heat transfer heat ex changers
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Slide 2
Heat transfer theory-review
Relation of heat transfer theory to shell and tube
heat exchangers
Design of a S&T exchanger--procedure outline
Design features and parameters of shell and tube
exchangers
What We Will Cover
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Slide 3
BASIC HEAT TRANSFER CONCEPTS
Flow of heat behaves like flow of fluids and flow ofelectrons
Driving Force
Rate K x Resistance (General)
Q K x Resistance (Fluids)Voltage
I = 1.0 x Resistance (Electricity)
Temperature Difference
Q K x Resistance (Heat)
DropPressure
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Slide 4
COMPARISON WITH FLUIDS
Fluids: 2 = K x (P2 - P1) (Remember Section 3?)
Heat: Q = 1 x (T2 - T1)
A RT
FLUIDS HEAT
Q = Volume / Second Q = Btu / Hour
P2, P1 = Higher, lower pressures T2, T1 = Higher, lower
temperatures
A = Area available for flow RT = Total specific
resistance
4 * = Number of fluid flow A = Area available for flow
resistance units of heat
Q
A fLD
fL
D
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Slide 5
BASIC HEAT TRANSFER EQUATION
Q = 1 x (T2 - T1)= 1 x TA RT RT
RT = Total Resistance, Hr x FT2 x F / Btu
I = Total Conductivity = U Btu / Hr x Ft2 x F
RT
Q = 1 x UTA
Q = U
x A x T Btu / HrUis Referred to as the Overall Heat Transfer Coefficient
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Slide 6
TOTAL RESISTANCE TO HEAT FLOW - HEAT EXCHANGERS
There are two areas through which heat must flow: Theinside tube area and the outside tube area. Resistance
occurs at both areas.
The Industry Standard Reference Area is the Outside Tube
Area.
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Slide 7
INDIVIDUAL COMPONENTS OF THE TOTAL RESISTANCE
Inside Film Resistance = R io = R i
Inside Fouling Resistance = rio
= ri
Tube Wall Resistance = rw = w/ k w
Outside Fouling Resistance = ro
Outside Film Resistance = Ro
Rio + rio + rw + ro + Ro = RT = I
Uw = Wall Thickness, FeetKw = Thermal Conductivity, Btu / Hr x Ft
2 x F
Ft
r = Resistances, Hr x Ft2
x F/Btu
A o
A iA o
A i
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Slide 8
INDIVIDUAL COMPONENTS OF THE TOTAL RESISTANCE
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Slide 9
TYPICAL RESISTANCE VALUES
Very Low Typical Very High
Film Resistances (Each) 0.00050 0.004 0.04
(Inverse = h) (2000) (250) (25)
Fouling Resistance (Each) 0.001 0.002 0.01
Inverse (1000) (500) (100)
Wall Resistance 0.000030 0.00027 0.00049
Inverse (32,000) (3760) (2030)
Total Resistance 0.00303 0.01227 0.10050
Inverse (330) (81) (10)
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Slide 10
THE CONTROLLING COEFFICIENT
Frequently One of the two film coefficients determines the value of the overall
coefficient:
Out side Coefficient, h = 75 75 150
Inside Coefficient, hio = 1000 3000 1000
Ro = 0.01333 0.01333 0.00667
Rio = 0.00100 0.00033 0.00100
rw + rio + ro = 0.00070 0.00070 0.00070
RT = 0.01503 0.01436 0.00837
U = 66.5 69.6 119.5
Improvement = Base +4.6% +80%
Hence his the Controlling Coefficient, and efforts to improve exchanger
performance should concentrate on this side of the exchanger.
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Slide 11
TEMPERATURE DROPS ACROSS THE RESISTANCES
Temperature drop across each of the resistances is
directly proportional to each resistance. For example, If T2 = 200 and T1 = 80, then total temperature
drop = 120F, and:
Temperature Drop
Ro = 0.01333 77.6 = 0.01333 x 120
Rio = 0.00500 29.1 0.02063
rw = 0.00030 1.7
rio+ ro = 0.00200 1.6
RT = 0.02063 120F
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Slide 12
TEMPERATURE DROPS ACROSS THE RESISTANCES
A Useful Concept is Heat Flux = = Btu
Hr x Ft2
Q = U x A x (T2 - T1) = U x A x T
Then T = Q =*
x R = Flux x ResistanceU x A
Then Q = T = 120A RT 0.02063
= 5817 Btu , and T across Ro = 5817 x 0.01333 = 77.6 FHr x Ft
as shown on that slide.
QA
Q
A
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Slide 13
BACK TO BASICS
Weve looked at basic theory, and discussed Q = U x A x T. Inrefinery work we usually know either Q or A, and need to calculate theother value.
How do we do it?
Either question requires calculating U orT. Well talk about Ulater, first lets discuss T, the temperature driving
force.
Note that capital letter T denotes the hot stream, while lower case t
denotes the cold stream:
T1 = Hot In T2 = Hot Out
t1 = Cold In t 2 = Cold Out
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Slide 14
FLOW PATTERNS AND TEMPERATURE DRIVING FORCE
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Slide 15
FLOW PATTERNS AND TEMPERATURE DRIVING FORCE
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Slide 16
FLOW PATTERNS AND TEMPERATURE DRIVING FORCE
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Slide 17
FLOW PATTERNS AND TEMPERATURE DRIVING FORCE
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Slide 18
TEMPERATURE DRIVING FORCE
From the preceding slides, it is clear that some sort of average driving force
must be used in design calculations.
What is this average? The average is called The Effective Mean Temperature Difference, or MTDe.
For true countercurrent and true cocurrent flow, the effective driving force
equals the log mean average of the two extreme (largest and smallest) deltas.
(T1 - t2) - (T2 - t1)Te = LMTD = (T1 - t2)LN (T2 - t1)
This is precisely true only when the heat release curves are straight lines.
Otherwise it is an approximation.
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Slide 19
TEMPERATURE DRIVING FORCE
What about mixed flow: Shell and Tube Exchangers?
The complex flow in these units was analyzed mathematicallymany years ago, resulting in rigorous equations for a
Correction Factor, Fn. This is multiplied by the LMTD to give
the correct MTDe.
MTDe = Fn x LMTD
Equations are valid only when heat release curves are linear.
Similar relations are available for transverse flow (air fin
coolers, for example).
CALCULATION OF F
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Slide 20
CALCULATION OF Fn
Depends on the number of shells in series (Shell Passes)
The more shells one has in series, the closer Fn approaches 1.0
Typically the minimum acceptable value of Fn is 0.8
What exactly do we mean by shells in series or shell
passes?
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CALCULATION OF F SHELL PASSES
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Slide 22
CALCULATION OF Fn - SHELL PASSES
CALCULATION OF F
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Slide 23
CALCULATION OF Fn
Complex equations simplified to charts
See TEMA Section 7, or Exxon DP IX-D
Applicable only to linear heat curves
CALCULATION OF Fn
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Slide 24
CALCULATION OF Fn
Example
T1 = 300 t1 = 85
T2 = 105 t2 = 115
P = j = 115 - 85 = 0.14
300 - 85
R = 300 - 105 = 6.5
115 - 85
Rn
(1 Shell) =
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Slide 25
CALCULATION OF Fn
Since this technique is applicable only to the case of
straight-line heat release, how do we estimate number
of shells and MTDe
for other cases?
NON-LINEAR HEAT RELEASE - MTDe SUGGESTION FOR COMPLEX
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Slide 26
e
CASES SUCH AS REFORMER FEED/EFFLUENT
Plot T Vs. Enthalpy
Step Off to Get MinimumNumber of Shells
Calculate MTDe for Each Shell (Discuss Later)
NON-LINEAR HEAT RELEASE--MTDe
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Slide 27
SUGGESTION FOR CONDENSERS
Plot the condensing curve
Assume cold side is linear and draw in cold side flow pattern
If two shells, assume equal duties
MTD FOR CONDENSERS (Continued)
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Slide 28
MTDe FOR CONDENSERS (Continued)
Calculate the LMTD for each zone, assuming that the cold temperature
in each zone is the average of the inlet/outlet cold temperatures of the
shell in which the zone occurs (see graph)
Then weight the overall MTDe as follows:
MTDe (Weighted) = Qtotal
Qzone1 + Qzone2 + Qzone3 + Qzone4
LMTD1 LMTD2 LMTD3 LMTD4
HEAT TRANSFER COEFFICIENTS
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Slide 29
HEAT TRANSFER COEFFICIENTS
Film coefficients are relatively easy to estimate:
They are a function of
Reynolds Number DV
Prandtl Number (Cp) ()K
Similarly, pressure drop is a function of Reynolds number and length of
flow path.
HEAT TRANSFER COEFFICIENTS (Continued)
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Slide 30
HEAT TRANSFER COEFFICIENTS (Continued)
The handouts just examined are suitable ONLY forestimates
of coefficients.
For detailed coefficients on which to base the purchase of an
exchanger, detailed computer calculations are necessary.
Detailed computer calculations examine the effects of many
other parameters, particularly shell-side effects such aschanneling and baffle leakage.
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EXCHANGER DESIGN PROCEDURE
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Slide 32
EXCHANGER DESIGN PROCEDURE
First need to know:
Permissible tube sizes - diameter, gauge, length.
(Frequently set by refinery maintenance department)
The appropriate tube material for the service
The allowable system pressure drops for each stream.
EXCHANGER DESIGN PROCEDURE (Continued)
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Slide 33
( )
(1) Assume an overall heat transfer coefficient (Uo) and calculatetube surface area (A).
(2) Using the required tube size and length, calculate the number
of tubes.
(3) Using a reasonable tube-side velocity (0.6-4.5 m/s), calculate
the tubeside cross sectional area required for each tube pass:Acs = m3/s
m/s
(4) Determine the EVEN number of tube passes which will mostclosely approximate the needed flow area.
# tubes/pass= Acs
/ single tube cross sectional area# passes = (# tubes/pass) / # tubes
EXCHANGER DESIGN PROCEDURE (Continued)
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Slide 34
( )
(5) Calculate the bundle diameter.
(6) Using a reasonable value of shell-side velocity, calculate theflow area required between shell-side baffles (gives baffle
spacing).
(7) Calculate tube-side and shell-side pressure drop. If
satisfactory, continue to step 8. If not, modify the exchanger
geometry until pressure drop requirements are met.
(8) Calculate the overall coefficient U.
(9) Compare [U(calculated) x A x MTDe ] with the required value of
Q. If it doesnt agree within about 10%, then change exchanger
geometry and repeat calculations.
HEAT EXCHANGER DESIGN
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Slide 35
There are several major types of heat exchanger used in
refineries/chemical plants:+ Shell-and-Tube
+ Air-Fin Coolers
+ Double-Pipe
+ Plate and Frame
The vast majority are S & T.
We will briefly review usage of the minor types and then
concentrate on the features of shell-and-tube exchangers.
AIR COOLED EXCHANGERS
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Slide 36
Used for cooling high to medium temperature streams where
heat recovery is not practical
Consists of tube bundle and motor driven fans
Can be forced or induced draft
Can be countercurrent or cocurrent to air flow
Tubes are usually equipped with circumferential fins
Design outlet temperature is limited by ambient air temperature
Detailed design of air-fins is left to the individual vendors.
Process Designers simply provide duty specification.
DOUBLE PIPE
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Slide 37
Consists of one or more pipes within a larger pipe
Internal pipes can be bare surface or have longitudinal fins
True cocurrent or true countercurrent flow can be achieved
Available in standard off-the-shelf sizes
Several standard units may be connected in series or inparallel
Not usually economical where surface requirements exceed
about 500 square feet
Especially suited for high-pressure applications
PLATE AND FRAME
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Slide 38
Consists of a series of alternating corrugated plates
pressed together in a compression frame
Process fluids flow on alternate sides of the plates in
channels formed by the corrugations
Units achieve true countercurrent flow
PLATE AND FRAME (Continued)
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Slide 39
ADVANTAGES
True countercurrent flow
Highly compact - take up much less space than an equivalent S& T
Much less expensive than S & T
Very small holdup of process fluids
Small probability for cross contamination of the two fluids
DISADVANTAGES
Limited to moderate temperatures and pressures (up to about
300F / 150C and 300 psig / 21 barg)
Some hydrocarbon streams attack the interplate gasketing
Require great time in assembly/disassembly
Best suited to aqueous streams, e.g. amines, water
SHELL AND TUBE
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Slide 40
Most common type in refinery service
Consists of tube bundle within external shell
Not truly cocurrent or countercurrent
NOMENCLATURE
Components of Shell and Tube Exchangers
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Slide 41
p g
1. SHELL 8. FLOATING HEAD COVER FLANGE 16. IMPINGEMENT BAFFLE
2. SHELL COVER 9. CHANNEL PARTITION PLATE 17. VENT CONNECTION
3. SHELL FLANGE 10. STATIONARY TUBESHEET 18. DRAIN CONNECTION
4. SHELL COVER END FLANGE 11. CHANNEL 19. TEST CONNECTION
5. SHELL NOZZLE 12. CHANNEL COVER 20. SUPPORT SADDLES6. FLOATING HEAD TUBESHEET 13. CHANNEL NOZZLE 21. LIFTING RING
7. FLOATING HEAD COVER 14. TIE RODS AND SPACERS 22. SPLIT RING
15. TRANSVERSE BAFFLES
OR SUPPORT PLATES
MAJOR TYPES OF S & T UNITS
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Slide 42
Fixed tube sheet (uncommon)
Floating tube sheet
+ Pull-through floating head
+ Split ring floating head
U-Tube
SHELL & TUBE EXCHANGERS
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Slide 43
Fixed Tube Sheet
Cleanest. Consider only when shell side fouling factor 0.004(m2*C/W) and shell side can be chemically cleaned.
Because of thermal stresses, this type is generally unacceptable if the
average shell temperature and average tube temperature differ by more
than 10C
U-Tube
Least expensive for high tubeside design pressure. Normally used
when tubeside fouling 0.004. (except for water)Split Ring Floating Head
This type is normally specified unless very frequent mechanical
cleaning is required
Pull-Through Floating Head
Most expensive type of S & T unit; thermally inefficient because of
shell bypassing. Use when both sides must be mechanically cleaned
PRELIMINARY DECISIONS:DESIGN OF SHELL-AND-TUBE UNITS
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Slide 44
Which fluid to put in the tubes
Tube nominal diameter, wall thickness and material
Tube length
Tube layout
Baffle orientation
Baffle pitch (spacing)
Maximum bundle diameter (bundle weight)
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TYPICAL TUBE DIAMETERS/WALL THICKNESS
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Slide 46
1. Oil Service - Ferrous Tubes Layout and
Severity of Service OD, In. Spacing, In. BWG Thickness, In.
Non-Fouling or Fouling 3/4 15/16 14 0.083(
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Slide 47
Refinery decision (local preference)
Most common length is 20 feet (6.1m)
Occasionally, 16 (4.9m) length is used
For special situations, 8 (2.4m) and 10 (3m) can be
considered
Longer tube bundles require more plot area for bundle
removal. Longer bundles are also more difficult to extract
from the shell and to handle.
TUBE LAYOUT
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Slide 48
3 Main Layouts--
Square 1. Use when ro > 0.004 and shellside
must be mechanically cleaned.
2. Reboilers/Vaporizers
Rotated Square Use as square, but only when flow is
laminar or for vibration problems
Triangular 30 1. Use when ro 0.0042. Cheapest, so use when applicable
TYPE OF BAFFLE
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Slide 49
Segmental - Most common
Double Segmental (modified disk and donut) is used to
obtain very low shell-side pressure drop
Tube Supports Only - No real baffles. Occasionally used
in certain reboiling or condensing services.
BAFFLE ORIENTATION AND CUT
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Slide 50
Vertical Chord - Most Common
Condensers, vaporizers and fluids containing suspended solids
Flow is side-to-side
Horizontal Chord
Sediment-free fluids being cooled through high temperature
range (200 to 300F / 90-150 C) in one shell
Flow is over-under
Baffle Cut
This is the percent of the baffle which is cut away to permit flow
Typical cut is 25% (40% for double segmental baffles).
BAFFLE PITCH
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Slide 51
Minimum allowable spacing (pitch) is 20% of the shell ID or two
inches, whichever is greater.
Maximum allowable pitch:
+ For no change of phase, equals shell ID
+ For change of phase
Tube Size Steel Copper Alloys 30 261 37 321 50 43.5
TEMA
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Slide 52
Tubular Exchanger Manufacturers Association
This is the basic industrial standard for shell-and-tube
exchangers
Covers heavy-duty type (TEMA R) as well as the lighter
duty (TEMA C) units
Latest edition is the eighth dated 1999
TEMA TYPE
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Slide 53
TEMA Type followed by three letters refers to the type of
+ Front end (channel) arrangement
+ Shell nozzle/baffle arrangement+ Rear end (floating head end) arrangement
These three characteristics are each identified by a single letter
of the alphabet
The result, for example, would be the entry TEMA Type AES
in the specification for the heat exchangers. The type MUST be
specified.
MOST COMMON TEMA TYPESFront End (Channel) Arrangement
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Slide 54
A Removable channel with removable cover plate
May be used with fixed or removable tube bundles
Tube cleaning easier since no piping disassembly required Flanged channel end is costly and prone to leakage
Most commonly used
B Removable channel with integral cover
May be used with fixed or removable tube bundles
Used for low tube side fouling services or where chemical
cleaning is specified. Mechanical cleaning requires piping
disassembly
Less costly and less prone to leakage than type A
C Channel integral with tubesheet and with removable cover
Two types: removable bundle and fixed bundle
MOST COMMON TEMA TYPES (Continued)
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Slide 55
Shell TypesE One pass shell
Most common type used
F Two pass shell with longitudinal baffle Used to improve cross flow correction factor Equivalent to two shells in series Maximum shellside pressure drop of 10 PSI Maximum shellside temperature range of 350 F
G/H Split flow arrangements Use internal baffles to split the shellside flow
Used to minimize pressure dropJ Divided flow
Also used to minimize pressure drop No internal baffle
K Kettle types Used for vaporizing services (reboilers, steam generators and
refrigeration services)X Cross flow
No baffles Low pressure drop
MOST COMMON TEMA TYPES (Continued)
R E d H d
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Slide 56
Rear End Head
S Floating tubesheet sandwiched between split ring and tubesheet cover Tubesheet assembly moves within shell cover to absorb expansion of the tubes
Requires removing rear shell cover and floating tubesheet cover forbundle removal, but results in a smaller diameter shell for the same heattransfer surface
Usually first choice for removable bundles if mechanical cleaning of shell sidewill be infrequent
T Pull through floating head Floating tubesheet cover bolted directly to floating tubesheet
Does not require rear head disassembly for bundle removal Results in larger diameter shell for same heat transfer surface than Type S Preferred where frequent mechanical cleaning of shellside is anticipated
U U-tube bundle No floating head. Tube bundle consists of U-tubes Not recommended where mechanical cleaning of tube side is anticipated Good for high pressure, clean services or where chemical cleaning of
tubeside is specified
TEMA HEAT EXCHANGER NOMENCLATUREDP IX-C Figure 2
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Slide 57
Notes: 1. Commonly referred to as channel or channel box.
2. Commonly referred to as bundle types.
3. Recommended for condensers and thermosiphons.
4. Recommended for thermosiphon reboilers only.
MOST COMMON TEMA TYPES (Continued)
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Slide 58
Therefore a TEMA AES exchanger has
A = Removable channel and removable channel cover plate
E = One pass shell (one inlet nozzle and one outlet nozzle)
S = Split ring type floating tube sheet construction
HEAT INTEGRATION PRINCIPLES
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Slide 59
Object is overall minimum surface/number of shells
Try to achieve maximum LMTDs
Avoid temperature crosses if possible
Incremental surface is cheaper than more shells
Do not match streams with large differences in
Heat content
Volume
HEAT INTEGRATION PROCEDURES
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Slide 60
Identify all heat sources and heat sinks
Prepare T-Q curves for sources and sinks
Match sources and sinks according to
principles
Try different arrangements using typical Uos to
estimate total surface
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Slide 61
Problem 5A
Heat Integration
TABLE 1.01DESIGN CONSTANTS FOR SHELL AND TUBE EXCHANGER CALCULATIONS
SHELL SIDE
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Slide 62
SHELL SIDE
Maximum Allowable Baffle Pitch Maximum Pb, Inches
Tube O.D. Inches Steel Copper, Aluminum Alloys
0.75 30.0 26.0
1.00 37.0 32.01.50 50.0 43.5
(For no change of phase, Pb should not exceed the shell ID.
Heat Transfer & Pressure Drop Factor B1 and B2
Baffle Position Tube Layout Transfer B1 Pressure Drop B2
Vertical to tube rows Square 0.50 0.30
On the bias (45) Square 0.55 0.40
Vertical to tube rows Triangular 0.70 0.50
Pressure Drop Fouling Factors, Fs
Fluid Fs
Liquids 1.15
Gases or condensing vapors 1.00
TUBE SIDE
Pressure Drop Fouling Factors Typical Tube Pitch
Tube O.D. Inches Ft Tube O.D. Inches Pitch In
0.75 Steel 1.50 0.75 Triangular 0.93751.00 Steel 1.40 0.75 Square 1.0
1.50 Steel 1.20 1.0 Square 1.25
0.75 Copper Based 1.20 1.5 Square 1.875
1.00 Copper Based 1.15
TABLE 1.01DESIGN CONSTANTS FOR SHELL AND TUBE EXCHANGER CALCULATIONS
(Continued)
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Slide 63
TUBE SIDE (Continued)
Design Cooling Water Velocity
Most Favorable Permissible
Material Type of Water Velocity, ft/sec Range, ft/sec (4)
Carbon Steel Fresh, non-inhibited 4 3 to 6
Fresh, inhibited 6 to 8 3 to 10
Red brass All types 6 to 8 3 to 4
Admiralty (inhibited) Fresh (inhibited or not) 6 to 8 3 to 10
Salt or brackish 3 3 to 5
Aluminum brass Fresh (inhibited or not) 6 to 8 3 to 10
Salt or brackish 5 4 to 8
Cupronickel (70-30) All types 7 to 8 6 to 12
Cupronickel (90-10) All types 7 to 8 6 to 12
Monel All types 8 6 to 12
Type 316 alloy steel All types 10 8 to 15
TABLE 1.02 - EXCHANGER TUBE DATAdo= O.D. of = Wall di = I.D. of Internal Cross External SurfaceTubing In BWG Thickness In (3) Tubing In Sectional Area Sq In Per Foot Length Sq Feet
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Slide 64
Tubing, In. BWG Thickness In. (3) Tubing, In. Sectional Area Sq. In. Per Foot Length Sq. Feet
12 0.109 0.532 0.223 0.1963
14 0.083 (1) 0.584 0.268 0.1963
16 0.065 (2) 0.620 0.302 0.1963
18 0.049 0.652 0.334 0.1963
1 10 0.134 0.732 0.421 0.2618
1 12 0.109 (1) 0.782 0.479 0.2618
1 14 0.083 (2) 0.0834 0.546 0.2618
1 16 0.065 0.870 0.594 0.2618
1 10 0.134 1.232 1.192 0.3927
1 12 0.109 1.282 1.291 0.3927
1 14 0.083 1.334 1.397 0.3927
GAGE EQUIVALENTS MAXIMUM RECOMMENDED NUMBER OF TUBE PASSESInches BWG Shell ID Inches Max. Passes
0.220 5
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Slide 65
Admiralty (71 Cu - 28 Zn - 1 Sn) 64
Type 316 Stainless Steel (17 Cr - 12 Ni - 2 Mo) 9
Type 304 Stainless Steel (18 Cr - 8 Ni) 9
Brass (70 Cu - 30 Zn) 57Red Brass (85 Cu 15 Zn) 92
Aluminum Brass (76 Cu - 22 Zn - 2 Al) 58
Cupro-Nickel (90 Cu - 10 Ni) 41
Cupro-Nickel (70 Cu - 30 Ni) 17
Monel (67 Ni - 30 Cu - 1.4 Fe) 15
Inconel 11
Aluminum 117Carbon Steel 26
Carbon-Moly Steel (0.5 Mo) 25
Copper 223
Lead 20
Nickel 36
Titanium 11
Chrome-Moly Steel (1 Cr - 0.5 Mo) 24
(2-1/4 Cr - 0.5 Mo) 22
(5 Cr - 0.5 Mo) 20
(12 Cr - 1 Mo) 16
TABLE 1.04TYPICAL FOULING FACTORS - CUSTOMARY
St T T i l
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Stream Type Typical ri or ro
Vapor Overheads 0.001
Virgin Distillate liquids to tankage 0.001
Virgin Distillate liquids from tankage 0.002
Cracked distillate liquids from tankage 0.002
Reduced Crudes 0.004
Tar, bitumen 0.005
Cracked Tar 0.010
Crudes 0.0102-0.004
Steam 0.001
BFW 0.001
Cooling Water, Fresh 0.0015 - 0.0025
Cooling Water, Salt 0.0025 -0.0035
TABLE 1.05SOME TYPICAL OVERALL COEFFICIENTS - CUSTOMARY
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Slide 67
Type of Source Typical Uo
Light Ends Liquid Coolers (Water) 120
Distillate Coolers (Water) 70-90
Light Ends Reboilers (Steam) 80
Light Ends Feed/Bottoms 100
Crudes/distillates 25-50Condensers (Tower overheads) 90
NOMENCLATUREA - Total exchanger are, ft2 Ro - Outside film resistance to heat transfer, (Note 1).
As - Area/shell, ft.2 Rt - Total resistance (duty) to heat transfer (Note 1).
B1 - Bundle factor for shell side heat transfer rio - Inside fouling factor corrected to outside area (Note 1)
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B1 Bundle factor for shell side heat transfer rio Inside fouling factor corrected to outside area, (Note 1).
B2 - Bundle factor for shell side pressure drop , dimensionless ro - Outside fouling factor (Note 1).
C - Specific heat at caloric temperature, Btu/Lb -F. rw - Resistance of tube wall metal at average wall temperature(Note 1).
Cf - Specific heat of the shell side fluid at average S - Free flow area between shell baffles, in.2
film temperature, Btu/lb-F TDS - Design temperature of the shell side, F.
D - Shell I.D., inches TDT - Design temperature of the tube side, F.
Dt - Diameter of tube bundle (outer tube limit), inches TM - Tube sheet design temperature, F.di - Tube I.D., inches T1 - Inlet temperature of fluid being cooled, F.
do - Tube O. D., inches T2 - Outlet temperature of fluid being cooled, F.
Fn - Correction factor for log mean temperature difference t1 - Inlet temperature of fluid being heated, F.
(due to partially concurrent flow), dimensionless t2 - Outlet temperature of fluid being heated, F.
Fs - Shell side pressure drop correction factor, dimensionless tf - Average shell side film temperature, F.
Ft - Tube side pressure drop correction factor, dimensionless ts - Caloric temperature of the shell fluid, F.
G - Mass velocity, lbs/sec - ft2 tt - Caloric temperature of the tube fluid, F.
hio - Inside film coefficient corrected to outside area, Btu/hr-ft2-F. tw - Average tube wall temperature, F.
ho - Outside film coefficient Btu/hr-ft2 -F Uc - Over-all clean coefficient of heat transfer, Btu/hr-ft
2-F.
k - Thermal conductivity at caloric temperature, Btu/hr-ft2-F/Ft. Uo - Over-all duty coefficient of heat transfer, Btu/hr-ft2-F.
kf - Thermal conductivity of the tube metal at average tube V - Velocity in the tubes or shell ft/sec.temperature, Btu/hr-ft2-F/ft VN - Velocity in the nozzles, ft/sec.
kw - Thermal conductivity of the tube metal at average W - Free width between baffles, in.
tube temperature Ysh - Shell side heat transfer correlation factor.
L - Tube wall thickness, in. Ysp - Shell side pressure drop correlation factor.
L - Tube length, ft. Yth - Tube side heat transfer correlation factor.
M - Mass rate, lbs/hr. Ytp - Tube side pressure drop correlation factor.
M - Density, lbs/ft3 z - Viscosity at caloric temperature, centipoises.
NB - Number of shell baffles zf - Viscosity of the shell side fluid at average film temperature, centipoises.
NP - Number of tube passes per shell. zw - Viscosity of the tube side fluid at tube wall temperature, centipoises.
NRe- Reynolds number, inch-lbs/sec-ft2 - centipoise Ptf - Tube pressure drop due to friction, psi/tube pass.
NS - Number of shells in series. Ptr - Tube pressure drop due to turns, psi/tube pass.
NT - Number of tubes across in the bundle Pt - Total tube side pressure drop, psi.NTC - Number of tubes across the center line of the bundle Psf - Shell side pressure drop due to friction, psi/shell.
Pb - Baffle pitch, inches. Psr - Shell side pressure drop due to friction, psi/shell.
Pt - Tube pitch, inches. PN - Nozzle Pressure drop, psi/shell.
Q - Rate of heat transfer, Btu/hr. Ps - Total shell side pressure drop, psi.
RC - Total resistance (clean) to heat transfer (Note 1) te - Long mean temperature difference corrected for non-ideal countercurrent
Rio - Inside film resistance corrected to outside area, (Note 1) flow (Effective temperature difference) F.
tew - Weighted effective log mean difference, F.
FIGURE 1.01 - LMTD CORRECTION FACTORS
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FIGURE 1.02 - LMTD CORRECTION FACTORS
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Slide 70
FIGURE 1.03 - LMTD CORRECTION FACTORS
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Slide 71
FIGURE 2.01FRICTIONAL PRESSURE DROP FOR FLUIDS FLOWING IN TUBES
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Slide 72
FIGURE 2.02HEAT TRANSFER COEFFICIENT FOR FLUIDS IN TUBES
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Slide 73
FIGURE 5.01FRICITONAL PRESSURE DROP FLUIDS FLOWING ACROSS TUBE BANKS
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Slide 74
FIGURE 5.02HEAT TRANSFER COEFFICIENT FLUIDS FLOWING ACROSS TUBE BANKS
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Slide 75
FIGURE 5.01VALUES OF THE THERMAL FUNCTION k(PRANDTL NO.)1/3 FOR LIQUID HYDROCARBONS
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Slide 76
FIGURE 5.02VALUES OF THE THERMAL FUNCTION K(PRANDTL NO.)1/3 FOR HYDROCARBON VAPORS
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Slide 77
ADDENDUM 5.02
FOR FLOW INSIDE TUBES APPROXIMATE EFFECT OF VARIABLES IN THE TRANSFER OF MOMENTUM AND
HEAT
To Find P2 To Find h2P t Ch d M lti l P1 B M lti l h1 B
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Slide 78
Property Changed Multiply P1 By: Multiply h1 By:NRe > 10,000 (Note 1) Turbulent Flow
Linear Velocity (V2/V1)1.8 (V2/V1)0.8
Tube Diameter (at constant linear velocity) (D1/D2)1.2 (D1/D2)
0.2
Viscosity (2/1)0.2 (2/1)0.5Density (at constant linear velocity) (2/1)0.8 (2/1)0.8NRe > 2,100 (Note 1) Laminar Flow*
Linear Velocity V2/V1 (V2/V1)0.33
Tube Diameter (at constant linear velocity) (D1/D2)2 (D1/D2)
0.33
Tube Diameter (at constant weight rate) (D1/D2)4 D1/D2
Density (at constant linear velocity No dependence (2/1)0.33Tube Length L
2
/L1
(L1
/L2
)0.33
Note 1: This is dimensionless Reynolds Number.
HEAT EXCHANGE EQUIPMENTDESIGN CONSIDERATIONS FOR ALL
TYPES OF HEAT EXCHANGERSPROPIETARY INFORMATION -For Authorized Company Use Only
EXXON DESIGN PRACTICES
Date
PageSection I X-B
TABLE 1
TYPICAL OVERALL HEAT TRANSFER COEFFICIENTS - U
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Slide 79
TYPICAL OVERALL HEAT TRANSFER COEFFICIENTS - Uo
U0(1) U0
(1)
Fluid Being Cooled Fluid Being Heated BTU W
Hr ft2 F m2 C
Shell and Tube Units with Smooth Tubes
Exchangers
Atmospheric P/S Top Pumparound Crude 60 - 70 340 - 400
Atmospheric P/S No. 3 S/S Crude 48 - 58 270 - 330Atmospheric P/S Bottom Pumparound Crude 55 - 85 310 480
Atmospheric P/S Bottoms Crude 26 45 150 - 260Reduced Crude Flashed Crude 25 140Lean Oil Fat Oil 60 340
Hydrocracker Effluent Hydrocracker Feed 75 430
Hydrogenation Reactor Effluent Hydrogenation Reactor Feed 51 55 290 310
Hydrofiner Effluent Hydrofiner Feed 50 68 280 390
Debutanizer Effluent Debutanizer Feed 70 400
Powerformer Effluent Powerformer Feed 50 80 280 450
Acetylene Converter Feed Acetylene Converter Effluent 22 30 120 170
Regenerated DEA Foul DEA 110 630
Catalyst-Oil Slurry Gas Oil Feed 40 230
Cracking Coil Vapors Gas Oil 30 170
Rerun Still Overhead Rerun Still Feed 50 280
Splitter Overhead Debutanizer Feed 55 310
HEAT EXCHANGE EQUIPMENTDESIGN CONSIDERATIONS FOR ALL
TYPES OF HEAT EXCHANGERSPROPIETARY INFORMATION -For Authorized Company Use Only
EXXON DESIGN PRACTICES
Date
PageSection I X-B
TABLE 1 - (Continued)
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Slide 80
U0(1) U0
(1)
Fluid Being Cooled Fluid Being Heated BTU W
Hr ft2 F m2 C
Coolers
Water Water 150 210 (2) 850 - 1190
Brine Sour Water 100 115 570 650
Debutanizer Bottoms Water 68 75 390 430
Debutanizer Overhead Products Water 85 90 480 - 510
Debutanizer Bottom Products Water 43 240
Vacuum P/S Bottoms Water 20 25 110 - 140
Absorber Oil Water 80 450
Lean Oil Water 70 400
Heavy Gas Oil Water 40 230Regenerated DEA Water 110 630
Reduced Crude Water 29 32 160 180
Gas Coolers
Air, 27 psig (186 kPa gage) Water 13 70
105 psig (724 kPa gage) Water 17 100
320 psig (2206 kPa gage) Water 23 130
Primary Fractionator Gas Water 27 150
Hydrocarbon Vapors (30 M.W.) Water 38 43 220 240
Hydrocarbon Vapors (25 M.W.) Water 55 60 310 340
Propylene Water 50 280
Ethylene Water 31 180
HEAT EXCHANGE EQUIPMENTDESIGN CONSIDERATIONS FOR ALL
TYPES OF HEAT EXCHANGERSPROPIETARY INFORMATION -For Authorized Company Use Only
EXXON DESIGN PRACTICES
Date
PageSection I X-B
TABLE 1 - (Continued)
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Slide 81
U0(1) U0
(1)
Fluid Being Cooled Fluid Being Heated BTU W
Hr ft2 F m2 CCondensers
Atmospheric P/S Overhead Water 80 90 450 510
Atmospheric P/S Overhead Crude 35 45 200 260
Atmospheric P/S Distillate Water 70 80 400 - 450
Vacuum P/S Overhead Water 115 130 650 740
Debutanizer Overhead Water 90 100 510 570
Deethanizer Overhead Water 110 620
Depentanizer Overhead Water 90 113 510 640
LPG Tower Overhead Water 99 560Hydrofiner Effluent Water 91 105 510 600
Stabilizer Overhead Water 75 85 430 480
Splitter Overhead Water 85 113 480 640
Rerun Still Overhead Water 70 400
DEA Regenerator Overhead Water 100 570
Primary Fractionator Overhead Water 40 (50% cond) 230
Primary Fractionator Overhead & Products Water 60 (25% cond) 340
Powerformer Effluent Water 55 60 310 340
Hydrocracker Effluent Water 85 480
Propylene Water 120 680Steam (3) Water 400 600 2270-3410
HEAT EXCHANGE EQUIPMENTDESIGN CONSIDERATIONS FOR ALL
TYPES OF HEAT EXCHANGERSPROPIETARY INFORMATION -For Authorized Company Use Only
EXXON DESIGN PRACTICES
Date
PageSection I X-B
TABLE 1 - (Continued)
U0(1) U0
(1)
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Slide 82
U0 U0
Fluid Being Cooled Fluid Being Heated BTU W
Hr ft2 F m2 C
Chillers
Ethylene (4) Propylene 98 560
Demethanizer Overhead (4) Ethylene 107 610
Deethanizer Overhead (4) Propylene 113 640
Depropanizer Overhead (4) Propylene 115 650
Ethylene Ethylene 99 105 560 600
Demethanizer feed Ethylene 96 113 550 640
Demethanizer Feed Propylene 100 122 570 690
Reboilers
Steam Demethanizer Bottoms 75 430
Lean Oil Demethanizer Bottoms 60 340
Steam Deethanizer Bottoms 73 86 410 490
Atmospheric P/S Top Pumparound Deethanizer Bottoms 66 370
Steam Depropanizer Bottoms 89 510
Steam Debutanizer Bottoms 74 100 420 570
Atmospheric P/S Top Pumparound Debutanizer Bottoms 65 370
Atmospheric P/S Bottoms Debutanizer Bottoms 56 320
Steam Depentanizer Bottoms 81 460Steam Debenzenizer Bottoms 102 580
Steam Detoluenizer Bottoms 77 440
Steam Splitter Bottoms 80 450
HEAT EXCHANGE EQUIPMENTDESIGN CONSIDERATIONS FOR ALL
TYPES OF HEAT EXCHANGERSPROPIETARY INFORMATION -For Authorized Company Use Only
EXXON DESIGN PRACTICES
Date
PageSection I X-B
TABLE 1 - (Continued)
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Slide 83
U0(1) U0
(1)
Fluid Being Cooled Fluid Being Heated BTU W
Hr ft2 F m2 C
Reboilers (Continued)
Dowtherm Splitter Bottoms 70 400
Steam Stripper Bottoms 82 470
Steam Stabilizer Bottoms 115 650
Steam Rerun Tower Bottoms 74 420
Dowtherm Rerun Tower Bottoms 47 270
Steam LPG Bottoms 70 400
Powerformer Effluent Powerformer Stabilizer Bottoms 75 77 430 440Steam K3PO4 Stripper Bottoms 145 820
Steam DEA Regenerator Bottoms 240 1360
Dowtherm Phenol 65 370
Preheaters
Steam Isobutane Tower Feed 82 520
Steam Rerun Tower Feed 80 100 450 570
Steam Debutanizer Tower Feed 110 620
Steam Hydrogenation Reactor Feed 75 89 430 510
Powerformer Stabilizer Bottoms Powerformer Stabilizer Feed 47 270
HEAT EXCHANGE EQUIPMENTDESIGN CONSIDERATIONS FOR ALL
TYPES OF HEAT EXCHANGERSPROPIETARY INFORMATION -For Authorized Company Use Only
EXXON DESIGN PRACTICES
Date
PageSection I X-B
TABLE 1 - (Continued)
U (1) U (1)
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Slide 84
U0(1) U0
(1)
Fluid Being Cooled Fluid Being Heated BTU W
Hr ft2 F m2 C
Steam Generators
Vacuum P/S Bottoms Feed Water 35 200
Vacuum P/S Bottom Pumparound Feed Water 67 86 380 490
Primary Fractionator Slurry Feed Water 30 55 170 310
Flue Gas Feed Water 8 15 50 90
Reformer Effluent Feed Water 45 60 260 340
Longitudinal Fin Units (Coefficients based on total outside surface)
Heavy Naphtha Water (6 ft/sec(1.8m/s) in annulus) 25 140
Water (3 ft/sec(0.9 m/s) in annulus) 20 110Light Naphtha Water (6 ft/sec(1.8 m/s) in annulus) 30 170
Water (3 ft/sec(0.9 m/s) in annulus) 25 140
Clean K3PO4 Water 40 230
Clean K3PO4 Foul K3PO4 42 240
Notes:
1. Coefficients given represent a range of typical coefficients. Where only one coefficient given, typical
coefficients can be higher or lower than the tabulated value.
2. Coefficient highly dependent on fouling factors.
3. Steam surface condenser. Refer to Heat Exchange Institute Standards for Steam Surface Condensers.
4. Condensing Service.
Attachment IX - Safety Factor Selection
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Slide 85
Correction Factor for Non-Condensables Calculation Procedure
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Slide 86See HEXTRAN Users Guide, located in HEXTRAN program folder
Attachment IXB - Pressure-Drop-Multiplier Selection
See also DP IX-D p. 40-41
Tubeside Pressure-Drop Multiplier (DPSCALAR)
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Slide 87
Attachment IXB - Pressure-Drop-Multiplier Selection (cont.)See also DP IX-D p. 40-41
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Slide 88
Shellside Pressure-Drop Multiplier (DPSCALAR)
Fluid DPSCALARLiquids 1.15 (1)
Gases or condensing vapors 1.0 (2)(1) This value may be increased for extremely dirty service(2) Use a larger number if vapors are known to be fouling.
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Heat transfer enhancement is obtained by increasing heat transfer coefficient, surface
are per unit volume or temperature driving force
Q = U x A x MTD
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Slide 90
PHE - Increase U by turbulence and MTD by countercurrency
SHE - Increase U by turbulence and MTD by countercurrency
RBE - Increase U by allowing higher flow rate
IFT - Increase A of tube surface; Increase U for condensing and vaporizing
NBT - Increase U by enhancing vaporizing heat transfer
TP - Increase U by enhancing HI
OMC - Increase U by reducing fouling; some types also increase HI
PLATE TYPE HEAT EXCHANGERS (PHE)
WHAT DOES IT DO?
It is an alternative to shell-and-tube exchangers.
P id t h t h b f hi h f it
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Slide 91
Provides a compact heat exchanger because of high surface area per unit
volume
Provides true counter current flow and high heat transfer coefficientsTypical Applications - Final product cooling (close approach
Tempered water cooling
Low temperature feed/effluent exchanger
Sea water cooling (high metallurgy)
WHAT DOES IT LOOK LIKE?
Multiple streams possible
PLATE & FRAME WELDED PLATE PLATE-FIN
WHAT DOES IT DO?
It is an alternative to shell-and-tube exchangers.
Provides a compact heat exchanger because of high surface area per unit
SPIRAL HEAT EXCHANGERS (SHE)
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Slide 92
Provides a compact heat exchanger because of high surface area per unit
volume
It can handle fluids with high viscosity or high solid particle contentTypical applications - Final product cooling (close approach)
Overhead condensers (tower top)
Tar cooling (high viscosity)
Slurry exchangers (solids)
WHAT DOES IT LOOK LIKE?
Two plates rolled together. Spacing maintained by studs.
ROD BAFFLEHEAT EXCHANGERS (RBE)
WHAT DOES IT DO?
It eliminates tube vibration in shell-and-tube heat exchangers
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Slide 93
It allows debottlenecking of pressure drop limited exchangers
Typical applications - To correct known vibration problemsCompressor inter/after coolers (high velocity
gas)
Reboilers (high velocity vapor or two-phase)
WHAT DOES IT LOOK LIKE?
Rod baffles replace conventional baffles on a S&T tube bundle
INTEGRAL FIN TUBES (IFT)
WHAT DOES IT DO?
Provides higher heat transfer area compared to plain tubes
Enhances shell side heat transfer coefficient in two phase applications
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Slide 94
Enhances shell side heat transfer coefficient in two-phase applications
Typical applications - Overhead condensers
Compressor inter and after coolers
Good for single or change of phase
WHAT DOES IT LOOK LIKE?
Commonly referred to as low-fin tubes
Note that ID is smaller than plain tube of same OD and thickness
New fin geometries developed and double (inside and outside) enhanced tubesare available.
NUCLEATE BOILING TUBES (NBT)
WHAT DOES IT DO?
Increases shell side heat transfer coefficient for boiling services
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Slide 95
g
Typical Applications - horizontal reboilers - shell side boiling
vertical reboilers - tubeside boilingexcellent in refrigeration systems (C3 reboilers)
WHAT DOES IT LOOK LIKE?
Coating on inside or outside tube surface (UOP high flux)
special fin geometry (Wieland)
TURBULENCE PROMOTERS (TP)
WHAT DOES IT DO?
Increases tubeside heat transfer coefficient by the following mechanisms:
Thermal mixing through bulk or near-wall flow disturbance
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Slide 96
Disruption of thermal boundary layer by changing bare tube surface
Impart swirl to mix flow, change flow direction or both
Typical Applications - Tar oil heating (high viscosity)
Lube oil cooling (high viscosity)
Tubeside condensers (increase HI and AI)
WHAT DOES IT LOOK LIKE?
BULK FLOW MIXERS
(LAMINAR OR TRANSITION)
NEAR-WALL MIXERS
(TURBULENT)
ON-LINE MECHANICAL CLEANING (OMC)
WHAT DOES IT DO?
Keep shell-and-tube heat exchangers clean, on the run
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Slide 97
Typical Applications - Crude preheat with crude on tube side
Hydrofiner feed on tube sideCooling water on tubeside
WHAT DOES IT LOOK LIKE?
Devices are permanently installed in the bundle
SPIRELF TURBOTAL BRUSH & BASKET
LOGIC DIAGRAM TO SELECT EHT
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Slide 98
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Ad d t ith t h l i
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Slide 99
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O Computer Programs
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HEAT EXCHANGER REFERENCES
Design Practices, Section IX (Heat Exchangers) and
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Slide 100
Design Practices, Section IX (Heat Exchangers) and
XIV (Fluid Flow)
Global Practices (GPs), Section 6
Heat Exchanger Specialists:
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AMERICAS(LACURCI)
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(LESEREB)
ADDENDUM 5.01
SECTION 5 - PROCESS DESIGN COURSE - HEAT EXCHANGER DESIGN
A shortcut procedure for approximate evaluation of shell and tube exchangers with no change of phase
IMPORTANT NOTE AND WARNING:
This procedure must not be used for the definitive design of heat exchangers. It is a shortcut
t h i hi h k i lif i ti i ll ith d t h ll id
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Slide 101
technique which makes many simplifying assumptions, especially with regards to shell-side
calculations
The Reynolds Number used in this addendum is dimensional.
INDEX
DESCRIPTIVE MATERIAL1. LMTD & Caloric Temperature/Properties2. Shell Side, Tube Side Flowrates3. Fouling4. Tube Side Calculations5. Shell Side Calculations
6. Duty & Clean Coefficients7. Design Temperature of Tube Sheet8. Calculation Form9. Nomenclature Summary
TABLE1.01 General Design Constants1.02 Exchanger Tube Data1.03 Thermal Conductivities of Metals1.04 Typical Fouling Factors1.05 Typical Overall Coefficients
FIGURES1.01-1.03 Fn Factors2.01-2.02 Tube Side Correlations3.01-3.02 Shell Side Correlations4.01-4.02 Thermal Function K (Pr)1/3
SHORTCUT PROCEDURE
SCOPEThe following subsection presents an approximate procedure for evaluating shell and tube exchangersin which there is no change of phase, (I.e., vapor/vapor, vapor/liquid or liquid/liquid exchangers). Theactual calculations can be made on the calculation form. Each Step of the procedure is explained in thefollowing paragraphs
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Slide 102
following paragraphs.
DETAILED PROCEDURE
1. Terminal Conditions and Effective Log Mean Temperature Differencea. Determine the following temperatures
Inlet temperature of fluid being cooled, T 1
Outlet temperature of fluid being cooled, T 2Inlet temperature of fluid being heated, t 1Outlet temperature of fluid being heated, t 2
b. Determine the log mean temperature difference, tm(T1- t2) - (T2- t1)
(T1- t2)
(T2- t1)
c. From Figure 1.01 - 1.03, determine the minimum number of shells required
for a temperature correction factor (Fn) of at least 0.8000.
d. Determine the effective log mean temperature differences, tet e= Fn tm
ln
tm =
SHORTCUT PROCEDURE (Continued)
2. Caloric Temperatures
a. Decide which fluid to pass through the tubes and which through the shellb Calculate the caloric temperatures
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Slide 103
b. Calculate the caloric temperatures.
For the fluid being heated, ttort s=0.4(t 2 - t 1) +t 1
For the fluid being cooled, t sort t= 0.4(T 1 - T 2) + T 2
3. Caloric Properties of Fluids
a. Tube Side of Exchanger
1. At the caloric temperature t t, determine the following tube side fluid
properties:
For water: density, mFor hydrocarbon liquids or vapors: density, m; viscosity, zFor other fluids: density, m; viscosity, z; specific heat, c; and thermalconductivity, k
b. Shell Side of Exchanger
1. At the caloric temperature, determine the density, m of the shell side fluid.
SHORTCUT PROCEDURE (Continued)
4. Shell Side and Tube Side Flow Rates
The values of the respective flow rates in lb/hr will normally be determined during the heatand material balance calculations
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Slide 104
5. Fouling Factors
a. Decide the tube side fouling factor ri (See Table 1.04)
b. Decide the shell side fouling factor ro (See Table 1.04)
6. Iteration, Tube Side
(1) The heat duty for the exchanger will normally be determined during the heat andmaterial balance calculations.(2) Assume U, the over-all coefficient (See Table 1.05)
(3) Calculate total area
A = Q / U te(4) Calculate the area per shell.
As = A / NsIf necessary, the number of shells should be increased to meet the maximum
shell size limitations (typically 48). This will require recalculating Fn te, A, A s(5) Decide the tube metal and determine tube thermal conductivity, kw (See Table
1.03).
SHORTCUT PROCEDURE (Continued)
(6) Choose the tube length, diameter, wall thickness, pitch, and layout(See Tables 1.01 and 1.02).
(7) Determine the number of tubes as follows:
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Slide 105
NT = 3.82 As
(L - 0.5) do
(8) Estimate Np, the even number of tube passes per bundle which will give a reasonable tube-
side velocity (3-20 fps).
(9) Calculate the linear velocity in the tubes and in the nozzles:
(d N = Nozzle ID) Np M M
19.6 mN T d i 19.6 m dN
(10) Tube side pressure drop and heat transfer coefficient (for water).a. Tube side heat transfer coefficient, hio for water from approximately 80F
to 180F.
1 = h io = 368 (Vd i)0.7 t t
0.26
R io do 100
2 2;
VN =V =
SHORTCUT PROCEDURE (Continued)
b. Total tube side pressure drop, P t, for water at approximately 100F.P t = 0.020 Ft N s N p + PNV 2 + 0.158L V 1.73
d i1.27
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Slide 106
ForPN, See Step 15 (nozzle pressure drop).(11) For fluids other than water:
a. Calculate the tube side mass velocity, G
G = mV
b. Calculate tube side Reynolds Number, Nre (dimensional)
N Re= di G
z
Note: At this point, check for a transition problem by calculating N Re using fluid propertiesat inlet (or outlet) conditions. An Exchanger design is not valid if the type of flow conditionschanges from viscous to turbulent (or vice- versa) within the unit.
(12) From Figure 2.01 determine the tube side pressure drop correlation factor, Y tp.
SHORTCUT PROCEDURE (Continued)
(13) Calculate the tube side velocity head and the nozzle velocity head.
mV 2N in the nozzles ; mV2 in the tubes
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Slide 107
N ;
9270 9270
(14) Calculate Ptf, the frictional pressure drop per tube pass.
Ptf= Ytp L 0.14 or 0.25di
The exponent 0.14 is for turbulent flow (N Re < 30); 0.25 is for streamline flow (NRe< 30).
(15) Calculate the pressure drop per tube pass due to turns, Ptr, and the nozzle pressuredrop, PN.
P t = 3 ; PN= 2 (two nozzles)
mV29720
Zwz
mV2
9270
mV2
9270
SHORTCUT PROCEDURE (Continued)(16) Calculate the total tube side pressure drop, Pt
Pt = F t N s N p (P tf+ P tr) + PNFor : Ft, see Table 1.01.
If th d i bl l t th l d i d d t th t
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Slide 108
If the pressure drop is reasonably close to the value desired, proceed to the next
step. If it seems too high or low, change number of tube passes and repeat step 9through 16 until the pressure drop is satisfactory.
(17) From Figure 2.02, determine the heat transfer correlation factor, Y th.
a. Calculate the thermal function:
For hydrocarbons, refer to Figures 4.01 and 4.02.
b. Calculate the tubeside heat transfer coefficient, hio.
Initially assume Z 0.14 = 1, until tube wall temperature is calculated.Z W
k cz 0.33
k
1 = h io = Y th
R io do
k cz 0.33 z 0.14
k zw
SHORTCUT PROCEDURE (Continued)
c. Estimate the average tube wall temperature, tw
t w= t t + U o(Rio+ rio) (ts- tt)d At the average tube wall temperature determine z and calculate:
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Slide 109
d. At the average tube wall temperature, determine z w and calculate:
(18) Recalculateh io using this viscosity correction.(19) Calculate the tube wall resistance, rw
(See Tables 1.02-1.03)
7. Iteration, Shell Side
(1) Estimate t f, the average shell side film temperature.
t f = ( t s + t t ) + (U o) (R io + rio + rw + ro) (T s- t t)
2 2
rw =
12 kw
Z 0.14
z w
(2) At the average shell side film temperature, determine the following shell fluid properties:
a. For hydrocarbon liquids or vapors: Viscosity, z f.
b. For other fluids: Viscosity, z f; specific heat, c f; and thermal conductivity, k f.
(3) Determine the number of tubes across the centerline of the tube bundle, NTC.
SHORTCUT PROCEDURE (Continued)
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Slide 110
For square tube layout:
N TC= 1.19 (N T)0.5
For triangular layout:
NTC= 1.10(NT)0.5
(4) Determine the outer tube limit, D t.
D t= (N TC - 1)(P t) + d o(5) Determine shell I.D. as follows:
D = D t / 0.9; except for the following limitations:1. Minimum D = D t + 1
2. Maximum D = D t + 3
(6) Determine the free width for fluid flow normal to and around the tubes.
One shell pass, W = D - (d o N TC) ; Two shell pass, W = D - (d oNTC )2
SHORTCUT PROCEDURE (Continued)
(7) Estimate the baffle pitch Pb which will give a reasonable shell-side velocity
(3-15 fps). See Table 1.01 for maximum Pb.
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Slide 111
(8) Calculate the number of shell side baffles, N B (always a whole number).
N B = 10L/Pb
(9) Determine the free area, S, for fluid flow across the tube bundle between each pair
of baffles.
For Calculating the For Calculating the
Film Coefficient, h Pressure drop, PSegmental Baffles: S = W (Pb - 0.375) S = W (Pb - 0.375)
Modified Disc &
Donut Baffles: S = W (Pb - 0.375) S = 0.85 W (Pb - 0.375)
In each case, 0.375 in. represents the approximate baffle thickness.
(10) Calculate the shell side mass velocity, G.
Disc and donut baffles, G = M/50 x S; Segmental baffles, G = M/25 x S
SHORTCUT PROCEDURE (Continued)
(11) Calculate the shell side linear velocity, V and the shell side nozzle velocity, VN
V = G/m
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Slide 112
V n= M (d N = Nozzle ID)19.6 md2N
(12) Calculate the shell side Reynolds number, N Re
N Re= d o G/Z f
(13) Calculate the ratio of the tube diameter to the tube spacing:
d o
P t - d o
From Figure 5.01 determine the shell side pressure drop correlation factor, YSP.
Total Shell Side Pressure Drop
(14) Calculate the shell side velocity head and the nozzle velocity head.
mV2N in the nozzles ; mV
2 in the shell.
9270 9270
SHORTCUT PROCEDURE (Continued)
(15) Calculate Psf, the frictional pressure drop per shell. Table 1.01 gives values for B2.Psf = B2YspN TC NB mV 2
9270
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Slide 113
9270
(Note!: For Disc & Donut baffles, divide NTC by 2.0)(16) Calculate the pressure drop per shell due to turns, Psr, and the nozzle pressure drop, PN.
Psr = (N B + 1) 3.5 - 2Pb mV2 ; PN = 2 mV 2 ND 9270 9270
(17) Calculate the total shell side pressure drop, Ps.Ps = FsN s(Psr+ Psf) + PN
For Fs, see Table 1.01.
If the pressure drop is reasonably close to the desired value, proceed to the next step. If it seems too
high or low, change the baffle pitch Pb and repeat steps 7 through 17 until the pressure drop is
satisfactory.
SHORTCUT PROCEDURE (Continued)Shell Side Heat Transfer Coefficient, ho
(18) From Figure 5.02 determine the heat transfer correlation factor, Ysh.
A. Calculate the thermal function:
kf c fz f1/3
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Slide 114
k f
(For hydrocarbon liquids or vapors, refer to Figures 4.01 and 4.02)
b. Calculate the correction factor for the deviation from ideal baffle pitch.
4Pb 0.1
D
1 = h o = B 1Ysh kf c fzf1/3 4Pb
0.1
Ro
d o
k f D
See Table 1.01 for B18. Duty Coefficient
Calculate Uo, the over-all duty heat transfer coefficient.
1 = Rt = Rio + rio + Ro+ rw+ ro
Uo
If Uocalculated does not agree with Uo assumed, repeat the calculations with a new Uoassumed until agreement is reached (10%).
SHORTCUT PROCEDURE (Continued)
9. Clean Coefficient
Calculate Uc, the over-all clean coefficient.
1 = Rc= Rio+ rw+ Ro+ 0.001
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Slide 115
c io w o
Uc10. Design TemperaturesDetermine the following mechanical design features:
1. The design temperature and pressure of the shell and tube sides.
2. The nozzle size and flange rating for the inlets and outlets on both the shell
and tube sides.
3. The design temperature of the tube sheet, TM.
a. For coolers (water on tube side), specify the higher result
of the following equations:R io (TDS - TDT)
RCor
(R io + rio) (TDS - TDT)
R t
b. For other exchangers:
(1) When the fluid being cooled is on the tube sideTM = TDT - 0.1(TDT - TDS)
(2) When the fluid cooled is on the shell sideTM = TDT + 0.3 (TDS - TDT)
TM = TDT +
TM = TDT +
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Slide 116
Problem 5 B-E
Heat Exchanger Design
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