6. exchangers ...piping design layout training lesson 6 exchangers page 3 of 46 15/11/2002 rev. 0...

PIPING DESIGN LAYOUT TRAININGLESSON 6

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6. EXCHANGERS

6.1 PREFACE

This lesson is designed around piping technical practices for exchangers. We will review exchangersand their function with the ultimate goal of developing an understanding of exchanger piping.

Within the chemical and petroleum industry, the term heat exchanger refers to a vessel for exchangingheat between two separate streams - for heating and cooling.

This lesson will cover the procedures required for EXCHANGER studies, and the piping connected tothem. Two things to keep in mind; first, use Fluor standards as a guide, and second, the guidelinesmentioned in this lesson may be different than jobs you may have worked on in the past. Some clientshave their own engineering standards.

6.1.1 Lesson Objectives

Lessons provide self-directed piping layout training to designers who have basic piping design skills.Training material can be applied to manual or electronic applications. Lesson objectives are:

• To familiarize you with Fluor's standards on exchangers. (Fluor's standards are a guide; thestandards used on your contract may differ.

• To familiarize you with exchanger piping Technical Practices 000.250.2600, Sht. 1, Exchangers -Tema Nomenclature and Sheet. 2, Shell and Tube Exchanger Types; 000.250.2601, Layout ofShell and Tube Heat Exchangers; 000.250.2602, Layout of Air Cooler Exchangers and000.250.2603, Layout of Double Pipe Exchangers.

• To identify basic types of exchangers.

• To develop basic process knowledge of heat exchanger piping.

• To establish proper location of heat exchangers.

• To understand servicing related to exchanger location.

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6.1.2 Lesson Study Plan

Take the time to familiarize yourself with the lesson sections. It should take you approximately 30hours to read this lesson plan and be prepared to take the lesson test.

If you have layout questions concerning this lesson your immediate supervisor is available to assistyou. If you have general questions about the lesson contact the Piping Staff Group.

Additional support information:

000.250.2601 Exchangers - Equipment Locationand Piping Layout Shell and Tube HeatExchangers

000.250.2602, Exchangers - Forced Draft and Induced Draft Air Cooler Arrangements

000.250.2603, Exchangers - Double Pipe Exchangers Piping Arrangements

6.1.3 Study Aid

Videos on Piping Design Layout Practices supplement your layout training. It is suggested that youview these videos prior to starting the layout training. You may check-out a copy of the videos from theKnowledge Centre (Library).

6.1.4 Proficiency Testing

You will be able to take a self-test to determine your comprehension of this lesson. Test and answersare at the end of this lesson.

You are encouraged to use the lesson as a reference when taking the self-test.

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6.2 EXCHANGER PIPING

Figures #6-01 through #6-04 show some types of exchangers used in refinery and petrochemicalplants.

Figure #6-01Aircoolers

Figure #6-02G-Fin (Double Pipe) Type Exchangers

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Figure #6-03Shell and Tube Exchangers

Figure #6-04Tube Bundle

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6.2.1 How to Design Heat Exchanger Piping

By following these details when designing exchanger piping, good access, ease of maintenance andbetter operation will result.

Exchanger piping represents a large portion of process unit piping cost. This lesson presents thedetails of exchanger and piping design, showing how to save material and labor cost besides makingquick and systematic exchanger piping design.

In order to know what changes and alterations can be contemplated to heat exchangers and toevaluate alternative possibilities of exchanger piping, the designer must know the construction details ofexchangers in petrochemical plants. Only with this knowledge can he design the most economicalpiping arrangements, satisfying engineering, plant operation, maintenance and safety requirements.

Piping connected to heat exchangers is generally simple. Piping economy and good engineeringdesign depends more on knowing what alterations can be made to exchangers than on actual pipingdesign know-how. In other words the piping designer can influence the exchanger design (direction offlow, nozzle location, etc.) in the interest of a better, more functional piping design. Alterations toexchangers, of course, should not affect their duty and cost. Money saved in simpler piping should notbe spent on making costly alterations to exchangers.

In order to know what changes and alterations can be contemplated to heat exchangers and toevaluate alternative possibilities of exchanger piping, the designer must know the construction details ofexchangers in petrochemical plants. Only with this knowledge can he design the most economicalpiping arrangements, satisfying engineering, plant operation, maintenance and safety requirements.

6.2.2 Shell and Tube Exchangers

Most exchangers used in petrochemical plants are welded construction. (See Figure #6-05.) Shellsare built up as a piece of pipe with flanged ends and necessary branch connections. Shells are ofseamless pipes up to 24 inches diameter, or rolled and welded steel plates above 24 inches. Channelsections, too, are usually of built up constructions with weldneck forged steel flanges, rolled steelbarrels and welded-in pass-partitions. Shell covers are either welded directly to the shell or are built upconstruction of flanged and dished heads and weldneck forged steel flanges.

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Figure #6-05

These sectional views show typical exchanger components used in refineries and petrochemical plants(See Figure #6-05).

Inlet and outlet nozzles, on both tube and shell side, are arranged to give the required flow through theunit with optimum heat transfer conditions. The shell and channel has vent and drain connections; inand outlet nozzles usually have temperature connections. Pressure, gauge glass, level controller, reliefvalve connections can also be arranged on the shell if required.

The internals of an exchanger consist of tubes with tube sheets and baffles. Tubes are in square ortriangular arrangement and roller expanded into the tube sheets. Cross baffles are one-eighth inch toone-fourth inch thick plates suitably cut and arranged for directing the flow through the shell. The tubebundle fits closely in the shell without interfering with tube bundle removal.

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Exchangers are constructed in a great variety for a wide range of purpose. The combination of manykind of shells, shell covers and channel sections, tubes and baffles are possible.

Figure #6-06 shows exchangers with fixed tube sheets. Exchangers with completely enclosed tubescan be used in clean service only (Sketch A). Cleaning can be done by flushing through the tube andshell side. Two bolted covers (Sketch B) facilitate easier inspection and cleaning of tube insides. Asno provision is made for tube expansion these exchangers are built for low temperature service.

Figure #6-06

Figure #6-07 shows U-tube exchangers. Here the tubes can freely expand and the tube bundle isremovable from the shell. This exchanger is used when fouling inside the tubes is not expected.

Figure #6-07

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The most often used type of exchanger in petrochemical plants is the floating head type exchanger.Basic tube design is shown on Figure #6-04. This is a more expensive type of exchanger than the fixedtube or U-tube type. Tubes can freely expand; channel, channel head and shell cover are provided forconvenient inspection, tube bundle removal and cleaning.

In the case of a single pass tube the floating head cover is extended with a tube through the channelhead (See Figure #6-05, upper left corner). Leakage is possible through the packing and it is notadvisable to put flammable liquid or gases through the shell for safety reasons.

Figure #6-08A and #6-08B show a tabulation of typical heat exchanger arrangements. Column Ashows a typical picture with basic nozzle locations and baffle arrangements, Column B indicates thetype of tube bundle, Column C gives brief construction designation, Column D typical duties.Terminology for the various typical functions is listed on Page 12.

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Figure #6-08ATabulation of typical exchangers showing possible alterations for better piping.www.IranPiping.ir



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Figure #6-08BTabulation of typical exchangers showing possible alterations for better piping.www.IranPiping.ir



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6.2.3 Terminology and Typical Functions of Shell and Tube Heat Exchangers

Exchanger Heats one stream and cools the other. There is no heat loss, and physicalchange does not take place in the flowing media.

Cooler Water cools liquid or gases without condensation. (Other designations:intercooler, aftercooler.)

Subcooler Condenses vapor with water and cools further the condensed liquid.

Condenser Condenses vapor or vapor mixture. Condensers can be water cooled, whichmeans the transferred heat is lost. Or sufficiently cold process stream can beheated while condensing the other process stream; consequently, there is noheat loss.

Chiller Uses refrigerants for cooling process stream below freezing point or belowprevailing cooling water temperature.

Heater Heats process stream generally up to its boiling point and without appreciablevaporization. Heater medium is usually steam or sometimes dowthern. (Otherdesignations: preheater.)

Reboiler Re-boils the bottom stream of tower for the fractionation process. Heatingmedium is generally steam of a hot process stream. When large quantities ofvapor have to be produced the kettle type reboiler is used.

Waste Heat Boiler Uses waste heat (for example gas turbine or diesel engine exhaust gas) forsteam generation.

Steam Generator Uses heat of process liquid or gas for producing steam.

Vaporizer Vaporizes part of a process liquid stream. (Other designation: evaporator.)www.IranPiping.ir



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6.2.4 Exchanger Design

The exchanger designer determines exchanger type, size, construction details, nozzle arrangements,and flow direction through shell and tube, without taking into account external piping arrangements.The piping designer usually has no influence in the basic design and selection of the various types ofheat exchangers. However, he can request alternate flow and nozzle arrangements in the interest ofmore economical and better-engineered piping. Figures #6-08A and #6-08B, Column E, list possiblealternate flow and nozzle arrangements to basic design.

Thermal design and sizing of exchangers is based on the well known formulae of:

Q = U.A. ( ∆T)

where Q = total heat transferred in Btu/hr

A = area of retaining wall between the two flowing media in sq. ft

∆T = Temperature difference, oF between the two media. (Logarithmic meantemperature difference is used with commonly accepted calculations.)

Q and ∆T are based on process requirements and

U = heat resistance coefficient, Btu/hr/sq. ft/oF

"U" is the function of many variables. Its proper selection is the duty of an experienced exchangerdesigner.

"A," then, can be calculated and the most important symbol is "U," because each time he wants tochange the flow direction in an exchanger or reposition a nozzle in the interest of better piping thiscoefficient can be affected. In turn, this can affect the exchanger's efficiency and thermal design.Consequently, at each contemplated change the piping designer should consult a competentexchanger designer.

6.2.5 Flow Changes for Better Piping

It has been mentioned above what is basically involved in making alterations to heat exchangers. Inthe following, two further principles of heat transfer are outlined which are helpful when doingexchanger piping design.

Figure #6-09A illustrates the first such principle. Generally, in heat exchangers the heated mediashould flow up and the cooled one should flow down. This, or course, is the simple physical behaviorfor any heated or cooled media. This rule is more important if in the flowing media physical changetakes place while passing through the heat exchanger (evaporation, condensation). Where liquid ornon-condensing gases pass through the exchanger this rule becomes a preference only.

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Figure #6-09A

This is why in most cases water inlet is at the bottom side of exchangers. Similarly, reboiler inlets areat the bottom side of exchangers and outlets at the top. And steam enters at the top channel nozzle ofreboiler and condensate leaves at the bottom channel nozzle. Condenser vapor inlet is at the top andliquid outlet at the bottom.

Where large quantities of vapor have to be condensed or released, the physical change takes placeusually in the shell where more volume can be provided than in the restricted space of tubes.

The second heat transfer principle - counterflow - gives better heat transfer than concurrent flow and ispreferred. This, of course, can only be fully satisfied with single pass exchangers on both the tube andshell side or with double pipe heat exchanging units. In case of multi-pass tubes with cross flow shellsthis second principle loses it importance.w

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Figure #6-09B shows typical process streams through heat exchangers and coolers.

Figure #6-09B

For better piping arrangement alterations to heat exchanger construction can be made without costincrease. These possible alterations - which practically will not affect thermal design - are listed onFigures #6-08A and #6-08B, Column E and checked against typical heat exchanger arrangements.(Unchecked items are sometimes also possible, but can affect thermal design more seriously. Thesecases must be investigated with an exchanger designer.)

6.3 EXCHANGER DESIGN ALTERATIONS

Interchange flowing media between the tube and shell side. This change is often possible, more sowhen the flowing media are similar, e.g., liquid hydrocarbons. Preferably, the hotter liquid shouldflow in the tube to avoid heat losses through the shell or to avoid possible thicker shell insulation.

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Change direction of flow (a) on tube side, (b) on shell side or (c) on both sides. These changes arefrequently possible and are accepted by the exchanger designer if the exchanger tubes are indouble or multi-pass arrangement and the shell has a cross flow arrangement. In exchangers wherecounterflow conditions can be arranged changing of flow direction should be made simultaneously intube and shell.

Change exchanger nozzle location on (a) tube side, (b) shell side. On most exchangers inpetrochemical plants these changes are also frequently possible on the shell and channel withoutaffecting the required duty of the exchanger.

Combinations of above alterations at certain exchangers are also possible. For example, one canchange flow direction and nozzle location at the same time on the exchanger shown under item 2 onFigure #6-08A.

Additional points that also can influence the piping designer's decision regarding changes in exchangerconstruction are:

Shell Leakage - When water is used to cool gases, liquid hydrocarbons or chemicals, the waterusually passes through the shell. A possible tube leakage will contaminate the water instead ofleaking to the atmosphere where it can become dangerous.

Pressure - Sometimes it is more economical to have higher pressure in the tubes than in the shell tohave minimum shell wall thickness.

Corrosion - Corrosive liquids should pass through the tubes so that the shell can be made of carbonsteel.

Only the tubes and channel have to be manufactured of more expensive alloy steel.

Fouling - If one media is dirty and the other clean, passing the clean through the shell will result inan easier tube bundle removal or even a simpler exchanger design.

Mechanical Changes for Better Piping - In the interest of saving cost, providing better access andimproving piping arrangement, mechanical alterations can also be made to the basic exchangerdesign. These alterations do not affect the thermal design and can be made to all types ofexchangers. Often slight cost increase caused by special nozzle arrangement is more than offset bymore economical piping.

Figure #6-10 shows frequently adopted nozzle arrangements on exchangers. Elbow-nozzles permitlowering exchangers closer to grade. Stacked exchangers in parallel or dissimilar service can bearranged closer, with elbow-nozzles between them. This facilitates better access to exchanger valvesand instruments besides easier maintenance.

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Figure #6-10

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Angular connections can save one or two bends in the pipeline. These connections are more oftenapplied to top nozzle of shell or tube side. Excessive angular connection at the bottom can mean aseparate drainage point on the shell or channel. The maximum angle from vertical centerline can beabout 30o. This angle depends on nozzle and shell size and internals of the exchanger: bafflearrangement in the shell and partitions in the channel.

Tangential connections are more expensive to make but can save fittings, make piping arrangementsimpler and improve access to valves.

6.3.1 Better Piping Design

Many design combinations are possible and are adopted in petrochemical plants. A piping designercan visualize an exchanger as a large diameter pipe with branch connections and he can designvirtually anything that is possible with pipe fittings, within the limitations of exchanger constructions.

Why do all these details interest a piping designer? He is not only responsible for the physicalarrangement of piping but also for the efficient and trouble free operation of process equipmentincluding exchangers. For example, if he blindly follows an exchanger designer's nozzle locations andflow requirements he can end up with a piping arrangement shown in Figure #6-11, Sketch A. It has apocket and a loop in the line, which means more pipe, more fittings, more vents and drains, longerpump suction with an undesired loop. Figure #6-11, Sketch B, has reversed the flow in the system,which means a better-engineered and more economical piping layout. A loop, pocket, vent and drainhave been eliminated. Friction losses through the piping system have been reduced and pump suctionshortened and simplified.

Figure #6-11

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Another example is shown in Figure #6-12. Relocating nozzles on the exchanger shell (Sketch B)results in a simpler piping arrangement than shown on Sketch A.

Figure #6-12

Figure #6-12 - Sketch A shows zigzag flow pattern that should be avoided. Sketch B shows howrelocating nozzles can provide a more functional flow pattern and shorter piping.

6.3.2 Information Required

Being familiar with heat exchangers is only part of a piping designer's know-how. The understandingand proper interpretation of process and project design data is also important. The data below is inorder of importance:

1. Specifications referring to details connected with (a) exchanger design (minimum shell size,type of exchanger, etc.) (b) exchanger handling requirements (tube bundle removal,handling steel requirement for elevated exchangers (c) piping design (headroom, access,valving, etc.) (d) special plant requirements (local regulations and safety codes).

2. Flow Diagrams. The proper evaluation of flow diagrams is perhaps the most importantfunction of the piping designer. The process flow diagram tells: (a) basic information forexchanger design: what medium is flowing, flow rate, temperatures and other physical data.(b) basic details for piping design: pipe sizes can be calculated, temperatures of piping areshown, interconnected equipment with exchangers are shown, main pipe runs can bevisualized, elevations of exchangers can be assessed. P&IDs show the complete processand utility piping system and details, as well as instrumentation.

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3. A plot plan is developed basically from the P&ID. The plot plan gives the location of heatexchangers with adjacent equipment, also relationship with access roads and pipeway.

Specifications, flow diagrams and plot plan are sufficient for initial design. Design ideas canbe produced, piping visualized and details arranged.

4. Exchanger drawings and data sheets give all the details of exchanger design. Size, type,number of units, nozzle arrangements, weight of bundle, exchanger internals, tube andbaffle arrangements. Suggestions can be made for locations and alterations of exchangerfooting, nozzles, and instrument connections; similarly, possible changes in direction of flowthrough the heat exchanger can be evaluated.

These suggestions of changes should be made at an early stage of design because itaffects exchanger design, fabrication, and delivery schedules.

5. Process data is required indicating the elevation of exchangers relative to grade or otherequipment.

6. Instrument sketches showing the location of instrument connections to the exchanger forlevel gauges, level controllers, pressure and temperature connections when required.

7. Manufacturers' catalogues or standard drawings are required for the physical details ofinstruments, equipment and pipe accessories.

8. Insulation details of exchangers and piping are also required.

This information is all necessary to make plot and exchanger piping arrangement. Thecustomer's requirements written in the specifications have to be remembered and applied. Theexchanger unit with all its piping, valving and instruments should be a functional part of theplant, properly designed with respect to related equipment, access and bundle removal spaceas shown on the plot plan. Piping systems should conform to all details as presented in the flowdiagrams. Exchanger drawings, instrument sketches and catalog will also influence thearrangement of exchanger piping.

6.3.3 Establishing Exchanger Elevation

• Most exchangers are at grade with centerline elevations of about 3'-0" to 5'-6" above grade forexchangers about 1 to 3 feet in diameter. Exchangers at grade are the most economicalarrangements. Most valves and instruments can be made accessible from grade, tube bundlehandling is convenient and maintenance easy.

• Some exchangers have a condensate or liquid holding pot after one of their outlets. In suchcase the centerline elevation from grade must be more carefully chosen. These exchangersmay have somewhat higher elevations than those at grade without a condensate pot.

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Figure #6-13 shows an example. This arrangement is really a high capacity steam trap. When settingthe elevation, the top of the condensate pot should be at least in line with the bottom of exchanger toavoid flooding the tubes with condensate and adversely affecting the exchanger heat transfer duty.

Figure #6-13www.IranPiping.ir



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Figure #6-14 is another example. Here holding of liquid level in an exchanger was required. Theprecise relationship between the exchanger and "control pot" is important and should be given by theprocess engineer for the physical arrangement.




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Figure #6-15 shows an example where a reboiler has been elevated by the NPSH requirement of acentrifugal pump. Such arrangement can elevate an exchanger from 5 to 18 feet. In most casesaccess to valves, instruments, exchanger flanges and tube removal platforms must be provided. (Thiselevated reboiler in turn elevates the tower, because the liquid level in the bottom of tower must behigher than the liquid level in the reboiler.)




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If gravity flow is required from the condenser outlet to a collecting drum, reflux drum or separator,exchangers must be elevated. Examples are shown on Figure #6-16 and Figure #6-17. When coolersin gravity flow are required they should be located above the respective tower inlet.

At the condenser-reflux system in Figure #6-16 the elevation of the condensers is influenced by severalfactors. First, the reflux drum must be elevated because of pump NPSH requirement, say 14'-0" to thebottom of drum (about 2-3 feet below this elevation a platform is required). To this 14'-0", the drumdiameter, estimated space for pipe lines, depth of structural steel members plus platform-to-exchanger-centerline dimension must be added for establishing the exchanger elevation above grade.

In general, in vacuum service and in certain fractionating services, where close pressure control isrequired, condensers are placed above the reflux drum. In most cases, condensers are located atgrade.

Figure #6-16

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Figure #6-17 shows coolers in a gravity flow system. If available pressure difference is small betweenexchanger inlet and outlet the exchangers must be placed above the respective tower inlet nozzle. Insuch cases exchangers are placed either on an adjacent structure or supported (preferably vertically)from the tower. Sometimes, the piping designer can suggest a pump in such circuits if supporting theexchanger becomes expensive. A pump in the circuit will bring the exchanger to grade.

Figure #6-17

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Process requirements can also elevate exchangers. Assessment of elevation from a flow diagram isdifficult. The process engineer must specify required conditions.

Figure #6-18

In Figure #6-18 close temperature control in the flowing liquid was required. The liquid was near itssolidifying point and was kept just flowing until forced through sprayers for prill formation. The wholearrangement of exchangers, holding drums and pumps were arranged on a high prill tower.

Finally, exchangers can be elevated for economical reasons. There was sufficient pressure in thesystem shown on Figure #6-19 to place the exchanger at grade. Investigation showed it was moreeconomical to support the small diameter exchanger on one of the adjacent towers, than to leave itat grade. This saved jacketed piping between the exchanger and towers.

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Figure #6-19

In certain areas it is less expensive to locate exchangers high on a tower than provide pumps andnecessary piping.

Generally, these points elevate exchangers. However, the necessity of elevating exchangers should becarefully investigated and alternative possibilities cost-evaluated. It is expensive to provide supportingsteel, access and handling steel, to elevated exchangers.

6.4 EXCHANGER STUDIES

Location of exchangers can also affect piping design. Process equipment in most plants is arranged inthe sequence of process flow. However, whatever plot development system is used the generalevaluation regarding exchanger positions is very similar.

Generally, the fractionation towers should be arranged first and other equipment after the proper towersequence had been established. The position of an exchanger in petrochemical plants usuallydepends on the position of towers or, sometimes, on other process equipment. This relative position ofexchangers can be readily evaluated from flow diagrams. For exchanger positions in a petrochemicalplant the following general classification can be made.

• Exchangers which must be next to other equipment. Such exchangers are the reboilers thatshould be located next to their respective towers, or condensers which should be next to their

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reflux drums close to the tower.

• Exchangers which should be close to other process equipment. For example, exchangers inclosed pump circuits such as some reflux circuits. Overhead condensers should also be close totheir tower. In case of tower−bottom-draw-off-exchanger-pump flow, exchangers should beclose to the tower or drum, to give short suction lines.

• Exchangers located between two distant items of process equipment as shown on Figure #6-20.These are, for example, exchangers with process lines connected to both shell and tube side.Where the two streams meet in the pipeway and have a parallel run is the preferred location ofexchanger. And on that side of the pipeway, where the majority of related equipment is placed.In Figure #6-20, the south side because the three related items are on this side. Other locationswill cost more in pipe runs

Figure #6-20

Figure #6-20 - This is a good design when exchangers must be provided between two pieces ofequipment.

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• Exchangers located between process equipment and the unit limit, as shown on Figure #6-21.Such exchangers are for example product coolers. These are frequently located near the unitlimit.

Figure #6-21

Figure #6-21 - Product coolers should be located along the way to the battery limit.

Stacked Exchangers. A further step in making studies is to establish which exchangers can be stackedfor simplifying piping and saving plot space. Most units in the same service are grouped automatically.Two exchangers in series or parallel are usually stacked. Sometimes, small diameter exchangers inseries can be stacked four high. Sufficient clearance must be provided for shell and channel sidepiping between the two exchangers. Reboilers and single condensers usually stand by themselvesbeside their respective towers.

Most client specifications usually limit the maximum height of exchangers to about 18 feet to the top ofshell, so that mobile plant equipment can conveniently handle tube bundles.

Figure #6-22A shows typical exchanger groupings. It is sufficient to provide access only on one side ofexchangers for valves and instruments. Pairs or batteries of exchangers are spaced with a minimum of1'-6" clearance between the outside of channel flanges.

Process conditions will dictate whether piping will be configured in a parallel or series flow (SeeFigures #6-22B and #6-22C).

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Figure #6-22A

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Figure #6-22B

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Figure #6-22C

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6.4.1 Anchor Locating Instructions - Horizontal Shell and Tube Heat Exchangers

All horizontal shell and tube heat exchangers and kettle type reboilers are purchased with slottedanchor holes in each saddle. This expedites purchase of equipment and prevents changes to vendordrawings and equipment when layout requires a shift of the anchor from one saddle to the other.

The anchor point may be at pier "A" or "B". Piping layout and stress analysis shall determine. (Seefigure #6-23A)

Figure #6-23A

Exchangers having cooling water from underground to channel shall have the anchor at the channelend. (See figure #6-23B)

Figure #6-23B

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Anchor locations for exchangers without underground piping connections shall be determined by pipingflexibility. (See figure #6-23C)

Figure #6-23C

Once anchor pier is selected, mark an "X" on that pier on the equipment location control plan drawingand indicate coordinate of anchor pier.

Thermosyphon reboilers may be supported from the adjacent vessel or from independent structures. Ineither case, the method and location of the support shall be determined by piping stress. Location ofthe supports will be determined on the basis of minimizing differential movement between the reboilerpiping and the vessel.

If steam is to be circulated through the reboiler prior to start-up or if there is an appreciable difference inthe temperature of the reboiler and the vessel, the reboiler may require spring supports.

When possible, support thermosyphon reboilers independent of platforms to improve maintenance andoperation accessibility.

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6.4.2 How to Analyze Exchanger Piping

After all information has been collected, exchangers located in the plant and elevations established, thenext step is to outline clearance and working space requirements around both ends of the heatexchanger. These working spaces should be kept clear of any piping to facilitate channel, shell coverand tube bundle removal for maintenance and cleaning. (These clearances are shown in Figure #6-24for about a 2'-0" shell diameter exchanger. Smaller units will require somewhat less and larger onesslightly more clearance.)

Besides providing adequate access, piping requirements result in simple and well-organized physicalarrangement giving three-dimensional reality to the piping systems and details presented in themechanical flow diagrams.

Figure #6-24

Figure #6-24 - This plan view shows provision for tube bundle removal with minimum removal of piping.

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Figure #6-25 shows an exchanger in elevation with adjacent process equipment and multi-levelpipeway. The main elevation for lines running between the exchanger nozzles and pipeway is about 2to 3 feet lower than the pipeway elevation. All steam lines will connect to the top of the header to avoidcondensate drainage towards the exchanger.

Figure #6-25

Lines interconnecting exchangers with other process equipment can run just above required headroomor about on the same level as the pipe way. Reboiler line elevations are determined by the draw offand return line nozzles on the tower. Symmetrical reboiler piping arrangements - between the towerdraw off and reboiler inlet nozzles; similarly between reboiler outlets and return connection on the tower- are preferred for equal flow in the reboiler circuit. But non-symmetrical arrangements are alsoaccepted to a more economical or more flexible piping design.

The overall plant design already influences the main arrangement of exchanger piping and necessaryaccess (See Figure #6-24). The channel end of exchangers face the main plant access for convenienttube removal. The shell cover faces the pipeway and should be as close to the pipeway steel aspractically possible (usually 10'-0" from column center to outside of shell cover).

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If piping is arranged on one elevation only between exchanger and pipeway, one line will be locatedright over the exchanger centerline. It is suggested to choose a top shell side nozzle for this location.The top tube side connection can be placed on a slight angle to miss the top shell side line without anoffset in the line. Lines turning right in the pipe way should be right of the exchanger centerline andthose turning left should approach the pipe way on the left hand side of exchanger centerline. Linesfrom bottom connections should also turn up on the right or left side of exchangers depending uponwhich way the line turns in the pipe rack. Lines with valves should turn towards the access aisle withvalves and control valves arranged close to exchanger.

Utility lines connecting to a header in the pipeway can be arranged on any side of exchanger centerlinewithout increasing pipe length.

Cooling water lines in most cases are below grade and should run right under the lined up channelnozzles of all coolers. Cooling water return header is usually adjacent to the cooling water supply line.

Access to valve hand wheels and instruments will influence piping arrangement around heatexchangers. Valve hand wheels should be accessible from grade and from a convenient access way.These access ways should be utilized for arranging manifolds, control valves and instruments.

In piping arrangement provision for tube removal access should also be provided. This usually meansa spool piece or flanged elbow in the pipeline connecting to the top of channel nozzle.

The requirements of good piping design in general apply to the design of heat exchanger piping. Theshortest lines and least number of fittings - temperature permitting - will obviously provide the mosteconomical piping arrangement. The designer should avoid unnecessary loops, pockets andcrossovers. And would investigate nozzle to nozzle, the whole length of piping routed from theexchanger to some other equipment, aiming to provide not more than one high point and one low point,no matter how long the line. Often a flat turn in the pipe way, an alternative position for control valvesor manifold, changed nozzle location on the exchanger, etc., can accomplish this requirement.

Avoid excessive piping loads on exchanger nozzles from actual weight of pipe, fittings and from forcesof thermal expansion.

For valves and blinds the best location is directly at the exchanger nozzle. In case of an elbow nozzleon an exchanger it should be checked that sufficient clearances are provided between valve handwheel and outside of exchanger. Elevated valves are usually chain-operated. The chain should hangfreely at an accessible spot near the exchanger. Figure #6-26 shows sketches highlighting exchangerpiping details.

Locally mounted pressure and temperature indicators on exchanger nozzles or on the process linesshould be visible from the access aisle. Similarly gauge glasses and level controllers should be visibleand associated valves accessible from this aisle. Care should be taken to give due consideration tointernal details of heat exchangers when arranging instrument connections.

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Figure #6-26

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6.4.3 Tube Bundle Handling

When doing maintenance work on an exchanger either the complete unit is removed, cleaned andrepaired where such facilities are available. Or, only the tube bundle is removed for cleaning andrepair; the shell is cleaned in place. In the first case all piping, in the second case only channel nozzlepiping need be disconnected. The piping designer can help maintenance in three ways.

• Designing and supporting piping so that no temporary support will be required when removingthe channel and tube bundle or at least temporary supports can easily be built.

• By providing easily removable spool pieces, breakout flanges, or short pipe runs to provideadequate clearances for tube removal equipment.

• By leaving space and access around the exchanger as shown already in Figure #6-24.

All tube removal shall be by mobile crane or as required by contract specifications and procedures.Figure #6-27, Figure # 6-28 and Figure #6-29 show alternatives to a mobile crane.

Hitching points in the front of exchangers facilitates the removal of tube bundles at grade. Chain orrope is fixed to the bundle and hitching point and a pulley transmits the necessary force and motion forremoval. The hitching point can be at grade as shown on Figure #6-27, Sketch A. The distancebetween the front of exchanger and hitching point is about twice the bundle length.

Figure #6-27

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Figure #6-27 - Typical tube bundle pulling arrangements. Sketch B is better for stacked exchangers.

A more positive pulling force can be exerted horizontally with hitching point in line with exchangercenterline. Existing structures in convenient positions can be used for rigging up pulling beam forbundle removal.

Figure #6-27, Sketch B shows trolley and pulling beams in a permanent structure over exchangers.

For handling many single or stacked exchangers at grade a traveling gantry can be provided. SeeFigure #6-28. The gantry consists of trolley beam, trolley and pulling beam on a structural frame whichcan be moved on rails along the front of exchangers.

Figure #6-28

A considerable saving can be achieved in capital outlay and maintenance with the hydraulic bundleremover shown on Figure #6-29. Using this equipment eliminates permanent trolley beams andstructures, gantry cranes and pulling structure. The yoke fits any diameter of shell and thesectionalized ram can push out any length of bundle with the hydraulic jack that can exert force up to12,000 pounds.

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Figure #6-29

The arrangement of exchangers and associated piping in a petrochemical plant is quite simple.However, it is hoped that this lesson has shown how many details are involved in designing this simplestudy.

Heat is one of the basic tools of the refining and petrochemical plant. It stands to reason then that heatexchangers are an important part of this industry.

The word heat exchanger is generally used to include the entire group of units designed to exchangeheat. In other words coolers, condensers, preheaters, chillers, vaporizers, reboilers, steam generators,partial condensers, subcoolers, etc., all fit into the general class of exchangers. All shell and tubeexchangers for the most part look alike, with the exception of the kettle type reboiler whose shape setsit apart from the others.

6.4.4 Exchangers - TEMA Nomenclature

Shell and tube exchangers may be divided into three basic types. These are floating head, fixed tubesheet, and U-tube. There are advantages and disadvantages to each type. Process conditions mostoften determine the type to be used. A given plant often has all three types in use depending on theserviced involved. Manufacturers have agreed on the nomenclature to be used to describe the varioustypes (See 000.250.2600, Exchangers - Tema Nomenclature and Figure #6-32).

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Figure #6-32

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6.5 KEY TO OUTLINE DRAWINGS

Once an order has been placed for a shell and tube exchanger, the most important need from thepurchaser's viewpoint is the outline (dimensional) drawing. Until this is available, final details ofstructural, and piping work necessary to integrate the exchanger into the system cannot be completed.Preparation of the outline drawing by the manufacturer requires complete detailed design of theexchanger - a time-consuming job. Usually, the outline drawing will be available two to three weeksafter order. Sometimes this period extends to a month or more. During this time the purchaser cancomplete preliminary study work, estimating exchanger dimensions by reference to the exchangerspecification sheet.

The data on the exchanger specification sheet which establish the general configuration of theexchanger are (1) the exchanger type, (2) the tube length, and (3) the shell diameter. With these and aknowledge of permissible nozzle arrangements and orientations, a quick estimate of exchangerdimensions can be made.

Important Dimensions

The following sketches illustrate important dimensions for floating head, fixed tubesheet, and U-tubeexchangers. (Figure # 6-33)

Figure #6-33

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6.5.1 Estimating Heat Exchanger Dimensions

Using tube length and shell diameter, dimensions can be approximate by formulas below. Theabbreviation T.L. stands for tube length; S.D. for shell diameter.

Possible Variation Tolerance

A = T.L. +2.DS

+ 26" +12" -6

B = T.L. ---

C =2.DS

+ 24" 4"

D =4.DS

+ 19" 4"

E = T.L. -2.DS

-20" 8"

F =2.DS

+ 9" 2"*

G =2A

- 1" 3"

H =2A

(Rounded off to next smaller foot dimension) *

J = T.L. - 24" 8"

K =2A


L = T.L. ---

M = T.L. - 24" (not valid if a nozzle is located 8" end of bundle)

N =2A


(*) Span between supports and projection of supports can vary considerably depending onstandards established by the manufacturer.

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Note: U-tube units, manufacturers customarily show the straight length of the tubes (to the tangentpoint of the U-bends) as a part of the size designation. For U-tube units, the tube length (T.L.)is this straight length plus one-half the shell diameter.

These formulas are based on exchangers with 8-inch nozzles. Corrections may be applied for nozzlesof different size as follows: (Note that CNS stands for the larger channel nozzle size; FSNS stands forthe front shell nozzle size; RSNS stands for the rear shell nozzle size.)

Dimension A - Add: CNS - 8"Dimension C - Add: (CNS - 8") ½ (FSNS - 8")Dimension D - Add: ½ (FSNS - 8") ½ (CNS - 8")Dimensions E, J, M - Subtract: ½ (FSNS - 8") + (RSNS - 8")

Unless there is a large difference in size, these corrections are not required.

6.6 OTHER EXCHANGER TYPES

Three basic exchanger types are illustrated (See Figure #6-33). Flat, removable channel covers(TEMA A) are shown for each type. Dimensions are nearly the same if bonnet covers (TEMA B) areused, providing nozzles are arranged as shown (perpendicular to the exchanger horizontal axis).

If fixed tube sheet construction is used with a single tube pass rather than multiple passes asillustrated, the overall length, A is increased by 16 inches. The distance between front and rearchannel nozzles is approximately [J+(2xD)].

Chillers, vaporizers, and reboilers represent a special case if they are kettle type (TEMA K). The overalllength will apply if S.D. is the larger diameter shown on the exchanger specification sheet. Add surgesection length to this if applicable. There is considerable latitude for nozzle location except that theoutlet vapor nozzle (shell side) should normally split the tube bundle.

In exchanger types with divided or split flow (single inlet and two outlets or vice versa, and single inletand outlet centrally located), the dimension between the channel nozzle centerline and the single shellnozzle is D + ½ E (or J or L).

Formulas are not applicable to special exchanger types and to high-pressure exchangers. However,data provided by the manufacturer is usually sufficient to determine at least limiting dimensions.

6.6.1 Space Requirements

The space "envelope" needed for the exchanger can be developed from the formulas:

Overall Length Required = A + B (or A + L with fixed tube sheet type)

Overall Height Required = 2 x F (Excluding foundation height)

Overall Width Required = 2 x F maximum (2 x F - 8" average)

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6.6.2 Nozzle Location and Orientation

In many cases there is more than one choice of nozzle location or orientation. The manufacturer'soutline drawing will show suggested location. A knowledge of the options available will permit thepurchase to either approve the manufacturer's suggested location or to select an arrangement moresuited for your needs.

Shell Nozzle Location and Orientation

With a single pass shell, nozzles can be located either in positions X-X or positions Y-Y (See Figure#6-33).

With a two-pass shell, nozzles are on the same centerline, located at the front of the shell.

Normal orientation of shell nozzles is top and bottom. When no change of phase occurs as withgases or liquids, nozzles can be side mounted, or inlet may be top or bottom as desired. Whencondensation occurs, the inlet is at the top and outlet at the bottom. When vaporization occurs, theinlet is at the bottom and the outlet at the top.

6.7 G-FINS AND AIR COOLERS

G-fins (Double pipe exchangers) are available in both single tube and multi-tube type construction.(See Figure #6-34.) Both are built in the hairpin style, i.e., inlet and outlet connections for both insideand outside the tube are at one end. The exchanger goes down and back to form a large U shape.The term G-fin, which is often used for this type of unit, was the trade name used by the Griscom-Russell Company that is no longer in business. The principal advantage of the double pipe type is itslow cost. Units may be used singly, or in multiples. They are easily manifolded to suit a variety ofconditions.

Figure #6-34Double-Pipe (G-Fin) Type Exchanger

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Air Coolers

There are two types of air cooler designs. (See Figure #6-35) One is the induced draft type where thefans are located above the finned tube sections, and the other is the forced draft type where the fansare below the tube bundle. Both styles enjoy almost equal popularity. Unlike other types ofexchangers such as shell and tube where you might have a single shell or several shells stacked oneabove the other, air coolers take up considerable amounts of space.

For this reason they are generally mounted above the pipe rack. It is not unusual for a single air coolerunit to require 100 feet or more of rack space. Units are furnished in what are called bays. Two fansper bay and one or more bays per unit. Fan drives are either gear or belt driven depending on thehorsepower required. Here again, unlike the shell and tube type that normally sits on two piers, the aircooler is apt to have walkways, ladders, maintenance platforms, etc., associated with each installation.

Figure #6-35

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EXCHANGERS – EXERCISE INSTRUCTIONSPage 1 of 6

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Exchangers - Exercise Instructions1. Generally review the Flow Diagram to become familiar with the piping and equipment.

Lesson 6Exchanger Piping Exercise

Flow Diagram

2. Do a "rough" transposition, for your own benefit.

3. Do equipment study of 21-E-16. (Exchanger flanges are 50" O.D.)

4. Do equipment study of 21-E-14A&B and 21-E-26. (Exchanger flanges are 30" O.D.)

5. Size exchangers. (See Lesson Section " Estimating Heat Exchanger Dimensions)

a. Give coordinate of anchor saddle.b. Exchanger information is on the plot plan.c. Completely dimension exchanger. (nozzles, supports, length)

6. Produce your study to scale: 3/8"=1'-0" with north arrow to the right.

7. "A" and "N" spec = 150# RF, 1-1/2" and smaller is socket weld."C" spec = 300# RF, 1-1/2" and smaller is socket weld."L" spec = 125# FF steel, 2" and smaller is 300# M.I. screwed."A" and "L" spec = 1/16" gaskets."C" and "N" spec = 1/8" gaskets.All pipe fittings and valve sizes can be found in your "Piping Design Guide" Practice 000.250.9810All Butt-welded branches are reducing tees.All flanges in all sizes are weld neck.

8. 21-E-14A&B and 21-E-16 have 2" thick insulation.21-E-26 has no insulation.No exchanger flanges are insulated.

9. Produce a nozzle block chart page E6 and set exchangers minimum to grade.

10. Line 21-13C-4" manifold will be located at the base of 21-C-4.

11. Route all lines, even those in the pipeway. Do not line-space or worry too much about sequence in the pipeway. Locate all manifolds and meter runs.

12. For 4" butterfly valve, use Pratt Model # 2F11

13. All pipeway steel is 14" wide flange.

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EXCHANGERS – EXERCISE INSTRUCTIONSPage 6 of 6

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NOZZLE CHART FOR EXCHANGER PIPING EXERCISE

Nozzle Description Size & Rating ElevationExample SHELL - IN 2" - 300# R.F. FACE EL. 106'-3"

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EXCHANGER PIPING TESTPage 1 of 3

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EXCHANGER PIPING TEST

All Questions - 5 Points Name ____________________________Except #15 - 10 Points

True or False

_______________ 1. Mobile handling equipment should be considered in location of exchangers.

_______________ 2. The maximum vessel liquid level is a prime factor in establishing the height relationship between vessel and reboiler.

_______________ 3. Two uses of exchangers are heating and cooling.

_______________ 4. In an exchanger using water as the cooling medium, the water flow should normally be from the bottom to the top.

_______________ 5. Fluid being heated should normally flow downward through the exchanger.

_______________ 6. Mechanical flow diagrams show required height of exchangers when required by process.

_______________ 7. The channel end of an exchanger directs the flow over the tube bundle.

_______________ 8. Pipe stress requirements should be considered in exchanger studies.

_______________ 9. Steam flow through as exchanger is normally from the bottom to the top.

_______________ 10. It is not necessary to know the nomenclature of an exchanger.

_______________ 11. Locations and rating of connections, including nozzles, should be verified on the squad check.

_______________ 12. Exchanger specification sheets can be used for preliminary study for basicequipment size and information.

_______________ 13. In locating air coolers above the pipeway, platforms are generally not required.

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Multiple Choice

14. What portion of an exchanger must be considered for clearance in the pulling area?

Shell

Tube Bundle

15. Sketch series and parallel flow. (Worth 10 points)

16. Which of the following symbols denotes "reboiler".

17. The maximum quantity of shells for stacked exchangers shall be:

2 high

4 high

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18. The height of a shell and tube exchanger to be set at a minimum elevation is determined by:

Clearance of bottom inlet/outlet line to grade.

Height of exchanger foundation.

Clearance from top of shell to grade.

19. Indicate support normally requiring anchor:

Support "A"

Support "B"


Support "A"

Support "B"

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EXCHANGERS - GRADING PLAN

All Questions are Worth Name _________________________________5 Point Except #15

True or False

TRUE 1. Mobile handling equipment should be considered in location of exchangers.

TRUE 2. The maximum vessel liquid level is a prime factor in establishing the height relationship between vessel and reboiler.

TRUE 3. Two uses of exchangers are heating and cooling.

TRUE 4. In an exchanger using water as the cooling medium, the water flow should normally be from the bottom to the top.

FALSE 5. Fluid being heated should normally flow downward through the exchanger.

TRUE 6. Mechanical flow diagrams show required height of exchangers when required by process.

TRUE 7. The channel end of an exchanger directs the flow over the tube bundle.

TRUE 8. Pipe stress requirements should be considered in exchanger studies.

TRUE 9. Steam flow through as exchanger is normally from the bottom to the top.

FALSE 10. It is not necessary to know the nomenclature of an exchanger.

TRUE 11. Locations and rating of connections, including nozzles, should be verified on the squad check.

TRUE 12. Exchanger specification sheets can be used for preliminary study for basicequipment size and information.

FALSE 13. In locating air coolers above the pipeway, platforms are generally not required.

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Multiple Choice

14. What portion of an exchanger must be considered for clearance in the pulling area?

Shell

Tube Bundle

15. Sketch series and parallel flow. (Worth 10 points)

16. Which of the following symbols denotes "reboiler".

17. The maximum quantity of shells for stacked exchangers shall be:

2 high

4 high

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18. The height of a shell and tube exchanger to be set at a minimum elevation is determined by:

Clearance of bottom inlet/outlet line to grade.

Height of exchanger foundation.

Clearance from top of shell to grade.


Support "A"

Support "B"


Support "A"

Support "B"

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6. exchangers ...piping design layout training lesson 6 exchangers page 3 of 46 15/11/2002 rev. 0...

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