Preparation and processing of sintered raw materials (4)
Second, crushing and screening
In order to ensure that the particle size of the raw fuel (rich ore concentrate and powder processed by the mine), flux and fuel need to be crushed and sieved in a sintering plant (also rich ore crushing plant powder fed from iron smelting plant). In order to ensure sinter The quality of the raw fuel is very important. For the ore-rich powder, it is generally required to enter the plant with a particle size below 10 mm. It is required to crush the flux and fuel below 3 mm before sintering the ingredients.
The common equipment for crushing flux is hammer crusher , which is combined with vibrating screen as a closed circuit system. The crushing and screening process is shown in Figure 13.
Figure 14 is a particle size curve of a crushed limestone product of a hammer crusher . It is based on the measured data of the 1430×1300 mm reversible hammer crusher of Anshan Iron and Steel Co., Ltd. There are 270 hammerheads, the average gap of the purlins is 18 mm, and the ore size is 40 to 0 mm. As the hammer head wears, the cumulative productivity on the screen gradually increases, that is, the cumulative productivity of the undersize material gradually decreases. For example, the content of <3 mm is reduced from 76.93% (new hammer) to 43.03% (before the replacement of the hammer). Therefore, the hammer must be replaced according to the actual situation. [next]
The gap between the hammer and the purlin has a significant impact on product yield and quality. The smaller the gap, the finer the product size. On the contrary, the larger the gap, the <3 mm content is reduced, and the sieve output is increased and the crushing cycle load is increased. The production practice proves that the high output and good quality can be guaranteed by keeping the gap between the hammer and the abacus at 10-20 mm. The jaws should be adjustable to create conditions for improved product yield and quality and to extend hammer life.
The hammer crusher starts to block when the raw material moisture is large (>3%), which affects the crushing ability and reduces the crushing pass rate.
In order to improve the production and quality of the hammer crusher, Shougang's operating experience is: 1) adjust the feeding amount according to the hammering condition and adjust the clearance between the hammer and the purlin; 2) wear according to the hammer and the purlin In time, the hammer and the conversion bar are reversed; 3) In the case of excessive moisture in the rainy season, the particle size of the incoming material should be appropriately relaxed or the hammerhead should be broken to enlarge the gap of the purlin.
In the crushing and screening system, the screening capacity affects the capacity of the hammer crusher, and the screening capacity is related to the following factors:
1) The effect of the amount of feed. When the conditions are the same, the feed amount is increased, and although the absolute output under the sieve is increased, the screening efficiency is correspondingly reduced. When the screening efficiency is 55 to 70%, high yield and good quality can be maintained.
2) The effect of the size of the mesh. After three tests of 2.6×2.6 mm, 3.6×3.6 mm and 4.8×4.8 mm for the three screens, the product quality of 2.6×2.6 mm is the best, and all the sieves are qualified, but the output is low.3.6×3.6 mm. The product quality and quantity are better than 4.8×4.8 mm. The latter has a coarse mesh and a mesh area of ​​only 79% of the former, so the hole is large and the output is not high.
3) The influence of raw material moisture. Because the sieve hole is small, the water is slightly high to block the net. When the mesh is 3.6 × 3.6 mm and the moisture is about 1.5%, it has higher screening efficiency and higher yield.
4) Sieve width. It is difficult to fill the screen surface with a wide flow, which affects the effective utilization of the screen surface. When the size of the sieved product is fine, the sieve opening is small, and increasing the length of the sieve is advantageous for improving the screening efficiency and increasing the yield. When using a sieve, it is preferred that the aspect ratio is greater than three.
In order to improve the quality of the vibrating screen, the operation should be: 1) adjust the feeding amount of the sieve according to the crushing condition of the hammer crusher, and increase the feeding amount appropriately when the breaking condition is good, and reduce the feeding amount; 2) In order to improve the screening efficiency, the feeding material is required to be evenly distributed on the screen surface; 3) In the rainy season, when the incoming water is large, the screen should be swayed frequently to avoid clogging; 4) Check the screen frequently and find that the damage should be replaced in time. .
Among the equipment for crushing flux, the impact crusher is a highly efficient crusher. Because of its simple structure, high production efficiency, large crushing ratio, and low power consumption per unit of output, it is widely used in sintering plants.
The fuel crushing and screening system has a relatively complete process with pre-screening and two-stage crushing equipment. The fuel crushing and screening system of Anshan Iron and Steel's new three-burning is shown in Figure 15. It consists of a 1800×9375 mm seated double-shaft equal-thickness sieve, a Ф750×1000 mm roll crusher and five sets of 900×700 mm four-roller crushing. Machine composition. The design pre-screens 3 to 0 mm of 40 to 50% of the incoming fuel, uses a four-roller crusher to directly crush 15 to 3 mm of fuel, and uses a pair of rolls instead of a counter crusher to crush >15 mm of fuel. This is to reduce over-grinding and improve the efficiency of the four-roller. The seat type double-axis equal-thickness screen has a front angle of 30°, a middle of 20°, and a rear section of 10°, which is suitable for screening fine-grain fuel. A 4 mm screen is used to reduce screen clogging. In addition, the pre-screening reduces the feed amount of the four-roller crusher, the two-stage crushing reduces the feed size, the number of four-roll crushers decreases, and the crushing power consumption decreases. [next]
The four-roll crusher is a common equipment for crushing fuel. When the feed size is below 25 mm, it can be crushed to less than 3 mm at a time without screening, and the crushing system is relatively simple.
1) The crushing pass rate of the four-roll crusher has a great relationship with the feed amount. In order to ensure the crushing pass rate, the feed amount must be strictly controlled. For the Ф900×700 four-roll crusher, when the feed size is <25 mm and the moisture is below 12%, the feed amount should not exceed 15-18 tons.
2) The pass rate of crushing also depends on the degree of wear of the roll skin. The longer the roll skin is used, the greater the degree of wear and the lower the pass rate. Fig. 16 is a view showing the wear of the roll skin after two months of operation of a No. 2 machine of a sintering plant. The wear gap in the middle of the lower roller reaches 3.6 mm, so even if the two ends are tight to zero, the yield of the broken product can not reach 80 to 90%. Therefore, it is necessary to adhere to the regular car roll skin system. Generally, the roll skin should be applied once every two weeks, and at the same time, the scraper plate should be refurbished.
3) The moisture in the fuel has a great influence on the crushing pass rate. When the water content exceeds 18%, the fuel powder sticks to the roller. At this time, the current is forced to rise, and the roller has to be loosened. Therefore, the particle size of the crushed product becomes coarse, and the yield is lowered.
4) Increasing the feed amount will inevitably increase the current. Although a similar pass rate can be obtained, the current exceeds the rated current of the four-roller, which inevitably causes the equipment to be overloaded, which is unfavorable for the safe operation of the equipment.
Therefore, in order to improve the crushing pass rate of the four-roll crusher, it must be operated according to the design capability of the equipment, and at the same time, the roller must be regularly used to avoid overload and over-current operation.
The disadvantage of the four-roller crusher is that it is difficult to repair.
Since the sintering plant is currently mostly used as fuel anthracite, anthracite coke ratio broken easily broken, and therefore breaking the gradual introduction of the fuel crusher. However, the phenomenon of excessive smashing is serious According to statistics, Anshan Iron and Steel Donganshan Sintering Plant crushed anthracite with a impact crusher, which was 15.65% before crushing and increased to 41.4% after crushing.
In order to ensure the supply of flux and fuel during the rainy season and prevent excessive moisture, a cylindrical silo is built in some factories for one week, and a fuel storage yard with a cover is also established.
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