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BECHTEL CORPORATION ENGINEERING PLANT DESIGN DESIGN GUIDE EXCHANGER PIPING 3DG-P22-00004, Revision 002, 2002 July 23 Reason for Issue: Issued for Use Prepared by: B. Tarr Checked by: P.R.Wood Approved by: R. Fox INTRODUCTION This Engineering Design Guide explains the different types of heat exchangers that are most commonly used in facilities. It addresses locations, elevation requirements, nozzle locations, exchanger supporting, associated piping supports, maintenance and operation access.

Electronic documents, once printed, are uncontrolled and may become outdated. Refer to the electronic documents in BecRef for current revisions.

Bechtel Confidential Bechtel Corporation 2002. Contains confidential and/or proprietary information to Bechtel and its affiliated companies which shall not be used, disclosed or reproduced in any format by any non-Bechtel party without Bechtels prior written permission. All rights reserved. 3DG-P22-00004-002 Page 1 of 52

TABLE OF CONTENTS INTRODUCTION ...................................................................................................................... 1 LIST OF FIGURES ................................................................................................................... 5 1.0 2.0 3.0 3.1 3.2 3.3 4.0 5.0 6.0 6.1 6.2 6.3 6.4 7.0 7.1 7.2 7.3 7.4 7.5 7.6 PURPOSE ....................................................................................................................... 7 EXCLUSIONS.................................................................................................................. 7 DISCUSSION................................................................................................................... 7 SAFETY........................................................................................................................... 7 OPERATION.................................................................................................................... 7 MAINTENANCE............................................................................................................... 7 TERMINOLOGY .............................................................................................................. 7 BASICS OF HEAT TRANSFER ...................................................................................... 9 TYPES OF EXCHANGERS ........................................................................................... 10 SHELL & TUBE............................................................................................................. 10 DOUBLE PIPE EXCHANGERS..................................................................................... 18 AIR COOLERS ............................................................................................................. 18 OTHER EXCHANGER TYPES..................................................................................... 20 EXCHANGER PLOT LOCATION AND ELEVATION OF EXCHANGERS.................... 24 SHELL & TUBE ARRANGEMENTS ............................................................................. 24 LOCATION BY ASSOCIATION..................................................................................... 24 EXCHANGER BATTERY ARRANGEMENTS............................................................... 27 ELBOW NOZZLES TO REDUCE SHELL ELEVATION................................................ 28 EXCHANGERS WITH CONDENSATE POTS ............................................................... 28 REBOILERS WITH CONDENSATE POTS ................................................................... 30

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7.7 7.8 8.0 8.1 8.2 8.3 8.4 9.0 9.1 9.2 9.3 9.4 9.5 9.6

DOUBLE PIPE EXCHANGERS..................................................................................... 30 RACK MOUNTED AIR COOLERS................................................................................ 30 SHELL AND TUBE NOZZLE LOCATION & NOZZLE TYPE ....................................... 33 SHELL & TUBE NOZZLE LOCATION OPTIONS......................................................... 33 SHELL & TUBE NOZZLE ORIENTATION OPTIONS................................................... 34 NOZZLE LOCATION WITH RESPECT TO FLOW ....................................................... 35 AIR COOLERS .............................................................................................................. 35 SUPPORTS ................................................................................................................... 37 SHELL & TUBE............................................................................................................. 37 SPACE FRAMES OR SPACERS .................................................................................. 38 SADDLE / FOUNDATION CLEARANCES.................................................................... 39 SHELL & TUBE PIPE SUPPORT LOCATIONS ........................................................... 40 VERTICAL REBOILER SUPPORTS ............................................................................. 41 AIR COOLER SUPPORTS............................................................................................ 42

10.0 MAINTENANCE AND OPERATIONAL ACCESS ......................................................... 43 10.1 SHELL & TUBE............................................................................................................. 43 10.2 BUNDLE EXTRACTOR................................................................................................. 46 10.3 CLEARANCES .............................................................................................................. 47 10.4 STACKED EXCHANGERS............................................................................................ 47 10.5 CRANE ACCESS........................................................................................................... 47 10.6 AIR COOLERS .............................................................................................................. 47 10.7 AIR COOLER HEADER BOX ACCESS ........................................................................ 48 10.8 PLATFORM OPTIONS FOR AIR COOLER MOTOR ACCESS .................................... 49 11.0 PIPE STRESS............................................................................................................. 50

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11.1 EXCHANGER ANCHOR LOCATION ............................................................................ 50 11.2 SHELL & TUBE NOZZLE LOADS ................................................................................ 51 11.3 AIR COOLER NOZZLE LOADS.................................................................................... 51 12.0 REFERENCES............................................................................................................ 52

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LIST OF FIGURES Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18 Figure 19 Figure 20 Figure 21 Figure 22 Figure 23 Figure 24 Figure 25 Figure 26 Figure 27 Figure 28 Figure 29 Figure 30 Figure 31 Figure 32 Figure 33 Figure 34 Figure 35 Figure 36 Figure 37 Figure 38 Figure 39 Figure 40 Figure 41 Figure 42 Standard Counterflow Patterns for Shell & Tube ................................................. 9 Exchanger Nomenclature................................................................................... 12 Shell & Tube Fabrication Tolerances................................................................. 14 Shell & Tube Fabrication Tolerances................................................................. 15 Vertical Vessel Mounted Reboilers .................................................................... 16 Condensate Pot Effect on Tower ....................................................................... 17 Vertical Direct Mount Condenser ....................................................................... 17 Double Pipe Exchanger Components ................................................................ 18 Air Cooler Header Box Types ............................................................................ 19 Air Cooler Components...................................................................................... 20 Stab-in Reboiler ................................................................................................. 21 Spiral Exchanger................................................................................................ 21 Plate Exchanger................................................................................................. 22 Aluminum Core Exchanger ................................................................................ 23 Core Exchanger Insulation................................................................................. 23 Standard Piping Arrangements for Shell & Tube Exchangers ........................... 24 Exchanger Placement ........................................................................................ 27 Arrangement of Exchanger Batteries ................................................................. 28 Elbow Nozzles ................................................................................................... 28 Alternative to Vertical Condensate Pot .............................................................. 29 Condensate Pot Piping Arrangement ................................................................ 29 Double Pipe Exchanger Method of Support.................................................... 30 Conventional Platform Design for Air Coolers ................................................... 31 Air Cooler Supports ........................................................................................... 32 Nozzle Adjustments to Standard Exchangers .................................................... 33 Possible Nozzle Arrangements for Shell & Tubes ............................................. 34 Change Nozzles to Improve Routing ................................................................. 35 Change Flow to Improve Routing ...................................................................... 35 Odd or Even Pass Air Coolers ........................................................................... 36 Standard Air Cooler Piping Arrangements......................................................... 36 Inserts for Air Coolers ........................................................................................ 37 Shell & Tubes at Grade with Same U/G Cooling Water Supply ........................ 38 Shell & Tubes on Elevated Platform .................................................................. 38 Space Framing................................................................................................... 39 Clearances for Shell & Tube Exchangers .......................................................... 40 Support Design for Piping at Shell & Tube ........................................................ 41 Vertical Reboilers............................................................................................... 42 Air Cooler Supports ........................................................................................... 43 Shell & Tube Exchanger Access........................................................................ 44 Tube Pulling Requirements ............................................................................... 45 Tube Bundle Extractor ....................................................................................... 46 Crane Access..................................................................................................... 47

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Figure 43

Plugged Header Box.......................................................................................... 48

LIST OF FIGURES (contd.) Figure 44 Figure 45 Figure 46 Figure 47 Air Cooler Platforming Alternatives.................................................................... 50 Slotted Holes for Shell & Tubes......................................................................... 51 Lateral Stresses on Air Cooler Nozzles ............................................................. 52 Spring Supports for Air Coolers ......................................................................... 52

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1.0

PURPOSE

To provide the layout designer with guidelines for the development of piping design for nonfired heat transfer exchangers. 2.0 EXCLUSIONS

All or part of this guide may be superseded by client mandatory standards or by the codes and regulations imposed by governmental jurisdictions covering the location where the piping is installed. 3.0 3.1 DISCUSSION SAFETY

Proper consideration for personnel safety around exchangers requires arranging piping and valves in a manner that does not obstruct access for operation, maintenance or egress. 3.2 OPERATION

Exchangers normally require minimal attention during operation. Valves however, must be located for easy access. Where valves cannot be operated from grade, chain operators shall be used. If chain operators are not allowed per client specifications, platform access to valves shall be considered. 3.3 MAINTENANCE

Piping shall be arranged in a manner to allow adequate access to removable channel covers without requiring excessive dismantling of the piping system. The bolting connecting the channel cover to the shell must be easily accessed in order to pull the tube bundle. Consideration shall be given for clearances in all directions for the use of bundle extractors (10.2). 4.0 TERMINOLOGY

Baffles: Partial interior walls set within the shell of an exchanger to redirect the flow in the exchanger to maximize contact time and thereby increase heat transfer (Fig. 1). Bundle: A group of tubes connected to common inlet and outlet head/heads. Bundles are usually associated with shell and tube type exchangers (Fig. 1), though at times they may be used independent of a shell (as in the case of stab-in heaters) (Fig. 11). Cell: A grouping of tubes connected to common inlet and outlet manifold boxes. Cells are usually associated with air coolers.

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Conduction: The ability of an object to pass (conduct) heat through its molecular structure; the distribution or transfer of heat (energy) from one end of an object or from one object to another through physical contact. Convection: The mixing action that occurs in any heated fluid (heated fluid rises displacing cool fluid which falls replacing heated fluid); the transfer of heat within a fluid or from one fluid to another by means of the thermal mixing action. Fins: Appendages affixed to the outer skin of tubes to augment their surface area to increase contact time and thereby heat transfer. Forced draft: A method of tube cooling in which fan driven air is blown directly through a tube cell (Fig. 10). Induced draft: A method of tube cooling in which fan drawn air is pulled (induced) through a tube cell (Fig. 10). Parallel: A method of interconnection of exchangers in which the flow stream is split between two or more exchangers capable of operating independently either simultaneously or in back-up of each other. Exchangers in parallel usually can be isolated from the flow stream to allow for maintenance or for temperature or output control (Fig. 16). Series: A method of interconnection of exchangers in which the flow stream must past through each exchanger in sequence. Exchangers operating in series are treated as one system component and usually cannot be isolated without shutdown of the system (Fig. 16). Shell: Closed conduit used to convey a medium around a set of tubes for the purpose of heat transfer between that medium and one being conveyed by the tubes (Fig. 1). TEMA: The Tubular Exchanger Manufacturers Association, an industrial association which has published standards for the design and manufacture of tubular exchangers (Fig. 2). Thermosiphon: A method of circulation based on a heated fluid's tendency to rise. This method of circulation is used most often in boiler and reboiler systems. Tubes: Closed conduit for a single heating/cooling media most often used in conjunction with a sealed outer conduit (shell), but may also be used in open contact with atmospheric cooling/heating media. They are also often referred to as channels (Fig. 1).

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5.0

BASICS OF HEAT TRANSFER

The most common method of heat transfer from one fluid to another in a process environment is by the use of exchangers. Exchangers, while varying greatly in design, all operate on the same principle. The principle that heat (energy) tends to equalize by dissipation. That is that heated objects try to equalize their temperature by transmitting their heat to surrounding cooler objects. This is similar to a liquid seeking its own level. Hot objects try to transmit their heat to any cooler objects around them, which in turn tend to absorb that heat. All exchangers employ this principle by using one or more of three heat transfer methods; conduction, convection and radiation. The tendency of the heated portions of a fluid to rise dictates the most common pattern of flow in exchanger piping. That pattern is for the fluid receiving heat to flow up through the exchanger and the fluid expending heat to flow down (Fig. 1).

Figure 1

Standard Counterflow Patterns for Shell & Tube

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6.0

TYPES OF EXCHANGERS

While often referred to by their design and construction characteristics, exchangers are most frequently identified by their process function. The following is a listing of process names often assigned exchangers relative to their function: Exchanger: Heats one stream while cooling another (Very efficient in that there is no waste heat loss). Cooler: Cools liquids or gases without condensation. Subcooler: Condenses vapor and further cools the condensate using water as a cooling medium. Condenser: Cools a vapor to its dew point in order to extract condensate from it. Chiller: Uses refrigerants to cool a stream below the standard temperature of available cooling water streams. Heater: Heats process stream (generally to its boiling point) with no appreciable vaporization (often uses steam as heating medium). Reboiler: Reboils (vaporizes) the bottom stream of a fractionating tower prior to its return to the tower. Often employs thermosiphon phenomenon rather than any mechanical flow enhancement. Waste Heat Boiler: Uses waste heat (i.e., gas-turbine exhaust) as a heating medium. Steam Generator: Uses process liquids or gases to produce steam (usually from boiler feed water). Vaporizer: Vaporizes part of a process stream (also called an evaporator). 6.1 SHELL & TUBE

The most common heat exchanger encountered in any process or power plant is the shell and tube exchanger. These exchangers, because of their reliability, low maintenance, and durability, generally offer the most economical method of heat control and transfer, while their "no moving parts" simple means of operation can be very efficient. They operate by conducting one fluid stream through the channel (tube) head of the exchanger into a set of tubes (the bundle) that is encased within the exchanger shell. A second fluid is simultaneously directed through the shell (usually in the opposite direction) while maintaining contact with the tubes. The heat transfer is effected through the tube walls without the fluids coming in direct contact with each other.

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6.1.1 Conventional TEMA Exchangers Of shell and tube exchangers the most common are those designed to meet TEMA standards of design and construction (Fig. 2).

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Figure 2

Exchanger Nomenclature

TEMA exchangers offer the following:

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Economy: they can be varied in size in accordance with the heat transfer required thereby utilizing the minimal material for the maximum result; they can handle large flow rates with a large range of pressure ratings; they can often reduce waste heat by heating one flow stream while cooling another. Maintenance: standardization allows standardized maintenance procedures with more readily obtainable parts; few parts subject to failure; minimal assembly/disassembly requirements. Efficiency: by multiple pass series flow these exchangers offer an almost unlimited range of transfer rates. Reliability and Consistency: design is made simpler and reliability increased by the standardization of design and construction tolerances set by TEMA.

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Figure 3

Sh ell & Tube Fabrication Tolerances

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Figure 4

Shell & Tube Fabrication Tolerances

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6.1.3 Reboilers A variation of the conventional shell and tube, still incorporating TEMA standardized components, is the reboiler (Figs. 5 and 6).

Figure 5

Vertical Vessel Mounted Reboilers

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Figure 6 Condensate Pot Effect on Tower 6.1.4 Direct Mount Condensers Occasionally condensers associated with separators, knockout drums, or accumulators are mounted directly on the vessel. Such configuration can be very cost effective in that they eliminate some of the components required for a stand alone condenser, the interconnecting piping between the equipment as well as the supports for said piping. (Fig. 7)

Figure 7

Vertical Direct Mount Condenser

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6.2

DOUBLE PIPE EXCHANGERS

Double pipe are probably the most economical exchangers available. They consist of a single tube enclosed within another. As with conventional shell and tube exchangers, double pipes rely on the cross flow of two fluid streams to affect a heat transfer. In an effort to increase the contact time of fluids in double pipe exchangers, most manufactures attach fins to the inner tube. This practice has resulted in this type of exchanger being referred to as fin-tubes or G-fins. (Fig. 8)

Figure 8 6.3

Double Pipe Exchanger Components

AIR COOLERS

Air coolers make up the second largest family of process and power plant exchangers. While not as efficient, compact or precise as shell and tubes, air coolers are often the answer when supplies of cooling fluids (cooling water, refrigerant, cool process fluids...) are limited. Their purchase cost is often lower than that of shell and tubes, which can also make them preferable for services where precise temperature control is less of a concern.Electronic documents, once printed, are uncontrolled and may become outdated. Refer to the electronic documents in BecRef for current revisions. Bechtel Confidential Bechtel Corporation 1995, 2002. All rights reserved. Engineering Design Guide Exchanger Piping 3DG-P22-00004-002

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Air coolers operate by flowing a fluid through a set of tubes (cell) while air is passed through the cell around the tubes. The passing air absorbs and carries away the heat. Header boxes for air coolers may be specified plugged or with cover plate. Plugged boxes allow the maintenance of damaged tubes without the disassembly of the box but are generally heavier and more prone to leakage. (Fig. 9)

Figure 9

Air Cooler Header Box Types

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6.3.1 Forced Draft Forced draft coolers operate by pushing air through the tube cells from fans mounted below them. This method of fan and motor mounting make them easily accessible from below the exchanger. These coolers are more efficient than induced draft because the cool air they move is denser (more air is moved), however, because the fans tend to channel the air, distribution may be uneven. This may result in the formation of hot spots in the cells and cause uneven tube wear. The cells of these coolers are exposed to the elements, also contributing to wear (Fig. 10). 6.3.2 Induced Draft Induced draft coolers draw air up through the tube cells with fans mounted above them. This arrangement reduces the formation of hot spots by flowing air more evenly across the tubes and do protect the cells from the elements by covering them with the fan cowlings. The air they move, however, is warm and less dense (having already passed through the cells), reducing their efficiency. The over head fan and motor mounting make these coolers more difficult to maintain (Fig. 10).

Figure 10 Air Cooler Components 6.4 OTHER EXCHANGER TYPESElectronic documents, once printed, are uncontrolled and may become outdated. Refer to the electronic documents in BecRef for current revisions. Bechtel Confidential Bechtel Corporation 1995, 2002. All rights reserved. Engineering Design Guide Exchanger Piping 3DG-P22-00004-002

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6.4.1 Stab-In Exchangers Also referred to as bayonet exchangers, they are often used where pressure loss through piping, space limitations or other circumstances preclude the use of more conventional exchangers. They are usually constructed of a TEMA standardized head and tube bundle. Often used as heating elements for tanks and occasionally in lieu of reboilers for fractionating towers. These exchangers, because of the way they are integrally connected to the equipment they service, usually cannot be worked on without shut down of that equipment. This limits their maintainability and often makes them a last choice method of heat control (Fig. 11)

Figure 11

Stab-in Reboiler

6.4.2 Spiral Exchangers These consist of a tube or set of tubes, twisted into a helical coil, contained in a barrel like shell or casing. The casing is usually split (most often vertically) and can be opened for maintenance. One fluid enters and exits the tubes through nozzles penetrating one side of the casing while the second fluid passes through the casing from nozzles on either end (Fig. 12).

Figure 12

Spiral Exchanger

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6.4.3 Plate Exchangers While not having true tubes, the plate exchanger operates on the same mechanical principles as the shell and tube. Instead of tubes the plate exchanger uses sets of tightly arranged thin, flat, hollow plates. The fluids flows through alternate contacting opposite walls of each plate, transferring their heat in the process. These exchangers can be very efficient in their ability to transfer heat attaining as low as a 2% heat differential between exiting fluids. Plates can also be added or removed to vary the performance or for maintenance and repair (Fig. 13).

Figure 13

Plate Exchanger

6.4.4 Core Exchanger Core exchangers (or core chillers) are a unique variation of plate exchangers. These exchangers use plates alternately set within a shell through which the flow media pass, as do plate exchangers. The plates in a core, however, are sealed together, in a process called brazing, to create a single monolithic unit. Materials used in these types of exchangers are often aluminum or aluminum alloys, which are great for heat transfer, but notoriously bad in terms of tinsel strength and stress durability. For that reason cores are used for low temperature or chilling services exclusively. Piping serving these exchangers is usually S.S., requiring a transition piece between the piping and exchanger. These are often supplied by a third party vendor specializing in such items. (Fig. 14 & 15)

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Figure 14 Figure 15

Aluminum Core Exchanger Core Exchanger Insulation

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7.0 7.1

EXCHANGER PLOT LOCATION AND ELEVATION OF EXCHANGERS SHELL & TUBE ARRANGEMENTS

With exchanger piping, as with most piping systems, the less piping required, the better the design. The designer shall investigate strategies such as stacking and banking exchangers in like service to minimize the piping required (Fig. 16)

Figure 16

Standard Piping Arrangements for Shell & Tube Exchangers

7.2

LOCATION BY ASSOCIATION

In setting locations for exchangers, attention shall be paid to the placement of associated equipment. (Fig. 17) Locations will be chosen with a view toward reducing the amount ofElectronic documents, once printed, are uncontrolled and may become outdated. Refer to the electronic documents in BecRef for current revisions. Bechtel Confidential Bechtel Corporation 1995, 2002. All rights reserved. Engineering Design Guide Exchanger Piping 3DG-P22-00004-002

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piping required to connect the system. The overall system flow will be reviewed and studies done to determine the optimal placement for exchangers.

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POOR LOCATION

PREFERED LOCATION

Example 1

PREFERED LOCATION

POOR LOCATION

Example 2 EXCHANGER PLACEMENT Fig. 17

Figure 17

Exchanger Placement

7.3

EXCHANGER BATTERY ARRANGEMENTS

Exchanger battery arrangements for maintenance and operational access and also serve as unobstructed escape routes from the area in case of emergency (Fig. 18).

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Figure 18 7.4

Arrangement of Exchanger Batteries

ELBOW NOZZLES TO REDUCE SHELL ELEVATION

The elevation of exchangers is frequently set by the requirements of the process they are trying to maintain. The designer shall be aware, however, of the opportunities for reducing piping runs that lowering or raising some exchangers may present (Fig. 19). It should be noted that elbow nozzles will, to a certain extent, fix the pipe routing local to the exchanger due to nozzle orientations. The customer shall be consulted prior to any decision to use elbow nozzles.

Figure 19 Elbow Nozzles 7.5 EXCHANGERS WITH CONDENSATE POTS The elevation of exchangers operating on steam is often set by the resident time of the downstream condensate pot, i.e. the time the condensate must remain in the pot prior to beingElectronic documents, once printed, are uncontrolled and may become outdated. Refer to the electronic documents in BecRef for current revisions. Bechtel Confidential Bechtel Corporation 1995, 2002. All rights reserved. Engineering Design Guide Exchanger Piping 3DG-P22-00004-002

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returned to the condensate header, and is critical to maintaining upstream and downstream pressure and temperature. If process conditions allow, use of a horizontal pot rather than a vertical one, it can significantly lower the elevation requirements of the exchanger (Figs.20 & 21).

Figure 20

Alternative to Vertical Condensate Pot

Figure 21

Condensate Pot Piping Arrangement

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7.6

REBOILERS WITH CONDENSATE POTS

With vertical reboilers the condensate pot is commonly at grade and once again backpressure is critical to maintaining temperature in the reboiler. The pot elevation in this case is often set by the pump or downstream condensate system requirements. Every effort must be made to keep the elevation of this pot as low as possible. The higher the pot has to be, the higher the reboiler must be and consequently the higher the tower liquid level must be. As the tower goes up so do all costs associated with it (additional skirt steel, additional piping, stronger foundation...) (Fig. 6). 7.7 DOUBLE PIPE EXCHANGERS

These exchangers are usually stacked in large banks and operated in series because of their relatively low heat transfer rates. Occasionally, when only one double pipe is required, it is good to keep in mind that there are options on mounting the exchanger that can result in significant cost savings. The standard method of support for such items is an independent two-pier foundation, but the light weight of the double pipe lends it to mounting on piers for other required equipment (such as drums) or even nearby structural columns by side bolting (Fig. 22). Such mounting eliminates the need for the foundation.

Figure 22

Double Pipe Exchanger Method of Support

7.8

RACK MOUNTED AIR COOLERS

Air cooler elevations (whether at grade or elevated on racks or structures) are generally set by their air drawing capabilities, therefore a certain amount of clear space must be maintained to ensure the performance of the cooler. It is necessary to provide maintenance platforming for access to the motors and header boxes (Fig. 23 & 24). Note that this platforming, because of its relative elevation when air coolers are rack mounted, makes a good place for locating relief valves.

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Area can be used for equipment relief valves to flare

HEADER BOXES

PLATFORMS

MOTORS

PLATFORMING

HEADER LEVEL

MOTOR / FAN LEVEL

CONVENTIONAL PLATFORM DESIGN FOR AIR COOLERS Fig. 23

Figure 23

Conventional Platform Design for Air Coolers

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PLANWHEN ENGINEERING CONTRACTOR PROVIDES SUPPORTING STEEL, INTERMEDIATE PIPE SUPPORTS CAN BE LOCATED MORE EASILY

ELEVATION

ACCESS WAY

ACCESS WAY

BY VENDOR BY ENG. CONTRACTOR BY VENDOR BY ENG. CONTRACTOR AT GRADE OR ON RACK

AIR COOLER SUPPORTS

Fig. 24

Figure 24

Air Cooler Supports

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8.0 8.1

SHELL AND TUBE NOZZLE LOCATION & NOZZLE TYPE SHELL & TUBE NOZZLE LOCATION OPTIONS

The designer shall be aware of the allowable variations to shell and tube exchanger nozzle locations (Fig. 25).

Figure 25

Nozzle Adjustments to Standard Exchangers

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8.2

SHELL & TUBE NOZZLE ORIENTATION OPTIONS

A rearrangement of nozzles, can in some cases, reduce the required piping for a system. While such relocation is something that must be discussed with and approved by the Responsible Engineer (RE), significant cost savings can be attained by such rearrangement. (Fig. 26 and 27)

Figure 26

Possible Nozzle Arrangements for Shell & Tubes

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Figure 27 Change Nozzles to Improve Routing 8.3 NOZZLE LOCATION WITH RESPECT TO FLOW As with relocation of nozzles, a change in the flow direction of an exchanger can at times result in an improved design (Fig. 28). As with nozzle relocation, any changes in the flow direction must be discussed with and approved by the RE prior to implementation in the design.

Figure 28 Change Flow to Improve Routing 8.4 AIR COOLERS 8.4.1 Nozzle Locations The locations of nozzles are based on the number of tube bundle cells manifolded together and the number of passes the tubes make between the inlet and outlet manifold boxes. An even number of passes place the inlet and outlet nozzles on the same side of the cooler, while an odd number of passes results in the nozzles being on opposite sides. This can be particularly important when the coolers are rack mounted. If the upstream and downstream equipment are on the same side of the rack an even pass arrangement is preferable, while if they are on opposite sides of the rack an odd number of passes could reduce piping runs (Fig. 29).

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Figure 29 Odd or Even Pass Air Coolers 8.4.2 Air Cooler Piping Arrangements The piping arrangements called for at air coolers can also greatly affect their placement and elevation. In cases where true symmetrical (cascaded) piping is required to stabilize two-phase flow, the required elevations of supports for the piping can become prohibitive. In such cases the use of header box inserts may reduce the need for symmetry to the point that a rake style arrangement may be used (Fig. 30 and 31). The RE shall be consulted about such possibilities.

Figure 30

Standard Air Cooler Piping Arrangements

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Figure 31

Inserts for Air Coolers

9.0 9.1

SUPPORTS SHELL & TUBE

Shell & Tube exchangers at grade operating off of the same underground cooling water supply line shall be aligned by the channel head nozzle (Fig. 32). The offset of the supports will have little cost effect at grade. Exchangers in upper levels of structures, however, shall be aligned by supports to minimize the requirement for structural steel (Fig. 33).

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Figure 32 Figure 33

Shell & Tubes at Grade with Same U/G Cooling Water Supply Shell & Tubes on Elevated Platform

9.2

SPACE FRAMES OR SPACERS

As a standard, shell and tube exchangers come with saddle supports. When ordered for a stacked application, the lower exchanger is generally ordered with opposed top and bottom saddles to support the upper exchanger. However, there are occasions when it is desirable to set the upper exchanger at a greater height than normally achievable with saddles (i.e., exchangers in different services that are stacked to save plot space or expansion of anElectronic documents, once printed, are uncontrolled and may become outdated. Refer to the electronic documents in BecRef for current revisions. Bechtel Confidential Bechtel Corporation 1995, 2002. All rights reserved. Engineering Design Guide Exchanger Piping 3DG-P22-00004-002

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existing unit requiring the placement of a new exchanger on an existing one). In these cases, space frames (or spacers) will be required (Fig. 34).

Figure 34

Space Framing

9.3

SADDLE / FOUNDATION CLEARANCES

Clearances for piping, valves, insulation, maintenance equipment and instrumentation shall always be checked (Fig. 35).Electronic documents, once printed, are uncontrolled and may become outdated. Refer to the electronic documents in BecRef for current revisions. Bechtel Confidential Bechtel Corporation 1995, 2002. All rights reserved. Engineering Design Guide Exchanger Piping 3DG-P22-00004-002

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Figure 35

Clearances for Shell & Tube Exchangers

9.4

SHELL & TUBE PIPE SUPPORT LOCATIONS

Often pipe supports at shell and tube exchangers can be incorporated with the exchangers support foundations or can be set upon the same foundation. This can save the expense ofElectronic documents, once printed, are uncontrolled and may become outdated. Refer to the electronic documents in BecRef for current revisions. Bechtel Confidential Bechtel Corporation 1995, 2002. All rights reserved. Engineering Design Guide Exchanger Piping 3DG-P22-00004-002

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separate support foundations (Fig. 36). Anchors set on such supports allow the pipe to grow with the exchanger instead of against it.

Figure 36

Support Design for Piping at Shell & Tube

9.5

VERTICAL REBOILER SUPPORTS

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In setting vertical reboilers, a number of options for method of support are possible. The best choice for any given application will depend on the process requirements as well as the availability of space, type and weight of the equipment being used. The maintenance requirements for these reboilers shall also be reviewed in deciding how best to support them in that bundle pulling for a vertical exchanger can require some unconventional clearances (Figs. 5, 37 & 40)

Figure 37

Vertical Reboilers

9.6

AIR COOLER SUPPORTS

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Air coolers can be ordered with two different types of supporting structures, with or without legs provided (Fig. 38). The latter of these two options can help reduce costs and increase flexibility of the exchanger's supports especially when the coolers are to set above a pipe rack. Coolers provided with legs can reduce costs for grade mounted air coolers and can also be mounted with air controlling louvers or walls to protect against freezing or reduce motor noise levels. The types of supporting structures for these coolers can affect the piping runs serving them.

Figure 38

Air Cooler Supports

10.0 10.1

MAINTENANCE AND OPERATIONAL ACCESS SHELL & TUBE

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Exchangers shall be piped with a view toward maximizing access to the tube bundle and other maintainable components (Figs. 39 & 40). Break out flanges at the channel end, however, are often an unnecessary added expense. Even at exchangers with fixed tube bundles (where bundle pulling is not a concern), sufficient room shall be allowed at the heads to allow rodding out of tubes. Usually an area equal to the length of the tubes will do. Clear accessways should be provided to allow operator access to valves. If chain operators are used for elevated valves, care should be taken to avoid chains obstructing the walkways.HEAD + 30" (750mm) 9" (230mm) min. (ALL BODY FLANGES) OPERATING VALVES (SUGGESTED LOCATIONS)

WALKWAY

30" (750mm) min.

HEAD REMOVAL AREA

18" (450mm) MIN. BETWEEN FLANGES OR INSULATION

18" (450mm) min. (TYPICAL) HEAD SWING (IF FITTED WITH A DAVIT)

TUBE LENGTH + 30" (750mm)

SHELL AND TUBE EXCHANGER ACCESS

FIG. 39

Figure 39

Shell & Tube Exchanger Access

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Figure 40

Tube Pulling Requirements

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10.2

BUNDLE EXTRACTOR

Most tube bundle pulling equipment can operate with a minimum of space allowance (Fig. 41). Check the client's clearance requirements for his particular bundle extractor.

Figure 41

Tube Bundle Extractor

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10.3

CLEARANCES

Clearances for maintenance, such as wrench clearance at flanges shall be provided in all cases. Often 12" (300mm) from bottom of pipe to grade is an adequate elevation for piping, however if a drain is provided in the line, a minimum of 4" (100mm) below the plug shall be provided for the removal of that plug. Knuckle clearance shall also be provided around spectacle blinds (where provided) (Fig. 36). As stated earlier, access ways shall be provided for the maintenance of all exchangers requiring maintenance. These access ways shall provide a minimum of 2-6" (750mm) of unobstructed walkway with a minimum of 7-0" (2200mm) headroom. The designer shall review the arrangement of exchangers and the placement of access ways as an overall scheme instead of in terms of individual components. Each access can be used to service more than one set of exchangers, optimizing the space allocated to their placement (Figs. 39, 40 & 42). 10.4 STACKED EXCHANGERS

Shell & Tube exchangers may be stacked up to a maximum of three shells high if approved by the customer. 10.5 CRANE ACCESS

For exchangers requiring the movement of large heavy components for maintenance, road and heavy equipment access must be a consideration. Clear unobstructed lift and laydown areas, and carry-out routes must be designated and kept clear of equipment, platforming and structures. A single crane lift area can service several pieces of equipment if properly located (Fig. 42).

Figure 42 10.6

Crane Access

AIR COOLERS

As well as platforming for header box maintenance, most air coolers (especially those mounted on racks) require platforming for motor access (Fig. 44). If the cooler is at grade and the motors are within the reach of and are accessible by mobile equipment, the platforms might be eliminated.Electronic documents, once printed, are uncontrolled and may become outdated. Refer to the electronic documents in BecRef for current revisions. Bechtel Confidential Bechtel Corporation 1995, 2002. All rights reserved. Engineering Design Guide Exchanger Piping 3DG-P22-00004-002

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10.7

AIR COOLER HEADER BOX ACCESS

Platform access at air cooler header boxes is often required. Such platforming shall provide enough access to allow the blinding of cells or the plugging of damaged tubes without interfering with the support and routing of manifold piping (Fig. 43)

Figure 43

Plugged Header Box

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10.8

PLATFORM OPTIONS FOR AIR COOLER MOTOR ACCESS

In cases where large platforms are needed to service several bays of coolers, use a solid pattern for platforming. Reducing the details required for design, and simplified construction, outweigh the savings in material (Fig. 44). Finger style platforming shall be used only after consulting with Civil/Structural engineer.

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FO R LONG A IR CO O LERS

CO NV E NTIONA L A P PRO ACH TO FA N MOTO R MA INT. P LA TFO RM

FAN MOTO RS CO NV E NTIONA L A P PRO ACH P RO VIDE S MO RE P LA TFO RMING , W HILE HA VING LITTLE CO ST IMPA CT V S. ALTE RNATE

A LTERNA TE AP PRO A CH

FAN MOTO RS

AIR COOLER P LATFORMING ALTERNATIVES FIG. 44

Fi

gure 44 11.0 11.1

Air Cooler Platforming Alternatives

PIPE STRESS EXCHANGER ANCHOR LOCATION

Anchors play a large role in determining the piping configurations for exchangers. In many cases the location of anchors can be adjusted to accommodate a better piping design. This is applicableElectronic documents, once printed, are uncontrolled and may become outdated. Refer to the electronic documents in BecRef for current revisions. Bechtel Confidential Bechtel Corporation 1995, 2002. All rights reserved. Engineering Design Guide Exchanger Piping 3DG-P22-00004-002

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to both pipe anchors and exchanger support anchors. With shell and tubes, anchors are generally placed to allow the piping to grow parallel to the growth of the exchanger. This minimizes the stress loads on the nozzles (Fig. 36). Anchor points of the exchangers themselves can often be manipulated to provide the best design. Slots can be cut into the exchanger support bolt holes to allow movement in a desired direction (Fig. 45). If friction forces created by the weight of the exchanger are excessive, slide plates can be introduced to allow greater ease of movement.

Figure 45

Slotted Holes for Shell & Tubes

11.2

SHELL & TUBE NOZZLE LOADS

The allowable loads at nozzles for shell & tube exchangers are not usually a problem. However, when exchangers in like service are banked, it shall be kept in mind that tight fitting-to-fitting configurations for the piping may generate unacceptable loads. Changes to the piping configuration or the addition of springs to piping supports can be used to reduce these loads. Adding springs to piping supports can also aid in vertical thermal load reduction when exchanger locations require lengthy vertical piping runs. 11.3 AIR COOLER NOZZLE LOADS

Air cooler piping anchors shall be placed close to the exchanger to minimize the growth toward the nozzles. Anchors on distribution headers shall be centered to equalize, as much as possible, the lateral growth parallel to the header boxes. Air coolers are notorious for the low limits of allowable stress at the points of piping connection. The header boxes for these exchangers are usually made of gage steel and configured in a fashion that affords little if any structural strength. When these conditions are applied to even moderately hot services the result is often stress loads at the nozzles that far exceed acceptable. Lengthening the piping riser between the piping header and the manifold box can help to reduceElectronic documents, once printed, are uncontrolled and may become outdated. Refer to the electronic documents in BecRef for current revisions. Bechtel Confidential Bechtel Corporation 1995, 2002. All rights reserved. Engineering Design Guide Exchanger Piping 3DG-P22-00004-002

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the lateral stresses (Fig. 46) and the addition of spring supports can reduce the load forces in the vertical (Fig. 47)

Figure 46

Lateral Stresses on Air Cooler Nozzles

Figure 47

Spring Supports for Air Coolers

12.0

REFERENCES

Tubular Exchanger Manufacturers Association Standards (8th Edition) 3DI-P21-00001 ISBL Equipment Layout 3GS-P34-00002 Piping Design and LayoutElectronic documents, once printed, are uncontrolled and may become outdated. Refer to the electronic documents in BecRef for current revisions. Bechtel Confidential Bechtel Corporation 1995, 2002. All rights reserved. Engineering Design Guide Exchanger Piping 3DG-P22-00004-002

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