Pellet screening and distributing system optimization method

Abstract

The invention discloses a pellet screening and distributing system optimization method which comprises the following steps that a pellet screening and distributing system comprises a swing type distributing machine, a large ball screen roller and a small ball screen roller, the swing frequency of the swing type distributing machine is controlled to be 8 rounds per minute through segmented frequency conversion control, the material level tends to be gentle, the whole material level is in the condition that the east is thick and the west is thin, and the pellet screening and distributing system is obtained. The material level angle is 10-15 degrees, the swing area moves towards the west side by a certain distance, the small ball screen roller spacing is adjusted to be 12 mm, and the large ball screen roller spacing is adjusted to be 18 mm. The method has the beneficial effects that the optimal screening and distributing process parameters are obtained by adjusting the swing frequency and the swing area of the swing type distributing machine and the distance and the distribution of the screen rollers of the large and small ball screen, the quality of finished pellets is remarkably improved, the average compressive strength reaches 2300 N or above, the swing type distributing procedure and the process parameters of large and small ball screening are optimized, and the production cost is reduced. And moreover, the output of the powder balls is reduced by 33% at a lower cost, and better economic benefits and social benefits are obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of pellet production, and particularly to an optimization method for the screening and feeding system of pellets. Background Art

[0002] In recent years, with the transformation of iron and steel enterprises towards refined production, energy conservation and emission reduction. As one of the main raw materials for iron and steel production, pellets have advantages such as high grade and environmental friendliness, and the quality of pellets directly affects the operation efficiency of blast furnaces and the product quality. Therefore, iron and steel enterprises have more realized the importance of increasing the ratio of pellets charged into the furnace to improve the burden structure of blast furnaces. This means that there will be higher requirements for the compressive strength, particle size and sphericity uniformity of pellets, and the effect of green pellets in the screening and feeding stage has an extremely important impact on the above parameters. Generally, in pellet plants, the screening and feeding effect of green pellets is not good, the flatness of the green pellet material surface on the traveling grate is unreasonable, or it is in the form of a "concave" surface, or in the form of a "convex" surface, or the inclination angle on one side is too large, resulting in uneven drying and soaking of green pellets and affecting the quality of pellets.

[0003] Regarding the improvement of the screening and feeding system, many enterprises have made unremitting explorations in this regard in recent years. For example, the pellet plant of a certain company adopts the roasting process of traveling grate - rotary kiln - annular cooler, and its green pellet screening and feeding system consists of a swing belt, a large ball roller screen, a wide belt and a roller feeder. When the system is working normally, 75 screen rollers roll simultaneously. Once a screen roller is damaged, the entire system must be shut down for maintenance, affecting the smooth operation of the production line. By improving the electrical start - stop control mode of the screen rollers, dividing the screen rollers into three groups for separate control, it is possible to perform maintenance without shutting down the machine when some screen rollers are damaged, improving the continuity and stability of the production line. The pellet production line of a certain company adopts the technology of large roller screen - shuttle feeder - wide belt - small roller screen. This system has problems such as uneven distribution of green pellets on the wide belt and uneven green pellets on the traveling grate of the traveling grate, resulting in uneven heating of green pellets and affecting the quality of pellets. By adding a cloth deviation balance disk on the large roller screen and adjusting the angle of the wide belt and other measures, the cloth uniformity is effectively improved and the quality of pellets is increased. However, there are few reports on the improvement of the screening system composed of a pendulum feeder - large and small ball screens.

[0004] For example, Chinese Utility Model Patent Publication No. CN216094821U discloses a pellet powder screener, which includes a pellet discharge chute arranged below the side of the finished product belt and a support frame for supporting the pellet discharge chute. A grate is arranged at the bottom end of the middle part of the pellet discharge chute; the grate is made of round steel, fixed on both sides by angle steel, and fixed on the bottom of the pellet discharge chute by perforated channel steel on the upper and lower sides with screws.

[0005] For another example, Chinese Utility Model Patent Publication No. CN218854838U discloses a green pellet screening device, including a fixed bottom plate. A screening mesh 3 for screening green pellets is arranged on the top of the fixed platform. A vibration assembly for improving the screening effect is arranged at the bottom of the screening mesh 3. The head of the cam driven by the motor continuously strikes the bottom of the receiving frame, causing the receiving frame to lift its own height. After the receiving frame is forced to rise, the sliding rod moves and drives the bottom telescopic spring to elongate. As the cam continues to rotate, the head of the cam moves away from the receiving frame. At this moment, under the fixing of the elastic force of the telescopic spring, the receiving frame will quickly descend, repeating in a cycle to generate vibration.

[0006] The above patents all improve the screening efficiency by setting a vibration assembly or a grate, without systematically considering the influence of unilateral air extraction in the PH section of the traveling grate, thus not considering how to solve the problems of uneven green pellet surface and uneven heat absorption from a systematic perspective; nor do they involve controlling the flatness of the green pellet surface through segmented variable-frequency control technology. Summary of the Invention

[0007] The technical problem to be solved by the present invention is that the existing screening system will cause uneven green pellet surface and uneven heat absorption. Therefore, an optimization method for the screening and feeding system of green pellets is provided.

[0008] The technical solution of the present invention is: an optimization method for the screening and feeding system of green pellets, including the following steps: The screening and feeding system of green pellets includes a pendulum feeder, a large ball screening roller, and a small ball screening roller. By segmented variable-frequency control, the pendulum frequency of the pendulum feeder is controlled at 8 reciprocations per minute, making the material surface tend to be flat, presenting a situation of thicker in the east and thinner in the west, with the material surface angle being 10° - 15°, and the swinging area moving a certain distance westward. The distance between the small ball screening rollers is adjusted to 12 mm, and the distance between the large ball screening rollers is adjusted to 18 mm.

[0009] In the above solution, the swinging area moves 6 cm westward.

[0010] In the above solution, the small ball screening roller includes 10 cloth rollers and 37 screening rollers.

[0011] In the above solution, the large ball screening roller includes 5 cloth rollers and 22 screening rollers.

[0012] The beneficial effect of the present invention is that by adjusting the swinging frequency, swinging area, and the distance and distribution of the large and small ball screening rollers of the pendulum feeder, the optimal screening and feeding process parameters are obtained, significantly improving the quality of the finished green pellets. The average compressive strength reaches more than 2300N. It not only optimizes the process parameters of the pendulum feeding process and the large and small ball screening, but also reduces the production of powder balls by 33% at a lower cost, achieving good economic and social benefits, meeting the expected goals, and providing a favorable reference for the refined production and energy conservation and emission reduction of iron and steel enterprises. Description of the Drawings

[0013] Figure 1 It shows the change in the average compressive strength of pellet ore for ten consecutive days after adjusting the roller spacing in the present invention; Figure 2 It shows the change in the average compressive strength of pellet ore for ten consecutive days after adjusting the distribution of sieve rollers in the present invention; Figure 3 It is the layout diagram of the proximity sensors of the pendulum type distributing machine with segmented variable frequency control in the present invention; In the figure, 1 is the motor, 2 is the proximity sensor, 3 is the disc, 4 is the rocker arm, and 5 is the pendulum type distributing machine. Detailed Embodiment

[0014] Next, in conjunction with the drawings, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0015] The equipment involved in the present invention includes a pendulum type distributing machine, a 27-roller large ball roller type screening machine, and a 47-roller small ball sieve type screening machine, all of which are manufactured by Beijing Jindu Metallurgical Machinery Factory.

[0016] A 1.2 million-ton pellet project of a certain company uses sulfuric acid residue and iron concentrate produced by acid making as raw materials, and adopts the grate-kiln process to produce high-quality furnace charge for blast furnace smelting - acidic oxidized pellet ore. The main components and metallurgical properties of the pellet ore are shown in Tables 1 and 2.

[0017]

[0018]

[0019] As can be seen from Tables 1 and 2, for the pellet ore fired from sulfuric acid residue, its total iron grade is above 62%, and the remaining indexes are FeO≤1%, S≤0.06%, P≤0.04%, basically meeting the requirements of industrial production. At the same time, the reduction expansion rate, reduction degree, and low-temperature reduction degradation rate of the pellet ore are analyzed. Its reduction expansion rate is below 20%, belonging to the normal expansion range, the low-temperature reduction degradation rate is relatively low, and the reduction degree is above 60%.

[0020] Based on the problems of unreasonable flatness of the charging surface of the green balls on the grate and uneven heating, the present invention proposes to optimize and transform the sieve distribution and feeding system. By respectively adjusting the swing frequency, swing area of the pendulum type distributing machine, and the sieve roller spacing and sieve roller distribution of the large and small ball sieves, the change of the green ball charging surface and the change of the quality of the finished pellet ore are observed to obtain the best sieve distribution and feeding process parameters.

[0021] 1. Influence of the swing area Combined with the single-sided air extraction on the west side of the pH section of the grate-kiln, compared with the west side, the heat distribution on the east side is not uniform, and the production of powder balls remains high. Therefore, in the present invention, the swing area of the pendulum feeder is adjusted to move it to the west side, and the changes in the shape of the material surface and the average production of powder balls in pellet ore are observed, as shown in Table 3.

[0022]

[0023] As can be seen from Table 3, when the swing frequency is 9 swings / minute, 10 swings / minute, and 11 swings / minute, the swing frequency of the pendulum feeder is relatively high, and the green balls converge to both sides, resulting in an uneven concave shape of the material layer on the cloth surface, which in turn causes uneven heating of the green balls during the drying stage, and finally powder balls appear during the roasting in the rotary kiln. When the swing frequency drops below 9 swings / minute, the production of powder balls decreases significantly, and the surface of the green ball material tends to be flat but tilts to the east side. And when the swing frequency drops to 7, the thickness of the material layer increases, the surface layer is not fully dried, and the production of powder balls increases instead. Therefore, it is more appropriate to control the swing frequency of the pendulum feeder at 8 swings / minute.

[0024] 2. Influence of the spacing between the screening rollers of the large and small ball screens The influence of the spacing between the screening rollers of the large and small ball screens on pellet ore is mainly reflected in the influence on the quality of green balls and production efficiency. A reasonable spacing between the screening rollers can ensure the uniform screening of green balls, prevent small balls and unformed materials from entering the furnace, and improve the quality of green balls and production efficiency.

[0025] According to the actual production requirements of the enterprise, the average compressive strength of iron pellets greater than 2200 N is a qualified product. Currently, the particle size of the balls controlled by the spacing between the screening rollers of the large and small ball screens is 8 mm - 16 mm. The compressive strength of pellet ore with different particle sizes in actual production is shown in Table 5. When the particle size of the pellet ore is less than 12 mm, the average compressive strength is difficult to reach 2200 N. Therefore, in the experiment, the spacing between the screening rollers of the large and small ball screens is adjusted to 12 mm for the small ball screen and 18 mm for the large ball screen, and the particle size range of the green balls is controlled at 12 mm - 18 mm. The sampling and observation results for 10 consecutive days are as Figure 1 shown.

[0026]

[0027] 3. Influence of the distribution of the screening rollers The main function of the distribution of the small ball sieve rollers is to ensure the uniform distribution of green balls during the screening process, improving the screening efficiency and output. A reasonable distribution of sieve rollers can prevent segregation, missed screening, or blockage of materials during the screening process, ensuring the uniform movement of green balls on the sieve surface, improving the screening accuracy and the stability of product quality. At the same time, it can extend the service life of the equipment, reduce the maintenance frequency and cost. The current distribution of sieve rollers is 8 feeding rollers and 39 screening rollers, enabling the green balls to be screened by 39 screening rollers and then evenly distributed by 8 feeding rollers before entering the traveling grate. Although the average compressive strength of the finished pellet ore is greater than 2200 N, meeting the production requirements, the overall compressive strength trend still fluctuates around 2200 N. To make the quality of pellet ore more stable, the distribution of sieve rollers was re-adjusted in the experiment to 10 feeding rollers and 37 screening rollers, maintaining the stability of the green balls before entering the traveling grate in advance, and continuously sampling and observing the change in the average compressive strength of the finished pellet ore for 10 days. The results are as Figure 2 shown.

[0028] As Figure 2 can be seen, after the re-adjustment of the sieve roller distribution, the average compressive strength of the overall pellet ore has been significantly improved, all above 2300 N. The number of feeding rollers increased from the original 8 to 10, enabling the green balls to be evenly distributed before entering the traveling grate, allowing the balls to be heated evenly and sufficiently during the drying stage, thus greatly ensuring the quality of pellet ore.

[0029] 4. Influence of the swing frequency The function of the pendulum type feeder 5 in the production of iron pellets is to evenly, flatly, and loosely distribute the green balls on the traveling grate to improve the air permeability of the material layer and obtain good drying conditions. The pendulum type feeder includes a swing arm 4, a disc 3, a motor 1, and four proximity sensors 2, which are distributed in the four quadrants of the disc. The use of the pendulum type feeder can improve the quality of green balls, providing favorable conditions for achieving high-quality and high-yield drying operations. The swing frequency of the pendulum type feeder plays a crucial role in the screening process of green balls. An excessively high swing frequency will cause the green balls to be squeezed and deformed during movement, affecting the air permeability and spherical uniformity of the material layer during the subsequent drying process. In the present invention, by setting 4 proximity sensors (1#, 2#, 3#, 4#) on the disc, as Figure 3 , the swing frequency is adjusted in sections, and the flatness of the green ball material surface (cross-section) and the average production amount of fine powder balls in the pellet ore are observed. The results are shown in Table 5.

[0030]

[0031] As can be seen from Table 5, with the adjustment of the swing frequency, the green balls converge to both sides, resulting in an uneven concave shape of the material layer on the feeding surface, which in turn causes uneven heating of the green balls during the drying stage. Eventually, powder balls appear during the roasting in the rotary kiln. When the swing frequency of the pendulum feeder is adjusted to make the east side of the green ball material surface slightly inclined, the generation amount of powder balls decreases significantly. Therefore, it is more appropriate to set the swing frequencies of the pendulum feeder at 30 Hz for the 23rd and 41st segments, 31 Hz for the 12th segment, and 32 Hz for the 34th segment, and control it at 8 reciprocations per minute. It should be noted that the 12th segment refers to the 1#-2# segment, the 23rd segment refers to the 2#-3# segment, the 34th segment refers to the 3#-4# segment, and the 41st segment refers to the 4#-1# segment.

[0032] In summary, the optimal adjustment parameters for the optimization of the pellet screening and feeding system are as follows: the swing frequencies of the pendulum feeder at 30 Hz for the 23rd and 41st segments, 31 Hz for the 12th segment, and 32 Hz for the 34th segment; the swing area of the pendulum feeder is shifted 6 cm to the west side; the spacing between the small and large ball screen rollers is adjusted to 12 mm for the small ball screen and 18 mm for the large ball screen; the distribution of the screen rollers is 10 feeding rollers and 37 screening rollers. The metallurgical properties such as the shape of the green balls and the compressive strength, reduction swelling (RSI), reduction degree (RI), and low-temperature reduction degradation (RDI+3.5) of the finished pellet ore before and after the test are compared, and the results are shown in Table 6.

[0033]

[0034] As can be seen from Table 6, after the optimization of the screening and feeding system, the material surface of the green balls on the traveling grate is flat and the heating is uniform. The generation amount of powder balls is reduced by 33%, the compressive strength of the pellet ore is enhanced, and the low-temperature reduction degradation rate is further reduced, with only a small amount of powdery materials. Thus, it can be seen that the optimization of the screening and feeding system significantly improves the quality of the pellet ore.

[0035] In the present invention, the swing frequency of the pendulum feeder is adjusted to 8 reciprocations per minute, the swing area is shifted 6 cm to the west side, the spacing of the small ball screen is set to 12 mm, the spacing of the large ball screen is set to 18 mm, and the distribution of the screen rollers is 10 feeding rollers and 37 screening rollers, successfully achieving the flatness and uniform heating of the green ball material surface, significantly improving the quality of the finished pellet ore, and the average compressive strength reaching over 2300 N.

[0036] As a preferred example of the present invention, 27 rollers of the large ball screen are designed as 5 feeding rollers plus 22 screening rollers, which can further improve the quality of the finished pellet ore.

[0037] The present invention not only optimizes the process parameters of the pendulum feeding process and the screening of small and large balls, strengthens the drying and preheating effect of unilateral air extraction, but also reduces the generation amount of powder balls by 33% at a low cost, achieving good economic and social benefits, meeting the expected goals, and providing a favorable reference for the refined production and energy conservation and emission reduction of iron and steel enterprises.

Claims

1. The optimization method of pellet sieving distribution system is characterized by: The following steps are involved: The pellet ore screen material distribution system includes a swing-type material distributor, a large ball screen roller and a small ball screen roller. The swing frequency of the swing-type material distributor is controlled at 8 back and forth / minute through segmented frequency conversion control, so that the material surface tends to be flat, and the overall material surface is thick in the east and thin in the west. The material surface angle is 10°-15°, and the swing area is moved a certain distance to the west. The spacing between the small ball screen rollers is adjusted to 12 mm, and the spacing between the large ball screen rollers is adjusted to 18 mm.

2. The method for optimizing the pelletizing screen distribution system according to claim 1, characterized in that: The swing area moved 6 cm to the west.

3. The method for optimizing the pelletizing screen distribution system according to claim 1, characterized in that: The ball screening rollers include 10 distribution rollers and 37 screening rollers.

4. The method for optimizing the pelletizing screen distribution system according to claim 1, characterized in that: The large ball screen rollers include 5 cloth rollers and 22 screening rollers.

Images