boilers & furnaces-refractory&insulation

8/18/2019 Boilers & Furnaces-Refractory&Insulation

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Note: The source of the technical material in this volume is the Professional

Engineering Development Program (PEDP) of Engineering Services.

Warning: The material contained in this document was developed for SaudiAramco and is intended for the exclusive use of Saudi Aramco’s employees.

Any material contained in this document which is not already in the public

domain may not be copied, reproduced, sold, given, or disclosed to third

parties, or otherwise used in whole, or in part, without the written permission

of the Vice President, Engineering Services, Saudi Aramco.

Chapter : Vessels For additional information on this subject, contact

File Reference: MEX30208 M.Y. Naffa’a

Engineering EncyclopediaSaudi Aramco DeskTop Standards

Boilers And Furnaces Refractory And Insulation


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Engineering Encyclopedia Vessels


Saudi Aramco DeskTop Standards

Contents Pages

INTRODUCTION................................................................................................................ 1

STANDARDS FOR PURCHASE AND INSTALLATION................................................... 2

Service Temperature ................................................................................................. 2

Design Temperature of Metallic Anchors................................................................... 2

Casing Temperature .................................................................................................. 3

REFRACTORY LINING SYSTEMS: TYPES, COMPONENTS, INSTALLATION

AND CRITERIA FOR SELECTION.................................................................................... 4

Refractory Components in Furnaces: Types and Components ................................... 4Thermal Ceramics Insulating Firebrick ........................................................... 6

Thermal Ceramics Firebrick ........................................................................... 8

Thermal Ceramics Refractory Castables ......................................................... 9

Thermal Conductivities of Lumnite-Concrete................................................11

Refractory Components in Boilers: Types and Components.....................................12

Brick Construction...................................................................................................13

Insulating Firebrick (IFB) Systems ................................................................14

Refractory Firebrick Systems ........................................................................17

Thermal Expansion .......................................................................................17

Castable Refractory ..................................................................................................18

Castable Refractory Lining Systems..........................................................................19

Anchors....................................................................................................................20

Installation ...............................................................................................................22

Thermal Expansion...................................................................................................24

Other Applications ...................................................................................................24

Ceramic Fiber...........................................................................................................24

Ceramic Fiber Lining Systems.......................................................................24

Anchors........................................................................................................27

Thermal Expansion .......................................................................................28

External Insulation ...................................................................................................28

Criteria for Selecting Refractory Lining Systems.......................................................28


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Fuel Sulfur Considerations............................................................................30

Fuel Ash Considerations ...............................................................................32

Saudi Aramco Fuels ......................................................................................33

CALCULATING HEAT TRANSFER.................................................................................34

Heat Transfer Equation ............................................................................................34

Thermal Resistance...................................................................................................34

Refractory Hot Face Temperature (T1) ....................................................................35

Casing Temperature (T2) .........................................................................................35

Interface Temperature (Ti) .......................................................................................36

Thermal Conductivities (k) .......................................................................................36

Determine Required Wall Thickness .........................................................................37

Checking Existing Refractory Design........................................................................39

Temperatures of Tiebacks and Supports ...................................................................42

Work Aid 1: Procedure for Calculating Heat Loss Through a Refractory

Wall..............................................................................................................43

Work Aid 2: Data Bases for Calculating Heat Loss--Heat Loss Versus

Casing Temperature......................................................................................44

Work Aid 3: Data Bases for Calculating Heat Loss--Thermal

Conductivities of Typical Refractories...........................................................45

GLOSSARY........................................................................................................................47

REFERENCE......................................................................................................................49

APPENDICES.....................................................................................................................50

Appendix A Refractory Wall Thickness - Calculation Sheet ......................................50

Appendix B Refractory Heat Loss - Calculation Sheet ..............................................51


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Table of Figures Pages

FIGURE 1 Typical Refractory Components In Furnaces............................................ 5FIGURE 2 Typical Refractory Properties .................................................................. 7

FIGURE 3 Typical Refractory Components - Ras Tanura Hp Boiler No. 8 ...............12

FIGURE 4 Typical Insulating Firebrick (Ifb) System.................................................14

FIGURE 5 Typical Tieback Details...........................................................................16

FIGURE 6 Castable Refractory Types ......................................................................18

FIGURE 7 Typical Castable Refractory Lining Systems............................................19

FIGURE 8 Typical Anchors For Castable Linings.....................................................21

FIGURE 9 Typical Anchor Arrangements For Castable Linings................................22

FIGURE 10 Typical Ceramic Fiber Lining Details ....................................................25

FIGURE 11 Typical Ceramic Fiber Lining Details ....................................................26

FIGURE 12 Typical Ceramic Fiber Anchors.............................................................27

FIGURE 13 Anchor Patterns For Ceramic Fiber Linings...........................................28

FIGURE 14 Criteria For Selecting Refractory Lining Systems ..................................29

FIGURE 15 Criteria For Lining Systems For Sulfur-Containing Fuels.......................31

FIGURE 16..............................................................................................................38

FIGURE 17 Calculation Of Refractory Heat Loss.....................................................40


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Saudi Aramco DeskTop Standards 2

STANDARDS FOR PURCHASE AND INSTALLATION

Saudi Aramco requirements for furnace refractories are covered by Standard AES-F-001, which

includes API Standard 560. Requirements for boiler refractories are covered by Standard 32-

AMSS-021. There is no industry boiler standard covering refractories. These specifications

provide some basic requirements, but generally permit manufacturers' standard designs to be used.

Some of the requirements in these standards need explanation or additions, and these are

discussed below.

Service Temperature

The service temperature of a refractory material is the temperature at which the material begins to

deteriorate, and therefore operating temperatures should never approach this limit. Refractory

materials in each component layer should have a service temperature of at least 300°F greater thanthe calculated hot face temperature of that layer. This applies to both the hot face and backup

layers. In the case of the backup layer, the hot temperature occurs where the backup layer meets

the hot face layer. The minimum service temperature of all refractory materials used in furnace

radiant and shield sections should be at least 1800°F (Standard 560, par. 7.1.3.). The minimum

service temperature of burner refractories should be at least 3000°F.

Design Temperature of Metallic Anchors

The design temperature of metallic anchors is considered to be the same as the calculated

refractory temperature at the tip of the anchor. The following guide can be used for selecting

metallic components:

Maximum Temperature

of Anchor Tip, °F

Acceptable

Materials (1)

800 Carbon Steel

1400 18Cr-8Ni (Type 304)

1700 25Cr-20Ni (Type 310),

Incoloy 800

1900 RA 330 Stainless Steel

2000 Inconel 601

Note (1): Austenitic materials shall be supplied and installed in the fully solution-annealedcondition. After annealing, anchors should not be bent except where the bend

point on the anchor will be below 1000°F.


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Casing Temperature

Reduction of heat loss is a primary consideration in selection and design of refractory lining

systems. The lining system for furnaces should be designed to achieve a casing temperature of

180°F in 80°F ambient still air (Standard 560, par. 7.1.1.). This corresponds to a heat loss of 218

Btu/hr-ft2 of surface area. Although this ambient temperature is unrealistic for Saudi Aramco, it

is a standard basis for setting casing heat losses and determining lining thicknesses. This basis is

equivalent to a casing temperature of about 200°F in 100°F ambient still air.

Saudi Aramco AES-F-001 adds one requirement to this design basis: that the casing

temperature, where the casing is easily accessible by operating personnel, shall not exceed 150°F

in 100°F ambient air. This is for personnel protection. Since it is impractical to design a furnace

refractory wall to meet this requirement, other means of protection must be provided. One

solution used on the Ras Tanura 493-F-301/2/3/4 Rheniformer Furnace was to provide wire meshfencing several inches away from the hot casing, so that it could not easily be touched.

For boilers, the thickness of the external insulation should be designed to give a cold-faced

surface temperature of 150°F, with a surface wind velocity of 5 mph and an ambient temperature

of 115°F (32-AMSS-021, Par. 5.7.1). This corresponds to a heat loss of

140 Btu/hr-ft2.


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REFRACTORY LINING SYSTEMS: TYPES, COMPONENTS, INSTALLATION AND

CRITERIA FOR SELECTION

Refractory Components in Furnaces: Types and Components

Refractory and insulation materials are used in boilers and furnaces primarily for the following

purposes:

• To protect the steel structure from overheating.

• To reduce heat loss through the boiler or furnace enclosure to the atmosphere.

• To protect portions of the tube surface from excessive heat transfer rates.

Refractory lining systems generally consist of high-temperature refractory materials that are

supported or reinforced by metallic components. Commonly used refractories are refractory

bricks, castable refractories, and ceramic fibers. In most high-temperature applications, it is

not practical to meet the heat loss requirements with a single-layer lining, so a dual-layer lining

system is used. A lower grade, better insulating material is used for the backup layer. These

refractory lining systems are discussed in this module.

Typical refractory components in process furnaces are shown in Figure 1 and are summarized

below. An internal refractory lining is used throughout the furnace to protect the enclosure and

structure, and to reduce heat losses.


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Header BoxBreeching

End Tube

Support

Unshielded

Endwalls

Side ViewEnd View

Stack

ConvectionSection

Sidewalls

Arch

Shielded

Sidewalls

Floor

Dividing Wall

Convection Section

Radiant

Section

Burners

FIGURE 1 Typical Refractory Components In Furnaces

Radiant Section:

• Walls and arches. The major lining systems used in furnaces consist of three types of

refractory linings:

- Insulating firebrick (IFB).

- Castable refractory.

- Ceramic fiber.

• Floor. Brick and castable linings that are strong enough to withstand maintenance

turnaround traffic and scaffolding.

Convection Section:

• Sidewalls. Insulating firebrick and castable refractory linings.

• Endwalls. Single-layer castable refractory lining is used on the flue gas side of the end tube

supports.


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• Header boxes. Single-layer castable refractory or ceramic fiber lining is used on the inside

surface.

Flue gas breeching and ducts. Single-layer castable refractory lining.

Stack. Where required, a single-layer castable refractory lining is used.

Burners. Burner blocks are constructed of high-temperature refractory firebricks or castable

refractories.

Refractory Properties. The chart in Figure 2 presents the characteristics of typical refractories.

Thermal Ceramics Insulating Firebrick

Lightweight insulating firebrick offers the low heat conductivity of efficient insulation plus the

ability to withstand direct exposure to furnace heat.


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Insulating firebrick series K-20 K-23 K-26 LI K-28 K-30 K-3000

Service temperatures, F

Exposed 2000 2300 2600 2800 2900 3000

Backup 2000 2300 2600 2800 2900 3000Density, avg (ASTM C 134-70)

Lb/9" straight 1.7 1.8 2.8 3.0 3.0 3.4

Lb/cu ft 29 31 48 51 51 58

Melting Point, F 2750 2750 3190 3190 3190 3350

Modulus of rupture, psi (ASTM C 93-67) 110 140 160 210 240 260

Cold crushing strength, psi (ASTM C 93-67) 110 145 170 220 295 275

Permanent linear change, % (ASTM C 210-68)

Fired @ 1950F 0 - - - - -

@ 2250F - 0 - - - -

@ 2550F - - -0.1 - - -

@ 2750F - - - -0.6 - -

@ 2800F - - - - -0.5* -

@ 2950F - - - - - -0.6

@ 3250F - - - - - -

Thermal conductivity, BTU•in./h•ft2•F (ASTM C 182-72)

Mean temperature@ 500F 0.8 0.9 1.7 1.7 2.0 2.1

@ 1000F 1.0 1.1 1.9 2.0 2.4 2.4

@ 1500F 1.2 1.3 2.2 2.3 3.0 2.8

@ 2000F - 1.6 2.7 2.9 3.8 3.4

@ 2400F - - - - - 4.0

Deformation under hot load, % @ 10 psi (per ASTM C 16-77)

1 1/2 hr @ 2000F 0 - - - - -

1 1/2 hr @ 2200F - 0.1 0.2 0.2 0.2 -

1 1/2 hr @ 2640F - - - - - 0.5

12.5 psi 1 1/2 hr @ 2730F - - - - - -

Chemical analysis, % (ASTM C 573-70)

Alumina Al2O3 39 39 46 46 46 64

Silica SiO2 44 44 52 52 52 34

Ferric oxide Fe2O3 0.7 0.6 1.0 1.0 0.9 0.6

Titanium oxide TiO2 1.1 1.1 1.4 1.4 1.4 0.7

Calcium oxide CaO 15.0 14.4 0.3 0.3 0.5 0.3

Magnesium oxide MgO 0.1 0.1 0.1 0.1 0.1 Trace

Alkalies, as Na2O 0.3 0.4 0.3 0.3 0.4 0.4

Coefficient of reversible thermal

expansion, in./in.F

3.0x10-6 3.0x10-6 2.9x10-6 2.9x10-6 2.9x10-6 2.9x10-6

Color code Green Red Brown Orange Black Purple

* ASTM C 113-74

Data are average results of tests conducted under standard procedures and are subject to variation. Results should

not be used for specification purposes.

Source: Thermal Ceramics

FIGURE 2 Typical Refractory Properties


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Thermal Ceramics Firebrick

Four grades of heavy-duty brick including two special refractory compositions offer marked resistance

to spalling, exceptional load carrying capacity at high temperatures and negligible reheat shrinkage.

Firebrick series Firebrick Firebrick Special refractory brick 80 80-D SR-90 SR-99

Melting point, F 3190 3190 3480 3660Density, avg (ASTM C 134-70)

Lb/9" straight 8.1 8.8 10.6 11.3Lb/cu ft 189 151 183 193

Hot modulus of rupture, psi (ASTM C 583-76)@Room temperature 1700 3500 3600 3800@2000F - - 4500 2900@2300F - - 4200 1600@2600F - - 2900 800@2800F - - 2100 650

Cold crushing strength, psi (ASTM C 133-72) 4000 10,000 12,000 10,000Permanent linear change, % (per ASTM C 113-74)

5 hr @2912F -1.0 -0.8 - -5 hr @3200F - - +1.5 -24 hr @3200F - - - +0.3

Thermal conductivity. Btu•in/h•ft2•F (ASTM C 202-71)Mean temperature @ 500F 16.0 20.8 26.5 47.5

@1000F 16.0 20.6 22.8 31.5@1500F 15.9 20.3 20.8 24.0@2000F 15.6 19.9 19.5 20.5@2500F 15.2 19.5 18.8 17.5

Deformation under hot load, % @ 25 psi (ASTM C 16-77)1 1/2 hr @2640F -1.0 -0.5 - -1 1/2 hr @2900F - - - -0.31 1/2 hr @3000F - - +0.1 -1 1/2 hr @3200F - - +0.1 -

150 hr @3200F - -


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Thermal Ceramics Refractory Castables

Dense Castables

Castable series Kaocrete Kaocrete Kaocast Kao-Tab Kao-Tab Kao-Tab Kaocrete HSB 28-LI 93 95 95-Gun (as cast) (as gunned)Recommended methods of application (X)

Cast or rammed X X X X X Rammed X XTrowled X X - X X Lim. Repairs X XGunned X X X X - X X X

Lb req'd to place one cu ft 100 126 123 150 165 165* 123 125***Required water, U.S.qt per bag

Vibrating 12-13 6-6.5 5-6 5.5-6 4-4.5 - 6-6.5 -Casting and rodding 13-13.5 6.5-7 6-6.5 6-6.5 4.5-5 - 6.5-7 -Ramming 5-6 3-4 3-4 2-3 2-3 - 3-4 -

Recommended use limit, F 2300 2800 3000 3300 3300 3300 2600 2600Melting point, F 2725 3100 3200 3400 3400 3390 3100 3100Density, lb/cu ft Fired 100 126 126 152 166 165 122 124Modulus of rupture, psi (ASTM C 268-70)

Dried 18 to 24 hr @ 220F 400 900 900 1700 1850 1700 1300 1400Fired 5 hr @1000F 350 600 350 1100 1400 1600 850 950

@1500F 160 400 250 900 1000 1500 700 900@1750F - - - - - - - -

@2000F 140 300 270 700 1200 1300 700 900@2200F 240 450 300 700 900 1500 900 1100@2400F - 600 550 700 900 1600 - -@2500F - - - - - - 1400 1600@2600F - 1500 1200 700 1000 1600 - -@2800F - 2000 1400 800 1200 1400 - -@3000F - - 1400 1200 1400 1500 - -@3200F - - - 1600 1800 1900 - -

Cold crushing strength, psi (Per ASTM C 133-72)Dried 18 to 24 hr @ 220F 1400 3000 2100 6000 6000 6800 4200 5500Fired 5 hr @1000F 700 2400 1200 3100 5600 6000 4000 4800

@1500F 700 2000 1000 2900 5200 5100 2800 4400@1750F - - - - - - - -@2000F 300 1400 1100 2300 5000 5800 2600 3200@2200F 450 1400 1200 1850 4400 5300 2800 3400@2400F - 1600 1400 1900 4500 5000 - -@2500F - - - - - - 3200 4000@2600F - 3200 3000 1950 4800 5000 - -@2800F - 4000 3800 2800 5000 5000 - -

@3000F - - 4200 2800 5200 5000 - -@3200F - - - 3000 5600 6100 - -

Dried 124 hr @2 20F 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0Fired 5 hr @1000F -0.5 -0.1 -0.2 -0.2 -0.2 -0.1 -0.2 -0.2

@1500F -1.2 -0.2 -0.2 -0.2 -0.2 -0.1 -0.2 -0.2@1750F - - - - - - - -@2000F -1.5 -0.2 -0.3 -0.2 -0.2 -0.2 -0.3 -0.3@2200F -1.8 -0.2 -0.3 -0.3 -0.3 -0.3 -0.2 -0.2@2400F - +0.1 -0.3 -0.3 -0.3 -0.5 - -@2500F - - - - - - +0.2 +0.2@2600F - +1.0 -0.3 -0.5 -0.5 -0.5 - -@2800F - +0.2 -0.2 -0.8 -0.8 +0.5 - -@3000F - - +0.2 -0.5 -0.3 0.0 - -@3200F - - - -0.2 -0.2 -1.0 - -

Porosity, %, fired 42 31 32 32 - - 29 -Chemical analysis, % fired basis (ASTM C 573-70)

Alumina Al2O3 38 49 60 93 95 95 47 47Silica SIO2 46 42 33 0.5 0.1 0.2 40 40

Ferric oxide Fe2O 1.3 0.9 1.0 0.1 0.1 0.2 1.0 1.0Titanium oxide TiO2 1.3 2.4 1.9 0.1 Trace Trace 2.0 2.0Calcium oxide CaO 12.1 6.0 3.4 6.0 4.6 4.2 8.5 8.5Magnesium oxide MgO 0.9 - 0.1 Trace Trace Trace 0.2 0.2Alkalies, as Na2O 0.3 0.2 0.2 0.1 0.1 0.1 0.3 0.3Phosphorous penta-oxide P2O5 - - - - - - - -

Thermal conductivity, (ASTM C 417-60)BTU•in./h•ht2•F 4.5 6.8 6.7 9.1 13.1 9.1 7.0 7.1

Pounds per bag 100 100 100 100 100 100 100 100

* Without rebound loss. **Water requirements indicated are offered as a guide. Actual water required may be subject to fieldconditions. Data are average results of tests conducted under standard procedures with cast samples, except as otherwise noted, andare subject to variation. Results should not be used for specification purposes.

FIGURE 2 Typical Refractory Properties(CONT'D)


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Insulating Castables

Castable series Kaolite Kaolite Kaolite Kaolite Kaolite Kaolite Kaolite2200 2200-HS 2300-LI 2500-LI 2500-HS 2800 3300

(as cast)(as gunned) (as cast) (as gunned) (as cast)(as gunned) (as cast)(as gunned)Recommended methods of application (X)

Cast or rammed X X X X X X X X X X XTrowled X X X X X X X X X X -Gunned X X X X X X X X X X -

Lb req'd to place one cu ft 56 71 82* 54 74 60* 78 85* 84 86* 68**Required water, U.S. qt per bag

Vibrating 11.5-12 11.5-12 - 11.5-12 12-13 - 13.14 - 9.5-10 - 4-4.5Casting and rodding 11.5-12 11.5-12 - 11.5-12 12-13 - 13-14 - 9.5-10 - 4.5-5

Recommended use limit, F 2200 2200 2200 2300 2500 2500 2500 2500 2800 2800 3300Melting point, F 2670 2495 2495 2670 2740 2740 2700 2700 3300 3300 3530Density, lb/cu ft Fired 58 74 82 58 67 60 77 84 85 88 68Modulus of rupture, psi (ASTM C 268-70)Dried 18 to 24 hr @ 220F 130 475 540 150 210 210 280 390 370 300 250Fired 5 hr @1000F 120 200 - 140 130 100 220 370 290 190 240

@1500F 100 200 160 110 110 - 180 360 260 200 180@2000F 150 200 - 190 130 100 140 310 350 250 180@2200F 200 250 130 190 - - 240 430 400 270 300@2300F - - - 240 - - - - - - -

@2400F - - - - - - 570 700 - - 350@2500F - - - - 370 230 570 750 410 490 -@2600F - - - - - - - - - -- 350@2800F - - - - - - - - 1400 610 550@3000F -- - - - - - - - - - 750@3200F - - - - - - - - - - 850

Cold crushing strength, psi (Per ASTM C 133-72)Dried 18 to 24 hr @ 220F 700 1600 1850 500 740 530 740 1240 1180 480 900Fired 5 hr @1000F 600 1400 - 450 590 300 670 1150 950 550 850

@1500F 500 1200 950 450 610 - 600 1120 900 460 700@2000F 550 1000 - 400 490 350 490 770 1070 860 700@2200F 600 1250 1000 500 - - 440 1110 1390 1150 800@2300F - - - 500 - - - - - - -@2400F - - - - - - 990 1150 - - 1200@2500F - - - - 950 680 1170 1210 2030 1480 -@2600F - - - - - - - - - - 1300@2800F - - - - - - - - 4150 1900 1400@3000F - - - - - - - - - - 1500@3200F - - - - - - - - - - 2200

Permanent linear change, % (ASTM C 269-70)

Dried 24 hr @ 220F -0.1 -0.1 - 0.0 - 0.0 0.0 0.0 0.0 0.0 -0.1Fired 5 hr @1000F -0.2 - - -0.2 -0.2 -0.2 -0.3 -0.3 -0.1 -0.3 -0.1@1500F -0.3 -0.2 -0.2 -0.4 -0.2 - -0.2 -0.3 -0.1 -0.2 -0.2@2000F -0.5 - - -0.6 -0.2 -0.2 -0.3 -0.3 -0.4 -0.4 -0.1@2200F -1.1 -0.7 -0.7 -0.9 - - -0.4 -0.4 -0.6 -0.5 -0.1@2300F - - - -1.8 - - - - - - -@2400F - - - - - - -0.5 -0.5 - - -0.1@2500F - - - - -0.1 +1.0 +0.6 +0.6 +0.5 +0.5 -@2600F - - - - - - - - - - +0.2@2800F - - - - - - - - -0.5 -0.3 -0.2@3000F - - - - - - - - - - -0.5@3200F - - - - - - - - - - -1.0

Chemical analysis, % fired basis (ASTM C 573-70)Alumina Al2O3 35 42 42 41 44 44 41 41 60 60 94Silica SIO2 36 26 26 37 35 35 37 37 33 33 0.5Ferric oxide Fe2O 5.6 6.9 6.9 0.9 0.9 0.9 3.2 3.2 0.4 0.4 0.2Titanium oxide TiO2 1.2 1.0 1.0 1.7 1.8 1.8 2.2 2.2 0.7 0.7 -Calcium oxide CaO 21.1 22.6 22.6 18.6 17 17 16.3 16.3 5.0 5.0 4.6Magnesium oxide MgO 0.2 0.6 0.6 0.4 0.2 0.2 0.3 0.3 0.1 0.1 0.1Alkalies, as Na2O 0.8 0.6 0.6 0.3 1.3 1.3 Trace Trace 0.8 0.8 0.5

Thermal conductivity, (ASTM C 417-60)BTU•in./h•ft2•F 1.6 1.9 2.1 1.6 1.9 1.6 2.5 2.9 3.4 3.5 4.5Pounds per bag 40 50 50 40 50 50 75 75 75 75 50

• Without rebound loss. **Water requirements indicated are offered as a guide. Actual water required may be subject to field conditions. Data areaverage results of tests conducted under standard procedures with cast samples, except as otherwise noted ,and are subject to variation. Resultsshould not be used for specification purposes.

FIGURE 2 Typical Refractory Properties(Cont'd)


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Refractory Components in Boilers: Types and Components

Typical refractory components in boilers are shown in Figure 3, which is an illustration of Ras

Tanura HP Boiler No. 8.

ExternalInsulation

Burner ThroatCastableRefractory

FloorRefractoryBrick

Flue GasBaffles

CastableRefractory

RefractoryBrick

Castable Refractory

FIGURE 3 Typical Refractory Components - Ras Tanura Hp Boiler No. 8


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Because of the membrane water wall construction used in most boilers, very little internal

refractory is needed to protect the outer casing and structure. However, to reduce heat losses,

most of the boiler is covered with an external layer of insulation.

Castable refractory is used to seal the enclosure in areas where the tube arrangement does not

permit a membrane water wall. Castable refractory is also used in the boiler section for flue gas

baffles.

Refractory firebricks are used for removable sections of flue gas baffles.

A layer of refractory bricks, or comparable castable refractory, covers the floor tubes to reduce

heat transfer to these tubes.

High-temperature castable refractory is used to form the burner throats and to protect the

surrounding tubes.

Flue gas ducts and stacks are often covered with an external layer of insulation.

Brick Construction

Two types of refractory bricks are widely used in boilers and furnaces: refractory firebrick and

insulating firebrick. Commonly used firebricks of both types are composed mainly of alumina

(Al2O3) and silica (SiO2), most having a composition of about 45% alumina and 50% or more

silica. For special applications, particularly when very high service temperatures are required, the

alumina content can be increased to over 99%.

Refractory firebricks are used for hot face applications in boilers, furnaces, and combustors where

high strength and temperature resistance are of primary concern. Refractory firebricks also have a

generally high resistance to spalling. The physical characteristics of refractory firebrick are

dependent upon the refractory and binder components used, the forming method, and the

temperature at which the firing is done. These bricks have a high density (about 180 lb/ft3) and

service temperatures of 3000°F or higher.

Insulating firebrick is used in applications, such as furnace linings, where a high insulating value is

more important than strength. Insulating firebrick is a type of porous refractory brick material. It is

manufactured by firing mixtures of high-quality clay, sawdust, and other constituents. Density of

the bricks is about 30-50 lb/ft3, and service temperatures are 2000-3000°F.

Firebricks can be purchased in many standard sizes and shapes. The most common standard brick

size is 9 in. x 4-1/2 in. x 2-1/2 in. Mortar is used to bond the bricks together. Expansion joints

must be provided in all brick linings to allow for thermal expansion of the bricks.


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Insulating Firebrick (IFB) Systems

This lining system consists of a wall of bricks at the inside hot face of the lining and a backup

layer of lightweight insulating block material next to the furnace casing. The IFB wall is usually

4-1/2 in. thick, although 9 in. thick walls are often used in very high-temperature furnaces. A

typical IFB wall is shown in Figure 4.

Although "brick and block" linings have been used successfully for many years, more recent

practice has been to use castable or ceramic fiber linings for process furnaces. These linings are

less costly than IFB walls and are more suitable for shop preassembly of furnace sections.

Steel Casing

Vertical Expansion Joints

Tieback (Staple Type)

She

Bricks

HorizontalExpansion

Joint

FIGURE 4 Typical Insulating Firebrick (Ifb) System

Backup Material

The backup material used in most IFB walls is a layer of mineral wool block insulation, typically

1-3 in. thick. Mineral wool is usually a low-melting-point glass material. Materials are available

with service temperatures of up to about 1900°F.


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Because of its superior properties and competitive cost, some recent IFB systems have used a

backup layer of ceramic fiber material instead of the mineral wool. Ceramic fiber can withstand

higher temperatures than can mineral wool, so it offers a better safety factor should the IFB wall

develop cracks.

Support System

IFB walls are supported by shelf angles that are attached to the furnace structure. Due to the

thermal expansion of the wall, it is necessary to support the wall vertically about every 6-10 ft.

Horizontal expansion joints are provided at each shelf angle.

Vertical expansion joints are also provided about every 10 ft. The expansion joints are typically

packed with ceramic fiber material.

Tiebacks are used to stabilize the wall and hold it in place. Each tieback must be designed to

permit some horizontal and vertical movement of the brick wall caused by thermal expansion. In

vertical walls, not all bricks need to be tied back. A common practice is to tie back half the bricks

in every fourth row of bricks, which is 12.5% of the wall. Other tieback patterns are also used.

Standard 560 requires a minimum of 10% of the bricks to be tied back (Par. 7.2.1). Typical

tieback details are illustrated in Figure 5.


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Casing

CS P

Blo

Insu

V-C

T

Elevation

Plan View - V-Clip

Tieback

Elevation

Plan View -

Staple-Type

Tieback

Expansion Joint

Filled with Ceramic

Fiber

Staple TypeTieback

Shelf Angle

FIGURE 5 Typical Tieback Details

In some furnaces, sloping walls or flat IFB arches are provided. In these cases, all bricks must be

tied back.

In vertical cylindrical furnaces, the arch effect of the bricks acts to hold the vertical wall in place.

Tiebacks are not usually required, unless the furnace diameter is extremely large (over about 25 ft

in diameter).


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Refractory Firebrick Systems

Floor Refractory

The floor tubes in boilers are covered with a layer of refractory firebricks to reduce heat transfer

to these tubes. The floor insulation in furnaces is also covered with a layer of refractory firebricks

to provide for wear during maintenance turnarounds. The bricks in both applications are laid in

place dry, and are not mortared. Castable refractory of equivalent density and service

temperature is sometimes used in place of bricks.

Dividing Walls

Dividing walls are used between the radiant section zones of multi celled furnaces, such as the Ras

Tanura 493-F-3-1/2/3/4 Rheniformer Furnace. These are gravity walls constructed of high-dutyrefractory firebrick. The maximum height of the wall is about 24 ft. The base width is

approximately 2 ft (2-1/2 to 3 bricks wide). The width decreases in 2-3 steps, so that the top few

feet is 9 in. wide (equivalent to 1 brick).

Vertical expansion joints are provided at the ends of the gravity wall. Intermediate expansion

joints are also provided, and these are usually lapped joints. Mortar is not used in lapped joints

(dry joints).

Sulfur Furnaces

High-duty refractory firebricks are used as the front layer in sulfur furnace refractory linings.These layers are typically 9 in. thick. Castable insulation is used in the backup layer.

Thermal Expansion

Refractory firebricks experience thermal expansion when heated, and this must be considered in

the design of refractory lining systems. Expansion joints are required in all types of brick

construction.

For IFB walls, the size of the expansion joint should be approximately twice the thermal

expansion calculated, using the manufacturer's thermal expansion data, and based on the

refractory design temperature. The expansion joint is filled with ceramic fiber material.

For refractory brick used as the top layer of the floor in boilers and furnaces, the allowance for

thermal expansion should be about 3/32 in./ft (unless the manufacturer's data indicate that a

greater allowance should be used). Expansion joints should be covered with refractory bricks to

keep debris out.


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In cases where expansion joints are provided in more than one layer of refractory, the joints

should be staggered so that there is no direct line of sight back to the casing.

Expansion joints should also be provided around burner blocks and tube supports.

Castable Refractory

Castables are concrete-like mixtures of "refractory" aggregates and cement that are formulated to

be mixed with water. The water allows the mixture to be formed into the desired shape and

structure. Most castables contain a hydraulic-setting calcium aluminate cement. A variety of

materials are used for the aggregate.

Several types of castable refractories are available. These are listed in Figure 6, according to

density. Strength, thermal conductivity, and service temperature generally increase with density.Lightweight castables are used for their insulating properties. Heavyweight castables are used for

their high strength and high service temperature properties. Dense castables have properties

similar to those of refractory firebricks.

Castable Type Dry

Installed

Density

lb/cu ft (1)(2)

Minimum

Compressive

Strength

pal (2)

Permanent

Linear

Change

%, max (2)

Service

Temperature

Limit,

°F (3)

30 -2.0 "Backup": >1500

1. Very Lightweight 20 to 45 100 -1.4 "Facing": >2000

2. Lightweight 45 to 75 300 -1.2 >2000

3. Mediumweight 75 to 115 500 -1.0 >2000

4. Heavyweight 115 to 150 2000 -0.8 >2400

5. Dense >150 5000 -0.8 >2400

Notes:

(1) In the installed condition after drying at 220°F for 18 hours.

(2) As determined by standard test procedures.

(3) Certified by manufacturer.

FIGURE 6 Castable Refractory Types


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Castable Refractory Lining Systems

Castable refractory lining systems consist of single- or dual-layer castable refractories held in

place by metallic anchors that are welded to the casing. Typical castable linings are shown in

Figure 7.

Mediumweight Hotface withLightweight Backup

Single-Layer Lining

FIGURE 7 Typical Castable Refractory Lining Systems

Castable linings are widely used in process furnaces. They are easy to install and repair, have a

low cost, and can be shop-installed.

In dual-layer castable linings, the hot face layer is constructed of a higher service temperature,

denser material and should be at least 3 in. thick. The backup layer is usually a very lightweight

castable material.

In some cases, mineral wool block insulation or ceramic fiber insulation is used for the backup

layer, because of their lower thermal conductivities. In these cases, a waterproof seal must be

applied to the insulation layer before applying the castable layer. Otherwise, the insulation will

soak up the water in the castable mixture, resulting in a much weakened castable layer.

One castable material commonly used in furnaces is a mixture of lumnite (a type of calcium

aluminate cement) and two refractory aggregates (haydite and vermiculite) in a 1:2:4 (L:H:V) mix

by volume. This is an inexpensive material having reasonably good insulation characteristics. It

has a maximum service temperature of 1900-2000°F, so that the hot face temperature should be

limited to about 1700°F. The three components of this material can be purchased separately and

combined in the field as the castable is prepared. However, this can result in variations in the

composition, resulting in inferior properties in portions of the lining.


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To avoid problems with field mixing, all castable materials (including "L-H-V") should be factory

premixed and packaged by the manufacturer.

It is also essential that refractory materials used in the field be properly stored. Exposure to any

amount of water will damage castable materials. These materials should be shipped and stored in

moisture proof containers. The storage area should be protected from the weather. Material

from broken bags, or any material showing signs of having been exposed to moisture (containing

lumps or hard throughout), should not be used.

Anchors

Castable linings are supported by the boiler or furnace casing, or shell, using metallic anchors.

Many anchor designs are used, with the most common consisting of "V" clips welded to the steel

casing. For dual-layer linings, separate anchors should be provided for each layer of castable.Typical anchors are shown in Figure 8. Anchor patterns are shown in Figure 9.


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FIGURE 8 Typical Anchors For Castable Linings


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Note (1)

Note (2)

Maximum Spacing for Anchors

Type of Arches and

Application Vertical Walls Hip Sections

Cast in Place 1 per 100 sq in. 1 per 81 sq in.

Precast Panel Construction As for Cast-In-place, Except that the Density of Anchors

Shall Be Increased About 50% in a 10 in. Wide Parallel

Border Around Edges of all Panels and Openings, IncludingObservation Doors.

Notes:

1. Figures in Parentheses Indicate Spacing for Arches and Hip Sections.

2. Anchors on a Staggered Pattern, with Tines Located in a Random Orientation.

FIGURE 9 Typical Anchor Arrangements For Castable Linings

Installation

Castable refractory systems can be installed by either pouring or gunning. Gunning is a technique

that involves shooting the cement mixture into place with a pneumatic gun. The material that falls

to the ground is called rebound and is waste material. Gunning is a very economical method of

application. However, gunning is a skilled craft, and the techniques of the applicator can make

the difference between the success and failure of the installation.


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Thermal Expansion

Hydraulic-setting castable refractories can be used to form a monolithic structure without expansion

joints. This is made possible by the shrinkage that takes place in most castable refractories during

initial heating (dry-out). With few exceptions, shrinkage cracking is large enough to accommodate

thermal expansion that occurs upon subsequent heating of the material. However, expansion joints

should be provided around burner blocks and tube supports.

Other Applications

Single-layer castable linings are used in many places with moderate temperatures to protect the

steel structure and to limit heat losses. These applications include header boxes, flue gas ducts,

and stacks. The lining should be a mediumweight castable, at least 2 in. thick. A commonly used

material in this service is a 1:4 mixture of lumnite and haydite (L:H).

Thin single-layer linings are usually supported by chain link fencing or wire mesh that is anchored to

the steel casing. Carbon steel or stainless steel material is used, depending on the temperatures.

Ceramic Fiber

Ceramic fiber construction is the most recent development for furnace insulation systems.

Ceramic fiber is manufactured by a blowing or spinning process in which a molten alumina-silica

raw material is transformed into very small-diameter fibers. These ceramic fibers are then formed

into blankets, 1-2 in. thick, about 2 ft wide, and several ft long.

Ceramic fiber blankets are available in densities of 4-12 lb/ft3, and with 2000-2600°F service

temperatures. Using special materials, service temperatures can be increased to 3000°F. In

contrast with other refractory materials, thermal conductivity decreases with increasing density,

up to a density of about 16 lb/ft3.

Ceramic fiber is also available in the form of rope, cloth, paper, board, vacuum-formed shapes,

and bulk material.

Ceramic Fiber Lining Systems

A ceramic fiber lining system consists of several layers of blanket, with a higher-density layer

(typically 8 lb/ft3) on the hot face and lower-density layers (typically 4 lb/ft3) as backup. Mineral

wool block insulation is sometimes used for the layers closest to the casing. The lining is held in

place by metallic anchors that are welded to the casing. Typical ceramic fiber lining details are

shown in Figures 10 and 11.


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Ceramic fiber blanket linings have advantages over conventional brick or castable lining systems:

• Low thermal conductivity.

• Low weight.

• Relatively low cost.

• Relatively low-skill installation.

• Quick installation and repair.

• Unlimited storage life.

• No dry-out required.

Ceramic fiber blankets are subject to shrinkage in service, and this shrinkage must be provided for

in the lining system design. The hot face blanket layers should be constructed with overlapped

joints, as shown in Figure 10. The overlapped joints should be in the direction of gas flow.

Gas FlowAlloy Stud and Washer

Lapped Joints

Steel Shell

Seal Punctures withViscous CeramicFiber Cement

Stainless Steel FoilOver Studs. Edges

Overlapped 8-12 in.

Ceramic Fiber Puttyto Protect Stud Endand Washer (or Wrapwith Wet Blanket)

Ceramic Fiber Lining

Installation of Vapor Seal

FIGURE 10 Typical Ceramic Fiber Lining Details

In the backup layers, butt joints can be used, with the blankets compressed at least 1 in. to allowfor shrinkage. Joints in successive layers should be staggered. This reduces the possibility of

direct heat flow back to the casing.

Corners/edges should be wrapped around to accommodate fiber shrinkage during service and to

ensure a continuous lining. Typical details are shown in Figure 11.


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External Corners

Joint

Joint

Burner Block

Shell Shell

CoatingCement

Pack Fiber Tightly

Against Burner

Burner Seams

FIGURE 11 Typical Ceramic Fiber Lining Details

Unprotected ceramic fiber blankets should be restricted to velocities of 40 ft/s across the surface.At higher velocities, the blanket may shred. For velocities up to 100 ft/s, "rigidized" ceramic

fiber, ceramic fiberboard, or ceramic fiber modules may be used.

Ceramic fiber linings can be easily damaged, and are not suitable for use on floors or in any

location where mechanical abuse is likely. However, when damage occurs, the lining is easily

repairable.

Ceramic fiber lining systems have been in use for about 20 years. Improvements are constantly

being made, so experienced manufacturers should be consulted before developing the final

specifications for or approving a ceramic fiber system design.

Some concerns have been expressed recently about potential health hazards to lining installers,

from breathing in tiny ceramic fibers. Installers should be provided with protective equipment to

avoid this problem.


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Anchors

Typical ceramic fiber anchors are shown in Figure 12. Anchors consist of the following

components:

• A metallic stud welded to the casing.

• Intermediate retaining clips to hold the first blanket layers in place during installation,

particularly on overhead sections.

• An anchor at the hot face. These are usually metal washers that twist and lock in place.

These washers are covered with a wet blanket patch for protection against direct radiation,

as shown in Figure 7. Alternatively, ceramic retainer cups, filled with moldable ceramic, can

be used. Typical anchor patterns are shown in Figure 13.

38

6x3 Section

67

25

38

Cup-Lock

50 EffectiveCeramicFerrule

A

Rapid-FixWasher

All DimensionsAre inMillimeters

FIGURE 12 Typical Ceramic Fiber Anchors


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Butt Joint forBackup Layers

For 24 in.Wide

Blanket

Lap Joint for Hot

Face Layer

X = 12 in. on Side WallsX = 9 in. on Arch

FIGURE 13 Anchor Patterns For Ceramic Fiber Linings

Thermal Expansion

Provision for thermal expansion is not required in ceramic fiber systems.

External Insulation

Blanket insulation (at least 2 in. thick) and weatherproofing is used on external boiler surfaces

(including tube waterwalls, drums, and headers) to reduce heat losses.

External blanket insulation is also used on flue gas ducts. This can keep the inside steel

temperature above the flue gas dewpoint. Sometimes, external insulation is also used on steel

stacks.

Criteria for Selecting Refractory Lining Systems

Guidelines for selecting refractory lining systems are contained in Figure 14. These can be used

to select appropriate linings for various sections of process furnaces and comparable sections of

boilers.

Selection of refractory lining systems and materials for their components is highly dependent upon

the fuels to be used in the boiler or furnace. Serious corrosion and refractory degradation

problems can be caused by high levels of sulfur and metals in the fuel.


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Heater Area Acceptable Lining Systems

Heater Wall, Arc, Breeching Single- or multilayer lining or ceramic fiber

linings. (Insulating firebrick is usually not

the most economical choice overall.)

Floor Multilayer lining, using block or castable

backup.

Breeching Single-layer lining.

Stack Single-layer lining.

Hot Air and Hot Flue Gas Ducting Single- or multilayer lining or ceramic fiber

lining.

Cold Air (For Noise Control) External insulation or internal single-layer

lining.

Cold Flue Gas Single-layer lining. (As an alternate

external insulation may be used.)

Header Boxes Single-layer lining or ceramic fiber lining.

Fans, Air Preheaters External insulation.

Access Doors, Observation Doors Same as wall or duct.

FIGURE 14 Criteria For Selecting Refractory Lining Systems


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Fuel Sulfur Considerations

When fuels that contain sulfur are fired, most of the sulfur is converted to SO2, with a small

percentage converted to SO3. The SO3 combines with water vapor to form sulfuric acid, which

can attack some refractory materials. Below the water dewpoint (about 300°F), liquid sulfuric

acid is formed, which is highly corrosive to the metallic components in the lining system.

The type of lining system and materials chosen must reflect the quantity of sulfur in the fuel. The

chart in Figure 15 can be used to select refractory lining systems based on fuel sulfur content.

These systems and materials are discussed below.


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Fuel Fired Lining Internal Lining Internal Coating

Contains: Facing Back-Up System Permitted Required? (3)

Oil3 and δ>60 Yes No

Brick Castable t75 Block Yes No

>0.5% (vol)

H2S Castable t75 Castable Yes No

(1) Castable t60

(Ducts, stacks, etc.)

None Yes No

Castable t


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Low-Sulfur Fuels

If the fuel contains less than 0.5 wt% sulfur, the potential for corrosion is small, and no special

materials considerations are required. Any combination of refractory lining materials should be

satisfactory.

High-Sulfur Fuels

If the fuel contains more than about 0.5 wt% sulfur, sufficient SO2/SO3 is produced that it can

easily penetrate any fiber structure. Provisions should be made in the design of refractory systems

to protect against potential casing corrosion and insulation damage.

• Block insulation should not be used in refractory lining systems where the hot face layer is

permeable (IFB, lightweight castable, ceramic fiber). This insulation can be severely

damaged by the acid condensate.

• Ceramic fiber materials have good resistance to sulfuric acid attack. However, fiber

insulation is easily permeated and offers no protection against casing corrosion. Stainless

steel foil can be used as a vapor barrier between layers of the ceramic fiber. This vapor

barrier should be located at a point in the lining where the temperature is above the

dewpoint. This is usually between the first and second layers of blanket from the casing.

• In lining systems that do not provide an effective barrier, a glass-filled polyester protective

coating should be applied to the inside casing surface.

• Castable refractory lining systems generally offer satisfactory service. Although castable

refractories are not completely impermeable, experience has shown that they offer good

protection against acid corrosion. Lightweight castable material can be used as a backup

layer in insulating firebrick and ceramic fiber lining systems.

• Insulating firebrick should contain less than 2.0 wt% CaO. This generally requires the IFB

to have a service temperature of 2600°F or greater. Sulfuric acid can react with the CaO,

causing refractory failure.

Fuel Ash Considerations

When the fuel fired contains significant quantities of metals (more than about 100 ppm vanadium

and sodium), the resulting metals in the fuel ash can cause some deterioration of the hot face

refractory. Higher concentrations of vanadium plus sodium (over 400 ppm) can severly attack the

refractory. In these cases, dense-type refractories should be provided for the hot face layer.

Since current Saudi Aramco fuels contain relatively low quantities of metals (vanadium and

sodium), these considerations do not apply to Saudi Aramco furnaces and boilers.


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Saudi Aramco Fuels

Design fuels for Saudi Aramco boilers and furnaces have various sulfur levels, which requires

using different types of refractory linings. For example, the following are the design fuels for two

Ras Tanura furnaces:

Furnace: 493-F-301/2/3/4 015-F-100A&B

Rheniformer Atmospheric

Design Fuels:

Gas Fuels: Fuel Gas Fuel Gas

H2S = 0.1 vol% H2S = negligible

Waste Gas

H2S = 7.6-8.1 vol%

Liquid Fuels: Vacuum Residuum

S = 3.9-5.5 wt%

V = 31-45 ppm

Na =


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CALCULATING HEAT TRANSFER

Heat transfer calculations are required for the design of refractory lining systems. The following

calculation procedures can be used to determine the rate of heat loss through the lining and the

resulting casing temperature, the required thicknesses of the component layers, and the design

temperatures of tiebacks and supports. These calculation procedures can also be used to

determine the adequacy of existing or proposed refractory linings.

Appendix A contains a calculation sheet for determining the required thickness for a refractory

lining. Appendix B contains a calculation sheet for determining the heat loss through a refractory

lining and the resulting casing temperature. These two appendices can be duplicated and used for

work assignments.

Heat Transfer Equation

The following general equation for conductive heat transfer is used to calculate the heat flow

through the refractory lining:

q = U (T1 - T2) (Eqn. 1)

=

T1-T 2

R , or: (Eqn. 1a)

R =T1-T 2

q (Eqn. 1b)

where: q = Heat loss, Btu/hr-ft2 of surface area.

U = Overall heat transfer coefficient, Btu/hr-ft2-°F.

R = Total thermal resistance, hr-ft2-°F/Btu.

=1

U.

T1 = Refractory hot face temperature, °F.

T2 = Cold face (casing) temperature, °F.

Thermal Resistance

The thermal resistance of the refractory lining is the sum of the resistances of the individualcomponent layers:

R = r 1 + r 2 + ... (Eqn. 2)

r1 =t1

k 1(Eqn. 3)

where: r 1 = Thermal resistance of first lining component, hr-ft2-°F/Btu.

t1 = Thickness of first lining component, in.

k 1 = Thermal conductivity of first lining component, Btu-in./hr-ft2-°F.


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Refractory Hot Face Temperature (T1)

This temperature is the most important factor in determining the design of the refractory lining.

Hot face operating temperatures should be realistic estimates of the actual temperatures

experienced in operation.

If not specified, the following can be used to estimate hot face operating temperatures in furnaces:

• Radiant section unshielded walls: use the temperature of the flue gas leaving the radiant

section (bridgewall temperature, T bw).

• Radiant section shielded walls (walls located behind tube rows): average of T bw and the

average radiant section tube metal temperature, + 100°F.

• Radiant section arch: T bw.

• Radiant section floor: T bw (minimum of 1800°F).

• Convection section walls: divide convection section into upper and lower sections. For

each section, use the entering flue gas temperature, less 200°F.

• Hot air and flue gas ducts: use the design air or flue gas temperature in the section of

ducting being considered.

Casing Temperature (T2)

The heat loss through the refractory lining is in equilibrium with the heat loss from the casing to

the atmosphere. Heat loss to the atmosphere can be determined from the following equations,

based on the temperature of the casing.

For standard design conditions (vertical wall, casing temperature of 180°F in 80°F ambient still

air), this corresponds to a heat loss of 218 Btu/hr-ft2 of surface area. For standard ambient air

conditions, Work Aid 2 can be used.

• Convection heat loss (qc), Btu/hr-ft2.

For still air:

qc = C1

Tavg + 460

0.18 T2 - Ta

1.27(Eqn. 4)

For wind conditions:qc = 1 + 0.33V T2 - Ta (Eqn. 5)


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• Radiation heat loss (hr ), Btu/hr-ft2.

q

r

= 17.4 x 10 -10 ε T

2

+ 460 4 - T

a

+ 460 4

(Eqn. 6)

• Total heat loss (ht), Btu/hr-ft2.

qt = qc + qr

where: C = Constant: C for arch = 0.96.

C for vertical wall = 0.74.

C for floor = 0.49.

Tavg =T2 + Ta

2,°F.

V = Wind velocity, miles/hr.

ε = Casing emissivity, use 0.95.

Interface Temperature (Ti)

This is the temperature between the two layers of refractory.

Ti = T1 -r1

R T1 - T2

Note that in these procedures, it has been assumed that the refractory lining consists of two

layers, as is the usual case. However, similar procedures can be used for any number of layers.

Thermal Conductivities (k)

Refractory conductivities can be obtained from manufacturers' literature. Conductivities of some

commonly used refractory materials are listed in Work Aid 3.

Thermal conductivities of refractory materials are temperature dependent, so that a trial and error

procedure is required in these heat transfer calculations. The thermal conductivities are first

estimated and then revised, based on the calculated refractory temperatures. Since the rate at

which thermal conductivities change with temperature is not great, repeated iterations are not

usually required.

Thermal conductivity of refractory components is based on the average temperature of the

refractory layer, as in the equation (T1 +Ti)/2 for the hot face layer.

For the first estimate of thermal conductivity, the interface temperature (Ti) between the two

layers can be estimated as follows:

Ti = T1 - X(T1 - T2) (Eqn. 8a)


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where: For hot face layer of 4-1/2 in. IFB,

X = 0.40 for an unshielded wall.

= 0.45 for a shielded wall.

For hot face layer of 3 in. mediumweight castable,

X = 0.20 for an unshielded wall.

= 0.30 for a shielded wall.

Determine Required Wall Thickness

This procedure can be used to determine the required wall thickness to meet specified conditions,

such as a heat loss rate, or a casing plate temperature. The sample problem in Figure 16

demonstrates this procedure.

1. For the specified conditions, determine the refractory hot face temperature. Calculate the heat

loss rate (or the corresponding casing plate temperature) using Eqns. 4-7.

2. Determine the thickness of the hot face layer. Unless otherwise specified, the following can

be assumed for standard furnace conditions:

• 4-1/2 in. IFB, or

• 3 in. mediumweight castable, or

• 2 in. ceramic fiber, 8 lb/ft3.

3. Estimate the refractory interface temperature, using Eqn. 8a. Calculate the average temperatureof the component layers, and determine the thermal conductivity of each layer.

4. Calculate required thermal resistance (R), using Eqn. 1a. Then, using Eqns. 2-3, calculate the

required thickness of the cold face layer (rounded up to the next 1/2 in.).

5. Calculate the interface temperature, using Eqn. 8.

6. Using the calculated interface temperature as the new estimated interface temperature,

recalculate the average temperatures of the refractory layers, thermal conductivities, heat

loss, etc.

7. Determine if the resulting temperatures and heat loss meet the specified requirements.


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Sample Problem - Calculation of Refractory Wall Thickness

The following sample problem illustrates the procedure for calculating the required refractory wall

thickness for a furnace similar to Ras Tanura 015-F-100A Atmospheric Furnace:Hot Face Temperature, T1 °F = 1706Ambient Temperature, Ta °F = 80 Wind Velocity, V m/h = 0Casing Temperature, T2 °F = 180 Corresponding Heat Loss Rate, q Btu/hr-ft2 = 218

Required Resistance, R=

T1 - T2q

=1706 - 180

218

hr-ft2-°F/Btu= 7.0

Estimated Interface Temperature:Ti = T1 - X(T1 - T2) = (1706) - (0.20) (1706 - 180) °F = 1401

Hot Face Layer: Material = 1:2:4 L:H:V Thickness, t1 in. = 3.0

1st Trial 2nd Trial

Avg. Hot Face Temp., Th =T1 + Ti

2 =

1706 + 1401

2 °F = 1553 1524Thermal Conductivity, k 1 (Work Aid 3) Btu-in./hr-ft2 - °F = 1.82 1.81

Thermal Resistance, r 1 =

t1

k 1 =

3.0)

1.82 hr - ft2 - °F/Btu= 1.65 1.66

Cold Face Layer:

Material = 1:6 L:V Required Thermal Resistance: r 2, = R - r 1 = (7.0) - (1.65) hr-ft2 - °F/Btu = 5.35 5.34

Avg. Cold Face Temp., Tc =

Ti + T2

2 =

1401 + 180

2°F

= 790 761 Thermal Conductivity, k 2 (Work Aid 3) Btu-in./hr-ft2 - °F = 0.95 0.94 Calculated Cold Face Thickness, t2 = r 2 k 2 = (5.35) (0.95) in. = 5.08 5.02 Use Cold Face Thickness, t2: in. = 5.0 5.0

Thermal Resistance, r 2=

t2

k 2 =

5.0)

0.95

hr-ft2 - °F/Btu= 5.26 5.32

Total Thermal Resistance, R = r 1 + r

2 hr - ft2 - °F/Btu = 6.91 6.98

Calculated Interface Temperature:

Ti = T1 -

r1

R T1 - T2 = 1706 -

1.65

6.91 1706 - 180

°F = 1342 1339

Calculated Heat Loss, q: =

T1 - T2

R =

1706 - 180

6.98 Btu/hr-ft2 = 218.6

Corresponding Casing Temperature, T2 (Work Aid 2) °F = 180

FIGURE 16


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Checking Existing Refractory Design

This procedure can be used to determine the heat loss rate through a refractory lining and the

resulting casing plate temperature. The sample problem in Figure 17 demonstrates this procedure.

1. Determine the refractory hot face temperature. Estimate the casing temperature. Calculate

the heat loss based on these conditions, using steps 3-6 above.

2 Locate the casing temperature/heat loss point on the chart in Work Aid 2.

3. Select another casing temperature, recalculate the heat loss, and plot a second point.

4. The actual heat loss should be located very close to the intersection of a line drawn between

these two points and the appropriate ambient air condition curve shown on Work Aid 2. If the appropriate ambient air conditions are not shown, it may be necessary to develop a new

curve, using Eqns. 4-7.

With practice, it should be possible to locate the second casing temperature point very close

to the final solution point.

5. Determine if the resulting temperatures and heat loss meet the specified conditions. If not,

some revisions to the design may be required.


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Sample Problem - Calculation of Refractory Heat Loss

The following sample problem illustrates the procedure for calculating the heat loss through a

refractory wall. The data are found on the fired heater data sheet for Ras Tanura 015-F-100A

Atmospheric Furnace.

Ambient Temperature, Ta °F = 108 Wind Velocity, V m/h = 0Calculated Hot Face Temperature, T1 °F = 1706Calculated Cold Face Temperature, T2 °F = 171Hot Face Layer: Material, = 1:2:4 L:H:V Thickness, t1 in. = 3.0Cold Face Layer: Material, = 1:6 L:V Thickness, t2 in. = 7.0

1st Trial - Estimated Casing Temperature, T2 °F = 171 Estimated Interface Temperature: (Calculated, or from Work Aid 5) Ti = T1 - X(T1 - T2) = (1706) - (0.2) (1706 - 171) °F = 1399

Hot Face Layer: 1st Trial 2nd Trial

Avg. Hot Face Temp., Th =

T1 + Ti

2 =

1706 + 1399

2°F = 1552 1565

Thermal Conductivity, k 1 Btu-in./hr-ft2 - °F = 1.82 1.83

Thermal Resistance, r1 =

t1

k 1 =

3

1.82 hr - ft2 - °F/Btu = 1.65 1.64

Cold Face Layer:

Avg. Cold Face Temp., Tc =

Ti + T2

2 =

1399 + 171

2°F

= 785 798

Thermal Conductivity, k 2 Btu-in./hr-ft2 - °F = 0.95 0.95


t2

k 2 =

7.0

0.95 hr - ft2 - °F/Btu = 7.37 7.37

Total Thermal Resistance, R = r 1 + r 2 hr - ft2 - °F/Btu = 9.02 9.01Calculated Interface Temperature:

Ti = T1 -r1

R T1 - T2 = 1706 -

1.65

9.02 1706 - 171

°F = 1425 1427

Calculated Heat Loss:

q =T1 - T2

R =

1706 - 171

9.01 Btu/hr - ft2 = 170

Corresponding Ambient Air Temperature, Ta °F = 90

FIGURE 17 Calculation Of Refractory Heat Loss


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2nd Trial - Estimated Casing Temperature, T2 °F = 184* Estimated Interface Temperature: (Calculated, or estimated from 1st Trial)

Ti = T1 - X(T1 - T2) = (_____) - (_____) (____ - ____) °F = 1430

Hot Face Layer 1st Trial 2nd Trial


T1 + Ti

2 =

1706 + 1430

2 °F = 1568

Thermal Conductivity, k 1 Btu-in./hr-ft2 - °F = 1.84


t1

k 1 =

3.0

1.84 hr - ft2 - °F/Btu = 1.63

Cold Face Layer:

Avg. Cold Face Temp., Tc =Ti + T2

2

=1430 + 184

2 °F= 807

Thermal Conductivity, k 2 Btu-in./hr-ft2 - °F = 0.95


t2

k 2 =

7.0

0.95 hr - ft2 - °F/Btu = 7.37

Total Thermal Resistance, R = r 1 + r 2 hr - ft2 - °F/Btu = 9.00Calculated Interface Temperature:

Ti = T1

r1

R T1 - T2 = 1706 -

1.63

9.0 1706 - 184

°F = 1430

Calculated Heat Loss:

q =

T1 - T2

R =

1706 - 184

9.00 Btu/hr -

ft2

= 169

Corresponding Ambient Air Temperature, Ta°F

= 108

Final Conditions (from Work Aid 2) Heat Loss, q: Btu/hr - ft2 = 169 Casing Temperature, T2

°F= 184

* This was estimated form the first trial. Any reasonable estimate can be used.

FIGURE 17 (CONT'D)


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0.5"

3" 7"

Temp at tip of Anchor:

1706 - 0.5 (1706 - 1430) = 1660

3

25/20 Tiebacks Req'd by Current

Standards

500

1000

1500

2000

°F

FIGURE 17 (CONT'D)

Temperatures of Tiebacks and Supports

Using the hot face, cold face, and interface temperatures calculated above, the temperatures of the

tiebacks and supports can be calculated. The temperature profile through each refractory layer isassumed to be linear. As stated earlier, the design temperatures of tiebacks and supports are

considered to be the same as the calculated refractory temperatures at the tip of the metallic

component. (The actual temperatures may be somewhat lower, due to the much higher thermal

conductivities and resulting heat flow through metallic components.) The diagram in Figure 17

illustrates the calculation of tieback temperatures.


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Work Aid 1: Procedure for Calculating Heat Loss Through a Refractory Wall

This Work Aid is designed to assist the participant in The Calculating Heat Loss Exercise.

An engineer may have to calculate the heat loss through a refractory wall to determine the design

requirements for refractory materials, tiebacks, and supports. Since several of the terms are

dependent on each other, calculating heat loss is an iterative process consisting of making an

initial estimate and refining the estimate based on the calculations.

Calculating Heat Loss

1. Determine x based on the information provided with Eqn. 8.

2. In the 1st Trial Column calculate the interface temperature, using the data provided.

3. Use the interface temperature, Ti, calculated in the 1st Trial and substitute it into the

formula at the top of the 2nd Trial column. Repeat the calculations in step 2.

4. Compare Ti in the two trials. They should be about the same. If they are not, repeat for a

3rd Trial.

5. Locate the casing temperature/heat loss point on the chart in Work Aid 2.

6. Select another casing temperature, recalculate the heat loss, and plot a second point.

7. The actual heat loss should be located very close to the intersection of a line drawn between

these two points and the appropriate ambient air condition curve shown on Work Aid 2. If

the appropriate ambient air conditions are not shown, it may be necessary to develop a new

curve, using Eqns. 4-7.

With practice, it should be possible to locate the second casing temperature point very close

to the final solution point.

8. Determine if the resulting temperatures and heat loss meet the specified conditions. If not,

some revisions to the design may be required.

9. Use the equation provided to determine the tieback temperature.


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Work Aid 2: Data Bases for Calculating Heat Loss--Heat Loss Versus Casing Temperature

This Work Aid is used in determining the corresponding Ambient Air Temperature in Exercise 1.


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Work Aid 3: Data Bases for Calculating Heat Loss--Thermal Conductivities of Typical

Refractories

This Work Aid is used in determining the thermal conductivity, k, in Exercise 1.


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THERMAL CONDUCTIVITY OF CERAMIC FIBER BLANKETS

Mean Temperature, °F


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GLOSSARY

arch The flat or sloped portion of the radiant sectionopposite the floor.

backup layer Any refractory layer behind the hot face layer.

casing A steel sheathing that encloses the heater box and

makes it essentially airtight.

castable An insulating concrete poured or gunned in place to

form a rigid refractory shape or structure.

center wall A refractory wall in the radiant section, that divides

it into two separate cells.

ceramic fiber A fibrous refractory insulation composed primarilyof silica and alumina. Applicable forms include

blanket, board, module, and vacuum-formed shapes.

convection section The portion of a heater, consisting of a bank of

tubes, that receives heat from the hot flue gases,

mainly by convection.

corbel A projection from the convection section sidewall to

prevent flue gas from flowing up the side of the

convection section, between the wall and the nearest

tubes, thereby bypassing the tube bank.

curing The initial chemical reaction causing bonding of

cement and aggregate after refractory placement,

usually essentially complete within 24 hours of

refractory placement.

firebox A term used to describe the structure that surrounds

the radiant coils and into which the burners

protrude.

fireclay An earthy or stony mineral aggregate that has

properties suitable for use in commercial refractory

products.firebrick A broad term covering any type of refractory brick,

used more narrowly to mean fireclay brick.

firebrick, insulating A refractory brick characterized by low thermal

conductivity and low heat capacity.

flue gas A mixture of gaseous products resulting from

combustion of the fuel.


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gravity wall A freestanding, self-supporting refractory structure

commonly consisting of firebrick.

hot face layer The refractory layer exposed to the highesttemperatures in a multilayer or multicomponent

lining.

hot face temperature For a single-layer lining, the temperature of the

refractory surface in contact with the flue gas or

heated combustion air. The design hot face

temperature is used to determine refractory layer

thickness and rating.

mortar refractory A preparation suitable for laying and bonding

firebrick.

multicomponent

lining

A refractory system consisting of two or more layers

of different refractory types; for example, castable

and ceramic fiber.

multilayer lining A refractory system consisting of two or more layers

of the same refractory type.

protective coating A coating applied to the casing interior to protect

against corrosion.

radiant section The section of the furnace in which heat is

transferred to the furnace tubes primarily by

radiation from high-temperature flue gas.

refractories Materials, usually nonmetallic, used to withstand

high temperature.

service temperature The temperature at which a refractory material

begins to deteriorate.

setting The furnace casing, brickwork, refractory, and

insulation, including the tiebacks or anchors.

thermal expansion The reversible change in size of materials, caused by

temperature changes.

vapor barrier A metallic foil placed between layers of refractory as

a barrier to flue gas flow.

wet blanket Ceramic fiber blanket presaturated with a liquid

hardening agent.


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REFERENCE

Saudi Aramco Standards

AES-F-001 Process Fired Heaters

32-AMSS-021Water-Tube Boilers

API Publications

Standard 560 Fired Heaters for General Refinery Service

ASTM Publications

Materials Specifications

Exxon Basic Practices

BP 19-3-3 Castable Linings for Fired Heaters


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APPENDICES

Appendix A Refractory Wall Thickness - Calculation Sheet

The following procedure can be used to calculate the required refractory wall thickness:

Plant Location Boiler/Furnace

Service Location

Hot Face Temperature, T1, °F = Ambient Temperature, Ta, °F =

Casing Temperature, T2, °F = Wind Velocity, V, m/h =

Corresponding Heat Loss Rate, q Btu/hr-ft2 =

Required Resistance

R =

T1 - T2q

=______ - ______

______ hr - ft2 - °F/Btu =

Estimated Interface Temperature:

Ti = T1 - X(T1 - T2) = (_____) - (____) (____ - ____) °F =Hot Face Layer:

Material =

Thickness, t1 in. =1st Trial 2nd Trial

Avg. Hot Face Temp., Th =T1 + T2

2 =

______ + ______

2 °F =

Thermal Conductivity, k 1 (Work Aid 2) Btu-in./hr-ft2 - °F =

Thermal Resistance, r1 =t1

k 1 =

hr - ft2 - °F/Btu =Cold Face Layer:

Material =

Required Thermal Resistance:

r 2 = R - r 1 = (_______) - (______) hr-ft2 - °F/Btu =


2 =

______ + ______

2 °F =


Calculated Cold Face Thickness,

t2 = r 2 k 2 = (______) (______) in. =

Use Cold Face Thickness, t2: in. =

Thermal Resistance, r

2

=t2

k 2

=

hr-ft2 - °F/Btu =Total Thermal Resistance, R = r 1 + r 2 hr - ft2 - °F/Btu =Calculated Interface Temperature:

Ti = T1 -r1

R T1 - T2 = _____ -

_____

_____ _____ - _____

°F =Calculated Heat Loss:

q =T1 - T2

R =

______ - ______

______ Btu/hr-ft2 =

Corresponding Casing Temperature, T2 °F =


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Appendix B Refractory Heat Loss - Calculation Sheet

The following procedure can be used to calculate the heat loss through a refractory wall:

Plant Location Boiler/Furnace

Service Location

Ambient Temperature, Ta °F =

Wind Velocity, V m/h =

Calculated Hot Face Temperature, T1 °F =

Calculated Cold Face Temperature, T2 °F =

Hot Face Layer: Material, =

Thickness, t1 in. =

Cold Face Layer: Material, = Thickness, t2 in. =

1st Trial - Estimated Casing Temperature, T2 °F =

Estimated Interface Temperature:

(Calculated, or from Appendix A)

Ti = T1 - X(T1 - T2) = (_____) - (_____) (____ - ____) °F =

Hot Face Layer:

1st Trial 2nd Trial


T1 + Ti

2 =

+

2 °F =



t1

k 1 =

hr - ft2 - °F/Btu =Cold Face Layer:


2 =

______ + ______

2 °F =


Thermal Resistance, r2 =t2

k 2 =

hr-ft2 - °F/Btu =

Total Thermal Resistance, R = r 1 + r 2 hr - ft2 - °F/Btu =Calculated Interface Temperature:

Ti = T1 -r1

R T1 - T2 = _____ -

_____

_____ _____ - _____

°F =Calculated Heat Loss:

q =

T1 - T2

R =

______ - ______

______ Btu/hr-ft2 =

Corresponding Ambient Air Temperature, Ta (Work Aid 3) °F =


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2nd Trial - Estimated Casing Temperature, T2 °F =

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