo 3. Assume material of construction for the tubes
thermal conductivity?
Table 1: Conductivity of Metals
For
other
configurations
use
the
following
Graph 1: Temperature correction factor: one shell pass; two or more even tube 'passes
charts
Graph 3: Temperature correction factor: divided-flow shell; two or more even-tube passes
Table 2: Typical Overall Coefficients
Table 3: Constants in calculating tube pitch and the bundle diameter
12. Provide/Assume the type of floating head of the exchanger and obtain the bundle diameter clearance BDC . Use the chart below:
13. Calculate the shell diameter. Ds Db BDC 14. Calculate the baffle spacing. Bs 0.4 Ds 15. Calculate the are for cross-flow, As
( pt d o ) Ds. Bs
16. Calculate the shell-side mass velocity, Gs 17. Calculate the shell equivalent diameter
pt
shell - side flowrate [kg/s] As
Graph 7: Shell-side friction factor, segmental baffles
27. Calculate the overall heat transfer factor Based on “inside tubes flow” U i
1
hi
Or based on “outside tubes flow” U o
1
1 d i ln( d o / d i ) 2k w
hdi
1 ho
1 hdo
d i d o hdo
1 d o ln( d o / d i ) 2k w
d i
d o ho
d o d i ho
d o d i hdi
Where hdi and hdo are the heat transfer coefficients for the scales (dirt) inside and outside tubes, respectively. 28. Compare the calculated overall heat transfer coefficient you obtained from the previous step with that you assumed in step 8. if it is close to what you assumed, then you had a valid assumption, then tabulate your results such as total surface area of tubes, number of tubes, exchanger length and diameter, heat duty and other design specification. Otherwise, use the calculated value in step 8 and do loop until the difference between the calculated U between two consecutive iterations is small.
V.
PROBLEM STATEMENT
Design a suitable heat exchanger for Gas oil which is to be cooled from 200°C to 40°C, with a given oil flow-rate equal to 22,500 kg/h. The cooling water is available at 30 °C and the temperature rise is limited to 20°C. Pressure drop allowance for each stream is 100 kN/m 2.
Figure 1 : 4- Pass Divided Flow type Shell and tube Heat Exchanger schematic diagram
A.
Thermal Design Calculations 1. Assumptions,
TUBEDIAMETER
D0 = 20 mm
Di = 16 mm
TUBE LENGTH
L 4m
BWG NUMBER
BWG =14
TUBE PATTERN
Triangular Pitch
2. Assumption of the fouling factor on the inside and outside tubes
FOULING FACTOR
Mass flow rate .
.
mh moil 22,500 .
kg h
.
mc m water
Heat duty equation qh qc .
q = m c cp c (Tc o - Tc i ) or .
q = m h cp h (Th o - Th i )
kg
h
q = (22,500 q = 2280
×
1h 3600s
)(2.28
kJ kg°C
kJ
s q = 2280 kW .
2280kW m c (4.18 .
m 27.27
kg
kJ o
kg C
)[(200 - 40)°C]
)(50 o C 30o C)
6. Temperature correction factor, F t
For 1 shell-2 tube pass exchanger TEMPERATURE CORRECTION FACTOR
R = S=
Th i - Th o Tco - Tci Tco - Tci Thi - Tci
=
=
200 - 40 50 - 30 50 - 30
200 - 30
= 8.0
= 0.12
These values do not intercept on the figure for a single shell-pass exchanger, graph
1, so use the figure for a two -pass shell, graph 3, which gives F t 0.94 7. Calculate the Mean temperature difference, ΔTm
ΔTm = Ft × ΔTlm
10. Number of tubes
N t =
A
πD o L
94m 2 N t = 1m π(20mm × )(4m) 1000mm N t = 374.5 tubes 375 tubes N t = 376 tubes, use even 11. Calculate tube pitch and the bundle diameter
TUBE PITCH
Pt = 1.25D O Pt = 1.25(20mm) Pt = 25 mm BUNDLE DIAMETER
13. Calculate the shell diameter, D s D s = Db + BDC D s = 575mm + 92mm D s = 667mm
14. Calculate the baffle spacing, B s Bs = 0.2Ds Bs = 0.2(667mm) B s 133mm
15. Calculate the area for cross-flow
As =
(Pt - D o ) Pt
A s = (0.5)
DsBs
(25 - 20)mm 25mm
A s = 8871.1mm 2
(667mm)(13 3mm)
17. Calculate the shell equivalent diameter, d e
For an equilateral triangular pitch arrangement de = de =
1.10 Do
2
2
(Pt - 0.917D o )
1.10 20mm
[(25mm) 2 - 0.917(20mm ) 2 ]
d e = 14.2mm
18. Calculate the shell-side Reynold’s number
Re =
u sd eρ μ
(0.83
m
Re =
s
)(14.2 × 10 -3 m)(850
0.17 × 10 Re 58930
-3
kg s-m
kg m3
)
21. Calculate pressure drop in the shell
ΔPs = 8jf (
Ds de
)(
L Bs
)(
ρu s 2
2
)(
μ μw
) 0.14
-3
-2
662 10 m
neglect t he viscositycorrelation
2 4
ΔPs = 8(3.8 ×10 )( )( )[ 14.2 10-3 m 132 10-3 m N ΔPs = 251481 2 m kN ΔPs = 252 2 m
22. Calculate the number of tubes per pass
Nt pp = Nt pp = Nt pp
N t number of passes 376
4 = 94 tubes per pass
(850
kg m
3
)(0.83 2
m s
)2 ]
25. Tube-side reynold’s number
Re =
ρdv μ
(992.8 Re =
kg m )(16 ×10-3 m)(1.45 ) 3 m s -6 N - s 671× 10 m
Re = 34378 Tube-side prandtl’s number
Pr =
μc p k (671× 10-6
Pr =
N - s J 3 )(4.18 × 10 ) m2 kg°C W (0.631 ) m°C
27. Calculate the overall heat transfer factor
U = o
1 d
d ln( o ) o d d d 1 1 i + o + o + + h h 2 × k dh dh o do w i i i di 1
U = o 1 1967
+ 0.0002 +
(20 × 10- 3 ) (20 × 10- 3 )ln (16 × 10- 3 ) 2 × 45
+
20 × 10- 3 20 × 10- 3 + (0.00025) 3 3 (16 × 10 )(6982) (16 × 10 )
W U = 800 o m 2 °C
28. Calculate the tube-side pressure drop
ΔP = (1.5 + N p [2.5 +
8j f L di
+(
μ μw
)
-m
])
ρ i υ 2 2
8(3.5 ×10 -3 )(4) 992.8(1.45 ) 2 ]( ) ΔP = 4[2.5 + 2 16 ×10 -3 N ΔP = 39660
B) Mechanical Design Calculations
Mechanical design of heat exchangers includes design of various pressure and nonpressure parts. Figure 2: Parts to consider on mechanical design
b) Design Pressure
10% greater than the maximum allowable working pressure P = 1.1×100
kN m
2
110
kN m
2
P 1.1bar
Materials of construction
The material of construction chosen is carbon steel which is cost effective and compatible with the process fluids and others parts of the heat exchanger. a) Carbon steel
Allowable fluid temperature = 540°C (1004°F)
Design component calculation
The major mechanical design components of shell and tube heat exchangers are: shell and
b. Torispherical Head i.
Inside depth of the head
h i = R i - [(R i -
Ds 2
)(R i +
Ds 2
h i = (667 mm) - [(667 mm -
1
) + 2r i ] 2 ; 667 mm 2
)(667mm +
h i = 89.29 mm ii. Effective Exchanger Length (L eff )
L eff = L t + 2 × h i L eff = 4m + 2 × 0.08929 m L eff = 4.18 m iii. Thickness of the Head
pR W
667 mm 2
1
) + 2(0.06)(66 7 mm)] 2
c. Channel Cover Thickness
Channel cover material: carbon steel
t cc =
t cc =
Dc 10
c1 p f
(671 mm) 10
(0.3)(1.1 × 10.26
kgf
cm 2 kgf
)
cm 2
t cc = 3.76 mm + c t cc = 6.76 mm : including corrosion allowance : use 7mm d. Tube Sheet Thickness FG p
p
e. Impingement plate
6.25 u g =
[
kg s
π(0.1524m) 2
4
u g = 0.06 m
][850
kg m
3
]
s
Impingemen t Parameter, ρν 2 = (0.85)(0.0 6 m ) s = 0.051 << 125 ∴
f.
Impingemen t protection is not required
Nozzle thickness
(0.11
tn =
N 2
)(152.4mm)
mm + 3mm N N 2(100.6 )(0.8) (0.11 ) 2 2 mm mm
i. Gasket Width, N
N = N =
(DOG - D IG ) 2 (747.32 mm - 667.25 mm)
2 N = 40.035 mm : Use 50 mm
ii. Mean Gasket Diameter, G
G=
DOG + DIG
2 G = 707 mm
iii. Basic Gasket Starting Width, B o
b o = b o =
N 2 50 mm 2
ii. The bolt load under tight pressure
Wm2 = 2 bGmp +
π 4
G 2 p
Wm2 = 2 (2.5 mm)(707 mm)(3.75)( 0.11
N
N π 2 ) + (707 mm) (0.11 mm2 4 mm2 )
Wm2 = 47764.88 N : Wm1 is the controllin g load because Wm1 > Wm2
iii. The minimum bolt cross-sectional area both material is carbon steel,
( f a = f b )
Am = Am =
Wm2 f a
47764.88N N 100.6 mm2
A m = 474.8 mm 2
M16 nominal thread diameter with bolt circle diameter ( ) of 860 mm, 32 bolts
i.
Flange thickness i.
For the gasket seating condition
W=
(Am + A b )f a 2 2 2 (474.8mm + 8143mm )(100.6 N
W=
mm
2
)
2 W = 433475.34 N : flange bolt load
M f =
M f =
W(C b - G) 2 (433475.34 N)(860mm - 707mm) 2
M f = 33160863.5 1N - mm : flange moment
j.
For operating condition i.
Hydrostatic end force on area inside of the flange
iii. Gasket load under operating conditions HG = W - H H=
H=
πG 2 p
4 π(707mm) 2 (0.11 N
2
mm
4
H = 43184 N W = Wm2 H G = 47764.88 N - 43184 N H G = 4580.88 N
iv. Moment due to HG MG = HG h G hG =
(C b - G) 2
)
VI.
DESIGN SPECIFICATIONS A. Thermal Design Tube diameter (D 0 )
20 mm
Tube diameter (Di )
16 mm
Tube length (L)
4m
BWG number
14
Tube pattern
Triangular pitch
1 Fouling factor for cooling water h id
0.00025
m 2 °C W
Log mean temperature (Tlm )
51.70°C
Temperatur e correction factor ( F t )
0.94
Mean temperature difference (Tm )
48.60 o C
Overall heat trans fer coefficien t (U o )
500
Provisional area (A)
94m 2
Number of tubes (N t )
376 tubes, use even
Tube pitch (Pt )
25 mm
Bundle diameter (Db)
574.5mm or 575mm
W m2 °C
Shell - side Prandlt' s number (Pr )
3.1
Shell - side heat trans fer coefficient (h o )
1967
Pressure drop in the shell (Ps )
252
Number of tubes per pass (Nt pp )
94 tubes per pass
Tube - side mass velocity (Gm )
1442.87
Tube - side velocity ( ν t )
1.45
Tube - side Reynold' s number (Re)
34378
W m2 °C
kN m
2
m s
kg s - m2
B. Mechanical Design
Design Temperature (T)
220°C
Design Pressure (P)
1.1bar
Carbon steel allowable fluid temperature
540°C (1004°F)
Shell thickness ( t s )
Inside depth of the head ( h i )
Effective Exchanger Length (L eff )
0.9mm
89.29 mm
4.18 m
Design of Gaskets ( D OG ) Gasket Width (N) Mean Gasket Diameter (G)
Basic Gasket Starting Width (B o )
Effective gasket seating width (b)
Bolts ( Wm1 )
The bolt load under tight pressure ( W )
747.32 mm
40.035 mm
707 mm
25 mm
2.5 mm
291428N
Hydrostatic end force on area inside of the flange ( H D )
155592.12 N
Moment due to HD ( MD )
214703455. 34 N - mm
Gasket load under operating conditions ( H G )
Moment due to HG ( M G )
4580.88 N
350437 N - mm
VII. 3-D representation of divided flow type shell and tube heat exchanger
Figure 4: Tubes and Baffles
VIII. CONCLUSION
Based on the computed values for the design of heat exchanger, the most suitable design is the 4-pass divided shell heat exchanger on which it reduces the pressure drop or flow.
RUBRIC FOR HEAT AND MASS TRANSFER DESIGN PROJECT EVALUATION Name: BENITO, ANGELICA JOYCE Z.
CABADDU, QUENNIE S. MAGANNON, JUDY ANN P. Title of Design Project: EVALUATION CRITERIA Identification of Problem or Definition of Project (3 points) Application of Engineering Principles (5)
Use of Computer – Aided Tools (2) Meeting Design Requirements
1 Beginning Insufficient identification of problem; inadequately objectives.
2 Developing Partial identification of problem; lack of specifics does impair solution of design.
No or erroneous application of engineering principles yielding unreasonable solution. Serious deficiencies in understanding the correct selection and/or use of tools. Few design requirements are met.
Serious deficiencies in proper selection and use of engineering principles. Minimal application and use of appropriate tools. Only basic requirements are met.
(5)
1
3 Proficient Adequate identification of problem; any lack of specifics does not impair solution or design. Effective application of engineering principles resulting in reasonable solution.
4 Exemplary Clear and complete identification of design goals and objectives.
Critical selection and application of engineering principles ensuring reasonable results. Computer – aided tools Computer – aided tools used with moderate are used effectively to effectiveness to develop develop and analyze designs. designs. Design requirements All design requirements are met. are met and exceeded
SCORE
Design Documentation and Presentation
Reports may have poor quality writing and mix jargon with engineering language.
Reports attempts appropriate language/format for the engineering field.
Reports use mostly appropriate language/format for the engineering field.
(5 points)
Reports miss many important topics and are not easy to read.
Reports are fairly informative and generally easy to read.
Reports are mostly informative and easy to read.
Information in report is Information in reports not organized. Data or organized into sections design features with data or design explanations very features explanation difficult to locate. present. Evidence of plagiarism.
Evidence of plagiarism.
Punctuation, Capitalization & Spelling (3)
There are a number of major errors in punctuation, grammar and/or spelling which make it difficult to read
Sources (2)
Attempt to document source used is not completely accurate Only 1 source was used
There are 3 or 4 minor errors in punctuation, grammar and/or spelling which do not break the flow for the reader All sources are accurately documented Only 1 or 2 sources were used
Reports use appropriate language/format for the engineering field. Reports are informative and easy to read. Information in reports is well organized so that data or design feature explanations are easy to found.
Information in reports is well organized. All data and design features can be found without difficulty. Avoid plagiarism, does not use information Both positive and without giving credit to negative results the appropriate source. presented. There are 1 or 2 minor There are no grammatical, spelling or grammatical, spelling or punctuation errors punctuation errors
All sources are accurately documented and in the desired format 2 or 3 sources were used
All sources are accurately documented and in the desired format
TOTAL SCORE
Rater:
Engr. CAESAR P. LLAPITAN
2
