Refractory linings thermal conductivity

Thickness of shell should not be less than 12 mm. Boiler quality steel should be used since these units run at high internal temperature for long time continuously. Internal lining details (e.g. type of insulating and refractory bricks used, their alumina percentage, thickness of layer, castable refractory, expansion joints provided. (Vendor to submit copies of their test certificates giving chemical analysis, refractory properties, thermal conductivities if asked for by the purchaser. The expected maximum temperature at outer surface of the shell should not normally exceed 60—65 °C.)... 

Refractories are materials that resist the action of hot environments by containing heat energy and hot or molten materials (1). There is no weU-estabhshed line of demarcation between those materials that are and those that are not refractory. The abiUty to withstand temperatures above 1100°C without softening has, however, been cited as a practical requirement of industrial refractory materials (see Ceramics). The type of refractories used in any particular apphcation depends on the critical requirements of the process. For example, processes that demand resistance to gaseous orHquid corrosion require low permeabihty, high physical strength, and abrasion resistance. Conditions that demand low thermal conductivity may require entirely different refractories. Combinations of several refractories are generally employed. 

The heart of this facility is a refractory-lined reactor cylinder with 20 cm in-diameier and a total height of about 6.5 m. The internal refractory forms two concentric cylinders (each one of thickness 6.5 cm) with different thermal conductivity and wearing properties. Additionally, the reactor tube, the cyclone and the recycling line are protected with outside insulation in order to minimise heat losses. The gasifier components (raiser, cyclone and standpipe) are equipped with ten thermocouples (K-type) and pressure transducers. The thermocouples probes are connected to a computer based data acquisition and control system. In addition, the feed rates of gasification... 

Despite its comparatively high price, silicon carbide is a significant refractory product due to its exceptional properties, such as its high thermal conductivity, high hardness and mechanical strength. It is used in zinc distillation kilns and in the manufacture of muffles, capsules and kiln furniture for the clay ceramic industry (see Section 5.5.4.7.2). In recent years silicon carbide has also been used in the refractory linings of blast furnaces and utilization in other sectors of the steel producing industry is in evaluation. 

Refractory materials are suitable for use in furnace linings such a material has a high melting point, low electrical conductivity and high thermal conductivity, and is chemically inert at the high operating temperatures of the furnace. 

Uses Reduction of iron ore in blast furnaces as source of synthesis gas refractory furnace linings in electrorefining of aluminum and other high-temp, service electrodes in electrolytic reduction of AI2O3 to aluminum filter medium fuel electrothermal prod, of phosphorus, silicon carbide, and calcium carbide plastics additive providing wear reduction in PTFE, creep resist., chemical inertia and stability, thermal conductivity and stability... 

Equipment is lined inside with refractory bricks for protection of the shell The shell is not subjected to the heating medium as well as the reaction medium. This type of equipment cannot have heating jackets due to poor thermal conductivity of the bricks. It has electrical heating by electrodes installed inside or has induction heating method. It can also have internal heating coils of special MOC which can resist the material to be heated. 

One of the main purposes of the brick lining is to provide thermal protection to the membrane. The protection afforded depends not only on the brick s thickness but also on its thermal conductivity. The thermal conductivity of refractory and carbon brick is generally higher than fireclay type. Table 7.2 provides the minimum brick thickness at various operating temperatures to protect a membrane with a maximum allowable temperature of 250°F/121°C. Table 7.3 provides the K factor (thermal conductivity) of the various corrosion resistant bricks. 

Materials for refractory lining are chosen based on several factors, including their stability and durability. While the main intention is to protect the steel shell, they can serve as an insulation material necessary to retain the heat within the kiln interior. At the sections near the combustion zone, conductive materials are preferred for lining so as to dissipate some heat away and prevent excessive temperature build-up and thereby avoid thermal stresses and associated refractory damage. Lining materials come in all forms including bricks and mortars of all consistency that can be spread or sprayed on surfaces. The material composition and thermo-physical properties of some lining materials are presented in Table 7.1. 

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