(5) Smelting effect The indicators of the 1513m 3 blast furnace are shown in Figure 12. The output of the 55m 3 blast furnace is increased by 7.4% and the coke ratio is reduced by 4.8%.
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(6) Aging and re-recognition After the 1980 test, although the operation indexes and furnace conditions on the large blast furnace reflect the high alkalinity and high MgO sinter and high MgO slag (MgO 8% to 10%), it has obvious superiority. However, due to the small improvement in economic indicators such as coke ratio, the improvement of alkali storage capacity is not fully recognized in the short term, and the production of high alkalinity and high MgO sintering index is worse, the consumption of broken dolomite hammer is increased, and the increase is increased. Sintering cost. At the same time, the blasting of the blast furnace is 5-10mm. The advantages and disadvantages of the blast furnace are not fully balanced. After the industrial test, the blast furnace is still transferred to the official production. The blast furnace still uses the high alkalinity sinter. Anti-tumor measures such as alkali discharge, but the blast furnace still often shows signs of thickening. In the winter of 1982, due to the weather, the difficulty of transporting limestone was forced to replace limestone with a part of dolomite. In fact, high-alkalinity MgO sinter was produced. During this period, the blast furnace operator saw the blast furnace antegrade without signs of nodules. All operational indicators and economic indicators have improved significantly. After careful analysis and discussion, everyone unanimously reaffirmed the role of MgO, and believed that in the case of Baotou Steel, the use of fluorine, potassium, sodium and other harmful elements, the production of high alkalinity high MgO sinter, improve the MgO content in the slag to improve the sinter The performance and slag performance are indispensable for the blast furnace forward and anti-tumor, and obtain good technical and economic indicators. It is then decided to transfer the high alkalinity high MgO sintering process to the official production until now.
(IV) Optimization of sintering and sinter composition of low-fluorine concentrate
1. Experimental study on low-fluorine sintering In the early 1990s, the fluorine ore beneficiation technology made a breakthrough. The fluorine content of iron concentrate decreased from about 2% to less than 1%, and the sintering entered the so-called "low fluorine" stage. . In order to grasp the characteristics of low-fluorine sintering, a comparison of fluorine-containing 1% or less and 1.5% sintering (hereinafter referred to as low-fluorine and medium-fluorine) was carried out in the laboratory.
In terms of process, low fluorine sintering has higher productivity than medium fluorine sintering, and the grade of sintered iron is higher and the drum strength is slightly lower. Low-fluoro-reduced sintered silica, magnesium oxide increases, the variation change alkalinity fluorine and sintered past Fluoride substantially similar. Low fluorine sintering maintains high productivity and drum strength under lower silica conditions. The variation of drum strength of low-fluorine sintered ore with different alkalinity is different from that of high fluorine. The high-fluorine sintered ore is an inflection point at the alkalinity of 1.5 to 1.6, and the strength is lower than 1.5. The low-fluorine sintered ore is a low point at the alkalinity of 1.6, and the strength is increased when the alkalinity is higher than or lower than 1.5, which corresponds to the increase of calcium ferrite and calcium olivine in the mineral phase composition.
In terms of mineral phase, the most change of low-fluorine sinter is that the amount of gunite consisting of calcium fluoride is greatly reduced, while the calcium ferrite is increased in a large amount under the same alkalinity condition, and the vitreous and calcium olivine are obviously increased under low alkalinity. .
The soft-melting and dripping temperature of low-fluorine sintered ore is 30-50 °C higher than that of medium fluorine. Under the condition of low magnesium oxide, a higher reflow temperature can be obtained, and the influence of magnesium oxide is slowed down. In addition, the dripping temperature is greatly increased under high alkalinity, and the soft melt interval is widened, which is an unfavorable factor.
It can be seen from the above test that although low fluorine brings many favorable changes to the sintering, the concentrate still contains a considerable amount of fluorine, and the potassium and sodium contents are not lowered, so that most of the characteristics of the fluorine-containing sintering still exist. In particular, the decrease in strength and the increase in dripping temperature are worthy of further study.
2. Low-silicon sintering test and production In order to suppress the adverse effect of fluorine on sintering, Baotou Steel Sinter has always maintained a high content of 6.8%-7.0% of silica, and it is realized by the method of blending high-silica lean iron ore powder. . Low-fluorinated concentrates offer the potential to reduce silica by sintering. A set of test results show that sinter silica is reduced from 7% to 6% and 5.5%, productivity is reduced by about 3% to 4% and 7%, and sinter iron grade can be increased by 2% and 3%, while sinter The reductibility is significantly improved and the reflow temperature is also improved. Sintering industrial tests and blast furnace smelting tests conducted on the basis of the above tests have achieved satisfactory results. In the 1990s, Baotou Steel's sinter silica remained at 6.2%, and recently dropped to 6% or lower, and the corresponding sinter grade increased by 5% compared with the 1980s.
(5) The application of fluorine-free iron ore in the sintering of fluorine-containing ore is blended into some fluorine-free ore-Australian ore and Hebei iron concentrate, one is to protect rare earth resources, to make up for the shortage of iron ore resources, and the second is to reduce sintering. The potassium and sodium content of the ore and the adverse effects of fluorine inhibition can also improve the iron content of the sinter, which is also an improvement of the fluorine-containing ore sintering technology.
Since the 1980s, Baotou Steel has been intermittently blended with Australian ore powder, a representative test result.
In recent years, some Hebei concentrates were purchased from the Jidong area for sintering, and the results of sintering tests of different Hebei concentrates were compared.
The two kinds of iron ore are blended with fluorine-containing sintering, and in common, the content of potassium, sodium and fluorine in the sintered ore can be reduced proportionally, thereby improving the remelting performance of the sintered ore. Both mines can improve the sintering productivity, and the Australian ore powder is mainly used to increase the sintering vertical velocity, and the effect is obvious. The larger difference is that the Australian ore fine silica is low and suitable for the production of low-silica high-alkalinity sinter; while the Hebei concentrate is generally high in silica, suitable for the production of low-sinter sinter. In addition, the Australian ore powder is hematite, which will increase the sintering fuel consumption, while the Hebei concentrate is magnetite, which can reduce the sintering fuel consumption.
In the production practice, 30% of Hebei concentrate or 15% of Australian ore fines are obtained according to the ratio of sintering ingredients, which is an effective measure to change the characteristics of fluorine-containing sintering. [next]
(VI) Exploration to improve the cold strength of low-fluorine sintered ore 1. Analysis of the causes of particle size reduction of low-fluorine sintered ore Since the early 1990s, the weighted average particle size of the blast furnace into the furnace has become significantly smaller, and the proportion of 10mm has risen sharply. High, the return rate of the sieve under the blast furnace ditch increases exponentially. The trend of the relevant indicators in the past 20 years is shown in Figure 13. The trend of particle size reduction of sintered ore is accompanied by a decrease in the content of fluorine and silica, an increase in iron grade and an increase in sintering productivity. Particle size fragmentation hinders further strengthening of blast furnace smelting, indicating that under new conditions, sinter strength has once again become an important issue. To this end, Baotou Steel and Steel Research Institute, North University of Science and Technology, etc. have conducted joint research.
In recent years, Baosteel has compared with the composition of sinter minerals of major domestic manufacturers. They are all high alkalinity sinter with similar alkalinity. The sintering alkalinity of the coated steel is the highest, but the content of calcium ferrite in the mineral phase is the lowest, but the glass and gun spar are higher.
Beikeda conducted a comparative study on fluorine-containing ore and Shougang concentrates. Tests show that under the same conditions, the formation of calcium ferrite in the fluorine-containing concentrate sintered cake is less and the liquid phase of the glass and crystalline silicate is more, and the sintered cake has more pores and larger pores. The vitreous hardness of the three sintered ores of Baotou Steel, Tangshan Iron and Steel and Anyang was measured by a dimensional microhardness tester, which were 650, 744 and 858, respectively, indicating that the glass fiber strength of the fluorine-containing sintered ore was the lowest. Scanning electron microscopy-energy spectroscopy analysis of the three vitreous components revealed that the biggest difference was that the total amount of potassium and sodium oxide in the fluorite ore was 50% higher than the other two sinter. After research authors believe that:
The more potassium, sodium and fluorine in the fluorine-containing ore make the vitreous formation more likely, and the glass fracture toughness is weakened due to the entry of potassium and sodium, resulting in the glass strength being significantly lower than other minerals.
Since the gun spar is easy to mineralize, it forms more early and captures calcium oxide, so the fluorine-containing sintered ore calcium ferrite is relatively low.
In the fluorine-containing sintered ore, the silicate slag having a low viscosity and a good fluidity is many, and a large number of shrinkage cavities are easily formed, so that there are many pores of the fluorine-containing sintered ore.
These studies illustrate the relatively low strength of low-fluorine sintered ore, suggesting that changing the composition and structure of the sintered mineral remains a fundamental way to increase strength and improve particle size. [next]
2. Process measures to improve the strength of sinter The process measures can increase the sinter drum index to a certain extent and increase the average grain size of the sinter. The thick material layer has obvious technical effects and has been used in production. At present, the thickness of the two sintering workshops is 500mm and 550mm respectively.
Insulation sintering also has a good effect, but it needs to add equipment and consume heat.
Process measures can change the sinter mineral structure and can be used as an auxiliary measure to increase strength.
3. Experimental exploration of low-silicon high-alkalinity sintering Further testing of minerals and structures has focused on the adjustment of alkalinity. The common rule obtained by different tests is that only the alkalinity is increased from the current base to about 2.0, the calcium ferrite in the sinter will increase significantly, the silicates such as vitreous will be significantly reduced, the sinter drum index and the average grain The diameter will increase significantly.
Comparing these test results, the low-silicon high-alkalinity scheme blended with some Australian mineral powders has the advantages of obvious strength effect, large yield increase effect, high grade of sintered ore, and less excess calcium oxide in the blast furnace.
It is selected to add 15% Australian ore powder, sinter SiO 2 or so, and alkalinity 2.0 to 2.2 as an industrial test program. The test was carried out simultaneously in July 1997 in two sintering plants and four blast furnaces. Since many conditions during the test were not stable enough, it ended when the blast furnace failed to enter the stability test period.
The test achieved its intended purpose in terms of sintering. In a period of time, the sinter drum index (>6.3mm) increased by 5%, the sinter mine and the blast furnace into the furnace 10mm part decreased by 7% and 4.52%, respectively, the average size of the sintered ore increased by 0.64mm, blast furnace ditch lower screen The return rate decreased by 6.33%. At the same time, the output of sinter increased The composition of minerals with low silicon and high alkalinity sinter is obviously improved, calcium ferrite increases by 8% to 10%, glass phase decreases by 5%, and calcium ferrite is etched and interwoven. In the metallurgical performance, reduced and low-temperature indicators improved powder sinter test but soft melting permeability tends to deteriorate.
The blast furnace did not achieve the expected results due to the long fluctuation period of the blast furnace caused by the early test and the short period of the test.
Industrial experiments have verified the effect and significance of low silicon and high alkalinity in changing the structure of low-fluorine sinter minerals and improving strength. The inadequacy is that the smelting characteristics of this sinter should be further studied.
(VII) Exploring the improvement of the soft-melt gas permeability of fluorine-containing sinter. The soft-melt gas permeability mentioned here refers to the characteristics of the sinter being heated in the blast furnace, softening during melting, melting, and resistance change during melting and dropping. The most important part of the high temperature metallurgical properties of the mine. This characteristic of fluorine-containing sinter has always been the key to affect the smelting and strengthening of blast furnace. At the low level of production, the low softening temperature is an important cause of blast furnace nodulation. At the high level of blast furnace production, the soft-melt permeability directly affects The air resistance in the middle and lower parts of the blast furnace restricts the air volume and productivity of the blast furnace.
Baotou Steel used the RDL type droplet furnace developed by Northeastern University to measure the soft-melt permeability. The inner diameter of the droplet furnace is 75mm, and the column is heated and reduced under pressure. The softening start temperature t 4 , the softening temperature t 1 0 , the softening end temperature t 40 , the differential pressure steep temperature t s , and the droplets can be measured respectively. The temperature t D , the maximum differential pressure Δp max of the column and the temperature tΔp max at the maximum differential pressure. The device automatically plots the softening and differential pressure curves. t 40 -t 4 is the softening interval and t D -t s is the droplet or melting interval.
1. Comparison of soft smelting permeability of several sinter ore in China. The test curves of soft and melt permeability of Panzhihua Iron and Steel, Baosteel, Shougang, Wuhan Iron and Steel and Baotou Steel Sinter are shown in Figure 12a, b, c, d, e. Compared with the low softening temperature, high softening interval, high maximum pressure difference, high drop temperature and high pressure interval of Baotou Steel sinter, it indicates that the soft sinter permeability of Baotou Steel Sinter is the worst, while Panzhihua Iron and Steel Co., Ltd. Baosteel sinter is relatively good. This difference corresponds to the blast furnace smelting effect of each family. This difference is consistent with the characteristics of many kinds of fluorine-containing iron ore minerals, large difference in melting point, and wide melting range of ore. [next]
2. Experimental study on improving the soft-melt permeability of fluorine-containing sinter. The soft-melt permeability of fluorine-containing sinter in various batching conditions was studied in the laboratory. Some test results are shown in Fig. 14.
Decreasing the potassium and sodium content of the sintered ore at the same alkalinity will significantly increase the sinter t 10 and have less effect on t D and Δp max .
In the fluorine ore sintering, the Hebei concentrate is blended. If the alkalinity is kept constant, t 1 0 can be increased, and t D and Δp max do not change much.
The sinter alkalinity has a great influence on the soft-melt gas permeability (Fig. 12e, f, g). With the change of alkalinity, t 1 0 is the highest among the alkalinity of 1.5 to 1.8%, and the alkalinity is lower than 1.5 and higher than 1.8. t 1 0 were decreased; t D and Δp max increased significantly with increasing alkalinity, alkalinity above 2.0 t D sinter up to 1550 ℃, Δp max up 10000Pa or more, and high differential pressure t D -t s . Wide enough above 250 °C. The problem of poor permeability of high alkalinity sinter soft-melt has been found in the low-silicon high-alkalinity industrial test. It may be the direct cause of the improvement of the grain size of the sinter or the blast furnace but not the blast. The phase analysis of the droplet residue shows that the substance which is difficult to drip by high alkalinity sintering is mainly dicalcium silicate which has a high melting point. On the contrary, the sintered ore having a basicity of 1.5 or less has a low t D , a small differential pressure t D -t s , and a low Δp max , that is, a good soft melt permeability.
According to the above results, combined with the conclusion that the strength of low-fluorine sintered ore will increase below the alkalinity of 1.5, a scheme to improve the soft-melt permeability and take into account the strength of the sintered ore is proposed, that is, 30% of Hebei concentrate is added, and the alkalinity is 1.4. Sinter. After repeated verification by the laboratory, the sintered ore has good soft-melt gas permeability and a certain cold strength, so that it can form a comprehensive iron structure with 20% acidic pellets without any flux. Increasing the ratio by more than 1.5%, the disadvantage is that the sintering productivity and the reduction property of the sinter are slightly lowered.
3. Introduction to industrial test for adjusting sinter alkalinity In July 1999, industrial tests were carried out in a burning workshop and No. 4 blast furnace according to the above scheme. The test work progressed smoothly and some preliminary results have been obtained:
Sintering production achieved the original goal, the iron content of the sinter increased by 2%; the test results of the soft-melt gas permeability were consistent with the test chamber (see Figure 12h); the strength of the sinter drum was not reduced; the sintering productivity decreased slightly, and the blast furnace The furnace particle size has a tendency to deteriorate.
The blast furnace smelting is stable and straightforward. The utilization factor of the test period has reached 1.8t/(m 3 •d). This scheme can achieve good economic benefits only when the ton iron ore ratio and the additional flux and the coke ratio are reduced. The cost of raw materials has increased and the overall economic benefits are still considerable.
Further production adjustments are still in progress as the test work is not yet completed.
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