Structural Improvement Scheme of Fire Channel Wall of Roasters and Application of New Refractory Materials

Roasting is a key process in the production of pre-baked anodes. With the large-scale development of domestic pre-baked anode aluminum electrolytic cells, the optimization of fused aluminum chrome sand aluminum electrolysis process and the continuous advancement of research on anode height in economical pole changing cycle The 550mm narrow material box roasting furnace restricts the production of pre-baked anodes for large aluminum electrolytic cells and economical pole changing cycles, and all face the re-engineered fused aluminum-chromium 85. In this paper, combined with the actual production of pre-baked anodes and the practice of overhauling the fire channel wall of the roaster, the structural optimization of the narrow-box anode roaster designed according to the anode height of 550mm is explored and practiced, and the practical method of structural optimization and transformation of the narrow-box roaster is proposed. Combined application with new refractory materials for fire channel walls.

1. Conditions and plans for renovation

 1.1 Conditions for Retrofit

 (1) Under the user's existing aluminum electrolysis equipment, the ideal pole-changing period of the anode is required to be 32 days or more. According to the requirements of the pole changing cycle, it is calculated that the economic height of the user's slotted anode is 605mm and above, and the corresponding requirement for the width of the roasting furnace material box is ≥740mm.

 (2) The fire channel wall of the roaster has reached the overhaul cycle. Due to the long-term continuous production of the roasting furnace, the fire channel wall has many deformations, and the size of the material box in some furnace chambers has changed greatly, which often causes the anode of the furnace to be damaged and the fire channel wall is squeezed. The serious fire channel wall deformation has affected the The normal production and use of the material box has reached the overhaul period. In recent years, a certain number of fire passage walls have been scheduled for overhaul, and a considerable number of fire passage walls are waiting for overhaul.

 Production of fused aluminum chrome 85

 1.2 Transformation plan

 Considering that the impact on the thermal process due to the change of the inner cavity of the fire channel wall is minimized, the modification implementation plan is determined as follows:

 (1) The width of fireway wall bricks (block components) is changed from 110mm to 100mm.

 (2) The specifications of the fire passage are: length 5246×width 490×height 5440mm; the width of the inner cavity of the fire passage wall is reduced from 310mm to 290mm, and the corresponding cross-sectional area of the inner cavity is reduced by 6.5%.

 (3) The specifications of the material box are: length 5246X width 743X height 5360mm; correspondingly control the thickness of the filling material on the side of the fire channel wall to ≥60mm on one side.

 (4) Adjust and improve the connecting fire passage between the horizontal wall furnace chambers, and add a vertical plug plate sealing device.

 2.2 Combined use of new refractory materials for fire wall

 In addition to the development and application of prefabricated large-size fire channel wall block components, new refractory materials developed by refractory manufacturers in recent years are also selected to improve the heat transfer and thermal insulation performance requirements of the fire channel wall, and significantly improve the radiation transfer in the fire channel. Heat capacity and heat transfer effect, reduce heat loss on the top of the furnace, prolong the service life of the furnace body, improve the air tightness of the observation hole on the top of the furnace, and reduce the heat loss caused by the escape of high-temperature gas.

 2.2.1 Side-fireway refractory bricks with heat storage and heat preservation function

 The fire channel at the side of the anode roasting furnace is generally difficult to control the temperature, the negative pressure of the fire channel during the roasting process is high, the gas supply opening of the burner is large, and the temperature lags behind the middle fire channel. Analysis of the reasons: mainly due to the heat on one side of the side fire channel wall and the high thermal conductivity of the refractory bricks used in the side fire channel wall, the heat energy in the fire channel wall is transferred too fast to the outer wall, resulting in high energy consumption of the side fire channel and high temperature. The failure to keep up with the middle fire channel will affect the balance of the operating temperature between the fire channels in the entire furnace chamber, and it will also greatly restrict the homogeneity of the product.

 The new heat storage and heat preservation refractory brick adopts the design of chimney structure. Features and performance: The difference is that the two sides of the convex groove of the new heat-storage and thermal insulation refractory bricks are equipped with a row of upper and lower through-holes. The upper and lower through-holes are used to reduce the thermal conductivity of the refractory bricks and prevent the rapid transfer of heat energy. The upper and lower through holes of the refractory brick can not only prevent the transfer of heat energy, but also store heat energy and play a role in heat preservation.

 2.2.2 Application of energy-saving furnace top refractories

 (1) Fire channel wall energy-saving furnace roof and double-layer furnace mouth sealing cover

 It is mainly aimed at solving the problems of poor sealing performance of the observation hole of the prefabricated block of the existing fire channel wall, serious air leakage, too high temperature of the furnace surface, and large heat loss. The new type of fire channel wall energy-saving furnace roof and double-layer furnace mouth sealing cover, its characteristics: mainly use two kinds of refractory materials, the upper part is a layer of high-strength semi-light insulation material with a bulk density of 1.6-1.7g/cm3, and the lower part is high-strength and heavy. High quality refractory material, made into composite insulation furnace roof. At the same time, in order to better reduce the heat loss and air leakage at the furnace mouth, the furnace mouth structure is changed to a double-layer sealed furnace mouth cover. After using the refractory material, the sealing performance of the observation hole is greatly improved, the furnace surface temperature is correspondingly reduced, and the furnace moving operation is simpler than the three-piece assembly, which shortens the furnace moving operation time.

 (2) High-strength heat-insulating castable cover bricks and high-temperature far-infrared radiation coatings

 The use of high-strength heat-insulating castable cover plate is an energy-saving measure mainly for the problem that the temperature of the furnace wall is too high and the heat loss is large. The main method is to change the original cover bricks on the upper part of the fireway wall to thermal insulation cover plates made of high-strength and semi-light insulation materials with a bulk density of 1.6-1.7g/cm. , the use temperature is above 1300 ℃.

 A technical feature of the high-strength heat-insulating castable cover plate is that a layer of high-temperature far-infrared radiation energy-saving paint with a thickness of 0.3-1.0mm is applied to the bottom of the cover plate in contact with the flame. The coating is a new high-efficiency, energy-saving and environmentally friendly product for industrial kilns. It can be directly sprayed on the surface of refractory materials of various high-temperature kilns to form a hard ceramic glazed hard shell, which can effectively reflect infrared rays in the furnace. The effect of thermal energy can significantly improve the heat transfer effect in the furnace, reduce the heat dissipation loss of the outer wall, improve the air tightness of the furnace body, and reduce the heat loss caused by the escape of high-temperature gas. At the same time, it can protect the furnace body and prolong the service life of the fire wall.

 (3) High temperature resistant far-infrared radiation coating

 The normal use temperature of high temperature far-infrared radiation coating is ≥1400℃-1600℃, and the use temperature is 1700℃. The coating uses transition group element oxides, zirconia, high-temperature system advanced refractory ultra-fine powder materials, and forms a solid solution through high-temperature doping, which not only increases the energy level of the material's electrons, improves the thermal energy infrared radiation coefficient, but also maintains the corresponding Heat resistance, high strength, strong corrosion resistance, excellent wear resistance, improve the overall strength and compactness of the coating. The incorporation of rare earth element oxides can improve the activity of the reactants and is also the preferred material for doping and stabilizing the coating structure.

 The coating forms a dense ceramic radiation coating on the high-temperature furnace and furnace lining, and improves the heat exchange conditions in the furnace through the infrared radiation of the coating. The combustion temperature and combustion uniformity make the fuel burn more fully, increase the heating efficiency, reduce energy consumption, save energy and prolong the service life of the furnace lining. The service life of the paint coating is 4-5 years, so spray/brush on the original paint coating every 4 years or so to keep the coating in working condition.

 3. Conclusion

 (1) The structure of the fire channel wall of the roaster is improved, so that the width of the charging box is increased from 703mm to 743mm, which solves the problem of economical anode production within a height of 620mm, and can produce high-level anodes that meet the user's economical pole changing cycle of 32 days and above.

 (2) The structural adjustment and improvement of the roasting furnace material box and fire channel wall are arranged in the form of overhaul of the fire channel wall, which avoids the loss of production stoppage of the roasting furnace, ensures the normal product demand and supply of customers, and provides a reference for the expansion and transformation of the narrow material box roasting furnace charging box. path of.

 (3) At present, the use of on-site prefabricated block component fire channel walls has accounted for nearly a quarter of the 34-room roaster fire channel walls. The prefabricated block component fire channel walls used in the earliest have been running for nearly three years, and no Subsidence, bending deformation, etc.

 (4) The prefabricated block components of the fire channel wall digest nearly 50% of the waste bricks of the fire channel wall, which not only reduces the production cost of the prefabricated block components, but also expands a new way for the comprehensive utilization of solid waste.

 (5) Combined use of new refractory materials for the fire channel wall of the roaster can meet the needs of different performances of heat transfer and thermal insulation of the fire channel wall, significantly improve the radiative heat transfer capacity and heat transfer effect in the fire channel, reduce the heat dissipation loss of the furnace top, and prolong the The service life of the furnace body, the improvement of the air tightness of the observation hole on the top of the furnace, and the reduction of heat loss caused by the escape of high-temperature gas have played a good role in reducing the fuel consumption during the roasting process and reducing the heat radiation of the furnace surface operators.