Pellet electric heat roasting method and shaft furnace system

Abstract

The application discloses a kind of pellet electric heat roasting method and shaft furnace system, by a certain amount of microwave absorbing material is mixed in iron-containing pellet to carry out coupling and then reach the purpose of full electric roasting, by reasonable distribution ideal pellet and microwave absorbing material distribution and air distribution are built, form small particle iron-containing pellet absorption high-energy microwave, large particle microwave absorbing material absorption low-energy microwave's cascade heat conversion system, in response to the adverse situation that the composition of pellet is changed from Fe3O4 into Fe2O3 and causes the decline of pellet wave absorbing capacity, make full use of the strong wave absorption and high efficiency heat conversion performance of microwave absorbing material microwave energy is converted into heat energy, ensure the uniformity of preheating section temperature and roasting soaking section temperature, to ensure the performance index of oxidized pellet.In addition, the present application is powered by green electricity throughout, significantly reduce the emission of NOx and SO2 due to the use of fossil fuels from the source, can greatly help the ultimate energy efficiency and near-zero carbon emission of full electric pellet production process.

Description

Technical Field

[0001] This invention relates to green electric pellet roasting technology, specifically to an electric pellet roasting method and vertical furnace system, belonging to the field of all-electric pellet roasting technology. Background Technology

[0002] Compared to sinter, pellets are a superior raw material for blast furnace ironmaking, boasting advantages such as high iron content, excellent metallurgical properties, and low energy consumption and pollutant emissions. However, pellet production, regardless of whether it's a vertical shaft furnace, chain grate rotary kiln, or belt roaster, still relies on heat generated from the combustion of anthracite or coal gas to roast the pellets via heat conduction / radiation. This inevitably leads to problems such as high roasting temperatures, uneven temperature fields within the pellets, and uneven pellet quality. For example, excessively high or low flame temperatures in rotary kilns can cause some pellets to be over- or under-roasted, while over-roasting in the upper layers and under-roasting in the lower layers of belt roasters results in uneven pellet quality. The "outside-to-inside" heating method of heat conduction leads to slow heating speeds and uneven consolidation between the inner and outer layers. Therefore, achieving low-carbon, low-temperature, rapid, and high-quality roasting of pellets has become a crucial focus in pellet production.

[0003] Guided by the goals of carbon peaking and carbon neutrality, my country's steel industry is striving to transform its energy structure, shifting from carbon-rich energy to hydrogen-rich energy and renewable energy sources such as hydropower, wind power, and photovoltaic power. For example, Baowu Group has incorporated the electrification of the entire steel smelting process into its carbon-neutral metallurgical technology roadmap. Building on this, and leveraging the advantages of high-quality, high-efficiency, and clean electricity, coupled with the continuous increase in national power generation capacity and clean energy generation, electrically heated pellet roasting technology has become a research hotspot. This technology aims to replace all or part of existing carbon-based fuels with clean and renewable green electricity, achieving near-zero carbon emissions in iron ore pellet production, promoting the green development of the steel industry, and fulfilling its dual-carbon mission. However, existing microwave roasting technology suffers from energy attenuation due to the inherent characteristics of microwave heating, making it difficult to achieve uniform heating of materials in large furnace loading conditions. Therefore, it often requires the use of fossil fuel heating to achieve uniform and stable heating, but this still results in significant carbon emissions. Summary of the Invention

[0004] To address the problem that existing microwave roasting methods for pellets cannot guarantee uniform and stable heating of materials, this invention provides an electrothermal roasting method for pellets. By incorporating a certain amount of microwave absorbing material into iron-containing pellets, and considering the adverse effect of the pellets' reduced microwave absorption capacity due to the conversion of the pellet composition from Fe3O4 to Fe2O3, the method fully utilizes the strong microwave absorption and high-efficiency thermal conversion performance of the microwave absorbing material to convert microwave energy into heat energy, thereby ensuring uniform and stable heating of the pellets. This ensures the performance indicators of oxidized pellets without the need for additional fossil fuels.

[0005] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0006] According to a first embodiment of the present invention, a method for electrothermal calcination of pellets is provided:

[0007] A method for electrothermal roasting of pellets, the method comprising the following steps:

[0008] S1. Mix iron-containing pellets with microwave-absorbing pellets to obtain mixed furnace charge.

[0009] S2. In the roasting furnace, the mixed furnace material is successively subjected to hot air drying, weak microwave preheating, strong microwave roasting and homogenization, and cooling treatment to obtain the mixed roasting material.

[0010] S3. The mixed calcined material is sieved to obtain oxidized pellets and residual microwave absorbing material.

[0011] Preferably, in step S1, the absorbing spheres are Fe x O y The microwave absorbing pellets are selected from at least one of the following: TiO2 / C composite pellets, silicon carbide pellets, silicon nitride, alumina, or mullite-based composite carbonaceous materials. Preferably, the amount of the microwave absorbing pellets is 10-40% of the mass of the iron-containing pellets, and more preferably 15-30%.

[0012] Preferably, in step S1, the iron-containing pellets have a particle size of 8-16 mm. The microwave-absorbing pellets have a particle size of 16-20 mm.

[0013] Preferably, in step S2, the temperature of the hot air drying is 250~400℃, and the drying time is 4~10min.

[0014] Preferably, in step S2, the temperature of the weak microwave preheating is 900~1020℃, and the preheating time is 5~20min.

[0015] Preferably, in step S2, the temperature for strong microwave roasting and homogenization is 1150~1250℃, the roasting time is 5~20min, and the homogenization time is 3~10min.

[0016] Preferably, in step S2, the cooling is air cooling, and the cooling rate is 20~40℃ / min.

[0017] Preferably, in step S2, the microwave frequency is 915±13MHz or 2450±50MHz, wherein the weak microwave power is between 100~200kW and the strong microwave power is between 300~650kW.

[0018] Preferably, in step S2, an oxidizing gas is introduced during the weak microwave preheating and strong microwave roasting and homogenization. Preferably, the oxidizing gas is air and / or oxygen.

[0019] Preferably, in step S2, the mixed furnace charge is distributed in the calcining furnace with a segregated distribution in which the particle size of the material near the furnace wall is smaller than that of the material in the center.

[0020] Preferably, in step S2, the cooling medium during cooling is room temperature air. The hot air used for drying is at least one of the following: cooled exhaust gas, preheated exhaust gas, calcined exhaust gas, and homogenized exhaust gas.

[0021] Preferably, in step S3, the sieving process includes a coarse sieve and a fine sieve, wherein the sieve aperture of the coarse sieve is not less than 16 mm (preferably consistent with the maximum particle size of the iron-containing pellets, for example, 16 mm), and the sieve aperture of the fine sieve is not greater than 8 mm (preferably consistent with the minimum particle size of the iron-containing pellets, for example, 8 mm).

[0022] Preferably, the residual microwave absorbing material is subjected to gravity separation to obtain iron-containing powder and microwave absorbing material. The iron-containing powder is recycled as raw material for iron-containing pellets (or the iron-containing powder and oxide pellets are used together as raw materials for ironmaking / steelmaking), and the microwave absorbing material is recycled as raw material for microwave absorbing pellets.

[0023] According to a second embodiment of the present invention, a vertical shaft furnace system for electrothermal roasting of pellets is provided:

[0024] A vertical shaft furnace system for electrothermal roasting of pellets, or a vertical shaft furnace system for the electrothermal roasting method of pellets described in the first embodiment, the vertical shaft furnace system includes a furnace shell and a furnace chamber. The furnace chamber is divided from top to bottom into a drying section, a preheating section, a roasting section, a homogenizing section, and a cooling section. A first microwave generator is installed on the furnace shell corresponding to the preheating section. A second microwave generator is installed on the furnace shell corresponding to the roasting section. A third microwave generator is installed on the furnace shell corresponding to the homogenizing section. A feed inlet is provided at the top of the drying section, and a discharge outlet is provided at the bottom of the cooling section.

[0025] Preferably, a drying bed is provided in the drying section, the drying bed including a grate and blower beams. The grate has a herringbone structure that is narrower at the top and wider at the bottom, and multiple blower beams are evenly arranged on the bottom side of the grate, with both ends of the blower beams connected to the furnace shell; the blower beams have a hollow tubular structure, and air outlet holes are opened on the tube wall of the blower beam facing the grate.

[0026] Preferably, at least one oxygen supply pipe connected to the soaking section is provided on the furnace shell corresponding to the soaking section. Preferably, at least one oxygen supply pipe connected to the calcination section is also provided on the furnace shell corresponding to the calcination section. Preferably, at least one oxygen supply pipe connected to the preheating section is also provided on the furnace shell corresponding to the preheating section.

[0027] Preferably, a cooling medium inlet pipe and a cooling medium outlet pipe are also provided on the furnace shell corresponding to the cooling section. The cooling medium inlet pipe is connected to the lower part of the cooling section, and the cooling medium outlet pipe is connected to the upper part of the cooling section.

[0028] Preferably, the cooling medium output pipe is connected to the lower part of the drying section through a cooling exhaust gas conveying pipe.

[0029] Preferably, the vertical shaft furnace system also includes a mixing chamber. The upper part of the preheating section is connected to the air inlet of the mixing chamber via a preheating waste gas conveying pipe. The upper part of the roasting section is connected to the air inlet of the mixing chamber via a roasting waste gas conveying pipe. The upper part of the homogenizing section is connected to the air inlet of the mixing chamber via a homogenizing waste gas conveying pipe. The upper part of the cooling section is connected to the air inlet of the mixing chamber via a cooling medium output pipe and a cooling waste gas conveying pipe. The exhaust port of the mixing chamber is connected to the lower part of the drying section via a mixed hot air conveying pipe. Preferably, an air replenishment pipe is also provided on the mixing chamber.

[0030] Preferably, the vertical furnace system also includes a screening mechanism. The screening mechanism includes a first screen and a second screen arranged sequentially below the cooling section. The aperture of the first screen is not less than 16 mm (preferably 16~20 mm), and the aperture of the second screen is not greater than 8 mm (preferably 6~8 mm).

[0031] In this invention, based on the concept of low-carbon clean oxidation pellet production using electric energy-microwave energy, a fully electric pellet electrothermal roasting method is proposed. The key to this method is to add a certain proportion of microwave absorbing material (i.e., microwave absorbing pellets) to iron-containing pellets (or iron ore pellets). After the material passes through the drying section, in the preheating section, the hot waste gas generated in the subsequent process (hot waste gas from the roasting section and / or hot waste gas from the homogenization section and / or hot waste gas from the cooling section) is coupled with weak microwave energy for heating. At this time, both the strong microwave absorbing magnetite pellets and the externally added microwave absorbing material can quickly convert microwave energy into heat energy, ensuring that the temperature in the preheating section is within the range of 900~1050℃, and ensuring the performance indicators of the preheated iron-containing pellets (meeting the compressive strength >400N / P). In the roasting section, only strong microwave energy is used for heating, without using fossil fuels such as carbon-based gaseous fuels for combustion and heat release. The heat generated by the strong microwave absorbing material compensates for the heat released by the weakly absorbing hematite pellets, thus ensuring that the roasting temperature is maintained at 1150~1250℃, ensuring the performance indicators of the iron-containing pellets after roasting (meeting the compressive strength >2000N / P). After roasting, the material is further homogenized and cooled to produce qualified oxide pellets and a mixture of residual microwave absorbing material. Then, through physical separation (e.g., grading and screening), the oxide pellets and a very small amount of microwave absorbing material are used as raw materials for ironmaking / steelmaking. The microwave absorbing material impurities (i.e., residual microwave absorbing material) undergo secondary separation (e.g., gravity separation), and the resulting iron-containing powder enters the steel plant's internal solid waste resource comprehensive recycling system. The fine-grained microwave absorbing material can be returned as material to the microwave absorbing material preparation system (formed into microwave absorbing pellets) for secondary recycling. This invention improves the microwave energy-to-thermal energy conversion efficiency in the microwave roasting process of iron ore pellets by adding microwave absorbing materials, which can help achieve ultimate energy efficiency and near-zero carbon emissions in the all-electric pellet production process.

[0032] In this invention, because microwave heating inherently has the characteristic of energy attenuation (a certain penetration depth), the furnace charge structure needs to be optimized. Firstly, the particle sizes of the iron-containing pellets and the microwave-absorbing pellets need to be differentiated. Generally, the iron-containing pellets have a particle size of 8-16 mm, while the microwave-absorbing pellets have a particle size of 16-20 mm (that is, controlling the particle size of the iron-containing pellets and the microwave-absorbing pellets within an appropriate range to achieve an ideal material layer distribution based on the pellet particle size, ensuring that microwaves fully penetrate the pellets for heating, and that the heat is rationally distributed from the edge to the center of the entire material). Then… Through the segregation effect of the drying bed, an ideal distribution pattern of pellets and microwave-absorbing materials is constructed in the roasting furnace. Small-diameter oxidized pellets are located near the furnace wall and the microwave generator, while large-diameter microwave-absorbing materials are located near the center of the furnace (the particle size of the microwave-absorbing pellets in this invention is larger than that of the iron-containing pellets). This results in the relatively smaller iron-containing pellets absorbing high-energy microwaves first. As the microwave energy attenuates, it encounters the relatively larger microwave-absorbing materials (i.e., the microwave-absorbing pellets), and through strong absorption, the weak microwave energy is efficiently converted into heat energy, thus making the heat distribution of the pellet layer uniform from the edge to the center. Furthermore, through the gas-solid heat transfer control optimized by traditional stepped airflow distribution, the technical problems of local overheating and underheating and uneven roasting during the pellet sintering process are effectively avoided, making the temperature field of the pellet material more uniform and improving the uniformity of pellet quality.

[0033] In this invention, a novel electrically heated microwave vertical furnace is used as the production equipment (such as the supporting production system provided by this invention). Iron-containing pellets and microwave-absorbing pellets are mixed and placed at the feed inlet. The mixture passes through a forced-air drying section, a preheating section (weak microwave), a roasting section (strong microwave), a homogenizing section (strong microwave), and a cooling section from top to bottom to obtain finished pellets and residual microwave-absorbing material. The preheating section, roasting section, and homogenizing section are all directly heated by a microwave device. The microwave energy comes from domestically developed green energy resources: hydropower, wind power, solar power, etc.

[0034] In this invention, during the initial stage of the preheating section, the main component of the iron-containing pellets is magnetite Fe3O4, which possesses high saturation magnetization and natural resonance characteristics. It can effectively dissipate microwave energy through mechanisms such as hysteresis loss and domain wall resonance. Combined with the absorption of microwaves by the newly formed, undamaged microwave absorbing material, weak microwaves can be used in the preheating section. The magnetite pellets and absorbing material can then rapidly convert microwave energy into heat energy, causing the entire pellet material to heat up quickly. Simultaneously, the pellet components oxidize Fe3O4 to Fe2O3, releasing chemical heat. These three heat sources ensure that the preheating section temperature remains within 900~1050℃, guaranteeing the performance indicators of the preheated pellets, namely, a compressive strength >400 N / P.

[0035] In this invention, when the material enters the roasting section, the required roasting temperature reaches 1150~1250℃. However, the main component of the pellets is transformed into hematite Fe2O3, which is characterized by dielectric loss and relatively weak magnetic loss. When used alone, its microwave absorption performance is limited. Therefore, under the premise of using a single microwave energy source to provide heat, the microwave absorbing material strongly absorbs and releases sufficient heat energy to compensate for the heat generated by the weak absorption of hematite during conversion. At the same time, the microwave energy in the roasting section is further enhanced to strong microwave energy to improve the energy supply per unit time. The efficient conversion of high-energy microwaves through auxiliary microwave absorbing materials ensures the roasting section temperature and preheated pellet performance indicators, meeting the requirement of compressive strength >2000N / P.

[0036] In this invention, after the roasted material in the furnace undergoes homogenization and cooling, a qualified mixture of oxidized pellets and residual microwave absorbing material is produced. The mixture is then physically separated through coarse and fine sieving to obtain oxidized pellets and a very small amount of microwave absorbing material as raw materials for ironmaking / steelmaking. The coarse sieving (>16mm) removes microwave absorbing material particles larger than the oxidized pellets and returns them to the microwave absorbing material preparation system, while the fine sieving (<8mm) removes microwave absorbing material particles smaller than the oxidized pellets. Then, the microwave absorbing material impurities from the fine sieving undergo a second separation via gravity separation. The iron-containing powder enters the steel plant's internal solid waste resource recycling system, while the fine-grained microwave absorbing material is returned to the microwave absorbing material preparation system for secondary recycling.

[0037] In this invention, the raw materials for the iron-containing pellets mainly include iron-containing minerals and binders. The iron-containing minerals are generally Fe3O4-containing minerals, such as magnetite concentrate and vanadium-titanium magnetite concentrate, followed by hematite; the binders are bentonite and organic binders. The microwave absorbing material is generally a solid waste-based microwave absorbing material, such as FexOy / TiO2 / C composite microwave absorbing material (e.g., pellets made from the composite microwave absorbing materials provided in 202510054526.6 and 202510054527.0), followed by high-temperature resistant microwave absorbing materials (such as silicon carbide, silicon nitride, alumina, or mullite-based composite carbonaceous materials, etc. For example, silicon carbide pellets are silicon carbide / carbon hollow porous microspheres provided in 201911081680.3), all suitable for scenarios with frequent temperature changes, acting as thermal catalysts. It should be noted that, in the preferred embodiment of the present invention, the thermal conversion efficiency (efficiency of converting microwave energy into heat energy) of the microwave absorbing material is preferably greater than 70%.

[0038] In this invention, a vertical furnace system is provided for the electrothermal roasting method of pellets. This system includes a vertical furnace and a microwave generator. The interior of the furnace (i.e., the furnace chamber) is divided from top to bottom into a drying section, a preheating section, a roasting section, a homogenizing section, and a cooling section. The microwave generator is installed on the furnace walls of the preheating, roasting, and homogenizing sections. It should be noted that since the preheating temperature is relatively low, the microwave generator in the preheating section is a weak microwave generator (relatively low power or a relatively sparse distribution of microwave generators). Conversely, the roasting and homogenizing sections require relatively high temperatures, therefore the corresponding microwave generators are strong microwave generators (i.e., relatively high power or a relatively dense distribution of microwave generators). To facilitate independent temperature control, the microwave generators for each section—preheating, roasting, and homogenizing—are generally set up independently. It should also be noted that the hot air used for drying in the drying section comes from single or mixed hot waste gas generated in the preheating section, roasting section, homogenizing section or cooling section, thus eliminating the need for additional fossil energy consumption for heating, achieving waste heat gradient utilization while avoiding increased carbon emissions.

[0039] In this invention, the drying section of the vertical furnace system employs a drying bed with segregated fabric for drying the fabric. The drying bed includes a grate and blower beams. The grate has an overall inclined roof-like / A-shaped structure, and the blower beams are hollow tubular structures used to support the grate and evenly blow drying air (e.g., waste heat air from the cooling section) to one side of the grate. Drying beds are generally classified into single-layer, double-layer, and triple-layer types (i.e., structures in which the grate and blower beams are laid alternately), and can also be configured with more layers according to actual needs. Waste hot air from the cooling section of the vertical furnace reaches the bottom of the drying bed grate through the cooling exhaust gas conveying pipe or the central guide wall. It then penetrates the pellet layer from bottom to top through the air outlets of the blower beam and the gaps in the grate, carrying away moisture and achieving hot air drying. Simultaneously, the green pellets from the mixed furnace charge entering the top of the drying bed roll down the grate. Utilizing the difference in gravity and inertia, smaller particles, with less inertia, tend to stay at the edge of the furnace wall, while larger particles, with greater inertia, tend to roll in the opposite direction towards the center of the roasting furnace, closer to the guide wall, achieving segregated distribution. The drying bed setup enables rapid drying of the mixed furnace charge and helps distribute the relatively larger absorbing pellets in the mixed furnace charge primarily in the central material, away from the furnace wall. This facilitates the generation of heat in the central material layer by the strong absorption characteristics of the absorbing pellets, compensating for the heat generated by the weakly absorbing iron-containing pellets. This results in uniform heating of the material, improving preheating, roasting, and homogenization effects, and ensuring the quality of the finished oxidized pellets.

[0040] In this invention, a multi-stage screening device is also installed at the bottom of the vertical shaft furnace. The coarse screen (i.e., the first screen with a larger aperture) separates the microwave absorbing pellets larger than the oxide pellets from the cooled mixed furnace charge. Simultaneously, the fine screen (i.e., the second screen with a smaller aperture) separates the fragments (including broken oxide pellets and microwave absorbing pellets) smaller than the oxide pellets. In other words, through the coarse and fine screening processes, oxide pellets of suitable particle size (allowing for a small amount of microwave absorbing material) are quickly screened from the mixed furnace charge for use as raw materials for ironmaking or steelmaking. Furthermore, the large microwave absorbing pellets from the coarse screen can be recycled, while the fragments from the fine screen can be re-processed into larger microwave absorbing pellets for recycling after removing iron-containing powder through gravity separation. The vertical shaft furnace system of this invention has a simple overall structure, is easy to operate, produces high-quality oxide pellets, and is fully electric, making it environmentally friendly. It should be noted that independent flow regulating valves can also be installed on the pipelines used for conveying various gases, hot air, or hot waste gas in this vertical shaft furnace system. A gas temperature sensor can also be installed in the mixing chamber to detect the temperature of the mixed hot air.

[0041] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0042] 1. This invention adds a certain proportion of microwave absorbing material to iron ore pellets and implements a heating mode of preheating section - weak microwave energy and roasting section - strong microwave energy. In the face of the adverse situation that the pellets' microwave absorption capacity decreases due to the conversion of the pellet composition from Fe3O4 to Fe2O3, the invention makes full use of the strong microwave absorption and high-efficiency heat conversion performance of the microwave absorbing material to convert microwave energy into heat energy, ensuring that the temperature of the preheating section is uniform with the temperature of the roasting homogenization section, thereby ensuring the performance indicators of the oxidized pellets.

[0043] 2: This invention uses direct microwave heating to uniformly heat the pellet material. By rationally distributing the material, an ideal distribution of pellets, microwave absorbing materials, and airflow is constructed, forming a tiered heat conversion system in which small pellets absorb high-energy microwaves and large microwave absorbing materials absorb low-energy microwaves, thus achieving the goal of roasting with all-electric power.

[0044] 3: Based on the differential coupling of iron-containing pellets and microwave-absorbing pellets, this invention can also achieve secondary separation of oxide pellets and microwave-absorbing materials through simple physical separation methods. This can not only ensure the uniformity of oxide pellets, but also help to realize the recycling of microwave-absorbing materials, thereby reducing production costs.

[0045] 4: This invention significantly improves the microwave energy-to-thermal energy conversion efficiency of the pure microwave roasting process of iron-containing pellets by coupling and roasting iron-containing pellets with microwave-absorbing pellets. This greatly reduces NOx and SO2 emissions caused by the use of fossil fuels from the source, and helps achieve ultimate energy efficiency and near-zero carbon emissions in the all-electric pellet production process. Attached Figure Description

[0046] Figure 1 This is a flowchart illustrating the method described in this invention.

[0047] Figure 2 This is a simplified structural diagram of the vertical furnace system described in this invention.

[0048] Figure 3 This is a schematic diagram of the overall structure of the vertical furnace system described in this invention.

[0049] Figure 4 This is a schematic diagram of the overall structure of the vertical furnace system of the present invention when it has a mixing chamber.

[0050] Figure 5 This is a schematic diagram of the drying bed structure of the vertical furnace system described in this invention.

[0051] Reference numerals: 1: Furnace shell; 101: Feed inlet; 102: Discharge outlet; 103: Oxygen supply pipe; 104: Cooling medium input pipe; 105: Cooling medium output pipe; 106: Cooling exhaust gas conveying pipe; 107: Preheating exhaust gas conveying pipe; 108: Calcination exhaust gas conveying pipe; 109: Homogenization exhaust gas conveying pipe; 2: Furnace chamber; 201: Drying section; 202: Preheating section; 203: Calcination section; 204: Homogenization section; 205: Cooling section; 3: First microwave generator; 4: Second microwave generator; 5: Third microwave generator; 6: Drying bed; 7: Mixing chamber; 701: Mixed hot air conveying pipe; 702: Air supply pipe; 8: Screening mechanism; 801: First screen; 802: Second screen. Detailed Implementation

[0052] The technical solution of the present invention will be illustrated below with examples. The scope of protection sought by the present invention includes, but is not limited to, the following embodiments.

[0053] A vertical shaft furnace system for electrothermal roasting of pellets includes a furnace shell 1 and a furnace chamber 2. The furnace chamber 2 is divided from top to bottom into a drying section 201, a preheating section 202, a roasting section 203, a homogenizing section 204, and a cooling section 205. A first microwave generator 3 is installed on the furnace shell 1 corresponding to the preheating section 202. A second microwave generator 4 is installed on the furnace shell 1 corresponding to the roasting section 203. A third microwave generator 5 is installed on the furnace shell 1 corresponding to the homogenizing section 204. A feed inlet 101 is provided at the top of the drying section 201, and a discharge outlet 102 is provided at the bottom of the cooling section 205.

[0054] Preferably, a drying bed 6 is provided in the drying section 201, the drying bed 6 including a grate plate 601 and blower beams 602. The grate plate 601 has a herringbone structure that is narrower at the top and wider at the bottom, and multiple blower beams 602 are evenly arranged on the bottom side of the grate plate 601, and both ends of the blower beams 602 are connected to the furnace shell 1; the blower beams 602 have a hollow tubular structure, and air outlet holes are opened on the tube wall of the blower beams 602 facing the grate plate 601.

[0055] Preferably, at least one oxygen supply pipe 103 connected to the soaking section 204 is provided on the furnace shell 1 corresponding to the soaking section 204. Preferably, at least one oxygen supply pipe 103 connected to the calcination section 203 is also provided on the furnace shell 1 corresponding to the calcination section 203. Preferably, at least one oxygen supply pipe 103 connected to the preheating section 202 is also provided on the furnace shell 1 corresponding to the preheating section 202.

[0056] Preferably, a cooling medium inlet pipe 104 and a cooling medium outlet pipe 105 are also provided on the furnace shell 1 corresponding to the cooling section 205. The cooling medium inlet pipe 104 is connected to the lower part of the cooling section 205, and the cooling medium outlet pipe 105 is connected to the upper part of the cooling section 205.

[0057] Preferably, the cooling medium output pipe 105 is connected to the lower part of the drying section 201 via the cooling exhaust gas conveying pipe 106.

[0058] Preferably, the vertical shaft furnace system also includes a mixing chamber 7. The upper part of the preheating section 202 is connected to the air inlet of the mixing chamber 7 via a preheating waste gas conveying pipe 107. The upper part of the roasting section 203 is connected to the air inlet of the mixing chamber 7 via a roasting waste gas conveying pipe 108. The upper part of the homogenizing section 204 is connected to the air inlet of the mixing chamber 7 via a homogenizing waste gas conveying pipe 109. The upper part of the cooling section 205 is connected to the air inlet of the mixing chamber 7 via a cooling medium output pipe 105 and a cooling waste gas conveying pipe 106. The exhaust port of the mixing chamber 7 is connected to the lower part of the drying section 201 via a mixed hot air conveying pipe 701. Preferably, an air replenishment pipe 702 is also provided on the mixing chamber 7.

[0059] Preferably, the vertical furnace system also includes a screening mechanism 8. The screening mechanism 8 includes a first screen 801 and a second screen 802 sequentially arranged below the cooling section 205. The aperture of the first screen 801 is not less than 16 mm, and the aperture of the second screen 802 is not greater than 8 mm.

[0060] Example 1

[0061] like Figure 2-5The invention relates to a vertical shaft furnace system for electrothermal roasting of pellets, comprising a furnace shell 1 and a furnace chamber 2. The furnace chamber 2 is divided from top to bottom into a drying section 201, a preheating section 202, a roasting section 203, a homogenizing section 204, and a cooling section 205. A first microwave generator 3 is installed on the furnace shell 1 corresponding to the preheating section 202. A second microwave generator 4 is installed on the furnace shell 1 corresponding to the roasting section 203. A third microwave generator 5 is installed on the furnace shell 1 corresponding to the homogenizing section 204. A feed inlet 101 is located at the top of the drying section 201, and a discharge outlet 102 is located at the bottom of the cooling section 205.

[0062] Example 2

[0063] The embodiment 1 is repeated, except that a drying bed 6 is provided in the drying section 201. The drying bed 6 includes a grate plate 601 and blower beams 602. The grate plate 601 has a herringbone structure that is narrower at the top and wider at the bottom. Multiple blower beams 602 are evenly arranged on the bottom side of the grate plate 601, and both ends of the blower beams 602 are connected to the furnace shell 1. The blower beams 602 have a hollow tubular structure, and air outlet holes are opened on the tube wall of the blower beams 602 facing the grate plate 601.

[0064] Example 3

[0065] Repeat Example 2, except that at least one oxygen supply pipe 103 connected to the heat soaking section 204 is provided on the furnace shell 1 corresponding to the heat soaking section 204.

[0066] Example 4

[0067] Repeat Example 3, except that at least one oxygen supply pipe 103 connected to the roasting section 203 is also provided on the furnace shell 1 corresponding to the roasting section 203.

[0068] Example 5

[0069] Repeat Example 4, except that at least one oxygen supply pipe 103 connected to the preheating section 202 is also provided on the furnace shell 1 corresponding to the preheating section 202.

[0070] Example 6

[0071] Example 5 is repeated, except that a cooling medium inlet pipe 104 and a cooling medium outlet pipe 105 are also provided on the furnace shell 1 corresponding to the cooling section 205. The cooling medium inlet pipe 104 is connected to the lower part of the cooling section 205, and the cooling medium outlet pipe 105 is connected to the upper part of the cooling section 205.

[0072] Example 7

[0073] Example 6 is repeated, except that the cooling medium output pipe 105 is connected to the lower part of the drying section 201 through the cooling exhaust gas conveying pipe 106.

[0074] Example 8

[0075] The system repeats Example 7, except that the vertical shaft furnace system also includes a mixing chamber 7. The upper part of the preheating section 202 is connected to the inlet of the mixing chamber 7 via a preheating waste gas conveying pipe 107. The upper part of the roasting section 203 is connected to the inlet of the mixing chamber 7 via a roasting waste gas conveying pipe 108. The upper part of the homogenizing section 204 is connected to the inlet of the mixing chamber 7 via a homogenizing waste gas conveying pipe 109. The upper part of the cooling section 205 is connected to the inlet of the mixing chamber 7 via a cooling medium output pipe 105 and a cooling waste gas conveying pipe 106. The exhaust port of the mixing chamber 7 is connected to the lower part of the drying section 201 via a mixed hot air conveying pipe 701.

[0076] Example 9

[0077] The same as Example 8 is repeated, except that an air supply pipe 702 is also provided on the mixing chamber 7.

[0078] Example 10

[0079] The embodiment 9 is repeated, except that the vertical furnace system also includes a screening mechanism 8. The screening mechanism 8 includes a first screen 801 and a second screen 802 sequentially arranged below the cooling section 205. The aperture of the first screen 801 is 16 mm, and the aperture of the second screen 802 is 8 mm.

[0080] Application Example 1

[0081] The iron-containing pellets were roasted using the vertical furnace system described in Example 10.

[0082] S1: Iron-containing pellets with a particle size range of 8~16mm and microwave-absorbing pellets with a particle size range of 16~20mm (i.e., Fe) x O y / TiO2 / C composite pellets: First, rare earth waste residue and soluble starch are mixed evenly at a mass ratio of 1:0.5 to obtain a mixed powder. Then, tetrabutyl titanate, glacial acetic acid, and anhydrous ethanol are mixed evenly at a volume ratio of 1:1.2:0.2 to obtain a mixed solution. Next, deionized water is added dropwise to the mixed solution, with the volume of added deionized water accounting for 2% of the total volume of the mixed solution, to obtain a sol. Then, the mixed powder is weighed and added to the sol, with the mass ratio of rare earth waste residue in the mixed powder to tetrabutyl titanate in the sol being 1:4. The mixture is then stirred evenly with magnetic stirring. The stirring speed was 100-200 r / min; finally, after aging at room temperature for 8 hours, a gel was obtained; then, the prepared gel was placed in an oven to dry at 80℃ for 12 hours to obtain a precursor dry gel; next, the precursor dry gel was placed in a tube furnace and calcined at a constant temperature of 700℃ for 2 hours in a N2 atmosphere, and then cooled to room temperature with the furnace to obtain the Fe3O4 / TiO2 / C composite microwave absorbing material; finally, the composite pellets were obtained by pelletizing using a disc pelletizer and mixed to obtain a mixed furnace charge. The amount of the microwave absorbing pellets was 20% of the mass of the iron-containing pellets.

[0083] S2: The obtained mixed furnace charge is added from the feed inlet 101 of the vertical furnace system and dried on the drying bed 6 of the drying section 201 by hot air from the cooling section (drying temperature approximately 320℃, drying time approximately 6 min). The dried mixed furnace charge enters the preheating section 202 under the action of the drying bed 6 and exhibits a segregated distribution in the preheating section 202, with the particle size near the furnace wall being lower than that at the center. Then, the first microwave generator 3 located in the preheating section 202 (microwave frequency approximately 915±13MHz, microwave power approximately 100kW) is activated to uniformly preheat the material to approximately 950℃ (preheating time approximately 10 min). The preheated material continues to descend into the calcination section 203 and is calcined at 1250℃ under the action of the second microwave generator 4 (microwave frequency 2450±50MHz, microwave power approximately 500kW) (calcination time approximately 10 min). The calcined material continues to descend into the homogenization section 204 and is calcined at 1250℃ under the action of the third microwave generator 5 (microwave frequency 2450±50MHz, microwave power approximately 500kW). Under the action of 450±50MHZ (power approximately 350kW), the material is homogenized at 1000℃ for approximately 5 minutes; during the preheating, roasting, and homogenization processes, oxygen (air) is supplied to the preheating section 202, roasting section 203, and homogenization section 204 through the corresponding oxygen supply pipe 103; after homogenization, the material enters the cooling section 205, and the cooling rate of the material after homogenization is maintained at 30℃ / min by controlling the flow rate of the cooling air (room temperature air) input from the cooling medium input pipe 104; the temperature drops to approximately 1℃. The mixed furnace charge, after reaching 00℃, is discharged from outlet 102 and enters screening mechanism 8. First, under the action of the first screen 801, large particles larger than 16mm (mainly microwave absorbing pellets) are screened out for reuse. Then, under the action of the second screen 802, fine particles smaller than 8mm (mainly crushed oxide pellets and microwave absorbing pellets) are screened out, finally yielding finished oxide pellets (containing a small amount of microwave absorbing material; the compressive strength of the finished oxide pellets is approximately 2582 N / P, and the yield of the finished pellets is approximately 90.2%). The fine particles are then gravity-separated to obtain iron-containing powder and microwave absorbing material. The iron-containing powder is recycled as raw material for iron-containing pellets, and the microwave absorbing material is also recycled as raw material for microwave absorbing pellets.

[0084] Application Example 2

[0085] The application of Example 1 was repeated, except that the absorbing pellets were silicon carbide pellets. The preparation process of the silicon carbide pellets was as follows: First, deionized water, anhydrous ethanol, and ammonia were mixed evenly at a volume ratio of 500:200:3, with the ammonia mass fraction being 25%. Then, hexadecyltrimethylammonium bromide surfactant (20 g / L) was added and stirred to dissolve. Next, resorcinol (4.0 g / L) was added and stirred to dissolve. Then, tetraethyl orthosilicate (25 ml / L) and formaldehyde solution (37% mass fraction, 8 ml / L) were added and stirred evenly at room temperature. Finally, melamine (2.0 g) was added. The mixture was stirred to obtain a silica / carbon composite powder. Then, the mixture was transferred to a high-temperature, high-pressure reactor at 100°C for 24 hours, centrifuged, washed, and dried. It was then calcined at 800°C for 3 hours under a nitrogen atmosphere to obtain silica / carbon composite powder. Finally, the silica / carbon composite powder was mixed with magnesium powder at a mass ratio of 1:4 and ground uniformly. It was then calcined at 700°C for 6 hours under a nitrogen atmosphere, stirred, washed, and dried in a 3 mol / L hydrochloric acid solution to obtain silicon carbide / carbon microwave absorbing material. Finally, a disc pelletizer was used to pelletize the material to obtain silicon carbide pellets. The compressive strength of the obtained finished silica pellets was approximately 2632 N / P, and the yield of the finished pellets was approximately 92.4%.

[0086] Application Example 3

[0087] The application of Example 1 was repeated, except that the absorbing pellets were silicon nitride-based composite pellets. The preparation process of the silicon nitride-based composite pellets was as follows: First, acrylamide, N,N'-methylenebisacrylamide, and ethanol were mixed at a mass ratio of 40:1:200 to prepare a premixed flux, and the pH of the solvent was adjusted to 7.0 with ammonia. Second, silicon nitride, ferric chloride, polymethyl methacrylate, polyacrylonitrile, and alumina were all crushed to 50 μm and then mixed at a mass ratio of 65:8:12:10:5 to obtain a powder mixture. Third, the powder mixture was mixed with the premixed flux at a mass ratio of 45:55, and ferric chloride (dosage amount) was added. The reactants (8% by mass of the total reactants) and polymethyl methacrylate (12% by mass of the total reactants) were used to fuse and react the components, generating a gel-like substrate. The prepared gel-like substrate was then cast into a mold, vacuumed, and dried at room temperature for 15 hours before demolding to form a blank. The blank was then degummed (at 600℃) to remove organic matter. Finally, the degummed blank was sintered under a nitrogen atmosphere at 1400℃ for 3 hours. After cooling, silicon nitride microwave absorbing material was obtained. Finally, a disc pelletizer was used to pelletize the material to obtain silicon nitride composite pellets. The compressive strength of the obtained oxide pellets was approximately 2566 N / P, and the yield of the finished pellets was approximately 89.1%.

[0088] Application Example 4

[0089] The application of Example 1 was repeated, except that the absorbing pellets were alumina-based composite pellets. The preparation process of the alumina-based composite pellets was as follows: First, porous alumina with a purity >99wt.%, a porosity of 36%, and an average pore size of 70μm was used as the matrix. It was then ultrasonically cleaned sequentially with acetone, anhydrous ethanol, and deionized water for 15 min each. After cleaning, it was placed in an oven at 80℃ and dried for 6 h to obtain a pretreated porous alumina matrix. Next, cobalt chloride hexahydrate, ammonium fluoride, and urea were weighed at a mass ratio of 3.2:1:4 and added to deionized water (solid-liquid mass ratio of 32:1). The mixture was magnetically stirred for 25 min until the solution was homogeneous to obtain the precursor solution. Next, the pretreated porous alumina matrix and precursor solution were placed in a polytetrafluoroethylene liner and placed in a vacuum drying oven. Vacuum was drawn and pressure was maintained for 30 minutes. Then, the mixture was placed in a reaction vessel and sealed tightly. The temperature was maintained at 120°C for 5 hours. After the reaction vessel cooled to room temperature, the loaded product was removed from the reaction vessel, washed with deionized water, and dried in a 60°C oven for 3 hours to obtain porous alumina loaded with transition metals. Finally, sodium hypophosphite (twice the mass of the porous alumina loaded with transition metals) was placed in an alumina crucible, and the porous alumina loaded with transition metals was placed in another alumina crucible. A corundum crucible containing sodium hypophosphite was placed near the gas inlet of a tube furnace. A corundum crucible containing porous alumina loaded with transition metals was placed in the center of the tube furnace. Phosphine gas from the decomposition of sodium hypophosphite was carried by the carrier gas to the other crucible, where it reacted with the porous alumina loaded with transition metals. Argon was used as the carrier gas during the reaction. The tube furnace was heated to 350°C and maintained for 2 hours, then naturally cooled to room temperature to obtain a porous alumina-based composite microwave absorbing material. Finally, a disc pelletizer was used to pelletize the material to obtain alumina-based composite pellets. The compressive strength of the obtained alumina pellets was approximately 2543 N / P, and the yield of the finished pellets was approximately 88.3%.

[0090] Application Example 5

[0091] The application of Example 1 was repeated, except that the absorbing pellets were mullite-based composite pellets. The preparation process of these mullite-based composite pellets was as follows: First, fly ash and gasification slag, common solid wastes in industrial production, were mixed evenly at a mass ratio of 0.8:1 to obtain a solid mixture. Second, the mixture was acid-hydrolyzed using a mixed solution of sulfuric acid and hydrochloric acid (volume ratio 1:2). The H ion concentration in the acid solution was 2 mol / L, the solid-liquid ratio was 5 L / kg, the acid-hydrolyzed temperature was 85℃, and the time was 3 hours, which promoted the absorption of appropriate amounts of soluble impurities. After the impurities are removed, the material is washed and dried to obtain an intermediate powder material at 90℃ for 10 hours. Next, activated carbon source, phenolic resin binder, and intermediate powder material are mixed, ground, and pressed into intermediate bulk material. The mass ratio of carbon source to intermediate powder material is 1:1, and the mass ratio of binder to intermediate powder material is 1:1. Finally, the intermediate bulk material is sintered at 1400℃ for 2 hours to obtain a mullite-based composite microwave absorbing material. Finally, a disc pelletizer is used to pelletize the material to obtain alumina-based composite pellets. The compressive strength of the obtained alumina pellets is approximately 2516 N / P, and the yield of the finished pellets is approximately 88.0%.

[0092] Application Example 6

[0093] Example 1 was repeated, except that the amount of microwave absorbing pellets was 30% of the mass of the iron-containing pellets. The compressive strength of the resulting oxidized pellets was approximately 2637 N / P, and the yield of the finished pellets was approximately 90.7%.

[0094] Application Example 7

[0095] Example 1 was repeated, except that the amount of microwave absorbing pellets was 40% of the mass of the iron-containing pellets. The compressive strength of the resulting oxidized pellets was approximately 2660 N / P, and the yield of the finished pellets was approximately 91.1%.

[0096] Application Example 8

[0097] Example 1 was repeated, except that the amount of microwave absorbing pellets was 15% of the mass of the iron-containing pellets. The resulting oxidized pellets had a compressive strength of approximately 2578 N / P and a yield of approximately 89.4%.

[0098] Application Example 9

[0099] Example 1 was repeated, except that the amount of microwave absorbing pellets was 10% of the mass of the iron-containing pellets. The compressive strength of the resulting oxidized pellets was approximately 2343 N / P, and the yield of the finished pellets was approximately 88.5%.

[0100] Application Example 10

[0101] Example 1 was repeated, except that the segregated fabric was not processed. The resulting oxidized pellets had a compressive strength of approximately 2305 N / P and a pellet yield of approximately 87.2%.

[0102] Application Example 11

[0103] Example 1 was repeated, except that the particle size of the absorbing pellets ranged from 8 to 16 mm. The compressive strength of the resulting oxidized pellets was approximately 2478 N / P, and the yield of the finished pellets was approximately 89.2%.

[0104] Application Example 12

[0105] Example 1 was repeated, except that the particle size of the absorbing pellets was 4-8 mm. The compressive strength of the resulting oxidized pellets was approximately 2356 N / P, and the yield of the finished pellets was approximately 88.3%.

[0106] Comparative Example 1

[0107] Example 1 was repeated, except that the amount of absorbing pellets was 0. The compressive strength of the resulting oxidized pellets was approximately 2275 N / P, and the yield of the finished pellets was approximately 89.3%.

[0108] Comparative Example 2

[0109] Oxidized pellets are produced using a chain grate-rotary kiln process. First, 100% iron concentrate is mixed with 2% bentonite to form green pellets with a particle size range of 8-16 mm. The green pellets are then fed into the drying section of the chain grate, undergoing sequential forced-air drying and forced-air drying stages: forced-air drying at 200℃ for 3 minutes; forced-air drying at 400℃ for 6 minutes, thus removing most of the moisture from the green pellets. The dried green pellets then enter the preheating section of the chain grate, where the first preheating stage is at 950℃ and the second preheating stage is at 1050℃ for 12 minutes. After thorough preheating, the pellets are then fed into a rotary kiln for high-temperature roasting at 1300℃ for 15 minutes. The roasted high-temperature pellets then enter an annular cooler and undergo staged cooling via a multi-stage forced-air cooling system. The compressive strength of the cooled oxidized pellets is approximately 2354 N / P, and the yield of the finished pellets is approximately 88.2%.

Claims

1. A method for electrothermal roasting of pellets, characterized in that: The pellet electrothermal roasting method includes the following steps: S1. Mixing iron-containing pellets with microwave-absorbing pellets to obtain mixed furnace charge; S2. In the calcining furnace, the mixed furnace material is successively subjected to hot air drying, weak microwave preheating, strong microwave calcination and homogenization, and cooling treatment to obtain the mixed calcined material. S3. The mixed calcined material is sieved to obtain oxidized pellets and residual microwave absorbing material.

2. The pellet electrothermal roasting method according to claim 1, characterized in that: In step S1, the absorbing pellets are Fe x O y The microwave absorbing pellets are selected from at least one of the following: TiO2 / C composite pellets, silicon carbide pellets, silicon nitride, alumina, or mullite-based composite carbonaceous materials; preferably, the amount of the microwave absorbing pellets is 10-40% of the mass of the iron-containing pellets, more preferably 15-30%. Preferably, the iron-containing pellets have a particle size of 8-16 mm; the microwave-absorbing pellets have a particle size of 16-20 mm.

3. The pellet electrothermal roasting method according to claim 1 or 2, characterized in that: In step S2, the hot air drying temperature is 250~400℃, and the drying time is 4~10 min; and / or In step S2, the temperature of the weak microwave preheating is 900~1020℃, and the preheating time is 5~20min; and / or In step S2, the temperature for strong microwave roasting and homogenization is 1150~1250℃, wherein the roasting time is 5~20min and the homogenization time is 3~10min; and / or In step S2, the cooling is air cooling, and the cooling rate is 20~40℃ / min.

4. The pellet electrothermal roasting method according to any one of claims 1-3, characterized in that: In step S2, the microwave frequency is 915±13MHz or 2450±50MHz, where the weak microwave power is between 100~200kW and the strong microwave power is between 300~650kW. Preferably, an oxidizing gas is introduced during weak microwave preheating and strong microwave roasting and homogenization; preferably, the oxidizing gas is air and / or oxygen.

5. The pellet electrothermal roasting method according to any one of claims 1-4, characterized in that: In step S2, the mixed furnace charge is distributed in the calcining furnace with a segregated distribution where the particle size of the material near the furnace wall is smaller than that of the material in the center. Preferably, in step S2, the cooling medium during cooling is room temperature air; the hot air used for drying is at least one of the following: hot exhaust gas after cooling, hot exhaust gas after preheating, hot exhaust gas after calcination, and hot exhaust gas after homogenization.

6. The pellet electrothermal roasting method according to any one of claims 1-5, characterized in that: The screening process includes a coarse screen and a fine screen, wherein the aperture of the coarse screen is not less than 16 mm and the aperture of the fine screen is not greater than 8 mm. As a preferred method, the residual absorbing material is reselected to obtain iron-containing powder and absorbing material; the iron-containing powder is recycled as raw material for iron-containing pellets, and the absorbing material is recycled as raw material for absorbing pellets.

7. A vertical shaft furnace system for electrothermal roasting of pellets or a vertical shaft furnace system for the electrothermal roasting method of pellets as described in any one of claims 1-6, characterized in that: The vertical furnace system includes a furnace shell (1) and a furnace chamber (2); the furnace chamber (2) is divided into a drying section (201), a preheating section (202), a roasting section (203), a homogenizing section (204), and a cooling section (205) from top to bottom; a first microwave generator (3) is provided on the furnace shell (1) corresponding to the preheating section (202); a second microwave generator (4) is provided on the furnace shell (1) corresponding to the roasting section (203); a third microwave generator (5) is provided on the furnace shell (1) corresponding to the homogenizing section (204); a feed inlet (101) is provided at the top of the drying section (201), and a discharge outlet (102) is provided at the bottom of the cooling section (205).

8. The vertical shaft furnace system according to claim 7, characterized in that: A drying bed (6) is provided in the drying section (201). The drying bed (6) includes a grate (601) and blower beams (602). The grate (601) is a herringbone structure that is narrow at the top and wide at the bottom. Multiple blower beams (602) are evenly arranged on the bottom side of the grate (601), and both ends of the blower beams (602) are connected to the furnace shell (1). The blower beams (602) are hollow tubular structures, and air outlets are provided on the tube wall of the blower beams (602) facing the grate (601).

9. The vertical shaft furnace system according to claim 7 or 8, characterized in that: At least one oxygen supply pipe (103) connected to the homogenization section (204) is provided on the furnace shell (1) corresponding to the homogenization section (204); preferably, at least one oxygen supply pipe (103) connected to the roasting section (203) is also provided on the furnace shell (1) corresponding to the roasting section (203); preferably, at least one oxygen supply pipe (103) connected to the preheating section (202) is also provided on the furnace shell (1) corresponding to the preheating section (202).

10. The vertical shaft furnace system according to any one of claims 7-9, characterized in that: A cooling medium inlet pipe (104) and a cooling medium outlet pipe (105) are also provided on the furnace shell (1) corresponding to the cooling section (205); the cooling medium inlet pipe (104) is connected to the lower part of the cooling section (205), and the cooling medium outlet pipe (105) is connected to the upper part of the cooling section (205); Preferably, the cooling medium output pipe (105) is connected to the lower part of the drying section (201) through the cooling exhaust gas conveying pipe (106); Preferably, the vertical shaft furnace system also includes a mixing chamber (7); the upper part of the preheating section (202) is connected to the air inlet of the mixing chamber (7) through a preheating waste gas conveying pipe (107); the upper part of the roasting section (203) is connected to the air inlet of the mixing chamber (7) through a roasting waste gas conveying pipe (108); the upper part of the homogenizing section (204) is connected to the air inlet of the mixing chamber (7) through a homogenizing waste gas conveying pipe (109); the upper part of the cooling section (205) is connected to the air inlet of the mixing chamber (7) through a cooling medium output pipe (105) and a cooling waste gas conveying pipe (106); the exhaust port of the mixing chamber (7) is connected to the lower part of the drying section (201) through a mixed hot air conveying pipe (701); preferably, an air replenishment pipe (702) is also provided on the mixing chamber (7). Preferably, the vertical furnace system also includes a screening mechanism (8); the screening mechanism (8) includes a first screen (801) and a second screen (802) arranged sequentially below the cooling section (205); the aperture of the first screen (801) is not less than 16 mm, and the aperture of the second screen (802) is not greater than 8 mm.

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