Low-calorific-value gas-based belt-type calciner thermal system and control method thereof

Abstract

The application provides a low-heat-value gas-based belt-type baking machine thermal system and a control method thereof. The belt-type baking machine thermal system comprises a blast drying section, an exhaust drying section, a preheating section, a baking section, a soaking section, a first cooling section, a second cooling section and a third cooling section, and is internally provided with multiple partition walls; the first cooling section and the second cooling section are provided with a first furnace cover, the second cooling section is provided with a second furnace cover, the first furnace cover is communicated with the cavities above the baking section and the soaking section, the second furnace cover is communicated with the cavity above the preheating section, the preheating section and the baking section are both provided with a first burner and a second burner, the first burner and the second burner are both communicated with a low-heat-value gas supply pipeline and an auxiliary combustion air pipeline, the first burner auxiliary combustion air pipeline is communicated with the second furnace cover, and the second burner auxiliary combustion air pipeline is communicated with the first furnace cover. The belt-type baking machine can realize stable combustion of low-heat-value coal gas and reach or approach the combustion temperature effect of high-heat-value coal gas, and the thermal efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of roasting technology, and in particular to a gas-fired belt roaster thermal system and its control method. Background Technology

[0002] Existing belt roasting processes for pelletizing iron ore powder can reach roasting temperatures of 1250–1380℃ or even higher, depending on the type and properties of the iron ore powder. Therefore, high-calorific-value gaseous fuels such as natural gas and coke oven gas are commonly used as heat sources. However, low-calorific-value fuels such as blast furnace gas and converter gas are unsuitable due to their low calorific value, insufficient heat supply, and inability to reach the required roasting temperatures, thus hindering the high-temperature roasting and solidification of pellets. Consequently, the reliance of existing belt roasting processes on high-calorific-value natural gas or coke oven gas has become the most significant technical drawback, directly impacting the widespread application of this technology.

[0003] Therefore, there is an urgent need to develop a pellet belt roasting thermal technology suitable for low-calorific-value gas (especially the large amount of blast furnace gas in steel plants), so that the advanced belt roasting process can be adapted to my country's energy characteristics and thus achieve large-scale popularization, significantly reducing the energy consumption level of high-energy-consuming processes in the steel industry.

[0004] Patent CN218435886U discloses an apparatus for producing ore pellets using low-calorific-value fuels. The apparatus first utilizes low-calorific-value coal gas to generate high-temperature, low-oxygen hot flue gas. This high-temperature flue gas is transported through a hot flue gas pipeline and introduced into the hoods of the preheating, roasting, and homogenizing sections of a belt roaster. In the drying and preheating sections, it mixes with the recycled tail gas from the cooling section of the belt roaster. Depending on the temperature requirements of different sections, this mixture is used for drying and preheating the pellets in the belt roaster process. In the high-temperature roasting section, a staged combustion process coupled with the high-temperature, low-oxygen hot flue gas is used to create a uniformly temperature-distributed high-temperature roasting environment, thereby increasing the roasting temperature of the pellets and supplying high-temperature heat. The number and arrangement of the high-temperature, low-oxygen burners are determined according to temperature and thermal control requirements to meet the roasting temperature requirements of the high-temperature sections. The drawback of this technology is that it requires an external combustion furnace to heat the hot air from the cold section with the flue gas generated in the furnace, raising its temperature before combustion with the low-calorific-value fuel gas. Because the cold section has a large air volume, the required flue gas volume for the combustion furnace also increases, increasing process energy consumption and preventing the utilization of the heat carried by the flue gas itself, resulting in low overall thermal efficiency. Summary of the Invention

[0005] The main objective of this invention is to provide a thermal system for a belt roaster based on low-calorific-value fuel gas and its control method, which aims to enable the use of low-calorific-value fuel gas in the belt roaster while improving its overall thermal efficiency.

[0006] To achieve the above objectives, the present invention provides a belt roaster thermal system based on low-calorific-value fuel gas, comprising a blower drying section, an exhaust drying section, a preheating section, a roasting section, a homogenizing section, a first cooling section, a second cooling section, and a third cooling section. The system is characterized in that partition walls are provided between the blower drying section and the exhaust drying section, between the exhaust drying section and the preheating section, between the preheating section and the roasting section, between the roasting section and the homogenizing section, between the section before and after the second cooling section, and between the second cooling section and the third cooling section. A first furnace hood is provided above the first cooling section and the front section of the second cooling section, and a second furnace hood is provided above the rear section of the second cooling section. The first furnace hood is connected to the chamber above the roasting section and the soaking section, and the second furnace hood is connected to the chamber above the preheating section. A first burner and a second burner are arranged above the preheating section and the roasting section. Both the first burner and the second burner are connected to the low-calorific-value gas supply pipeline and the combustion air pipeline. The combustion air pipeline of the first burner is connected to the second furnace hood, and the combustion air pipeline of the second burner is connected to the first furnace hood.

[0007] Preferably, a regenerating fan is connected to the lower outlet of the roasting section, and the outlet of the regenerating fan is connected to the top inlet of the preheating section and the exhaust drying section through a pipe.

[0008] Preferably, a first heat exchanger is installed on the pipe between the lower outlet of the roasting section and the regenerating fan. The first heat exchanger is connected to the low-calorific-value gas supply pipeline to preheat the gas in the first stage.

[0009] Preferably, a second heat exchanger is installed inside the second furnace shroud, and the control valve of the low-calorific-value gas supply pipeline of the second burner is connected to the gas inlet of the second heat exchanger, and the gas outlet of the second heat exchanger is connected to the second burner to achieve secondary preheating of the gas.

[0010] Preferably, the upper outlet of the three cooling sections is connected to the lower part of the blower drying section via a pipe and a blower to dry the green pellet layer.

[0011] Preferably, the upper outlet of the third cooling section is connected to the lower part of the first cooling section via a pipe and a blower.

[0012] Preferably, the lower outlet of the heat exchange section is connected to the inlet of the regenerating fan via a pipe.

[0013] Preferably, the front section of the second cooling section accounts for 30% to 40% of the total length of the second cooling section.

[0014] Preferably, both the first burner and the second burner are oxygen-enriched burners, and the burners adopt unbalanced plasma arc ignition; both the first burner and the second burner are equipped with control functions such as flame detection, automatic ignition, gas flow detection and automatic adjustment, gas high and low pressure alarm and automatic cut-off.

[0015] This invention also proposes a control method for the thermal system of a belt roaster based on the above-mentioned low-calorific-value fuel gas, comprising: Real-time monitoring of the thickness of green balls at multiple points on the belt roasting machine trolley, controlling the material supply and return of the feeding system and the speed of the roasting machine to maintain a constant material thickness on the trolley; The exhaust gas temperature of the air box in the exhaust drying section and preheating section is monitored in real time, and the motor frequency of the main exhaust fan is controlled to maintain the end temperature of the preheating section at 190℃~210℃. The exhaust gas temperature of the air box in the roasting section and the homogenization section is monitored in real time, and the motor frequency of the regenerating blower is controlled to maintain the final roasting temperature at 590℃~610℃. The pressure of the furnace hood above the first cooling section is monitored in real time, and the motor frequency of the cooling fan is controlled to maintain the pressure of the furnace hood above the first cooling section at -48Pa to -52Pa. The pressure of the furnace hood above the third cooling section is monitored in real time, and the motor frequency of the blower is controlled to maintain the pressure of the furnace hood above the third cooling section at -48Pa~-52Pa. The furnace hood pressure in the blast drying section is monitored in real time, and the motor frequency of the exhaust fan is controlled to maintain the furnace hood pressure in the blast drying section at -90Pa to -110Pa. The temperature of each measuring point in the furnace hood where the first burner is located is monitored in real time, and the gas flow rate corresponding to the first burner is controlled in coordination with the high-temperature secondary air temperature and gas preheating temperature, so that the temperature of each measuring point corresponding to the first burner is maintained at 600℃-1300℃. The temperature of each part of the furnace hood where the second burner is located is monitored in real time, and the gas flow rate corresponding to the second burner is controlled in coordination with the high-temperature secondary air temperature and the gas preheating temperature, so that the temperature of each temperature measuring point corresponding to the second burner is maintained at 1250℃~1350℃.

[0016] The thermal system of the belt roaster based on low-calorific-value fuel gas proposed in this invention has the following beneficial effects: 1. Through the comprehensive synergistic effect of preheating gas and precise cascade utilization of waste heat, stable combustion of low-calorific-value gas is achieved and the combustion temperature effect of high-calorific-value gas is reached or close to that of high-calorific-value gas, thus ensuring the temperature requirements of the roasting process. 2. Unlike existing technologies that add supplementary heat burners to the furnace hood to increase the secondary air temperature in the roasting section, the segmented air distribution (high-temperature air from the cooling section enters the preheating section and the roasting section in segments) maintains the high oxygen content (21%) of the secondary air and is conducive to the reaction rate of the oxidation process in the roasting process. 3. By using the roasting machine's own thermal system (high-temperature air from the cooling section) instead of adding an external heat source (such as adding a hot air furnace) to preheat the gas or increase the secondary air temperature, this thermal system has the highest thermal efficiency and low process energy consumption compared to other systems. 4. The preheating section and the calcination section are heated in stages, which satisfies the requirements of the preheating section for higher oxygen content and appropriate lower temperature, and also satisfies the requirements of the calcination section for higher process temperature and appropriate lower oxygen content. 5. The thermal system of this belt roaster has the advantages of simple structure, stable and reliable operation and easy implementation. It can significantly reduce the energy consumption level of high energy-consuming processes in the steel industry (based on an energy saving of 5 kgce / t, 1 billion tons of steel production capacity, approximately 500 million tons of standard coal and related carbon emissions saved annually). Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the thermal system of the belt roaster based on low-calorific-value gas according to the present invention.

[0018] In the diagram, 1-blown drying section, 2-exhaust drying section, 3-preheating section, 4-calcination section, 5-soaking section, 6-first cooling section, 7-second cooling section, 8-third cooling section, 9-first furnace hood, 10-second furnace hood, 11-first burner, 12-second burner, 13-low calorific value gas supply pipeline, 14-cooling fan, 15-regenerative fan, 16-exhaust fan, 17-first heat exchanger, 18-second heat exchanger, 19-blown drying fan, 20-desulfurization and denitrification equipment, 21-control valve, 22-partition wall, 23-main exhaust fan.

[0019] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0021] It should be noted that in the description of this invention, the terms "lateral," "longitudinal," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used solely for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0022] This invention proposes a thermal system for a belt roaster based on low-calorific-value fuel gas.

[0023] Reference Figure 1In this preferred embodiment, a belt roaster thermal system based on low-calorific-value gas includes a blower drying section 1, an exhaust drying section 2, a preheating section 3, a roasting section 4, a homogenizing section 5, a first cooling section 6, a second cooling section 7, and a third cooling section 8 arranged sequentially. Partition walls 22 are provided between the blower drying section 1 and the exhaust drying section 2, between the exhaust drying section 2 and the preheating section 3, between the preheating section 3 and the roasting section 4, between the roasting section 4 and the homogenizing section 5, between the front section and the rear section of the second cooling section 7, and between the second cooling section 7 and the third cooling section 8. A first furnace hood 9 is installed above the front section of the first cooling section 6 and the second cooling section 7, and a second furnace hood 10 is installed above the rear section of the second cooling section 7. The first furnace hood 9 is connected to the chamber above the roasting section 4 and the homogenizing section 5, and the second furnace hood 10 is connected to the chamber above the preheating section 3. A first burner 11 and a second burner 12 are respectively arranged above the preheating section 3 and the roasting section 4. The burners are connected to the low-calorific-value gas supply pipeline 13 and the combustion air pipeline. The combustion air pipeline of the first burner 11 is connected to the second furnace hood 10, and the combustion air pipeline of the second burner 12 is connected to the first furnace hood 9.

[0024] Low-calorific-value gas refers to gas with a calorific value of less than 1000 kcal / Nm³. 3 This typically refers to blast furnace gas. In this embodiment, multiple partition walls 22 are installed to achieve differentiated pressure distribution within the furnace between different process sections. The partition walls 22 are suspended using refractory materials, and the material selection must meet the operating temperature requirements of the area. The bottom of the refractory material of the partition wall 22 is 90mm~110mm from the top of the material layer, ensuring airtightness without hindering material transport. Specifically, in this embodiment, multiple first burners 11 and second burners 12 are installed. Cooling fans 14 are installed below the third cooling section 8 and the second cooling section 7. Desulfurization and denitrification equipment 20 is installed at the lower outlet of the exhaust drying section 2 and the preheating section 3, and the outlet of the desulfurization and denitrification equipment 20 is connected to the main exhaust fan 23. An external exhaust fan 16 is connected to the top outlet of the forced-air drying section 1.

[0025] Furthermore, a regenerating fan 15 is connected to the lower outlet of the roasting section 4, and the outlet of the regenerating fan 15 is connected to the top inlet of the preheating section 3 and the exhaust drying section 2 via a pipe. By connecting the regenerating fan 15 to the top inlet of the preheating section 3 and the exhaust drying section 2, the heat of the flue gas in the roasting section 4 is effectively utilized.

[0026] Furthermore, a first heat exchanger 17 is installed on the pipe between the lower outlet of the roasting section 4 and the regenerating blower 15. The first heat exchanger 17 is connected to the low-calorific-value gas supply pipeline 13 to preheat the gas in the first stage.

[0027] The first heat exchanger 17 is set up to exchange heat between the flue gas and the gas in the first heat exchanger 17. The high-temperature flue gas (400℃-600℃) extracted from the roasting section 4 heats the gas in the low-calorific-value gas supply pipeline 13 to 200℃-300℃, thereby realizing the cascade utilization of flue gas waste heat.

[0028] Furthermore, a second heat exchanger 18 is installed inside the second furnace shroud 10. The control valve 21 of the low-calorific-value gas supply pipeline 13 of the second burner 12 is connected to the gas inlet of the second heat exchanger 18, and the gas outlet of the second heat exchanger 18 is connected to the second burner 12 to achieve secondary preheating of the gas.

[0029] Through the second heat exchanger 18, the gas from the low-calorific-value gas supply pipeline 13 of the second burner 12 enters the second burner 12 after exiting the control valve 21. The gas is heated to 500℃-800℃ and then enters the second burner 12 to participate in combustion, thereby achieving high-temperature preheating of low-calorific-value gas.

[0030] In this embodiment, the low-calorific-value gas supply pipeline 13 of the roasting section 4 exits the control valve 21 and is then preheated separately, instead of the control valve 21 of the control valve of the single burner in the prior art where the gas is preheated centrally. This method reduces the temperature resistance requirements of the control valve 21 and increases the upper limit of the gas preheating temperature, so that the preheating temperature of the low-calorific-value gas in the roasting section 4 reaches about 800°C, which is much higher than the temperature that the gas can be preheated by the prior art (<400°C).

[0031] Furthermore, the upper outlet of the third cooling section 8 is connected to the lower part of the blower drying section 1 via a pipe and a blower 19 to dry the green pellet bed. The blower 19 recovers heat from the flue gas, thereby improving the overall thermal efficiency.

[0032] Furthermore, the upper outlet of the third cooling section 8 is connected to the lower part of the first cooling section 6 via a pipe and a blower 19, thereby further improving the thermal efficiency of this thermal system.

[0033] Furthermore, the lower outlet of the heat exchange section 5 is connected to the inlet of the regenerating fan 15 through a pipe, and the flue gas is recovered and then enters the exhaust drying section 2 and the preheating section 3, further improving the thermal efficiency of this thermal system.

[0034] Specifically, in this embodiment, the front section of the second cooling section 7 accounts for 30% to 40% of the total length of the second cooling section 7.

[0035] In this embodiment, both the first burner 11 and the second burner 12 are oxygen-enriched burners. Both burners employ unbalanced plasma arc ignition to ensure stable combustion of low-calorific-value gas. Both burners 11 and 12 are equipped with control functions including flame detection, automatic ignition, gas flow detection and automatic adjustment, and high / low pressure gas alarms and automatic shut-off.

[0036] By combining and synergistic effects of preheating gas, oxygen-enriched combustion, precise cascade utilization of waste heat, and plasma arc ignition, stable combustion of low-calorific-value gas is achieved, reaching or approaching the combustion temperature of high-calorific-value gas, thus ensuring the temperature requirements of the roasting process.

[0037] The working process of the thermal system of this belt roaster is as follows.

[0038] Low-temperature hot air (<300℃) from the upper part of the third cooling section 8 is mostly (60%~90%) sent to the lower part of the blower drying section 1 through the blower 19 to dry the green pellet layer. The dried hot air containing moisture (<200℃) is discharged to the environment from the upper part of the blower drying section 1 through the exhaust fan 16, and the remaining hot air (10%-40%) is sent to the lower part of the first cooling section 6.

[0039] The air drawn in by the cooling fan 14 from the atmosphere is pressurized and blown into the lower part of the second cooling section 7 and the third cooling section 8 to cool the high-temperature material layer and obtain high temperature. The high-temperature air (950-1050℃) coming out of the upper part of the first cooling section 6 and the front section of the second cooling section 7 flows into the first furnace hood 9 and then enters the roasting section 4 as the secondary air of the second burner 12. The high-temperature air (750-900℃) coming out of the upper part of the rear section of the second cooling section 7 flows into the second furnace hood 10 and enters the preheating section 3 as the secondary air of the first burner 11.

[0040] In the preheating section 3, the high-temperature secondary air (750-900℃) and coal gas in the first fume hood are mixed and burned by the first burner 11. The resulting high-oxygen (O2 content > 17%) high-temperature flue gas (900℃-1150℃) penetrates downward through the material layer and heats the pellets to the temperature required by the process. After desulfurization and denitrification treatment, it is discharged into the environment through the main exhaust fan 23.

[0041] The high-temperature secondary air (950-1050℃) and coal gas in the second furnace hood 10 are mixed and burned in the second burner 12. The resulting high-temperature flue gas (1200℃-1350℃) penetrates the material layer downwards, heating the pellets to the roasting temperature required by the process. Then, it is drawn into the upper part of the exhaust drying section 2 and the front part of the preheating section 3 by the regenerating blower 15, penetrates the material layer downwards, and uses the residual heat to dry and preheat the pellets to the process temperature. After being treated by the desulfurization and denitrification equipment 20, it is discharged into the environment by the main exhaust fan 23.

[0042] The thermal system of the belt roaster based on low-calorific-value fuel gas proposed in this invention has the following beneficial effects: 1. Through the comprehensive synergistic effect of preheating gas and precise cascade utilization of waste heat, stable combustion of low-calorific-value gas is achieved and the combustion temperature effect of high-calorific-value gas is reached or close to that of high-calorific-value gas, thus ensuring the temperature requirements of the roasting process. 2. By setting up partition wall 22 in conjunction with furnace hood, segmented air distribution is achieved (the high-temperature air of the cooling section enters the preheating section 3 and the roasting section 4 in segments). Unlike the existing technology that adds heat-generating burners to the furnace hood to increase the secondary air temperature of the roasting section 4, this thermal system can maintain the high oxygen content (21%) of the secondary air without reducing it, which is beneficial to the reaction rate of the oxidation process in the roasting process. 3. By using the roasting machine's own thermal system (high-temperature air from the cooling section) instead of adding an external heat source (such as adding a hot air furnace) as in existing technologies to preheat the gas or increase the secondary air temperature, this thermal system has the highest thermal efficiency and low process energy consumption compared to other methods. 4. The first furnace hood 9 and the second furnace hood 10 are set up, so that the preheating section 3 and the roasting section 4 can be heated in stages. This satisfies the requirements of the preheating section 3 for higher oxygen content and appropriate lower temperature, and also satisfies the requirements of the roasting section 4 for higher process temperature and appropriate lower oxygen content. 5. The thermal system of this belt roaster has the advantages of simple structure, stable and reliable operation and easy implementation. It can significantly reduce the energy consumption level of high energy-consuming processes in the steel industry (based on an energy saving of 5 kgce / t, 1 billion tons of steel production capacity, approximately 500 million tons of standard coal and related carbon emissions saved annually).

[0043] This invention also proposes a control method for the thermal system of a belt roaster based on low-calorific-value fuel gas.

[0044] This invention proposes a control method for a belt roaster thermal system based on low-calorific-value fuel gas, comprising: Real-time monitoring of the thickness of green pellets at multiple points on the belt roaster trolley controls the material supply and return of the feeding system and the speed of the roaster to maintain a constant thickness of material on the trolley (this avoids the trolley being directly impacted by the hot gas from the furnace hood and maintains a fixed amount of pellets passing through the roaster per unit time). The exhaust gas temperature of the air box in the exhaust drying section 2 and the preheating section 3 is monitored in real time, and the motor frequency of the main exhaust fan is controlled to maintain the final temperature of the preheating section 3 at 190℃~210℃ (to ensure that a certain amount of hot gas passes through the pellet material layer from top to bottom to dry and preheat the pellets. In addition, the hot and humid exhaust gas is discharged into the atmosphere through the main exhaust fan). The exhaust gas temperature of the wind box in roasting section 4 and homogenization section 5 is monitored in real time, and the motor frequency of the regenerating blower is controlled to maintain the roasting end temperature at 590℃~610℃ (which ensures that a certain amount of high-temperature hot gas passes through the pellet material layer from top to bottom to oxidize and solidify the pellets, and also ensures that the gas temperature entering the furnace hood of exhaust drying section 2 and preheating section 3 is within the range required by the process). Real-time monitoring of the furnace hood pressure above the first cooling section 6, and control of the motor frequency of the cooling fan to maintain the furnace hood pressure above the first cooling section 6 at -48Pa~-52Pa (ensuring that a certain amount of cooling air passes through the hot material layer to effectively cool the pellets). Real-time monitoring of the furnace hood pressure above section 8 of the third cooling section, and control of the motor frequency of the blower to maintain the furnace hood pressure above section 8 of the third cooling section at -48Pa to -52Pa (ensuring a certain amount of low-temperature hot gas enters the blower box of the blower drying section 1 to dry the pellets from bottom to top through the pellet material layer). The pressure of the furnace hood in the blower drying section 1 is monitored in real time, and the motor frequency of the exhaust fan is controlled to maintain the pressure of the furnace hood in the blower drying section 1 at -90Pa to -110Pa (to ensure that the hot and humid exhaust gas is effectively discharged into the atmosphere through the exhaust fan). The temperature of each measuring point in the furnace hood where the first burner 11 is located is monitored in real time. The gas flow rate corresponding to the first burner 11 is controlled in coordination with the high-temperature secondary air temperature and the gas preheating temperature to maintain the temperature of each measuring point corresponding to the first burner 11 between 600℃ and 1300℃ (each measuring point gradually increases from 600℃ to 1300℃ along the length of the preheating section 3 to ensure that the furnace hood temperature of the preheating section 3 is within the range required by the process). The temperature of each part of the furnace hood where the second burner 12 is located is monitored in real time. The gas flow rate corresponding to the second burner 12 is controlled in coordination with the high-temperature secondary air temperature and the gas preheating temperature to keep the temperature of each temperature measuring point corresponding to the second burner 12 between 1250℃ and 1350℃ (ensuring that the temperature of the furnace hood in the roasting section 4 is within the roasting temperature range required by the process).

[0045] The control method proposed in this invention ensures that each section of the roasting machine is controlled within the corresponding range by monitoring the temperature at multiple points, thereby guaranteeing the quality of product production.

[0046] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A thermal system for a belt calciner based on low-calorific-value fuel gas, comprising a forced-air drying section, a forced-air drying section, a preheating section, a calcination section, a homogenization section, a first cooling section, a second cooling section, and a third cooling section, characterized in that, Partition walls are provided between the blower drying section and the exhaust drying section, between the exhaust drying section and the preheating section, between the preheating section and the calcination section, between the calcination section and the homogenization section, between the front section and the rear section of the second cooling section, and between the second cooling section and the third cooling section. A first furnace hood is installed above the first cooling section and the front section of the second cooling section, and a second furnace hood is installed above the rear section of the second cooling section. The first furnace hood is connected to the chamber above the calcination section and the soaking section, and the second furnace hood is connected to the chamber above the preheating section. A first burner and a second burner are arranged above both the preheating section and the calcination section. Both the first burner and the second burner are connected to a low-calorific-value gas supply pipeline and a combustion air pipeline. The combustion air pipeline of the first burner is connected to the second furnace hood, and the combustion air pipeline of the second burner is connected to the first furnace hood. The calorific value of the gas in the low-calorific-value gas supply pipeline is less than 1000 kcal / Nm³. 3 A regenerating fan is connected to the lower outlet of the roasting section, and the outlet of the regenerating fan is connected to the top inlet of the preheating section and the exhaust drying section via a pipe. A first heat exchanger is installed on the pipe between the lower outlet of the roasting section and the regenerating fan. The first heat exchanger is connected to a low-calorific-value gas supply pipeline for primary preheating of the gas. A second heat exchanger is installed inside the second furnace hood. The control valve of the low-calorific-value gas supply pipeline of the second burner is connected to the gas inlet of the second heat exchanger, and the gas outlet of the second heat exchanger is connected to the second burner to achieve secondary preheating of the gas. The gas in the low-calorific-value gas supply pipeline is heated to 200℃-300℃ after heat exchange in the first heat exchanger, and heated to 500℃-800℃ after heat exchange in the second heat exchanger.

2. The thermal system of the belt roaster based on low-calorific-value fuel gas as described in claim 1, characterized in that, The upper outlet of the three cooling sections is connected to the lower part of the blower drying section via a pipe to dry the green pellet layer.

3. The thermal system of the belt roaster based on low-calorific-value fuel gas as described in claim 2, characterized in that, The upper outlet of the third cooling section is connected to the lower part of the first cooling section via a pipe and a blower.

4. The thermal system of the belt roaster based on low-calorific-value fuel gas as described in claim 1, characterized in that, The lower outlet of the heat exchange section is connected to the inlet of the regenerating fan via a pipe.

5. The thermal system of the belt roaster based on low-calorific-value fuel gas as described in claim 1, characterized in that, The front section of the second cooling section accounts for 30% to 40% of the total length of the second cooling section.

6. The thermal system of a belt roaster based on low-calorific-value fuel gas as described in any one of claims 1 to 5, characterized in that, Both the first and second burners are oxygen-enriched burners, and the burners adopt unbalanced plasma arc ignition. Both the first and second burners are equipped with flame detection, automatic ignition, gas flow detection and automatic adjustment, gas high and low pressure alarm and automatic cut-off control functions.

7. A control method for a belt roaster thermal system based on low-calorific-value fuel gas as described in any one of claims 1 to 6, characterized in that, Includes the following steps: Real-time monitoring of the thickness of green balls at multiple points on the belt roasting machine trolley, controlling the material supply and return of the feeding system and the speed of the roasting machine to maintain a constant material thickness on the trolley; The exhaust gas temperature of the air box in the exhaust drying section and preheating section is monitored in real time, and the motor frequency of the main exhaust fan is controlled to maintain the end temperature of the preheating section at 190℃~210℃. The exhaust gas temperature of the air box in the roasting section and the homogenization section is monitored in real time, and the motor frequency of the regenerating blower is controlled to maintain the final roasting temperature at 590℃~610℃. The pressure of the furnace hood above the first cooling section is monitored in real time, and the motor frequency of the cooling fan is controlled to maintain the pressure of the furnace hood above the first cooling section at -48Pa to -52Pa. The pressure of the furnace hood above the third cooling section is monitored in real time, and the motor frequency of the blower is controlled to maintain the pressure of the furnace hood above the third cooling section at -48Pa~-52Pa. The furnace hood pressure in the blast drying section is monitored in real time, and the motor frequency of the exhaust fan is controlled to maintain the furnace hood pressure in the blast drying section at -90Pa to -110Pa. The temperature of each measuring point in the furnace hood where the first burner is located is monitored in real time, and the gas flow rate corresponding to the first burner is controlled in coordination with the high-temperature secondary air temperature and gas preheating temperature, so that the temperature of each measuring point corresponding to the first burner is maintained at 600℃-1300℃. The temperature of each part of the furnace hood where the second burner is located is monitored in real time, and the gas flow rate corresponding to the second burner is controlled in coordination with the high-temperature secondary air temperature and the gas preheating temperature, so that the temperature of each temperature measuring point corresponding to the second burner is maintained at 1250℃~1350℃.

Images