Calcium silicate thermal insulation

FIGURE 5.171 Thermal conductivity for typical calcium silicate pipe insulation. 

Aluminum-jacketed calcium silicate insulation with an emissivity factor of 0.05. To convert inches to miUimeters, multiply by 25.4, to convert dollars per 1 miUion British thermal units to dollars per 1 nulhon kilojoules, multiply by 0.948, = 5/9 ( F — 32). 

Mineral wool is resilient, lightweight, fibrous, wool-like, thermally efficient, and fire resistant up to 1100°C (2000 F), and forms a sound barrier. Mineral wool insulation comes in the form of blankets, rolls, or blocks. Calcium silicate is a solid material that is suitable for use at high temperatures, but it is more expensive. Also, it needs to be cut with a. saw during installation, and thus it takes longer to install and there is more waste. 

Wollastonite and diopside are utilized as abrasion-resistant materials for road surfaces and fillers for rubber and plastics (Jacob, 1976), and also as thermally insulating materials for a variety of applications (Demidenko et al., 2001). Currently, these calcium and caldum magnesium silicates are synthesized starting with mixtures of moist lime (CaO) or burned dolomite (CaO + MgO) and finely ground quartz flour. The mixtures are heated hydrothermally between 200 and 250 °C for 7-16 h to yield xonotlite or mixtures of xonotlite and serpentine according to >... 

Almost all steam and hot-process piping systems operate in the temperature range of 212 to 1000°F (100 to 538°C).The products most frequently used are calcium silicate, fiberglass, mineral wool, and expanded perhte. Choices are usually based on thermal conductivity and resistance to physical abuse where applicable. Hberglass products are the most thermally efficient at lower temperatures, with calcium sihcate being the best at higher temperatures. It is important to use the insulation mean temperature when comparing thermal conductivities in order to make the proper comparison. 

Although in refractory practice there are hundreds of heat insulation materials, the list of heat insulation materials for the lining of reduction cells is rather limited. For one thing, economic considerations add some limitations, but for another, the heat insulation materials in reduction cells should withstand mechanical compression loads without deformation at temperatures up to 900 °C for a long time, and numerous inexpensive fiber heat insulation materials don t correspond to this requirement. In the Hall-Heroult reduction cell, the heat insulation materials should withstand the pressure of the layer of the electrolyte, the layer of molten aluminium, cathode carbon blocks (taking into account collector bars), and the refractory layer. Currently, only four or five heat insulation materials are used in the lining of reduction cells diatomaceous (moler) and perlite bricks, vermiculite and calcium silicate blocks (slabs), and sometimes lightweight fireclay bricks (but their thermal conductivity is relatively big, while the cost is not small) and fiber fireclay bricks. 

Fig. 2.85 Thermal conductivity of heat insulation materials 7, 2—diatomaceous bricks 3— lightweight fireclay brick 4—diatomaceous brick 5— vermiculite slab 6—calcium silicate slab...

In Chap. 1, we showed that the temperature dependence of refractory and heat insulation materials usually is a complex function. Yet for diatomaceous, vermic-ulite, lightweight fireclay, and calcium silicate materials in temperature intervals, the temperature dependence is linear (Fig. 2.91). The linear character of the temperature dependence of thermal conductivity reveals the peculiarities of heat transfer in lightweight refractory materials [206] (Fig. 2.85). 

Calcium silicate materials have the finest structure the thermal conductivity of calcium silicate is approximately 1.5 times lower compared to diatomaceous and vermiculite thermal insulation. The inner surface temperature of calcium silicate materials is--80 m /g, and the particles have dimensions of 0.05-0.1 pm. Such a structure gives a very high thermal resistance of pores and intergrain contacts, which is the reason for such a small conductivity of calcium silicates. 

Rossiter and Brown, 1990). The foamed cement was formulated as a calcium magnesium oxychloride silicate composition and was pumped into the cavity walls of the test house. The density of cement was 46.5 kg m-3 and had a measured thermal conductivity of 0.0430 W/m°C at 24°C, which is comparable to other commercially available insulation materials. 

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