9 heaters / boilers 2 · piping training lesson 9 page 2 of 100 date 25 march, 2004 rev. 0 9...

PIPING TRAININGLESSON 9

of 100Date 25 March, 2004

Rev. 0

TABLE OF CONTENTS

9 HEATERS / BOILERS 2

9.1 Preface 2

9.2 Definition 4

9.3 Two Basic Types of Heaters (Vertical & Box) 4

9.4 Specification - General Contract Data 18

9.5 Plot Layout 21

9.6 Flexibility and Support Problems 24

9.7 Two-Phase Feed Lines To Furnaces 31

9.8 Piping Design 34

9.9 Burner Piping 39

9.10 Steam Systems 51

9.11 Process Heater Steam-Air Decoking Guide 57

9.12 Pigging for Internal Cleaning of Tubes 61

9.13 Heater Platforms 63

9.14 Squad Checking 72

9.15 Fired Equipment Basic Stress Considerations 73

9.16 Instrumentation for Heaters 86

9.17 Sample Layouts 89

9.18 Glossary 97

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9 HEATERS / BOILERS

9.1 Preface

This lesson will cover the procedures required for heater equipment studies, their supporting equipmentand the piping connected to them. Two things to keep in mind; first, use Fluor Daniel standards as aguide, and second, the guidelines mentioned in this lesson may be different than jobs you may haveworked on in the past. Some clients have their own engineering standards.

9.1.1 Lesson Objectives

� Provide self-directed piping layout training to designers who have basic piping design skills.Training material can be applied to manual or electronic applications.

� Become familiar with the more commonly used heaters, how they operate and some of theiruses.

� Learn the types of heaters.� Learn to determine where heaters should be located.� To enable you to make heater studies avoiding major mistakes and costly changes.� To familiarize you with Fluor Daniel standard heater design. (Fluor Daniel standards are a

guide, the standards used on your contract shall govern.� Learn procedure for checking foreign prints of heaters.

9.1.2 Lesson Study Plan

� Take the time to familiarize yourself with the lesson sections.� The following information will be required to support your self study:

� Previous lesson plans; e.g. Pipe Stress Lesson #1� Your copy of the Reference Data Book (R.D.B.)� Fluor Daniel Technical Practices. The following Practices (not included) support this

lesson:000.250.2520 – Fired Equipment Piping – Plot Layout000.250.2521 – Fired Equipment Piping000.250.2525 – Fired Equipment Piping – Piping Design

000.250.2526 – Fired Equipment Piping – Burner Piping000.250.2561 – Fired Equipment – Ladder and Platform Requirements - Heaters000.250.2580 – Fired Equipment Piping – Heater Squad Checking

� It should take you approximately 80 hours to read this lesson plan and be prepared to take thelesson test.

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

� Additional support information:� Your copy of the Piping Engineering Design Guide� Previous lesson plans; e.g. Pipe Stress section, Lesson #1

9.1.3 Study Aid

� Videos on Piping Design Layout Practices. These videos supplement your layout training. It issuggested that you view these videos prior to starting the layout training. Where available, youmay check out a copy of the videos from the Fluor Daniel Library or your Department Library.

9.1.4 Proficiency Testing

� You will be tested on your comprehension of this lesson. Proficiency testing will be scheduledthree to four times per year. Piping Staff will notify you of the upcoming testing schedule.

� The test is divided into three separate test sections:� General introduction and administration activities of Fired Heaters� Plot Layout & Layout Guide� Heater Specialty Items

� Testing� Questions are manual fill-in and True False� The tests should take approximately one and one half hours.� You may use your layout training Reference Data Book and material from previous layout

training lessons during the testing.� Your test results will be reviewed with you by the test facilitator at a later date.� Test results will be given to Piping Staff.

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9.2 Definition

A heater is a piece of equipment with burners used to heat a process commodity. The fuel for theburners may be gas or oil, or a combination of the two depending on the availability and operating costof these items. Fired heaters come in a great variety of sizes, shapes, and construction. In the realmof this discussion, however, the type of heater does not play too important of a role; it will suffice todistinguish between horizontal (box) and vertical (can) heater. The term "horizontal" and "vertical"refers to the position of the tubes in the radiant section.

9.3 Two Basic Types of Heaters (Vertical & Box)

9.3.1 Can (Vertical) Heater:

Cylindrical in shape, made of steel plate and internally lined with brick (insulating medium). Routedalong the inside walls are suspended vertical "U" tubes, which carry the process commodity (SeeFigure #9-1A). The heat is generated at the bottom of the heater by gas or oil fired burners. Theheater stack is self-supporting and exhausts to atmosphere. A damper on the stack is used to controlthe discharge. Ladders and platforms are provided for maintenance, inspection and tube removal.

The vertical heater not only has the advantage of saving space, but also the benefit of simpler piping.Since all tubes can be removed vertically from the top platform by means of the stack monorail, nopiping, except for the top connections, will interfere with inspection or removal of the tubes.Arrangement of the vertical tubes in a circular fashion provides the piping designer with more freedomin orienting the inlet and outlet nozzles.

In a vertical heater, the product will go up and down, again and again until it works its way through tothe heater outlet. Occasionally, the process is routed back and forth between the radiant section to theconvection section. Therefore, from the flow standpoint, it makes little difference whether the productenters the tubes from the bottom or top of the heater. If the heater has a separate convection section,(See Figure #9-1B) the tubes are heated by the flue gases, the product will first enter the heater at thetop, since the cold product should meet the coolest heater section to attain maximum temperaturedifference throughout the entire pass. This assumes that the convection section is not used for anentirely different product, as it is sometimes done. It also assumes an "updraft" heater.

Tubes can be supported at the bottom of the heater or at the top with guides directing the tube growth.Knowing the placement of the supports is important in your layout because the thermal growth of thetubes will affect your piping layout.

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Figure #9-1A Figure # 9-1B

Single Flow: See Figure # 9-2 shows the tube arrangement for single pass. Inlet and outlet will be atadjacent tubes and, with an even number of tubes, on the same end.

Figure # 9-2

Split Flow: The flow may and frequently does enter the heater in a split stream (multi-pass). In thiscase, it is of greater significance that the parallel sections are absolutely symmetrical with exactly equaltravel paths to assure identical heating.

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Figure # 9-3 illustrates this symmetrical tube layout for two-pass and four-pass next to a single-passarrangement.

Figure # 9-3

By knowing the number of passes and number of tubes per pass, it is possible to determine easily thepossible location of inlet and outlet connections, and can therefore, start the layout before receipt of theVendor's drawings!

9.3.2 Box Heater:

Rectangular in shape, made of steel plate and internally lined with brick (insulating medium). Along theinside walls in a horizontal plane are "U" tubes which carry the process commodity. The gas or oilburners may be on the side, end, or bottom.

This type of heater may also be used to produce super-heated steam (additional tubes in its convectionsection) as well as heating a process commodity.

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In designing piping for horizontal furnaces, greater care has to be applied to avoid obstruction of accessto the tubes and to allow for erection of maintenance scaffolding. Ladders and platforms are provided,for maintenance and inspection. In a horizontal heater, flow may progress downward from the uppertubes or upward from the lower tubes. Normally downflow is preferred since it is also the direct routefrom the convection section. The tubes are arranged along the walls (See Figure #9-4). One obviousadvantage of the horizontal position of the tube lies in the fact that it allows drainage on shutdown. Thisrepresents an important safety factor in case of fire.

Figure # 9-4

9.3.3 Parts of a Heater

� Headers and Header Boxes

The connection of one tube end to the start of the next tube can be made by means of a welding fitting(U-bend). This is not always satisfactory since it does not permit inspection and mechanical cleaning ofthe tubes. Special return fittings, called "headers," are often used which, by means of removable plugs,allows both inspection and cleaning. Because of the possible leakage and the resulting danger,headers must be completely enclosed in header boxes. In vertical furnaces, headers would be locatedon top and bottom, while in horizontal the headers would be placed at both ends. The header boxesthemselves must be provided with independent permanent snuffing steam connections. Maintenanceplatforms are often required at the header boxes for inspection, cleaning and tube removal.

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� Burners and Fire Box

Heating is accomplished by means of burners using either gas or oil depending on the availability ofeach fuel. In some cases both fuels can be burned separately or simultaneously. This will ensureuninterrupted operation in case of curtailment of either fuel.

� Tubes

The stream (liquid, vapor or mixed), frequently called "stock" will flow through tubes usually spacedfrom 1.8 to 2 pipe diameters on center which are heated by the flame of the burners through direct andreflected radiation (radiant section or combustion chamber) and additionally, in many cases, throughconvection (convection bank).

Combustion occurs in the combustion chamber which, depending on the intended reference is alsocalled "radiant section" or "fire box." This box also must be provided with permanent steamoutconnection, mainly to allow purging before lighting of burners.

� Tube Pulling Doors

Tube pulling doors are provided to remove or repair damaged tubes. On vertical heaters the doors willbe located at the top of the convection section. With box heaters the doors will be located on the ends.Verify that there is enough pull space on the side of the tube pulling door to remove the tubes. Thisrequirement will be noted on vendor drawings. In early layout stage, get this information from yourMechanical Engineer.

� Sight Doors

To observe the flame pattern and to discover possible "hot spots" (overheated tubes) observationopenings, referred to as "sight doors", "sight ports", or "peep holes" are provided. Their location abovethe tip of the flame requires access by means of the "firing platform". This platform is considered an"operating" platform and should be easily accessible by means of a stairway.

� Explosion Doors (Pressure Relief Doors)

Explosion doors are designed to open when there is a severe over pressure within the heater. In theorythe door will prevent severe damage to the heater and it's internals. The doors will be located awayfrom platforms, piping and directed to blow away from adjacent equipment. In the event of an explosionthese doors can be thrown hundreds of feet.

� Stack and Stack Damper

For the discharge of the combustion gases at a safe height above ground and for the induction of theair into the heater (draft), a stack is required. It should be higher, by at least 15 feet, than any operatingplatform located within 40 feet.

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To regulate the draft, a single disc (butterfly) or a split disc stack damper is used which, by means ofmechanical linkage is operated either from the firing platform or from ground level as shown in Figure #9-5 for a horizontal heater. The damper control should stay clear of the space reserved for piping.Nowadays, dampers are equipped with electric motors / pneumatic cylinders. While designing platformat damper level, one should take into account the space taken by the motor or actuator and ensure thatthe platform allows all round access.

Figure # 9-5

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� Air / Steam EductorsAir or steam eductors are mounted on the stack to purge out the firebox prior to lighting pilot burners.Figure # 9-6 below shows typical piping details for such an arrangement. Details vary as per projectguidelines.

Typical Stack Eductor DetailsFigure # 9-6

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Review Figure #9-7 through 9-13 for typical heater configurations and nomenclature.

Typical Box Heater ElevationFigure # 9-7

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Typical Vertical Heater ElevationFigure # 9-8

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Box HeaterFigure # 9-9

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Box HeaterFigure # 9-10

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Typical horizontal U-tube arrangement for a Box Heater.Figure # 9-11

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Vertical HeatersFigure # 9-12

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Typical tube arrangement for Vertical HeaterFigure # 9-13

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9.4 Specification - General Contract Data

The Heat Transfer Equipment Specification, which is an overlay to API-650, is a very important contractdocument used by designers working with fired equipment. This narrative originates from the firedequipment group of the Mechanical Engineering department. Because it is a contract wide document itis general in nature. It is an accepted overview of the various engineering and design requirements.This document is used to communicate to the prospective heater vendor the basic requirements of theheater.

When a designer is assigned to a contract for fired heater designs the first step is to obtain the latestcomplete issue of the Heat Transfer Specification. The spec should be examined thoroughly andhighlighted by margin notes any items that refer to the areas of piping design and engineering. It isessential that all these notes be supported and complimented by Heat Transfer Specification. Anydiscrepancies should be brought to the attention of the piping design supervisor and fired equipmentengineer.

Often, a condition will exist where some facet of a particular heater installation will require someadjustment to either the Heat Transfer Specification data sheets, flow sheets, etc. This is to beexpected, even desirable because it allows the engineer and designer the feasibility of making a "local"adjustment for improvements. It is very important to document and track the exceptions to the basicspecs. Obviously, the vendor must be aware of these changes via the fired equipment engineer.

9.4.1 In Summary

The fired heater narrative Heat Transfer Specification relates to the vendor, client, piping design, etc.and various design requirements:

� Criteria for ladder, stairs and platform design� Description and location of assorted instruments� Special attachments; i.e., decoking, air preheaters, etc.� Process and thermal design requirements� Burner descriptions� Other items not directly related to piping design

Obtain the latest complete copy of the Heat Transfer Specification and:

� Examine in detail for items relating to piping design - "yellow-off" the portions so noted� Compare the various items to piping design specs., etc.� Compare results to copies of specification previously issued to vendors� Report design inconsistencies to the design supervisor and fired equipment engineers

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� Place a separate copy of Heat Transfer Specification in each fired equipment job-book, (seejob-book section for comments)

� Mark-up, adjust and document exceptions to the Heat Transfer Specification for each particularheater in the job-book Heat Transfer Specification

9.4.2 Fired Heater Specification Data Sheets

These data sheets cover in great detail the process, combustion and mechanical design of theequipment. In the early stages of contract development, Data Sheets provide data to develop thepreliminary layout. The following is a brief discussion of the data sheets: (Other data sections are selfexplanatory).

� "Heater Type" refers to box or vertical, etc. This affects plot space and orientation.� "Heater-section" refers to radiant or convection and which cell of multi-celled heaters.� Temperatures @ "Inlet conditions" and "Outlet conditions" provide preliminary data for stress

analysis.� "Type of Fuel" indicates gas, oil or combination firing for preliminary burner piping design.� "Coil-Design" this section allows the preliminary design of a heater without any drawings.� "Number of Passes" is the number of coil Inlet or Outlet terminals.� "Effective tube length" is the length of pipe exposed to the high temperature conditions of the

heater.� "Tube Spacing" sets dimensions for overall width of the heater section described.� "Tubes-Vertical or Horizontal" sets the orientation of the heater coils at each section.� "Maximum Tube Wall Temperature" provides data for determining thermal growth of the various

heater tubes--very important for preliminary stress design.� The other tube characteristics provide additional data for preliminary stress design.� "Terminals" section gives a description of connections to Fluor Daniel piping, flanged or

buttwelded, etc.� "Tube Supports," this section strongly directs the efforts of stress analysis and must be

thoroughly investigated.� "Header Boxes," this section describes the outline of the heater at the coil terminals.� "Burners," this is required for burner piping layout, model number and quantity are indicated.� "Miscellaneous," in this section is a brief description of the location of ladders, stairs, platforms,

access doors, instruments, and various other small piping connections.� "Special Equipment" lists all of the extra hardware that does not normally come with a heater,

although has impact on heater design

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9.4.3 Primary Objectives

If there are any blank spaces in the data sheets, that effect design, the designer must communicatewith Mechanical for either a "Best-Data" or "Best Guess" approach, for information to complete thedesign package. By using the foregoing data in various combinations it is possible to achieve theprimary objectives:

� Develop a preliminary layout with or without vendor drawings.� To accept or alter the design to provide a more economical solution: i.e., change top-supported

tubes to bottom supported tubes for economies in stress analysis.� Up-date the design package earlier in the contract development.

Drawing & Data Commitment-Fired Heater

This document lists all the key drawings the vendor is required to submit for Fluor Daniel approval.Most importantly, it will give the listing of the priority status of each drawing. That is, the sequence ofdelivery and scheduled delivery date of each drawing. The design supervisor must verify the priorityaccording to his or her needs. Using the scheduled delivery dates, the designer is able to update andrevise the piping activities accordingly. This document is the schedule the vendor will maintain.

For the designer supervisor to develop the preliminary package he or she must obtain the heaternarrative specifications, data sheet, and vendor's drawings and commitment sheet. This informationshould be in the hands of the layout designer.

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9.5 Plot Layout

9.5.1 Plot Location:

It is assumed that the designer is familiar with the ground rules for locating heaters. Nevertheless, itseems appropriate and necessary to recall some of the considerations which are essential for theplacement of the furnace within the plant, since the heater location will direct us in our approach to thepiping design.

The first consideration is prevailing wind direction. Fired equipment must be located upwind or at leastcross wind from sources of hydrocarbon leaks. The next consideration is to minimize fire hazard bylocating the heater a "safe distance" away from equipment where leakage of hydrocarbons is morelikely to occur, such as pumps or compressors. This distance varies from about 50 to 100 ft, dependingon the degree of hazard, refinery practice, and available space; 50 ft. is usually adequate. In high-pressure hydrogen processes (Platformer, Hydrogenation and Isocracking), equipment can be placedas close as 10 ft from the heater, with the exception of pumps. By doing this, access and space for tuberemoval is provided( See Figure # 9-14).

Figure # 9-14

The next consideration, economy, influences the placement of the heater in such a way that unusedspace and length of lines can be kept to a minimum. Frequently transfer lines (i.e., lines carrying theheated stream from the heater to its destination) are expensive alloy steel and the other utility lines arequite numerous so that with every foot of separation, it is costly plant space and many feet of pipe willbe wasted.

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Figure # 9-15

9.5.2 Heater Sub-Pipeway:

A correct plot plan design will provide a pipeway to the heater - except in some relatively rare cases(See Figure #9-20) where the heater is directly adjacent to the main pipeway - large enough toaccommodate product lines, fuel lines, fuel oil supply and return, and fuel gas, steam, condensate,snuffing steam, air and water. The heater pipeway, which does not fall under the "safe distance"restriction, frequently forms the bar of a T or L-shaped pipeway system. This not only makes the bestpossible use of the free space between furnace and equipment but must be regarded as a practicalnecessity whenever dealing with more than one heater or where another heater is expected in thefuture as seen in Figure #9-16. Besides symmetry, this layout (Figure #9-16) offers great "freedom" inpiping, i.e., the ability to solve practically any piping problem with ease and without recourse toexpensive design patterns. It also provides excellent possibilities for extension of piping to serviceadditional heaters.

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Figure # 9-16 Figure # 9-17

It is not advisable to place the heater so that the pipeway points directly at it (See Figure #9-17), even ifthe plant will never require more than one heater. It can be easily shown that pipeways which aimdirectly at a piece of equipment will have the sequence of their lines dictated by this equipment, a factwhich would complicate the design of the pipeway based on entirely different considerations than thespacing of lines at any piece of equipment. An attempt to make a transition from sequence of the pipesand their spacing in the pipeway to the order and spacing required for the equipment can only beaccomplished by means of costly and unsightly pipe configurations.

Whether the heater pipeway should be established at a higher or lower elevation than the mainpipeway is determined to a great extent by the number of lines which will not allow pocketing such assome process lines, atomizing and snuffing steam, etc.

9.5.3 Heater Transfer Lines

The transfer line, which connects with the outlet of the tubes, may in its travel from the heater make useof the heater pipeway. It is desirable to use established pipeways for routing of transfer lines and toconcentrate the bulk of the lines in one area where they will not obstruct maintenance or operation andwhere supports are available. In the case of alloy or large lines, a good assumption is that they will, forreasons of flow and economy, follow their own separate ways.

It is possible to deviate from the commonplace piping and not rely on established pipeways. Investigatethe routing of the transfer lines as soon as the plot plan is taking shape. The careful designer shouldhave a mental picture of the transfer route while developing the plot plan.

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9.6 Flexibility and Support Problems

The first problem, as in all high temperature lines, is flexibility. There is no doubt that there are manyways to obtain this requirement regardless of conditions. (Expansion joints are not considered here) Arelatively inexpensive and many times absolutely costless means is the proper placing of the heateroutlet and the vessel inlet nozzles. This will simplify engineering, improve appearance and save money.

The designer has to recognize the lack of flexibility, which fortunately is not too difficult. Straightconnections without any bends, L - or Z-shaped pipe configurations with very short offsets can be easilyspotted as too "stiff". The problem is not to come up with a flexible system but rather with a design thatcan be easily rendered flexible if the formal stress analysis requires it.

Whenever the designer has attained such a layout, he should under all circumstances refrain fromadding anything he might consider necessary by intuition. All too often systems are designed withunneeded bends and oversize expansion loops. The designer should leave it entirely to the assignedpiping stress engineer to ascertain the sufficiency of a system, which does not obviously appear too"stiff". The Designer should, however, perform his / her stress nomograph study of the piping layoutbefore passing the design on to Stress Engineering.

Frequently, the path of a high temperature line need be no different from the direct one a cold linewould take because of the physical relationship of the terminal points. Whenever this route follows goodpiping practice and is still flexible, the most economical and, therefore, the ideal solution has beenobtained. For this reason, always investigate the "cold line" route first before attempting to design forflexibility as such.

The second problem is very closely related to the first one: It is the question of supporting the transferline and, if required, regulating its motions by guides, anchors and heater terminal movements.

The statement pointing out the importance of providing proper support and anchorage for hightemperature piping and demanding that layout of piping should be made with the support problem inmind, should be particularly respected when dealing with transfer lines. For reasons of economy, asstated before, the lines might not follow established pipeways thus requiring special supports, the costof which could possibly outweigh the intended savings.

The practical way, of course, is to tackle the problem of flexibility and support together, and to consultwith the structural engineer whenever doubts about the ease of support arise. Only then is it possible toevaluate the routing of the line and obtain the best possible solution with respect to both flexibility andsupport.

9.6.1 Design Method

The actual design of the transfer lines will proceed in two stages, the line route study and the finalpiping study.

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9.6.1.1 Line Route Study:

As soon as information as to the type and approximate size of the heater becomes available,commence with this study. There is no need for heater vendor prints as helpful as they might be;approximate dimensions (about so many feet wide by so many feet high) will suffice.

The purpose of the line route study is threefold:

To confirm the soundness of judgment in the placement of the heater relative to the equipment itserves;

To pave the way for the orientation of the heater, the tube inlet and outlet nozzles, the stairway to thefiring platform, the ladder to the maintenance platform, and approximate location of damper controls;

To supply the piping stress engineer with enough information to analyze the line from standpoints offlexibility and support, and determine heater terminal movement requirements.

It must be stressed that it would be completely unwarranted either to go into details or to extend thescope of the study beyond the routing of the transfer lines and the tentative location of the stairs andladders. On the basis of this limited investigation, receive the answers to the questions whether or notto reconsider the location of the heater, and what suggestions are possible to give the heater vendor inorder to adjust the heater design.

The information needed by the piping stress engineer for the purpose of the flexibility check isconveyed by means of a rough isometric sketch (not to scale) with approximate dimensions. At leasttwo additional modifications of the same layout as to the critical dimensions can be fed to the stressengineer, since the incremental cost is almost negligible, and in case of a unsatisfactory result, stressre-run will be avoided.

Line route examples:

To illustrate the practical approach to the so-called "line route study", let us look at the followingexample:

In the plot plan (Figure #9-18), two vertical heaters face two columns; heater outlets are approximately50 feet above grade, while the tangential inlet nozzles at the columns are approximately 38 feet abovegrade.

It was the intention of the plot plan design to route the two transfer lines, F-1 to C-1 and F-2 to C-2, asdirectly as possible. Considering the horizontal and vertical plane, when using the established pipeway,this routing seems more than reasonable to satisfy stress requirements.

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Figure # 9-18

Figure #9-24 indicates the possible positions of the heater outlet and column inlet nozzles. Some of thepossible routes are indicated in Figure #9-20 radius.

Figure #9-19

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Route #I & II appears too stiff and does not lend itself to conversion into a more flexible configuration,since it is not good practice to have the transfer line leaving the heater in a non-radial direction(elongation of removable spool and obstruction of adjacent tubes).

Route #III is more promising: It simplifies the support problem by grouping both transfer lines togetherwhile at the same time the forces are no longer directed towards the center of the heater or column.

Figure # 9-20

The plot plan (Figure #9-21) shows two horizontal heaters, their outlets facing the heater pipeway (anextension of the main pipeway), as illustrated for F-2 in Figure #9-22.

Caution must be taken when flat turning a rack, even a heater rack. The process lines may need to beon a separate rack level so that other piping can be extended from the main rack to the heaters or tofuture heaters. w

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Figure # 9-21

Note that in Figure 9-21, the process piping for Heater F-1 / C-1 will require a different routingrequirement because the offset heater rack causes a longer run to C-1.

Figure # 9-22

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Figure # 9-23

After combining the heater passes into the one transfer line at E (See Figure #9-23) where the legs ACand BD are minimum (enough to clear the platform and the vertical pipeway) a layout is obtained whichsatisfies all requirements: if the loop ACBD is not flexible enough, it can be easily made so byincreasing legs AC and BD. The transfer line will, in its most direct way to the column, follow thepipeway so that no support problem exists. The actual location of the inlet nozzle on the column willdepend on the design of the column itself.

Route #III should be ruled out as superfluous elongation of the main run which will only aggravate ourflexibility problem

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Figure #9-24

Examining the line routes from the flow standpoint, they are both free of any pockets (self-draining),and free of any unvented high points - except at the horizontal run above the outlet of the verticalheater in Example 1, which is unavoidable. This is clearly demonstrated by the isometric sketch of thetransfer lines (See Figure #9-24).

9.6.1.2 Final Study

After receipt of the vendor's drawings, commence the final design, which will eventually cover all facetsof the heater layout. Unlike the "line route study" this will in some respects require a very closeinvestigation of conditions and a study of well definable details, which will be examined later

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9.7 Two-Phase Feed Lines To Furnaces

To guarantee equal distribution over the passes of a heater or furnace, flow control is required of thevapor flow and the liquid flow to each pass separately. In a lot of cases, this is not practical or evenimpossible and a split of a two-phase flow is required to two or even more passes. This has to be donein a very special way to get an equal split in flow, vapor-wise as well as liquid-wise.

Figure # 9-25Over-the-Top Two-Phase Flow Splitter

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Figure # 9-25 shows the preferred way to split a two-phase feed line to a two-pass heater inlet. A welldeveloped two-phase feed flow (annular-mist preferred) runs at a pipe rack level towards a furnace.Try to avoid slug flow in the vertical upward line, also at turndown flow rates, otherwise an equal split ofthe flow to the two furnace inlets will be very hard to guarantee. If the line diameter has to bedecreased, install a bottom-flat reducer in the horizontal line part to increase the velocity before goingupwards.Never split a flow in an impacting T-junction in a vertical upward line, irrespective of the kind of flowpattern in the pipe. So first, go horizontal before an impacting T-junction is applied. Or even better, gofirst a few meters downwards before splitting the flow in a T-junction. In case, it is not possible to runhorizontally for 2-3 meters, before going downwards, alternatively a long-radius 180 degree bend canbe used.

It is very important that the T-junction is at the right angle and the 90° angle is a must for equaldistribution (� 1° is the maximum deviation).Never run the feed lines to the heater nozzles inclined upwards. Horizontal is preferred or a smallinclination downwards.

Figure # 9-26, on the left side, shows the way the piping was designed for a two-pass furnace feed line.The vertical riser was designed with the same diameter as the horizontal feed line, resulting in a slugflow pattern. The flow to the two passes was split in a vertical impacting T-junction, going upwardsstraight after the split, again with some kind of slug flow pattern. The pulsating liquid flow at theT-junction will have the tendency of partly falling downwards again. The liquids being split at the T-junction will separate again at the upper bend and partly flow backward towards the T-junction anddown the main riser.

So this way of splitting the flow will not work that well and will cause pulsating flows with the possibilityof unequal distribution to the two passes. The inclined line parts, to create space to make theconnections at the nozzles of the furnace, do not help in that respect either, because the liquid has thetendency to separate in that section and flow downwards. So all in all, never design any two-phase linethis way.

The picture in the center shows the best improvement possible, provided the stress engineer can find away to support it sufficiently.

For new plants, it normally will be possible to implement a good design, but when debottlenecking, itsometimes will not be possible to have a good supporting, and then the best possible alternative layouthas to be found together with the piping layout engineer and the piping stress engineer.For the proposed layout no liquids can fall backwards into the risers and in case of liquid separationafter the T-junction only small slugs of liquid can be sent upwards to the furnace inlets.

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Figure # 9-26Proposed Furnace Feed Line

The alternative layout at the right-hand side of Figure # 9-26, will give a good split of the flow in bothdirections, but still liquids can flow backwards into the main riser, although this will be less than for theoriginal design at the left-hand side.

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9.8 Piping Design

Piping Systems

One approach to simplify the design analysis of fired heaters is to break down the big problem to anumber of smaller ones. The basis for the break-down is the piping system; which is really a number ofsmaller systems when combined appear very complicated. Two major categories are:

� Process Piping System� Heater Utility Piping System

Process Piping System

� Main product inlet & outlet piping� Other product inlet & outlet piping

Heater Utility Piping System

� Burner Piping� Gas piping...fuel gas, flare vent� Fuel oil piping...fuel oil supply, fuel oil return� Atomizing steam piping...condensate return� Pilot gas piping� Waste gas piping

� Utility Systems Piping� Plant air� Steam piping...condensate return� Plant water

� Fire Protection Systems� Snuffing steam piping� Firewater monitors

� Decoking System Piping� Steam piping� Air piping� Process swing-ell connections� Decoking outlet header...water quench piping� Sootblower Steam Piping...Condensate Piping

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The outline on the previous page is provided to groom the designer to be aware of the possible extentof the design effort. While examining the flow diagram, the designer is advised to view the material asa number of elements which can be analyzed one by one. Even though heaters represent one of themost complicated type of equipment found in refineries, they are composed of a number of simplesystems.

Pre-Order Vendor Conferences

Objectives of Piping Design

- To establish the Piping Design criteria for fired heaters prior to vendor conferences with onlypreliminary information.

- To document the design criteria for the vendor which will permit a realistic heater design in the earlystages of contract development.

- To keep equipment and piping costs to a minimum

- To reduce the amount of squad checking to an absolute minimum

Information Required

- Preliminary outline of heater from Mechanical Engineering Group

- Fluor Daniel narrative specifications (000.250.50001 & xxx.257.57103) and the specification (data)sheets from Mechanical Engineering Group

- Vendor specifications from Mechanical Engineering Group

- Client specifications, etc. from Project Engineering

- Mechanical Flow Diagram - Consult with Process for special requirements; i.e., symmetrical flow,decoking, regeneration conditions

Layout Requirements(Refer to Engineering Design Guide Practices 000.250.2520, 2521, 2525, 2526, 2561, & 2580)

Contract Piping Specifications 000.250.50001

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Documents & Information Sources

The very minimum documents required in order to develop a preliminary design package are:

- Plot plan

- Fired equipment narrative; Specification xxx.257.57103

- Piping narrative Specification 000.250.50001

- Heater Specification data sheets

- Mechanical flow diagrams

- Line sizes & pressure/temperature information

- Client specifications

To finalize layouts the following documents are required:

- Vendor general arrangement drawings

- Burner outlines

- Sootblower and control panel outlines

- Air pre heater or for ced draft system outlines

- Steam drum, stop-check valve, etc. outlines

- Drawing & data commitment fired heater

- Material specifications & line list

Naturally, the foregoing list will depend on the actual contract practice and conditions. The supervisormust insure the rapid and timely delivery of this information to the layout designer.

Piping:

- Layout all piping connected to the heater. Indicate size, type, rating, facing, orientation, projectionand elevation of all piping terminals.

- After pipe stress evaluation and revision, the Process Engineer must check process piping

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configuration for pressure drop and line sizing.

- Define points of pipe supports from heater and establish loads - make 8.5 x 11 sketches of eachsupport of separate detail on layout drawings - work closely with Pipe Stress Engineering

- Define forces and moments on each nozzle: Also, establish required tube movements as dictatedby stress conditions

- Define Hydrotest requirements; i.e. drain and vent requirements

- Burner Observation Ports, floor sight ports - orient for maximum burner viewing - keep piping clear

- Access Doors - Locate to clear process, crossover and burner piping. Watch for hinged doors

- Explosion Doors - Orient away from operating areas and other equipment - keep clear of piping andstructural bracing

- Tube Pulling Doors - Orient to allow access by mobile equipment and keep piping clear

- Floor Access Door - Locate to rear of heater clear of piping

Prepare Questions to Vendor:

- All items that need clarification and identification

- When possible list several possible alternative answers

- Be brief, simple and direct

- Prepare triplicate copies - one each for Piping Design, Mechanical Equipment and Vendor

Client Reviews:

- Client is to be presented with basic layout drawings for preliminary comments and approval

- Client reviews final layout drawings, before Vendor conference to avoid conflict of directions andexcessive changes.

The Vendor Conference

Prior to conference, the Piping Designer, Area Project Engineer, Stress Engineer, Structural Engineer,Unit Supervisor and Equipment Engineer are to review layout and questions to Vendor.

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� Assemble total package of design data: (Re: Fired Equipment Job-Book)

- Plan and section drawings

- Detailed sketches of supports, etc.

- Question lists

- Heater specification data sheets

- Flow diagrams

- Narrative specifications

- Vendor copies of information - drawings, etc

Piping personnel required to attend are the Unit Supervisor and the Piping Designer doing the heaterlayout.

Meeting minutes as related to piping layout are recorded by the Unit Supervisor and/or the PipingDesigner for future reference

Assuming the Piping Design is correct, changes in piping should not be made after the Vendorconference. Should piping changes be required the Vendor is to be notified immediately via the FiredEquipment Engineer. Needless changes defeat the purpose of conferring with Vendors prior to receiptof equipment drawings and significantly increase costs.

Summation

� Fired Equipment represents a unique, but not a distinct piping design problem. There are manyvariables that must be considered and weighed by the layout designer. In larger installations,scheduling the workload is a challenging undertaking.

� It is understood that the designer must adapt the "Standard" documents to the specific case ofthe contract unit. Once the unit schedule of activities is structured, then the attention may nowbe focused on obtaining design documentation (Narrative Specs, data sheets, etc.). Theinformation generated is then maintained in a Fired Equipment Job Book. Now, it is the task ofthe layout designer to develop the total package and finalize designs.

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9.9 Burner Piping

9.9.1 Fuel Gas, Fuel Oil and Atomizing System

It is important for the designer to understand the basic difference in the use of oil or gas as fuels. Whilefuel gas can be used for combustion as is, fuel oil must be heated to a higher temperature, dependingon its viscosity, to facilitate atomization and vaporization. No matter how far from the source of theheated oil the heater is (the facilities for heating and circulating fuel oil are usually located outside of theprocess plant), and regardless whether the burners are going full blast or are turned down to thesmallest flame, the oil must reach the burners at the desired temperature. The greater the distancefrom the source, the greater the heat loss which can only be offset by increased flow rate of the hotmedium.

The oil is returned to its source to be heated again, (recirculate oil). Consequently, the fuel oil systemnecessitates two lines: supply and return.

For reasons which will be evident in later discussions, hot oil is not circulated past each individualburner, but the supply line can be brought so close to the heater that the non-circulating branch fromthe supply line to the heater becomes relatively short. In design, never lose sight of this important factby locating the fuel oil supply header on the pipeway near the side of the heater and by running thebranch to the heater as direct as possible.

There are different ways to atomize the oil jet for combustion; it is usually accomplished by steam. Theso-called "atomizing steam" must be free of condensate, since steam containing slugs of water canextinguish the flame momentarily and cause an explosion. By the addition of a steam trap at the lowpoint and by allowing the line to drain back to it, carry-over of condensate to the burners will beavoided.

9.9.2 TRC-PdC-Manifolds:

It is the function of the heater to supply stock at a particular temperature. Once this outlet temperaturehas been reached, the heat input must be reduced. This means that the flow of the fuel to the burners,oil and gas alike, must be regulated automatically by a control valve which receives its signals from thetemperature connection on the transfer line. The Temperature Recording Controller (TRC) manifolddiffers from the ordinary process control manifold only in one respect:

It requires a second by-pass with valve locked open to assure a minimum fuel flow which will preventflame shut-off. An exception to this requirement is the relatively rare case when pilots are provided ateach burner. The pressure of the fuel gas supply must be definite and constant; for this purpose aPressure Control Valve (PCV) manifold is frequently necessary. It is best located outside of the "safedistance," close to the snuffing steam manifold, since it can be used as an emergency shut-off of thefuel supply to the heater, and can frequently serve all the heaters in the area.

While there is no other control manifold required for fuel gas, the fuel oil system needs a (DifferentialPressure Controller) PdC manifold for the automatic control of the atomizing steam. This control valve

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is actuated directly by the pressure in the fuel oil line downstream of the TRC valve and assures thatthe difference between the higher steam pressure and the oil pressure remains constant.

In the interest of freeing the steam line of any condensate, the atomizing steam manifold deviates fromthe standard process manifolds somewhat. The steam supply line will branch from the top of the steamheader and drop vertically, preferably with a small "boot leg", into the steam trap. The by-pass valveshall be located close to the riser in the horizontal so that condensate will drain back to the riser and tothe steam trap. Similarly the upstream block valve will be in the horizontal run next to the control valve,this will help keep the steam free of condensate (See Figure #9-27).

Figure # 9-27

In selecting a place for these control manifolds, recall the importance of keeping the fuel oil piping asshort as possible (non circulating) and the atomizing steam manifold as close to the heater as feasible(condensate). The location at grade, close to the start of the stairway leading to the firing platform, andparallel to it offers all these advantages and many more:

Figure # 9-28

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The manifolding is in a very convenient position for the operator, whether he is at grade lighting theburners or going up the stairs to the firing controls. At the same time it does not create an obstructionto access being alongside the stairs. Until the underside of the stairway rises to 7'-0" above grade, nohead clearance and consequently no passage exists so that about 8 feet along the stairs is available formanifolding without obstruction to passage (See Figure #9-28).

Figure #9-29 indicates the approximate location of the manifolding previously discussed.

Figure # 9-29

9.9.3 Firing Valves

The location of the manually operated valves controlling the flow of the fuel (this includes atomizingsteam) to the individual burners is dictated by the position of the sight doors. In floor fired heaters, thismeans an elevation of approximately 10 to 15 feet above grade, which necessitates the firing platformmentioned previously.

Relative to this platform, the sight doors are at a convenient height (eye-level), and are the referencepoints about which to arrange the valves in such a manner that the operator can observe the flame andoperate the valves. No matter which sight door the operator is standing, he must face the sameidentical valving arrangement (this is a must). With his head slightly bent forward while looking throughthe sight door, the operator can conveniently regulate valves which are from 18 to 30 inches to his right(assume him to be right handed), and about 3 to 4 feet above the platform. Figure # 9-30 shows atypical design for a gas and oil fired heater, but a fully designed heater might have up to 8 lines(snuffing steam, fuel oil warm-up bypass, flare vent and utility lines). Investigation is required tounderstand fully the clients' criteria for burner valve operation and burner light-off procedure. Thesetwo items are related. Most importantly, there is no universal burner standard that fits the varioussystems encountered.

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Figure # 9-30

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The width of the firing platform should be approximately 4 feet, allowing 18 inches for the valves and 2'-6" for passageway.

9.9.4 Circular And Rectangular Fuel Headers

The headers, from which the individual lines to the firing valves branch off, follow the cross-sectionalshape of the heater. Thus for the vertical heater, they are mostly circular; this does not rule out othergeometrical shapes (polygon) if layout conditions (number and symmetry of branches and supportpoints) and economical considerations (cost of bending versus cost of welding) would make itattractive. For the horizontal heater, the headers are either straight (controls on one side) or U-shaped(controls on both sides).

Neither the fuel oil nor the fuel gas header should be designed as a closed circle or completedrectangle (See Figures #9-31 and 9-32). In the case of fuel oil, assure at start-up a definite flow of theheated oil through the entire header via the "warm-up bypass" back to the fuel oil return line. A closedloop might easily starve part of the header. In the case of fuel gas, we must be able to purge theheader completely of any air before startup. Moreover, there is no advantage in extending the headerany farther than required for the last take-off.

Figure # 9-31

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Figure # 9-32

It is preferable to stack the headers vertically as shown in Figure # 9-30 versus the alternate of creatinga horizontal pipeway. The lines are easily supported from the structural members of the heater and donot create an undesirable "roof" over the firing platform which would prevent the placement of a ladderclose to the heater wall. Furthermore, stacking of the headers permits a more direct branch design bythe reduction of the horizontal run from header towards the heater and the resulting elimination of somefittings.

The headers should be stacked in the following sequence, starting with the lowest:

Fuel oil - 7'-0" above platformFuel gasAtomizing steam

Both the atomizing steam and the fuel gas headers must drain back to the manifolds at grade, and theirbranches should take off similarly to Figure #9-30. This will prevent carry-over of condensate fromheader to burner.

9.9.5 Burner Piping

There are two major requirements to consider in the design of the piping at the burners:

Minimum obstruction of access to the burners: After routing the lines down through the firing platform,route them with a head clearance of 7"-0" above grade (6'-8" min per OSHA) keeping them at thiselevation until they are almost at the burners, yet still far enough that they will not obstruct removal ofthe burner body for maintenance. Then route them down to a shut-off valve (if required) and the

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removable spool piece or (flexible hose) connecting the burner. Be carefull not to block sight doors,access openings, and other connections (steam snuffing) on the underside of the heater. Vendor'sdrawings should be checked in this respect immediately upon receipt; by mere inspection ascertainwhether there is an unrestricted path from the region of the peep holes towards the center of theburners.

Identical Piping Arrangement: In the vertical heater the burners are arranged in a circle, concentric withthe heater and equally spaced. Thus the lines will be directed towards the center of the heater, and willautomatically form identical arrangements unless the sequence of the pipes after leaving the identicalfiring valve manifolds has changed.

In a horizontal heater the burners are not always equidistant and sometimes placed in two parallelrows. Here the temptation to design one row the mirror picture of the other; i.e. symmetrical about theheater center line, is so great that many times these arrangements are encountered. Since theoperator changing from one row to the other, would find the valves reversed, this is not an acceptablepractice. Figure #9-33 illustrates identically manifolded burners of a horizontal heater.

See Figures #9-34 through 9-37 for Vendor burner information as a example of client providedinformation for the design of heater burner piping, etc.

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Figure # 9-33

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Figure # 9-34

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BurnersFigure # 9-35

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BurnersFigure # 9-36

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Burners and tubes in Radiant sectionFigure # 9-37

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9.10 Steam Systems

9.10.1 Snuffing Steam System

Uses

Snuffing Steam Is Used For Two Primary Reasons:

- To purge the firebox area of unburned fuel gases during start-up

- To provide a means of quenching or smothering out internal fires in various sections of the heater

Reference

Piping Practice 000.250.2525 for General Comments Concerning Snuffing (Smothering) Steam.

Important Points Concerning Snuffing Steam Piping

- Locate block valve control station at least 50' from fired equipment. Operator must be able toobserve heater while operating the valves. (Locate main fuel block valves near this station).

- Orient 1/4" weep hole minimum distance down stream of block valve, 1800 from handwheel

- Provide 1/4" weep holes (@ bottom of pipe) at all piping lowpoints

- Moderate overspans are permitted, even expected in snuffing piping runs

- Do not apply safety insulation (Is) on snuffing piping around the fired equipment

- Do not hydrotest snuffing steam lines

Point of Use

Unless other instructions are received, run separate snuffing steam lines to each of the following areas:

- Convection section

- Convection section header boxes (both ends)

- Floor of heater (hearth level)

- Separate sides of heater radiant section

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- Radiant section header boxes (both ends)

- Burner plenum

Rarely is snuffing steam required in self supporting stacks, breeching (ducting connecting stacks ofseveral heaters) or stack dampers.

Note:Because of the foregoing items, a sizable portion of pipe rack space is allocated to snuffing steampiping. This is especially true of multiple heater systems. For some heater trains there may be asmuch as thirty to forty snuffing steam lines.

Line Numbers

Many new line numbers are often required....keep track. Some effort is required to insure line taggingat the snuffing control station indicates the proper location of the line terminals on the fired equipment.See instrument group for contract procedure.

Flow diagrams rarely indicate the full extent of snuffing steam piping. Many new line numbers will haveto be assigned as required for the final routing. Use the lowest rating material spec and pipeconnections as possible. This is an open-ended pipe system....screwed or socket welded spec ispreferred.

Terminals

Snuffing steam terminals on the fired equipment are very flexible in most cases as to the exact location,elevation and orientation. The designer must control the terminal locations...verify with fired equipmentengineer. Never allow snuffing steam passages to direct steam directly on to heater tubes.... tuberupture may occur. Always branch off supply header on the top of line. Slightly slope line to gravityflow condensate to weep holes. In vertical heater burner areas keep snuffing lines clear of burnerpiping. There should never be any block valves located anywhere downstream of the snuffing steamcontrol station.

Sources Of Information

- Requirements For Snuffing Steam Are Found On:- Flow diagrams (be sure it's is up to date)- The Heat Transfer Equipment Specification- Heater specification data sheets- Client design criteria- Consulting with process and fired equipment engineers

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9.10.2 Sootblower Systems

Definition

Sootblowers are mechanical devices to spray a jet of swirling steam or air onto heater or boiler tubes toremove soot (ash from burned fuel) by physically dislodging particles. There are two types ofsootblowers:

Rotary sootblowers - small, compact non-retractable (steam pipe always in location, nested amongstthe heater tubes).

Retractable sootblowers - long (up to 30 feet), narrow and the steam pipe runs in and out of the tubepattern. Additional bracing from top of sootblower back to heater may be required. Confirm withMechanical

Platforms

Sootblowers generally require extensive plaforming, ladder or stair access and structural supportmembers. A great deal of effort is required to locate and make the sootblowers accessible.Retractable sootblowers often require many times (4 to 10) the platforming used by rotary sootblowers.Early layout is required so that the fired equipment vendor may proceed with the design of supportstructure. Since there are formidable structures involved, spacing and orientation of fired equipmentrequires carefully layout with attention to projection of sootblower equipment.

Sootblower piping is generally quite simple in concept if the following items are noted:

A branch header feeding several blowers shall be sloped 1/16" per foot towards the steam trapconnection

There is only one piping connection per blower...at the bottom of the mechanically operated "poppet"valve

Always branch off the top of steam or air supply header.

Consider pipe expansion of steam headers when running branches to the strain sensitive "poppet"valve

Be sure to squad check sootblower outline for size, rating and facing of the piping connection

Sootblowers do come in left or right configurations: Consider left and right hand parallel units so that acommon platform may be utilized, be sure to verify in the data sheet the exact number of left and/orright units to be used.

Note that occasionally a vendor supplied control valve is required in the Fluor Daniel steam supplypiping to the sootblowers, this is often missed on the flow diagrams.

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Flow Diagrams

Initially, flow diagrams seldom reflect the quantity, type or location of sootblowers. Contact the firedequipment engineer for missing data. Also, many lines are frequently missing on flow diagrams inregards to branch steam supply systems and steam trap lines. It is preferred to break up steambranches into several new line numbers (similar to snuffing steam lines).

Review Figures #9-38 and 9-39 for Vendor supplied information.

Control Panels

Sootblower control panels are required to sequence automatically the operation of the blowers. In mostcases:

Locate panel at grade near front of heater, near the draft gage assembly

Locate panel on the sootblower side for visibility of the blowers

An estimate of panel size for rough layout is 3' x 3' x 6' high

The panel requires a concrete foundation and in rare circumstances weather protection such as acovered shed

The sootblower control panels require front and back access

Sources Of Information

Requirement For Sootblowers Are Found On:

Flow diagrams

Heater narrative specs

Heater data sheets for client design criteria

Consulting with process and fired equipment engineers

Vendor Drawings

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Retractable SootblowerFigure # 9-38

Note support lugs shown on top of soot blower

SootblowerFigure # 9-39

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9.10.3 Steam Generation Systems

Elements Of The System

Steam generating systems are often found in the convection sections of the larger box type heaters.This generally consists of the following items:

Steam coils in convection section

A number of collection headers at the pipeway end of the heater

Boiler feed water pumps and feed piping to and from the pumps at grade

A steam drum normally is a horizontal vessel supported off the heater structure is provided by thevendor

A de-super heating system... to reduce steam temperature to a desired level

A steam silencer (estimated size about 3' dia x 6' long w/10' high 8" dia stack and weights about 3000#)to reduce blow off noise. Normally, Fluor Daniel provides the silencer mounted near the top of theconvection section while the vendor supplies the supports. Drain piping from silencer to grade isdesigner's responsibility.

ASME Code

Code restrictions require that nearly all the piping, valves, drum and boiler tubes require ASME Codestamps and designed according to Code requirements. The flow diagrams will define the extent ofASME Code piping. Note: Local or state boiler codes may be more stringent than ASME. Verify thatlocal / state codes are met.

For instance, the Code requires a stop-check valve at the outlet of steam piping. This may be angletype (hand wheel in vertical only) or the horizontal type.

Since the steam is very hot and comes under Code jurisdiction, the pipe stress engineer must analyzeall the ASME piping excluding instrument piping. Particular attention must be paid to communicate allthe known tube movements, etc. to the stress engineer.

Blowdown Piping

Blowdown piping from the steam drum to final terminal of the blowdown header must be approved bythe pipe stress engineer

Downstream of the blowdown valves all turns and bends must be made using 5 dia minimum bendradius. Heavy wall pipe must be used (Sch. 80-min). Supports and guides must be evaluated from thestandpoint of thermal and physical shock. The use of hanger springs should be avoided.

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9.11 Process Heater Steam-Air Decoking Guide

9.11.1 Introduction

The practice of steam-air decoking heaters (instead of mechanical cleaning) has been usedsuccessfully in refineries for many years. The purpose of this guide is to present a general designprocedure to be used for steam-air decoking of all types of process heaters. Each decokingoperation is an individual job and different in certain aspects from any other decoking usingessentially the same procedure.

9.11.2 Facilities For Decoking

The necessary facilities and piping manifold for decoking are shown schematically on Figure # 9-40 &9-43. The manifold and piping should be installed according to usual design practices for theconditions and services involved.

This steam-air decoking manifold provides for passing steam and air separately or in combinationthrough the heater tubes in either normal or reverse flow. It provides for quenching the decokingeffluent with water before it flows to a sump. A sample connection with a water quench is providedfor continuous observation of the characteristics of the heater coil effluent during decoking while thebulk is discharged to the sump.

The heater should be equipped with special drop-out pipe spool pieces at the heater inlet and outletto isolate the heater from the rest of the unit.

Also provide special removable decoking fittings so that each pass of the heater may be decokedseparately while steam is admitted through the remaining passes to prevent overheating of the tubes.

Steam or water must be circulating through steam superheater and steam generation coils in theconvection section of heaters during the entire decoking period as a protective measure againstoverheating of the tubes.

For good control, it is desirable to have a portable temperature recorder located near the decokingmanifold to record firebox and effluent temperatures.

The effluent from the heater should not be discharged into the normal sewer or into a gaseous area.An effluent quench sump or decoking pot, fixed or portable, should be provided for the steam-airdecoking operation. The flushing water line if required, should be blinded before it joins the decokingmanifold during decoking to avoid admitting water to the hot heater tubes by mistake.

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Figure # 9-40

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9.11.3 Mechanics of Decoking

Decoking furnace tubes is a process of heating tubes from the outside while steam blows coke from theinside of coil. After steam has spalled (cracked) most of the coke from the coil, air is introduced to burnthe remaining coke from the tubes. Burning the coke shows as a red, hot spot which progressesthrough the coils as the coke burns. Normally, one pass is decoked separately while steam is admittedthrough the remaining passes for cooling and to prevent burning of the tubes.

Figure # 9-41

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9.11.4 Major Precautions - Piping Design

Piping design of decoking is complicated due to the necessity of additional control manifolds and swingells. However, the decoking effluent transfer line and decoking sump / pot pose problems that requirespecial investigation. The piping designer shall obtain the various process conditions from the processengineer. The designer is advised to work closely with pipe stress and pipe materials engineers forguidelines in order to effectively design the system.

The following is a list of items that should be noted:

- The very high line temperatures (up to 1400oF) should be identified and noted on the various lineswith particular attention to temperature gradients.

- Decoking lines may be consumable (carbon steel) or non consumable (alloy).

- Decoking sumps or pots may be portable (skid-mounted) or fixed (permanent installation).

- Water injection via a special mixing tee may be required on the decoking transfer line.

- Pipe liners may be used to overcome problems of thermal expansion and erosion in larger (18" orabove) decoking lines.

- Heavier pipe schedules may be required at ells, etc. to accommodate erosion effects.

- Clean-out blinds or special fittings may be required to remove trapped coke deposits.

- Pipe spans of decoking transfer lines are greatly reduced (six feet C. to C.) because of very lowstress allowable at these higher temperatures.

- Extra sight ports (w/platforms) are occasionally required for observing radiant section tubes.

- The foregoing material must be developed as early as possible and communicated to the heatervendor in order to reduce squad checking and back-charges

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9.12 Pigging for Internal Cleaning of Tubes

Instead of trying to remove deposits by burning or dissolving them, this process scrapes build-upaway in a series of controlled, incremental cleaning runs.

Pigs of various types and materials are used. Flexible polymer pigs with adjustable metal cleaningstuds are one of the types of pigs. These pigs can negotiate short radius elbows and U-bends.

9.12.1 How It Works

Water pressure drives a pig through the tube, the protruding metal cleaning studs scrape depositsloose. Some of the water flows around the pig and past the cleaning studs, flushing looseneddeposits ahead of the pig and into a collection tank at the outlet. Because it works at ambienttemperatures, it can be used to clean the convection section, external crossover lines, coke transferlines, and other sections that cannot be steam-air decoked.

Figure # 9-42

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Pigs are driven by plain water or water with chemicals, with driving pressures typically around 70psig. All operations are at or near ambient temperature.

9.12.2 The Pigging Procedure

The equipment needed for furnace tube cleaning is usually transported to a single trailer. Piglaunchers are mounted on the furnace tube, and water and electricity are connected. Before cleaningbegins, soft foam pigs are pumped through the furnace to obtain information about the minimuminside diameter and locations of major deposits. As the job progresses, pig size, stud type, and studheight are adjusted for maximum cleaning performance. A cleaning run typically takes from 5 to 20minutes; the entire process can be accomplished in as little as 12 hours. In the event a pig gets stuck,water flow is reversed to dislodge it.

9.12.3 Requirements at Heater / Site

� Breakout Spools with Flanges at the inlet and outlet� Water supply and lighting� Vacuum truck or effluent hose to process drain for cleaning tanks� Drums or other receptacles for coke� A small lifting unit

9.12.4 Design Considerations

The requirements of pigging must be taken into account at the equipment layout stage itself. Designermust ensure that there is enough space around the heater for the trailer and lifting unit to move in.Since this procedure involves physical removal of coke instead of burning, there should be space forreceptacles and/or a lifting unit to collect and transfer the coke being removed from the tubes.Designer should ensure that a utility station is in the vicinity to supply water.

The designer must ascertain the length of the pig launcher from the contractor in order to arrive at thelength of the breakout spool. If breakout spools for pig launcher are provided at a high elevation e.g.at the crossover piping, designer must ensure that there is a platform and proper access to the areafor the pigging operation. Also, one must ensure that the platform is adequate to support theadditional weight of whatever pigging equipment will be placed on it.w

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9.13 Heater Platforms

Types

There are three types of platforms which are required for both vertical and horizontal heaters. Theyare:

The Operating (Firing) Platform for burner valve operation, observation ports, operation of multi-passinlet piping and valuing and decoking operations

The Maintenance Platform for inspection, testing, cleaning and removal of tubes, furnished piping andprocess piping

The Access Platform for access to instrument connections, soot blowers (Rotary and Retractable),steam lance doors, damper shaft/wheel, roof platforms and bridging platforms (connecting platformbetween two different pieces of equipment)

9.13.1 Criteria

The criteria to develop the extent and location of platforms is found in the Heater, Data Sheets, ClientRequirements and the Piping Design Specification. Consultation with the instrument engineer will helpdefine the access requirements for instruments. In addition, the designer is expected to use his abilitiesto determine the orientation and extent of the platforming. It is true that platforming is expensive;however, lack of required platforming for a safe and efficient operation of a heater is more expensive.In other words, "Minimum platform widths" is not meant to reduce the platforms to smallest possiblesizes.

Very often, platform support steel is extended to accommodate pipe supports, guide (guide frames),spring hangers, etc. The heater vendor must be alerted as soon as possible. When piping manifolds,etc. are located on platforms, support steel under the platform is required for additional support.Grating type platforms should have bearing plates or beams for pipe loads on the grating. It isimportant to remember:

Avoid dropping pipe through platforms. It is seldom done correctly (originally) and results in extrasquad-check costs and does not lend itself to design variations as the project progresses.

It may be required that the designer will:

Re-route vendor cross-over piping to reduce unnecessary projection into the platform area.

Re-orient thermowells to reduce projection into operating areas.

Re-locate draft gages, etc. on the heater shell for better access by platform or ladder (obtain ControlSystem Engineer's approval)

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9.13.2 Vertical Heaters:

In the case of the vertical heaters, the circular platforms are different from the conventional ones forcolumns and vessels only in one respect: They encircle the heater for a full 360 degrees.

Firing Platform

Considering first the firing platform, with access by means of a stairway, there is the choice of two basicarrangements: tangential (Figure # 9-43), or radial stairs (Figure # 9-44). The tangential type demandsslightly less space and usually lends itself to most layouts.

It is imperative not to have any obstruction lower than 7'-0" above grade between the support columns,since fuel lines could not be run to the burners at the minimum elevation of 6'-0". For this reason it isimportant that the heater foundation does not provide either a curb of surface raised above the HPFS,except at the supports for the structural members.


Maintenance Platform

The maintenance platform is accessible by ladder (See Figure #9-45). The side access type landing as

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shown in Figure # 9-46 is not permissible since it requires an opening which would not only interrupt thecontinuity of the platform but also prevent access to the tubes at the landing. This is consideredhazardous from the standpoint of safety.


Avoid the ladder arrangement in Figure #9-46 by moving the ladder outside of the platform and addinga landing (similar to the one shown in Figure # 9-49). The ladder no longer infringes on the access tothe tubes and there would be no objection to a side access type landing. Generally, side accesslanding is preferred.

Figure # 9-47

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If the maintenance platform is more than 30'-0" above grade but less than 30'-0" above the firingplatform, the simplest arrangement would be: Stairway and second egress ladder to firing platform andladder from there to maintenance platform, as shown in Figure # 9-50.

Figure # 9-48

If the maintenance platform is not more than 30'-0" above grade (maximum allowable reach for oneladder) the simplest arrangement would be: Stairway to firing platform and ladder from grade tomaintenance platform with step-off from ladder to firing platform, as illustrated in Figures # 9-48 and 9-48.

Should it be desirable to have this ladder as a second way of egress from the firing platform (to beeffective, a second egress must be as far away from the first as possible), then the addition of a landingat the firing platform on either side of the ladder would accomplish it (See Figure # 9-48).

If the maintenance platform is more than 30'-0" above the firing platform but less than 60'-0" abovegrade, there is a need for an intermediate platform between firing and maintenance platforms. It ispossible to make one ladder serve from grade to firing platform landing as in Figure # 9-47 andintermediate platform, and a second ladder from there to the maintenance platform as illustrated inFigure # 9-49.

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Whenever there is an intermediate platform, and only then, is there a basically different alternate bymoving the ladder leading from the firing platform to the intermediate platform closer to the heater.Such an arrangement is shown in Figure # 9-52. This design is attractive since it is possible to arrangeinstrument connections (skin points) along the ladder and especially on the intermediate platform itself,to which it is impossible to otherwise provide access. It is, however, very important to provide for thefollowing easily forgotten requirements in the layout:

Allow for pipe header space plus minimum clearance of 8 inches when moving the ladder closer to theheater

Place the ladder far enough to the side of the sight door so there is no obstruction to burner controlvalves

Make sure there is at least 2'-6" left between the ladder and the edge of the firing platform

The ladder from intermediate platform to maintenance platform must be (when on the same center line,as shown in Figure # 9-52 about 3'-2" further out.

9.13.3 Box Heaters

The platform design for the box heaters offers less variety. Since the firing platform is, as a rule,

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considerably longer than the one for vertical heaters, a stairway on each end is provided. While thefiring platform extends all along the heater where the sight doors are (sometimes on both sides), themaintenance platforms are on the tube header ends only, as shown in Figure # 9-51.

Figure # 9-51

The platform in front of the inlet and outlet should allow for the piping (at least 4'-0" from header box toedge of platform).

It is extremely undesirable to have the firing platform for box heaters at a height of less than 8'-0" abovegrade, since it is then impossible to run lines which connect either to the underside of the heater(snuffing steam to the fire box) or to some manifold at grade (air, water, steam to utility stations)underneath the platform.

It is imperative not to have any obstruction lower than 7'-0" above grade between the support columns,since fuel lines could not be run to the burners at the minimum elevation of 6'-0". For this reason it isimportant that the heater foundation does not provide either a curb or surface raised above the HPFS,except at the supports for the structural members.

From the standpoint of safety the area should drain away from the heater and never locate any drainsunder the heater.

Review Figures # 9-52 and 9-53 for further platform considerations

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Figure # 9-52

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Figure # 9-53

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9.13.4 General Notes For Heater Platforms

- Ladders - When ladder runs exceed 30 feet, a directional offset ladder and platform shall beprovided.

- Stack ladders shall be provided for access to stack instrument connections. Locate on upwind sideof stack if possible for personnel protection.

- Hinged doors for header boxes - If doors cannot be opened due to interference's with handrails,provided removable handrail.

- Provide platform with ladder access to each observation port.

- Sootblower platforms shall be provided for operation and maintenance of retractable and rotarysootblowers.

- Escape ladder required when platform length exceeds 30 feet.

- If tube mechanical cleaning (turbining) is required, check for method of turbining and spacerequired.

- Cages are not required on ladders 8'-0" in length or less.

- Platforms to be provided for steam Lance Doors when doors are not accessible from Radiant Roof.

- All instrument connections selected to be used require at least ladder access.

- Cut-outs required for steam drum gage glass operator chains and mirrors.

- Establish pipe routing and clearance area free of structure, bracing, etc.

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9.14 Squad Checking

� For Squad checking requirements refer to Fluor Daniel Technical Practice 000.250.2580.

9.14.1 Sources of Information

A listing of sources of information for heaters follows. Its purpose is to serve as a guide of when to lookfor certain items. There are two principal sources of data by which to squad check heaters. They are:

9.14.2 Design Basis - (input)� Heater Narrative Specs. xxx.257.57103� Heater Specification Data Sheets� Flow Diagrams� Proposed/Actual Vendor Outlines� Client Requirements

9.14.3 Design Results - (Output)

� Plan Layouts & Arrangement Drawing� Various Spools and Stress Sketches� Past Issues of Squad Checks

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9.15 Fired Equipment Basic Stress Considerations

9.15.1 Introduction

The most important consideration in laying out Heater piping is to use the heater tube as a tool tominimize the amount of flexibility required in the process piping. By locating the heater tubes in themost advantageous position, the length and number of fittings required in the process piping may beminimized.

Basically there are two types of Heaters. They are : 1) the Box and 2) Vertical Heaters. Consider theVertical Heater since it is the simpler of the two.

9.15.2 Vertical Heaters

All vertical heaters have vertical tubes in the radiant section and horizontal tubes in the convectionsection if one is required.

The Radiant Section

The tubes in the radiant section are arranged in even or odd numbers. Tubes are frequently added toreduce the height of the heater while elimination of a tube will increase the height of the heater. Evennumbers of tubes will place the inlet and outlet nozzles at the same end of the heater. See Figure # 9-54.

Figure # 9-54

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Odd number of tubes place the inlet and outlet at opposite ends of the heater. See Figure # 9-55.

Figure # 9-55

Occasionally there is an option to increase or decrease the height of the heaters and consequentlyreposition the nozzles to the advantage of the piping system. (3-40' tubes = 4-30' tubes). However,when there is a convection section involved with a direct tie to the radiant section, the support andnozzle locations for the interconnecting pipe will invariably be set by the heater Vendor with little optionfor change. See Figure # 9-56.

Figure # 9-56

Normally the supports in this case are located at the top of the radiant section to minimize growth intothe crossover piping which minimizes the length and number of fittings required in the crossover pipingfor flexibility purposes.

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The location of the nozzles has a direct bearing on the location of the tube supports as related to thepiping system. Therefore, an understanding of the type of supporting arrangements available isnecessary before continuing with the layout.

Bottom Supports

Tubes supported at the bottom of the heater have advantages which may or may not be of value in thelayout of the piping system. Each must be considered on its own merit and evaluated with respect tothe effect on that particular system of piping. See Figure # 9-57.

Figure # 9-57

The long unstable tube columns require guiding to avoid buckling from their own weight and anyexternal load applied parallel to the center line of the pipe. Columns under compressive loads aremuch more critical than columns in tension. To avoid eccentric column loading, the deflection" " of the bottom support in a horizontal direction must be minimized. The weight of the tubes issupported at a lower elevation within the heater structure. Expansion is tube movement into the pipingsystem. Displacement is allowable piping movement into the heater.

Top Supports

As with bottom supported tube arrangements, top supports have decided advantages which must beevaluated for each individual piping application.

(*1) Min. Exp. = Tube change in length is minimum thermal expansion growth.

(*2) Min. Exp. = Tube change in length is maximum thermal expansion growth.

(*3) L.D. = Tube deflection is a limited displacement due to such things as tubebending stress and physical design of the heater components.

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The long tubes are in tension and are in no danger of buckling! Horizontal displacement is limited bythe stress in the tube and the limit accepted by the heater vendor. The weight of the tube is located atthe top of the radiant section. See Figure # 9-58.

Figure # 9-58

Floating Coils

This is by far the most expansive method of absorbing displacement into the heater. There are manyinstances where the floating coil is the only solution to the flexibility of the piping system and is inactuality a dire necessity.

Methods of floating the coil employ either the use of spring hangers or counter-weights. The mostcommon approach used by heater Vendors is the counter-weighted piping system. The code demandsthat all counter-weights are installed with fail safe devices for personnel protection in the event that thecounter-weight assembly fails. Usually the counter-weights are attached to the ring headers welded tothe heater tubes. The counter-weight lifts the tubes by means of a cable and pulley system or by acantilever beam system (See Figure #9-59).

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Displacement limited in all directions only by Heater Vendor and pipe stress.

Figure # 9-59 Floating Coils

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The other method of floating the coil is with the use of spring hangers. See Figure # 9-60.

Figure # 9-60 Floating Coils

The Convection Section

The length of tubes in the convection section of the vertical heater are generally very short because ofthe limited available on top of the radiant section (6' to 12'). They may be controlled easily by theaddition of directional anchors on the face of the convection section. Normally, the heater Vendor willonly supply controls on request. The standard approach is to rely on friction to provide a natural anchorin the center allowing the tube to expand outward from that point. Since the commodity in the line isheated as it flows from one end of the tube to the other, the tube metal will generally be hotter at theoutlet end than on the inlet end and the metal temperature is 100oF to 200oF hotter than the flowingcommodity (See Figure # 9-61).

Figure # 9-61

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The same phenomena will occur regardless of the number of passes or the length of the tube althoughto a lesser degree on shorter tubes (See Figure # 9-62).

Figure # 9-62

There are too many factors which tend to control the direction of the expansion if positive methods arenot utilized; i.e., weld splatter, crooked supports, crooked guides, etc. The correct approach is to addrestraints to the tube. This action will have the additional benefit of providing effective wind and seismicstops which is definitely lacking in the frictional restrained state. The three locations available forproviding control on the tube are the front face of the convection section, the rear face of the convectionsection and the internal supports for the tubes. Any one of these locations may be selected. Neverselect more than one. Furthermore, the stop may only be provided on the first or the last pass onlybecause of the difference in the metal temperature of the tubes (See Figure # 9-63).

Assuming linear heater buildup and a tube metal temperature 100oF higher than the commodity-321SStubes (See calculations below):

Calculations For Figure # 9-63

Temp. @ inlet = 100oF + 600oF = 700oFTemp. @ return bend = 800oF (avg.)Temp. @ outlet = 100oF + 800oF = 900oF

Average temperature of tube #one = 750oF (e = .0815 "/Ft.) 750oFAverage temperature of tube #two = 850oF (e = .0914 "/Ft.) 850oF

1 = [(10 x .0815) - (10 x .0941)] = .126" OUT Direction Due To 2 = [(10 x .0815) - (10 x .0941)] = .126" IN Location of Stop

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Figure # 9-64

1 = [(10 x .0815e 750o F = .815"2 = [(10 x .0941e 850o F = .941"

Installation of internal guides and anchors is not desirable because the support steel and pipingattachment are exposed to the direct heat in the section and have no flowing commodity to cool them(See Figure #9-65).

Figure # 9-65Large forces must be restrained by Face of Plates.

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Temp. Inlet = 700o

Avg = 725o; �1 = 5 x .0783 = .3915"Temp. Stop = 750o

Temp. Return Bend = 800o Avg = 775o; -5 x .0848 = -.424"

Temp. Center = 850o Avg = 825o; +5 x .0911 = +.4555

Temp. Outlet = 900o Avg = 875o; 5 x .0972 = +.486"

� 2 = 5 x 1.035 = +.5175"

Floating coils in the convection section are not considered because of the extreme difficulty insupporting the long horizontal tubes on springs or counter-weights.

The coils may be displaced perpendicular to the centerline of the tube with only the tube stress level asa limit. Displacement of the coil parallel to the centerline of the tube is not allowed. Verticaldisplacement is limited to the upward direction so that the tube is lifted off of the pipe support. Theadditional weight from loss of the supports must be absorbed by the first internal and external supportthat is effective 9See Figure #9-66).

Figure # 9-66

Figure # 9-67

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*The amount of lift off is proportional to vertical expansion, which is dependent on: Line Temperature,Pipe Material and Dimension "L", to first vertical support.

The weight resting on the first four supports inside the convection section must now be added asadditional load on the third internal support and on the external support. The new unsupported spanmust also be considered (See Figure #9-67)

Regeneration And Decoking

During catalyst regeneration and especially during decoking operations the line temperature willincrease considerably. The effect of the line expansion, whether the decoking-regeneration system isindependent of the process system or not, must be taken into account in the design of the heater. Thedecoking temperature generally is in the vicinity of 1300oF, and will affect the displacement required atthe heater tube nozzles (See Figure #9-68).

Figure # 9-68

Thermal expansion is from the anchor point to the heater, thus deflecting the tubes

The heater tube in the decoking operation is displaced nearly twice as much as in the design condition.The allowable pipe spans and the pipe material are severely limited at 1300oF. Because of thesefactors, water quenches are introduced into the lines to reduce the temperature. Invariably thesequenches require mixing tees to reduce the temperature rapidly to a maximum of 1000oF or less (SeeFigure #9-69).

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* "L", Critical length determined by Process Eng & Mechanical Eng Consultant

Figure # 9-69

The critical length shown is a factor of the injected material, temperature and velocity. It is required toprevent wear (erosion) on the elbow from the effect of the injected material striking the elbow at highvelocity. The length must be sufficient so that the injected material is thoroughly mixed with the flowingcommodity before the elbow. Using the weld reducer to attach the injection line removes the thermalshock from the crotch and allows the injection to be made without weld cracking and bowing at thejunction point. The connection at the junction point will be designed by stress.

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O.S.H.A. has had a drastic effect on Fluor Daniel's attitude toward "throw away" or "consumable" pipingin decoking systems. In order to avoid law suits for accident cases resulting from non-conformance tocode, Fluor Daniel is obligated to recommend material which is within the temperature limits recognizedby code. At temperatures above 1100oF Carbon Steel material is no longer acceptable. Fluor Danielwill recommend alloy or stainless steel pipe for these installations. In the event that the customerinsists on using Carbon Steel pipe he must indicate that his decision is to override Fluor Daniel'srecommendation. The customer must also provide allowable stress for computing wall thickness, pipespans and thermal expansion for all temperatures beyond the range of the code. Fluor Daniel will thendesign to the specific parameters dictated by the customer. This approach is mandatory for all plantswhich fall under the jurisdiction of the O.S.H.A!

Ring Headers

The ring header must always be supplied by the heater Vendor. Tube connections are difficult to locateon the header, also, the support and tube movements from the ring header expansion are removedfrom the area of responsibility of the Vendor or when he does not design and fabricate the ring. Sincethere is no flexibility between the ring and the tube, the tube must absorb the expansion of the ringheader. The weight of the header is on the tube support.

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9.16 Instrumentation for Heaters

Figure # 9-70

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Following are some of the instruments used for heaters:

� Thermowell/Thermocouple

- Retractable thermowells are usually provided at jumpover piping. This location is preferred becausethe tubes are easily accessible at this point and moreover, the heat gain in the convection sectioncan be also ascertained. Permanent access is usually required for these thermowells. Spacerequirements for removal of the analyser should be ascertained during the design stage to preventinterference with piping / structure.

- Skin type thermocouples are preferred for tubes in radiant section. Usually, permanent access isnot required for these.

� Draft Gauge

- Essentially, it is a pressure gauge, which measures absolute pressure due to partial vacuum in theheater. These are usually located at the base of the radiant section, at the top of the radiant section,above convection section (or bottom of stack) and at the top of stack.

Figure # 9-71Typical Draft Gauge Piping Assembly

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- Due to rodding-out requirements to clean soot deposits, draft gauge piping assembly can take up alot of space as shown in the figure. This should be taken care while designing piping / platforms.(See Figure # 9-71)

- Sometimes, permanent air supply is required for these connections- Permanent access either from platform or ladder is required for these connections

� Gas / Oxygen Analyzer Connection

- This is usually provided on the arch of radiant section. It is usually accessible from the platform atthe top of the radiant section. Space requirements for removal of the analyzer should beascertained during the design stage or prevent interference with piping / structure

� Flame Scanners

- To detect presence /quality of flame- Can be UV or IR type- Mounted in such a way that it points to tip of burner- Sometimes, permanent air supply is required for these connections

� Damper Controls

- Nowadays, dampers are equipped with electric motors / pneumatic cylinders which can be of largesizes.

- Platform access to be provided at the damper level.- Designer should ensure that the platform be adequately sized so that damper controls do not hinder

access

� Sampling Connections

- One or more sampling connections are provided on the stack to measure the emission levels.Permanent access is required. A platform should be provided access and operation at theseconnections.

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9.17 Sample Layouts

Figure 9-73

Figure 9-72

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Figure # 9-73

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4-Pass Circular Heater

Notes for Figure # 9-73

1. Heater Feed line with flow element. Supported at main pipe rack.2. Axial stop on heater feed line to ensure loads are not transferred to heater. Line not vertically

supported on secondary rack or line stop to ensure free downward expansion of vertical sectiongoing to heater. However, shoes provided below line with gap so that the line can be supported byadding shims for changing line blind or flow element during maintenance/shutdown

3. Secondary Pipe Rack perpendicular to primary rack for lines to and from heater4. Symmetrical cascading inlet piping. Supports placed so as to ensure sufficient leg for flexibility5. Axial line stop. These ensure that loads from lower leg are not passed towards nozzle above. Also

ensures symmetrical expansion of both branches above. The line stop is designed with lugs / shoesabove the dummy leg. Since the line above is supported from platform, this design ensures freedownward expansion. Also, this does not leave room for construction error as there is no memberto support the dummy leg below.

6. Flanged removable spool on individual pass of inlet piping for pigging7. Expansion loop ensures minimal transfer of piping load to nozzles8. All round platform at convection section (supported) on top of radiant section arch. 2’ 6” clear space

around all piping / valves / utility station.9. Utility station with air and steam connections for maintenance activities10. Removable flanged spool on individual pass of outlet piping for pigging11. Accessible draft gauge connections. Note that they slope backwards into heater

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Figure # 9-74

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Figure # 9-75

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Figure 9-76

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Figure # 9-79Figure # 9-79

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9.18 Glossary

ATOMIZING STEAM Steam used to vaporize the fuel oil at burners.AIR PLENUM Chamber enclosing burners underneath furnace. Equipped with

louvers which control combustion air flow to burners.AIR PREHEATER Device that heats combustion air by utilizing flue gas a heat source.ARCH Roof of radiant section.BREACHING Ducting that connects one or more heater stacks into a common

stack. Also, ducting from sections of one heater that discharges intothe heater stack.

BRIDGEWALL Brick walls inside heater that divides the radiant section intoseparately fired zones.

BUCKSTAYS External structural steel that forms the supporting framework of theheater.

BURNER Devices that feed fuels and air of proper mix to the radiant section ofthe heater. Burners can be either for fuel gas or oil or a combinationof gas and oil.

CASING Steel shell which encloses the heater.CONVECTION SECTION Section above radiant section that houses convection tubes which

receive convection heat before flue gases pass out of the stack.CROSSOVERS Piping which connects convection tubes to the radiant tubes.

Normally, crossovers are exterior of the casing.COIL See “PASS”DECOKING Cleaning coke deposit from interior of tubes with steam and air as the

tubes are heated externally.DRAFT GAGE Instrument that measures the pressure flow of gases through the

heater.DAMPER Rotating steel plate in stack which controls the draft of exhaust gases

released through the stack to atmosphere.DAMPER CONTROLLER Manual or automatic (Bialy Operator) device, normally operated from

grade that regulates the position of the damper.FLUE GAS Spent gases, which pass through the stack to atmosphere.FINS (EXTENDED SURFACE) Metal – fins or studs – welded to tube exterior for the purpose of

increasing heat surface of tubes.“FIRE EYE” Flame scanning device which, when a burner fails, cuts off fuel

supply.HEADERS Tubes and return bends joined together to form a pass.HEADER BOX Housing for return bends, normally provided when heater is equipped

with plug-type return bends.LANCE DOORS Access doors in convection section provided for insertion of a steam

lance to clean exterior of convection tubes.MANIFOLD Common header (external) into which all terminals from each pass

are connected.OBSERVATION DOORS(PORTS)

Doors used to observe burner flames or heater tubes (sight ports,observation ports or peep holes).

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PASS Bank of consecutive tubes through which the fluid travels from thepoint it enters until it leaves the furnace.

PLUG HEADERS Special type return bends having removable plugs for inspection andcleaning of tubes.

REFRACTORY Ceramic insulation that reduces heat loss and protects casing andstructure.

RETURN BENDS Welded U-bends or plugged, rolled fittings that connect tubes.SHIELD TUBES (SHOCK) The bottom tubes in the convection section which see the radiant

flame.SKIN THERMOCOUPLE Special thermocouple attached to outside of the tube wall which

measures the metal temperature.SNUFFING STEAM Has two purposes: (1) Extinguish a fire caused by tube rupture; (2)

Purge heater before light-off.SOOTBLOWER Retractable or non rectractable permanently installed lances that

rotate and spray steam to clean tube exterior.TUBES Straight lengths of pipe joined by return bends.TUBESHEET Metal sheet with tube openings near the return bends for separating

convection or radiant section from header box.TURBINING Mechanical cleaning device used to clean inside of tubes; normally a

flexible hose with rotating or vibrating cleaning head on the end anddriven by air.

TERMINALS Inlet and outlet connections.

1.

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