A refractory lining is a protective layer that provides high-temperature resistance and protects the structure from thermal shock, wear, and erosion in industrial furnaces, pipes, or equipment. The refractory lining shields the pipe or equipment material from direct heat from fire or fluids. They are vital parts of boilers, furnaces, and certain pipes. Refractory installation is critical to ensuring the safe and efficient operation of furnaces and boilers. This article will teach us about refractory lining materials, selection, and procedure. Let us begin with a definition of the subject.
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What is a Refractory Lining?
Refractory lining acts as a protective layer inside the equipment and acts as insulation for high-temperature services. High temperatures, thermal shock, wear, and chemical corrosion is all tolerated by the refractory lining. The refractory lining for furnaces is typically made of refractory brick or amorphous refractory. Typical refractory lining applications include fired heaters, blast furnaces, electric furnaces, boilers, drying equipment, high-temperature differential heat meters, muffle furnaces, and so on.
Functions of Refractory Lining
Refractory lining is commonly used in extremely high-temperature services to act as a thermal barrier between the pipe/equipment wall and the hot medium.
- Physically withstand stress.
- Keep corrosion and erosion at bay.
- Thermal insulation is provided.
As a result, refractories can be found in a variety of useful applications. They are widely used in furnaces, kilns, reactors, fired heaters, hydrogen reformers, ammonia primary and secondary reformers, cracking furnaces, utility boilers, catalytic cracking units, air heaters, sulfur furnaces, and other vessels that handle hot mediums like metal and slag.
Materials for Refractory Linings
The following materials are commonly used as refractory lining materials:
- Aluminum oxide or Alumina (High Alumina bricks)
- Carbide of hafnium
- Molybdenum disilicide
- Oxide of silicon
- Magnesium oxychloride
- Calcium oxychloride
- Fire clays (Clay bricks)
- Carbide of silicon
- Wrought tungsten carbide
- Nitride of boron
Selecting Refractory Lining
Choosing a refractory lining is not a simple task. The choice of refractory lining is influenced by several factors, including:
Thermal Prerequisites: The refractory lining material selected must withstand the maximum operating and design temperatures. The material must be resistant to thermal shock and be resistant to thermal fatigue, excessive expansion, and other factors.
Lifespan: During operation, the refractory material will be subjected to mechanical and thermal loads, which may result in wear and failure. To increase its lifespan, the chosen material must be able to absorb dynamic loads, mechanical impacts, severe erosion and corrosion, tensile loads, large hydraulic loads, pinch spalling, and so on.
Chemical Attack: A chemical reaction with the content at high temperatures is possible. As a result, the refractory materials chosen should be inert against them.
Installation: The refractory lining material must be easily accessible and installed. During repair or maintenance, the chosen refractory material must be quickly delivered to the required location.
Cost: Finally, all choices are governed by cost or economy. The material chosen must be cost-effective for the range of services.
Types of Refractory Lining Materials
Multiple parameters, as listed below, can be used to classify refractories.
According to chemical composition:
- Acidic refractories (silica, zirconia, aluminosilicate refractories);
- Refractories of basic composition (Magnesite refractories, Dolomite refractories, Magnesia-chrome refractories);
- Neutral refractory materials (Carbon graphite refractories, Alumina refractories, Chromite refractories)
- Manufacturing method: dry press process Hand-molded, fused cast, formed, and unformed
- Normal refractories, High refractories, and Super refractories have different fusion temperatures.
- Super duty, High duty, Intermediate duty, and Low duty refractoriness.
Thickness of Refractory Lining
The thickness of the refractory lining is usually between 80mm and 300mm depending on the type of furnace and the smelting substance.
In some applications, two layers of refractory lining of different materials may be used. The refractory lining of the converter, for example, has two layers. The outer layer is made of magnesium refractory with a thickness of 50-100mm, and the inner layer is made of magnesium brick with a thickness of 300-500mm.