No abstract

With the introduction of new capacity for the production of fused materials at the Magnesite Combine, a production process has been developed and mastered for producing powders made from fused periclase; tamping masses and articles based on them have been produced for lining the electric smelting furnace aggregates, including induction furnaces for smelting pig iron and steel. The fused periclase powders are made from the highest quality magnesite, e.g., the PPM-96 ) must contain at least 96.5% of MgO,* ~ 1.5% SiO=, and ~ 1.6% Fe203. The choice of batch and the development of the technology for the production of periclase was done after taking into account the requirements laid down in . Normally, for making periclase in accordance with the above specifications, the batch is a sintered powder of fractions 3-0.5 mm, obtained by firing Satkinsk magnesite in shaft furnaces and containing 93-95% MgO, 0.8-1.5% SiO=, 0.i-0.5% AI2Os, 1.5-2.2% Fe203, 1.4-2.1% CaO, and O.i-0.3~ loss on ignition. The batch is fused into a block in OKB-955N ore-smelting furnaces. The smelting process can be divided into three characteristic periods.The first period lasts for 30-120 min and begins as soon as the furnace is switched on and continues until the predetermined current (6.6 kA) is reached when intensive melting of the block begins. The form of the volt--ampere characteristics (Fig. i) indicates that during the first period the furnace operates in a nonarc regime.The second firing period generally lasts for 15-24 h and includes the portional charging of batch and melting of the portions of the powder. In this period the electrodes are raised up, alternating with a short periodic descent in the interval between the charges at moments when the batch under them is effectively melted (Fig. 2). The furnace operates in the arc regime (Fig. la). During this period the main, dense zone of the block is melted; the block cross section is in the shape of a trefoil (Fig. 3) and consists of highest-quality periclase.The third and final firing period is limited to the moment when the tank is completely filled with batch (end of charging) and the furnace is switched off. The furnace is mainly operated with open arcing which is accompanied by significant heat loss and the formation of a conchoidal zone (Fig. 3) in the upper part of the block.Judging from the character of the path of the electrodes (Fig. 2), the rate of melting of the block in the vertical direction when firing in the fifth voltage setting of the transformer (84V) is higher than when firing is carried out in the ninthvoltage setting (70.8 V). The block melted at the ninth voltage setting is found to be slightly more evolved in the horizontal section than the block melted at the fifth setting.The overwhelming majority of firings were carried out at the fifth, ninth, and partly at the seventh (77 V) voltage setting (Table i). With a change from the ninth to the fifth voltage setting, the duration of firing is shortened and furnace productivity is increased. The melting at the first t...

One of the basic conditions for high wear resistance of slide gate periciase plates is a low content of silicon, calcium, iron, and aluminum oxide impurities. Therefore, a study of the influence of the brucite melting cycle and solidification of the molten compound on periclase quality is a pressing one.The transformers of OKB-955 furnaces have nine voltage steps from 105 to 70 V, the current may be varied from 0.6 to 6.6 kA, and the total power from 1050 to 160 kW. The recorded form of the voltage--current characteristic is experimental confirmation of the arc character of electric power liberation in the working volume of the furnace. One portion of the introduced electric power is liberated in the arc (Pa) and the other in the melt (Pm) in passage of the electrical current in it. The arc intensely transmits heat to the charge being loaded and, with melting, the electrodes are lowered to the position providing the specified current. Therefore, movement of the block in the vertical direction, which is determined by the power Pb, occurs.With movement of the block upward the deep-seated molten material releases heat to the material primarily in the horizontal direction. The energy is used for additional melting of the periclase, firing of the crust, and heating and dehydration of the screes. Therefore~ it may be assumed that the power Pm liberated in the melt determines the development of the block in the horizontal direction and an important role in this process is played by circulation flows in the melt and the melting time.In melting with the first step of transformer voltage and a current of 6~ kA, there is a high vertical rate of fusion of the block (time of the process 20-22 h) in which three limited columns of fused material, only directly under the electrodes for the whole height of the furnace and fused to each other only at the level of charging of the bottom, are obtained. In melting with the ninth voltage step and a current of 6.6 kA (time of the process 60-65 h) a block of periclase well developed in the horizontal plane is obtained.The maximum furnace productivity (140-150 kg/h) with the minimum power consumption is obtained in melting with transformer step five and a current of 6.6 kA, when the power introduced into the furnace is divided between Pa and Pm approximately equally. Therefore, the maximum furnace productivity is provided with obtaining of a block with the correct ratio of volumes of fused material in the vertical and horizontal directions. However, with the high rates of fusion of the block using the fifth voltage step, and with the maximum furnace productivity, the impurity oxides are not able to migrate into the center and peripheral portions of the block but solidify in the volume of the periclase in the intergranular areas, thereby having a detrimental effect on its quality. Fusion of the block Magnesite Combine. "Tsentroenergochermet" PTP.

The process of obtaining fused periclase in the block in the OKB-955N furnace involves a high outlay of energy and raw materials. Thus, during the melting of brucite raw materials in an ordinary round bath of diameter 2800 mm the consumption of electric power over a period of about 50 h is approximately 5100 kW-h per ton of finished product, and the consumption of batch amounts to 3.9-4.0 ton per ton of finished product.The raw materials delivered for melting, depending on the heat assimilation of the energy from the electric arcs, undergo a series of sequential changes. A typical feature is that only part of the batch fed into the furnace is subjected to melting, while the remainder plays the role of heat-insulating layers between the melt and the furnace housing, passing through the stages of only heating, dehydration, and slntering. The formation of the insulating layers commences under the action of the energy of the electric arcs and continues on account of the extraction of heat from the melt, in which is separated part of the applied electrical power P , and also on account of the transmission of heat to the material within the deep layers of Pmelt in a horizontal direction [1], During the processes of sintering and dehydration the boundaries of the insulating layers (skin, dust, brucite) are displaced in the direction from the melt to the housing. After a certain time the accumulation of heat by the batch is discontinued, the temperature of the external surface reaches a maximum, and the transfer of heat from the melt becomes stationary; and under these conditions the process of forming the insulating layers is completed, and the following equality is justified:where ~., ~_, and ~b are the thermal conductivity values of the layers of skin, dust, and brua cite, k~/(m.K); Sk, Sd, and Sb, thicknesses of the respective layers, m; tm, temperature of the melt, ~ and tsi, temperature of the start of sintering, ~ tde, temperature of dehydration of the brucite, ~ th, temperature of the external surface of the housing, =C; t u , temperature of the surroundings, eC; a~ coefficient of heat transfer from the housing s rr 2 into the surroundings, kW/(m .K).The equation shows that a reduction in the overall thickness of the insulating layer of batch causes an increase in the capacity for heat transfer from the external surface, and conversely an increase in the heat transfer from the surface of the housing displaces the corresponding layers towards the melt. Moreover, the higher the heat transfer from the external surface, the lower the consumption of heat by the layers of batch between the melt and the housing. Therefore, the main factors influencing the formation of the insulating layers are the total thickness of the layers of batch between the melt and the housing, and the capacity for heat transfer, which in the final account determines the thickness of the sintering part of the batch (skin). In the cross section of the block of the fusing part of the periclase there forms a triangle, and therefore in the ordinary ...