Electric heating rotary kiln for directly reducing iron

Abstract

An electric heating rotary kiln for direct reduction iron is used for reducing iron ore into direct reduction iron. A plurality of heating sections are arranged in a hearth reduction section of the rotary kiln, and each heating section is heated through a plurality of direct-current power supplies with independently adjustable power output. The positive electrode and the negative electrode of the heating power source of each heating section in the hearth are in contact with the solid material in the hearth, current is fed into the solid material, and the material is heated through resistance heating of the solid material. The heating power supply anodes of the adjacent heating sections are adjacent to or share the anodes, or the cathodes of the adjacent heating sections are adjacent to or share the cathodes. And the contact part of each electrode and the material is made of high-temperature-resistant alloy. The direct reduction iron rotary kiln has the advantages that the rotary kiln can be large-sized, the service life of the electrode is long, the length of each heating section is convenient to set, the over-high heating power supply voltage to the ground is avoided, the production efficiency of the direct reduction iron rotary kiln is greatly improved, and the carbon emission is greatly reduced.

Description

Technical Field

[0001] The invention belongs to the field of iron and steel metallurgy and relates to electric heating rotary kiln equipment for producing direct reduced iron. Background Art

[0003] Coal-based direct reduced iron generally adopts the rotary kiln process. During the reduction process, secondary air is blown into the middle of the rotary kiln, and burns with CO in the atmosphere in the kiln to generate heat for the reduction reaction. Since the reaction rate of CO and iron oxide reduction is slow when the temperature is lower than 800℃, the temperature in the kiln is generally controlled to be above 800℃. At this time, CO2 will react with solid carbon to generate CO. In addition, CO2 generated by CO reducing iron oxide will also undergo the above reaction. Therefore, in general, solid carbon reduces iron oxide to generate direct reduced iron, and solid carbon reacts with oxygen to generate CO. The reaction of solid carbon reducing iron oxide to generate metallic iron and CO is a strong endothermic reaction. Therefore, a large amount of carbon is burned to provide heat for the main reduction reaction and to provide heat for other heat dissipation processes. Only part of the solid carbon is used as a reducing agent. This also leads to a relatively low content of reducing gas in the rotary kiln tail gas, and it also contains a large amount of nitrogen brought in by the secondary air, making the recycling cost of the tail gas high and the value low.

[0004] In the process of producing direct reduced iron in coal-based rotary kiln, in order to effectively transfer heat and mass, the material filling rate in the rotary kiln is relatively low, generally not exceeding 20%.

[0005] In short, coal-based rotary kilns produce direct reduced iron, with low mass and heat transfer efficiency, low gas conversion rate, low furnace utilization rate, and low equipment capacity. It consumes about 1 ton of coal per ton of iron, and its carbon emissions are higher than blast furnace ironmaking.

[0006] The gas-based rotary kiln direct iron reduction process uses natural gas, coal gas, hydrogen and other gases as reducing agents. The reaction of reducing iron oxides to produce metallic iron is still an endothermic reaction. Generally, heat is provided for the reduction reaction of iron oxides by introducing oxygen combustion or preheating the reducing gas to about 1000℃ to bring in sensible heat.

[0007] Due to the huge scale of direct reduced iron production, the existing direct reduced iron rotary kiln is affected by low filling rate and low heat transfer efficiency. Even if the length of the rotary kiln is more than 60m and the inner diameter of the furnace is more than 2.5m, the annual production capacity of a single rotary kiln is only about 150,000 tons, and the production efficiency is very low.

[0008] The existing self-heating rotary kiln that uses electricity to heat the material can overcome the problems of low material filling rate and low heat transfer efficiency, but it is difficult to achieve large-scale production due to factors such as the small number of heating sections, unreasonable electrode settings, and the use of single-phase or three-phase AC heating. In addition, the direct reduction iron process may generate CO, water and carbon dioxide during the reaction process, and the gas phase reducing agent may also contain hydrogen, which puts forward special requirements on the composition of the electrode material of the self-heating rotary kiln. As the rotary kiln rotates, the iron ore particles, oxidized pellets, and metallized pellets will scour and wear the electrodes of the self-heating rotary kiln, and high requirements are placed on the wear resistance and strength of the electrode materials. In large-scale self-heating rotary kilns, the current flowing through the electrodes is also large, and high requirements are also placed on the conductivity of the electrode materials. Damage to the electrode will cause the interruption of the direct reduction iron production process, and the low electrode life will make the self-heating rotary kiln process unfeasible.

[0009] In summary, due to the huge production capacity of the steel industry, the gas-based reduction ironmaking process is generally planned to have an annual production capacity of more than 500,000 tons. It is difficult for the existing rotary kiln to directly reduce iron to such a large scale. However, the coal-based rotary kiln adopts the method of blowing secondary air into the furnace to provide heat for the reduction reaction, and the tail gas is difficult to recycle, and the filling rate is low. The production efficiency is low and the carbon emission is high. The existing self-heating rotary kiln cannot adapt to large-scale direct reduction iron production due to factors such as power supply form, electrode layout, heating section setting, and electrode material. Whether using a vertical furnace or a rotary kiln, whether using coal-based, gas-based or full hydrogen reducing agent, heat supply and heat transfer are a huge challenge for large-scale endothermic reactions. Since hydrogen is expensive and coke oven gas and blast furnace gas are not easy to obtain; using water gas as the reducing gas actually still uses coal or coke as the reducing agent. The requirement to reduce carbon emissions has also made it inevitable to replace coal with electricity and use coal-based raw materials only as reducing agents. A direct reduction iron electric heating rotary kiln that can provide an annual production capacity of hundreds of thousands to millions of tons has become the preferred equipment. Summary of the invention

[0010] The purpose of the present invention is to provide an electric heating rotary kiln with a large production scale to meet the production needs of direct reduced iron with an annual output of hundreds of thousands of tons per set. The specific goals are: the rotary kiln has a large size, a high filling rate, uses electric energy as the heat source for endothermic reactions and heat loss, is safe in electricity use, has high electric heating efficiency, has low carbon emissions, and has a long service life; can use the oxidized pellets or sintered iron ore from existing blast furnace ironmaking as raw materials; can use coal-based, gas-based or full hydrogen gas raw materials as reducing agents for the production of direct reduced iron; and overcomes the difficulty of heating the material by passing electricity through the material during the production of direct reduced iron, which has a large change in resistivity.

[0011] The object of the present invention is achieved in that: A direct iron reduction electric heating rotary kiln is used to reduce iron ore materials into direct reduced iron, characterized in that: the rotary kiln has an internal cavity that is close to cylindrical or prismatic as a furnace, one end of the rotary kiln has a solid material feed port and an exhaust gas outlet, and the other end has a solid material discharge port; the furnace is provided with a reduction section. A preheating section is provided at the solid material feed end of the reduction section, and the iron ore materials enter the rotary kiln furnace from the feed end and pass through the preheating section and the reduction section in sequence. A heating power supply electrode is provided in the reduction section, which is used to energize the conductive material in the section to heat the material.

[0012] The heating power supply is a DC power supply with adjustable output power, and the heating power supply electrodes arranged in the reduction section have more than three positive electrodes and more than three negative electrodes. Multiple positive electrodes and negative electrodes divide the reduction section furnace into more than three heating sections in the length direction of the rotary kiln. And the electric heating power of each heating section is controlled by more than three heating power supplies respectively. Each heating section feeds current to the material in the furnace in parallel, that is, the positive electrodes of the heating power supplies of adjacent heating sections are adjacent to or share the positive electrodes, or the negative electrodes of adjacent heating sections are adjacent to or share the negative electrodes. Each electrode is a conductive material embedded in the inner wall of the refractory material of the furnace. Corresponding to this form of electrode arrangement, more than three heating power supplies are set, and the positive electrode of each power supply is connected to the positive electrode of the corresponding heating section, and the negative electrode of the heating power supply is connected to the negative electrodes on both sides of the positive electrode, that is, the negative electrodes at both ends of the heating section. Multiple negative electrodes are connected by conductive bars outside the rotary kiln furnace. Each heating power supply is a DC power supply, and the output power can be adjusted separately, or the output power can be automatically adjusted according to the temperature of the section.

[0013] The contact part of the electrode with the material in the furnace is a high temperature resistant alloy. High temperature resistant alloy is also called high temperature alloy. Or metal ceramic materials containing metal carbides, nitrides, carbonitrides, are collectively referred to as high temperature resistant alloys in the present invention.

[0014] The iron ore contains iron oxides, which are iron oxide, ordinary iron ore, ilmenite, vanadium-titanium magnetite, hematite, recycled iron-containing dust particles, and one or more of the graded preselection, molding, pre-burning, and pre-reduction products of the above materials. The total iron content in the iron ore is above 40%. After entering the furnace of the rotary kiln, the iron ore material passes through the preheating section and the reduction section in sequence. In the preheating section, the temperature is preheated and the iron oxide therein is partially reduced and metallized, so that it already contains some metallic iron when entering the reduction section, or the iron element therein has been partially reduced and contains some metallic iron when entering the preheating section of the rotary kiln furnace, so that the iron ore has conductivity, so that the iron ore material can be electrically heated in the reduction section.

[0015] The raw materials for blast furnace ironmaking, including oxidized pellets and sintered ore, can be used as the direct reduction iron raw materials of the rotary kiln of the technical solution of the present invention. After the iron ore material enters the furnace of the rotary kiln from the feed end, it passes through the preheating section and the reduction section in sequence. In the preheating section of the rotary kiln, the raw material is preheated and pre-reduced by the gas coming through the reduction section, wherein part of the iron oxide is reduced to metallic iron, so that the solid raw material has conductivity, and when it enters the reduction section, it can allow current to flow through the material pile and generate heat itself.

[0016] Furthermore, the rotary kiln is provided with a cooling section at the solid material discharge end of the reduction section, and the iron ore material enters the cooling section after passing through the reduction section.

[0017] Furthermore, an air inlet is provided at one end of the furnace where the solid materials are discharged. One or more reducing gases selected from CO, coke oven gas, water gas, methanol, hydrogen, ammonia, and volatile organic matter enter the furnace of the rotary kiln from the air inlet, and exchange heat with the solid materials in countercurrent in the cooling section, so that the reducing gas is preheated and the direct reduced iron is cooled or cooled.

[0018] Furthermore, the furnace discharge port is provided with a baffle plate to increase the filling rate of solid materials in the furnace. The filling rate of solid materials in the reduction section of the rotary kiln furnace can be greater than 40%. Compared with the existing coal-based direct reduction iron rotary kiln, the production capacity is more than doubled, the equipment production efficiency is improved, the heat loss per ton of product is reduced, and the carbon emission is reduced.

[0019] Furthermore, the electrode materials in contact with the materials in the furnace are screened. The electrode materials need to meet the requirements of being resistant to corrosion by CO, hydrogen, carbon dioxide and / or water vapor at a temperature of ≥1000°C, and the influence of metal hydrogen embrittlement should also be considered. In addition, the electrode materials also need to have sufficient strength, toughness and wear resistance at a temperature of ≥1000°C. The electrode materials also need to have good electrical conductivity to avoid overheating of the electrode materials themselves, which reduces their strength and corrosion resistance.

[0020] The high temperature resistant alloy contains more than 15% of metallic nickel.

[0021] Alternatively, the high temperature resistant alloy contains more than 15% of metallic chromium, which increases the high temperature alloy's ability to resist high temperature corrosion from carbon dioxide and water.

[0022] Alternatively, the high temperature resistant alloy contains carbides of metal nickel and chromium, which is an alloy of metal nickel and chromium carbide, or a hard alloy called metal ceramic. The chromium carbide is one or more of chromium carbide, chromium dicarbide and chromium carbide.

[0023] Alternatively, the high temperature resistant alloy contains metal nickel and silicon carbide, and is an alloy of metal nickel and silicon carbide or a metal ceramic.

[0024] Alternatively, the high temperature resistant alloy is metal molybdenum or a molybdenum alloy.

[0025] Alternatively, the high temperature resistant alloy is metal tungsten or a tungsten alloy.

[0026] The present invention carries out a series of investigation and tests on various influencing factors of the heating system. The investigation results are expressed in three levels: poor, general, good or high, medium and low, and some of the results are specially explained.

[0027] Rotary kiln parameters 1. Investigation and selection of heating power supply form The form of the heating power supply was investigated on an electric heating tube furnace with a total heating power of 15kw. When a DC power supply is used, the electrothermal efficiency reaches more than 90%, that is, more than 90% of the electric power input to the tube furnace is converted into thermal power. When 50Hz AC power is used, the electrothermal power is about 70%, and the power supply power is adjusted by a thyristor, which pollutes the stability and waveform of the AC power grid. When a 1kHz medium frequency power supply is used, the electrothermal efficiency is less than 50%, which also pollutes the stability and waveform of the power supply on the AC power supply side. Therefore, in the present invention, a DC power supply is used as the heating power supply, and preferably a full-wave rectified pulse width modulated DC power supply is used as the heating power supply.

[0028] Rotary kiln parameters 2. Investigation and selection of the number of heating sections The form of heating power supply is investigated on an electric heating tube furnace with a total heating power of 15kw. The reduction section with a total length of 3m is divided into different numbers of heating sections, and each section is independently temperature controlled. The materials are oxidized pellets with different reduction degrees, which are distributed from left to right in the tube furnace according to the reduction degree from low to high, and the corresponding material resistivity is from high to low. The heating current passes through the material, and the material generates heat as a resistor.

[0029] When the 3m length is heated as a whole section, the left section with higher resistivity generates more heat, while the right section generates less heat. During the rapid heating process, the temperature difference of the four temperature measuring points can reach up to 300°C. The more sections there are for distributed temperature control, the better the temperature control accuracy and the more uniform the temperature. In the actual operation of the industrial direct reduction iron self-heating rotary kiln, materials with higher resistivity enter the reduction section from the side with higher resistance in the reduction section. The material temperature here is lower, and the amount of reduction reaction is also larger, requiring more heat supply. Despite this, the entire reduction section as a whole only has one heating section or temperature control section, which still cannot meet the temperature control of industrial large-scale rotary kilns.

[0030] It is divided into three sections with independent temperature control and heating, using three-phase AC as the power supply, and the three heating sections are connected in a triangle. It is found that the three-phase current is unbalanced and the power factor of the power supply is reduced. This will affect the three-phase balance of the power grid when industrial-scale equipment is heated at high power. Abandon this heating solution.

[0031] Therefore, the present invention adopts a technical solution of dividing the reduction section into three or more sections and controlling the heating separately, which not only takes into account the needs of temperature control and heat demand of each section, but also facilitates the production of heating power supply, and controls the electrode current and voltage within an appropriate range, and has a better technical effect.

[0032] Rotary kiln parameters 3. Investigation and selection of multi-stage heating power supply connection form The connection form of the heating power supply is investigated on an electric heating tube furnace with a total heating power of 15kw. The reduction section with a total length of 3m is divided into three heating sections, and each section is independently temperature controlled. The materials are oxidized pellets with different reduction degrees, which are distributed from low to high reduction degrees from left to right in the tube furnace, and the corresponding material resistivity is from high to low. The heating current passes through the material, and the material generates heat as a resistor. The heating power supply is 3 5kw DC power supplies.

[0033] Three independent power supplies are connected in parallel, and four negative electrodes are set in the length direction of the tubular furnace reduction section. These four negative electrodes separate the furnace reduction section in the length direction of the rotary kiln to form three intervals, which are three heating sections. A positive electrode is set between the negative electrodes at both ends of each heating section, for a total of three positive electrodes. The three power supplies independently control the temperature of the three heating sections. The four negative electrodes are short-circuited with a conductive bar and grounded.

[0034] Three independent power supplies are connected in series, and four electrodes are set in the length direction of the reduction section of the tubular furnace. The leftmost electrode is the negative electrode of the first power supply, and the rightmost electrode is the positive electrode of the third power supply. The two middle electrodes are shared by the positive electrode of the left power supply and the negative electrode of the right power supply. The leftmost negative electrode is grounded.

[0035] When the three power supplies are connected in parallel, the highest voltage to ground on the electrode of the tube furnace during the heating process is low and does not exceed the maximum allowable voltage of each voltage. When the three power supplies are connected in series, the highest voltage to ground on the electrode of the tube furnace during the heating process is high, exceeding more than twice the maximum allowable voltage of a single power supply.

[0036] Therefore, the present invention adopts a plurality of DC power supplies in parallel for heating. Another advantage of the parallel connection of power supplies is that the electrodes at the ends of both sides of the reduction section are negative and grounded, so that the two ends of the rotary kiln do not need to be insulated or a more convenient insulation method can be used.

[0037] Rotary kiln parameters 4. Investigation and selection of electrode materials At 950℃, the corrosion resistance of various materials was investigated in different atmospheres for 48 hours. The atmospheres investigated were 70%CO+30%CO2 (hereinafter referred to as atmosphere 1), 70%hydrogen+30%water (gaseous) (hereinafter referred to as atmosphere 2), and 33.3%CO+66.6%hydrogen (hereinafter referred to as atmosphere 3) by volume. The material samples were weighed before and after the investigation. The smaller the weight change, the better. Weight increase or decrease was considered as a manifestation of corrosion resistance. Pressure was applied to the material samples after the above high temperature test, and its strength was assessed by the size of the fracturing force.

[0038] High-power electrode graphite, high-purity iron, ferrosilicon (containing 5% silicon), metallic nickel, metallic chromium, metallic molybdenum, metallic tungsten, 310S, electric furnace wire (0Cr27AL7Mo2), Incoloy MA956, Inconel MA6000, nickel-bonded chromium carbide, and nickel-bonded silicon carbide were investigated according to the above method.

[0039] After being treated in atmosphere 1 and atmosphere 2, high-power electrode graphite loses weight severely and its compressive strength becomes lower. High-purity iron gains weight after being treated in atmosphere 1. Ferrosilicon (containing 5% silicon) gains weight after being treated in atmospheres 1 and 2, and its compressive strength becomes extremely low. After being treated in the three atmospheres, the weight of metallic nickel changes little, but the surface glossiness decreases.

[0040] After being treated with atmosphere 1, the weight of metallic chromium increased by ~0.1% to test the surface resistance, which was significantly increased.

[0041] After being treated in three atmospheres, the weight of metal molybdenum and tungsten can not be measured. Good compressive strength.

[0042] After the electric furnace wire was treated with atmospheres 1 and 2, the surface resistance increased significantly and the compressive strength was poor. The performance of Incoloy MA956 was similar to that of the electric furnace wire.

[0043] After Inconel MA6000 was treated with three kinds of atmospheres, no weight change was detected and the compressive strength remained good.

[0044] The surface gloss of nickel-bonded chromium carbide and nickel-bonded silicon carbide decreased after being treated in atmospheres 2 and 3. The weight change was not obvious after being treated in the three atmospheres, and the change in compressive strength was small. The addition of chromium carbide and silicon carbide increased the wear resistance of the two materials. The resistivity of these two materials is also relatively low.

[0045] Rotary kiln parameters 5. Selection of baffle plate at furnace discharge port The length of the rotary kiln furnace is 16m, and the equivalent inner diameter of the furnace is 58cm. Baffles of different heights are set at the furnace discharge port. When the rotary kiln speed is 0.3 rpm, the effect of the baffle height on the filling rate of iron ore oxide pellets in the 6m-long furnace in the middle of the furnace is investigated. In order to increase the filling rate of the iron ore pellet material in the furnace, the preferred solution is to select the height of the baffle plate to be more than 30% of the inner diameter of the furnace.

[0046] Invention content 6. Selection of preheating section When there is no preheating section, oxygen pellets are directly fed into the reduction section of the rotary kiln furnace. The material temperature is low and a long heating process is required. In addition, the material is an insulator and cannot be heated by electricity. The solid material with good conductivity and high temperature in the middle of the reduction section is returned to the feeding port of the furnace, which is difficult to operate, the internal structure of the furnace is complex, and the return effect is not guaranteed. Without a preheating section, the length of the reduction section, i.e. the heating section, is extended on the surface, but the production capacity of the rotary kiln is not actually increased. In addition, due to the addition of a return mechanism in the furnace, the equipment reliability is reduced and the equipment life is shortened.

[0047] In a rotary kiln with a furnace length of 16m, a furnace length of 5m is set as the preheating section. After the iron ore oxidized pellets enter the furnace feed port, they pass through the preheating section and the reduction section in sequence. The oxidized pellets are preheated to a maximum of 750°C in the preheating section, where part of the iron oxide is reduced to metallic iron, and obtain sufficient conductivity, so that the process of energizing the pellet material, heating the material by the resistance heating of the pellet material itself, and providing heat for the reduction reaction can be carried out effectively. The heat in the preheating section comes from the high-temperature gas in the reduction section.

[0048] Compared with the prior art, the present invention has the following advantages: 1) Adopt DC power supply, high electric heating efficiency and high safety.

[0049] 2) The reduction section is divided into three or more sections for segmented control and heating, and the temperature control of the entire reduction section is more accurate. It can adapt to the problem that the resistivity of solid materials in the furnace varies greatly during the production of direct reduced iron, and the voltage and current requirements of the heating power supply for each section of materials are different. This makes it feasible to use the solution of directly heating the materials in the furnace to produce direct reduced iron on a large scale.

[0050] 3) The heating power supply is connected in parallel, so that the heating power supply voltage is maintained at a lower value, and the power safety of the production process is improved.

[0051] 4) The solid material filling rate in the reduction section of the rotary kiln furnace can reach more than 40%, which is more than double that of the existing coal-based rotary kiln that uses secondary blast combustion for heating. The production efficiency of direct reduction iron in the rotary kiln has increased exponentially. The floor space and investment cost of the production device have been greatly reduced.

[0052] 5) High temperature resistant alloy is used as the electrode in the furnace of the heating power source. The electrode has a long service life, so that the process of heating the material in the furnace by electricity can run stably.

[0053] 6) The reaction of reducing iron oxide to metallic iron by coal gas or solid carbon is a strong endothermic reaction. By electrically heating the materials in the furnace, the process of blowing secondary air into the furnace for combustion in the existing coal-based rotary kiln direct iron reduction process is avoided, and a large amount of nitrogen is avoided to be mixed into the atmosphere in the kiln, so that the rotary kiln tail gas recovery and utilization value is higher, and the amount of reducing agent used per ton of direct reduced iron is greatly reduced. The existing coal-based direct iron reduction rotary kiln consumes about 1 ton of coal per ton of iron. With the self-heating rotary kiln of the present invention, coal is only used as a reducing agent, and the coal consumption per ton of iron can be reduced to about 170 kg in theory.

[0054] 7) The rotary kiln of the present invention is provided with a preheating section, and cold iron ore oxidation pellets can be directly used as raw materials to enter the kiln directly, and the process equipment is simple and the reliability is high.

[0055] In summary, the electric heating rotary kiln for producing direct reduced iron of the present invention has high equipment efficiency, large production capacity, safe and reliable operation, and low carbon emissions by replacing coal with electricity, thus realizing the industrialization of producing direct reduced iron by direct electric heating. DETAILED DESCRIPTION

[0056] The specific technical solution of the present invention is described below in conjunction with embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 Schematic diagram of the rotary tube of the electric heating rotary kiln in Example 1, which is a cross-sectional view passing through the rotating axis of the rotary tube.

[0058] Figure 2 It is a left view of the rotary tube of the electric heating rotary kiln in Example 1. Example 1

[0059] The electric heating rotary kiln used for large-scale industrial production of direct reduced iron has a rotary tube length of 56m, a preheating section length of 10m, a reduction section length of 36m, a cooling section length of 10m, and a furnace inner diameter of 1.8m. Figure 1As shown. In the figure, 1 is a heat preservation and / or refractory material, 2 is a rotary tube, 3 is a furnace surrounded by refractory materials, 12 is a preheating section of the furnace, and 13 is a cooling section of the furnace. In the figure, 4, 6, 8, and 10 are metal molybdenum electrodes, which are the negative electrodes of the power supply, and 5, 7, and 9 are the positive electrodes of the power supply. The material is also metal molybdenum. The 4-1, 5-1, 6-1, 7-1, 8-1, 9-1, and 10-1 corresponding to the 7 electrodes are connected to the corresponding molybdenum electrodes, and are connected to the conductive bars outside the rotary tube, and then connected to the copper slip rings and carbon brushes respectively, and further connected to the corresponding power supply electrodes. The metal molybdenum electrodes inside the furnace are all in the form of circular rings, embedded in refractory materials, and sterilized with the rotary tube 2. The three positive electrodes 5, 7, and 9 are respectively connected to the positive electrodes of the three heating power supplies, and the negative electrodes on both sides of each positive electrode are connected to the negative electrodes of the corresponding power supply. Since electrodes 4 and 6 are connected to the negative electrode of the same heating power supply, and negative electrodes 6 and 8 are simultaneously connected to the negative electrode of another heating power supply, the four negative electrodes 4, 6, 8, and 10 are short-circuited outside the rotary tube. In this embodiment, the four negative electrodes of the power supply are reliably grounded. The three heating power supplies are all fully rectified pulse width modulated adjustable DC power supplies, the power supply voltage and output power are adjustable, and the output power is controlled by the thermocouple temperature. The three heating power supplies heat the three heating sections of the reduction section, which are the furnace between the negative electrodes 4 and 6, the furnace between the electrodes 6 and 8, and the furnace between the electrodes 8 and 10. In this embodiment, the length of each heating section is 12m, and is divided into two parallel 6m lengths by the positive electrode in the middle of the section. The lengths of the heating sections of the electric heating rotary kiln of the present invention may also be unequal, and the number of heating sections, the length of each heating section, and whether the lengths are equal are not limited by this embodiment.

[0060] After the vanadium-titanium magnetite oxide pellets or the sintered ore of the general ore enter the furnace, they pass through the preheating section, reduction section and cooling section in sequence, and then withdraw from the rotary kiln furnace.

[0061] Attached Figure 2 The middle 14 is a baffle plate, which is placed at the furnace discharge port and does not rotate with the rotary tube. The upper edge of the baffle plate is nearly parallel to the inclined surface of the material in the furnace. The baffle plate allows the filling rate of the solid material in the reduction section of the furnace to be maintained at more than 40%.

Claims

1. A direct reduced iron electric heating rotary kiln, used for reducing iron ore materials into direct reduced iron, characterized in that: The rotary kiln has an internal cavity that is nearly cylindrical or prismatic as a furnace, one end of the rotary kiln has a solid material feed port and an exhaust gas outlet, and the other end has a solid material discharge port; the furnace is provided with a reduction section; a preheating section is provided at the solid material feed end of the reduction section, and the iron ore material enters the rotary kiln furnace from the feed end and passes through the preheating section and the reduction section in sequence; a heating power supply electrode is provided in the reduction section, which is used to energize the conductive material in the section to heat the material; The heating power supply is a DC power supply with adjustable output power. The heating power supply electrodes arranged in the reduction section have more than three positive electrodes and more than three negative electrodes. The multiple positive electrodes and negative electrodes divide the reduction section furnace into more than three heating sections in the length direction of the rotary kiln, and the electric heating power of each heating section is controlled by more than three heating power supplies respectively. Each heating section feeds current to the material in the furnace in a parallel manner, that is, the positive electrodes of the heating power supplies of adjacent heating sections are adjacent to the positive electrodes or share the positive electrodes, or the negative electrodes of adjacent heating sections are adjacent to the negative electrodes or share the negative electrodes. The part of the electrode in contact with the material in the furnace is made of a high temperature resistant alloy; The iron ore contains iron oxides, which are iron oxide, ordinary iron ore, ilmenite, vanadium-titanium magnetite, hematite, recycled iron-containing dust particles, and one or more of the graded pre-selection, molding, pre-burning and pre-reduction products of the above materials; the iron content in the iron ore is above 40%; after entering the rotary kiln furnace, the iron mineral material is preheated and heated in the preheating section, and the iron oxide therein is partially reduced and metallized, so that it already contains some metallic iron when entering the reduction section, or the iron element therein has been partially reduced and contains some metallic iron when entering the rotary kiln furnace preheating section, so that the iron mineral material has conductivity.

2. A direct reduction iron electric heating rotary kiln according to claim 1, characterized in that: The rotary kiln is provided with a cooling section at the solid material discharge end of the reduction section, and the iron ore material enters the cooling section after passing through the reduction section.

3. A direct reduction iron electric heating rotary kiln according to any one of claims 1 to 2, characterized in that: An air inlet is arranged at one end of the furnace where the solid materials are discharged.

4. A direct reduction iron electric heating rotary kiln according to any one of claims 1 to 3, characterized in that: The furnace discharge port is provided with a baffle plate to increase the filling rate of solid materials in the furnace.

5. A direct reduced iron electric heating rotary kiln according to any one of claims 1 to 4, characterized in that: The high temperature resistant alloy contains more than 15% of metallic nickel.

6. A direct reduction iron electric heating rotary kiln according to any one of claims 1 to 5, characterized in that: The high temperature resistant alloy contains more than 15% of metallic chromium.

7. A direct reduction iron electric heating rotary kiln according to any one of claims 1 to 5, characterized in that: The high temperature resistant alloy contains carbides of metal nickel and chromium.

8. A direct reduction iron electric heating rotary kiln according to any one of claims 1 to 5, characterized in that: The high temperature resistant alloy contains metal nickel and silicon carbide.

9. A direct reduction iron electric heating rotary kiln according to any one of claims 1 to 4, characterized in that: The high temperature resistant alloy is metal molybdenum or a molybdenum alloy.

10. A direct reduction iron electric heating rotary kiln according to any one of claims 1 to 4, characterized in that: The high temperature resistant alloy is metal tungsten or a tungsten alloy.

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