Research on ways to improve the air permeability of mixtures and application of conical countercurrent graded pelletizing technology 1. Introduction The sintering machine of Tangshan Guofeng Ironmaking Plant was put into operation in December 1997. The original design capacity was 2 24m2 sintering machines machine, and later transformed into a 29.7 m2 sintering machine and a 35.6 m2 sintering machine. Due to the serious shortage of sinter production capacity, our factory has been committed to the transformation of the mixture granulation process. It has implemented a mixture of atomized water, The second-mix atomized water pumping in stages and the mixing silo steam preheating technology have played a good role in improving the air permeability of the mixture. In order to further enhance the granulation performance of the mixer, based on long-term research, our factory and Qinhuangdao Xinte Technology Co., Ltd. jointly analyzed the factors that improve the pelletizing of the mixture and jointly researched and developed a new product that can be used for sintered pellets. The countercurrent graded mixing pelletizing technology in the pellet industry has obtained a national patent (02294526.1) and has achieved remarkable results. 2. Analysis of ways to improve the granulation of mixtures. Air permeability is an important indicator of sintered mixtures. It refers to the ease with which the solid bulk material layer allows air to pass through. It is also a measure of the porosity of the mixture. The formula proposed by DW.Mitchell is as follows: In the case of laminar flow: In the case of turbulent flow: Where: g--gravity acceleration ε--material layer porosity η---gas viscosity coefficient s--material particle specific surface area ρ --Gas density From the formula, the main factors affecting the air permeability of the material layer are the specific surface area of ??the material particles and the porosity of the material layer. That is to say, increase ε and decrease s. The air permeability of sintered materials includes two aspects. One is the breathability before ignition, and the other is the breathability after ignition. The air permeability of sinter material determines the efficiency of sintering production. The two are inseparable, with the former influencing the latter. From the actual production of sintering, it is found that the resistance loss between each sintering zone varies greatly. At the beginning of sintering, the lower part is too wet, which causes the pellets to be damaged, stick to each other or block the pores, so the resistance of the material layer is large. Although the thickness of the preheating zone and the drying zone is small, the resistance loss is also large, because the wet bulb will break when drying and preheating, and the porosity of the material layer will become smaller. The combustion zone has the smallest air permeability. This is because the temperature in this zone is high and there is a liquid phase, which has great resistance to gas. The sinter zone has the least resistance due to its large number of pores. However, when melted strongly, the sinter structure is dense, with few pores and poor air permeability. Therefore, in sintering production, the air permeability of the mixture must be improved. 2.1 To improve the particle size and particle size composition of raw materials, it is mainly to use raw materials with coarser particle sizes, because coarse-grained materials have larger porosity and relatively better air permeability. By adding some rich ore powder or appropriately increasing the amount of returned ore, you can Good results are obtained in improving air permeability and increasing sintering yield. In the production of tissue sintering, it is beneficial to increase the particle size of raw materials and use appropriate combinations of thick and fine raw materials when possible. However, the possibility of increasing the particle size of raw materials is limited. In actual production, there are not many 8-0mm mineral powders, and not all factories have them. 2.2 Add additives to improve the balling performance of the mixture. Add viscous substances such as hydrated lime, quicklime, bentonite, water glass, sulfite solution, sodium chloride, calcium chloride and humic acid substances to the sintered mixture. It has a good effect on improving the air permeability of sintered mixture. These particulate additives are often a surface-active substance, which can improve the hydrophilicity of the mixture and also have gelling properties in many cases. Therefore, the balling performance of the mixture can be greatly improved by the addition of additives. The most commonly used method in sintering production is to add quicklime and slaked lime. Especially after quicklime is digested with water, it becomes extremely fine slaked lime colloidal particles. The Ca(OH)2 colloidal particles distributed in the mixture have obvious colloidal properties. , its surface can form a hydration film of a certain thickness, and the colloidal particles have the characteristics of an electric double layer structure. Because these hydrophilic Ca(OH)2 particles widely dispersed in the mixture have a water-holding capacity much greater than that of iron ore and other materials. , will capture the ore particles and surface moisture, bring these particles close to the slaked lime particles, and generate the necessary capillary force to connect the ore and other materials to form small balls. Under laboratory conditions, we studied the effect of white ash ratio on the granulation effect of the mixture.
Under the same raw material conditions, the air permeability index of the mixture was measured when adding 3 and 5 white ash. The results are as follows: This shows that the air permeability of the mixture is greatly improved after the white ash ratio is increased. In order to solve the problem of white ash digestion, we conducted experiments on the digestion process of quicklime. The research shows that: 1. Digesting one ton of quicklime requires 0.42 tons of water, and the final slaked lime is sticky; 2. The digestion time of quicklime is 10-15 minutes. However, in actual production, it usually takes less than 8 minutes from the batching room to the secondary mixing. The white ash cannot be completely digested, and there are white spots in the mixture when it reaches the sintering machine. Not only is it of little benefit to pelletizing, but the expansion effect of the white ash digestion is detrimental to the pelletizing process. Good balls play a destructive role, so the sintering process must solve the problem of timely digestion of white ash, otherwise it will be counterproductive. 2.3 Traditional enhanced mixed granulation process Gao Weimin of the University of Science and Technology Beijing and others simulated the raw materials and equipment conditions of Angang's new third burner and conducted experimental research on enhanced granulation in the laboratory. The research results show that: 1. Under certain raw material conditions and equipment conditions, the The discharge port of the existing secondary mixer shrinks to increase its filling rate, which not only increases the amount of mixed material in the mixer, but also increases the residence time of the material. It is one of the effective measures to improve the pelletizing effect. 2. Appropriately adjust the rotation speed of the cylinder mixer to increase the Fr accuracy so that the operating point of the mixture is within the optimal area, which can also significantly improve the pelletizing effect. 3. Appropriately reduce the inclination angle of the secondary mixer and further extend the granulation time, which can increase the average diameter of quasi-particles. 4. Water addition is the most basic factor to ensure the granulation effect, including optimal water addition, stable water addition and the use of atomized water. According to the mixing and granulation requirements, the water supply amount and the use of atomized water should be optimized along the length direction. 5. The lining structure of the cylinder mixer has a great influence on the movement pattern and granulation effect of the mixture. Materials with hydrophobicity and large friction coefficient can advance the transition zone of the mixture from sliding to rolling, which is beneficial to improving the granulation effect. The test also found that without lining, the sliding area of ??the mixture was large and the granulation effect was poor. In addition, the size of the ribs in the barrel is also a key structure that affects the granulation effect of the mixer. Without ribs, the granulation effect is poor; if the ribs are too high, leakage will be serious and the granulation effect will be poor. Therefore, the modification of the lining structure of the cylinder mixer is also an important means to strengthen granulation. The above measures have been proven by production practice and have achieved obvious results. Different sintering plants should choose them according to their own conditions. 2.4 For many years, engineers and technicians from all over the world have been conducting in-depth research on the conical countercurrent classified cylinder mixing and pelletizing technology due to its many advantages in improving the granulation effect of the mixture, and have achieved gratifying results: developed The pellet sintering technology is characterized by pelletizing disk and fuel distribution, and the new small pellet sintering technology is characterized by lowering the angle of the cylindrical mixer, adding a cloth scraper or baffle ring, and melting and burning distribution. In the past two years, due to the latter's advantages of not changing the original process configuration and low investment, it has been widely used in existing sintering plants in China, and has achieved certain results. my country's sintering technology has achieved a new leap forward. Despite this, everyone's research on the mechanism of mixed ball making is limited to traditional methods such as reducing the inclination angle, increasing the diameter, increasing the length, changing the rotation speed, and adding a distributor inside the machine. Everyone is interested in changing the stress state of the mixture to improve the performance of the mixture. The pelletizing rate of the cylinder mixer lacks research and application, so the mixing and granulating effect is still in a low-efficiency state, which limits the production efficiency and affects product quality and consumption. Ball making time, filling rate, mixture properties, and appropriate mixture moisture are the keys to traditional cylinder mixing technology. The conical countercurrent graded cylinder mixing and pelletizing technology adopts reverse thinking and was researched and developed by Beijing Airui Machinery Factory and has obtained a national patent. The purpose is to provide a conical countercurrent classification cylinder mixing and pelletizing machine.
The basic points of this technology are: by changing the internal structure of the mixer, the stress state of the mixture is changed to compress the "pitch" of the movement process of the mixture, extend the effective pelletizing time, increase the effective rolling distance of the material, and improve the pelletizing effect; The in-machine segmented cone classification technology is used to realize the automatic classification of the mixed material particle size, so that the large particle materials go out first and the small particle materials return to pelletizing; the new cloth lining technology is used to completely solve the problem of material accumulation at the root of the mixer and realize The recycling of dead materials during the mixing process improves the pelletizing effect and the effective power of the mixer. 3. Our factory’s mixer pelletizing implementation plan. Our factory’s existing primary mixer is ∮3×7m and the secondary mixer is ∮3×10m. Although the pellet sintering modification has been carried out, the pelletizing effect is still not ideal, which seriously affects The output and quality of sinter restrict the development of ironmaking technology. Based on the above principles and the actual situation that our unit needs to stop production for a short period of time, the transformation content was re-formulated and fully implemented within 24 hours. 3.1 Improve the mixing and moistening method. The mixture is automatically moistened with atomized water in the batching room in advance. At the same time, a biaxial quicklime digester with the function of automatically cleaning sticky materials is used to completely digest the added quicklime and moisten the sintered material in advance. . 3.2 Optimize the mixer process parameters, mainly including the design adjustment of the mixer inclination angle, filling rate, rotation speed, and pelletizing time. The water added to the mixer is changed from the traditional pipe drilling and the water flow is columnar to the newly developed atomizing nozzle to add atomized water into the mixer. According to the requirements for water adding intensity in different areas of the mixer, the water adding method of the one-time mixer is changed to three Add water to each section; the secondary mixer adds water to one section. 3.3 Implementation of conical countercurrent classification pelletizing technology After the raw material properties, mixer speed, diameter, tilt angle, and mixer length are determined, this technology is an important part of the mixer granulation. This technology classifies the particle size by setting up a conical counter-flow spiral in the mixer, extending the path of the mixture in the mixer, and meeting the needs of the pelletizing effect. In this transformation, we completed the replacement with a special composite liner with conical counter-flow characteristics. The construction was simple and the transformation period only took 36 hours. 3.4 Effects after the transformation After the transformation, the tapered counterflow guide liner is used to make the material move in the reverse direction. Since the height of the guide groove changes in grades, only materials with suitable particle size can roll out of the pelletizing machine over the guide groove step by step, thus improving the mixing. The ball making quality of the machine. The comparison effect before and after the transformation is shown in Tables 1 and 2 below. Comparison table of effects before and after transformation 1 Mixture particle size composition Sintering negative pressure kpa Machine speed m/min Unit hour output t/unit h Material layer thickness mm 0-3 3-5 >5 1# 2# 1# 2# 1# 2# Before transformation 40 28 32 9.0 13 0.96 1.2 112 400 450 After transformation 13.7 43.2 43.1 8.7 12.5 1.2 1.44 125 460 520 Comparison difference 26.3 15 11.1 0.3 0.5 0.24 0.24 13 60 70 Comparison of effects before and after transformation Table 2 Drum pulverization rate FeO Fuel consumption kg/t Utilization coefficient t/m2.h RDI 6.3 RDI 3.15 RDI-0.5 Before transformation 74.70 59.2 80.1 7.1 11.3 58 1.7 After transformation 76.30 63.4 83.2 7.1 8.5 46 1.9 Comparison difference 1.60 4.2 3.1 0 -2.8 -12 0.2 From Table 1, 2 It can be seen that: 1. After the transformation, the pelletizing effect of the mixer has been significantly improved, and the part less than 3mm has been reduced by 26.3; the air permeability of the mixture has been improved, and the thickness of the material layer of the two sintering machines has been increased. The 1# machine has been increased from 400mm to 460mm, 2 #The machine is increased from 450mm to 520mm; the sintering negative pressure is reduced, and the sintering machine utilization coefficient is increased from 1.7t/m2h to 1.9t/m2h, with an increase of 11.76.
2. After the transformation, the pellet solid-state reaction in the sintering process was added to achieve low-temperature thick layer sintering. The fuel consumption per ton of sinter was reduced by 12Kg/t, with a reduction range of 20.7; the output was increased from 2700t/day to 3200t/day. The effect is obvious. 3. After the transformation, the sinter drum index increased by 1.6, FeO decreased by 2.8, and the metallurgical properties were improved, which is very beneficial to blast furnace production. 3.5 Calculation of economic benefits 1 Calculated based on the tax-included price of sinter ore being 671.6 yuan/ton, the cost being 594.37 yuan/ton, the market price being 1150 yuan/ton, and the annual effective operating days being 330 days, the annual income is: (1150-671.6) × (3200) -2700) The pulverization rate of the sinter transported to the blast furnace was reduced by about 5% after on-site measurement. The total investment in the transformation process was 616,700 yuan. After the transformation, the total of benefits 1, 2, and 4 of our plant was: 278.8 + 7893 .67-61.67=81.118 million yuan. 4 Conclusion 1. The series of technological transformations aimed at the poor mixing and granulation effect of our factory have achieved great success. They have improved the air permeability of the sintered mixture, increased the thickness of the sintered layer, and increased the sintering machine speed, thus achieving low-temperature thick layer sintering. technology, and improved the quality of sinter, with huge economic benefits. 2. Conical countercurrent pelletizing technology is a major breakthrough in the theory of sintering pelletizing. It is easy to implement and suitable for the construction of new sintering plants and the technical transformation of traditional sintering plants. It has great promotion value.