Electric heating shaft furnace for oxidized pellet production based on hot air internal circulation and pellet production method

Abstract

The invention discloses an electric heating shaft furnace for oxidized pellet production based on hot air internal circulation and a pellet production method. The electric heating shaft furnace comprises a furnace shell and a hearth. The interior of the hearth is divided into a drying section, a preheating section, an electric heating roasting section, a first cooling section, a second cooling section and a third cooling section from top to bottom, and a material inlet and a material outlet are respectively formed in the top and the bottom of the hearth. And a microwave generating device is arranged on the side wall of the furnace body at the electric heating roasting section. By means of the microwave pure electric heating coupling cascade hot air internal circulation heat compensation mode, low-temperature (not exceeding 1200 DEG C) uniform heating oxidation of pellets and green production with zero carbon emission, low smoke amount and low pollution are achieved, and the method has the advantages of being simple in process, easy to operate, remarkable in energy conservation and emission reduction effect and capable of achieving large-scale industrial practical application.

Description

Technical Field

[0001] The invention relates to oxidation pellet production technology, in particular to an electric heating vertical furnace for oxidation pellet production based on hot air internal circulation and a pellet production method, belonging to the oxidation pellet production technology field. Background Art

[0002] Compared with sintered ore, pelletized ore is a higher quality raw material for blast furnace ironmaking, with the advantages of high iron grade, good metallurgical properties, low process energy consumption and pollutant emissions. In recent years, with the development of the steel industry, the domestic output of pelletized ore has shown a gradual upward trend, and a number of large-scale chain grate-rotary kiln and belt roaster pelletizing projects have been newly built. Therefore, promoting the progress and development of existing pelletizing processes and further developing energy-saving and emission reduction technologies for pelletizing production processes are effective measures to help the steel industry.

[0003] At present, my country's steel industry is striving to transform its energy structure from carbon energy to hydrogen-rich energy and green electricity energy, and complete the task of green low-carbon production and carbon emission reduction. However, for the production process of pellet ore, whether it is a vertical furnace, a chain grate-rotary kiln or a belt roaster, the heat generated by the combustion of fuels such as anthracite or coal gas is used to roast the pellets through heat conduction. Therefore, how to reduce carbon energy consumption has become the primary concern of pellet production.

[0004] For a long time, pellet production has more or less had problems such as high roasting temperature, uneven temperature field in the pellet material, and uneven pellet quality. The flame temperature of the rotary kiln is too high or too low, causing some pellets to be over-burned or under-burned. The upper layer of the belt roaster is over-burned and the lower layer is under-burned, resulting in uneven pellet quality. The "outside to inside" heating method of heat conduction leads to slow heating speed and uneven consolidation inside and outside. Therefore, how to achieve low-temperature, fast and uniform heating of pellets has become another important concern in pellet production. In addition, the treatment of pellet flue gas pollutants and ultra-low flue gas emissions have become a chronic disease in pellet production, causing headaches for pellet plants. Reducing pollutants at the source is crucial.

[0005] In summary, it is necessary to develop a new pellet roasting process to replace the existing carbon-based fuel with all clean energy, change the energy supply mode of combustion heat release and the roasting method of high-temperature heat conduction, form a new energy flow and air flow circulation system, improve the uniformity of the temperature field during the pellet roasting process, reduce the roasting temperature, achieve emission reduction and consumption reduction at the source, and help the green development of the steel industry. Summary of the invention

[0006] In view of the problems in the existing oxidation pellet production technology, such as uneven pellet quality, high content of flue gas pollutants, large emissions, and large carbon emissions due to high roasting temperature and uneven temperature field in the pellet material, the present invention provides an electric heating vertical furnace for oxidation pellet production based on hot air internal circulation and a pellet production method. The present invention utilizes microwave pure electric heating coupled with stepped hot air internal circulation heating to achieve uniform heated oxidation consolidation of pellets at a relatively low temperature (not exceeding 1200°C) as well as "zero carbon emissions", low flue gas volume, and low pollution green production, which has the characteristics of significant energy-saving and emission reduction effects and large-scale industrial practical applications.

[0007] In order to achieve the above technical objectives, the technical solutions adopted by the present invention are as follows:

[0008] According to a first embodiment of the present invention, an electric heating vertical furnace for producing oxidation pellets based on internal circulation of hot air is provided:

[0009] An electric heating vertical furnace for producing oxidation pellets based on hot air internal circulation, the electric heating vertical furnace comprises a furnace shell and a furnace chamber. The interior of the furnace chamber is divided into a drying section, a preheating section, an electric heating roasting section, a cooling section 1, a cooling section 2 and a cooling section 3 which are connected in sequence from top to bottom. A material inlet and a material outlet are respectively provided at the top and bottom of the furnace chamber. A microwave generating device is provided on the side wall of the furnace body located in the electric heating roasting section.

[0010] The air inlet of the third cooling section is connected to the first air inlet duct, and its air outlet is connected to the air inlet of the drying section through the third hot air circulation duct. The air outlet of the drying section is connected to the air inlet of the second cooling section through the second air inlet duct, and the air outlet of the second cooling section is connected to the air inlet of the drying section or the third hot air circulation duct through the second hot air circulation duct. The air outlet of the first cooling section is connected to the air inlet of the preheating section through the first hot air circulation duct, and the air outlet of the preheating section is connected to the air inlet of the first cooling section through the third air inlet duct.

[0011] Preferably, the air outlet of the drying section is also connected to the air inlet of the desulfurization device through the first exhaust duct. The air outlet of the preheating section is also connected to the air inlet of the desulfurization device through the second exhaust duct. Preferably, an oxygen supply duct is also connected to the first hot gas circulation duct.

[0012] Preferably, a hood is provided between the drying section and the preheating section, between the preheating section and the electric heating roasting section, between the electric heating roasting section and the first cooling section, between the first cooling section and the second cooling section, and between the second cooling section and the third cooling section. The hood is a flat plate or a convex arc plate structure.

[0013] Preferably, the hood has a cavity inside, and an air outlet connected to its inner cavity is provided on the top wall of the hood. The air inlets of the drying section, the preheating section, the electric heating roasting section, the cooling section one, and the cooling section two are all arranged on the side walls at their respective bottoms, and are connected to the inner cavities of the hoods located at their respective bottoms. The air outlets of the drying section, the preheating section, the cooling section one, the cooling section two, and the cooling section three are all arranged on the side walls at their respective tops, and extend to the bottom of the bottom wall of the hoods located at their respective tops. The air inlet of the cooling section three is arranged on its bottom wall. Preferably, the air outlet of the cooling section three is also connected to the air inlet of the electric heating roasting section through the fourth hot air circulation duct.

[0014] Preferably, the drying section, preheating section, electric roasting section, cooling section one, cooling section two, and cooling section three are all independently segmented designs, and the connection between any two of them is a sleeve connection that can be moved in the vertical direction.

[0015] Preferably, the bottom end of the drying section is sleeved inside the top of the preheating section, the bottom end of the preheating section is sleeved inside the top of the electric roasting section, the bottom end of the electric roasting section is sleeved inside the top of the cooling section, the bottom end of the cooling section is sleeved inside the top of the cooling section 2, and the bottom end of the cooling section 2 is sleeved inside the top of the cooling section 3. Preferably, the drying section, the preheating section, the electric roasting section, the cooling section 1, the cooling section 2, and the cooling section 3 are each independently a cylindrical or square cylindrical structure with the same inner diameter up and down, or with a larger inner diameter at the top and a smaller inner diameter at the bottom, or with a larger inner diameter in the middle and a smaller inner diameter at the top and down. The widths of the side walls of the square cylinder are the same or different.

[0016] According to a second embodiment of the present invention, a method for producing oxidation pellets based on electric heating is provided:

[0017] A method for producing oxidized pellets based on electric heating or a method for producing oxidized pellets using the electric heating shaft furnace described in the first embodiment, the method comprising the following steps:

[0018] 1) According to the direction of the material, the green pellets enter from the material inlet at the top of the furnace and pass through the drying section, preheating section, electric roasting section, cooling section one, cooling section two, cooling section three from top to bottom, and then are discharged from the material outlet at the bottom of the furnace to obtain finished oxidized pellets.

[0019] 2) According to the direction of the wind flow, the oxygen-containing cooling air enters the cooling stage 1, cooling stage 2, and cooling stage 3 from the air inlet at the bottom of the furnace from bottom to top to cool the hot pellets, and the hot exhaust gas generated during the cooling process is circulated to the drying stage as hot air for drying or circulated to the preheating stage as hot air for preheating.

[0020] Preferably, in the third cooling section: oxygen-containing cooling air enters through the first air inlet duct from the air inlet located at the bottom of the third cooling section and enters the top of the third cooling section to form low-temperature hot waste gas after cooling the hot pellets in the third cooling section upward. A part of the low-temperature hot waste gas enters the bottom of the second cooling section upward, and another part of the low-temperature hot waste gas is circulated and transported to the wind cap located at the bottom of the drying section through the third hot gas circulation duct.

[0021] Preferably, in the second cooling section: the hot air discharged from the air outlet at the top of the drying section enters the hood at the bottom of the second cooling section through the second air inlet duct from the air inlet at the bottom of the second cooling section, and together with part of the low-temperature hot exhaust gas from the third cooling section, cools the hot pellets in the second cooling section upwards and then enters the top of the second cooling section to form medium-temperature hot exhaust gas. Part of the medium-temperature hot exhaust gas enters the bottom of the first cooling section upwards, and the other part of the hot exhaust gas is circulated and transported to the hood at the bottom of the drying section through the second hot gas circulation duct.

[0022] Preferably, in the first cooling stage: the hot air discharged from the air outlet at the top of the preheating stage enters the hood at the bottom of the first cooling stage through the third air inlet duct from the air inlet at the bottom of the first cooling stage, and together with part of the medium-temperature hot waste gas from the second cooling stage, cools the hot pellets in the first cooling stage upwards and then enters the top of the first cooling stage to form high-temperature hot waste gas. Part of the high-temperature hot waste gas enters the bottom of the roasting stage upwards, and the other part of the high-temperature hot waste gas is circulated and transported to the hood at the bottom of the preheating stage through the first hot gas circulation duct.

[0023] Preferably, part of the low-temperature hot exhaust gas at the top of the third cooling stage is circulated through the fourth hot gas circulation pipe to the wind hood at the bottom of the electric roasting stage, and together with part of the high-temperature hot exhaust gas from the first cooling stage, the pellets in the electric roasting stage are roasted upward. The hot gas generated after roasting enters the preheating stage upward to preheat the pellets.

[0024] Preferably, part of the hot air discharged from the top air outlet of the drying section is also transported to the desulfurization device through the first exhaust duct for desulfurization treatment before being discharged outside.

[0025] Preferably, part of the hot air discharged from the top air outlet of the preheating section is also transported to the desulfurization device through the second exhaust duct for desulfurization treatment before being discharged outside.

[0026] Preferably, the oxygen-containing cooling wind is a gas at normal or room temperature with an oxygen content of not less than 18%, preferably air at normal or room temperature.

[0027] Preferably, the temperature of the low temperature hot exhaust gas is 250-400°C, preferably 300-350°C, for example, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 305°C, 310°C, 315°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C, 400°C.

[0028] Preferably, the temperature of the medium-temperature hot exhaust gas is 600-800°C, preferably 650-750°C, for example, one of 600°C, 605°C, 610°C, 620°C, 630°C, 650°C, 680°C, 700°C, 720°C, 750°C, 780°C, and 800°C.

[0029] Preferably, the temperature of the high-temperature hot exhaust gas is 1000-1150°C, preferably 1050-1100°C, for example, one of 1000°C, 1010°C, 1020°C, 1030°C, 1040°C, 1050°C, 1060°C, 1070°C, 1080°C, 1090°C, 1100°C, 1110°C, 1120°C, 1130°C, 1140°C, and 1150°C.

[0030] Preferably, oxygen-enriched gas is added to the preheating section through an oxygen supply pipeline, so that the oxygen content in the hot air used to preheat the pellets is not less than 20%, preferably 20-30%, more preferably 22-25%, for example, one of 20%, 20.5%, 21%, 21.5%, 22%, 22.5%, 23%, 23.5%, 24%, 24.5%, 25%, 26%, 27%, 28%, 29%, and 30%.

[0031] Preferably, in the cooling section, the hot air transported through the third air inlet duct accounts for 80% or more of the total hot air discharged from the top air outlet of the preheating section, preferably 80% to 95%, for example, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%. The high-temperature hot exhaust gas circulated and transported to the preheating section through the first hot gas circulation pipeline accounts for 85% or more of the total high-temperature hot exhaust gas, preferably 85% to 95%. For example, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%.

[0032] Preferably, in the second cooling stage, the hot air transported through the second air inlet duct accounts for 0-20% of the total hot air discharged from the top air outlet of the drying stage, preferably 5%-15%. For example, it is one of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, and 20%. The medium-temperature hot exhaust gas circulated and transported to the drying stage through the second hot air circulation duct accounts for 20%-50% of the total medium-temperature hot exhaust gas, preferably 30-40%. For example, it is one of 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, and 50%.

[0033] Preferably, in the third cooling stage, the low-temperature hot exhaust gas circulated and transported to the drying stage through the third hot gas circulation pipeline accounts for 50% to 70% of the total low-temperature hot exhaust gas, preferably 55% to 65%, for example, one of 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, and 70%.

[0034] Preferably, the electric heating roasting section is heated by electric microwave, that is, a microwave generator is arranged outside the side wall of the electric heating roasting section. Preferably, the microwave generator is arranged on the two opposite side walls of the electric heating roasting section.

[0035] Preferably, the operating frequency of the microwave generator is such that the temperature in the electric heating roasting section does not exceed 1200°C, preferably 1050-1200°C, more preferably 1100-1150°C. For example, it is one of 1050°C, 1060°C, 1070°C, 1080°C, 1090°C, 1100°C, 1110°C, 1120°C, 1130°C, 1140°C, 1150°C, 1180°C, and 1200°C.

[0036] Preferably, the green pellets are iron-containing pellets. Preferably, the particle size of the green pellets is 6-20 mm, preferably 8-15 mm. For example, it is one of 6 mm, 6.5 mm, 7 mm, 7.5 mm, 8 mm, 8.5 mm, 9 mm, 9.5 mm, 10 mm, 10.5 mm, 11 mm, 11.5 mm, 12 mm, 12.5 mm, 13 mm, 13.5 mm, 14 mm, 14.5 mm, 15 mm, 15.5 mm, 16 mm, 16.5 mm, 17 mm, 17.5 mm, 18 mm, 18.5 mm, 19 mm, 19.5 mm, and 20 mm.

[0037] Preferably, the temperature of the finished oxidized pellets discharged from the material outlet at the bottom of the furnace is not higher than 150°C, preferably 100-150°C, for example, one of 100°C, 105°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, and 150°C.

[0038] In the prior art, the existing heating method for oxidized pellets is mostly radiant heat generated by the heat released by fuel combustion. Since there is a large heat loss in the process of the radiant heat of fuel combustion acting on the pellets, in order to ensure that the pellet material layer is fully heated, the heat released by the fuel combustion often needs to be greater than the heat required for the oxidative roasting of the pellets. Therefore, there are inevitably problems such as local high temperature (over 1250°C) and uneven heating of the temperature field. Higher temperatures and full combustion of fuel require an oxygen-rich environment, so a large amount of thermal nitrogen oxides and a large amount of fuel consumption are inevitably generated. In addition, the sulfur entrained in the mineral fuel will also be released and oxidized into sulfur dioxide and enter the flue gas. Based on the above problems, it ultimately leads to a large amount of flue gas treatment and high treatment costs, and uneven consolidation of the oxidized pellets inside and outside.

[0039] In the present invention, based on the concept of producing low-carbon clean oxidized pellets by electric heating, a traditional vertical furnace is cut and segmented, and a microwave generator is coupled to the vertical furnace body, so as to provide an electric heating vertical furnace for producing oxidized pellets with multi-stage microwave heating and hot air internal circulation. The electric heating vertical furnace has an easy-to-match external structure, low difficulty in combination, and each section of the furnace can be shrunk or stretched. In addition, the pellet material is distributed and controlled to form an ideal pellet distribution with small particle size in the middle and large particle size at the edge in the horizontal width direction (i.e., microwave transmission direction). The ideal pellet distribution and airflow distribution are constructed through reasonable distribution, forming a stepped heat and air volume distribution with large particle pellets coupled with large air volume heat transfer and small particle pellets coupled with small air volume heat transfer, so as to achieve uniform and uniform heating of pellets of different particle sizes; a shrinkable and elongated furnace is used to ensure the preheating and roasting time of the pellet material; oxygen-enriched gas is used for preheating and roasting, so as to comprehensively promote the full oxidation and crystallization of the pellet ore, improve the quality of the pellet ore, and reduce the roasting temperature. At the same time, the heating method of direct microwave heating replaces the heating method of carbon-based fuel combustion in the existing technology, achieving "zero carbon emission" and low SO2 emissions in the pellet production process. Microwave heating directly acts on the inside of the material, which can achieve roasting at a lower temperature (below 1200℃), greatly reducing the generation of thermal NOx. While ensuring the quality of the pellet ore, energy conservation and emission reduction in the pellet production process are achieved.

[0040] In the present invention, the interior of the electric heating vertical furnace includes a drying section, a preheating section, an electric heating roasting section, a cooling section, a cooling section and a cooling section from top to bottom, which are connected in series in sequence; a microwave generator is arranged on the side wall of the furnace body located in the electric heating roasting section, that is, the electric heating roasting section is directly heated by the microwave device; the microwave device is a cavity structure, and microwave generators are arranged on the left and right surfaces of the cavity. The microwave direct heating method has the following advantages: on the one hand, the heating principle of the pellet material by the microwave heating method and the fuel combustion heating method is completely different. Microwave heating mainly realizes internal friction heat generation through ion conduction and dipole rotation, which can quickly and evenly heat up. The material layer heating process is not affected by the heat conduction of ordinary combustion heating, so the sintering temperature of the pellet material can be effectively reduced (not exceeding 1200°C), while the temperature gradient is inevitably generated due to the heat conduction in the process of fuel combustion heating, so that a higher sintering temperature (over 1200°C) is required for fuel sintering to obtain a higher sintering efficiency. On the other hand, the microwave heating method itself has the characteristics of fast heating, uniform heating and energy attenuation (certain penetration depth). By constructing an ideal distribution of pellets in the roasting furnace and setting microwave generators on the left and right surfaces of the material layer, the pellet layer can be heated evenly from the edge to the center. Then, through the control of gas-solid heat transfer optimized by the stepped air volume distribution, the technical problems of local overheating and underheating and uneven sintering in the sintering process of the pellet material can be effectively avoided, making the temperature field of the pellet material more uniform and improving the uniformity of the pellet quality. Thirdly, it can significantly reduce the NOx and SO2 emissions caused by the use of fossil fuels from the source, and achieve "zero carbon emissions" in the pellet production process.

[0041] In the present invention, the working frequency of the microwave generator is generally 915MHz-2450MHz, mainly realizing heating the pellets to 1000℃~1200℃ (preferably 1100~1150℃). The traditional fuel combustion roasting temperature is mostly above 1250℃~1280℃, and by adopting high-frequency microwave heating, the roasting temperature can be effectively reduced to below 1200℃, greatly reducing the energy consumption of pellet sintering. At the same time, the generation of thermal NOx is reduced.

[0042] In the present invention, the particle size of the pellets is generally 6 to 20 mm (preferably 8 to 15 mm). The particle size of the pellets is controlled within an appropriate range to achieve an ideal material layer distribution based on the pellet particle size, ensure that microwaves fully penetrate the pellets for heating, and reasonably distribute the heat of the entire material from the edge to the center.

[0043] In the present invention, the hot exhaust gas generated by the cooling section (cooling section 1, cooling section 2, cooling section 3) and the low-temperature hot air generated by the drying section and the preheating section are internally circulated, that is, the hot exhaust gas of the cooling section is circulated as the drying air and preheating air of the drying section and the preheating section, while fully realizing the waste heat utilization of the sensible heat of the hot pellets, the amount of exhaust gas and the cost of flue gas treatment are greatly reduced. Compared with the chain grate-rotary kiln-annular cooler system at the same output, the air volume is reduced by about 60% to 70%, the direct energy consumption is reduced by about 20% to 30%, no nitrogen oxides are produced, the desulfurization efficiency is high, the product performance is optimized (the sulfur content of the pellets is significantly reduced, and the desulfurization rate is increased from 80 to 85% to 90 to 95%), the roasting temperature is reduced, the product is more homogenized, and the production is smooth.

[0044] In the present invention, in the cooling section (cooling section 1, cooling section 2, cooling section 3), the high-temperature hot pellets from the roasting section are cooled at a rate of 50-80°C / min, thereby controlling the temperature of the final finished pellets to be lower than 150°C. The cooling gas required for cooling section 3 is air at room temperature or normal temperature. The air enters from the air inlet at the bottom of cooling section 3, and after heat exchange with the descending hot pellets, it is collected at the lower side of the top hood of cooling section 3 to form low-temperature hot waste gas with a temperature of 250-350°C. The low-temperature hot waste gas is discharged in two paths, a small part of which directly enters cooling section 2 upward, and most of the low-temperature hot waste gas is circulated to the drying section by exhaust or blowing to be used as drying air.

[0045] Furthermore, the sources of cooling gas required for the cooling stage are: one is the medium-temperature hot exhaust gas formed in the cooling stage 2, and the other is part of the hot exhaust gas recycled in the preheating stage, and at the same time a certain amount of oxygen-rich or pure oxygen gas is coupled (directly added from the air inlet of the cooling stage 1 through the oxygen supply pipe or added to the preheating stage through the oxygen supply pipe and then circulated to the cooling stage 1). After mixing, the medium-low temperature oxygen-rich gas enters the cooling stage 1 to cool the high-temperature hot pellets while promoting the secondary oxidation and consolidation of the high-temperature pellets. Further, it can also effectively ensure that the oxygen content in the high-temperature hot exhaust gas discharged from the cooling stage 1 is not less than 20% (for example, 21% to 23%). The temperature of the high-temperature hot exhaust gas is 1000 to 1150°C. The high-temperature hot exhaust gas is also discharged in two paths. A small part of the high-temperature hot exhaust gas directly enters the electric roasting stage, and most of the hot exhaust gas is circulated to the preheating stage through exhaust air for use as preheating air. In the electric roasting section, oxygen-rich, high-temperature gas (due to the formation of gas circulation and oxygen supplementation, the entire furnace can be kept in an oxygen-rich state as much as possible. Generally, the oxygen concentration in the roasting section is basically above 19% without side effects) combined with microwaves is used to consolidate and roast the pellets, so that the pellets are heated up quickly. The oxygen-rich environment improves the oxidation degree of the pellets, which is beneficial to the close combination of Fe2O3 crystal phases, improves the microstructure of the pellets, and improves the quality of the pellet ore.

[0046] In the present invention, the sources of preheating gas in the preheating section are: first, the high-temperature hot exhaust gas from the oxidation roasting section, and second, the high-temperature hot exhaust gas from the cooling section. The composition ratio of the two is regulated to ensure that the oxygen content in the preheating gas is not less than 20% (oxygen-enriched or pure oxygen gas can be directly supplemented through the oxygen supply pipeline when necessary), and the temperature is 1000-1150° C. By strictly controlling the oxygen content and temperature, most of the chemical reactions such as oxidation, desulfurization, carbonate decomposition and preliminary microcrystallization can be completed in the preheating section before microwave roasting, providing favorable conditions for the microwave rapid roasting process and strengthening the consolidation of the pellets in the microwave roasting section.

[0047] In the present invention, the sources of drying gas in the drying section are: one is the low-temperature hot exhaust gas from the cooling three-stage cycle, and the other is the medium-temperature hot exhaust gas from the cooling two-stage cycle. The composition ratio of the two is adjusted to ensure that the temperature of the drying hot air gas is 400-500°C to meet the drying and dehydration process of the pellet material.

[0048] In the present invention, the pellet material of the present invention is an iron ore sintered pellet material (iron-containing pellet), which mainly includes iron-containing minerals, binders and additives, etc. Iron-containing minerals include magnetite, hematite and vanadium-titanium magnetite, etc., binders include but are not limited to bentonite and organic binders (sodium carboxymethyl cellulose, starch, polyvinyl alcohol, humic acid, etc.), and additives include but are not limited to calcium-containing additives and magnesium-containing additives.

[0049] In the present invention, the height of the electric heating vertical furnace is generally 10-100 m, preferably 15-80 m, and more preferably 20-60 m.

[0050] In the present invention, the height of the electric heating roasting section accounts for 10-90% of the height of the entire electric heating vertical furnace, preferably 20-80%, and more preferably 30-70%.

[0051] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0052] 1: Compared with the traditional oxidation pellet production equipment, the electric heating vertical furnace of the present invention cuts and segments the vertical furnace, couples the microwave generator with the vertical furnace body, makes its appearance structure easy to match, reduces the difficulty of combination, and thus creates a retractable and elongated oxidation roasting furnace chamber. By using microwave pure electric heating coupled with stepped hot air internal circulation heat supplement, the green production purpose of uniform thermal oxidation of pellets at a lower temperature (not exceeding 1200°C) is achieved, with significant energy-saving and emission reduction effects.

[0053] 2: The present invention replaces the heating method of carbon-based fuel combustion in the prior art with direct microwave heating, and adopts oxygen-rich gas for preheating and oxidative roasting, which comprehensively promotes the full consolidation of the pellet material, improves the quality of the pellet ore, reduces the roasting temperature, realizes "zero carbon emission" in the pellet production process, and greatly reduces the emission of NOx and SO2.

[0054] 3: The present invention performs step-by-step internal circulation and distribution of airflow according to the distribution of pellets, forming a mode in which large-particle pellets are coupled with large air volume heat transfer, and small-particle pellets are coupled with small air volume heat transfer. This not only improves the utilization of sensible heat of hot pellets and reduces system energy consumption, but also greatly reduces the air intake and flue gas emissions, significantly saving energy consumption.

[0055] 4: The electric heating vertical furnace of the present invention has a simple structure, is easy to operate, has the characteristics of uniform heating of pellet oxidation, small flue gas volume, low pollutant emissions, low energy consumption, etc., and has significant economic benefits and promotion and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a structural schematic diagram of the electric heating vertical furnace of the present invention.

[0057] Figure 2 The figure is a process flow chart of the method for producing oxidized pellets of the present invention.

[0058] Figure numerals: 1: furnace shell; 2: furnace chamber; 201: drying section; 202: preheating section; 203: electric roasting section; 204: cooling section one; 205: cooling section two; 206: cooling section three; 207: microwave generating device; 208: first air inlet duct; 209: third hot gas circulation duct; 210: second air inlet duct; 211: second hot gas circulation duct; 212: third air inlet duct; 213: first hot gas circulation duct; 214: first exhaust duct; 215: second exhaust duct; 216: oxygen supply duct; 217: fourth hot gas circulation duct; 3: desulfurization device; 4: wind hood. DETAILED DESCRIPTION

[0059] The technical solution of the present invention is illustrated below by way of example, and the scope of protection requested by the present invention includes but is not limited to the following embodiments.

[0060] An electric heating vertical furnace for producing oxidation pellets based on hot air internal circulation, the electric heating vertical furnace comprises a furnace shell 1 and a furnace chamber 2. The interior of the furnace chamber 2 is divided from top to bottom into a drying section 201, a preheating section 202, an electric heating roasting section 203, a cooling section 1 204, a cooling section 2 205 and a cooling section 3 206 which are connected in sequence. A material inlet and a material outlet are respectively provided at the top and bottom of the furnace chamber 2. A microwave generating device 207 is provided on the side wall of the furnace body 1 located in the electric heating roasting section 203.

[0061] The air inlet of the third cooling section 206 is connected to the first air inlet duct 208, and its air outlet is connected to the air inlet of the drying section 201 through the third hot air circulation duct 209. The air outlet of the drying section 201 is connected to the air inlet of the second cooling section 205 through the second air inlet duct 210, and the air outlet of the second cooling section 205 is connected to the air inlet of the drying section 201 or the third hot air circulation duct 209 through the second hot air circulation duct 211. The air outlet of the first cooling section 204 is connected to the air inlet of the preheating section 202 through the first hot air circulation duct 213, and the air outlet of the preheating section 202 is connected to the air inlet of the first cooling section 204 through the third air inlet duct 212.

[0062] Preferably, the air outlet of the drying section 201 is also connected to the air inlet of the desulfurization device 3 through the first exhaust pipe 214. The air outlet of the preheating section 202 is also connected to the air inlet of the desulfurization device 3 through the second exhaust pipe 215. Preferably, the first hot gas circulation pipe 213 is also connected to an oxygen supply pipe 216.

[0063] Preferably, a hood 4 is provided between the drying section 201 and the preheating section 202, between the preheating section 202 and the electric heating roasting section 203, between the electric heating roasting section 203 and the first cooling section 204, between the first cooling section 204 and the second cooling section 205, and between the second cooling section 205 and the third cooling section 206. The hood 4 is a flat plate or a convex arc plate structure.

[0064] Preferably, the hood 4 has a cavity inside, and an air outlet connected to its inner cavity is provided on the top wall of the hood 4. The air inlets of the drying section 201, the preheating section 202, the electric heating roasting section 203, the cooling section 1 204, and the cooling section 2 205 are all arranged on the side walls of their respective bottoms, and are connected to the inner cavity of the hood 4 located at their respective bottoms. The air outlets of the drying section 201, the preheating section 202, the cooling section 1 204, the cooling section 205, and the cooling section 3 206 are all arranged on the side walls of their respective tops, and extend to the bottom of the bottom wall of the hood 4 located at their respective tops. The air inlet of the cooling section 3 206 is arranged on its bottom wall. Preferably, the air outlet of the cooling section 3 206 is also connected to the air inlet of the electric heating roasting section 203 through the fourth hot air circulation duct 217.

[0065] Preferably, the drying section 201, the preheating section 202, the electric roasting section 203, the cooling section 1 204, the cooling section 205, and the cooling section 3 206 are all independently segmented designs, and the connection between any two of them is a sleeve connection that can be moved in the vertical direction.

[0066] Preferably, the bottom end of the drying section 201 is sleeved inside the top of the preheating section 202, the bottom end of the preheating section 202 is sleeved inside the top of the electric roasting section 203, the bottom end of the electric roasting section 203 is sleeved inside the top of the cooling section 1 204, the bottom end of the cooling section 1 204 is sleeved inside the top of the cooling section 2 205, and the bottom end of the cooling section 2 205 is sleeved inside the top of the cooling section 3 206. Preferably, the drying section 201, the preheating section 202, the electric roasting section 203, the cooling section 1 204, the cooling section 2 205, and the cooling section 3 206 are each independently a cylindrical or square cylindrical structure with the same inner diameter at the top and the bottom, or with a larger inner diameter at the top and a smaller inner diameter at the bottom, or with a larger inner diameter at the middle and a smaller inner diameter at the top and the bottom.

[0067] Example 1

[0068] like Figure 1 As shown, an electric heating vertical furnace for producing oxidation pellets based on hot air internal circulation includes a furnace shell 1 and a furnace chamber 2. The interior of the furnace chamber 2 is divided from top to bottom into a drying section 201, a preheating section 202, an electric heating roasting section 203, a cooling section 1 204, a cooling section 2 205, and a cooling section 3 206 that are connected in sequence. A material inlet and a material outlet are also provided at the top and bottom of the furnace chamber 2, respectively. A microwave generating device 207 is provided on the side wall of the furnace body 1 located in the electric heating roasting section 203.

[0069] The air inlet of the third cooling section 206 is connected to the first air inlet duct 208, and its air outlet is connected to the air inlet of the drying section 201 through the third hot air circulation duct 209. The air outlet of the drying section 201 is connected to the air inlet of the second cooling section 205 through the second air inlet duct 210, and the air outlet of the second cooling section 205 is connected to the third hot air circulation duct 209 through the second hot air circulation duct 211. The air outlet of the first cooling section 204 is connected to the air inlet of the preheating section 202 through the first hot air circulation duct 213, and the air outlet of the preheating section 202 is connected to the air inlet of the first cooling section 204 through the third air inlet duct 212.

[0070] Example 2

[0071] Example 1 is repeated, except that the air outlet of the drying section 201 is also connected to the air inlet of the desulfurization device 3 through the first exhaust pipe 214. The air outlet of the preheating section 202 is also connected to the air inlet of the desulfurization device 3 through the second exhaust pipe 215.

[0072] Example 3

[0073] Example 2 is repeated, except that an oxygen supply pipeline 216 is further connected to the first hot gas circulation pipeline 213 .

[0074] Example 4

[0075] Example 3 is repeated, except that a hood 4 is provided between the drying section 201 and the preheating section 202, between the preheating section 202 and the electric heating roasting section 203, between the electric heating roasting section 203 and the first cooling section 204, between the first cooling section 204 and the second cooling section 205, and between the second cooling section 205 and the third cooling section 206. The hood 4 is a convex arc plate-shaped structure.

[0076] Example 5

[0077] Example 4 is repeated, except that the interior of the hood 4 has a cavity, and an air outlet connected to its inner cavity is provided on the top wall of the hood 4. The air inlets of the drying section 201, the preheating section 202, the electric heating roasting section 203, the cooling section 1 204, and the cooling section 2 205 are all arranged on the side walls of their respective bottoms, and are connected to the inner cavities of the hoods 4 located at their respective bottoms. The air outlets of the drying section 201, the preheating section 202, the cooling section 1 204, the cooling section 205, and the cooling section 3 206 are all arranged on the side walls of their respective tops, and extend to the bottom of the bottom wall of the hood 4 located at their respective tops. The air inlet of the cooling section 3 206 is arranged on its bottom wall. Preferably, the air outlet of the cooling section 3 206 is also connected to the air inlet of the electric heating roasting section 203 through the fourth hot air circulation duct 217.

[0078] Example 6

[0079] Example 5 is repeated, except that the drying section 201, the preheating section 202, the electric roasting section 203, the cooling section 1 204, the cooling section 205, and the cooling section 3 206 are all independently segmented designs, and the connection between each other is a sleeve connection that can be moved in the vertical direction.

[0080] Example 7

[0081] Repeat Example 6, except that the bottom end of the drying section 201 is sleeved inside the top of the preheating section 202, the bottom end of the preheating section 202 is sleeved inside the top of the electric roasting section 203, the bottom end of the electric roasting section 203 is sleeved inside the top of the cooling section 1 204, the bottom end of the cooling section 1 204 is sleeved inside the top of the cooling section 2 205, and the bottom end of the cooling section 2 205 is sleeved inside the top of the cooling section 3 206.

[0082] Example 8

[0083] Example 7 is repeated, except that the drying section 201, the preheating section 202, the electric heating roasting section 203, the cooling section 1 204, the cooling section 205, and the cooling section 3 206 are each independently a cylindrical structure with the same inner diameter.

[0084] Example 9

[0085] Example 7 is repeated, except that the drying section 201, the preheating section 202, the electric heating roasting section 203, the cooling section 1 204, the cooling section 205, and the cooling section 3 206 are each independently a cylindrical structure with a larger inner diameter at the top and a smaller inner diameter at the bottom.

[0086] Example 10

[0087] Example 7 is repeated, except that the drying section 201, the preheating section 202, the electric heating roasting section 203, the cooling section 1 204, the cooling section 205, and the cooling section 3 206 are each independently a cylindrical structure with a smaller inner diameter at the top and a larger inner diameter at the bottom.

[0088] Embodiment 11

[0089] Example 7 is repeated, except that the drying section 201, the preheating section 202, the electric heating roasting section 203, the cooling section 1 204, the cooling section 205, and the cooling section 3 206 are each independently a cylindrical structure with a larger inner diameter in the middle and smaller at the top and bottom.

[0090] Example 12

[0091] like Figure 2 As shown, a method for producing oxidation pellets using an electric heating vertical furnace comprises the following steps:

[0092] 1) According to the direction of the material, the raw pellets enter from the material inlet at the top of the furnace 2 and pass through the drying section 201, the preheating section 20, the electric roasting section 203, the cooling section 1 204, the cooling section 205, and the cooling section 3 206 from top to bottom, and then are discharged from the material outlet at the bottom of the furnace 2 to obtain finished oxidized pellets.

[0093] 2) According to the direction of the wind flow, the oxygen-containing cooling air enters the cooling section 1 204, the cooling section 205, and the cooling section 3 206 from the bottom to the top from the air inlet at the bottom of the furnace to cool the hot pellets, and the hot exhaust gas generated during the cooling process is circulated to the drying section 201 as hot air for drying or circulated to the preheating section 202 as hot air for preheating.

[0094] Example 13

[0095] Example 12 is repeated, except that in the cooling third section 206: the oxygen-containing cooling air enters from the air inlet located at the bottom of the cooling third section 206 through the first air inlet duct 208 and enters the top of the cooling third section 206 to form low-temperature hot waste gas after cooling the hot pellets in the cooling third section 206 upward. A part of the low-temperature hot waste gas enters the bottom of the cooling second section 205 upward, and the other part of the low-temperature hot waste gas is circulated and transported to the hood 4 located at the bottom of the drying section 201 through the third hot gas circulation duct 209.

[0096] Embodiment 14

[0097] Example 13 is repeated, except that in the second cooling section 205: the hot air discharged from the top air outlet of the drying section 201 enters the hood 4 located at the bottom of the second cooling section 205 through the second air inlet duct 210 from the air inlet located at the bottom of the second cooling section 205, and together with part of the low-temperature hot exhaust gas from the third cooling section 206, it cools the hot pellets in the second cooling section 205 upwards and then enters the top of the second cooling section 205 to form medium-temperature hot exhaust gas. A part of the medium-temperature hot exhaust gas enters the bottom of the first cooling section 204 upwards, and the other part of the hot exhaust gas is circulated and transported to the hood 4 located at the bottom of the drying section 201 through the second hot gas circulation duct 211.

[0098] Embodiment 15

[0099] Example 14 was repeated, except that in the first cooling section 204: the hot air discharged from the top air outlet of the preheating section 202 entered the hood 4 at the bottom of the first cooling section 204 through the third air inlet duct 212 from the air inlet at the bottom of the first cooling section 204, and together with part of the medium-temperature hot exhaust gas from the second cooling section 205, cooled the hot pellets in the first cooling section 204 upwards and then entered the top of the first cooling section 204 to form high-temperature hot exhaust gas. Part of the high-temperature hot exhaust gas entered the bottom of the roasting section 203 upwards, and the other part of the high-temperature hot exhaust gas was circulated and transported to the hood 4 at the bottom of the preheating section 202 through the first hot gas circulation duct 213.

[0100] Example 16

[0101] Example 15 is repeated, except that part of the low-temperature hot exhaust gas at the top of the third cooling section 206 is circulated through the fourth hot gas circulation pipe 217 to the hood 4 at the bottom of the electric roasting section 203, and together with part of the high-temperature hot exhaust gas from the first cooling section 204, the pellets in the electric roasting section 203 are roasted upward. The hot gas generated after roasting enters the preheating section 202 upward to preheat the pellets.

[0102] Embodiment 17

[0103] Example 16 is repeated, except that part of the hot air discharged from the top air outlet of the drying section 201 is also transported to the desulfurization device 3 through the first exhaust duct 214 for desulfurization treatment before being discharged.

[0104] Embodiment 18

[0105] Example 17 is repeated, except that part of the hot air discharged from the top air outlet of the preheating section 202 is also transported to the desulfurization device 3 through the second exhaust duct 215 for desulfurization treatment before being discharged.

[0106] Embodiment 19

[0107] Example 18 was repeated except that the oxygen-containing cooling air was room temperature air.

[0108] Embodiment 20

[0109] Example 19 was repeated except that the temperature of the low temperature hot exhaust gas was 250-400°C.

[0110] Embodiment 21

[0111] Example 20 was repeated except that the temperature of the medium-temperature hot exhaust gas was 600-800°C.

[0112] Embodiment 22

[0113] Example 21 was repeated except that the temperature of the high temperature hot exhaust gas was 1000-1150°C.

[0114] Embodiment 23

[0115] Example 22 is repeated, except that oxygen-rich gas is added to the preheating section 202 through the oxygen supply pipe 216 so that the oxygen content in the hot air used to preheat the pellets is 20-25%.

[0116] Embodiment 24

[0117] Example 23 is repeated, except that in the cooling section 204, the hot air delivered through the third air inlet duct 212 accounts for 80-95% of the total hot air discharged from the top air outlet of the preheating section 202. The high-temperature hot exhaust gas circulated and delivered to the preheating section 202 through the first hot gas circulation duct 213 accounts for 85-95% of the total high-temperature hot exhaust gas.

[0118] Embodiment 25

[0119] Example 24 is repeated, except that in the second cooling section 205, the hot air delivered through the second air inlet duct 210 accounts for 5% to 15% of the total hot air discharged from the top air outlet of the drying section 201. The medium-temperature hot exhaust gas circulated and delivered to the drying section 201 through the second hot air circulation duct 211 accounts for 30% to 40% of the total medium-temperature hot exhaust gas.

[0120] Embodiment 26

[0121] Example 25 is repeated, except that in the third cooling section 206, the low-temperature hot exhaust gas circulated and transported to the drying section 201 through the third hot gas circulation pipeline 209 accounts for 50-70% of the total low-temperature hot exhaust gas.

[0122] Embodiment 27

[0123] Example 26 is repeated, except that the heating method of the electric heating roasting section 203 is electric microwave heating, that is, a microwave generating device 207 is provided on the outside of the side wall of the electric heating roasting section 203.

[0124] Embodiment 28

[0125] Example 27 is repeated, except that the microwave generating device 207 is arranged on the opposite side walls of the electric heating roasting section 203.

[0126] Embodiment 29

[0127] Example 28 was repeated, except that the operating frequency of the microwave generating device 207 was such that the temperature in the electric heating roasting section 203 was 1100-1200°C.

[0128] Embodiment 30

[0129] Example 29 was repeated except that the green pellets were iron-containing pellets.

[0130] Embodiment 31

[0131] Example 30 was repeated except that the particle size of the green pellets was 8-15 mm.

[0132] Embodiment 32

[0133] Example 31 was repeated except that the temperature of the finished oxidized pellets discharged from the material outlet at the bottom of the furnace 2 was 100-150°C.

Claims

1. An electric heating vertical furnace for producing oxidation pellets based on hot air internal circulation, characterized in that: The electric heating vertical furnace comprises a furnace shell (1) and a furnace (2); the interior of the furnace (2) is divided from top to bottom into a drying section (201), a preheating section (202), an electric heating roasting section (203), a cooling section (1) (204), a cooling section (2) (205) and a cooling section (3) (206) which are connected in sequence; a material inlet and a material outlet are respectively provided at the top and bottom of the furnace (2); a microwave generating device (207) is provided on the side wall of the furnace body (1) located in the electric heating roasting section (203); The air inlet of the third cooling section (206) is connected to the first air inlet duct (208), and the air outlet is connected to the air inlet of the drying section (201) through the third hot air circulation duct (209); the air outlet of the drying section (201) is connected to the air inlet of the second cooling section (205) through the second air inlet duct (210), and the air outlet of the second cooling section (205) is connected to the air inlet of the drying section (201) or the third hot air circulation duct (209) through the second hot air circulation duct (211); the air outlet of the first cooling section (204) is connected to the air inlet of the preheating section (202) through the first hot air circulation duct (213), and the air outlet of the preheating section (202) is connected to the air inlet of the first cooling section (204) through the third air inlet duct (212).

2. The electric heating vertical furnace according to claim 1, characterized in that: The air outlet of the drying section (201) is also connected to the air inlet of the desulfurization device (3) through a first exhaust pipe (214); the air outlet of the preheating section (202) is also connected to the air inlet of the desulfurization device (3) through a second exhaust pipe (215); preferably, an oxygen supply pipe (216) is also connected to the first hot air circulation pipe (213).

3. The electric heating vertical furnace according to claim 1 or 2, characterized in that: A wind cap (4) is provided between the drying section (201) and the preheating section (202), between the preheating section (202) and the electric heating roasting section (203), between the electric heating roasting section (203) and the first cooling section (204), between the first cooling section (204) and the second cooling section (205), and between the second cooling section (205) and the third cooling section (206); the wind cap (4) is a flat plate or a convex arc plate-shaped structure; Preferably, the hood (4) has a cavity inside, and an air outlet hole connected to its inner cavity is arranged on the top wall of the hood (4); the air inlets of the drying section (201), the preheating section (202), the electric roasting section (203), the cooling section (204), and the cooling section (205) are all arranged on the side walls of their respective bottoms, and are connected to the inner cavities of the hoods (4) located at their respective bottoms; the air outlets of the drying section (201), the preheating section (202), the cooling section (204), the cooling section (205), and the cooling section (206) are all arranged on the side walls of their respective tops, and extend to below the bottom walls of the hoods (4) located at their respective tops; the air inlet of the cooling section (206) is arranged on its bottom wall; preferably, the air outlet of the cooling section (206) is also connected to the air inlet of the electric roasting section (203) through a fourth hot air circulation duct (217).

4. The electric vertical furnace according to any one of claims 1 to 3, characterized in that: The drying section (201), the preheating section (202), the electric heating roasting section (203), the cooling section (204), the cooling section (205), and the cooling section (206) are all designed in an independent segmented manner, and the connection between each other is a sleeve connection that can be moved in the vertical direction; Preferably, the bottom end of the drying section (201) is sleeved inside the top end of the preheating section (202), the bottom end of the preheating section (202) is sleeved inside the top end of the electric roasting section (203), the bottom end of the electric roasting section (203) is sleeved inside the top end of the cooling section (204), the bottom end of the cooling section (204) is sleeved inside the top end of the second cooling section (205), and the bottom end of the second cooling section (205) is sleeved inside the top end of the third cooling section (206); preferably, the drying section (201), the preheating section (202), the electric roasting section (203), the cooling section (204), the second cooling section (205), and the third cooling section (206) are each independently a cylindrical or square cylindrical structure with an inner diameter that is consistent from top to bottom, or with an inner diameter that is larger at the top and smaller at the bottom, or with an inner diameter that is smaller at the top and larger at the bottom, or with an inner diameter that is larger in the middle and smaller at the top and bottom.

5. A method for producing oxidation pellets based on electric heating or a method for producing oxidation pellets using the electric heating shaft furnace as claimed in any one of claims 1 to 4, characterized in that: The method comprises the following steps: 1) According to the direction of the material, the raw pellets enter from the material inlet at the top of the furnace (2) and pass through the drying section (201), the preheating section (20), the electric heating roasting section (203), the cooling section (1) (204), the cooling section (2) (205), and the cooling section (3) (206) from top to bottom, and then are discharged from the material outlet at the bottom of the furnace (2) to obtain finished oxidized pellets; 2) According to the direction of the wind flow, the oxygen-containing cooling air enters the cooling stage 1 (204), the cooling stage 2 (205), and the cooling stage 3 (206) from the bottom to the top from the air inlet at the bottom of the furnace to cool the hot pellets, and the hot exhaust gas generated during the cooling process is circulated to the drying stage (201) as hot air for drying or circulated to the preheating stage (202) as hot air for preheating.

6. The method according to claim 5, characterized in that: In the third cooling section (206): oxygen-containing cooling air enters through the first air inlet duct (208) from the air inlet located at the bottom of the third cooling section (206) and flows upward to cool the hot pellets in the third cooling section (206) before entering the top of the third cooling section (206) to form low-temperature hot waste gas; a portion of the low-temperature hot waste gas flows upward to the bottom of the second cooling section (205), and another portion of the low-temperature hot waste gas is circulated through the third hot gas circulation duct (209) and transported to the wind hood (4) located at the bottom of the drying section (201); and / or In the second cooling section (205): the hot air discharged from the air outlet at the top of the drying section (201) enters the hood (4) at the bottom of the second cooling section (205) through the second air inlet duct (210) from the air inlet at the bottom of the second cooling section (205), and together with part of the low-temperature hot waste gas from the third cooling section (206), cools the hot pellets in the second cooling section (205) and then enters the top of the second cooling section (205) to form medium-temperature hot waste gas; part of the medium-temperature hot waste gas enters the bottom of the first cooling section (204), and the other part of the hot waste gas is circulated through the second hot gas circulation duct (211) and transported to the hood (4) at the bottom of the drying section (201); and / or In the cooling section (204): the hot air discharged from the top air outlet of the preheating section (202) enters the hood (4) at the bottom of the cooling section (204) through the third air inlet duct (212) from the air inlet at the bottom of the cooling section (204), and together with part of the medium-temperature hot waste gas from the second cooling section (205), cools the hot pellets in the cooling section (204) and then enters the top of the cooling section (204) to form high-temperature hot waste gas; part of the high-temperature hot waste gas enters the bottom of the roasting section (203), and the other part of the high-temperature hot waste gas is circulated through the first hot gas circulation duct (213) and transported to the hood (4) at the bottom of the preheating section (202).

7. The method according to claim 6, characterized in that: Part of the low-temperature hot exhaust gas from the top of the third cooling section (206) is circulated through the fourth hot gas circulation pipe (217) to the hood (4) at the bottom of the electric roasting section (203), and together with part of the high-temperature hot exhaust gas from the first cooling section (204), the pellets in the electric roasting section (203) are roasted upward, and the hot gas generated after roasting enters the preheating section (202) upward to preheat the pellets; and / or Part of the hot air discharged from the top air outlet of the drying section (201) is also transported to the desulfurization device (3) through the first exhaust duct (214) for desulfurization treatment before being discharged; and / or Part of the hot air discharged from the top air outlet of the preheating section (202) is also transported to the desulfurization device (3) through the second exhaust duct (215) for desulfurization treatment before being discharged.

8. The method according to claim 6 or 7, characterized in that: The oxygen-containing cooling air is a gas at normal or room temperature with an oxygen content of not less than 18%, preferably air at normal or room temperature; and / or The temperature of the low temperature hot exhaust gas is 250-400°C, preferably 300-350°C; and / or The temperature of the medium-temperature hot exhaust gas is 600-800° C., preferably 650-750° C.; and / or The temperature of the high-temperature hot exhaust gas is 1000-1150°C, preferably 1050-1100°C.

9. The method according to any one of claims 5 to 8, characterized in that: Oxygen-enriched gas is added to the preheating section (202) through the oxygen supply pipe (216) so that the oxygen content in the hot air used to preheat the pellets is not less than 20%, preferably 20-30%, and more preferably 22-25%.

10. The method according to any one of claims 5 to 9, characterized in that: In the cooling section (204), the hot air transported through the third air inlet duct (212) accounts for 80% or more of all the hot air discharged from the top air outlet of the preheating section (202), preferably 80% to 95%; the high-temperature hot exhaust gas circulated and transported to the preheating section (202) through the first hot air circulation duct (213) accounts for 85% or more of all the high-temperature hot exhaust gas, preferably 85% to 95%; and / or In the second cooling section (205), the hot air transported through the second air inlet duct (210) accounts for 0% to 20%, preferably 5% to 15%, of all the hot air discharged from the top air outlet of the drying section (201); the medium-temperature hot waste gas circulated and transported to the drying section (201) through the second hot air circulation duct (211) accounts for 20% to 50%, preferably 30% to 40% of all the medium-temperature hot waste gas; and / or In the third cooling section (206), the low-temperature hot waste gas circulated and transported to the drying section (201) through the third hot gas circulation pipeline (209) accounts for 50% to 70% of the total low-temperature hot waste gas, preferably 55% to 65%.

11. The method according to any one of claims 5 to 10, characterized in that: The electric roasting section (203) is heated by electric microwave heating, that is, a microwave generating device (207) is arranged outside the side wall of the electric roasting section (203); preferably, the microwave generating device (207) is arranged on the side walls of the electric roasting section (203) on both sides opposite to each other; Preferably, the operating frequency of the microwave generator (207) is such that the temperature in the electric roasting section (203) does not exceed 1200°C, preferably 1050-1200°C, and more preferably 1100-1180°C.

12. The method according to any one of claims 5 to 11, characterized in that: The green pellets are iron-containing pellets; preferably, the particle size of the green pellets is 6-20 mm, preferably 8-15 mm; and / or The temperature of the finished oxidized pellets discharged from the material outlet at the bottom of the furnace (2) is not higher than 150°C, preferably 100-150°C.

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