heat transfer heat ex changers

7/29/2019 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



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Slide 16



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Slide 17



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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


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.



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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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Slide 66

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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Slide 68

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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Slide 69



70/116

Slide 70



71/116

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


73/116

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




Date

PageSection I X-B

TABLE 1 - (Continued)


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Slide 80

U0(1) U0

(1)


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




Date

PageSection I X-B



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Slide 81

U0(1) U0

(1)


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




Date

PageSection I X-B


U0(1) U0

(1)


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Slide 82

U0 U0


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




Date

PageSection I X-B



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Slide 83

U0(1) U0

(1)


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




Date

PageSection I X-B


U (1) U (1)


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Slide 84

U0(1) U0

(1)


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.


89/116

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.


SPIRAL HEAT EXCHANGERS (SHE)


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Slide 92


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)


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)


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


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)


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)


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


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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+ Traditional heat exchanger design practice

Ad d t ith t h l i


99/116

Slide 99

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O Computer Programs

+ Mainframe programs for heat exchanger design/rating/simulation

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O Source of Available Outside Technology

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O Technical Training

+ Courses at EMR&E or affiliate location

+ Subjects include:

Advanced heat transfer

ExxonMobil computer programs

HEAT EXCHANGER REFERENCES

Design Practices, Section IX (Heat Exchangers) and


100/116

Slide 100

Design Practices, Section IX (Heat Exchangers) and

XIV (Fluid Flow)

Global Practices (GPs), Section 6

Heat Exchanger Specialists:

L.A. (Lou) Curcio, (281) 834-7892,

AMERICAS(LACURCI)

R.C. Tomotaki, (281) 834-4419, AMERICAS

(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


103/116

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.


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


104/116

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).


(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 =


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.


(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


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:


109/116

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.



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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


(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


(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


(15) Calculate Psf, the frictional pressure drop per shell. Table 1.01 gives values for B2.Psf = B2YspN TC NB mV 2

9270


113/116

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%).


9. Clean Coefficient

Calculate Uc, the over-all clean coefficient.

1 = Rc= Rio+ rw+ Ro+ 0.001


115/116

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

heat transfer heat ex changers

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