Boilers & Furnaces-Refractory&Insulation

Engineering Encyclopedia Saudi Aramco DeskTop Standards

Boilers And Furnaces Refractory And Insulation

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 Saudi Aramco 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 File Reference: MEX30208

For additional information on this subject, contact M.Y. Naffa’a

Engineering Encyclopedia

Vessels Boilers And Furnaces Refractory And Insulation

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 ................................... 4 Thermal 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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Engineering Encyclopedia

Vessels Boilers And Furnaces Refractory And Insulation

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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Engineering Encyclopedia

Vessels Boilers And Furnaces Refractory And Insulation

Table of Figures

Pages

FIGURE 1 Typical Refractory Components In Furnaces............................................ 5 FIGURE 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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Engineering Encyclopedia

Vessels Boilers And Furnaces Refractory And Insulation

INTRODUCTION Refractory and insulation systems are essential components in Saudi Aramco boilers and furnaces. The primary purposes of refractory and insulation systems are to protect the steel structure and tubes from overheating, and to reduce heat loss. MEX 105.08 will introduce the participant to the types, components, installation procedures and criteria used to select refractory and insulation materials for Saudi Aramco boilers and furnaces. This module will also present the procedure for calculating the heat transfer through refractory and insulation materials. This procedure is used in determining the required thickness of the refractory and insulation materials.

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Engineering Encyclopedia

Vessels Boilers And Furnaces Refractory And Insulation

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 32AMSS-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 than the 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 800 1400 1700 1900 2000

Acceptable Materials (1) Carbon Steel 18Cr-8Ni (Type 304) 25Cr-20Ni (Type 310), Incoloy 800 RA 330 Stainless Steel Inconel 601

Note (1): Austenitic materials shall be supplied and installed in the fully solution-annealed condition. 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 mesh fencing 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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Vessels Boilers And Furnaces Refractory And Insulation

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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Vessels Boilers And Furnaces Refractory And Insulation

Stack Breeching Convection Section Sidewalls

Header Box

End Tube Support

Arch Convection Section

Shielded Sidewalls

Dividing Wall

Radiant Section Floor

Burners

Unshielded Endwalls

End View

Side View

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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Vessels Boilers And Furnaces Refractory And Insulation

Insulating firebrick series K-20 K-23 Service temperatures, F Exposed 2000 2300 Backup 2000 2300 Density, avg (ASTM C 134-70) Lb/9" straight 1.7 1.8 Lb/cu ft 29 31 Melting Point, F 2750 2750 Modulus of rupture, psi (ASTM C 93-67) 110 140 Cold crushing strength, psi (ASTM C 93-67) 110 145 Permanent linear change, % (ASTM C 210-68) Fired @ 1950F 0 @ 2250F 0 @ 2550F @ 2750F @ 2800F @ 2950F @ 3250F Thermal conductivity, BTU•in./h•ft2•F (ASTM C 182-72) Mean temperature@ 500F 0.8 0.9 @ 1000F 1.0 1.1 @ 1500F 1.2 1.3 @ 2000F 1.6 @ 2400F Deformation under hot load, % @ 10 psi (per ASTM C 16-77) 1 1/2 hr @ 2000F 0 1 1/2 hr @ 2200F 0.1 1 1/2 hr @ 2640F 12.5 psi 1 1/2 hr @ 2730F Chemical analysis, % (ASTM C 573-70) Alumina Al2O3 39 39 Silica SiO2 44 44 Ferric oxide Fe2O3 0.7 0.6 Titanium oxide TiO2 1.1 1.1 Calcium oxide CaO 15.0 14.4 Magnesium oxide MgO 0.1 0.1 Alkalies, as Na2O 0.3 0.4 Coefficient of reversible thermal 3.0x10-6 3.0x10-6 expansion, in./in.F Color code Green Red

K-26 LI

K-28

K-30

K-3000

2600 2600

2800 2800

2900 2900

3000 3000

2.8 48 3190 160 170

3.0 51 3190 210 220

3.0 51 3190 240 295

3.4 58 3350 260 275

-0.1 -

-0.6 -

-0.5* -

-0.6 -

1.7 1.9 2.2 2.7 -

1.7 2.0 2.3 2.9 -

2.0 2.4 3.0 3.8 -

2.1 2.4 2.8 3.4 4.0

0.2 -

0.2 -

0.2 -

0.5 -

46 52 1.0 1.4 0.3 0.1 0.3 2.9x10-6

46 52 1.0 1.4 0.3 0.1 0.3 2.9x10-6

46 52 0.9 1.4 0.5 0.1 0.4 2.9x10-6

64 34 0.6 0.7 0.3 Trace 0.4 2.9x10-6

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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Vessels Boilers And Furnaces Refractory And Insulation

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 Melting point, F Density, avg (ASTM C 134-70) Lb/9" straight Lb/cu ft Hot modulus of rupture, psi (ASTM C 583-76) @Room temperature @2000F @2300F @2600F @2800F Cold crushing strength, psi (ASTM C 133-72) Permanent linear change, % (per ASTM C 113-74) 5 hr @2912F 5 hr @3200F 24 hr @3200F Thermal conductivity. Btu•in/h•ft2•F (ASTM C 202-71) Mean temperature @ 500F @1000F @1500F @2000F @2500F Deformation under hot load, % @ 25 psi (ASTM C 16-77) 1 1/2 hr @2640F 1 1/2 hr @2900F 1 1/2 hr @3000F 1 1/2 hr @3200F 150 hr @3200F Permeability, fr3/hr ft2 in./psi

Firebrick 80 3190

Firebrick 80-D 3190

8.1 189

8.8 151

10.6 183

11.3 193

1700 4000

3500 10,000

3600 4500 4200 2900 2100 12,000

3800 2900 1600 800 650 10,000

-1.0 -

-0.8 -

+1.5 -

+0.3

16.0 16.0 15.9 15.6 15.2

20.8 20.6 20.3 19.9 19.5

26.5 22.8 20.8 19.5 18.8

47.5 31.5 24.0 20.5 17.5

-1.0 1000 17

-0.5 100 5.2 8

+0.1 +0.1 60 Brick Yes Yes (5) Castable t75 Block >0.5% (vol) H2S Block No (4) Castable t75 Castable (1) Castable Yes Yes (5) Castable t60 None (Ducts, stacks, etc.) Yes Yes(5) Castable t