exh400 shell and tube exchanger design and selection.pdf

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Chevron Corporation 400-1 December 1989

400 Shell and Tube ExchangerDesign and Selection

Abstract

This section contains information on TEMA nomenclature, selecting the most

economic exchanger configuration for a defined service, allocating the streams toshell or tube side, specifying appropriate mechanical components, defining baffle

layout, deciding if a small predesigned exchanger is appropriate, and estimating thesize and cost of shell and tube exchangers.

Contents Page

410 TEMA (Tubular Exchanger Manufacturers Assoc.) Nomenclature 400-2

420 General Design Considerations 400-2

430 Stream Placement 400-11

440 Pass Arrangements and Multiple Shells 400-12

450 Bundle and Tubesheet Arrangements 400-13

451 Front Head Design

452 Fixed Tubesheets

453 U-tubes Versus Floating Rear Heads

454 TEMA F Shell

460 Shell Side Baffle and End Spaces 400-14

470 Small Exchangers 400-15

480 Estimating Methods 400-16

481 Step by Step Procedure

482 Surface Area Calculations

483 Tube Count and Number of Tube Passes

484 Shell Diameter

485 Exchanger Investment Cost



400 Shell and Tube Exchanger Design and Selection Heat Exchanger and Cooling Tower Manual

December 1989 400-2 Chevron Corporation

410 TEMA (Tubular Exchanger Manufacturers Assoc.) Nomenclature

The Tubular Exchanger Manufacturers Association (TEMA) has developed nomen-clature for describing shell and tube heat exchangers. It includes a simple code fordesignating the size and type of the exchanger. In addition, standard terminologyhas been set up to specify typical parts and connections.

TEMA size is the shell inside diameter in inches rounded to the nearest integer,followed by the straight length of the tubes in inches rounded to the nearest integer.The two dimensions are separated by a hyphen (-).

For kettle reboilers, the port diameter in inches precedes the shell inside diameter.The two dimensions are separated by a slash (/). Port diameter is the size of the

opening the bundle slides through.

TEMA type consists of three letters describing the stationary or front end head,shell, and rear head, in that order. The letter designations are shown onFigure 400-1.

For example, a 20-foot straight length U-tube bundle, 3-foot shell diameter, with asingle shell pass and removable shell cover would be a TEMA SIZE 36-240 TYPEAEU. The same bundle installed in a 5-foot diameter kettle reboiler would be aTEMA SIZE 36/60-240 TYPE AKU.

Standard terminology to describe components and connections of shell and tubeexchangers is provided in Figure 400-2.

TEMA sets mechanical standards for three classes of exchangers reflecting theseverity of the service. For most refinery services, the most restrictive class isused—TEMA Class R. For other services (chemical plants for example), TEMAClass C or B exchangers are used. In general, Class R exchangers have thicker

shells, larger and thicker heads, thicker tubes, and larger miscellaneous parts.TEMA requirements are noted where appropriate throughout this manual.

420 General Design Considerations

Single- and two-phase exchangers and most condensers have very similar configura-tions. The typical layout is summarized in the following list and shown in Figures400-3 and 400-4. (Steam generators (2 types), reboilers, and condensers aredescribed in Sections 340, 350, 360 and 370.)

The typical shell and tube exchanger geometry includes the following items:

• TEMA E shell style

• U-tubes for rear head type with full support plate at tangent

• TEMA A-type front head

• Single segmental baffles with cut of 18 to 25% of shell I.D. and with cutoriented vertically

• Baffle spacing of 20 to 100% of shell I.D

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Heat Exchanger and Cooling Tower Manual 400 Shell and Tube Exchanger Design and Selection


Fig. 400-1 Heat Exchanger Nomenclature (TEMA, Figure N-1.2) (Courtesy of TEMA)





Fig. 400-2 Heat Exchanger Components (1 of 3) (TEMA, Table N-2 and Figure N-2) (Courtesy of TEMA)

1. Stationary Head—Channel

2. Stationary Head—Bonnet

3. Stationary Head Flange—Channel or Bonnet

4. Channel Cover5. Stationary Head Nozzle

6. Stationary Tubesheet

7. Tubes

8. Shell

9. Shell Cover

10. Shell Flange—Stationary Head End

11. Shell Flange—Read Head End

12. Shell Nozzle

13. Shell Cover Flange

14. Expansion Joint

15. Floating Tubesheet

16. Floating Head Cover

17. Floating Head Flange

18. Floating Head Backing Device

19. Split Shear Ring

20. Slip-on Backing Flange

21. Floating Head Cover—External

22. Floating Tubesheet Skirt

23. Packing Box

24. Packing25. Packing Gland

26. Lantern Ring

27. Tierods and Spacers

28. Transverse Baffles or Support Plates

29. Impingement Plate

30. Longitudinal Baffle

31. Pass Partition

32. Vent Connection

33. Drain Connection

34. Instrument Connection

35. Support Saddle

36. Lifting Lug

37. Support Bracket

38. Weir

39. Liquid Level Connection



C h e v r o n C o r p

o r a t i o n

4 0 0 -7

D e c e m b e r 1 9 8 9

Fig. 400-3 Typical Longitudinal Section Shell and Tube Exchanger





Fig. 400-4 Typical Cross Section, Shell and Tube Exchanger





• 3/4-inch O.D., 14 BWG (average) thickness (0.584 inch I.D.) carbon steel tubes

• Tube length variable with one or two tube passes depending on service

• 45 degree rotated square layout with tube pitch = 1.25 × tube O.D. for liquidand two-phase hydroprocessing shell side service

• 90 degree square layout with tube pitch = 1.25 × tube O.D. for boiling,condensing, and single-phase gas shell side service

• Two or more pairs of sealing strips (bars)

• Dummy tubes in pass partition lane when two tube passes

• Two rows of impingement rods at inlet nozzle when warranted

Overall Exchanger Configuration

The Company preference is a TEMA AEU exchanger for most services. U-tubesare the cheapest rear head type that allows for thermal expansion of the tubes. The

TEMA A type front head has a removable channel cover. This allows for inspectionand cleaning of the tube side without pulling spool pieces in the piping.

Shell Side Nozzle Placement

Single inlet and outlet shell side nozzles are normally located at opposite ends ofthe exchanger with one on the top and one on the bottom of the shell. This arrange-ment allows vents and drains to be located in piping.

Route two-phase flow based on the following rule: “Heat up and cool down.” This

means hot fluid being condensed should enter on the top and exit on the bottom ofthe exchanger. Likewise, cold fluid being boiled should enter on the bottom andexit on the top. The “Heat up and cool down” rule does not apply to single-phase

flow.

Transverse and Support Baffles

The normal configuration for the tube side consists of U-tubes with a full supportplate at the tangent. This is shown in Figure 400-3. The plate blocks flow over theU-bends. Otherwise, the bends must be supported to protect against vibration.

For baffles, use single segmental baffles with a cut of around 18 to 25% of the shellI.D. for most efficient conversion of pressure drop to heat transfer. The baffle cutshould be vertical for best drainage of the shell side at shutdown. Baffle thickness isset by TEMA.

Baffle spacing should be 20 to 50% of the shell I.D. It is usually set to maintaingood heat transfer (economic pressure gradient or shear controlled flow regime).Guidelines for economic exchanger velocity and pressure drop are provided inSection 220 of this manual. In some cases (particularly for gas and two-phase flow

shell side), additional supports may be required to prevent vibration. SeeSection 260 of this manual for more information.









Tube Selection

Tubes are normally 3/4-inch outside diameter, 14 BWG (minimum) thickness (0.56-inch inside diameter), and made of carbon steel. Length is limited by the plot spacefor pulling the bundle and standard bundle pulling equipment. TEMA has named 8,10, 12, 16 and 20 feet as standard tube lengths. Other lengths are possible.

Alloy tubes are appropriate for some services. The cost of upgrading to alloy tubesshould always be weighed against possible process adjustments to permit carbonsteel construction. Section 800 of this manual discusses materials selection fordifferent services.

Tubepass Layout

Most exchangers should be limited to one or two tube passes. Using U-tubes withtwo passes is best and cheapest, however some services dictate 1 pass with a moreexpensive rear head (vertical thermosiphon reboilers or crude/overhead condensers,for example).

Tube PitchFor liquid and two-phase services, use 1-inch, 45 degree rotated square pitch. Thispromotes mixing. Use 1-inch, 90 degree square pitch for boiling, condensing, andsingle-phase gas on the shell side. For boiling, the vertically oriented lanes promote

circulation. For condensing and single-phase gas, in-line tubes minimize pressuredrop without sacrificing heat transfer. Both 45 and 90 degree pitch provide 0.25-inch inspection and cleaning lanes through the bundle.

Preventing Shell Side Flow Bypassing

Single- and two-phase exchangers with impingement protection typically include

two pairs of sealing strips (bars). The bars block the leakage stream flowing around

the baffles between the bundle and shell (“C” stream shown in Figure 200-3 inSection 213). For vertical cut baffles, the bars straddle the nozzles (located at thetop and bottom of the bundle). Note that the bars on the bottom act as skid bars forbundle removal.

For an exchanger with two tube passes, the single pass partition lane runs perpendic-ular to the baffle cuts. Dummy tubes are positioned in the pass partition lane toblock flow bypassing (“F” stream shown in Figure 200-3 in Section 213). Dummytubes are spaced four to six tube rows apart between baffle cuts and are the samediameter as the tubes.

Impingement Protection

When impingement protection is warranted, the preferred method is to install tworows of rods (typically tubes over solid rods) adjacent to the inlet nozzle.Section 524 contains design details and applications of impingement rods alongwith descriptions of other types of impingement protection.

Tolerances and Clearances

All tolerances and clearances are TEMA.

















430 Stream Placement

Allocating the streams to the shell or tube side is determined by weighing factorswhich sometimes conflict. These factors include stream temperature, pressure, rela-tive flowrate, viscosity, corrosiveness, relative heat transfer film coefficient, andpressure drop limitations. Guidelines for allocating the streams to the shell or tube

side are given in Figure 400-5.

Fig. 400-5 Allocating the Streams for Shell and Tube Heat Exchangers

In Order of Decreasing Priority:

Stream PropertyCompared to Other Stream

Preferred Side

Reasons for This ChoiceShell Tube

Match Coefficients and Pumping

Power

— — Minimize cost

Lower Film Coefficient Expected

(hshell

/ h tube

<0.3)

X Enhance outside surface to raise

limiting side coefficient (single-

phase gas only)

Condensing — — Determined by coolant

Treated Cooling Tower Water X Corrosion inhibitors effective tube-

side; otherwise use alloy tubes

Viscosity above 2 cP X Staggered tube layout induces

good heat transfer at low Reynold’s

number

Alloy Required for Corrosion X Allows cheaper shellside compo-

nents

Very Low System Pressure or ∆P

Available

X Can use J or X shell style to

shorten flow path and reduce pres-sure drop

High System Pressure X Reduces shell thickness;

however, tube rupture design

sometimes controls

High ∆T across one Bundle (Over

200°F)

X Excessive ∆T in stationary

tubesheet if placed on

tubeside

Normal Fouling — — Does not matter

Deposits Too Hard to

Hydroblast (Rare)

X Use floating rear head for straight

tubesComplete Tube Plugging (Rare) X Use floating rear head for straight

tubes





440 Pass Arrangements and Multiple Shells

The appropriate stream pass arrangements for a particular service are based on:

• Providing economic pressure gradient on both sides of exchanger

• Operating in shear controlled flow regime for two-phase flow

• Limiting pressure drop

• Controlling temperature efficiency

On the tube side, the pressure gradient is adjusted by changing the number of tubesper pass. To get more area, increase the flow path length either by using longertubes, by adding more shells in series, or by increasing the number of tube passes.

Note that two tube passes are typical because more passes dramatically increasepressure drop. Not only does the pressure drop increase proportionally to the

increase in flow path length, but to the square of velocity. For example, going fromtwo to four passes increases the pressure drop by a factor of eight with the tubecount held constant.

On the shell side, the pressure gradient is adjusted by changing the baffle spacing.

To get more area, the exchanger (tube length) is made longer. When more area isneeded and the tube length is maximum, add another shell with the shell side flow

in series.

The shell style is changed from a TEMA E-type to a TEMA J- or X- type when theresulting pressure drop is too large at the target pressure gradient. This shortens theflow path allowing the pressure gradient to be maintained.

Use parallel exchangers only when a single exchanger is too large, and the pressure

drops can not be increased at the target pressure gradients. Exchanger size islimited by the manufacturer’s fabricating equipment and the user’s maintenance

equipment. Space availability may also limit size, especially when modifying anexisting unit.

Parallel units with isolation valves have been used to provide an installed spare orwhen flow rates will vary more than 50% from normal. When the flow rate varies,the number of units onstream is changed to maintain reasonable operating pressuredrop.

Consider using a mixed parallel/series arrangement of shell and tube passes inmultiple units only when required to meet pressure drop restrictions. The overalltemperature efficiency of the units is reduced. Note that the F-factor described inSection 211 of this manual is the common measure of temperature efficiency.

Temperature efficiency will vary with service. Area is most effectively used whenshell and tube side stream routing approaches pure countercurrent flow (F-factor of1.0). Going to multiple units in series increases the temperature efficiency. Keep the

F-factor above approximately 0.85.

When performance is limited by a temperature pinch between the streams (smalllocal temperature difference reflected as low F-factor), multiple shells become cost







effective by reducing the total area requirement. Countercurrent flow of both fluidsthrough the shells maximizes efficiency.

For condensing services, significant subcooling loads are usually processed in aseparate exchanger following the condenser. This allows the geometry to bechanged to accommodate the much lower volumetric rate of the liquid. As a result,the area needed for subcooling is reduced.

450 Bundle and Tubesheet Arrangements

This section covers front head selection, fixed tubesheet applications, U-tubesversus floating rear heads, and TEMA F shells (two shell pass exchangers).

451 Front Head Design

The TEMA Type A front stationary head is normally used. It has a removal channelcover so the tube side can be inspected without disconnecting nozzles or removing

pipe spools. The bonnet channel (Type B) is cheaper and is appropriate for smallexchangers with small easily removed pipe spools. For operating pressures above

1000 psig, a special front head is required. Options are discussed in Section 532.

452 Fixed Tubesheets

Fixed tubesheets are the cheapest type of head. They are typically used when theshell side service is nonfouling and noncorrosive, and the metal temperature of theshell and tubes operate within 50°F (including startup, shutdown and steam outconditions). The bundle is not removable.

The shell side is not accessible for inspection or mechanical cleaning since the

tubesheets are seal welded to the shell. If the temperature difference is larger than50°F, an expansion joint may be required in the shell.

Steam generators with very high (1000°F and above) process side temperatures andwater on the shell side must have fixed tubesheets. See Section 350 of this manualfor more information.

453 U-tubes Versus Floating Rear Heads

U-tube and floating head bundles are removable. Both permit thermal expansion ofthe tubes. The various types of rear heads are shown on Figure 400-1.

U-tubes (TEMA Type U) are the cheapest of the two types and are preferred. Thebends can be mechanically cleaned by hydroblasting for typical fouling deposits—as long as complete plugging does not occur.

One disadvantage of U-tube bundles is that corrosion is difficult to monitor. Spec-imen tubes can only be taken from the outside perimeter of the bundle.

TEMA Type S and T floating rear heads cost more than U-tubes. Maintenance iscomplicated by the added bundle flange. Floating heads can be taken apart and the









straight tubes drilled out. Floating heads are recommended for services leavingdeposits too hard to hydroblast.

The differences between the S- and T-type heads are minor. The split ring (S) typeallows for tight clearance between the shell and bundle. However, a shell bodyflange and the split ring flange must be taken apart before the bundle can be pulled.The pull through (T) type allows the bundle to be removed prior to taking apart thefloating head and does not require a shell body flange. However, the shell is over-sized to allow the floating head to pass through.

Floating heads (versus fixed tubesheets) are usually necessary for single tube passexchangers to accommodate thermal expansion. Head design must account forstartup, shutdown, and steam out conditions. Single pass exchangers with a floating

head are commonly used for atmospheric column overhead condensers in crudeunits and vertical thermosiphon reboilers.

454 TEMA F Shell

The TEMA F shell has a longitudinal baffle running through the middle of theexchanger. This provides two shell passes within one shell. Both the inlet and outletshell side nozzles are located adjacent to the tubesheet (channel end).

When coupled with two tube passes, the F shell provides pure countercurrent flow.F shells have been used instead of multiple shells in series to avoid temperature

pinches. F shells are cheaper than multiple shells in series. However, experience hasshown the seal between the two shell passes to be very difficult to maintain.Increased maintenance time and performance loss due to leakage by the longitu-dinal baffle is reported frequently.

As a result, TEMA F shells are currently recommended for noncorroding and

nonfouling services only—where the tube bundle is rarely if ever pulled for mainte-nance.

If the bundle from a F shell is pulled, the seal (described in Section 523) is usuallyreplaced. The bundle must be handled carefully when reinstalled. The seal is easilyruined if the slings twist the seal or the bundle goes in crooked.

460 Shell Side Baffle and End Spaces

The number of crosspasses, the baffle spacing (central, inlet and outlet spacing),and the straight tube length are related mathematically. For a TEMA E shell with U-tubes fully supported at the bend tangent, the following relationship applies.

F = C (cp - 2) + D + E + tbst(Eq. 400-1)

where:

F = Straight (total) tube length in inches

C = Central baffle spacing in inches







cp = Number of crosspasses per shellpass

D = Inlet baffle spacing in inches

E = Outlet baffle spacing in inches

tbst = Tubesheet thickness in inchesEnd (inlet and outlet) spaces are set to keep the transverse baffles clear of the inletand outlet nozzles. The spacing accounts for mechanical constraints which force thenozzle position. These include flange thickness, body and nozzle flange clearances,nozzle reinforcement and access. For a TEMA E shell with U-tubes, end spaces canbe estimated using the following equations.

End space at channel or tubesheet in inches:

1.1 (nozzle I.D., inches) + 0.1 (shell I.D., inches) + 8.0

End space at rear end or free end of bundle in inches:

1.1 (nozzle I.D., inches) + 2.0

The actual spacing can be wider, but should not be excessive. Heat transfer in theend spaces is not as good as between transverse baffles.

470 Small Exchangers

There are two types of small exchangers: the double pipe and the multitube hairpin.Both are predesigned in set configurations, and provided by vendors off the shelf.They are designed to be stacked nozzle to nozzle as shown in Figure 400-6.

Figure 400-7 is diagram of a double pipe exchanger. It is simply a single pipewithin a pipe. Fluid flow on the shell side simplifies to flow through an annulus.

Fig. 400-6 Typical Stack of Small Exchangers





Figure 400-8 is a diagram of a multitube hairpin exchanger. It is a shell and tubeexchanger with one U-shell and one U-tube pass. Figure 400-9 gives typicalexchanger geometries.

The same economic considerations for setting pressure gradient or velocity apply tosmall exchangers as to conventional shell and tube exchangers. Small exchangersare cost effective when the required surface area is less than about 250 ft2 for

double pipes and less than 1000 ft2 for multitube hairpins.

Because the configuration is already fixed, you should confirm exchanger geometrywith the vendor. The HTRI programs can be used to model double pipe and multi-tube hairpin exchangers. See the Heat Exchanger Design Program User’s Guide for

details.

480 Estimating MethodsThis section gives procedures for estimating the size and cost of a shell and tubeexchanger. The procedures are recommended for:

• Preliminary sizing and layout of a new exchanger prior to rigorous computermodeling

• Developing project economics

• Comparing performance or configuration of an existing exchanger to a definedstandard or baseline exchanger

Fig. 400-7 Double Pipe Exchanger Fig. 400-8 Multitube Hairpin Exchanger



C h e v r o n C o r p

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4 0 0 -1 7

D e c e m b e r 1 9 8 9

Fig. 400-9 Multitube Hairpin Exchanger Information (1 of 2)



D e c e m b e r 1 9 8 9

4 0 0 -1 8

C h e

v r o n C o r p o r a t i o n

Fig. 400-9 Multitube Hairpin Exchanger Information (2 of 2)





481 Step by Step Procedure

482 Surface Area CalculationsArea (A) for heat transfer is calculated from the overall heat transfer expression forthe service.

(Eq. 400-2)

where:

A = Surface area for heat transfer, ft2

Q = Heat duty for service, Btu/hr

MTD = Mean temperature difference for service, °F

U = Overall service heat transfer coefficient, Btu/hr⋅°F⋅ft2

Step 1. Estimate physical and thermal properties for streams. Calculateexchanger duty (MMBtu/hr). Allocate streams to shell and tube sides

using the guidelines in Section 430.Step 2. Plot heat release curve for stream(s) undergoing phase change. Esti-

mating techniques must be carefully applied to streams with dramaticslope changes. More information and an example are provided inSection 211.

Step 3. Estimate the actual mean temperature difference (MTD). This dependson the service of the exchanger. See Section 211.

Step 4. Determine if multiple shells in series are required. See Section 440.

Step 5. Select appropriate film coefficients from Figure 400-10. Appropriatesections of this manual that contain more accurate methods are refer-enced in Figure 400-10.

Step 6. Calculate a overall service heat transfer coefficient U. See Section 212.

Step 7. Calculate the required surface area for the service. See Section 482.

Step 8. Determine the number of tubes per shell and pass configuration. SeeSection 483.

Step 9. Estimate the shell diameter for given tube count. See Section 484.

Step 10. Estimate shell and tube side pressure drop, if needed. See Section 220.

Step 11. Cost the exchanger, if needed. See Section 485.

AQ

U MTD⋅----------------------=













483 Tube Count and Number of Tube Passes

The number and length of the tubes is determined through trial and error. The twoare related by the necessary mechanical configuration of the exchanger to providethe surface area (A) calculated in Section 482.

(1) This table applies to well designed exchangers (fouling is controlled and flow regime is shear controlled or turbulent to promote heat

transfer).

(2) The film coefficients are on a clean basis. Allowance for extra area is applied separately.

(3) Cooling tower water film coefficient includes thermal resistance of corrosion inhibitor film.

(4) Subcooling coefficient applies for condensate cooling in the condenser. Typically subcooling is accomplished in a separate conden-

sate cooler.

(5) Tubes are finned.

A = (#tubes) (L) (π) (O.D.) / 12 (Eq. 400-3)

where:

#tubes = Number of tubes per pass, dimensionless

= Mt / [(ρt) (Vt) (3600) (At)]

At = Cross sectional area of single tube, ft2

Fig. 400-10 Approximate Heat Transfer Film Coefficients for a Well Designed Heat Exchanger(1) (2)

Service or Fluid

Shell or Tube Side Coefficient,Btu/hr⋅°F⋅ft2 [based on bare

outside area] Reference

SENSIBLE

Pure Water

C.T. Water(3)

HC, 0.5 cP

HC, 2 cP

HC, 10 cP

1400

450

400

250

150

Figure 200-4

Section 213

GASES

Light HC, 150 psig

Air, 10 psig

Air, 300 psig

100

15

60

Appendix B

CONDENSING

Steam

Light HC

Heavy HC

Subcooling(4)

1000

200

100

50

Section 370

BOILING

Water

Light HCHeavy HC

1000

300150

Section 360

AIR COOLED (FIN FAN)

Air Side(5) 175 Section 600



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= (π) (I.D./12)2 /4

L = Flow path length, ft (in heat transfer)

π = 3.142

O.D. = Tube outside diameter, inchesI.D. = Tube inside diameter, inches

Mt = Mass flow rate of tube side fluid, lb/hr

ρt = Fluid density of tube side fluid, lb/ft3

Vt = Velocity of tube side fluid, ft/sec

For single-phase, two-phase, and some condensing services, use the economicsizing guidelines (Section 220) to select velocity (Vt), or a range of reasonablevelocities. Use an initial flow path length of 40 feet. This assumes a 20-foot long U-tube exchanger with two tube passes and a full support plate at the bend tangent.

Through trial and error calculations, determine a tube count that meets the area andvelocity requirements. The flow path length may change. Consider leaving the flowpath at 40 feet, and ending up with more excess area. Be careful when specifyingexchangers with other than two tube passes. Be careful of a long flow path. Thepressure drop can be excessive.

Note that multiple tube pass exchangers have an even number of tube passes toaccommodate thermal expansion.

If tube side fluid is pure component condensing or boiling, velocity can generallybe ignored. Set tube length and calculate tube count for area. For vertical thermosi-phons (VTSR) with tube side boiling, 8- to 12-foot tubes are typical with only one

tube pass. The actual length depends on the service as well as velocity and exit pipeflow regime. Further definition is beyond the scope of this section.

484 Shell Diameter

For a typical U-tube exchanger with two tube passes, 0.75-inch tubes on a 1-inchrotated square (45 degree) pitch and impingement rods, the shell diameter in inches

is given by:

Shell I.D. = 1.95 [#tubes]0.433 (for shell I.D. between 15 and 51 inches)(Eq. 400-4)

Shell diameter should be rounded to the nearest 1/16 inch. The correlation is basedon shell side nozzle diameters between 20 to 30% of the shell inside diameter.Within the constraints, the correlation is good to plus or minus 2%. If nozzles arerelatively smaller, the tubes may fit into a smaller shell. And, if nozzles are larger, alarger shell may be required to accommodate all the tubes.






485 Exchanger Investment Cost

Exchanger investment cost is calculated using techniques from the Company CostEstimating Books. For shell and tube heat exchangers with design pressure below600 psi for both sides, the installed cost is:

HEX = (EDMI/655) (I) (T) [ (MTL) (A) + CMP (F + m A) ](Eq. 400-5)

where:

HEX = Installed cost of exchanger, $

EDMI = Chevron material index, dimensionless

I = Installation factor for heat exchanger, dimensionless

T = Multiplier for geographic location adjustment, sales and othertaxes, dimensionless

MTL = Tube material adjustment, $/ft2

(at 655 EDMI)

A = Area for heat transfer, ft2 (Note that installed cost is directlyproportional to area—exponent of 1.0.)

CMP = Configuration and component adjustment including componentmaterial multipliers, dimensionless (See Cost Estimating Book)

F = Fixed cost add on which is a function of exchanger class (smallor large) and design pressure, $ (at 655 EDMI)

m = Multiplier reflecting linear cost change with area, $/ft2; the multi-plier is a function of exchanger class—small or large—and

design pressureFor a typical exchanger configuration with all carbon steel construction and 300 psidesign pressure (both sides), the expression simplifies to:

HEX = (EDMI/655) 5.5 [13,100 + (8.8 A)](Eq. 400-6)

This equation assumes that the installation factor (I) is 5.5, area and tax adjustment(T) is 1.065, material add on (MTL) is 0, and configuration adjustment (CMP) is0.935. CMP is for 20 feet (straight length) U-tubes. F and m are for exchangerswith 1000 ft2 or more.

The cost expression is different for high pressure shell and tube heat exchangers(design pressure well above 600 psi). Cost varies with the area to the 0.64 power.

See the Cost Estimating Books for details.

exh400 shell and tube exchanger design and selection.pdf

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