A method for determining the shatter temperature of metallurgical green pellets on a production line

Abstract

The application discloses a method for measuring the burst temperature of metallurgical pellet green balls on a production line. The method is as follows: firstly, raw materials are mixed according to a preset material ratio; then, the mixed raw materials are balling in a laboratory; then, the prepared green balls with a diameter of 10-16 mm are sealed and sent to a belt-type roaster for drying; the speed of the roaster, the temperature, the pressure and the air volume change of each section are recorded in detail; the material box is taken out from the observation hole at the tail of the roaster by using a material hook; the number of burst green balls and the number of un-burst green balls are counted after cooling; and the burst green ball number ratio is 4.5%-5%. The burst temperature of the green balls is the sum of 40% of the entering drying section furnace cover temperature and 60% of the entering preheating section furnace cover temperature when the burst green ball number ratio is 4.5%-5%. The detection method reduces the laboratory detection workload and reduces the error between the laboratory detection data and the production site due to different working conditions; and the method is convenient for quickly and accurately determining the suitable material ratio and the on-site thermal control parameters.

Description

Technical Field

[0001] The invention belongs to the technical field of sintering pellets, and in particular relates to a method for measuring the burst temperature of metallurgical pellets on a production line. Background Art

[0002] The burst temperature of green pellets refers to the ability of a certain number of green pellets to resist the rapid evaporation and disintegration caused by the rapid evaporation of their contained water (physical water and crystalline water) during drying and heating on the roasting equipment under specific environmental conditions (air volume, pressure, temperature, etc.). This is also known as thermal shock strength. The impact of green pellet burst temperature on pellet production primarily occurs during the drying and roasting processes. A low burst temperature can easily cause green pellet breakage during the drying process, increase resistance in the pellet column (material layer), reduce air volume, slow the drying rate of green pellets, and reduce roasting machine productivity and the quality of the finished pellets. Therefore, the burst temperature of green pellets can also serve as an important basis for determining thermal control parameters in pellet production.

[0003] Usually, the bursting temperature of green balls is measured in the laboratory. The measurement method is to use a heating plate as a heating element to make a simple heating furnace that simulates the heating environment of green balls, simulating the stable heating environment for heating green balls. Then, green balls with a diameter of 10~16mm are placed in the green ball heating environment simulated by the simple heating furnace through a supporting device. They are heated from 150℃ to 950℃ in steps of 50℃ and kept warm for 5~30 minutes. Finally, the green balls are taken out and the number of burst green balls and unburst green balls are counted respectively. The highest point temperature at which the green ball burst ratio is <5% is taken as the bursting temperature. However, since the laboratory working conditions are quite different from those of the production line, the test data are different from the actual production, and the test process is complicated and time-consuming.

[0004] A certain factory's 2.6 million tons / year belt roaster pellet production line suffers from unstable raw material usage and frequent adjustments to iron raw material types and ratios. Different iron raw materials have varying pelletizing properties, resulting in varying green ball burst temperatures. To improve the economic and technical performance of blast furnace ironmaking, light-burned dolomite powder with a high MgO content has been added to the pellet production process to produce magnesia-based pellets. Because this material primarily consists of MgCO₃, which has a low melting point, it decomposes at a certain temperature, generating MgO and CO₂ gases. This lowers the green ball burst temperature, impacting yield and smooth production. This invention aims to provide a method for online determination of green ball burst temperature. Summary of the Invention

[0005] The object of the present invention is to provide a method for measuring the bursting temperature of green balls on a production line.

[0006] The object of the present invention is achieved by providing a method for measuring the burst temperature of green metallurgical pellets on a production line, which is achieved by following the steps below:

[0007] 1) Mix the materials according to the pre-used material ratio, make balls in the laboratory, and then seal the green balls with a diameter of 10-16mm and send them to the feeding position of the belt roaster;

[0008] 2) Take 200 green balls and put them into the material box. Record the working conditions of the belt roaster at that time. Then hook the material box with green balls with the material hook and put it into the position 30~50cm away from the edge on both sides of the belt roaster. Keep the material box and the material surface of the trolley level.

[0009] 3) Record in detail the changes in machine speed, temperature, pressure and air volume during the period when the material box is placed in the roasting machine. When adjusting, use the temperature displayed by the thermocouple entering the drying section and preheating section furnace cover as the benchmark, and adjust the temperature in a gradient of 10~20℃;

[0010] 4) Use the material hook to take out the material box at the observation hole at the rear of the machine. After cooling, count the number of cracked and exploded green balls. The sum of 40% of the temperature of the furnace hood entering the drying section and 60% of the temperature of the furnace hood entering the preheating section when the number of green balls burst accounts for 4.5% to 5% is used as the green ball bursting temperature.

[0011] Green pellets burst because the saturated vapor pressure inside the pellets increases dramatically during heating, exceeding the stress the pellets can withstand, resulting in cracks or bursts. The moisture within the green pellets is primarily adsorbed water, also known as free water, which is bound together by capillary action and adsorption. This water is generally expelled at temperatures between 105°C and 130°C. Green pellets containing additives (such as bentonite) also contain crystallization water, which must be above 200°C for it to escape. Furthermore, the raw materials contain a very small amount of chemical water (such as bentonite), which often escapes at temperatures above 500°C (necessary to reach its decomposition temperature). Therefore, the drying stage primarily removes adsorbed and crystallized water.

[0012] This method exposes a certain number of pellets to hot air streams at different temperatures to detect when the number of pellets that burst reaches or approaches the acceptable bursting limit (typically 4.5% to 5%). Specifically, the drying process involves gradually increasing the temperature in stages. By controlling the temperature gradients in the drying and extraction stages, the temperature rise is controlled to minimize overheating. Drying is then continued for a period of time to maximize moisture evaporation. The pellets then come into direct contact with the hot air stream (drying medium), transferring heat to the pellets, heating them and vaporizing their moisture. Simultaneously, the generated water vapor is removed by the air stream, drying the pellets. The hot air stream lowers the temperature and increases the humidity. The entire drying process occurs below the "bursting temperature" while gradually increasing the drying speed. Specifically, the pellets are initially dried below the "bursting temperature." As the moisture content of the pellets decreases, the "bursting temperature" increases accordingly. The medium temperature and flow rate are gradually increased, increasing the drying intensity and speeding up the drying process.

[0013] φ=ρw / ρs

[0014] Where:

[0015] φ—Relative humidity

[0016] ρw—absolute moisture content in the medium, kg (steam) / m 3

[0017] ρs—saturated absolute moisture content of the medium at a certain temperature, kg (steam) / m 3

[0018] The beneficial effects of the present invention are: the detection method of the present invention reduces the workload of laboratory detection and reduces the

[0019] It can reduce the errors caused by different working conditions between laboratory test data and production site; it is convenient to quickly and accurately determine the appropriate ratio of materials and on-site thermal control parameters. DETAILED DESCRIPTION

[0020] The present invention is further described below with reference to the embodiments, but the present invention is not limited in any way. Any changes or substitutions made based on the teachings of the present invention fall within the scope of protection of the present invention.

[0021] The present invention provides a method for measuring the burst temperature of green pellets on a production line. First, various concentrates are mixed according to a specific ratio. A specific proportion of adhesive and flux is then added to the mixed concentrates (pre-mixed materials) and a certain amount of water for further mixing. Third, the mixed materials are gradually fed into a rotating pelletizing disc. Mechanical force causes the disc to rotate continuously, bringing the pelletized material to the top of the disc. Fine water droplets are added to the disc. During this process, due to the continuous addition of materials and water, as well as the rotation of the disc, the mother balls continuously roll down, become compacted, and adhere to the pelletizing material over multiple cycles, forming green pellets with a certain strength and a qualified particle size. Green pellets produced by the disc are screened out by a screening device, sealed, and delivered to the feeding position of a belt roaster. A certain number of qualified green pellets are loaded into a material box, hooked with a material hook, and placed in the belt roaster for drying and roasting according to the corresponding production process. The material box is removed at the end of the machine, and the number of burst balls is counted as a percentage of the total number of green pellets loaded.

[0022] The specific implementation steps are as follows:

[0023] 1. Tool preparation: Use stainless steel round steel to make a material box for raw balls; use ordinary steel pipes and steel bars to make material hooks for placing and taking out the material box.

[0024] 2 Batching: Determine the pre-use ratio of materials: such as iron ore concentrate 1 (A%) + iron ore concentrate 2 (B%) + iron ore concentrate 3 (C%) for pre-batch; then mix the pre-batch with a certain ratio of bentonite (D%) and a certain ratio of light-burned dolomite powder.

[0025] 3. Make balls of the mixed materials in the laboratory, screen out the green balls with a diameter of 10~16mm, seal them and send them to the feeding position of the belt roaster.

[0026] 4. Take 200 raw balls and put them into the material box, record the working conditions of the belt roaster at that time (machine speed, air volume, negative pressure, temperature of each section of the belt roaster), and then hook the material box filled with raw balls with material hooks and put it on both sides of the belt roaster (30~50cm away from the edge to ensure that the material box will not be displaced outside the roasting machine trolley or affect the operation of the trolley due to the impact of raw balls in the normal production process), and keep the material surface of the material box and the trolley flat.

[0027] 5. Record in detail the changes in machine speed, temperature, pressure and air volume in each section (drying, drying and preheating) when the material box is placed in the roasting machine.

[0028] 6. Calculate the time it takes for the material box to reach the observation hole at the end of the machine (t=l / v) by using the machine speed and the distance from the material distribution position of the roasting machine to the observation hole at the end of the machine. Then use the material hook to take out the material box at the observation hole at the end of the machine. After cooling, count the number of burst balls and unburst balls. The sum of 40% of the furnace hood temperature entering the drying section and 60% of the furnace hood temperature entering the preheating section when the number of burst balls accounts for 4.5%~5% is used as the burst temperature of the balls.

[0029] 7. Adjust the hood temperature of the drain and preheat sections based on the number of pellets bursting. If the number of bursts exceeds 5%, lower the hood temperature of the drain section until the number of pellets bursting is less than 5%. If the number of bursts is less than 5%, appropriately increase the hood temperature of the drain and preheat sections until the number of pellets bursting approaches 5%. Adjustments should be based on the temperature indicated by the thermocouples entering the drain and preheat sections, and should be made in increments of 10-20°C.

[0030] The present invention is further described below with reference to the examples.

[0031] Examples 1 to 3 are for measuring the bursting temperature of green balls with different light-burned dolomite powders and different concentrate ratios.

[0032] Example 1

[0033] Experiment 1: Pellets were produced in the laboratory according to the proportions in Tables 1 and 2. After sealing, they were transferred to the distribution position on the belt roaster. 200 green pellets with diameters of 10-16 mm were placed in a hopper. The belt roaster speed was 2.3 m / min. The hood temperature in the blast drying section was 120 ± 10°C, the hood temperature in the exhaust drying section was 560°C, and the hood temperature in the preheating section was 600°C. The hood temperature at the end of the roasting section was controlled at 1250 ± 10°C, and the temperature of the #12 air box was controlled at 500 ± 20°C. After the hopper reached the tail of the machine, the dried and roasted pellets were removed and poured out to air cool naturally. Testing revealed that 6 pellets had popped, representing a popping ratio of 3%. The calculated popping temperature was 584°C (560 × 0.4 + 600 × 0.6 = 584). The pellet strength was 2397 N / pellet, meeting the popping temperature requirements and meeting the pellet quality standards.

[0034] Experiment 2: Adjusting the drying temperature based on the first-stage pellet cracking test results: 200 green pellets with a diameter of 10-16 mm were loaded into a material box and laid out on a belt roaster for drying. The belt roaster speed was 2.3 m / min. The furnace hood temperature in the blast drying section was 120±10°C, the furnace hood temperature in the exhaust drying section was 580°C, and the furnace hood temperature in the preheating section was 620°C. The furnace hood temperature at the end of the roasting section was controlled at 1250±10°C, and the temperature of the 12# air box was controlled at 500±20°C. After the material box reached the tail of the machine, the dried and roasted pellets were removed and poured out to air cool naturally. After testing, the number of cracked pellets was 9, with a cracking ratio of 4.5%. The calculated cracking temperature was 604°C (580×0.4+620×0.6=604). The pellet strength was 2592N / pellet, meeting the cracking temperature requirements and meeting the pellet quality standards.

[0035] Experiment 3: Adjust the drying temperature according to the burst detection results of the raw balls in the experiment: put 200 raw balls with a diameter of 10~16mm into the material box and put them on the belt roaster for drying. The speed of the belt roaster is 2.3m / min, the furnace hood temperature of the blast drying section is 120±10℃, the furnace hood temperature of the exhaust section is 600℃, the furnace hood temperature of the preheating section is 640℃, the furnace hood temperature at the end of the roasting section is controlled at 1250±10℃, and the temperature of the 12# bellows is controlled at 500±20℃. After the material box arrives at the tail of the machine, the dried and roasted pellets are taken out, poured out and placed in the air to cool naturally. After testing, the number of burst balls is 12, and the burst ratio is 6%. At this time, the burst temperature is calculated to be 624℃ (600×0.4+640×0.6=624), and the pellet strength is 1952N / piece. Ball, which does not meet the burst temperature requirement. The quality of the pellets does not meet the standard (compressive strength is less than 2000N / piece. Ball).

[0036] Based on the furnace hood temperature of 580℃ entering the drying section and the furnace hood temperature of 620℃ entering the preheating section in Experiment 2, the proportion of bursts is close to 5%, and the calculated burst temperatures are 604℃. Compared with the burst temperatures of 590℃ and 600℃ obtained from two laboratory tests, the results are relatively close, indicating that this method is feasible.

[0037] Example 2

[0038] Experiment 1: According to the ratios in Table 1 and Table 2, pelletizing was carried out in the laboratory. 200 green pellets with a diameter of 10-16 mm were loaded into a material box and placed on a belt roaster for drying. The speed of the belt roaster was 2.1 m / min, the hood temperature of the blast drying section was 100±10°C, the hood temperature of the exhaust section was 480°C, the hood temperature of the preheating section was 580°C, the hood temperature of the roasting section terminal was controlled at 1250±10°C, and the temperature of the 12# wind box was controlled at 500±20°C. After the material box arrives at the tail of the machine, the dried and roasted pellets are taken out, poured out and placed in the air to cool naturally. After testing, the number of burst balls is 13, and the burst ratio is 6.5%. At this time, the burst temperature is calculated to be 540℃ (480×0.4+580×0.6=540), and the pellet strength is 1876N / ball, which does not meet the burst temperature requirement. The compressive strength of the pellet quality does not meet the standard.

[0039] Experiment 2: Adjusting the drying temperature based on the first-stage pellet cracking test results: 200 green pellets with a diameter of 10-16 mm were loaded into a material box and laid out on a belt roaster for drying. The belt roaster speed was 2.1 m / min. The furnace hood temperature in the blast drying section was 100±10°C, the furnace hood temperature in the exhaust drying section was 420°C, and the furnace hood temperature in the preheating section was 480°C. The furnace hood temperature at the end of the roasting section was controlled at 1250±10°C, and the temperature of the 12# air box was controlled at 500±20°C. After the material box reached the tail of the machine, the dried and roasted pellets were removed and poured out to cool naturally in air. After testing, the number of cracked pellets was 9, with a cracking ratio of 4.5%. The calculated cracking temperature was 456°C (420×0.4+480×0.6=456). The pellet strength was 2597N / ball, meeting the cracking temperature requirements and meeting the pellet quality standards.

[0040] Experiment 3: 200 green pellets with a diameter of 10-16 mm were loaded into a material box and laid out on a belt roaster for drying. The belt roaster speed was 2.1 m / min. The furnace cover temperature in the blast drying section was 100 ± 10°C, the furnace cover temperature in the exhaust drying section was 400°C, and the furnace cover temperature in the preheating section was 440°C. The furnace cover temperature at the end of the roasting section was controlled at 1250 ± 10°C, and the temperature of the 12# air box was controlled at 500 ± 20°C. After the material box reached the tail of the machine, the dried and roasted pellets were removed and poured out to air for natural cooling. After testing, the number of pellets burst was 7, and the burst ratio was 3.5%. The calculated burst temperature was 424°C (400 × 0.4 + 440 × 0.6 = 424). The pellet strength was 2513 N / ball, meeting the burst temperature requirement. The pellet quality met the standard. The chemical composition of the pellets is shown in Table 3.

[0041] This embodiment is based on the furnace hood temperature of 420°C entering the drying section and the furnace hood temperature of 480°C entering the preheating section in Experiment 2. The proportion of the number of bursts is close to 5%, and the calculated burst temperature is 456°C. Compared with the burst temperatures of 450°C and 460°C obtained by two laboratory tests, the results are relatively close, indicating that this method is feasible.

[0042] Example 3

[0043] Experiment 1: According to the ratios in Table 1 and Table 2, pelletizing was carried out in the laboratory. 200 green pellets with a diameter of 10-16 mm were loaded into a material box and placed on a belt roaster for drying. The speed of the belt roaster was 2.1 m / min, the hood temperature of the blast drying section was 80±10°C, the hood temperature of the exhaust section was 380°C, the hood temperature of the preheating section was 440°C, the hood temperature of the roasting section terminal was controlled at 1250±10°C, and the temperature of the 12# wind box was controlled at 500±20°C. After the material box arrives at the tail of the machine, the dried and roasted pellets are taken out, poured out and placed in the air to cool naturally. After testing, the number of burst balls is 13, and the burst ratio is 6.5%. At this time, the burst temperature is calculated to be 416℃ (380×0.4+440×0.6=416), and the pellet strength is 1856N / ball, which does not meet the burst temperature requirement. The compressive strength of the pellet quality does not meet the standard.

[0044] Experiment 2: Adjusting the drying temperature based on the first-stage pellet cracking test results: 200 green pellets with a diameter of 10-16 mm were loaded into a material box and laid out on a belt roaster for drying. The belt roaster speed was 2.1 m / min. The furnace cover temperature in the blast drying section was 80±10°C, the furnace cover temperature in the exhaust drying section was 360°C, and the furnace cover temperature in the preheating section was 420°C. The furnace cover temperature at the end of the roasting section was controlled at 1250±10°C, and the temperature of the 12# air box was controlled at 500±20°C. After the material box reached the tail of the machine, the dried and roasted pellets were removed and poured out to cool naturally in air. After testing, 10 pellets cracked, with a cracking ratio of 5%. The calculated cracking temperature was 396°C (360×0.4+420×0.6=396), and the pellet strength was 2597N / ball, meeting the cracking temperature requirements and meeting the pellet quality standards.

[0045] Experiment 3: 200 pre-made green pellets with a diameter of 10-16 mm were loaded into a material box and laid out on a belt roaster for drying. The belt roaster speed was 2.1 m / min. The furnace cover temperature in the forced air drying section was 80 ± 10°C, the furnace cover temperature in the exhaust drying section was 340°C, and the furnace cover temperature in the preheating section was 400°C. The furnace cover temperature at the end of the roasting section was controlled at 1250 ± 10°C, and the temperature of the 12# air box was controlled at 500 ± 20°C. After the material box reached the tail of the machine, the dried and roasted pellets were removed and poured out to air for natural cooling. After testing, 8 pellets burst, with a burst ratio of 4%. The calculated burst temperature was 376°C (340 × 0.4 + 400 × 0.6 = 376). The pellet strength was 2413 N / ball, meeting the burst temperature requirement and meeting the pellet quality standards. The chemical composition of the pellets is shown in Table 3.

[0046] This embodiment is based on the furnace hood temperature of 360°C entering the drying section and the furnace hood temperature of 420°C entering the preheating section in Experiment 2. The bursting number ratio is 5%, and the calculated bursting temperature is 396°C. Compared with the bursting temperatures of 380°C and 390°C obtained by two laboratory tests, the results are relatively close, indicating that this method is feasible.

[0047] Table 1 Pre-batch and proportion of green balls in Examples 1 to 3

[0048]

[0049] Table 2 Ingredients and proportions of raw balls in Examples 1 to 3

[0050]

[0051] Table 3 Chemical composition of pellets

[0052]

Claims

1. A method for measuring the burst temperature of metallurgical pellets on a production line, characterized in that: Follow these steps to achieve this: 1) Mix the materials according to the pre-used material ratio, make balls in the laboratory, and then seal the green balls with a diameter of 10-16mm and send them to the feeding position of the belt roaster; 2) Take 200 green balls and put them into the material box. Record the working conditions of the belt roaster at that time. Then hook the material box with green balls with the material hook and put it into the position 30~50cm away from the edge on both sides of the belt roaster. Keep the material box and the material surface of the trolley level. 3) Record in detail the changes in machine speed, temperature, pressure and air volume during the period when the material box is placed in the roasting machine. When adjusting, use the temperature displayed by the thermocouple entering the drying section and preheating section furnace cover as the benchmark, and adjust the temperature in a gradient of 10~20℃; 4) Use the material hook to take out the material box at the observation hole at the rear of the machine. After cooling, count the number of cracked and exploded green balls. The sum of 40% of the temperature of the furnace hood entering the drying section and 60% of the temperature of the furnace hood entering the preheating section when the number of green balls burst accounts for 4.5% to 5% is used as the green ball bursting temperature.

2. The method for measuring the burst temperature of metallurgical pellets on a production line according to claim 1, characterized in that: In step 4), when the number of green balls bursting is greater than 5%, adjust the temperature of the furnace cover of the drying section and the preheating section until the number of green balls bursting is less than 5%; when the number of bursting is less than 5%, increase the temperature of the furnace cover of the drying section and the preheating section until the number of green balls bursting is close to 5%.

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