What is Refractory?
Refractories are ceramic materials designed to withstand the very high temperatures (in excess of 1,000°F [538°C]) encountered in modern manufacturing. More heat-resistant than metals, they are used to line the hot surfaces found inside many industrial processes.
Refractories are produced from natural and synthetic materials, usually non-metallic, or combinations of compounds and minerals such as alumina, fireclays, bauxite, chromite, dolomite, magnesite, silicon carbide, and zirconia.
Type of refractory
A ) Acid Refractory: –
Used in Acidic Environment
- Silicon Refractories (93% SiO2)
- Zirconia Refractories (ZrO2)
- AluminoSilicate Refractories (Al2O3 and SiO2)
B ) Basic Refractory
If environment contain Slag and Base.
- Magnesite Refractories (More than 85% MgO).
- Dolomite refractories (Calcium magnesium carbonate)
- Magnesia Chrome Refractories (MgO + Cr2O3)
C ) Neutral Refractory
If environment contain Slag and it is neutral to acid and base.
- Carbon Graphite Refractories
- Chromite Refractories
- Alumina Refractories (≥ 50% alumina (Al2O3)
Other Commercial Terms
It is essentially Acid Refractory and consist of ( 25% to 45% Al2O3 and 50% to 80% SiO2 ). It is readily available refractory and widely used.
2. High Alumina
If Al2O3 is more than 45% it is called High Alumina
3. Silica Brick
If SiO2 is more than 93% it is called Silica Brick
After Refractory application
Refractory has huge application in Crude oil Refinery sector. After application of refractory, it needs to be dried properly with Furnace heating. Furnace heat up is critical activity but when a huge project is in progress, furnace heat up get only little attention. This led to: –
- Refractory failure before Furnace reaches its normal operating temperature.
- Unexpected failure of Furnace refractory lining before its standard age.
- Sudden shutdown may be required for repair.
- Loss of life of equipment which get exposed.
Refractory dry out is a sophisticated process of applying heat to a refractory lining to remove extra water without affecting its strength and damaging it.
Important Terms of Refractory:-
- Dryout – The initial application of heat under controlled rates to safely remove retained free and chemically combined water from the refractory lining after completion of the curing process.
- Free or Physical Water – Excess water remaining in the castable material pores after installation. This independent molecules of water will boil off at normal temperatures as free water.
- Chemically Combined Water – Water that is tied up in the cement hydrate phases (bond structure). This water does not boil off at 212ºF as does free water, but is released in stages at elevated temperatures.
Free water in the castables material is removed with help of dry out methods. In dry out method, furnace get heated with gas or oil burning. The heated flue flow across the equipment and remove the water molecule by raising inside temperature of the equipment.
Dry out plan may vary from contractor to contractor and process unit to process unit. It is advisable to use a very much customized schedule chart for dry out plan. The schedule should be prepared in consultation with the refractory manufacturer.
Dry out may be carried with existing main burner or a third-party burner. Heating up process should be controlled method to make a slope for temperature rise and time. Rapid heating and local hot spots creating stresses which cause severe cracking or worth damages. Thermocouples should be placed in the expected hottest areas near the burners and at the coldest exhaust points.
A sudden rise in temperature may boil the water molecules trapped inside lining and during release of these molecule, it may create pressure on the lining. It is advisable to keep a hold point after achieving a specific temperature and raise the temperature in installment. Same philosophy should be used during heat removal of the refractory.
At some location, dry out exhaust can not be released in open atmosphere due to environment norms.
List of Refractory Manufacturers :-