Method for waste gas circulation in a pellet production process in a belt furnace

Abstract

The application discloses a waste gas circulation method in a pellet production process of a belt-type indurating machine. The belt-type indurating machine is divided into three cooling sections from the end of the soaking section to the discharging end, and the three cooling sections include a front cooling section, a first cooling section and a second cooling section in sequence. A part of waste gas of the second cooling section leads to the front cooling section, and another part leads to the blast drying section. The method can reduce the wind mixing between the soaking section and the cooling section, improve the effect of the soaking section, reduce the initial cooling speed, increase the adjustable range of the air temperature and air volume of the blast drying section, avoid the air volume diffusion of the second cooling section, and finally reduce the fuel consumption of the belt-type indurating machine by 1-8%, and reduce the diffusion air volume by 5-15%.

Description

Technical Field

[0001] This invention relates to a waste gas recirculation method in the pellet production process of a belt roaster, belonging to the field of iron and steel pellet production technology. Background Technology

[0002] Belt roasters are the main equipment for producing iron ore pellets. However, the uneven quality of pellets produced by belt roasters has long been a problem. This is mainly manifested in the fact that the upper layer maintains a higher temperature for a longer period during roasting than the lower layer, resulting in insufficient effective roasting time for the lower layer. Although the purpose of the homogenizing section is to transfer the temperature from the upper layer to the lower layer, thus reducing this unevenness, in actual production, severe air leakage occurs between the homogenizing and cooling sections. Heat from the upper layer cannot be effectively transferred downwards, so the homogenizing section fails to achieve its intended effect. Furthermore, when the high-temperature pellets from the homogenizing section enter the cooling section, ambient-temperature cooling air flows upwards through the pellet layer, causing excessively rapid cooling of the pellets, especially in the lower layer, which does not conform to the optimal pellet cooling rate curve and deteriorates the pellet quality.

[0003] In addition, the hot exhaust gas from the second cooling section is transferred to the blower drying section through the blower. Due to the limitations of the air temperature and air volume in the blower drying section, the hot exhaust gas from the second cooling section is released to varying degrees, resulting in a loss of air volume and energy. Summary of the Invention

[0004] To address the technical problems existing in the prior art, the purpose of this invention is to provide a method for circulating exhaust gas in the secondary cooling section during the pellet production process of a belt calciner. This method, by adding a pre-cooling section, extending the secondary cooling section, and controlling the circulation of exhaust gas from the secondary cooling section to the blower drying section and the pre-cooling section, can reduce cross-flow between the homogenizing section and the cooling section, improve the effect of the homogenizing section, reduce the initial cooling rate, increase the adjustable range of air temperature and air volume in the blower drying section, and avoid the release of air volume in the secondary cooling section. This can reduce the fuel consumption of the belt calciner by 1% to 8% and reduce the release air volume by 5% to 15%.

[0005] To achieve the above-mentioned technical objectives, the present invention provides a waste gas circulation method in the pellet production process of a belt roaster. The main improvement is that the belt roaster is divided into three cooling sections from the end of the homogenization section to the discharge end. The three cooling sections include a pre-cooling section, a first cooling section, and a second cooling section in sequence. Part of the waste gas from the second cooling section goes to the pre-cooling section, and the other part goes to the blower drying section.

[0006] The key improvement of the technical solution of this invention lies in the following aspects: On the one hand, a pre-cooling section is set between the heating section and the first cooling section. The pre-cooling section is used to reduce the cross-flow of air to the heating section, thereby enhancing the effect of the heating section. The heat of the upper material layer can be fully diffused to the lower layer, thereby reducing the temperature curve difference between the upper and lower material layers and improving the quality of the lower pellets. On the other hand, part of the exhaust gas from the second cooling section is directed to the pre-cooling section and the other part is directed to the blower drying section. This ensures that the exhaust gas from the second cooling section meets the required air temperature and volume for the blower drying process, while the excess air volume is transferred to the air box at the cooling front end. This avoids the venting caused by the mismatch between the required air temperature and volume of the blower drying section and the air temperature and volume of the second cooling section hood, and improves the utilization rate of gas and energy.

[0007] As a preferred embodiment, the inlet air pressure of the pre-cooling section is 1000Pa to 2500Pa, which is lower than the inlet air pressure of the first cooling section. Generally, the inlet air pressure of the first cooling section is greater than 2500Pa. By controlling the inlet air pressure of the pre-cooling section air box to be lower than that of the first cooling section air box, the cross-flow of air into the homogenizing section can be reduced, thereby enhancing the effect of the homogenizing section. The heat from the upper material layer can be fully diffused to the lower layer, thus reducing the temperature difference between the upper and lower material layers and improving the quality of the lower pellets.

[0008] As a preferred embodiment, the inlet air temperature of the pre-cooling section is higher than the ambient air temperature. On the one hand, this can reduce the initial cooling rate of the pellets and increase the heat preservation time of the pellet bed; on the other hand, it optimizes the cooling rate curve of the pellet bed, thereby enhancing the thermal state of the pellet bed.

[0009] As a preferred embodiment, the exhaust gas from the pre-cooling section is recirculated to the homogenizing section. If the outlet air volume of the pre-cooling section is greater than the required air volume of the homogenizing section, the excess portion is carried by the exhaust gas from the first cooling section to the preheating and calcining sections; otherwise, the exhaust gas from the first cooling section supplements the required air volume of the homogenizing section. This operation can increase the inlet air temperature of the homogenizing section, enhance its effectiveness, and improve the thermal state level of the material layer in the homogenizing section.

[0010] As a preferred embodiment, the exhaust gas composition of the second cooling section is similar to that of air, the temperature is 150℃~600℃, and the exhaust gas volume accounts for 25%~35% of the total exhaust gas volume of the entire cooling section.

[0011] As a preferred embodiment, the secondary cooling section uses an exhaust gas switching valve to adjust the exhaust gas direction, thereby regulating the air temperature and air volume of the exhaust gas in the blower drying section and the pre-cooling section. The exhaust gas switching valve adjustment strategy is: open first and then close.

[0012] As a preferred embodiment, the exhaust gas switching valve is installed at the corresponding position of the exhaust hood outlet pipe in the secondary cooling section, used to adjust the air temperature and air volume in the blower drying section and the pre-cooling section. The secondary cooling section is equipped with a set of exhaust hoods, each with an exhaust gas switching valve at its outlet pipe. The adjustment strategy for the exhaust gas switching valves is: open first, then close, to avoid both branches of the same exhaust hood duct being closed. Simultaneously, by adjusting the opening and closing degree of the exhaust gas switching valves for different exhaust hoods, the air temperature and air volume passing through the blower drying section are adjusted, and then the remaining gas is passed to the pre-cooling section.

[0013] As a preferred embodiment, the lengths of the pre-cooling section, the first cooling section, and the second cooling section account for 5%–15%, 50%–65%, and 25%–35% of the total cooling section length, respectively. The relatively longer length of the second cooling section allows the exhaust gas from the second cooling section to meet the air volume required by the blower section, while a certain amount of hot air is allowed to enter the pre-cooling section, thereby enhancing the effects of the heat equalization section and the pre-cooling section.

[0014] As a preferred embodiment, the second cooling section is connected to the first cooling section by a low-power first cooling fan, and the fan needs to withstand a temperature of 250℃~500℃.

[0015] Compared with the prior art, the advantages of the technical solution of the present invention are as follows:

[0016] (1) In this invention, a front cooling section is set between the heating section and the first cooling section. The heating section is not connected to the first cooling section, but is connected to the front cooling section. The inlet air pressure of the front cooling section air box is less than that of the first cooling section air box, thus reducing the air leakage to the heating section. The effect of the heating section is enhanced, and the heat of the upper material layer can be fully diffused to the lower layer, thereby reducing the temperature curve difference between the upper and lower material layers and enhancing the quality of the lower pellets.

[0017] (2) The inlet air temperature of the front cooling section air box of the present invention is greater than that of the inlet air temperature of the first cooling section air box, which can reduce the initial cooling rate of the pellets, increase the heat preservation time of the material layer, optimize the cooling rate curve of the material layer, and thus enhance the thermal state of the pellet material layer. At the same time, it can increase the inlet air temperature of the heat equalization section, enhance the effect of the heat equalization section, and improve the thermal state level of the material layer in the heat equalization section.

[0018] (3) The hot exhaust gas from the outlet of the two cooling section of the present invention is regulated by the exhaust gas switching valve. First, it meets the air temperature and air volume required for the blower drying process. Then, all the remaining air volume is transmitted to the air box at the cooling front end. This avoids the release caused by the mismatch between the air temperature and air volume required for the blower drying section and the air temperature and air volume of the two cooling section hood, and improves the utilization rate of gas and energy.

[0019] In summary, the waste gas circulation method in the belt calciner pellet production process provided by this invention reduces cross-flow between the homogenization section and the cooling section by changing the gas circulation mode in the cooling process, increases the maximum temperature of the lower material layer and the high temperature holding time, improves the utilization rate of the belt calciner, reduces the phenomenon of uneven calcination between the upper and lower material layers, and improves the compressive strength and distribution uniformity. At the same time, it precisely controls the air temperature and air volume in the drying section, avoids gas venting in the cooling section, and increases gas utilization. This is of great significance for improving the output and quality of belt calciner pellets and reducing energy consumption. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the waste gas circulation system from the homogenization section to the cooling section in the pellet production process of the belt roaster of the present invention.

[0021] Figure 2 This is a schematic diagram of the waste gas circulation system from the homogenization section to the cooling section in the original belt roaster pellet production process. Detailed Implementation

[0022] The following specific embodiments are intended to further illustrate the content of the present invention, rather than to limit the scope of protection of the claims.

[0023] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0024] like Figure 1 As shown: The belt roaster consists of a homogenizing section, a pre-cooling section, a first cooling section, and a second cooling section, moving from the homogenizing section along the material layer movement direction to the discharge end. The air boxes and fume hoods are divided into four groups: the first group of air boxes and the first group of fume hoods correspond to the homogenizing section; the second group of air boxes and the second group of fume hoods correspond to the pre-cooling section; the third group of air boxes and the third group of fume hoods correspond to the first cooling section; and the fourth group of air boxes and the fourth group of fume hoods correspond to the second cooling section. It also includes a pre-cooling fan, an exhaust gas switching valve, and a blower. The inlet of the pre-cooling fan is connected to the outlet pipe of the fume hood in the second cooling section, and the outlet of the pre-cooling fan is connected to the inlet of the air boxes in the pre-cooling section. The exhaust gas switching valve is used to adjust the inlet air temperature and volume of the pre-cooling fan and the air temperature and volume of the blower. All exhaust gas switching valves in the second cooling section are connected to the automatic control system.

[0025] Example 1

[0026] This embodiment, based on a 400t / a belt calciner production line in China, calculates the effect after implementation under the same process conditions and equipment parameters. Table 1 shows the number and length of air boxes for each section before and after implementation. Tables 2 and 3 show the inlet and outlet air temperatures and air volumes of each section of the belt calciner from the homogenization section to the secondary cooling section before and after implementation. Combining the enhanced effect of the homogenization section with the role of the primary cooling section, at a machine speed of 3.5m / min, the high-temperature holding time for different material layer heights can be extended by 20-100s. Under the condition of production quality indicators, it can save 1%-4% of gas consumption. In addition, based on a 10% reduction in venting air volume, the venting air volume is reduced by approximately 15,000-20,000 Nm³. 3 / h.

[0027] Table 1 Specifications of each section before and after implementation

[0028]

[0029]

[0030] Table 2. Air temperature and air volume in each section before implementation.

[0031]

[0032] Table 3 shows the air temperature and volume of each section after implementation.

[0033]

[0034] Example 2

[0035] This embodiment, based on a 500t / a belt calciner production line in China, calculates the effect after implementation under the same process conditions and equipment parameters. Table 4 shows the number and length of air boxes for each section before and after implementation. Tables 5 and 6 show the inlet and outlet air temperatures and air volumes of each section of the belt calciner from the homogenization section to the secondary cooling section before and after implementation. Combining the enhanced effect of the homogenization section with the role of the primary cooling section, at a machine speed of 4.0m / min, the high-temperature holding time for different material layer heights can be extended by 20-120s. Under the condition of production quality indicators, it can save 1%-5% of gas consumption. In addition, based on a 10% reduction in venting air volume, the venting air volume is reduced by approximately 15,000-20,000 Nm. 3 / h.

[0036] Table 4 Specifications of each section before and after implementation

[0037]

[0038] Table 5. Air temperature and air volume in each section before implementation.

[0039]

[0040] Table 6 shows the air temperature and volume of each section after implementation.

[0041]

[0042] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are protected by the present invention.

Claims

1. A method for waste gas recirculation during pellet production using a belt calciner, wherein the belt calciner is divided into three cooling sections from the end of the homogenization section to the discharge end, characterized in that: The three cooling sections are, in sequence, a front cooling section, a first cooling section, and a second cooling section; Part of the exhaust gas from the second cooling section goes to the first cooling section, and the other part goes to the blower drying section. The inlet air pressure of the pre-cooling section is 1000Pa to 2500Pa, which is less than the inlet air pressure of the first cooling section. The lengths of the front cooling section, the first cooling section, and the second cooling section account for 5%–15%, 50%–65%, and 25%–35% of the total length of the cooling section, respectively.

2. The waste gas recirculation method in the pellet production process of a belt roaster according to claim 1, characterized in that: The inlet air temperature of the pre-cooling section is higher than the ambient air temperature.

3. The waste gas recirculation method in the pellet production process of a belt roaster according to claim 1, characterized in that: The exhaust gas from the first cooling section is circulated to the heat equalization section. If the outlet air volume of the first cooling section is greater than the air volume required by the heat equalization section, the excess part will be carried by the exhaust gas from the first cooling section to the preheating section and the calcination section. Otherwise, the exhaust gas from the first cooling section will supplement the air volume required by the heat equalization section.

4. The waste gas recirculation method in the pellet production process of a belt roaster according to claim 1, characterized in that: The second cooling section uses an exhaust gas switching valve to adjust the exhaust gas direction in order to regulate the air temperature and air volume of the gas in the blower drying section and the pre-cooling section. The exhaust gas switching valve adjustment strategy is: open first and then close.

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