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

Saudi Aramco DeskTop Standards



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




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




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.


1



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.


2



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.


3



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.


4



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.


5



•

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.


6



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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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 <0.25 35 7.3 18

-0.3 30 13.5 17

3.0 -

NR* -

0

2.6

Relative abrasion resistance vol loss when abraded cc's (ASTM C 704-76) 11.0

Porosity, % (ASTM C 20-74) Panel spall loss, % (Per ASTM C 122-76) 12 cycles @ 2550F 24 hr preheat @3000F 24 hr preheat @3100F

Special refractory brick SR-90 SR-99 3480 3660

Static corrosion resistance to molten glass, corrosion, % (ASTM C 621-68) soda, lime, silica cullet - one inch cylinder

72 hrs @2250F Chemical analysis, % (ASTM C 573-70) Alumina Al2O3 Silica SiO2 Zirconia ZrO2 Ferric oxide Fe2O3 Titanium oxide TiO2 Calcium oxide CaO Magnesium oxide MgO Alkalies, as Na2O

-

-

-

-

45 52 1.4 1.7 0.1 Trace 0.3

45 52 1.4 1.7 0.1 Trace 0.3

90 10 0.1 Trace 0.1 0.1 0.1

99.4 0.4 0.1 Trace Trace Trace 0.1

* Not recommended for severe spalling conditions. Data are average results of tests conducted under standard procedures and are subject to variation. Results should not be used for specification purposes.

FIGURE 2 Typical Refractory Properties(Cont'd)


8



Thermal Ceramics Refractory Castables Dense Castables Castable series

Kaocrete B Recommended methods of application (X) Cast or rammed X Trowled X Gunned X Lb req'd to place one cu ft 100 **Required water, U.S.qt per bag Vibrating 12-13 Casting and rodding 13-13.5 Ramming 5-6 Recommended use limit, F 2300 Melting point, F 2725 Density, lb/cu ft Fired 100 Modulus of rupture, psi (ASTM C 268-70) Dried 18 to 24 hr @ 220F 400 Fired 5 hr @1000F 350 @1500F 160 @1750F @2000F 140 @2200F 240 @2400F @2500F @2600F @2800F @3000F @3200F Cold crushing strength, psi (Per ASTM C 133-72) Dried 18 to 24 hr @ 220F 1400 Fired 5 hr @1000F 700 @1500F 700 @1750F @2000F 300 @2200F 450 @2400F @2500F @2600F @2800F @3000F @3200F Dried 124 hr @2 20F 0.0 Fired 5 hr @1000F -0.5 @1500F -1.2 @1750F @2000F -1.5 @2200F -1.8 @2400F @2500F @2600F @2800F @3000F @3200F Porosity, %, fired 42 Chemical analysis, % fired basis (ASTM C 573-70) Alumina Al2O3 38 Silica SIO2 46 Ferric oxide Fe2O 1.3 Titanium oxide TiO2 1.3 Calcium oxide CaO 12.1 Magnesium oxide MgO 0.9 Alkalies, as Na2O 0.3 Phosphorous penta-oxide P2O5 Thermal conductivity, (ASTM C 417-60) BTU•in./h•ht2•F 4.5 Pounds per bag 100

Kaocrete 28-LI

Kaocast

Kao-Tab 93

Kao-Tab 95

X X X 126

X X 123

X X X 150

X X 165

6-6.5 6.5-7 3-4 2800 3100 126

5-6 6-6.5 3-4 3000 3200 126

5.5-6 6-6.5 2-3 3300 3400 152

4-4.5 4.5-5 2-3 3300 3400 166

900 600 400 300 450 600 1500 2000 -

900 350 250 270 300 550 1200 1400 1400 -

1700 1100 900 700 700 700 700 800 1200 1600

3000 2400 2000 1400 1400 1600 3200 4000 0.0 -0.1 -0.2 -0.2 -0.2 +0.1 +1.0 +0.2 31

2100 1200 1000 1100 1200 1400 3000 3800 4200 0.0 -0.2 -0.2 -0.3 -0.3 -0.3 -0.3 -0.2 +0.2 32

49 42 0.9 2.4 6.0 0.2 6.8 100

Kao-Tab Kaocrete HS 95-Gun (as cast) (as gunned) Rammed Lim. Repairs X 165*

X X X 123

X X X 125*

3300 3390 165

6-6.5 6.5-7 3-4 2600 3100 122

2600 3100 124

1850 1400 1000 1200 900 900 1000 1200 1400 1800

1700 1600 1500 1300 1500 1600 1600 1400 1500 1900

1300 850 700 700 900 1400 -

1400 950 900 900 1100 1600 -

6000 3100 2900 2300 1850 1900 1950 2800 2800 3000 0.0 -0.2 -0.2 -0.2 -0.3 -0.3 -0.5 -0.8 -0.5 -0.2 32

6000 5600 5200 5000 4400 4500 4800 5000 5200 5600 0.0 -0.2 -0.2 -0.2 -0.3 -0.3 -0.5 -0.8 -0.3 -0.2 -

6800 6000 5100 5800 5300 5000 5000 5000 5000 6100 0.0 -0.1 -0.1 -0.2 -0.3 -0.5 -0.5 +0.5 0.0 -1.0 -

4200 4000 2800 2600 2800 3200 0.0 -0.2 -0.2 -0.3 -0.2 +0.2 29

5500 4800 4400 3200 3400 4000 0.0 -0.2 -0.2 -0.3 -0.2 +0.2 -

60 33 1.0 1.9 3.4 0.1 0.2 -

93 0.5 0.1 0.1 6.0 Trace 0.1 -

95 0.1 0.1 Trace 4.6 Trace 0.1 -

95 0.2 0.2 Trace 4.2 Trace 0.1 -

47 40 1.0 2.0 8.5 0.2 0.3 -

47 40 1.0 2.0 8.5 0.2 0.3 -

6.7 100

9.1 100

13.1 100

9.1 100

7.0 100

7.1 100

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

FIGURE 2 Typical Refractory Properties(CONT'D) Saudi Aramco DeskTop Standards

9



Insulating Castables Castable series

Kaolite Kaolite 2200-HS 2300-LI (as cast) (as gunned) Recommended methods of application (X) Cast or rammed X X X X Trowled X X X X Gunned X X X X Lb req'd to place one cu ft 56 71 82* 54 **Required water, U.S. qt per bag Vibrating 11.5-12 11.5-12 11.5-12 Casting and rodding 11.5-12 11.5-12 11.5-12 Recommended use limit, F 2200 2200 2200 2300 Melting point, F 2670 2495 2495 2670 Density, lb/cu ft Fired 58 74 82 58 Modulus of rupture, psi (ASTM C 268-70) Dried 18 to 24 hr @ 220F 130 475 540 150 Fired 5 hr @1000F 120 200 140 @1500F 100 200 160 110 @2000F 150 200 190 @2200F 200 250 130 190 @2300F 240 @2400F @2500F @2600F @2800F @3000F -@3200F Cold crushing strength, psi (Per ASTM C 133-72) Dried 18 to 24 hr @ 220F 700 1600 1850 500 Fired 5 hr @1000F 600 1400 450 @1500F 500 1200 950 450 @2000F 550 1000 400 @2200F 600 1250 1000 500 @2300F 500 @2400F @2500F @2600F @2800F @3000F @3200F Permanent linear change, % (ASTM C 269-70) Dried 24 hr @ 220F -0.1 -0.1 0.0 Fired 5 hr @1000F -0.2 -0.2 @1500F -0.3 -0.2 -0.2 -0.4 @2000F -0.5 -0.6 @2200F -1.1 -0.7 -0.7 -0.9 @2300F -1.8 @2400F @2500F @2600F @2800F @3000F @3200F Chemical analysis, % fired basis (ASTM C 573-70) Alumina Al2O3 35 42 42 41 Silica SIO2 36 26 26 37 Ferric oxide Fe2O 5.6 6.9 6.9 0.9 Titanium oxide TiO2 1.2 1.0 1.0 1.7 Calcium oxide CaO 21.1 22.6 22.6 18.6 Magnesium oxide MgO 0.2 0.6 0.6 0.4 Alkalies, as Na2O 0.8 0.6 0.6 0.3 Thermal conductivity, (ASTM C 417-60) BTU•in./h•ft2•F 1.6 1.9 2.1 1.6 Pounds per bag 40 50 50 40 •

Kaolite 2200

Kaolite Kaolite Kaolite Kaolite 2500-LI 2500-HS 2800 3300 (as cast) (as gunned) (as cast)(as gunned) (as cast)(as gunned) X X X 74

X X X 60*

X X X 78

X X X 85*

12-13 12-13 2500 2740 67

2500 2740 60

13.14 13-14 2500 2700 77

2500 2700 84

210 130 110 130 370 -

210 100 100 230 -

280 220 180 140 240 570 570 -

740 590 610 490 950 -

530 300 350 680 -

-0.2 -0.2 -0.2 -0.1 -

X X X 84

X X X 86*

X 68

9.5-10 9.5-10 2800 3300 85

2800 3300 88

4-4.5 4.5-5 3300 3530 68

390 370 360 310 430 700 750 -

370 290 260 350 400 410 1400 -

300 190 200 250 270 490 -610 -

250 240 180 180 300 350 350 550 750 850

740 670 600 490 440 990 1170 -

1240 1150 1120 770 1110 1150 1210 -

1180 950 900 1070 1390 2030 4150 -

480 550 460 860 1150 1480 1900 -

900 850 700 700 800 1200 1300 1400 1500 2200

0.0 -0.2 -0.2 +1.0 -

0.0 -0.3 -0.2 -0.3 -0.4 -0.5 +0.6 -

0.0 -0.3 -0.3 -0.3 -0.4 -0.5 +0.6 -

0.0 -0.1 -0.1 -0.4 -0.6 +0.5 -0.5 -

0.0 -0.3 -0.2 -0.4 -0.5 +0.5 -0.3 -

-0.1 -0.1 -0.2 -0.1 -0.1 -0.1 +0.2 -0.2 -0.5 -1.0

44 35 0.9 1.8 17 0.2 1.3

44 35 0.9 1.8 17 0.2 1.3

41 37 3.2 2.2 16.3 0.3 Trace

41 37 3.2 2.2 16.3 0.3 Trace

60 33 0.4 0.7 5.0 0.1 0.8

60 33 0.4 0.7 5.0 0.1 0.8

94 0.5 0.2 4.6 0.1 0.5

1.9 50

1.6 50

2.5 75

2.9 75

3.4 75

3.5 75

4.5 50

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

FIGURE 2 Typical Refractory Properties(Cont'd)


10



Thermal Conductivities of Lumnite-Concrete Mix by Volume Lumnite

(sacks) 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

: : : : : : : : : : : : : : : : : : :

cu ft 4 6 4 6 8 4 6 4 6 4 6 5 4 3 2 4 4 6

Aggregate Calcined Diatomaceous Earth Calcined Diatomaceous Earth Perlite Perlite Perlite Vermiculite Vermiculite Pumice Pumice Haydite Haydite Haydite : 1 Vermiculite Haydite : 2 Vermiculite Haydite : 3 Vermiculite Haydite : 4 Vermiculite Crushed Insulating Firebrick Grog

Crushed Firebrick** Crushed Firebrick**

Unit Weights Volume lb/cu ft in Place Dried Fired cu ft 57.2 52.9 4 49.6 47.0 6 47.6 42.0 4 36.4 6 24.6 23.2 8 44.2 38.5 3-4 36.6 32.3 4-6 77.7 71.2 4 71.6 69.0 6 97.1 91.3 4 89.9 86.2 6 85.9 82.0 5.5 78.4 75.1 5.25 65.2 62.1 5 58.6 55.1 4.5 92.0 83.0 4 119.3 114.5 4 117.1 112.6 6

BTU/sq. ft/hr/in./°F Mean Temperatures 500°F 1.50 1.36 1.10 0.93 0.73 1.02 0.83 2.36 2.12 3.31 3.06 2.75 2.08 1.70 1.45 2.60 5.40 5.30

1000°F 1.66 1.53 1.32 1.22 1.08 1.24 1.04 2.67 2.50 3.43 3.23 2.93 2.32 1.96 1.62 3.10 5.68 5.64

1500°F 1.84 1.66 1.53 1.48 1.43 1.44 1.27 2.98 2.88 3.53 3.40 3.11 2.55 2.18 1.80 3.30 5.94 5.92

Max Service Temp. 1800°F 1800°F 2000°F 2000°F 2000°F 2000°F 2000°F 2000°F 2000°F 2000°F 2000°F 2000°F 2000°F 2000°F 2000°F 2400°F 2000°F 2600°F

* ASTM Method: C 182-47 **ASTM Method: C 202-47 FIGURE 2 Typical Refractory Properties(Cont'd)


11



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.

Castable Refractory External Insulation

Burner Throat Castable Refractory

Floor Refractory Brick

Flue Gas Baffles Castable Refractory

Refractory Brick

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


12



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.


13



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.

Tieback (Staple Type) Steel Casing Horizontal Expansion Joint

Shelf Ang

Bloc Insula

Vertical Expansion Joints

Bricks

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.


14



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.


15



Casing

CS Pipe

Staple Type Tieback

Block Insulation

Shelf Angle Expansion Joint Filled with Ceramic Fiber

V-Clip Ty Tiebac

IFB

Elevation Elevation Plan View Staple-Type Tieback

Plan View - V-Clip Tieback

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).


16



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-duty refractory 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.


17



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 Minimum Permanent Installed Compressive Linear Density Strength Change lb/cu ft (1)(2) pal (2) %, 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


18



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 with Lightweight 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. Saudi Aramco DeskTop Standards

19



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.


20



FIGURE 8 Typical Anchors For Castable Linings


21



Note (2) Note (1)

Type of Application Cast in Place Precast Panel Construction

Maximum Spacing for Anchors Arches and Vertical Walls Hip Sections 1 per 100 sq in. 1 per 81 sq in. 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, Including Observation 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.


22



Castable refractory linings can also be installed as panels. The castable is poured at grade, and then the panel is lifted into place. The panels are bolted together, and the metal backing becomes the furnace casing. Almost all refractory problems are the result of irregularities in the installation process. The quality of castable refractory applications is highly dependent upon the use of proper installation and curing procedures. This is particularly important for gunned refractories. Experienced refractory workers should be used for all castable refractory jobs. The water used in mixing castables should be clean and potable. Because of the possible variations in the quality of castable refractory installations, the installation process should be carefully monitored with a series of tests and inspections. •

Before installation. Samples of each batch of castable should be tested to ensure that the material properties meet the specifications and have not deteriorated during storage. Compressive strength, density, and permanent linear change should be tested in accordance with standard ASTM testing procedures. For gunned linings, the skill of each operator should be determined by having the operator gun a test panel of each refractory to be used. The panels should be tested for soundness, using a hammer test, and for density.

•

During installation. For each castable being applied, random samples should be taken during each shift. These should be tested for strength, density and linear change to ensure that the materials, as applied, have the required properties. Test panels should also be taken for each operator to ensure proper operation of the equipment.

•

After installation. A hammer test should be used to determine the soundness of refractory linings. When defective areas in the lining are encountered, such as voids or dry-filled areas, a dull sound will be heard. Any unsound areas should be cut out and replaced.

After the installation is completed, castable refractory linings must be cured and dried out before they are ready for service. These steps should be carried out in accordance with the refractory manufacturer's instructions. •

Curing is a process in which the calcium aluminate cement binder in the castable sets up, and achieves a satisfactory strength. During this period of time, which is usually 24 hours, moisture is required to complete the hydration reaction.

•

After the curing step is completed, castable refractories must be dried out to remove any free water remaining in the lining. This is accomplished by gradually heating the furnace or boiler, over a period of 2 to 3 days, to near operating temperatures. If the lining is not properly dried out, excessive quantities of steam can form inside the refractory, causing sections of the lining to spall.


23



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.


24



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 Flow

Alloy Stud and Washer

Lapped Joints Stainless Steel Foil Over Studs. Edges Overlapped 8-12 in.

Steel Shell Seal Punctures with Viscous Ceramic Fiber Cement

Ceramic Fiber Putty to Protect Stud End and Washer (or Wrap with 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 allow for 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.


25



Joint

Joint

External Corners Shell

Coating Cement

Shell

Burner Block 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.


26



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

25 67 Rapid-Fix Washer 38

A

6x3 Section Cup-Lock

All Dimensions Are in Millimeters

50 Effective Ceramic Ferrule

FIGURE 12 Typical Ceramic Fiber Anchors Saudi Aramco DeskTop Standards

27



For 24 in. Wide Blanket Lap Joint for Hot Face Layer Butt Joint for Backup Layers

X X

= =

12 in. on Side Walls 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.


28



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


29



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.


30



Fuel Fired Contains: Oil <0.5% (wt) Sulfur AND

Lining Facing

Brick, Castable, Ceramic Fiber

Back-Up

Any

Internal Lining Internal Coating System Permitted Required? (3)

Yes

No

Gas <0.5% (wt) H2S

Oil Brick Block No (4) >0.5% (wt) Sulfur Brick Yes No Castable t>3 and δ>60 Brick Yes Yes (5) Castable t<3 or δ<60 OR Gas Yes No Castable t>4 and δ>75 Block >0.5% (vol) H2S Block No (4) Castable t<4 or δ<75 Yes No Castable t>3 and δ>75 Castable (1) Castable Yes Yes (5) Castable t<3 or δ<75 Ceramic Fiber Block No (4) Ceramic Fiber Ceramic Fiber Yes Yes (5) Yes No Castable t>3 and δ>60 None (Ducts, stacks, etc.) Yes Yes(5) Castable t<3 and δ<60 None Ducts, stacks, etc.) NOTES: (1) Total concentration of free alkali, MgO, and iron in the aggregate shall be less than 10%; facing shall be a mediumweight or heavier castable, and have a calcium binder. (2) t, is the refractory thickness in inches, and δ is the installed fired density, lb/ft3. (3) No internal coating is required with low sulfur levels, or when a castable layer of sufficient thickness and density is used. (4) Block will deteriorate due to facing permeability. (5) Casing corrosion without coating due to system permeability. FIGURE 15 Criteria For Lining Systems For Sulfur-Containing Fuels


31



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.


32



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 Rheniformer

015-F-100A&B Atmospheric

Fuel Gas H2S = 0.1 vol%

Fuel Gas H2S = negligible

Design Fuels: Gas Fuels:

Waste Gas H2S = 7.6-8.1 vol% Liquid Fuels:

Wall Construction:


Vacuum Residuum S = 3.9-5.5 wt% V = 31-45 ppm Na = <5 ppm IFB/block

Dual-layer Castable

33



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) = R=

where: q U R

T 1 -T 2 , or: R T 1 -T 2 q

(Eqn. 1) (Eqn. 1a) (Eqn. 1b)

= Heat loss, Btu/hr-ft2 of surface area. = Overall heat transfer coefficient, Btu/hr-ft2-°F. = Total thermal resistance, hr-ft2-°F/Btu. 1

=U T1 T2

. = Refractory hot face temperature, °F. = Cold face (casing) temperature, °F.

Thermal Resistance The thermal resistance of the refractory lining is the sum of the resistances of the individual component layers: R = r1 + r2 + ... (Eqn. 2) t r1 = 1 k1

where: r1 t1 k1

(Eqn. 3)

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


34



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, Tbw).

•

Radiant section shielded walls (walls located behind tube rows): average of Tbw and the average radiant section tube metal temperature, + 100°F.

•

Radiant section arch: Tbw.

•

Radiant section floor: Tbw (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 = C

1 T avg + 460

0.18

T 2 - T a 1.27

(Eqn. 4)

For wind conditions: q c = 1 + 0.33V


T2 - Ta

(Eqn. 5)

35



•

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 C for vertical wall C for floor

= 0.96. = 0.74. = 0.49.

T2 + T a ,°F. 2

T avg

=

V ε

= Wind velocity, miles/hr. = Casing emissivity, use 0.95.

Interface Temperature (Ti) This is the temperature between the two layers of refractory. r Ti = T1 - 1 T1 - T 2 R

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)


36



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 temperature of 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.


37



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 = 1706 Ambient Temperature, Ta °F = 80 Wind Velocity, V m/h = 0 Casing Temperature, T2 °F = 180 Corresponding Heat Loss Rate, q Btu/hr-ft2 = 218 =

Required Resistance, R

T1 - T2 1706 - 180 = q 218

hr-ft2-°F/Btu

=

7.0 1401

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

°F

=

Hot Face Layer: Material Thickness, t1

in.

= =

Avg. Hot Face Temp.,

T + Ti 1706 + 1401 = Th = 1 2 2

Thermal Conductivity, k1 (Work Aid 3)

1553 1.82

1524 1.81

hr - ft2 - °F/Btu

=

1.65

1.66

= hr-ft2 - °F/Btu

1:6 L:V

=

5.35

5.34

Btu-in./hr-ft2 - °F

= =

790 0.95

761 0.94

in. in.

= =

5.08 5.0

5.02 5.0

=

5.26

5.32

=

6.91

6.98

=

1342

1339

Btu/hr-ft2 = °F =

218.6 180

T + T2 1401 + 180 Tc = i = 2 2

t2 5.0) = Thermal Resistance, r2= k 2 0.95

°F

hr-ft2 - °F/Btu hr - ft2 - °F/Btu

Total Thermal Resistance, R = r1 + r2 Calculated Interface Temperature:

r 1.65 T i = T 1 - 1 T 1 - T 2 = 1706 R 6.91

2nd Trial

= =

Cold Face Layer: Material Required Thermal Resistance: r2, = R - r1 = (7.0) - (1.65)

Thermal Conductivity, k2 (Work Aid 3) Calculated Cold Face Thickness, t2 = r2 k2 = (5.35) (0.95) Use Cold Face Thickness, t2:

1st Trial

°F Btu-in./hr-ft2 - °F

t1 3.0) = Thermal Resistance, r1 = k 1 1.82

Avg. Cold Face Temp.,

1:2:4 L:H:V 3.0

1706 - 180

°F

T -T 1706 - 180 Calculated Heat Loss, q: = 1 2 = R 6.98

Corresponding Casing Temperature, T2 (Work Aid 2) FIGURE 16 Saudi Aramco DeskTop Standards

38



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.


39



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 Wind Velocity, V Calculated Hot Face Temperature, T1 Calculated Cold Face Temperature, T2 Hot Face Layer: Material, Thickness, t1 Cold Face Layer: Material, Thickness, t2

°F m/h °F °F

in.

= = = = = = = =

108 0 1706 171 1:2:4 L:H:V 3.0 1:6 L:V 7.0

°F

=

171

°F

=

1399

in.

1st Trial - Estimated Casing Temperature, T2 Estimated Interface Temperature: (Calculated, or from Work Aid 5) Ti = T1 - X(T1 - T2) = (1706) - (0.2) (1706 - 171) Hot Face Layer: Avg. Hot Face Temp.,

Thermal Conductivity, k1

t 3 r1 = 1 = k1 1.82

Thermal Resistance,

Cold Face Layer: Avg. Cold Face Temp.,

Tc =

2nd Trial


= =

1552 1.82

1565 1.83

hr - ft2 - °F/Btu

=

1.65

1.64

= =

785 0.95

798 0.95

=

7.37

7.37

=

9.02

9.01

=

1425

1427

T i + T2 1399 + 171 = 2 2

t 7.0 r2 = 2 = k 2 0.95

°F

hr - ft2 - °F/Btu hr - ft2 - °F/Btu

Total Thermal Resistance, R = r1 + r2 Calculated Interface Temperature: r 1.65 T i = T 1 - 1 T 1 - T 2 = 1706 R 9.02

°F


Thermal Conductivity, k2 Thermal Resistance,

1st Trial T + Ti 1706 + 1399 Th = 1 = 2 2

1706 - 171

°F

Calculated Heat Loss: q=

T1 - T2 1706 - 171 = R 9.01

Btu/hr - ft2 =

170

°F =

90

Corresponding Ambient Air Temperature, Ta FIGURE 17 Calculation Of Refractory Heat Loss


40



2nd Trial - Estimated Casing Temperature, T2 °F Estimated Interface Temperature: (Calculated, or estimated from 1st Trial) Ti = T1 - X(T1 - T2) = (_____) - (_____) (____ - ____) °F

=

184*

=

1430

Hot Face Layer 1st Trial T + Ti 1706 + 1430 = Th = 1 2 2



t 3.0 r1 = 1 = k1 1.84

Cold Face Layer: Tc =


= =

1568 1.84

hr - ft2 - °F/Btu

=

1.63


= =

807 0.95

hr - ft2 - °F/Btu hr - ft2 - °F/Btu

=

7.37

=

9.00

=

1430

T i + T2 1430 + 184 = 2 2



t 7.0 r2 = 2 = 0.95 k2

Total Thermal Resistance, R = r1 + r2 Calculated Interface Temperature: r 1.63 T i = T 1 1 T 1 - T 2 = 1706 R 9.0

1706 - 184

°F

2nd Trial


T1 - T2 1706 - 184 = R 9.00

Btu/hr -

=

169

=

108

Btu/hr - ft2 = = °F

169 184

ft2 Corresponding Ambient Air Temperature, Ta Final Conditions (from Work Aid 2) Heat Loss, q: Casing Temperature, T2

°F

* This was estimated form the first trial. Any reasonable estimate can be used. FIGURE 17 (CONT'D)


41



2000

1500

Temp at tip of Anchor: 1706 -

0.5 (1706 - 1430) = 1660 3

25/20 Tiebacks Req'd by Current °F

1000

Standards

500

0.5" 3"

7"

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 is assumed 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.


42



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.


43



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.


44



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.


45



THERMAL CONDUCTIVITY OF CERAMIC FIBER BLANKETS

Mean Temperature, °F


46



GLOSSARY arch

The flat or sloped portion of the radiant section opposite 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 primarily of 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.


47



gravity wall

A freestanding, self-supporting refractory structure commonly consisting of firebrick.

hot face layer

The refractory layer exposed to the highest temperatures 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.


48



REFERENCE Saudi Aramco Standards AES-F-001 Process Fired Heaters 32-AMSS-021 Water-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


49



APPENDICES Appendix A Refractory Wall Thickness - Calculation Sheet The following procedure can be used to calculate the required refractory wall thickness: Plant Location Service Hot Face Temperature, T1, °F = Casing Temperature, T2, °F = Corresponding Heat Loss Rate, q Required Resistance R=

T1 - T 2 ______ - ______ = q ______

Boiler/Furnace Location Ambient Temperature, Ta, °F = Wind Velocity, V, m/h = Btu/hr-ft2 =

hr - ft2 - °F/Btu

Estimated Interface Temperature: Ti = T1 - X(T1 - T2) = (_____) - (____) (____ - ____) Hot Face Layer: Material Thickness, t1

=

°F

=

in.

= = 1st Trial


Thermal Conductivity, k1 (Work Aid 2) Thermal Resistance,

t r1 = 1 = k1

Cold Face Layer: Material Required Thermal Resistance: r2 = R - r1 = (_______) - (______)

°F = 2 Btu-in./hr-ft - °F = hr - ft2 - °F/Btu = = hr-ft2 - °F/Btu =

T + T2 ______ + ______ Tc = i = 2 2


Thermal Conductivity, k2 (Work Aid 2) Calculated Cold Face Thickness, t2 = r2 k2 = (______) (______) Use Cold Face Thickness, t2: Thermal Resistance,

2nd Trial

T + T2 ______ + ______ Th = 1 = 2 2

t r2 = 2 = k2

Total Thermal Resistance, R = r1 + r2

°F = Btu-in./hr-ft2 - °F = in. = in. = hr-ft2 - °F/Btu = hr - ft2 - °F/Btu =

Calculated Interface Temperature:

r _____ T i = T 1 - 1 T 1 - T 2 = _____ R _____ Calculated Heat Loss:

q=

T1 - T2 ______ - ______ = R ______

Corresponding Casing Temperature, T2 Saudi Aramco DeskTop Standards

_____ - _____

°F = Btu/hr-ft2

=

°F = 50



Appendix B Refractory Heat Loss - Calculation Sheet The following procedure can be used to calculate the heat loss through a refractory wall: Plant Location Service

Boiler/Furnace Location

Ambient Temperature, Ta Wind Velocity, V Calculated Hot Face Temperature, T1 Calculated Cold Face Temperature, T2 Hot Face Layer: Material, Thickness, t1 Cold Face Layer: Material, Thickness, t2

°F m/h °F °F

in.

= = = = = = = =

°F

=

°F

=

in.

1st Trial - Estimated Casing Temperature, T2 Estimated Interface Temperature: (Calculated, or from Appendix A) Ti = T1 - X(T1 - T2) = (_____) - (_____) (____ - ____) Hot Face Layer:

1st Trial T + Ti = Th = 1 2



t r1 = 1 = k1


Tc =

°F = Btu-in./hr-ft2 - °F = hr - ft2 - °F/Btu =

T i + T2 ______ + ______ = 2 2


2nd Trial

+ 2

t r2 = 2 = k2

Total Thermal Resistance, R = r1 + r2 Calculated Interface Temperature:

r _____ T i = T 1 - 1 T 1 - T 2 = _____ R _____

°F = Btu-in./hr-ft2 - °F = hr-ft2 - °F/Btu = hr - ft2 - °F/Btu =

_____ - _____

°F =


T1 - T2 ______ - ______ = R ______

Corresponding Ambient Air Temperature, Ta (Work Aid 3) Saudi Aramco DeskTop Standards

Btu/hr-ft2 = °F = 51



2nd Trial - Estimated Casing Temperature, T2 °F Estimated Interface Temperature: (Calculated, or estimated from 1st Trial) Ti = T1 - X(T1 - T2) = (_____) - (_____) (____ - ____) °F

=

=

Hot Face Layer 1st Trial T + Ti Th = 1 = 2



t r1 = 1 = k1

2nd Trial

+ 2

°F = 2 Btu-in./hr-ft - °F = hr - ft2 - °F/Btu =


Tc =

T i + T2 ______ + ______ = 2 2


t r2 = 2 = k2

Total Thermal Resistance, R = r1 + r2 Calculated Interface Temperature: _____ r T i = T 1 - 1 T 1 - T 2 = _____ R _____

°F = Btu-in./hr-ft2 - °F = hr-ft2 - °F/Btu = hr - ft2 - °F/Btu =

_____ - _____

°F =


T1 - T2 ______ - ______ = ______ R

Corresponding Ambient Air Temperature, Ta (Work Aid 3) Final Conditions Heat Loss, q: Casing Temperature, T2


Btu/hr-ft2 = = °F Btu/hr-ft2 = °F =

52

Boilers & Furnaces-Refractory&Insulation

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