Blast furnace slags, thermal

Insulation. Impure sdiceous limestone and blast-furnace slag are the main raw materials for making rock-wool insulation bats and peUets (see Insulation, thermal). 

Thermal property is another critical property for furnace slag. Because of their more porous structure, blast furnace slag aggregates have lower thermal conductivities than conventional aggregates. Their insulating value is of particular advantage in applications such as frost tapers (transition treatments in pavement subgrades between frost-susceptible and nonfrost-susceptible soils) or pavement base courses over frost-susceptible soils. 

Many cements used today are composites of Portland cement and industrial waste materials that can enter into the hydration reactions and contribute to the strength of the hardened product. These substances include pulverized fuel ash (PFA) from burning of pulverized coal in thermal power stations, crushed blast-furnace slag (Section 17.7), and natural or artificial pozzolanas—that is, volcanic ash and similar finely particulate siliceous or aluminosilicate materials that can react with the Ca(OH)2 in Portland cement to form hydrated calcium silicates and aluminates. As noted earlier, the solubility of Ca(OH)2 is such that the pH of pore water in Portland cements will be about 12.7, at which the Si-O-Si or Si-O-Al links in the solid pozzolanas will be attacked slowly by OH- to form discrete silicate and aluminate ions and thence hydrated calcium silicate or aluminate gels. 

The possibility of using Aswan clay combined with industrial waste products, e.g., blast-furnace slag and air-water cooled converter slag, has been investigated with the assistance of thermal analysis The results... 

Other proposed sources of calcium chloride include the thermal decomposition (at 270-280°C) of scrap PVC, with the flue gas being absorbed in a Ume or limestone scmbber (Aoki et al, 2002). Others have suggested the washing of incinerator or fly ashes to recover calcium chloride, or the leaching of blast furnace slag with acids. Dust from scrap steel shredders could also yield calcium chloride in the absorbed incinerator flue gas. 

Figure 4.6 XRD scans of common SCMs siliceous fly ash from coal combustion (FA), blast furnace slag from iron smelting (SL), thermally activated metakaolin (MK) and a volcanic tuff natural pozzolan (Po). The broad hump beneath the diffraction peaks of the crystalline phases indicates the presence of one (or more) amorphous phases. The main crystalline phases identified are mullite (M), quartz (Q), gehlenite (G), anatase (An) and albite (Al).

For the purposes of discussion, it is useful to consider the blast furnace as operating in four consecutive zones. At the fourtlr, bottom, zone the oxidation of coke at the tuyeres canres the temperamre to levels in excess of 2100 K. The next zone, which operates in the temperature range 1600-1900 K is where the liquid metal and slag are formed. The second zone, sometimes referred to as the thermal reserve zone, is where the CO2-C reaction to produce CO, the so-called solution reaction mainly occurs, and die reduction of h on is completed. In the first zone, at the top of the furnace, tire primaty reduction of... 

The indirect environmental impact is carried over into the blast furnace where steel is produced. The slag chemistry and properties must be continually adjusted to drive the coke impurities, as well as impurities from other raw materials, into the slag rather than into the pig iron. The materials added to the blast furnace in order to affect this slag volume, chemistry, and properties must also be melted. Slag components arising from coke impurities create a thermal drain on the blast furnace and occupy furnace volume that could have otherwise contributed to productivity. 

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