A method for sintering mixture

Abstract

The present application provides a method for sintering and mixing, which is applied to a sintering and mixing system, wherein the sintering and mixing system includes a sintering and mixing cylinder, a squirrel-cage motor and a frequency converter, the squirrel-cage motor driving and connecting the sintering and mixing cylinder, the frequency converter and the squirrel-cage motor being electrically connected for frequency conversion driving the squirrel-cage motor, and the method for sintering and mixing includes: the sintering and mixing system includes a startup mode and an operation mode, and when the sintering and mixing system is in the startup mode, the output frequency of the frequency converter is X. When the sintering and mixing system is in the operation mode, the output frequency of the frequency converter is Y, and the ratio of X to Y is 5:3.5‑4. When the sintering and mixing system is in the startup mode, the ratio of the power of the frequency converter to the power of the squirrel-cage motor is ≥1.25. The sintering and mixing method can reduce the probability of system failure while ensuring the normal operation of the sintering and mixing system, and can reduce the energy consumption of the entire system.

Description

Technical Field

[0001] The present application relates to the field of metallurgy technology, and in particular to a method for sintering mixed materials. Background Art

[0002] Sintering, a crucial process in steelmaking, aims to combine iron ore with other materials, such as lime, to form pellets, providing a synthetic, rich ore with a defined particle size and metallurgical properties for subsequent smelting. The sintering process begins with mixing, which is accomplished using a sintering mixing system. This system includes a motor and a sintering mixing drum. Raw materials, such as iron ore and other materials, are placed into the drum, which is then driven by the motor to fully mix the materials.

[0003] To improve mixing efficiency, existing sintering mixing drums are typically large devices. Coupled with the large amount of sintered raw materials contained within, this requires heavy-load starting of the drum. Wound-type motors, with their low starting current, easy control, and high starting torque, are naturally widely used in sintering mixing systems.

[0004] However, during the mixing production process, electrical failures often occur in the sintering mixing system, requiring a lot of time and effort to repair or replace equipment, seriously affecting production efficiency and cost loss. Summary of the Invention

[0005] The inventors found that when the sintering and mixing system is in operation, the sintering and mixing cylinder rotates, causing dust to fly on site. The dust will inevitably be sucked into the inside of the wound-type motor. Since the rotor of the wound-type motor is made of copper wire, the motor rotor part is prone to material jamming, and the motor carbon brushes cannot operate normally and flexibly, causing the wound-type motor to malfunction, thereby causing the entire sintering and mixing system to fail to operate normally.

[0006] Regular on-site cleaning of the sintering and mixing system can alleviate dust and reduce the chance of rotor jams in wound-rotor motors, leading to motor failures. However, this requires downtime, which is extremely labor-intensive and resource-intensive. Therefore, to reduce the chance of motor failure, the inventors replaced the wound-rotor motor with a squirrel-cage motor. Because the squirrel-cage motor's rotor is cast from aluminum or copper bars and short-circuit rings, its inherent structure effectively reduces the chance of rotor jams, thereby reducing the chance of motor failure.

[0007] However, compared to linear motors, squirrel-cage motors require increased power to achieve heavy-load startup of the sintering mixing drum, which results in increased energy consumption and increased costs. Further research by the inventors has revealed that, after the sintering mixing drum has been properly started and the sintering mixing system is operating normally, appropriately reducing the squirrel-cage motor's input frequency can both ensure normal operation of the entire system and reduce energy consumption.

[0008] Based on this, the purpose of this application is to provide a sintering mixing method, which is applied to a sintering mixing system to ensure the normal operation of the sintering mixing system while reducing the probability of system failure and the energy consumption of the system.

[0009] To achieve the above objectives, this application adopts the following technical means:

[0010] The present application provides a sintering mixing method, which is applied to a sintering mixing system. The sintering mixing system includes a sintering mixing cylinder, a squirrel-cage motor, and a frequency converter. The squirrel-cage motor is connected to the sintering mixing cylinder, and the frequency converter is electrically connected to the squirrel-cage motor for frequency conversion driving the squirrel-cage motor. The sintering mixing method includes:

[0011] The sintering mixing system includes a start-up mode and an operation mode. When the sintering mixing system is in the start-up mode, the output frequency of the inverter is X. When the sintering mixing system is in the operation mode, the output frequency of the inverter is Y. The ratio of X to Y is 5:3.5-4.

[0012] When the sintering mixing system is in the startup mode, the power ratio of the inverter to the squirrel cage motor is ≥1.25.

[0013] In the sintering and mixing system, in startup mode, the inverter power must be no less than 1.25 times the power of the squirrel-cage motor. This allows the inverter to drive the squirrel-cage motor, which in turn drives the connected sintering and mixing cylinder, and the entire sintering and mixing system to start. After starting the sintering and mixing system, the system enters run mode. At this point, the inverter output power can be appropriately reduced to a ratio of 5:3.5-4 between the inverter output frequency in startup mode and run mode. This setting still allows the sintering and mixing system to operate normally.

[0014] A squirrel-cage motor replaces a wound-rotor motor. Due to its inherent structure, the squirrel-cage motor prevents dust from adhering to the motor rotor during operation, significantly reducing the risk of motor failure. In startup mode, the frequency converter provides a smooth starting torque for the squirrel-cage motor, minimizing startup shock to connected equipment and extending its service life. The frequency converter's power must be at least 1.25 times that of the squirrel-cage motor, ensuring the entire system starts normally. The frequency converter also adjusts the system's output frequency between startup and operating modes, maintaining a ratio of 5:3.5-4 in operating mode to startup mode. This ensures proper system operation while reducing energy consumption. Furthermore, the frequency converter reduces its output frequency in operating mode, which in turn reduces the rotational frequency transmitted to the sintering mixing drum. This decreases the speed, resulting in more uniform mixing of the raw materials within the drum.

[0015] Furthermore, when the sintering and mixing system is in the startup mode, the output frequency of the frequency converter is set to 45 Hz-50 Hz. When the sintering and mixing system is in the operation mode, the output frequency of the frequency converter is set to 35 Hz-40 Hz.

[0016] The VFD changes the output frequency of the sintering mixing system between startup and operating modes. When the sintering mixing system is in startup mode, the VFD output frequency is adjusted to 45-50 Hz, which in turn causes the squirrel-cage motor's input frequency to be 45-50 Hz, consistent with the grid's power supply frequency. This maximizes the squirrel-cage motor's power, resulting in a higher starting torque and easier starting of the sintering mixing drum. When the sintering mixing system enters operating mode, the VFD output frequency is adjusted to 35-40 Hz, reducing the squirrel-cage motor's input frequency accordingly. The output frequency in operating mode is lower than that in startup mode, ensuring proper system operation while reducing energy consumption. This also reduces the rotational frequency transmitted to the sintering mixing drum, resulting in a lower speed and more uniform mixing of the raw materials within the drum.

[0017] Furthermore, the duration of the startup mode is 50s-100s. During this period, the sintering and mixing system enters a stable operation mode from startup, and the rotation speed of the sintering and mixing drum is stable.

[0018] Furthermore, the duration of the startup mode is 60 seconds, ensuring that the sintering mixing system can enter the operation mode as quickly as possible from startup, the system enters a stable state, the output frequency of the inverter is reduced, and the energy consumption of the system is further reduced.

[0019] Furthermore, when the sintering mixing system is in startup mode, the ratio of the inverter power to the squirrel-cage motor power is 1.3-1.5:1. This ratio ensures the entire system can start normally and also saves money by eliminating the need to purchase an inverter with significantly greater power than the squirrel-cage motor.

[0020] Furthermore, the sintering mixing method further includes: the materials in the sintering mixing cylinder include iron material, fuel, and flux. When the startup mode is switched to the operating mode, the input current of the squirrel-cage motor is detected as I1. The input current of the squirrel-cage motor is then continuously monitored as I2. When I2 ≥ 1.3 × I1, it is determined that there is severe sticking in the sintering mixing cylinder, the sintering mixing system is stopped, and the sticking in the sintering mixing cylinder is cleaned.

[0021] When the sintering mixing system switches from startup mode to operating mode, the squirrel-cage motor's input current I1 remains within a certain range. However, the inventors discovered that when the system is in operating mode, as raw materials continue to adhere to the inner wall of the sintering mixing cylinder during the mixing process, the squirrel-cage motor's input current I2 generally increases as the amount of adhered raw materials increases, and the two are positively correlated. When I2 ≥ 1.3 × I1, the sintering mixing cylinder's inner wall is severely adhered to, requiring personnel to shut down the system and clean the adhered material inside. By measuring the squirrel-cage motor's input current I2 when in operating mode and comparing it with the input current I1 when switched to operating mode, the adhered material situation in the sintering mixing cylinder can be determined quickly and accurately, allowing for timely removal of the adhered material. This prevents adhered raw materials from solidifying on the cylinder wall due to untimely cleaning, which not only makes cleaning difficult but also may cause large chunks of the solidified raw materials to fall off during the cleaning process, posing a safety hazard to the cleaning personnel.

[0022] Furthermore, when I2 ≥ 1.5 × I1, the sintering and mixing system is stopped and the sticky material in the sintering and mixing cylinder is cleaned. Setting the cleaning of the sticky material in the sintering and mixing cylinder when I2 ≥ 1.5 × I1 makes the cleaning cycle of the sticky material reasonable, avoiding frequent shutdowns that seriously affect normal production, and also avoiding excessive cleaning cycles that lead to excessive sticky materials and increase the difficulty of cleaning. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, without paying any creative work, other related drawings can be obtained based on these drawings, which also fall within the scope of protection of the present application.

[0024] Figure 1 This is a circuit diagram of a sintering mixing system according to an embodiment of the present application;

[0025] Figure 2 This is a schematic diagram of the inner wall adhesion of the sintered mixing cylinder in an embodiment of the present application. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application.

[0027] When the sintering and mixing system is in operation, the sintering and mixing cylinder rotates, causing dust to fly on site. The dust will inevitably be sucked into the winding motor. Since the rotor of the winding motor is made of copper wire, the motor rotor part is prone to material jamming. The motor carbon brushes cannot operate normally and flexibly, causing the winding motor to malfunction, thereby causing the entire sintering and mixing system to fail to operate normally.

[0028] Regular cleaning of the sintering mixing system on-site can eliminate dust and reduce the chance of rotor jams and motor failures in wound-rotor motors. However, this requires frequent downtime for cleaning, which is very labor-intensive and resource-intensive. Therefore, to reduce the chance of motor failure, wound-rotor motors are replaced with squirrel-cage motors. Squirrel-cage motors, with their rotors cast from aluminum or copper bars and short-circuit rings, have a structure that effectively reduces the chance of rotor jams, thereby reducing the chance of motor failure.

[0029] However, compared to linear motors, squirrel-cage motors require increased power to achieve heavy-load startup of the sintering mixing drum, which results in increased energy consumption and costs. Further research by the inventors has revealed that, after the sintering mixing drum has been properly started and the sintering mixing system is operating normally, appropriately reducing the squirrel-cage motor's input frequency can both ensure proper operation of the entire system and reduce energy consumption. In fact, the overall system energy consumption is lower than that of a wound-rotor motor. A detailed energy consumption analysis will be provided in the following sections.

[0030] Figure 1 This is the circuit diagram of the sintering mixing system of the embodiment of the present application. Figure 1 An embodiment of the present application provides a sintering mixing method, which is applied to a sintering mixing system. The sintering mixing system includes a sintering mixing cylinder, a squirrel-cage motor and a frequency converter. The squirrel-cage motor drives and connects the sintering mixing cylinder. The frequency converter is electrically connected to the squirrel-cage motor for frequency conversion driving of the squirrel-cage motor.

[0031] The raw materials for sintering generally include iron-containing materials, fuel and flux. Generally speaking, the iron material is selected from at least one of mixed ore, dust ash and return ore, the fuel is selected from at least one of coke powder and anthracite, and the flux is selected from at least one of dolomite powder, limestone powder and quicklime powder.

[0032] Before starting the system, the raw materials are added into the sintering mixing cylinder from the inlet in a certain proportion. After the raw materials are added, the inlet of the sintering mixing cylinder is closed.

[0033] Next, the sintering mixing system needs to be started and put into stable operation. The sintering mixing method includes:

[0034] The sintering mixing system mode also includes the start-up mode and the operation mode, which is used to mix the raw materials in the sintering mixing cylinder. Figure 1 , QF1 is the user's 10kV circuit breaker, QF2 and QF3 are circuit breakers matched with the frequency converter, PT is a voltage transformer, QF1, QF2 and QF3 are closed in sequence to put the sintering mixing system into the startup mode. At this time, the power ratio of the frequency converter to the squirrel cage motor is required to be ≥1.25. The frequency converter drives the squirrel cage motor, and the squirrel cage motor drives the sintering mixing cylinder connected to it. The entire sintering mixing system is started normally, and the output frequency of the frequency converter is adjusted to X, where X is 45HZ-50HZ.

[0035] In this embodiment, the sintering mixing drum has a radius of 2.2 meters and a length of 20 meters. The selected inverter has a rated power of 1260 kW and the squirrel-cage motor has a rated power of 900 kW. When the sintering mixing system is in startup mode, the inverter's output frequency is adjusted to 45 Hz-50 Hz, consistent with the grid power frequency. This ensures that both the inverter and the squirrel-cage motor reach their rated power during startup, resulting in a correspondingly high starting torque for the squirrel-cage motor, making it easier to start the sintering mixing drum. At this point, the inverter power to squirrel-cage motor power ratio is 1.4. This ratio is not only greater than or equal to 1.25, but also falls within the range of 1.3-1.5. This ensures the entire system can start normally and also saves costs by eliminating the need to purchase an inverter with a power significantly greater than that of the squirrel-cage motor. At the same time, when in starting mode, the inverter makes the starting torque of the squirrel cage motor smooth, reducing the starting impact on the equipment connected to it and extending the service life of the equipment.

[0036] After 60 seconds of startup mode, the sintering and mixing system entered a stable state, with the sintering and mixing drum rotating at a steady and consistent speed. At this point, the inverter output frequency was adjusted to Y, where Y = 40 Hz, putting the sintering and mixing system into operational mode. The ratio of X to Y was 5:4. At 40 Hz, the squirrel-cage motor continued to operate normally, and the sintering and mixing system continued to function. However, the reduced inverter output frequency reduced system energy consumption. This also reduced the rotational frequency transmitted to the sintering and mixing drum, resulting in a more uniform mixing of the raw materials within the drum.

[0037] In other embodiments, the startup mode duration can be 50s, 80s, or 100s to ensure that the sintering and mixing system enters a stable operating mode from startup and that the rotation speed of the sintering and mixing drum is stable. X can also be set to 45 Hz and Y to 35 Hz; X can also be set to 47 Hz and Y to 37 Hz. The X:Y ratio should be within the range of 5:3.5-4.

[0038] A squirrel-cage motor is used in the sintering mixing system. Due to the structure of the squirrel-cage motor itself, dust is not easy to adhere to the motor rotor when the sintering mixing system is running, which greatly reduces the probability of motor failure.

[0039] Figure 2 Schematic diagram of the sticky material situation on the inner wall of the sintering mixing cylinder of the embodiment of the present application. In this embodiment, the sintering mixing system is started at 13:00 on June 7, 2021. At this time, the output frequency of the inverter is 50HZ and the input current of the squirrel cage motor is 53.12A. After 1 minute, the startup mode is switched to the operation mode. When the sintering mixing system is switched from startup mode to operation mode, when the output frequency of the inverter is changed from 50HZ to 40HZ, it is detected that the input current of the squirrel cage motor at this time is I1. The current generally remains within a certain range, which is 39A-43A. In this embodiment, I1=40.02A. Then continue to detect the input current of the squirrel cage motor as I2, and record I1 and I2, as shown in Table 1. When the sintering mixing system is in operation mode, as the raw materials continue to adhere to the inner wall of the sintering mixing cylinder during the mixing process, as the adhered raw materials increase, the detected input current I2 of the squirrel cage motor shows an overall upward trend, and the two are positively correlated. The input current I2 of the squirrel cage motor is measured every 30 minutes. This time interval can be adjusted accordingly according to the actual production situation. In this embodiment, when the input current I2 of the squirrel cage motor is not less than 60.03A, I2≥1.5×I1, and I2≥1.3×I1 is satisfied. It is judged that the sticking material in the sintering mixing cylinder is serious. The sticking situation is as follows: Figure 2 At this time, disconnect QF3 to stop the sintering mixing system, and personnel enter the sintering mixing cylinder to clean the sticky material.

[0040] Table 1 Input current of squirrel cage motor

[0041]

[0042]

[0043] By measuring the squirrel-cage motor's input current, I2, in operating mode and comparing it with the input current, I1, when switched to operating mode, the system can quickly and accurately identify the sticking and promptly remove it. This prevents adhered material from solidifying on the cylinder wall due to delayed cleaning, which not only makes cleaning difficult but also potentially causes large chunks of the material to fall during the cleaning process, posing a safety hazard to the cleaning personnel. Furthermore, cleaning the sintering mixing cylinder starts when I2 ≥ 1.5 × I1. This ensures a reasonable cleaning cycle, preventing both frequent shutdowns that seriously impact normal production and excessive cleaning cycles that increase cleaning difficulty due to excessive sticking.

[0044] Of course, different companies and different sintering mixing cylinders may have different assessments of the severity of sticking. In this case, adjusting the multiple relationship between I2 and I1 can achieve the monitoring and judgment of the sticking situation in the mixed sintering mixing cylinder. In other embodiments, it is also possible to set the machine to stop and clean the sticking material in the sintering mixing cylinder when I2 ≥ 1.3 × I1 or I2 ≥ 1.7 × I1.

[0045] Next, the energy consumption of the sintering and mixing system using a wound-rotor motor and the energy consumption of the sintering and mixing system using a combination of a frequency converter and a squirrel-cage motor provided in an embodiment of the present application are specifically analyzed.

[0046] Because the winding motor has characteristics such as large starting torque, its rated power selection of 800kW can start the sintering mixing cylinder of the same specifications as the embodiment of the present application. The winding motor adopts the power frequency operation mode, and the frequency of the starting mode and the operating mode is 50HZ. The input current of the winding motor remains between 50-53A for a long time. In the embodiment of the present application, when the sintering mixing system is in the operating mode, since the frequency is reduced from 50HZ to 40HZ, the input current of the squirrel cage motor will remain between 39A-43A for a long time. Even if the input current of the motors of the two systems rises due to the sticking of the sintering mixing cylinder, the rising trend of the input current of the two systems is basically consistent. Therefore, compared with the sintering mixing system using a winding motor, the input current of the motor of the sintering mixing system of the embodiment of the present application is about 10A less, and the energy consumption per hour can be reduced by about 173 degrees of electricity. The energy consumption of the sintering mixing system using the inverter provided by the embodiment of the present application combined with the squirrel cage motor is much less than that of the sintering mixing system when using a winding motor.

[0047] In the embodiments of the present application, one or a combination of the above technical solutions has the following beneficial effects:

[0048] (1) Due to the structure of the squirrel cage motor, dust is not easy to adhere to the motor rotor when the sintering mixing system is running, which greatly reduces the probability of motor failure;

[0049] (2) The frequency converter makes the starting torque of the squirrel cage motor smooth, reducing the starting impact problem on the equipment connected to it and extending the service life of the equipment;

[0050] (3) The ratio of the output frequency of the inverter in the running mode to the output frequency in the starting mode is 5:3.5-4, which not only ensures the normal operation of the system but also reduces energy consumption; and when the system is in the running mode, the rotation frequency transmitted to the sintering mixing cylinder is reduced, and the speed is reduced, so that the raw materials in the sintering mixing cylinder are mixed more evenly;

[0051] (4) The sticking condition of the sintering mixing cylinder is determined by measuring the input current I2 of the squirrel cage motor when it is in the running mode and comparing it with the input current I1 when it is switched to the running mode. The sticking condition can be quickly and accurately known, and the sticking material can be removed in time, thus avoiding the consolidation of the adhered raw materials on the cylinder wall due to untimely cleaning, which not only makes cleaning difficult, but also the solidified raw materials may fall off in large pieces during the cleaning process, posing a safety hazard to the cleaning personnel.

[0052] The foregoing is merely a partial embodiment of the present application and is not intended to limit the present application. Persons skilled in the art will readily appreciate that the present application may be modified and altered in various ways. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A method for sintering a mixed material, characterized in that: Applied to a sintering and mixing system, the sintering and mixing system includes a sintering and mixing cylinder, a squirrel-cage motor and a frequency converter, the squirrel-cage motor is drivingly connected to the sintering and mixing cylinder, the frequency converter is electrically connected to the squirrel-cage motor for variable frequency driving of the squirrel-cage motor, and the sintering and mixing method includes: The sintering and mixing system includes a startup mode and an operation mode; when the sintering and mixing system is in the startup mode, the output frequency of the frequency converter is X; when the sintering and mixing system is in the operation mode, the output frequency of the frequency converter is Y; the ratio of X to Y is 5:3.5-4; When the sintering mixing system is in the startup mode, the ratio of the power of the frequency converter to the power of the squirrel cage motor is ≥1.25; The method for sintering the mixed material further comprises: The materials in the sintering mixing cylinder include iron material, fuel and flux; When the starting mode is switched to the running mode, the input current of the squirrel-cage motor is detected to be I1; Then continue to monitor the input current of the squirrel cage motor as I2; When I2≥1.3×I1, it is determined that the sticky material in the sintering mixing cylinder is serious, the sintering mixing system is stopped, and the sticky material in the sintering mixing cylinder is cleaned.

2. The method for sintering the mixed material according to claim 1, characterized in that: When the sintering and mixing system is in the startup mode, the output frequency of the frequency converter is set to 45HZ-50HZ; when the sintering and mixing system is in the operation mode, the output frequency of the frequency converter is set to 35HZ-50HZ.

3. The method for sintering the mixed material according to claim 2, characterized in that: The duration of the startup mode is 50s-100s.

4. The method for sintering the mixed material according to claim 3, characterized in that: The duration of the startup mode is 60 seconds.

5. The method for sintering the mixed material according to claim 1, characterized in that: When the sintering mixing system is in the startup mode, the ratio of the power of the frequency converter to the power of the squirrel cage motor is 1.3-1.5:

1.

6. The method for sintering the mixed material according to claim 1, characterized in that: When I2≥1.5×I1, the sintering and mixing system is stopped, and the sticky material in the sintering and mixing cylinder is cleaned.

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