Clinker for high-alumina cement is burnt in some countries, for example in Poland, in rotary kilns using the wet method of calcination.In the USSR the less energy-consuming dry method is used with pelletization (granulation) of the raw mixtures in a plate granulator [i, 2]. The main advantages of the rotary kilns are the possibility of mechanization and ensuring uniform calcination cf the cement clinker. However, with a low strength in the granules during firing dust removal is possible which reduces the cost-benefit factors of the equipment, complicates its operation, and impairs the environmental conditions of the plant. Considering this, we investigated the preparation of hlgh-alumina clinker in rotary kilns using two methods of preparing the raw mixtures: granulation in a plate granulator and briqueting on a roller press. In order to evaluate their effectiveness we used the level of the dust removal in the firing process.In compiling the batches we used alumina specified by GOST 6912-74 with mass proportions of more than 99% A1203, and limestone from the Uglovsk deposits, characterized by the following concentrations of oxides in an average sample (mass, %): CaO 52.4, Si02 3.4, Al2Os 1.8, Fe203 0.2, MgO 0.3, K20 0.04, NazO 0.4; Amcalc 41.6%. The limestone milled to 1.5-0 mm and the alumina were mixed and fed to the tube mill to obtain a combined-grind mixture. The mixture contained not more than 5% fractions plus 0.088 mm.The finely milled mixture was moistened in the mixing runner mills with a water solution of sulfite lye and then fed to the roller presses with a tooth-rachet bandage attachment for preparing the pellets of oval shape and measuring 40 • 30 x 25 mm, or into the plate granulator to obtain the granules with diameters of not more than 30 mm. The production technology for the briquets and granules and their properties were described in [3].The size of the granules obtained on the granulator was regulated by moistening the body. The average grain-size composition of the granules was: 9.5% fractions plus 25 ran, 16.1% 25-20 mm, 72.9% 20-10 mm, 1.5% minus l0 mm. The raw granules did not break when dropped from a height of 5 m, The pelletized and granulated mixtures were dried in natural conditions. The average moisture content and loss on ignition of the materials loaded into the kiln were, respectively, 8.9 and 20.8% (for pellets) and 3.9 and 23.2% for granules.The clinker was fired in a 15-m rotary kiln at the experimental-technology section of the All-Union Institute of Refractories. The working factors are shown in Table i. As a result of the material balance~ .determined during the firing, we established the levels of dust removal, which amounted to 4% for briquetted and 33% for granulated mixtures. The significant difference in dust-removal levels completely corresponds to the visual picture of the process. Thus, during the firing of the brlquetted mixture the kiln space was clean, the briquet (pellet) left the furnace whole and kept its shape. During firing of the granules we observed signif...
Firing of high-alumina cement clinker in a shaft kiln is promising from the point of view of economy and also mechanization and automation of the production operation.The mixture of original materials for production of the clinker is fired in the shaft kiln in the form of briquettes or granules preserving their wholeness under the mechanical loads occurring in heat treatment. Three variations of preparation of the raw material mixture were studied, with the use of a disk granulator and friction and roll presses.The clinker is produced from G-00 commercial alumina to GOST 6912--74 and Uglovka deposit limestone with weight %'s of oxides in the mean sample of 52.42 CaO, 3.45 SiO=, 1.81 A1203, 0.17 Fe203, 0.30 MgO, 0.04 K20, and 0.36 Na20 and Amcalc = 41.61%.The limestone was ground in a jaw crusher (<40 mm), dried in a drying drum to a moisture content of 1% max,, ground in a ball mill to a grain size of 1.5 mm max., loaded into a tube mill together with the alumina in a weight ratio of 35:65, and ground until obtaining not less than 95% of the finer than 0,088-mm fraction, Granulation and Investigation of the Granules.The mixture of original materials was granulated in a disk granulator with a disk diameter of I m and a height of the rim of 130 mm with a rate of rotation of 14 rpm. The optimum angle of slope of the disk to the horizontal in obtaining granules with a diameter up to 60 mm was 40 ~ The desirability of adding to it a sulfite-yeast mash soiution to a moisture content of 7-8% before placing the charge in the granulator was established.The charge was moistened in mixing mills with rotating cups and raised rolls and embryos of granules up to 5-8 mm in diameter were formed, which increased the granulation rate. The mixture was delivered by a bucket to the feeder, from which it was fed to the granulator, where it was additionally moistened with sulfite-yeast mash with a density of i.i0-I.12 g/cm ~ to a moisture content of 18-19%.The quantity of 30-60-mm-diameter pellets was not less than 75% and of less than 20 mm up to 7%. The apparent density of the moist granules varied within limits of 2.15-2.24 g/ cm 3. Such granules withstood dropping from a height of 5 m without failure and only deformation of them was observed.Firing of the granulated materials in a shaft kiln was preceded by laboratory investigations of the processes occurring in heat treatment of the mixture of original materials and of the physicomechanical properties of the granules. The changes occurring in a charge containing 35% limestone and 65% alumina and sulfite-yeast mash as a binder are shown in Fig. i. In heating of the mixture to I080~ a 24.50% decrease in specimen weight is observed. This process occurs most intensely in the three temperature ranges I00-150~ (2.25%), 220-480~ (7.00%), and 650-810~ (12.25%). An exothermal effect with a maximum at 330~ corresponds to temperatures of 220-480~ on the DTA curve and an endothermal effect with an extreme at 795~ to the 650-810~ range (Fig. i), The results obtained may be explained by the lib...
The largest unit in the world for stream vacuum degassing of steel with teeming in a Progress continuous casting machine has been installed and placed in use in No. 2 Oxygen Converter Shop of Novolipetsk Metallurgical Combine [i, 2].In the "Progress" unit the processes of stream vacuum degassing and continuous casting of steel melted in 350-ton converters are rationally combined. The principle of its action is chown schematically in Fig. i. The metal from the steel teeming ladle I enters the vacuum chamber 2 where under the action of the vacuum degassing and refining of both the open stream and of the layer of metal on the bottom of the chamber occurs. The metal treated in the vacuum passes through the tube 3 into the pony ladle 4 and then into the mold 5 of the continuous casting machine.The advantage of such a process of vacuum degassing over batch, circulation, or ladle type units used at present is the universality and teh reduction in the time of the steel in the steel teeming ladle, which eliminates the necessity of superheating of it in the steel melting furnace. This also reduces the interaction of the metal being degassed with the ladle lining and secondary impregnation of the metal by gases during teeming.Before building at Novolipetsk Metallurgical Combine of Zhe unit for vacuum degassing of steel experience in the creation of a production lining for degassing of converter steel in equipment of this type was lacking. This article presents the results of investigations on selection of the most resistant refractories in vacuum degassing steels primarily of types 08Yu, 08GSYuT, 03KhGYu, 08ps, 06KhGSYu, etc.The temperature of the molten metal before vacuum degassing varies within limits of 1570-1600~ the rate of teeming is 0.8-0.9 m/min, and the time for teeming a single heat is 70-85 min. The protective slag in the pony ladle in contact with the outer lining of the tube is characterized by a comparatively low basicity and a high aluminum oxide content. A typical oxide content in the slag in wt.% is 23. 6-24.2 CaO, 20.1-22.7 SiO2, 35.5-39.9 A1203, 3.9-5.9 Fe203, 2.0-3.6 MgO, 7.1-8.9 MnO, and 0.7-0.9 TiO 2.The outer lining of the tube was made of MKN-94 hydraulically hardening corundum compound to Technical Specification 14-8-359-80 produced by Borovichi Refractory Combine.For the purpose of selection of the most wear resistant variation of the inner lining of the tube and of the vacuum chamber comparative tests were made in these zones of refractories of corundum and magnesia compositions. The inner lining of hte tube was made of refractory rings and the working lining of the bottom and the walls of the vacuum chamber was laid of straight and trapezoidal brick, respectively.
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