Dolomite dead burned

Dead-burned dolomite is used in the production of refractory bricks, shaped refractories and for monolithic refractories. High purity, low iron dolomite for brickmaking is generally sintered at temperatures of 1800 °C or higher (see section 16.9). A lower purity product (which is often pre-blended with 5 to 10 % of iron oxide to assist sintering) is used for fettling purposes. It is sintered at 1400 to 1600 °C. 

Even after sintering, dolomite is susceptible to hydration and should be protected from undue exposure to atmospheric moisture. Hydration resistance is increased by impregnating the bricks with pitch, resin or tar. 1 to 3 % of zirconia is sometimes added to increase the resistance to thermal shock. 

Dolomite used in the production of refractories should be of high purity and, in particular, should contain less than 0.6 % of Si02 to limit the amount of dicalcium silicate formed in the sintering process, which can cause dusting owing to phase changes [32.2]. 

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Dead-burned dolomite is a specially sintered or double-burned form of dolomitic quicklime which is further stabilized by the addition of iron oxides. Historically, it was used as a refractory for lining steel furnaces, particularly open hearths, but as of this writing is used primarily in making dolomite refractory brick (see Refractories). 

PefractoTy lime is synonymous with dead-burned dolomite, an unreactive dolomitic quicklime, stabilized with iron oxides, that is used primarily for lining refractories of steel furnaces, particularly open hearths. 

Except for dead-burned dolomite, all limes are much more reactive with acids than limestone. The high calcium types are the most reactive. 

In Germany and Japan, pulverized quicklime is used in making self-fluxing sinters, partially replacing limestone. Granular dead-burned dolomite is stiU used to protect the refractory lining of open-hearth and electric furnaces, but not the basic oxygen furnace. Refractory time has declined with the... 

Dead-block coders, 7 691 Dead-burned dolomite, 15 27, 53 Dead-end filtration, 11 388 15 827, 829 Dead end hydrogenation reactor, 10 811, 812... 

Porosity. Part of the porosity of particles of commercial quicklime arises from the porosity of the limestone, and part from the decomposition process. The porosity of conunercially produced quicklime can be as high as 55% (by volume), when a porous limestone is lightly burned. Exposure to elevated temperatures results in sintering (see sections 15.4 and 15.5), which can reduce the porosity to below 25 %. Dead-burned dolomite has a porosity of about 10 %. 

Hardness. Most commercial quicklime products have a hardness of 2 to 3 Mohs. The value for dead-burned dolomite is in the range 3 to 5 Mohs [13.1]. 

The concentration of NOx in the exhaust gases reflects the temperatures in the flame and/or in the kiln. In kilns such as rotaries, the flame influences the NOx level, and a low NOx burner may be used to reduce the NOx level [33.5, 33.6]. Further experience is probably required to asses the effects of such burners on other aspects of kiln operation. Production of dead-burned dolomite in rotary kilns requires temperatures of up to 1900 °C. This results in very high NOx levels (Table 33.2). 

Dead-burned dolomite is a highly sintered form of dolomitic quicklime which is... 

Although pure magnesite decomposes at 700 C and calcite at 900 C, dolime is too porous for most refractory uses. Therefore, prior to use it is calcined at a higher temperature of ca. 1700°C. This harsh treatment allows the material to shrink thoroughly and render it less reactive than calcined dolomite. The product obtained is called dead burned dolomite and is generally used for the refractory made by firing dolomite, with or without additives, at high temperatures to produce dense, well-shrunk particles. 

Industrial applications and uses. Dead burned dolomite exhibits high refractoriness and can withstand temperatures up to 2300 C. It is widely used as a refractory material wherever steel is refined using basic slag. It is used for original hearth installations in open hearth furnaces as well as for hearth maintenance. These hearths are installed using tar-dolomite ramming mixes and rammed dolomite. Dolomite refractories are also used in electrical furnaces and in the cement industry during cHnker manufacture. 

Rotary kilns are couunonly used to produce granular sintered dolomite (dead-burned dolomite) at temperatures >1700°C. This dense product is pressed into brick which are used to line steelmaking vessels and cement kilns. 

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