IRON MAKINGIRON MAKINGREFRACTORY SYSTEMSREFRACTORY SYSTEMSN. PRAKASANME METALLURGY
IRON MAKING REFRACTORY SYSTEMSIRON MAKING REFRACTORY SYSTEMSREFRACTORY MATERIAL: A material having the ability to retain its physical shapeand chemical identity when subjected to hightemperatures. Refractories are inorganic, nonmetallic, porous andheterogeneous materials composed of thermally stablemineral aggregates, a binder phase and additives. Refractories are heat resistant materials used in allprocesses involving high temperatures and/orcorrosive environment.
IRON MAKING REFRACTORY SYSTEMSIRON MAKING REFRACTORY SYSTEMSA refractory material should be able to,Withstand high temperaturesWithstand action of molten metal, hot gassesand slag erosion etc;Withstand load at service conditions;Resist contamination of the material with whichit comes into contact;Maintain sufficient dimensional stability at hightemperatures and during repeated thermalcycling;
IRON MAKING REFRACTORY SYSTEMSIRON MAKING REFRACTORY SYSTEMSImportant Properties of Refractories:Melting point◦ Melting temperatures specify the ability of materialsto withstand high temperatures without chemicalchange and physical destruction.◦ For Alumina 3720oF; Graphite C Pure 6300oFSize and Dimensional Stability:◦ Dimensional accuracy and size is extremelyimportant to enable proper fitting of the refractoryshape and to minimize the thickness and joints inconstruction.
IRON MAKING REFRACTORY SYSTEMSIRON MAKING REFRACTORY SYSTEMSImportant Properties of Refractories:Porosity:◦ Low porosity materials are generally used in hotterzones, while the highly porous materials (Highlyinsulating) are usually used for thermal backup.◦ Refractory materials with high porosity are usuallyNOT chosen when they will be in contact with moltenslag because they cannot be penetrated as easily.Bulk Density:◦ An increase in bulk density increases the volumestability, the heat capacity, as well as the resistanceto abrasion and slag penetration.
IRON MAKING REFRACTORY SYSTEMSIRON MAKING REFRACTORY SYSTEMSImportant Properties of Refractories:Refractoriness under load:◦ The ability to withstand exposure to elevatedtemperatures without undergoing appreciabledeformation is measured in terms of refractoriness.The refractoriness under load test (RUL test) givesan indication of the temperature at which the brickswill collapse, in service conditions with similar load.Creep at high temperature :◦ Refractory materials must maintain dimensionalstability under extreme temperatures (includingrepeated thermal cycling) and constant corrosionfrom very hot liquids and gases.
IRON MAKING REFRACTORY SYSTEMSIRON MAKING REFRACTORY SYSTEMSImportant Properties of Refractories:Thermal Conductivity:◦ High thermal conductivity refractories are requiredfor some applications where good heat transfer isessential such as coke oven walls, regenerators,muffles and water cooled furnace walls.◦ However, refractories with lower thermalconductivity are preferred in industrial applications,as they help in conserving heat energy.◦ Porosity is a significant factor in heat flow throughrefractories. The thermal conductivity of a refractorydecreases on increasing its porosity.
IRON MAKING REFRACTORY SYSTEMSIRON MAKING REFRACTORY SYSTEMSClassification of Refractories Refractories are typically classified on the basis of theirchemical behavior: Acid Refractories:◦ Acid refractories are those which are attacked byalkalis (basic slags). These are used in areas whereslag and atmosphere are acidic. Examples:◦ 1) Silica (SiO2), 2) Zirconia (ZrO2),Neutral Refractories:◦ Neutral Refractories are chemically stable to bothacids and bases and are used in areas where slagand atmosphere are either acidic or basic. Example:◦ 1) Carbon graphite (most inert)◦ 2) Chromites (Cr2O3); 3) Alumina
IRON MAKING REFRACTORY SYSTEMSIRON MAKING REFRACTORY SYSTEMSClassification of RefractoriesBasic Refractories:◦ Basic refractories are those which are attacked byacid slags but stable to alkaline slags, dusts andfumes at elevated temperatures.◦ Since they do not react with alkaline slags, theserefractories are of considerable importance forfurnace linings where the environment is alkaline;Example:◦ Magnesia (MgO) - caustic, sintered and fusedmagnesia◦ Dolomite (CaO*MgO) - sintered and fused dolomite◦ Chromite -main part of chrome ore
IRON MAKING REFRACTORY SYSTEMSIRON MAKING REFRACTORY SYSTEMSBLAST FURNACE REFRACTORIES:The life of the lining under the conditionsprevailing inside the furnace decides thefurnace compaign which should not be les thana few years.The thickness of the lining depends on thefurnace size.
Blast furnace regionsBlast furnace regionsIRON MAKING REFRACTORY SYSTEMSIRON MAKING REFRACTORY SYSTEMS
IRON MAKING REFRACTORY SYSTEMSIRON MAKING REFRACTORY SYSTEMSSTACK LINING:• The lining in stack should have good abrasionresistance and resistance to carbon monoxide attack.• In general, Armour plates are used at the throat towithstand abrading action of the falling burden.• The entire stock below the top few meters (2-3m) ofheight is lined with high duty fire bricks.• A 35-40% Al2O3 fire bricks with a close texture isusually preferred.• These bricks are made by machine molding under highpressure with absence of air.
IRON MAKING REFRACTORY SYSTEMSIRON MAKING REFRACTORY SYSTEMSHEARTH LINING:• The lining in hearth should prevent breakouts and havehigh refractoriness.• Carbon blocks are used for lining whole wallthickness and considerable bottom thickness of thehearth. The remaining bottom thickness is made byhigh duty fire bricks.• Water cooled copper or steel plates are laid inside thewalls to protect the lining.• Effective cooling of the hearth walls is improved byemploying graphite as the backing layer with carbonblocks facing.
IRON MAKING REFRACTORY SYSTEMSIRON MAKING REFRACTORY SYSTEMSBOSH LINING:• Considering the severity of temperature and chemicalattack in the bosh region the lining should possess,• Good refractoriness• Resistance to the action of the molten metal limy andalkali slags.• High duty fire bricks with 45-65% Al2O3 are used forlining of bosh region with copper cooling pates.• Carbon blocks also used for lining the bosh regionsince carbon refractory have better properties thanconventional high duty fire bricks. Carbon lined wallscan be cooled by spray coolers.
IRON MAKING REFRACTORY SYSTEMSIRON MAKING REFRACTORY SYSTEMSAdvantages of Carbon lining:• Increase in overall compaign life of the furnace.• Minimum breakouts and reduced scaffolds.• Cooling design becomes more simple.• More uniform wear of the lining.• Clean surface in contact with slag and metal• A relatively thin lining is adequate.• Disadvantages of Carbon lining• Higher cost than conventional bricks• Formation of steam and gases in the metal & slag taphole region and faulty coolers can damage the carbonlining.
IRON MAKING REFRACTORY SYSTEMSIRON MAKING REFRACTORY SYSTEMSThe causes of failure of the linings are,◦ Carbon monoxide attack◦ Action of Limy and alkali vapours◦ Abrasion by solids, liquids and gases◦ Temperature◦ Action of molten metal◦ Action of volatile matters
IRON MAKING REFRACTORY SYSTEMSIRON MAKING REFRACTORY SYSTEMSReferences:◦ Modern Iron Making _ R H Tupkary