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Refractories

By Haleem Haider Farrukh Shahzad Muzammil Javed

Uploaded by FARRUKH SHAHZAD

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Contents tableRefractoryClassificationProperties of RefractoriesGeneral Manufacturing (flow sheet)Selection of RefractoriesApplications

-Refractories in Cement Industry.Some Common Refractories

RefractoryA refractory material is one that retains its strength and do

not fuse at high temperatures.

ASTM defines refractories as "non-metallic materials having those chemical and physical properties that make them applicable for structures, or as components of systems, that are exposed to environments above 1,000 °F (811 K; 538 °C)“.

Examples Fire clay.Silica.Chromite magnesite.

ClassificationRefractories can be classified

-on the basis of chemical composition

-method of manufacture

-according to their refractoriness.

On the basis of chemical composition

Acidic refractories These are used in areas where slag and atmosphere are acidic.

They are stable to acids but attacked by alkalis. e.g. fire clay, silica, Quartz, Zirconia.

Basic refractoriesThese are used on areas where slags and atmosphere are basic,

stable to alkaline materials but reacts with acids. e.g. Magnesia , Alumina, Dolomite.

Contd…

Contd.. Neutral refractories

These are used in areas where the atmosphere is either acidic or basic and are chemically stable to both acids and bases.

e.g. Chromite, Carbide, Mullite.

Based on refractoriness Low heat duty refractoriesFor low temperature environment i.e. 1520 —1630 ºC

Medium heat duty refractories For temperature ranging from 1630—1670 ºC

High heat duty refractoriesFor temperature ranging from 1670—1730 ºC

Super duty refractoriesFor temperature above 1730 ºC

On basis of Manufacture

Dry pressed Fused Cast Hand molded Formed Unformed

Properties PorosityGreater the porosity of the refractory great is the

chance of chemical attack of material Refractoriness or Fusion pointThe temperature at which the refractory fuses, so it

must be higher than the operating temperature of the refractory.

StrengthIt is the resistance of the refractory to loads tension

and shear stresses. Contd..

Contd.. Thermal ConductivityFor a given composition, a better pressed,less permeable

product has higher thermal conductivity. -For use in Furnace and kiln Thermal conductivity should be

low. -For use in coke oven and regenerators thermal conductivity

should be high.

SpallingIt is the fracture of refractory due to its uneven

expansion on account of heat when they are subjected to rapid heating and cooling.

Contd..

Contd.. Slag Resistance

It is the resistance to slag action which depends on nature of the slag and refractory.

Abrasion resistance

It is the resistance to abrasion which can be increased by using dense (low porosity) fine grained and wear resistance refractory.

Erosion resistance

Resistance to erosion due to mechanical action.

Manufacturing steps Transportation of Raw material Grinding Pre-Treatment Calcination Stabilizer addition Mixing Bonding material Wet Mixing (14-20% water) Semi plastic Dry Mixing ( < 5% water) Moulding Hand Moulding (Wet Mixed) Machine Moulding (Dry and Semi wet Mixed) Contd..

Contd..

Drying

Avoids high shrinkage and gives strength.

Make refractories safe for handling. Firing

Removes water of Hydration,

30% Shrinkage in Volume.

Selection of Refractories Area of application Working temperatures Extent of abrasion and impact Stress due to temperature gradient Heat transfer and fuel conservation Cost consideration

ApplicationsRefractories are meant to sustain at high temperature so

the very common applications are Used in furnaces such as blast furnace and coke oven. Used in boilers. Mostly used in cement industry in

Preheater

Rotary Kiln

Burner pipe

Clinker cooler

Some Common Refractories

Fire Clay refractories Common in industry: materials available

and inexpensive Consist of aluminium silicates Decreasing melting point with increasing

impurity and decreasing AL2O3

High Alumina Refractories 45 - 100% alumina High alumina % = high refractoriness Applications: hearth and shaft of blast

furnaces, ceramic kilns, cement kilns, glass tanks

Silica Bricks >93% SiO2 made from quality rocks Iron & steel, glass industry Advantages: no softening until fusion point is

reached; high refractoriness; high resistance to spalling, flux and slag, volume stability

Zirconia refractories Zirconium dioxide ZrO2 Stabilized with calcium, magnesium, etc. High strength, low thermal conductivity, not

reactive, low thermal loss Used in glass furnaces, insulating refractory

Question ?

 

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