1. Introduction
The sintering machine of Tangshan Guofeng Ironmaking Plant199765438+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 first mixture, pumping water from the second mixed atomized water section, preheating the steam in the mixing bin and so on. 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. Analysis of ways to improve mixture granulation
Permeability is an important index of sintering mixture, which refers to the difficulty of air passing through solid block layer and is also a sign to measure the porosity of mixture. The formula proposed by DW. Mitchell is as follows:
In that case of laminar flow:
In case of turbulence:
Where: g-acceleration of gravity
ε-porosity of material layer
η-gas viscosity coefficient
Specific surface area of s- material particles
ρ-gas density
According to the formula, the main factors affecting the permeability of material layer are the specific surface area of material particles and the porosity of material layer. That is to say, 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 improve the particle size and composition of raw materials.
Coarse-grained raw 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 Add additives to improve the balling performance of the mixture.
Adding sticky substances such as slaked lime, quicklime, bentonite, water glass, sulfite solution, sodium chloride, calcium chloride and humic acid into the sintering mixture has a good effect on improving the permeability of the sintering 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, and the results are as follows:
This shows that the permeability of the mixture is greatly improved after the proportion of white ash increases. In order to solve the problem of lime digestion, we conducted experiments on the digestion process of quicklime. Research shows that:
1, it takes 0.42 tons of water to digest one ton of quicklime, and finally the slaked lime becomes 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 strong mixing granulation process
Gao Weimin, University of Science and Technology Beijing, etc. By simulating the raw materials and equipment conditions of the new No.3 sintering plant in Angang, the experimental study on intensified granulation was carried out in the laboratory. The results show that:
1. Under certain raw material and equipment conditions, narrowing the outlet of the existing secondary mixer to increase its filling rate not only increases the amount of mixed materials in the mixer, but also increases the retention time of materials, which is one of the effective measures to improve the pelletizing effect.
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 conical counter-current classification cylinder mixing granulation technology
For many years, engineers and technicians from all over the world have been deeply studying the advantages of improving the granulation effect of the mixture, and have achieved gratifying results: the pellet sintering technology characterized by pelletizing disc and fuel addition, and the 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. I plant mixer granulation implementation plan
The existing primary mixer in our factory is ∮3×7m, and the secondary mixer is ∮3× 10m. Although the pelletizing is reformed, the pelletizing effect is still not ideal, 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
The mixture is automatically wetted in advance with atomized water in the batching room, and at the same time, a double-shaft quicklime digester with the function of automatically cleaning sticky materials is used, so that the added quicklime is completely digested and the sintered material is wetted in advance.
3.2 Optimize the process parameters of the mixer.
It 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 Implement conical countercurrent grading granulation technology.
After determining the properties of raw materials, the speed, diameter, inclination and length of mixer, this technology 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 the effect of the transformation
After the transformation, the conical counter-current guide liner is used to make the material move in the opposite direction. Because the height of the guide groove changes step by step, only materials with suitable particle size can pass through the guide groove step by step and roll out of the granulator.
So as to improve the pelletizing quality of the mixer. See table 1 and table 2 for the comparison effect before and after the transformation.
Comparison table of effects before and after transformation 1
Sintering negative pressure of mixture particle size composition percentage
Kpa machine speed
Meter/minute output per hour
T/ h layer thickness
millimetre
0-3 3-5 >5 1# 2# 1# 2# 1# 2#
Before transformation, 40 28 32 9.0130.961.2112 400 450.
After transformation,13.7 43.2 43.18.712.51.21.44125 460 520.
The contrast difference is 26.3151.1.30.50.2413+60+70.
Comparison of effects before and after transformation Table 2
Drum% crushing rate% FeO% fuel consumption
Kg/t utilization rate
coefficient
Ton/m2. hour
RDI+6.3 RDI+3. 15 RDI-0.5
Before the renovation, 74.70 59.280.17.1.1.3581.7.
After transformation, 76.30 63.4 83.27.18.5461.9
Contrast difference1.604.23.10-2.8-120.2
As can be seen from table 1 and table 2:
1, after modification, the pelletizing effect of the mixer is obviously improved, and the part less than 3mm is reduced by 26.3%; The permeability of the mixture is improved, the thickness of two sintering machines is increased, and the 1# machine is increased from 400mm to 460mm, and the 450mm to 520mm for the 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 Benefits
1 If the tax-included price of sinter is 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, the annual income is:
(1150-671.6) × (3200-2700 )× 330 = 78.9367 million yuan.
2 Reduce fuel consumption 12Kg/t and 220 yuan /t of coke powder, and the annual benefits of reducing fuel consumption are as follows:
12× 3200× 330× 220 = 2.788 million yuan.
The improvement of pelletizing effect reduces the pulverization rate of sinter transported to blast furnace, which is reduced by about 5% by field measurement
The total investment in the transformation process is 6 1.67 million yuan. After the transformation, according to the benefit of our factory, the total amount is 278.8+7893.67-61.67 = 811.8 million yuan.
4 conclusion
1, aiming at the problem of poor mixed granulation effect in our factory, a series of technical transformations have been carried out, which have achieved great success, improved the permeability of sintered mixture, increased the thickness of sintered layer and increased the sintering speed, thus realizing the low-temperature thick-bed sintering technology, improving the quality of sintered ore and having 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.