Dolomite tar-impregnated refractories with a ceramic bond

Abstract

One of the most important causes of the low life of periclase chromite linings in the sintering zone of rotary kilns used to fire Portland cement clinker is the increase in their diameter.Thus, an increase in furnace diameter from3.2-4m to 5.6-6.4 m when all other conditions were the same led to a reduction in the service life by a factor of 2-3 and accordingly to a sharp reduction in the efficiency factor of the furnace, a rise in the specific consumption of refractories, and a fall in the output of Portland cement clinker.It became necessary to develop a technology for producing new types of magnesia refractories which will ensure at least a doubling of the furnace life for large-diameter furnaces.The linings of large-diameter furnaces abroad [i] are being effectively made from dolomite tarred refractories with a ceramic bond.It is noted that these refractories are clinker resistant and have outstanding physical and ceramic properties.High-purity dolomites are used to make dolomite refractories that are ceramically bonded. The large stocks of dolomites in our country with low contents of mineral impurities, meeting the requirements of raw materials for the production of dolomite refractories, make their output highly promising and desirable.The organization of the manufacture of such goods will also lead to a considerable reduction (by 100,000-200,000 tons) in the consumption of periclase powder and the exclusion of ineffective utilization of large amounts of chromite ores.The use of dolomite tarred refractories with a ceramic bond is also prospective for steel-melting production.For the development of the main technical parameters of dolomite tarred ceramic bonded refractories we selected five samples from dolomites taken from 83 deposits: Kvarkensk, Bosninsk, Lis'egorsk, Kuzinsk, and Tkvarchel'sk. These dolomites have a low (not more than 2%) concentration of impurity oxides (Table i); their deposits are situated in regions not far from the main centers of the cement and metallurgical industries and close to iron ores. As a result of petrographic analysis it was found that the samples investigated consist of dolomite with inclusions of calcite. The sizes of the crystals, the open porosity and the mass proportion of calcite are shown in Table 2.

Dolomía y dolomita: un abordaje desde las perspectivas geológica, cerámica y refractaria

“…Algunos autores exponen que una de las causas principales de la baja sinterabilidad de la dolomía es una elevada porosidad. Savchenko et al (1985) demostraron que esta proposición no siempre es verdadera, sino que el tamaño de partícula juega un rol preponderante (Tabla 2).…”

Temporary preservative binders for lime and lime-periclase refractories

“…The specific volume of portlandite is 1.5 times greater than that of CaO. The crystallization pressure of portlandite causes cracking and fracture of articles in storage or in the course of firing at 900 -1000 K. Consequently, the use of high-strength binders such as the basic processing binder for refractories (BPBR) [3,5,6] does not guarantee that the articles will be intact after molding and firing, because the physically bound water remains in the article and binder components containing [OH-] groups react with CaO and form portlandite [4,7].These facts imply that the development of temporary binders for refractories containing CaO should be based on the following considerations:-the temporary binder should contain a hydrophobic plasticizing component, which should protect CaO from contact with atmospheric moisture, have sufficient strength and plasticity, and be ecologically safe; on the one hand be insoluble in water and on the other hand suit the plasticizer; -at a minimum content of the temporary binder it should mix well with CaO particles and wet them properly without foaming, i.e., it should contain a surface active substance in an amount of 0.1 -1.0%; -the temperature of the beginning of intense decomposition or evaporation of the binder should be at least 700 K, when the equilibrium CaO + H20 ~:~ Ca(OH)2 is already strongly shifted to the left; -the processes of removal of physically bound water and the water formed in the interaction of CaO and Ca(OH)2 with the binder components should be completely finished during the preparation, mixing, and soaking; this determines the duration of mixing or soaking at a temperature of at least 380 -400 K. The upper temperature is limited by the beginning of intense evaporation and decomposition of the binder constituents.Even impure higher alkanes (from ceresin to petrolatum) can be a suitable least toxic and most available hydrophobic plasticizer having sufficient strength and thermal stability. Since CaO is a strong base with respect to a large number of substances, the choice of the second component of the binder is determined by the hydrophobicity, thermal stability, and minimum solubility of its calcium salts in water.…”