Refractories are materials used in a wide variety of industrial processes to protect equipment from high heat, chemicals and abrasion. They are essential in the metallurgical, glass and chemical industries and in waste management, pulp and paper, and energy-related industries. They provide mechanical strength, protection against corrosion and thermal insulation to equipment.
Refractory applications are found in furnaces, kilns and reactors in both the metallurgical and non-metallurgical sectors of industry. In the metallurgical sector, they are installed in a number of types of furnaces and kilns including fired heaters, hydrogen reformers, ammonia primary and secondary reformers, cracking furnaces, coke calciners, sulfur furnaces, air heaters, boilers and stacks etc. Generally speaking, refractories can be classified into three categories: (1) firebricks (2) insulating refractories and (3) special refractories. They are manufactured from refractory grains, usually synthetic (fused / sintered), free from impurities and under highly controlled production parameters. Alumina and firebricks are the most common refractory materials employed in a wide range of furnace and kiln types. They are mainly used for lining the interiors of these machines, providing a solid and durable surface to protect the equipment from intense heat. In a furnace, the refractory material is able to withstand extremely high temperatures without breaking down or melting. Its ability to withstand temperatures up to 2000C makes it a vital component in many types of equipment. It can also withstand sudden changes in temperature, abrasion and pressure from hot gases and liquids that come into contact with the refractory. Refractories must also have adequate dimensional stability at extreme temperatures and after repeated thermal cycling. These properties are achieved through a combination of refractory particles, fine filler materials and a binder phase. The binder phase helps the refractory to maintain the refractory's shape and resist cracking. The refractory's physical properties are typically defined by its density, pore size and tensile strength. Types of refractories vary from very dense to less dense, depending on the refractory's application and requirements. The most dense refractories, such as firebricks, can handle higher temperatures than the less dense refractories. Dense refractories are usually high-density (>120 lb/ft3), offering exceptional resistance to the extreme temperatures and chemical reactions of operating conditions. These refractories have good insulating properties, which can help to conserve heat and improve process control by keeping the refractory cooler than the surrounding environment. This allows the operator to operate the equipment in an optimal condition for the longest possible time without having to replace the refractory. It is also beneficial in reducing the environmental impact of the equipment, thereby minimizing costs associated with fuel consumption. Moreover, it offers great abrasion resistance, even under extremely high temperatures and is capable of containing acidic slags. Among the most commonly used refractory materials are silica refractories, carbon refractories, and neutral oxides. Silica gravel deposits and quartzites that have a low alumina and alkali content are primarily used for making silica refractories. They are bonded with 3-3.5 percent lime, and offer a wide range of performance and utility across numerous applications. Unlike their alumina and carbon counterparts, they do not react with acids or bases in the atmosphere.
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