CN114410958A - A kind of production method for reducing pellet pulverization - Google Patents

Abstract

The invention discloses a production method for reducing pellet pulverization, and belongs to the technical field of pellet preparation. The method of the invention comprises the following steps: step 1, pretreatment of raw materials; drying the mineral powder with low burst temperature, fully mixing with binder and additives in proportion, and then adding water for mixing; step 2, pelletizing treatment The raw materials processed in step 1 are pelletized to make green pellets; step 3, green pellet processing is performed to obtain finished pellets; the green pellets screened in step 2 are spread into a belt roaster for low-temperature drying , roasting and cooling to obtain finished pellets. The technical scheme of the invention can achieve the purpose of greatly increasing the bursting temperature of the pellets and reducing the pulverization of the pellets in the drying stage of the belt roaster, thereby effectively reducing the manufacturing cost, and is suitable for the preparation of pellets with different raw materials.

Description

A kind of production method for reducing pellet pulverization

technical field

The invention belongs to the technical field of pellet preparation, and more particularly relates to a production method for reducing pellet pulverization.

Background technique

As a high-quality iron-making charge, pellets are widely used in blast furnace production because of their unique advantages in improving blast furnace utilization coefficient, improving column permeability, reducing exhaust gas emissions, and facilitating transportation. In recent years, with a series of environmental protection and capacity reduction requirements issued by the state, the proportion of pellets in blast furnace charges has been increasing, and the output of pellets across the country is also increasing year by year. The main raw materials for the production of pellets are fine iron ore concentrate powder and binder. In order to meet the requirements of the blast furnace for the iron grade of iron-containing raw materials, the production of iron ore concentrate powder for pellets usually requires enrichment and grinding of iron ore. , The produced iron concentrate powder generally has the characteristics of high iron grade, less harmful impurities and fine particle size.

The traditional method of producing pellets is mainly: mixing raw materials and adding water to make green pellets, drying to remove moisture; then preheating the pellets and roasting and consolidating them to improve the strength of the pellets, and finally cooling to obtain finished pellets agglomeration. However, for conventional pellets, especially those made from concentrates with a lower burst temperature, green pellets tend to burst during the drying process. Although the mechanism of green pellet bursting is mainly due to the excessive vapor pressure of water inside the pellet and the low strength of the spherical shell, which causes the green pellet to explode and crack, in fact, the burst temperature of the pellet is affected by many aspects, which is also a Indicators that are difficult to control. For example, in the process of pelletizing green pellets, in order to ensure that the falling strength and compressive strength of the green pellets are qualified, a binder will be added to the iron ore concentrate. The presence in turn causes the pellets to absorb more moisture, increasing the vapor pressure inside the pellets.

After searching, there are relevant disclosures of invention patents for reducing the drying, bursting and pulverization of pellets. For example, the Chinese patent application number is: 201210191221.2, the application date is: June 11, 2012, and the name of the invention and creation is: an improved ball Additive preparation method and product for briquette burst temperature and quality. The method disclosed in this application includes processes such as beneficiation, crushing, drying, etc. It is characterized in that the content of the used ore raw material MgO is 35-47%; after crushing to a particle size of ≤ 5.0 mm, roasting at 750-900 ° C for 30-120 min , and then cooled and ground to obtain the additive. The chemical composition of the additive in percentage by weight is: 77≤MgO≤86, 5≤SiO ₂ ≤10, 1≤Al ₂ O ₃ ≤2, 6≤burning loss≤15, the water of the additive Chemical activity ≥ 80%, specific surface area ≥ 45m ² /g. In this application, the air permeability of pellets is increased by blending minerals (that is, additives are added) to make it easier for pellet moisture to escape, and the pelletizing parameters are optimized to reduce the moisture of green pellets. It has a good effect in the iron ore concentrate, but it is not universally applicable, because the pelletizing properties of each iron concentrate powder are very different, and each additive has a great influence on the improvement of the burst temperature of the specific pellets. If only If you want to increase the burst temperature of pellets by mixing ore and optimizing the pelletizing parameters, you have to spend a lot of time and energy to test and adjust the ratio. A process route that has strong adaptability to pellet raw materials and can greatly increase the pellet burst temperature without ore blending and optimization of pelletizing parameters is particularly important.

SUMMARY OF THE INVENTION

1. The problem to be solved

In view of the problems raised in the above-mentioned background technology, the present invention provides a production method for reducing the pulverization of pellets, by reducing the blast temperature of the blast drying section of the belt roaster in the pellet production, and increasing the blast drying air volume The gas circulation method can greatly increase the burst temperature of the pellets and reduce the pulverization of the pellets in the drying stage of the belt roaster, thereby effectively reducing the manufacturing cost, and is suitable for the preparation of pellets with different raw materials.

2. Technical solutions

In order to solve the above problems, the technical scheme adopted in the present invention is as follows:

A production method for reducing pellet pulverization of the present invention comprises the following steps:

Step 1, raw material pretreatment;

After fully mixing the mineral powder with low burst temperature, binder and additives in proportion, add water for mixing;

Step 2. Pelletizing treatment;

The raw material obtained from the treatment in step 1 is pelleted to make green pellets;

Step 3, raw pellet processing, to obtain finished pellets;

The green pellets screened in the second step are spread into a belt roaster for drying, roasting and cooling at a low temperature and a large air volume to obtain finished pellets.

Further, in step 3, the belt roaster is provided with a blast drying section, a suction drying section, a preheating section, a roasting section, a soaking section, a cooling section and a cooling section, and the prepared green balls pass through successively. The continuous process section set on the belt roaster is processed.

Further, in step 3, when the green pellets are processed in the blast drying section, the processing temperature is controlled to be 150-180° C., the processing time is 2-4 min, and the blast wind speed is 3-4 m/s.

Furthermore, when the raw balls are processed in the blast drying section, in addition to the conventional blast section, the air volume of the preheating section, the roasting section, the soaking section and the second cooling section on the belt roaster will also be blasted. To the blast drying section, increase the drying air volume.

Further, for the belt roaster of 300m ² , the air volume from the second cooling section to the blast drying section is controlled at 6000-7000m ³ /min, and the air volume from the soaking section to the blast drying section is controlled at 3000-4000m ³ /min, the air volume from the preheating section and the roasting section to the blast drying section is controlled at 6000-8000 m ³ /min.

Further, in the first step, the used mineral powder has a low burst temperature after being formed into pellets, and is prone to pulverization during drying.

Further, in step 2, the time for ball making is controlled to be 16-18 min, and the consolidation is 2 min.

Further, in the second step, the moisture content of the green pellets is controlled to be 7-8%, and the green pellets are screened after the pelletizing is completed, and the diameter of the green pellets is controlled to be 12.5-13.5 mm.

3. Beneficial effects

Compared with the prior art, the beneficial effects of the present invention are:

(1) a kind of production method of reducing pellet pulverization of the present invention, by adopting belt roaster to process the pellet, especially by reducing the blast temperature of the blast drying section of the belt roaster in the production of pellets, Increase the blast air volume, on the basis of ensuring that the pellets do not burst in the blast drying section, remove part of the moisture in the green pellets, reduce the vapor pressure of the pellets when the green pellets enter the draft drying section, so as to greatly improve the pellets. The burst temperature and the purpose of reducing pellet pulverization in the drying section of the belt roaster have strong universality and low manufacturing cost.

(2) A production method for reducing pellet pulverization of the present invention, on the one hand, by optimizing the design of the temperature and length of blast drying, the burst temperature of pellets can be effectively increased, and the drying section of the belt roaster can be reduced. chalking occurs. On the other hand, by carrying out the air mixing operation in the blast drying section, the removal of water in the green pellets is further improved by increasing the air flow rate, so as to ensure that the vapor pressure inside the pellets is at a low level, so that pulverization is not easy to occur.

(3) A kind of production method of reducing pellet pulverization of the present invention, when the green pellets are dried in the blast drying section, the preheating section, the roasting section, the soaking section and the second cooling section on the belt roaster are At the same time, by controlling the air volume of different air mixing sections respectively, the overall air volume can reach about 2 to 3 times the air volume of conventional blast drying, and different treatment stages are used. The air is mixed into the blast drying section, which can not only create a suitable drying environment for the green pellets to be treated, which is conducive to the evaporation of water vapor in the pellets, but also facilitates the realization of gas recycling and further reduces the manufacturing cost.

(4) A production method for reducing pellet pulverization of the present invention, by optimizing the overall treatment process, compared with the prior art, the method of the present invention does not require ore blending, changing pelletizing parameters, Improve the bentonite, add surface anti-explosion agent, etc. to improve the burst temperature of pellets, thereby reducing its pulverization. At the same time, the method of the present invention has low manufacturing cost, has strong adaptability to different pelletizing raw materials, and can provide an effective solution for increasing the bursting temperature of pellets with different raw materials.

Description of drawings

Fig. 1 is the schematic flow sheet that green pellet of the present invention is processed on the belt roaster;

Fig. 2 is the main chemical composition of the mineral powder used in the present invention;

Fig. 3 is the particle size composition of the mineral powder used in the present invention;

Fig. 4 is the burst temperature detection result of the obtained green balls in each embodiment and comparative example in the present invention.

In the picture:

1. Blast drying section; 2. Exhaust drying section; 3. Preheating section, 4. Roasting section; 5. Soaking section; 6. Cooling section; 7. Cooling section 2; 8. Exhaust cooling air end; 9. 10. Exhaust end.

Detailed ways

In the traditional process of producing pellets, the green pellets need to be dried to remove moisture, so that the green pellets can withstand the change of temperature stress without cracking and other phenomena when passing through the preheating section. In the conventional drying process, the pellets are very easy to burst and pulverize, which greatly affects the air permeability of the pellet production material layer, resulting in a negative impact on the service life of the equipment, product quality and output.

The main reason for the bursting of the green pellets is that the moisture inside the pellets becomes water vapor under the condition of a dry airflow at a certain temperature, and part of the vapor pressure is generated in the pellets, and part of the steam escapes. At the same time, the outer surface of the pellets is dried, forming Shell with a certain strength, in the production of green pellets with different burst temperatures, if the drying temperature is higher for green pellets with low burst temperature, the steam pressure inside the pellet will be greater than the maximum pressure of the shell of the pellet. , the green pellet will burst. Based on this phenomenon, the present invention provides a production method for reducing pellet pulverization. The method of air drying air volume (the blast air speed is 3 ~ 4m/s) makes the raw pellets in the case of low blast temperature, the moisture inside the pellet evaporates slowly, the vapor pressure is low, and no burst occurs; The increase of the air volume increases the hot air that the green pellets can contact without the need to extend the time of the blast drying section, and can have a sufficient amount of moisture removal. Then, when the green pellets dried by the low temperature and large air volume are subjected to ventilation drying, since part of the moisture has been removed, the internal vapor pressure will be greatly reduced, and the strength of the pellet shell will be much greater than that inside the green pellets. The steam pressure can effectively increase the burst temperature of the pellets and reduce the pellet pulverization in the drying section of the belt roaster.

Specifically, in the present invention, the technological process comprises the following steps:

Step 1, raw material pretreatment;

After drying the mineral powder with a low burst temperature, it is fully mixed with the binder and additives in proportion, and then water is added for mixing; wherein, the content of each component in the raw material is: mineral powder 100%, and the binder is bentonite. 2.0%, the additive is calculated according to the alkalinity, and the moisture content of the powder after adding water is 6%.

It should be noted that the embodiments of the present invention mainly relate to two kinds of concentrates with relatively low bursting temperatures, one is ultra-fine-grained iron ore concentrate powder, the other is coarse-grained iron ore concentrate powder, and the main chemical components of the two kinds of ore are The table is shown in Figure 2, and the particle size composition is shown in Figure 3. Under the condition that 2.0% bentonite and an appropriate amount of slaked lime are used to ensure the falling strength and compressive strength of the pellets, the bursting temperature of the two kinds of ores is relatively low, among which the bursting temperature of the ultra-fine iron ore concentrate pellets is lower The main reason is that the green pellets prepared by it are relatively dense, it is difficult for the steam inside the pellets to escape, and the steam pressure is large, which leads to the low burst temperature of the pellets; although the coarse-grained iron concentrates are easier to escape, the steam is easier to escape. However, the falling strength of green pellets is high, the compressive strength is low, the pellets are easily deformed, and the strength is low, so that the shell strength is lower than the vapor pressure inside the pellets, which leads to the low burst temperature of the pellets. For these two kinds of concentrate powders, in the process of raw material preparation, the two kinds of mineral powders are first completely dried, and then 2.0% bentonite is added according to the mass ratio or slaked lime is added as a binder according to the alkalinity, and fully mixed. , and then add 6% water to mix, and finally sieve and break up to prevent agglomeration.

Step 2. Pelletizing treatment;

The raw material obtained from the treatment in step 1 is pelleted to make green pellets;

When making pellets, the diameter of the disc pelletizer used is 1000mm, the rotational speed is set to 23r/min, the disc inclination angle is 47°, the pelletizing time is controlled to be 16-18min, the consolidation time is 2min, and the moisture content of the green pellet is 7-8 %, of which, the moisture content of ultra-fine iron concentrate pellets should be controlled at 7%, and the moisture content of low-silicon coarse particle pellets should be controlled at 8%. 12.5～13.5mm.

Step 3, raw pellet processing, to obtain finished pellets;

The green pellets screened in the second step are spread into a belt roaster for drying, roasting and cooling to obtain finished pellets.

When using a belt roaster for processing, the belt roaster is mainly divided into blast drying section 1, suction drying section 2, preheating section 3, roasting section 4, soaking section 5, cooling section 6 and cooling section 7, When the raw balls are dried, they are processed through the blast drying section 1 and the exhaust drying section 2 respectively. In the blast drying section 1, the air mixing end 9 is used for air mixing; in the exhaust air drying section 2, the bottom is provided with an exhaust end. 10; A cold air extraction end 8 is arranged at the air inlets of the first cooling section 6 and the cooling second section 7, and the supplementary cold air is used to cool the pellets after roasting.

It should be noted that in the belt roaster, the air is the carrier of drying and heat transfer. In the present invention, in order to reduce the pulverization of the pellets, the air temperature is lowered, but the decrease in the air temperature will lead to incomplete drying of the pellets at the same time. . The applicant has found through experimental research that the drying effect of pellets can be achieved by reducing the air temperature while increasing the air volume. However, considering the service life and technical limitations of the existing blower, it is difficult to obtain a large change in the air volume through the blower. . In view of these difficulties, the applicant adjusted the gas circulation mode of the belt roaster, so that the air volume of the preheating section 3, the roasting section 4, the soaking section 5 and the second cooling section 7 was mixed with the air to the blast drying section 1, the third section. After the air flow is combined, after an appropriate amount of air mixing operation 9, blast drying is performed in the blast drying section 1 under the condition of low temperature and large air volume at 150-180°C. Specifically, for a 300m ² belt roaster, the air volume from the second cooling section 7 to the blast drying section 1 can be controlled at 6000-7000 mm m ³ /min, and the air volume from the soaking section 5 to the blast drying section 1 can be controlled Controlled at 3000～4000m ³ /min, the air volume from preheating section 3 and roasting section 4 to blast drying section 1 can be controlled at 6000～8000m ³ /min, and the air volume from blowing end 9 to blast drying section 1 can be controlled at 3000～4000m ³ /min, so that the air volume after the combined addition of the three stages will be about 2 to 3 times that of the original cooling stage 2 to the blast drying section 1. On the basis of increasing the drying time, reducing the speed of the belt roaster, affecting the yield, and extending the length of the belt roaster, increasing the construction cost, a more reasonable dehydration rate is guaranteed.

After the blast drying was completed, the burst temperature of the pellets was measured to test the degree of increase of the burst temperature of the pellets under the conditions of different temperatures and different drying air volumes. The detection method refers to the dynamic measurement method of AC Company in the United States. Each time, 20 pre-dried green balls are put into a burst temperature furnace, in a vertical tube with a wind speed of 1.5m/s (cold state), and the green balls are placed in a drying cup. After staying in the middle for 5min, take it out, take 4%, 20 pieces explode 1 maximum thermometer, unit: °C. The burst temperature of the prepared green balls is shown in Figure 4.

The present invention will be further described below with reference to specific embodiments.

Example 1

1.1. Ordinary drying at low temperature: First, mix 100% ultra-fine iron ore concentrate powder with 2.0% bentonite agent, add 6% water and mix, control the moisture content of green balls to 7% during the pelletizing process, and the pelletizing time is 18min, 2min of consolidation, sieving to control the diameter of the green balls to be 12.5-13.5mm; then, the green balls are dried at low temperature, and the wind speed of blast drying is controlled to be 1.5m/s, the drying temperature is 155°C, and the drying time is 2min.

1.2 Drying at low temperature and large air volume: the ingredients and the raw pellets are the same as in Example 1.1, and the improved belt roaster of the present invention is used to carry out the blast drying process (the preheating section, the roasting section, the soaking section and the cooling two sections). The air volume is mixed with air to the blast drying section), which effectively increases the air volume. The blast drying wind speed is 3m/s, the drying temperature is 155°C, the drying time is 2min, and the blast drying air volume is twice the original.

Comparative Example 1

The ingredients and pellets are the same as those in Example 1.1, the difference is that the pellets in this comparative example are not subjected to low-temperature and high-volume blast drying, and the burst temperature is directly detected.

As shown in Figure 4, before the low-temperature and high-volume blast drying was performed, the burst temperature of the ultrafine iron ore concentrate green pellets in Comparative Example 1 was 335 °C, and bursting could easily occur in the drying section of the belt roaster. In Example 1, the burst temperature after ordinary drying at low temperature was higher than that in Comparative Example 1. Specifically, compared with Comparative Example 1 in Example 1 1.1, after drying at 155°C and 2min with low temperature and large air volume, the burst temperature of green pellets increased from 335°C to 393°C, an increase of 58°C, but It is still lower than the standard of 400°C; compared with 1.2 in Example 1, the burst temperature of green pellets increased from 335°C to 483°C after drying at 155°C and 5min with low temperature and large air volume. This means that the raw pellets, which are originally due to the ultra-fine particle size of the mineral powder, the dense pellets and the low burst temperature, will greatly affect the air permeability of the material layer after drying. Green pellets are dried in the dry section without popping and chalking.

Example 2

2.1. Ordinary drying at low temperature: 100% ultra-fine iron ore concentrate, mixed with slaked lime calculated at 1.2 alkalinity, and then mixed with 6% water to mix thoroughly. 2min, the diameter of the green ball is 12.5~13.5mm, the low temperature is ordinary drying, the blast drying wind speed is 1.5m/s, the drying temperature is 158 ℃, and the drying time is 2min.

2.2. Drying at low temperature and large air volume: the ingredients and pellets are the same as in Example 2.1, and the blast drying method of the present invention is used for drying treatment. The blast drying wind speed is controlled to be 3m/s, the drying temperature is 158 ° C, and the drying time for 2min.

Comparative Example 2

The ingredients and raw pellets are the same as those in Example 2.1, without the low temperature and high air volume blast drying treatment, and the burst temperature detection is directly carried out.

As shown in Figure 4, the burst temperature of the green pellets in Comparative Example 2 is 254 °C. If it is not treated, bursting and pulverization will easily occur in the belt roaster, resulting in the inability of the pellets to be produced, which greatly deteriorates the air permeability of the material layer. Then, the burst temperature of the green pellets was significantly higher than that of Comparative Example 2 after the low-temperature and high-volume blast drying treatment. Specifically, Example 2.1 was ordinary drying at low temperature, and the improvement effect was only 111 °C, which was significantly different from that of Example 2.2. This shows that under low temperature conditions, the increase of air volume has a good effect on improving the burst temperature. Compared with Comparative Example 2, Example 2.2 was subjected to low temperature and large air volume drying at 158 ° C and the blast drying wind speed of 3 m/s. Afterwards, the burst temperature of green pellets increased from 254°C to later greater than 500°C, which was much higher than required for production.

Example 3

3.1 Ordinary drying at low temperature: 100% coarse-grained iron ore powder, add 2.0% bentonite, add 6% water and mix thoroughly, the moisture content of the green ball is 8%, the ball making time is 16 minutes, and then consolidated for 2 minutes. The diameter of the green ball is 12.5～13.5mm, low temperature ordinary drying blast drying wind speed is 1.5m/s, drying temperature is 152℃, drying time is 2min.

3.2 Drying at low temperature and large air volume: the ingredients and raw pellets are the same as in Example 3.1, and the blast drying method of the present invention is used for drying treatment. The blast drying wind speed is controlled to be 3m/s, the drying temperature is 152 ° C, and the drying time is 2min .

Comparative Example 3

The ingredients and raw pellets are the same as those in Example 3.1, without the low-temperature and high-volume blast drying treatment, and the burst temperature is directly detected.

As shown in Figure 4, the burst temperature of the green pellets in Comparative Example 3 is 342 °C, and the bursting phenomenon will occur in the drying section of the belt roaster. Example 3. Specifically, compared with Comparative Example 3, Example 3.2, after drying at 152°C with a low-temperature and large air volume with a blast drying wind speed of 3 m/s, the burst temperature of the green pellets increased from 342°C to a later Compared with Example 3.1, increasing the air volume at low temperature can significantly improve the burst temperature of pellets.

Claims (7)

1. a production method that reduces pellet pulverization, is characterized in that: comprise the steps: Step 1, raw material pretreatment; After drying the mineral powder with low burst temperature, it is fully mixed with the binder and additives in proportion, and then water is added for mixing; Step 2. Pelletizing treatment; The raw material obtained from the treatment in step 1 is pelleted to make green pellets; Step 3, raw pellet processing, to obtain finished pellets; The green pellets screened in the second step are spread into a belt roaster for drying, roasting and cooling at a low temperature and a large air volume to obtain finished pellets. 2. a kind of production method that reduces pellet pulverization according to claim 1, is characterized in that: in step 3, described belt roaster is provided with blast drying section (1), exhaust air drying section (2) , the preheating section (3), the roasting section (4), the soaking section (5), the cooling section (6) and the cooling section (7), and the green balls made pass through the continuous process set on the belt roaster in turn. segment is processed. 3. A production method for reducing pellet pulverization according to claim 2, characterized in that: in step 3, when the green pellets are processed in the blast drying section (1), the control processing temperature is 150-180° C. , the treatment time is 2~4min, and the blast speed is 3~4m/s. 4. a kind of production method that reduces pellet pulverization according to claim 2, is characterized in that: when raw pellets are processed in blast drying section (1), except for conventional blowing section (9), blasting is carried out. , and the air volume of the preheating section (3), roasting section (4), soaking section (5) and cooling second section (7) on the belt roaster will be transferred to the blast drying section (1) to increase the drying rate. air volume. 5. a kind of production method that reduces pellet pulverization according to claim 4, is characterized in that: to the belt roaster of 300m ² , wherein cooling two sections (7) to blast drying section (1) The air volume is controlled at 6000～7000m ³ /min, the air volume from the soaking section (5) to the blast drying section (1) is controlled at 3000～4000m ³ /min, the preheating section (3) and the roasting section (4) to the drum The air volume of the air drying section (1) is controlled at 6000-8000 m ³ /min. 6. A production method for reducing pellet pulverization according to any one of claims 1-5, characterized in that: in step 2, the pelletizing time is controlled to be 16-18 min, and the consolidation is 2 min. 7. A production method for reducing pulverization of pellets according to claim 6, characterized in that: in step 2, the moisture content of the green pellets is controlled to be 7-8%, and the diameter of the green pellets is controlled to be 12.5-13.5% mm.

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