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Materials of Construction - Sulphur Furnace
November 8, 2002


Refractory Brick Lining
Insulating Brick
Fire Brick

Associated Links

Sulphur Burning
Sulphur Furnace
Sulphur Systems


A sulphur furnace is exposed to high temperatures from the combustion of sulphur to sulphur dioxide.  The materials of construction must be capable of withstanding temperatures as high as 1200ºC (2192ºF).


The furnace shell is generally carbon steel.  The specific grade of steel will vary depending on the expected operating shell temperature (i.e. Cold Shell or Hot Shell design).  For cold shell design A36 steel will be adequate.  For hot shell designs A515 Gr. 70, A516 Gr. 70 or A285 Gr. C may be used.  The selection of material will be a function of maximum operating temperature of the shell, design pressure and availability and cost of the material.

If the shell can see extreme low temperatures an impact tested steel may be required.

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Refractory Brick Lining    

The brick lining serves two purposes:

The above is achieved by using both refractory brick and insulating brick.  Multiple layers are typical for mechanical reasons and to eliminate a direct leak path to the shell.  For most furnaces a 343 mm (13½”) layer of refractory (insulating and fire brick) is adequate to maintain shell temperatures at acceptable levels.  When the furnace operating temperature is higher, increased thickness (457 mm (18”)) of refractory brick will be necessary.

Refractory brick comes in standard brick sizes regardless of the supplier.  Standard brick dimensions are 9” x 4½” x 2½” and 9” x 4½” x 3”.  Other sizes and shapes are available as standard. 

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Insulating Brick

Insulating brick is generally applied between the steel shell and the exposed layer of fire brick.  As its name implies its purpose is to reduce heat transfer and insulate the shell from the hot process gases.  Insulating brick should conform to ASTM C155 – Standard Classification of Insulating Firebrick which covers heat insulating materials known as insulating firebrick.  Insulating bricks are classed according to their bulk density and the behaviour in the reheat change test conducted at the specified temperature.  Eight groupings are defined in the specification:

Group No. Reheat Change, Not more than 2% when tested at °F (°C) Bulk Density Not Greater Than lb/ft³ (g/cm³)

1550 (845)

34 (0.54)
20 1950 (1065) 40 (0.64)
23 2250 (1230) 48 (0.77)
26 2550 (1400) 54 (0.86)
28 2750 (1510) 60 (0.96)
30 2950 (1620) 68 (1.09)
32 3150 (1730) 95 (1.52)
33 3250 (1790) 95 (1.52)

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Fire Brick

Fire brick provides protection from the high operating temperatures in the furnace and are more resistant to mechanical damage and chemical attack than insulating brick.  Fire bricks are composed of various combinations of alumina and silica containing materials.  The chemical composition can vary from almost 100% alumina and little silica to 100% silica and little alumina.  Fire bricks are classified into two broad categories; fireclay and high-alumina bricks.  Fireclay brick are classified based on physical propeties while high-alumina bricks are classified primarily on alumina content.

Class Type PCE
Modulus of Rupture
(MPa/psi) (min)
Alumina Content
(% Al2O3)
Fireclay Brick        
Super-duty Regular 33 4.14 / 600  
Spall Resistant 33 4.14 / 600  
Slag Resistant 33 6.89 / 1000  
High-duty Regular 31ln$    
Spall Resistant 31ln$ 3.45 / 500  
Slag Resistant 31ln$ 8.27 / 1200  
Semi-silica     2.07 / 300  
Medium-duty     3.45 / 500  
Low-duty     4.14 / 600  
High-Alumina Brick        
50   34   50 ± 2.5
60   35   60 ± 2.5
70   36   70 ± 2.5
80   37   80 ± 2.5
85       85 ± 2.0
90       90 ± 2.0
99       97 (min)

Typically, a super duty (a fireclay refractory having an Orton pyrometric cone equivalent above 33) fire brick is used containing 45 wt% or greater alumina content.

Bulk density of refractory materials ranges from 2.19 to 2.24 g/cm³.

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Castable refractory may be used in parts of the sulphur furnace design.  Areas where castable refractory may be used are the front of the furnace where the sulphur gun and nozzles are located, manways, sightglasses, etc.  The castable refractory is held in place by anchors which are resistant welded to the shell.

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ASTM C16 Test Method for Load Testing Refractory Brick at High Temperatures
ASTM C20 Standard Test Methods for Apparent Porosity, Water Absorption, Apparent Specific Gravity, and Bulk Density of Burned Refractory Brick and Shapes by Boiling Water
ASTM C24 Test Method for Pyrometric Cone Equivalent (PCE) of Fireclay and High-Alumina Refractory Materials
ASTM C27 Standard Classification of Fireclay and High-Alumina Refractory Brick
ASTM C113 Test Method for Reheat Change of Refractory Brick
ASTM C133 Test Methods for Cold Crushing Strength and Modulus of Rupture of Refractories
ASTM C134 Standard Test Methods for Size, Dimensional Measurements, and Bulk Density of Refractory Brick and Insulating Firebrick
ASTM C155 Standard Classification of Insulating Firebrick
ASTM C210 Standard Test Methods for Reheat Change or Insulating Firebrick
ASTM C800  Standard Test Methods for Apparent Porosity, Water Absorption, Apparent Specific Gravity, and Bulk Density of Burned Refractory Brick and Shapes by Boiling Water
ASTM C914 Standard Test Method for Bulk Density and Volume of Solid Refractories by Wax Immersion