Study on the method of improving the permeability of mixture and the application of conical countercurrent grading granulation technology. The sintering machine of Tangshan Guofeng Ironmaking Plant1997 65438+was put into operation in February. The original design capacity was two 24m2 sintering machines, which were later transformed into a 29.7 m2 sintering machine and a 35.6 m2 sintering machine. Due to the serious shortage of sintering capacity, our factory has been committed to the transformation of mixture granulation process, and has successively implemented technologies such as adding atomized water to the primary mixture, drawing water from the atomized water section of the secondary mixture, and preheating the steam in the mixing bin, which has played a good role in improving the permeability of the mixture. In order to further improve the performance of mixed-mechanism pelletizing, on the basis of long-term brewing research, our factory and Qinhuangdao Xinte Technology Co., Ltd. * * * analyzed the factors to improve the pelletizing of the mixture, and jointly developed the countercurrent graded mixed pelletizing technology which can be applied to the sintering pelletizing industry, and obtained the national patent (029638+0), and achieved obvious results. 2. Improving the granulation mode of mixture Permeability analysis is an important index of sintered mixture, which refers to the difficulty of air passing through the solid loose layer and is also a sign to measure the porosity of mixture. The formula proposed by DW. Mitchell's formula is as follows: in the case of laminar flow: in the case of turbulent flow: where: g- gravitational acceleration ε-porosity η of material layer-gas viscosity coefficient S- specific surface area ρ of material particles-gas density As can be seen from the formula, the main factors affecting the permeability of material layer are specific surface area of material particles and porosity of material layer. In other words, ε should be increased and S should be decreased. The permeability of sinter includes two aspects. One is the air permeability before ignition and the other is the air permeability after ignition. The permeability of sinter determines the efficiency of sintering production. The two are inseparable, and the former affects the latter. It is found from the actual sintering production that the resistance loss between sintering zones is very different. At the initial stage of sintering, because the lower part is too wet, the pellets are destroyed, bonded or blocked, so the resistance of the material layer is large. Although the thickness of preheating zone and drying zone is small, the resistance loss is not small, because the wet ball will be broken and the porosity of the material layer will become smaller when drying and preheating. The gas permeability in the combustion zone is the smallest, because the temperature in this zone is high, there is liquid phase, and the resistance to gas is great. Sintered ore belt has the least resistance because of many pores. However, in the process of intense melting, the sinter has compact structure, few pores and poor permeability. Therefore, it is necessary to improve the permeability of the mixture in sintering production. 2. 1 To improve the granularity and composition of raw materials, coarse-grained materials are mainly used, because coarse-grained materials have large porosity and relatively good air permeability. Adding some rich ore powder or increasing the amount of ore return properly can improve the permeability and increase the sintering output. In the production of tissue sintering, it is beneficial to improve the particle size of raw materials and use coarse and fine raw materials appropriately under possible conditions. However, the possibility of improving the particle size of raw materials is limited, and there are not many 8-0mm mineral powder in actual production, and not all factories have it. 2.2 Adding additives to improve the balling performance of the mixture Adding sticky substances such as hydrated lime, quicklime, bentonite, water glass, sulfite solution, sodium chloride, calcium chloride and humic acid to the sintered mixture has a good effect on improving the air permeability of the sintered mixture. These particle additives are often a kind of surface active substance, which can improve the hydrophilicity of the mixture, and also have gelation in many occasions, so the function of additives can greatly improve the balling performance of the mixture. In sintering production, quicklime and hydrated lime are widely used, especially after quicklime is digested with water, the colloidal particles of hydrated lime have extremely fine particle size. The colloidal particles of Ca(OH)2 distributed in the mixture have obvious colloidal properties and can form a hydrated film with a certain thickness on their surface. Colloidal particles have the characteristics of electric double layer structure. Because these hydrophilic Ca(OH)2 particles widely dispersed in the mixture have much greater water holding capacity than iron ore and other materials, they will catch the ore. Under the laboratory conditions, the influence of the ratio of white to lime on the granulation effect of mixture was studied. Under the same raw material conditions, the air permeability index of the mixture with 3% and 5% white ash was measured respectively. The results are shown in the figure: This shows that the air permeability of the mixture has been greatly improved after the proportion of white ash increases. In order to solve the problem of lime digestion, we conducted experiments on the process of lime digestion. The results show that: 1, curing 1 ton of quicklime requires 0.42 tons of water, and finally the slaked lime is sticky; 2. The slaking time of quicklime is 10- 15 minutes. However, in actual production, it usually takes less than 8 minutes from the batching room to the second stirring, and the digestion of white ash is incomplete. The mixture on the sintering machine has white spots, which is not only unfavorable for pelletizing, but also destructive to the pellets due to the expansion effect of white ash digestion. Therefore, it is necessary to solve the problem of timely digestion of white ash in the sintering process, otherwise it will be counterproductive. 2.3 Traditional Enhanced Mixed Granulation Process Gao Weimin, University of Science and Technology Beijing and others simulated the raw materials and equipment conditions of Angang No.3 Sintering Plant, and conducted experimental research on enhanced granulation in the laboratory. The results show that: 1, under the condition of certain raw materials and equipment, narrowing the outlet of the existing secondary mixer to improve its filling rate is one of the effective measures to improve the mixing amount and material residence time in the mixer. 2. Properly adjusting the rotating speed of the drum mixer, improving the Fr criterion, and making the running point of the mixture in the best area can also obviously improve the pelletizing effect. 3. The average diameter of quasi-particles can be increased by properly reducing the inclination angle of the secondary mixer and further prolonging the granulation time. 4. Water addition is the most basic factor to ensure the granulation effect, including the best water addition, stable water addition and the use of atomized water. According to the requirements of mixed granulation, the use of water supply and atomized water is optimized along the length direction. 5. The lining structure of the drum mixer has a great influence on the movement law and granulation effect of the mixture. Materials with high hydrophobicity and friction coefficient can advance the transition zone from sliding to rolling, which is beneficial to improve the granulation effect. It is also found that the sliding zone of the mixture is very large, and the granulation effect is poor without lining. In addition, the size of ribs in the cylinder is also the key structure that affects the granulation effect of the mixer. No ribs, poor granulation effect; If the rib plate is too high, the bleeding is serious and the granulation effect is not good. Therefore, the improvement of the lining structure of drum mixer is also an important means to strengthen granulation. The above measures have been proved by production practice and achieved obvious results. Different sintering plants should be selected according to their own conditions. 2.4 Cone countercurrent classification cylinder mixed pelletizing technology For many years, engineers and technicians from all over the world have made in-depth research on the advantages of improving the pelletizing effect of the mixture, and achieved gratifying results: a pellet sintering technology characterized by pelletizing disk and adding fuel and a new pellet sintering technology characterized by reducing the angle of the cylinder mixer, adding distribution scraper or retaining ring and melting combustion addition have been developed. In recent two years, the latter has been widely used in domestic sintering plants because of its advantages of not changing the original process configuration and less investment, and has achieved certain results, and China's sintering technology has achieved a new leap. However, the research on the mechanism of mixed pelletizing is limited to traditional methods, such as reducing the inclination angle, increasing the diameter, increasing the length, changing the rotating speed and adding distributors in the machine. Lack of research and application to improve the pelletizing rate of drum mixer by changing the stress state of mixture makes the pelletizing effect of mixing still in an inefficient state, which limits the production efficiency and affects the product quality and consumption. Granulation time, filling rate, mixture properties and suitable mixture moisture are the keys of traditional cylinder mixing technology. The mixed granulation technology of conical counter-current classification cylinder adopts reverse thinking, which was developed by Beijing Airui Machinery Factory and has obtained national patent. The purpose is to provide a conical counter-current classification cylinder mixing granulator. The basic points of this technology are: by changing the internal structure of the mixer and changing the stress state of the mixture, the "pitch" of the mixture movement process can be compressed, the effective pelletizing time can be prolonged, the effective rolling distance of the material can be increased, and the pelletizing effect can be improved; The automatic grading of mixture particle size is realized by using the segmented cone grading technology in the machine, so as to achieve the purpose that large particle materials are discharged first and small particle materials are returned to pelletizing; The new cloth lining technology is adopted, which completely solves the problem of material accumulation at the root of the mixer, realizes the recycling of dead materials in the mixing process, and improves the pelletizing effect and the useful power of the mixer. 3. Pelletizing implementation scheme of mixer in our factory The existing primary mixer in our factory is ∮3×7m, and the secondary mixer is ∮3× 10m. Although the pelletizing transformation has been carried out, the pelletizing effect is still not satisfactory, which seriously affects the output and quality of sinter and restricts the development of ironmaking technology. Based on the above principles, combined with the actual situation that our unit needs to stop production in a short time, the transformation content has been re-formulated and fully implemented within 24 hours. 3. 1 Improve the mixed wetting mode. In the batching room, the mixture is automatically wetted by atomized water in advance. At the same time, a double-shaft quicklime digester with automatic cleaning function is adopted to completely digest the added quicklime and wet the sintered material in advance. 3.2 The optimization of mixer process parameters mainly includes the design adjustment of mixer inclination, filling rate, rotating speed and granulation time. The water in the mixer is changed from the traditional pipe drilling to the columnar flow of water to the newly developed atomizing nozzle to add water to the mixer for atomization. According to the requirements of different areas in the mixer for water addition intensity, the water addition mode of the mixer is changed to three-stage water addition. The secondary mixer is the stage of adding water. 3.3 After the implementation of conical countercurrent grading granulation technology, the raw material properties, mixer speed, diameter, inclination angle and mixer length are determined, which is an important part of mixer granulation. In this technology, a conical counter-current spiral is arranged in the mixer to classify large and small particles, so as to extend the travel of the mixture in the mixer and meet the needs of pelletizing effect. In this transformation, we replaced it with a special composite lining with conical countercurrent characteristics. The construction is simple, and the reconstruction period only takes 36 hours. 3.4 After the transformation, the material moves in the opposite direction with the conical counter-current guide liner. Because the height of the guide groove changes in stages, only materials with appropriate particle size will pass through the guide groove and gradually roll out of the granulator, thus improving the pelletizing quality of the mixer. See table 1 and table 2 for the comparison effect before and after the transformation. Effect comparison table before and after transformation 1 mixture particle size composition% sintering negative pressure kpa machine speed m/min, Output t/ h material layer thickness mm 0-3 3-5 > 51# 2 #1# 2 # before transformation 40 28 32 9.0130.961.212 400 450 after transformation/. Comparison of the effects of kloc-0/511.1.30.50.24 0.2413+60+70 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 59.280.17.1.3581.7 after transformation 76.30 63.886/. 0-2.8-65438+. The air permeability of the mixture is improved, the thickness of two sintering machines is increased, and 1# machine is increased from 400mm to 460mm, and 450mm to 520mm for 2# machine; With the decrease of sintering negative pressure, the utilization coefficient of sintering machine increased from 1.7t/m2h to 1.9t/m2h, with an increase rate of 1 1.76%. 2. After modification, the solid-state reaction of pellets is increased in the sintering process, and the low-temperature thick-bed sintering is realized, and the fuel consumption per ton of sinter is reduced by 12Kg/t, with a reduction rate of 20.7%; The output increased from 2700 tons/day to 3200 tons/day, and the effect was obvious. 3. After transformation, the sinter drum index increased by 65438 0.6%, FeO decreased by 2.8%, and metallurgical properties were improved, which is very beneficial to blast furnace production. 3.5 Calculation of economic benefit 1, based on the sinter tax-included price of 67 1.6 yuan/ton, the cost is 594.37 yuan/ton, the market price is 1 150 yuan/ton, and the annual effective working days are 330 days. Annual income: (65,438+065,438+050-6,765,438+0.6) × (3,200-2,700 )× 330 = 78,936, and the fuel consumption of 700 yuan 2 is reduced by 65,438+02kg/t. 4. The total investment in the transformation process is 6 16700 yuan. After the transformation, it is based on the benefits of our factory 1, 2, 4. Conclusion 1. A series of technical reforms in our factory have achieved great success in view of the poor mixed granulation effect, which have improved the permeability of sintered mixture, increased the thickness of sintered layer, increased the sintering speed, realized the low-temperature thick-bed sintering technology, improved the quality of sintered ore, and achieved great economic benefits. 2. Conical counter-current pelletizing technology is a breakthrough in sintering pelletizing theory, which is simple to implement, suitable for technical transformation of new sintering plants and traditional sintering plants, and has great promotion value.