WO2024124896A1

WO2024124896A1 - Pellet drying and roasting process based on roasting system

Info

Publication number: WO2024124896A1
Application number: PCT/CN2023/106987
Authority: WO
Inventors: 王兆才; 储太山; 代友训; 何璐瑶; 师本敬; 周晓青; 谢朝明; 王春林
Original assignee: 中冶长天国际工程有限责任公司
Priority date: 2022-12-15
Filing date: 2023-07-12
Publication date: 2024-06-20
Also published as: CN115927841A

Abstract

A pellet drying and roasting process based on a roasting system (1). The roasting system (1) is provided with a blast drying section (101), a draft drying section I (102), a draft drying section II (103), a preheating section (104), a roasting section (105), a soaking section (106), a cooling section I (107), and a cooling section II (108) in sequence. The process comprises: 1) a pellet material sequentially passes through the blast drying section (101), the draft drying section I (102) and the draft drying section II (103) to undergo drying, then sequentially passes through the preheating section (104), the roasting section (105) and the soaking section (106) to undergo preheating and roasting, and finally sequentially passes through the cooling section I (107) and the cooling section II (108) to undergo cooling to obtain pellet ore; and 2) air runs through a cooling fan and then cools the pellet ore in the cooling section II, and the discharged air is divided into two parts, which are respectively conveyed to the blast drying section (101) for blast drying of the pellet material and conveyed to the draft drying section I (102) for draft drying of the pellet material. The process increases the tolerable air temperature of the draft drying section II (103) and ensures that pellets would not burst during drying, thereby reducing energy consumption, enhancing roasting, and improving the productivity of an apparatus.

Description

A pellet drying and roasting process based on roasting system

This application claims the priority of the Chinese patent application filed with the China Patent Office on December 15, 2022, with application number 202211614023.2 and invention name “A pellet drying and roasting process based on roasting system”, the entire contents of which are incorporated by reference in this application.

Technical Field

The invention relates to a thermal system for roasting metal oxide agglomerates, and in particular to a pellet drying and roasting process based on a roasting system, and belongs to the field of ferrous metallurgy and nonferrous metallurgy raw material preparation.

Background technique

Metal oxide agglomerates refer to agglomerates obtained by finely grinding and granulating materials containing metal oxides, including metal minerals and recycled materials from metallurgical plants, and are usually spherical. The metal oxide agglomerates are roasted at high temperature in a roaster to obtain furnace materials suitable for smelting, such as pellets. The granulated metal oxide agglomerates (i.e., pellet materials) need to be dried and dehydrated in a roaster first, then preheated, roasted at high temperature, and cooled to obtain metallurgical furnace materials that meet the requirements of physical and metallurgical properties.

The process diagram of the traditional belt roasting machine is shown in Figure 3. During the drying and roasting process of the pellet material, it is necessary to fully utilize the sensible heat of the high-temperature material to reduce heat consumption. At the same time, a large amount of waste gas will be generated during the roasting process. The existing pellet roasting process has the following problems:

(1) The temperature of the exhaust gas from the blast drying section is over 100°C, which results in heat waste and greatly increases the exhaust gas emissions;

(2) After the raw balls are dried by blast drying, the moisture migrates to the upper layer of the balls. When they are dried by exhaust air, the hot air temperature should not be higher than 450°C, otherwise the upper layer of the balls will burst. The exhaust gas from the exhaust drying section comes from the exhaust gas from the roasting section and the soaking section. The exhaust gas temperature from the roasting section and the soaking section is often higher than 500°C. In order to avoid the bursting of the balls in the exhaust drying section, a cold air valve is usually added in front of the heat recovery fan to add a large amount of cold air, so that the heat recovery air temperature is lower than 450°C. However, based on the consideration of process configuration and simplicity of engineering implementation, the exhaust gas from the roasting section and the soaking section must be supplied to the preheating section in addition to the exhaust drying section. The temperature of the preheating section is required to reach 900°C. For this reason, it is necessary to heat the heat recovery air from below 450°C to above 900°C through burner combustion in the preheating section hood, which consumes fuel. In addition, after a large amount of cold air is added, the amount of heat recovery air is greater than the demand of the exhaust drying section and the preheating section. A connecting pipe is often added between the heat recovery fan and the main exhaust fan for diversion, thereby increasing the load of the main exhaust fan.

(3) After the roasting and soaking stages, the pellet temperature is as high as 1200°C or above. Direct cooling with natural wind will cause intense gas-solid heat exchange, which is not conducive to the crystallization of the pellets and will affect the strength of the finished pellets to a certain extent.

Summary of the invention

In view of the problems existing in the above-mentioned prior art, the present invention proposes a pellet drying and roasting process based on a roasting system. In the technical scheme of the present invention, the blast drying section of the traditional belt roasting machine is divided into the blast drying section and the exhaust drying section I in the roasting system of the present application, and the gas discharged from the cooling section II is divided into two, and transported to the blast drying section and the exhaust drying section I respectively. After the blast drying section is divided into two in the present application, the pellet material is first dried by blast drying with low-temperature hot air from the cooling section II, and the moisture migrates to the upper pellets, and then dried by exhaust drying with low-temperature hot air from the cooling section II, and the moisture migrates to the lower pellets. At this time, the moisture content of the upper pellets is reduced, and accordingly, the bursting temperature of the upper pellets is significantly improved. Therefore, the reheated air from the roasting section and the equalizing section can be directly used as the hot air of the exhaust drying section II for recycling without additional cold air, that is, the drying efficiency of the pellet material is greatly improved under the premise of ensuring that the pellet material will not burst. At the same time, since no cold air is added, the reheated air entering the preheating section is more likely to meet the preheating temperature requirements, which has a significant effect on saving fuel consumption and improving the preheating roasting effect of pellets.

According to an embodiment of the present invention, a pellet drying and roasting process based on a roasting system is provided.

A pellet drying and roasting process based on a roasting system, wherein the roasting system is provided with a blast drying section, an exhaust drying section I, an exhaust drying section II, a preheating section, a roasting section, a soaking section, a cooling section I, and a cooling section II in sequence. The air inlet of the cooling section II is connected to a cooling fan. The air outlet of the cooling section II is connected to a first pipeline, which is divided into two, namely a second pipeline and a third pipeline. The second pipeline is connected to the air inlet of the blast drying section, and a blower is provided on the second pipeline. The third pipeline is connected to the exhaust drying section I. The process comprises the following steps:

1) The pelletized material is sequentially dried in the blast drying section, dried in the exhaust drying section I, dried in the exhaust drying section II, preheated in the preheating section, roasted in the roasting section, heated in the soaking section, cooled in the cooling section I and the cooling section II on the roasting system to obtain pelletized ore.

2) The air passes through the cooling fan to cool the pellets in the second cooling stage, and is divided into two after being discharged. The air is respectively transported to the blast drying stage through the second pipeline to blow dry the pellets, and is transported to the exhaust drying stage I through the third pipeline to exhaust dry the materials.

In the present invention, the process further comprises the steps of:

3) The hot air discharged from the blast drying section is transported to the cooling section to cool the pellets. The gas discharged from the cooling section is transported to the soaking section, roasting section and preheating section to participate in the preheating and roasting of the pellets. The exhaust gas from the first stage of the drying section is transported to the exhaust drying section II and the preheating section to participate in the drying and preheating of the pellets. The exhaust gas from the exhaust drying section I, exhaust drying section II, preheating section and the front section of the roasting section is discharged through the exhaust fan.

In the present invention, the total length of the blast drying section and the exhaust drying section I of the roasting system is fixed, and the length of the blast drying section is adjusted so that the moisture content of the pelletized material after passing through the blast drying section is lower than x ₀ .

Where: _x0 is the upper limit of moisture content of the pellet material at which the pellet material explodes during the blast drying process. The value range of _x0 is 10% to 16%.

In the present invention, the length of the blast drying section is adjusted specifically as follows:

A1) According to the material processing volume per unit time of the roasting system, the power of the cooling fan is determined, and then the air volume delivered by the cooling fan is determined.

A2) Based on the roasting temperature and the temperature of the pellets after cooling, calculate the temperature T of the exhaust air from the second cooling stage.

A3) According to the temperature of the exhaust air from the second cooling stage in the blast drying stage, determine the upper limit x ₀ of the moisture content of the pellet material at which bursting occurs during the blast drying process.

A4) According to the upper limit of moisture content at which the pellet material bursts, combined with the moisture enrichment of the pellet material during the drying process in the blast drying section, the maximum length of the blast drying section is determined, and the length of the blast drying section is adjusted to be less than or equal to the maximum length.

In the present invention, the determination of the maximum length of the air drying section in step A4) is specifically:

Detect the initial moisture content of the pellet material, design the thickness of the pellet material on the roasting system, and use wind with a temperature of T to blast dry the pellet material on the blast drying section. Detect the position where the moisture content of the pellet material on the surface of the blast drying section on the roasting system reaches x ₀ , and set this position as the limit position. The length from the starting position to the limit position of the blast drying section is the maximum length of the blast drying section.

In the present invention, the total length of the blast drying section and the exhaust drying section I of the roasting system is fixed, wherein the length ratio of the blast drying section to the exhaust drying section I is 2 to 6:1, preferably 3 to 4:1.

In the present invention, a first control valve is provided on the second pipeline, and a second control valve is provided on the third pipeline. The first control valve and the second control valve are adjusted so that the ratio of the air volume delivered to the blast drying section through the second pipeline to the air volume delivered to the exhaust drying section I through the third pipeline is equal to the length ratio of the blast drying section to the exhaust drying section I.

Preferably, the wind speeds of the blast drying section and the exhaust drying section I are detected, and the first control valve and the second control valve are adjusted to make the wind speeds of the blast drying section and the exhaust drying section I equal.

In the present invention, the air outlet of the blast drying section is connected to the air inlet of the cooling section via a fourth pipe. A cooling fan is provided on the pipeline. The speed of the cooling fan is adjusted so that the furnace hood pressure of the roasting section is within a set range. The setting range of the furnace hood pressure of the roasting section is -100Pa to -50Pa.

Preferably, a cold air valve is provided on the fourth pipeline at an upstream position of the cooling first stage fan. The opening of the cold air valve is adjusted so that the air entering the cooling first stage from the fourth pipeline meets both the air volume requirement and the energy requirement.

The traditional belt roasting machine is generally equipped with seven process sections, namely, air drying section, exhaust drying section, preheating section, roasting section, soaking section, cooling section one, and cooling section two. The green balls are first dehydrated in the air drying section and the exhaust drying section, then preheated in the preheating section, and then enter the roasting section for high-temperature roasting. Subsequently, they enter the cooling section one and cooling section two through the soaking section for cooling, and pelletized mineral products are obtained. In the prior art, after the green balls are air dried, the moisture will migrate to the upper pellets, causing the moisture content in the upper pellets to continue to increase. The moisture in the green balls will cause the green balls to plastically deform, causing the green balls to crack or burst in the subsequent exhaust drying stage or preheating stage. The higher the moisture content in the green balls, the lower the corresponding bursting temperature of the green balls (i.e., the temperature at which the pellet structure is destroyed during the heating process). In this way, when the raw balls discharged from the blast drying section are dried by exhaust air, the temperature of the exhaust drying section must be controlled (for example, the air temperature entering the exhaust drying section must be controlled below 450°C, such as 400°C), otherwise the balls with high moisture content in the upper layer will burst. The exhaust gas from the exhaust drying section comes from the exhaust gas from the roasting section and the equalizing section. The exhaust gas temperature of the roasting section and the equalizing section is often higher than 500°C. In order to avoid the bursting of the balls in the exhaust drying section, a cold air valve is usually added in front of the heat recovery fan to add a large amount of cold air, so that the heat recovery air is lower than 450°C. However, in addition to supplying the exhaust drying section, the exhaust gas from the roasting section and the equalizing section must also be supplied to the preheating section. The temperature of the preheating section is required to reach 900°C. Obviously, the heat recovery air after adding cold air cannot meet the temperature requirements of the preheating section. For this reason, it is necessary to heat the heat recovery air from below 450°C to above 900°C through burner combustion in the preheating section hood, which increases fuel consumption. In addition, after a large amount of cold air is added, the amount of heat recovery air is greater than the demand of the exhaust drying section and the preheating section, as shown in Figure 3. A connecting pipe is often added between the heat recovery fan and the main exhaust fan for diversion, thereby increasing the load of the main exhaust fan.

In view of the shortcomings of the above-mentioned prior art that the upper layer of pellets is prone to bursting due to over-humidity during the drying process, and the hot air temperature of the exhaust drying section and the preheating section is limited, which affects the roasting process and increases fuel consumption, the present invention proposes a pellet drying and roasting process based on a roasting system. In the technical scheme of the present invention, the blast drying section of the traditional belt roasting machine is divided into the blast drying section and the exhaust drying section I in the roasting system of the present application, and the gas discharged from the second cooling section is divided into two, and is respectively transported to the blast drying section to blast dry the pellet material, and is simultaneously transported to the exhaust drying section I to exhaust dry the pellet material. After the present application divides the blast drying section into two, the pellet material is first dried by low-temperature hot air blast drying from the second cooling section, and the moisture migrates to the upper layer of the pellets, and then dried by low-temperature hot air exhaust drying also from the second cooling section, and the moisture migrates to the lower layer of the pellets. At this time, the moisture content of the upper layer of the pellets is reduced, and accordingly, the upper layer of the pellets The bursting temperature is significantly improved. Therefore, the reheated air from the roasting section and the soaking section can be directly recycled as the hot air of the exhaust drying section II without additional cold air, that is, the drying efficiency of the pellet material is greatly improved under the premise of ensuring that the pellet material will not burst, so that the roasting process can be strengthened. At the same time, since the cold air is not added, the reheated air entering the preheating section is also easier to meet the preheating temperature requirements, which has a significant effect on saving fuel consumption and improving the preheating roasting effect of the pellets. In addition, since the cold air is not added, the reheated air volume will not increase significantly. Under the premise that the reheated air volume meets the air volume requirements of the exhaust drying section and the preheating section, there is no need to use a connecting pipe for diversion between the reheated fan and the main exhaust fan. Compared with the traditional belt roasting machine, the roasting system in this application eliminates the cold air valve and the connecting pipe, reduces the load of the main exhaust fan, and reduces production costs.

In the traditional belt roasting machine, the exhaust gas discharged after the pellet material is blown and dried is often directly discharged after dust removal and purification, and its sensible heat cannot be recovered, and the exhaust gas emission in the process of pellet roasting is greatly increased. In order to overcome this defect, the present invention recycles the hot exhaust gas discharged from the blow drying section as the cooling air of the cooling section, thereby realizing the recovery of the sensible heat of this part of the exhaust gas, reducing heat consumption, and greatly reducing exhaust gas emissions. It also increases the temperature of the hot exhaust gas discharged from the cooling section, which helps to reduce the fuel consumption of the burners in the roasting section and the preheating section. Moreover, in the cooling section, the hot exhaust gas (low-temperature hot air, such as 100°C) of the blow drying section is used to cool the high-temperature pellets (such as 1200°C), which reduces the gas-solid temperature difference, is conducive to the crystallization of the pellets, and improves the strength of the pellets. In addition, the dust concentration is often not high during pellet production. When the dust content of the exhaust gas from the blast drying section is lower than the tolerable capacity of the fan (usually <100 mg/ ^m3 ), the dust removal device can be removed and the fan of the cooling section can be directly blown into the cooling section, reducing the fixed investment of the exhaust gas dust removal system for this part.

The present invention subdivides the blast drying section in the prior art into the blast drying section and the exhaust drying section I in this application, so the total length of the blast drying section and the exhaust drying section I in this application is fixed, and the exhaust drying section II in this application corresponds to the exhaust drying section in the prior art. According to the above analysis, in order to increase the wind temperature that the exhaust drying section II can withstand while ensuring that the pellets entering the exhaust drying section II will not burst, it is necessary to reduce the moisture content in the pellets to increase the bursting temperature of the pellets. When the pellets pass through the blast drying section and the exhaust drying section I, the blast drying section will cause the moisture to migrate to the upper pellets, and the exhaust drying section I will cause the moisture to migrate to the lower pellets. Therefore, the pellets with the highest moisture content are located at the boundary between the blast drying section and the exhaust drying section I, and the pellets with the highest moisture content (i.e., the lowest bursting temperature) are the surface pellets at the boundary. Based on this, the present invention adjusts the length of the blast drying section, that is, determines the boundary position between the blast drying section and the exhaust drying section I, so that the moisture content of the pellets after the blast drying section is lower than the upper moisture content limit x ₀ of the pellets bursting during the blast drying process.

In the present invention, the adjusting the length of the air drying section comprises the following steps:

In step A1), first, the air volume required to process the corresponding amount of material is determined based on the material processing volume of the roasting system per unit time, and then the fan models are selected according to the overall air volume demand of the roasting system, thereby determining the power of the cooling fan connected to the second cooling stage, and then determining the air volume delivered by the cooling fan.

In step A2), according to the temperature of the pellets entering the second cooling stage after roasting, the temperature of the pellets after cooling, and the temperature of the cooling air entering the second cooling stage through the cooling fan, the temperature T of the exhaust air from the second cooling stage can be calculated based on the heat balance formula. The present application does not require actual testing, and the temperature of the exhaust air from the second cooling stage can be obtained through online process simulation, so as to guide and adjust the actual production process.

The higher the moisture content in the pellet material, the lower the corresponding burst temperature of the pellet material. The inventor of the present application has obtained the corresponding relationship between the moisture content of the pellet material (i.e., moisture content, %) and the burst temperature (°C) of the pellet material through multiple experiments, as shown in Table 1:

Table 1 Comparison table of moisture content and burst temperature of pellet materials

Based on Table 1, in step A3), the present application can determine the upper limit x ₀ of moisture content at which the pellet material explodes during the blast drying process according to the temperature of the exhaust air from the second cooling stage in the blast drying stage.

In the present application, the upper limit of the moisture content at which the pellet material bursts in the blast drying section is known, and then the moisture enrichment of the pellet material in the blast drying section, especially the moisture enrichment of the surface pellet material in the blast drying section, is used to determine the position corresponding to the upper limit of the moisture content at which the pellet material bursts. This position is the boundary between the blast drying section and the exhaust drying section I, that is, the maximum length of the blast drying section is determined. By adjusting the length of the blast drying section to be less than or equal to the maximum length, the pellets can be prevented from bursting during the drying process. In addition, since the wind of the blast drying section in the present application is circulated to the cooling section for use, and the wind of the exhaust drying section I is directly discharged, the length of the blast drying section is adjusted to be maximized (i.e., equal to the maximum length), which can minimize exhaust gas emissions and maximize benefits.

In step A4), the maximum length of the air drying section may be determined by the following operations:

Detect the initial moisture content of the pellet material, design the thickness of the pellet material on the roasting system, and use wind with a temperature of T (i.e., wind with a temperature of T discharged from the second cooling stage) to blast dry the pellet material on the blast drying section. Detect the position where the moisture content of the pellet material on the surface of the blast drying section on the roasting system reaches x ₀ , and set this position as the limit position. The length from the starting position to the limit position of the blast drying section is the maximum length of the blast drying section.

Under the premise that the wind temperature and the thickness of the pellet material in the blast drying section are determined, the inventors of the present application have obtained the corresponding relationship between the moisture content of the pellet material on the surface of the blast drying section and the length of the blast drying section through multiple experiments, as shown in Table 2:

Table 2 Comparison table of moisture content of surface pellet material and length of blast drying section

Note: As the thickness of the material layer increases, the equipment length of the entire roasting system will increase accordingly. Therefore, under the same wind temperature, the length of the blast drying section corresponding to different material layer thicknesses is also different.

Based on Table 2, the present invention can quickly obtain the moisture content of the surface pellets in the blast drying stage according to the moisture content of the surface pellets in the blast drying stage. The length position corresponding to the drying section, when the moisture content of the surface pellet material reaches x ₀ , the corresponding length position at this time is the limit position of the blast drying section length. The length from the starting position of the blast drying section to the limit position is the maximum length of the blast drying section.

It should be noted that the present application divides the existing blast drying section into two, that is, three drying sections are set. According to the above analysis, such a setting can effectively reduce the moisture content of the pellet material, increase the bursting temperature of the pellet material, and thus greatly increase the wind temperature of the exhaust drying section II. Therefore, the present application can adopt thick material layer operation (for example, including the thickness of the bottom material, the stacking height of the entire pellet material can reach 600mm), the roasting process can be strengthened, the roasting heat consumption can be reduced, and the equipment productivity can be improved.

In addition, in the prior art, the air temperature of the blast drying section may be relatively low, that is, the moisture content at the end of the blast drying section (i.e., the boundary between the blast drying section and the exhaust drying section) will not reach the upper limit of the moisture content corresponding to the air temperature, and the raw balls will not burst in the blast drying section. However, due to the high air temperature of the exhaust drying section, there is still a situation where the pellets in the blast drying section burst after entering the exhaust drying section. At this time, in order to avoid the pellets bursting, it is still necessary to add cold air to reduce the air temperature of the exhaust drying section, that is, the problems existing in the aforementioned prior art have not been solved. Based on this situation, the inventor of the present application divides the blast drying section into two parts according to experience, namely, including the blast drying section and exhaust drying section I in the present application. When the moisture content of the surface pellets at the end of the blast drying section reaches the highest, as mentioned above, the moisture content of the surface pellets is reduced by the same low-temperature hot air entering the exhaust drying section I, that is, the situation that the subsequent exhaust drying section II wind temperature is too high and causes the pellets to burst can be avoided, and there is no need to perform the cold air addition operation. Under the premise that the total length of the blast drying section and the exhaust drying section I is fixed, the length ratio of the blast drying section to the exhaust drying section I is 2 to 6:1, preferably 3 to 4:1, for example 4:1.

As a preferred solution, the present invention is provided with a first control valve on the second pipeline, and a second control valve on the third pipeline. The first control valve is used to adjust the air volume delivered from the cooling section 2 to the blast drying section through the second pipeline, and the second control valve is used to adjust the air volume delivered from the cooling section 2 to the exhaust drying section I through the third pipeline. In view of the fact that the air volume balance and energy balance are crucial to the quality assurance of the pellets in the roasting system, the present application adjusts the first control valve and the second control valve so that the ratio of the air volume delivered to the blast drying section through the second pipeline to the air volume delivered to the exhaust drying section I through the third pipeline is equal to the length ratio of the blast drying section to the exhaust drying section I, thereby ensuring that the wind speeds of the blast drying section and the exhaust drying section I are the same.

In the present invention, the wind speeds of the blast drying section and the exhaust drying section I can also be directly detected. If the detection results show that the wind speeds of the two sections are the same, no adjustment is required. If the detection results show that the wind speeds of the two sections are different, the first control valve and the second control valve are adjusted to make the wind speeds of the blast drying section and the exhaust drying section I the same.

Considering the importance of air volume balance and energy balance in the roasting system, the present invention also adjusts the rotation speed of the cooling fan to make the furnace hood pressure of the roasting section within a set range. The setting range of the furnace hood pressure of the roasting section is -100Pa to -50Pa (for example, -50Pa). In addition, the present application also provides a cold air valve upstream of the cooling fan, and adjusts the opening of the cold air valve so that the air entering the cooling section can meet the system air volume demand and energy demand at the same time.

Compared with the prior art, the present invention has the following beneficial technical effects:

1. The present invention subdivides the existing blast drying section into a blast drying section and an exhaust drying section I, and divides the gas discharged from the cooling section II into two, which are respectively transported to the blast drying section and the exhaust drying section I. The pellet material is first dried by low-temperature hot air blast from the cooling section II, and the moisture migrates to the upper pellets. Then, it is dried by low-temperature hot air exhaust from the cooling section II, and the moisture migrates to the lower pellets. At this time, the moisture content of the upper pellets is reduced, and accordingly, the bursting temperature of the upper pellets is significantly improved. Therefore, the reheated air from the roasting section and the equalizing section can be directly recycled as the hot air of the exhaust drying section II without additional cold air exchange, that is, the drying efficiency of the pellet material is greatly improved while ensuring that the pellet material will not burst, so that the roasting process can be strengthened.

2. In the present invention, since the reheated air from the roasting section and the soaking section is not replaced with cold air, the reheated air entering the preheating section is also more likely to meet the preheating temperature requirements, thereby saving fuel consumption and improving the preheating roasting effect of the pellets. Since the reheated air is not replaced with cold air, the amount of reheated air will not increase significantly, so there is no need to use a connecting pipe between the reheating fan and the main exhaust fan for diversion. Compared with the traditional belt roasting machine, the roasting system in this application eliminates the cold air valve and the connecting pipe, reduces the load of the main exhaust fan, and reduces the production cost.

3. The present invention recycles the hot exhaust gas discharged from the blast drying section as cooling air for the cooling section, thereby recycling the sensible heat of the exhaust gas, reducing heat consumption, and greatly reducing exhaust gas emissions. It also increases the temperature of the hot exhaust gas discharged from the cooling section, which helps to reduce the fuel consumption of the burners in the roasting section and the preheating section. Moreover, the cooling section uses the hot exhaust gas from the blast drying section to cool the high-temperature pellets, which reduces the gas-solid temperature difference, is beneficial to the crystallization of the pellets, and improves the strength of the pellets. In addition, when the pellet production is low in dust concentration, the dust removal device can be removed and the fan of the cooling section can be directly blown into the cooling section, reducing the fixed investment of the exhaust gas dust removal system.

4. The present invention first determines the air volume delivered by the cooling fan according to the material processing capacity of the roasting system, and then calculates the temperature of the exhaust air of the second cooling stage according to the amount of pellet material, the cooling air volume, the temperature of the pellet material before and after cooling, and the temperature of the cooling air. Then, based on this temperature, the upper limit _x0 of the moisture content of the pellet material that causes bursting during the blast drying process is determined. Finally, based on this upper limit of moisture content, the maximum length of the blast drying section is determined, and the length of the blast drying section is adjusted to be less than or equal to the maximum length, so that the pellets can be prevented from bursting during the drying process. By maximizing the length of the blast drying section, exhaust gas emissions can be reduced to the greatest extent, thereby maximizing benefits. In addition, when the prior art When the moisture content at the end of the blast drying section does not reach the upper limit of the moisture content corresponding to the wind temperature of the blast drying section, the length ratio of the blast drying section is determined according to experience to ensure that the pellets will not burst in the subsequent exhaust drying II section.

5. The present invention also provides a cold air valve upstream of the cooling fan, and adjusts the opening of the cold air valve so that the air entering the cooling section can meet the system air volume demand and energy demand at the same time, thereby enhancing the quality assurance of the pelletized ore in the roasting system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic flow diagram of a pellet drying and roasting process based on a roasting system according to the present invention;

FIG2 is a schematic diagram of the structure of a roasting system in the present invention;

FIG. 3 is a schematic structural diagram of a belt roasting machine in the prior art.

Reference numerals:

1: roasting system; 101: forced air drying section; 102: exhaust air drying section I; 103: exhaust air drying section II; 104: preheating section; 105: roasting section; 106: soaking section; 107: cooling section I; 108: cooling section II; 2: first control valve; 3: second control valve; 4: cold air valve;

L1: first pipeline; L2: second pipeline; L3: third pipeline; L4: fourth pipeline.

Detailed ways

The technical solution of the present invention is illustrated below by way of example, and the scope of protection requested by the present invention includes but is not limited to the following embodiments.

Example 1

2) The air passes through the cooling fan to cool the pellets in the second cooling stage, and is divided into two parts after being discharged. The pelletized material is transported to the blast drying section through the second pipeline for blast drying, and is transported to the exhaust drying section I through the third pipeline for exhaust drying.

Example 2

A pellet drying and roasting process based on a roasting system, as shown in FIG2, wherein the roasting system is provided with a blast drying section, an exhaust drying section I, an exhaust drying section II, a preheating section, a roasting section, a soaking section, a cooling section I, and a cooling section II in sequence. The air inlet of the cooling section II is connected to a cooling fan. The air outlet of the cooling section II is connected to a first pipeline, and the first pipeline is divided into two, namely a second pipeline and a third pipeline. The second pipeline is connected to the air inlet of the blast drying section, and a blower is provided on the second pipeline. The third pipeline is connected to the exhaust drying section I. The process comprises the following steps:

3) The hot air discharged from the blast drying section is transported to the cooling section to cool the pellets. The gas discharged from the cooling section is respectively transported to the soaking section, roasting section and preheating section to participate in the preheating and roasting of the pellets. The gas discharged from the rear section of the roasting section and the soaking section is respectively transported to the exhaust drying section II and the preheating section to participate in the drying and preheating of the pellets. The gas discharged from the exhaust drying section I, exhaust drying section II, preheating section and the front section of the roasting section is discharged through the exhaust fan.

Example 3

Example 2 was repeated, except that the total length of the blast drying section and the exhaust drying section I of the roasting system was fixed, and the length of the blast drying section was adjusted so that the moisture content of the pelletized material after passing through the blast drying section was lower than x ₀ .

Where: _x0 is the upper limit of moisture content of pellet materials that explodes during the blast drying process. The value range of _x0 is 14% to 15%.

Example 4

As shown in FIG1 , Example 3 is repeated, except that the length of the blast drying section is adjusted as follows:

Example 5

Repeat Example 4, except that the maximum length of the air drying section is determined as described in step A4), specifically:

Example 6

Example 5 is repeated, except that the first control valve is provided on the second pipeline and the second control valve is provided on the third pipeline. The first control valve and the second control valve are adjusted so that the ratio of the air volume delivered to the blast drying section through the second pipeline and the air volume delivered to the exhaust drying section I through the third pipeline is equal to the length ratio of the blast drying section to the exhaust drying section I.

Example 7

Repeat Example 6, except that the wind speeds of the blast drying section and the exhaust drying section I are detected, and the first control valve and the second control valve are adjusted to make the wind speeds of the blast drying section and the exhaust drying section I equal.

Example 8

Example 7 was repeated, except that the air outlet of the blast drying section was connected to the air inlet of the cooling section via a fourth pipe, and a cooling section fan was provided on the fourth pipe. The speed of the cooling section fan was adjusted so that the furnace hood pressure of the roasting section was within a set range. The setting range of the furnace hood pressure of the roasting section was -50 Pa.

Example 9

Example 8 is repeated, except that a cold air valve is provided on the fourth pipeline, upstream of the cooling first stage fan. The opening of the cold air valve is adjusted so that the air entering the cooling first stage from the fourth pipeline meets both the air volume requirement and the energy requirement.

Example 10

Example 2 is repeated, except that the total length of the blast drying section 101 and the exhaust drying section I 102 of the roasting system 1 is fixed. The length ratio of the blast drying section 101 to the exhaust drying section I 102 is 4:1.

Embodiment 11

Example 10 was repeated, except that the length ratio of the forced air drying section 101 to the suction air drying section I 102 was 2:1.

Application Example 1

The process described in Example 5 was used for drying and roasting of pellets. Different wind temperatures and material thicknesses in the blast drying section correspond to different upper limits of moisture content x ₀ at which the pellets burst during the blast drying process. Four groups of wind temperatures and material thicknesses were set, and the same batch of pellets were dried and roasted respectively. The position where the moisture content of the surface pellets in the blast drying section reached x ₀ was detected, and the maximum length of the blast drying section was obtained. The experimental results are shown in Table 3:

Table 3 Comparison of different wind temperatures, material thicknesses, upper limits of moisture content at which pellet materials burst, and maximum length of the blast drying section

Note: As the thickness of the pellet material increases, the length of the entire roasting system will increase accordingly. Therefore, under the condition of constant wind temperature, the length of the blast drying section corresponding to different material layer thicknesses is also different. For example, the same wind temperature corresponds to the same upper limit of moisture content for Group 1 and Group 3, Group 2 and Group 4, but corresponds to different blast drying section lengths.

Comparative Example 1

As shown in Figure 3, the belt roasting machine is equipped with a blast drying section, an exhaust drying section, a preheating section, a roasting section, a soaking section, a cooling section 1, and a cooling section 2 in sequence. The cooling air required for the cooling section 1 and the cooling section 2 comes from the air introduced by the cooling fan. The hot exhaust gas discharged from the cooling section 2 is transported to the blast drying section to dry the green balls. The exhaust gas discharged from the blast drying section is directly discharged after dust removal and purification.

In Comparative Example 1, the wind temperature and material thickness of the air drying section used were the same as those of Group 1 of Application Example 1. The same batch of pellet materials was dried and roasted, and various process data during the pellet roasting process were detected and recorded.

Comparative Example 2

Comparative Example 1 was repeated, except that in Comparative Example 2, the air temperature and material thickness of the blast drying section used were different from those of the actual application. The second group of Example 1 is the same as that of Example 1, in that the pellet materials of the same batch are dried and roasted, and various process data during the roasting process of the pellets are detected and recorded.

Comparative Example 3

Comparative Example 1 was repeated, except that in Comparative Example 3, the wind temperature and material thickness of the blast drying section were the same as those of Group 3 of Application Example 1. The same batch of pellet materials was dried and roasted, and various process data during the pellet roasting process were detected and recorded.

Comparative Example 4

Comparative Example 1 was repeated, except that in Comparative Example 4, the wind temperature and material thickness of the blast drying section were the same as those of Group 4 of Application Example 1. The same batch of pellet materials was dried and roasted, and various process data during the pellet roasting process were detected and recorded.

The various process data of the pellet roasting process under four different conditions in Application Example 1 were detected and recorded, and compared with Comparative Examples 1-4. The experimental results are shown in Table 4:

Table 4 Comparison table of various process data during pellet roasting under different conditions in Comparative Examples 1-4

Note: In comparative examples 1-4, the air temperature of the exhaust drying section II corresponds to the air temperature of the exhaust drying section.

Comparative Examples 1-4 are conventional processes for drying and roasting pellets using an existing belt roaster, and Comparative Examples 1-4 correspond to the process conditions of Group 1 to Group 4 in Example 1 (i.e., the wind temperature in the blast drying section and the material thickness). The same). By comparing the experimental verification data between Group 1 and Comparative Example 1, Group 2 and Comparative Example 2, Group 3 and Comparative Example 3, and Group 4 and Comparative Example 4 in the above table, it can be seen that the 4 groups of data obtained by using the new process of the present application in Application Example 1 are compared with the conventional process in Comparative Examples 1-4. The wind temperature of the exhaust drying II section of each group in Application Example 1 is significantly improved, and accordingly, the gas or fuel consumption, the amount of exhaust gas discharged, and the actual power consumption of the fan are significantly reduced, and the final yield and compressive strength of the pellets obtained are greatly improved. Therefore, the present application subdivides the existing blast drying section into a blast drying section and an exhaust drying I section, which greatly improves the drying efficiency of the pellet materials while ensuring that the pellet materials will not burst, so that the roasting process can be strengthened, and at the same time, various indicators of the pellet roasting process are significantly improved or improved.

In addition, the process conditions adopted in Comparative Examples 1 and 3 are respectively the same as those of Group 1 and Group 3 in Application Example 1, that is, the wind temperature in the blast drying section of Comparative Examples 1 and 3 is 300°C, but the material layer thickness of Comparative Example 1 is 400mm, and the material layer thickness of Comparative Example 3 is 600mm; similarly, the process conditions adopted in Comparative Examples 2 and 4 are respectively the same as those of Group 2 and Group 4 in Application Example 1, that is, the wind temperature in the blast drying section of Comparative Examples 2 and 4 is 360°C, but the material layer thickness of Comparative Example 2 is 400mm, and the material layer thickness of Comparative Example 4 is 600mm. Comparing the data of Comparative Examples 1 and 3, Comparative Examples 2 and Comparative Examples 4 in the above table, it can be found that when the conventional process is used for pellet roasting, under the condition of the same air temperature in the blast drying section, the thickness of the material layer is directly increased. The experimental results obtained are that when the fuel consumption remains unchanged, except for a slight change in the air temperature in the exhaust drying section, the exhaust gas volume, fan energy consumption, pellet yield rate and its compressive strength and other indicators will deteriorate. On the other hand, the first and third groups, the second and fourth groups in the application example 1 of the new process of the present application are used. The experimental results obtained are that under the condition of the same air temperature in the blast drying section, the wind temperature, gas or fuel consumption, exhaust gas volume, actual power consumption of the fan, and compressive strength of the pellets in the exhaust drying II section after increasing the thickness of the material layer are improved. Therefore, it can be seen that the new process of the present application is helpful to achieve thick material layer roasting.

Claims

A pellet drying and roasting process based on a roasting system, characterized in that: the roasting system (1) is provided with a blast drying section (101), an exhaust drying section I (102), an exhaust drying section II (103), a preheating section (104), a roasting section (105), a soaking section (106), a cooling section I (107), and a cooling section II (108) in sequence; the air inlet of the cooling section II (108) is connected to a cooling fan; the air outlet of the cooling section II (108) is connected to a first pipeline (L1), and the first pipeline (L1) is divided into two, namely, a second pipeline (L2) and a third pipeline (L3); the second pipeline (L2) is connected to the air inlet of the blast drying section (101), and a blower is provided on the second pipeline (L2); the third pipeline (L3) is connected to the exhaust drying section I (102); the process comprises the following steps:

1) The pelletized material is sequentially passed through a blast drying section (101) for blast drying, a suction drying section I (102) for suction drying, a suction drying section II (103) for further suction drying, a preheating section (104) for preheating, a calcining section (105) for calcining, a soaking section (106) for soaking, a cooling section I (107) and a cooling section II (108) for cooling on a roasting system (1) to obtain pelletized ore;

2) The air passes through the cooling fan to cool the pellets in the second cooling section (108), and is divided into two after being discharged. The air is respectively transported to the blast drying section (101) through the second pipeline (L2) to carry out blast drying of the pellets, and is transported to the exhaust drying section I (102) through the third pipeline (L3) to carry out exhaust drying of the materials.
The pellet drying and roasting process according to claim 1 is characterized in that the process further comprises the steps of:

3) The hot air discharged from the forced air drying section (101) is transported to the cooling section (107) to cool the pellets; the gas discharged from the cooling section (107) is respectively transported to the equalizing section (106), the roasting section (105) and the preheating section (104) to participate in the preheating and roasting of the pellets; the gas discharged from the rear section of the roasting section (105) and the equalizing section (106) is respectively transported to the exhaust drying section II (103) and the preheating section (104) to participate in the drying and preheating of the pellets; the gas discharged from the exhaust drying section I (102), the exhaust drying section II (103), the preheating section (104) and the front section of the roasting section (105) is discharged through an exhaust fan.
The pellet drying and roasting process according to claim 1 or 2 is characterized in that: the total length of the blast drying section (101) and the exhaust drying section (102) of the roasting system (1) is fixed, and the length of the blast drying section (101) is adjusted so that the moisture content of the pellet material after passing through the blast drying section (101) is lower than x 0 ;

Wherein: x0 is the upper limit of moisture content at which the pellet material explodes during the blast drying process; the value range of x0 is 10% to 16%.
The pellet drying and roasting process according to claim 3 is characterized in that: the blast drying section (101) is adjusted The length is:

A1) determining the power of the cooling fan according to the material processing amount per unit time of the roasting system (1), and further determining the air volume delivered by the cooling fan;

A2) calculating the temperature T of the exhaust air from the second cooling stage (108) based on the roasting temperature and the temperature of the pellets after cooling;

A3) determining the upper limit x 0 of the moisture content of the pelletized material at which bursting occurs during the blast drying process according to the temperature of the exhaust air from the second cooling stage (108) in the blast drying stage (101);

A4) According to the upper limit of moisture content at which the pellet material bursts, combined with the moisture enrichment of the pellet material during the drying process in the blast drying section (101), the maximum length of the blast drying section (101) is determined, and the length of the blast drying section (101) is adjusted to be less than or equal to the maximum length.
The pellet drying and roasting process according to claim 4 is characterized in that: the determination of the maximum length of the blast drying section (101) in step A4) is specifically:

The initial moisture content of the pellet material is detected, the thickness of the pellet material on the roasting system (1) is designed, and the pellet material on the air drying section (101) is air dried using wind at a temperature of T; the position where the moisture content of the pellet material on the surface of the air drying section (101) on the roasting system (1) reaches x 0 is detected, and the position is set as the limit position; the length from the starting position to the limit position of the air drying section (101) is the maximum length of the air drying section (101).
The pellet drying and roasting process according to claim 1 or 2 is characterized in that the total length of the blast drying section (101) and the exhaust drying section I (102) of the roasting system (1) is fixed; wherein the length ratio of the blast drying section (101) to the exhaust drying section I (102) is 2 to 6:1, preferably 3 to 4:1.
The pellet drying and roasting process according to claim 5 or 6 is characterized in that: a first control valve (2) is provided on the second pipeline (L2), and a second control valve (3) is provided on the third pipeline (L3); the first control valve (2) and the second control valve (3) are adjusted so that the ratio of the air volume delivered to the blast drying section (101) through the second pipeline (L2) and the air volume delivered to the exhaust drying section I (102) through the third pipeline (L3) is equal to the length ratio of the blast drying section (101) to the exhaust drying section I (102).
The pellet drying and roasting process according to claim 7 is characterized in that: the wind speed of the blast drying section (101) and the exhaust drying section I (102) is detected, and the first control valve (2) and the second control valve (3) are adjusted to make the wind speeds of the blast drying section (101) and the exhaust drying section I (102) equal.
The pellet drying and roasting process according to any one of claims 1 to 8, characterized in that: The air outlet of the section (101) is connected to the air inlet of the cooling section (107) via a fourth pipe (L4), and a cooling section fan is provided on the fourth pipe (L4); the rotation speed of the cooling section fan is adjusted so that the furnace hood pressure of the roasting section (105) is within a set range; wherein the setting range of the furnace hood pressure of the roasting section (105) is -100Pa to -50Pa.
The pellet drying and roasting process according to claim 9 is characterized in that: a cold air valve (4) is provided on the fourth pipeline (L4) at an upstream position of the cooling first stage fan; the opening of the cold air valve (4) is adjusted so that the air entering the cooling first stage (107) from the fourth pipeline (L4) meets both the air volume requirement and the energy requirement.