Method for improving hydrogen reduction of iron ore coal-based direct reduction rotary kiln

Abstract

The invention provides a method for improving hydrogen reduction of an iron ore coal-based direct reduction rotary kiln, aiming at the current situation that in the direct reduction process of an iron ore rotary kiln, volatile components produced by fully pyrolyzing high volatile component coal sprayed into the kiln from a discharging end contain a large amount of H2, and the utilization rate of H2 in the direct reduction process of the iron ore is not high. Three retaining rings are arranged at different positions in the rotary kiln body, the pea coal spray gun arranged on the kiln head cover at the discharge end of the rotary kiln is subjected to eccentric displacement, and the rotary kiln burner is selected to be a sleeve type burner, so that the contact area between materials and the kiln wall can be increased on the basis of reducing the fall of the materials in the rotary kiln, and the energy consumption of the rotary kiln is reduced. And the rotating speed, the material filling rate and the temperature uniformity in the rotary kiln are improved. According to the invention, the fuel consumption of the rotary kiln is reduced, and the utilization efficiency of hydrogen in iron ore coal-based reduction and the quality and yield of iron ore reduction are improved.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, specifically to a method for improving hydrogen reduction in a rotary kiln for direct reduction of iron ore based on coal. Background Technology

[0002] In the direct reduction process of iron ore in a rotary kiln, a mixture of iron ore and reducing coal is added to the feed end of the rotary kiln. Under the rotation of the kiln, the mixture continuously flows from the feed end to the discharge end during the tumbling process, exchanging heat with the counter-flowing high-temperature flue gas. This causes the temperature of the mixture to rise while the flue gas temperature decreases. When the temperature of the mixture rises above 450℃, the iron ore and reducing coal begin to undergo a reduction reaction. As the temperature of the mixture increases, the reduction reaction rate accelerates, resulting in a greater amount of metallurgical gas overflowing from the material. This metallurgical gas overflows from the material bed and enters the kiln space. Under the action of combustion air blown in by the kiln back fan, the metallurgical gas burns, and the heat released from the combustion heats the mixture. As the mixture moves to the middle and rear sections of the rotary kiln, its temperature rises to 900-1100℃. At this point, the iron ore reduction reaction reaches its maximum rate, and the amount of metallurgical gas released is also at its maximum. The temperature of the combusted metallurgical gas is also higher. By adding excess reducing coal to the iron ore, the heat released from the combustion of the metallurgical gas can meet the production needs of the rotary kiln. Subsequently, as the ore-coal mixture flows within the kiln and the reduction reaction continues, the iron oxide and reducing coal content in the material decreases, and the amount of metallurgical gas released from the internal reduction reaction gradually decreases. When the mixture reaches the discharge section of the rotary kiln, the temperature of the space after the metallurgical gas combustion decreases. To increase the temperature of the discharge section, a heating burner is installed at the center of the discharge end of the rotary kiln. Figure 1 This is a schematic diagram of an existing rotary kiln for direct reduction of iron ore.

[0003] In rotary kilns, premixed burners with stable flames are generally used, with combustion air pressure of only 6-7 kPa. The flame length of this type of burner is only 5-7 m, and the heat load of the combustion zone is relatively high. During the operation of the rotary kiln, the flame head is prone to ring formation on the kiln body and material softening due to high temperature, which affects the hydrogen reduction efficiency of the rotary kiln. At the same time, the temperature is lower in the area not reached by the flame at the discharge end of the kiln, resulting in uneven temperature in the rotary kiln.

[0004] In the patent application "A Coal-Based Hydrogen Metallurgical Process and Apparatus for Iron Ore" (application number 201910518199X), to improve the reduction reaction rate of iron ore, a granular coal spray gun is installed above the heating burner on the kiln head hood at the discharge end, based on the aforementioned rotary kiln structure. The granular coal spray gun can spray granular high-volatile coal into the high-temperature reduction zone of the rotary kiln according to the process requirements. After the high-volatile coal mixes with the high-temperature mixture, its temperature rises rapidly, and the volatiles in the granular coal begin to be released. Under the high temperature inside the material layer, the volatiles further pyrolyze to produce a large amount of H2. H2 acts as a reducing agent to reduce the iron ore. Because the material inside the rotary kiln is rotating, it settles at the bottom of the rotary kiln, diagonally above the bottom in the direction of rotation. Figure 2 This diagram illustrates the distribution of roasted materials on the cross-section of a rotary kiln for direct reduction of iron ore. The rotary kiln rotates counterclockwise. When the granular coal ejected from the granular coal nozzle falls, some of it lands on the kiln bottom, which is not covered by the mixed material. Under the high temperature inside the kiln, the volatile matter in this portion of the granular coal is rapidly released and enters the kiln space. After the volatile matter is fully pyrolyzed, the resulting volatile matter cannot play a role in reducing the iron ore, thus reducing the utilization rate of H2. Simultaneously, to improve the filling rate of the rotary kiln and extend the reduction time of the material within the kiln, the rotary kiln speed is controlled below 0.4 r / min. The low rotation speed of the rotary kiln significantly reduces the tumbling speed of the material inside the kiln. The surface of the material in contact with the high-temperature flame inside the kiln is subjected to prolonged heating, which easily leads to liquefaction on the material surface. Once the liquid phase appears in the material, it easily adheres to the surrounding powder, resulting in flaky material on the material surface. The formation of flaky material hinders the transfer of heat to the material below, thereby reducing the production capacity and product quality of the rotary kiln.

[0005] In rotary kilns, the back fan's air pressure is typically 2-3 kPa. This relatively low air pressure causes the air blown out by the back fan to rapidly disperse at the nozzle and flow for 2-3 meters within the kiln. Its velocity then matches the flow velocity of the flue gas, causing it to flow together with the flue gas. This air mixes with the metallurgical gas overflowing from the material bed and undergoes combustion, resulting in localized high temperatures within 2-3 meters of the back fan nozzle. In this area, the material is prone to forming a liquid phase during roasting, leading to material sticking to the kiln and affecting the normal roasting of iron ore. Simultaneously, the reduction of iron ore in a rotary kiln is a strongly endothermic process; the temperature is lower in areas where fuel is not burned, further impacting the normal reduction of iron ore.

[0006] Figure 1This is a schematic diagram of an existing rotary kiln for direct reduction of iron ore. The existing rotary kiln for direct reduction of iron ore mainly consists of the following equipment: kiln body, kiln back fan, roasting material, kiln tail feeding end, kiln head discharging end, feeding end, discharging end, kiln head burner, refractory material, pulverized coal spray gun, pulverized coal feeding port, Roots blower, waste heat boiler, high-temperature and high-pressure steam, water, cyclone dust collector, bag filter dust collector, and fume extractor. Along the length of the kiln, from the feeding end to the discharging end, the rotary kiln is divided into five sections according to temperature: feeding section, rear section of the kiln body, middle section of the kiln body, front section of the kiln body, and discharging section. Summary of the Invention

[0007] This invention provides a method for improving the hydrogen reduction efficiency of a rotary kiln in the direct reduction of iron ore, reducing the fuel consumption of the rotary kiln, and thereby improving the quality and yield of iron ore reduction.

[0008] Therefore, the present invention adopts the following technical solution: In view of the fact that the volatile matter produced by the full pyrolysis of high volatile coal injected into the kiln from the discharge end of the iron ore rotary kiln in the direct reduction process of iron ore contains a large amount of H2, and the utilization rate of H2 in the direct reduction of iron ore is not high, in order to improve the utilization rate of H2 in the rotary kiln of iron ore coal-based direct reduction, a method and device for improving the hydrogen reduction of the rotary kiln of iron ore coal-based direct reduction is invented. The process flow is as follows: (1) Iron ore and residual carbon are batched and mixed evenly in a weight ratio of 100:25-35, and then added into the rotary kiln from the feed end of the iron ore rotary kiln; (2) Under the rotation of the rotary kiln, the mixture continuously flows from the feed end to the discharge end during the tumbling and flow process, and exchanges heat with the high temperature flue gas flowing counterclockwise in the kiln, so that the temperature of the mixture continuously rises. (3) When the temperature of the mixture rises to 600℃, the iron ore begins to undergo a reduction reaction under the action of carbon in the residual carbon. As the temperature of the mixture rises, the reduction reaction rate of the iron ore accelerates. The metallurgical gas overflowing from the mixture is burned under the action of air blown in by the kiln back fan and heats the rotary kiln. (4) By controlling the reduction temperature of the iron ore to 900-1100℃ and the reduction time to 90-180min, the iron ore can be fully reduced. (5) The high-temperature reduced material obtained after the reduction of the iron ore is discharged from the iron ore rotary kiln and enters the oxygen-free cooling device for oxygen-free cooling. After being cooled to room temperature, the reduced material enters the residual carbon separation device to separate the reduced material into metallized material and residual carbon. The residual carbon is returned to the batching system of the iron ore rotary kiln for utilization, and the metallized material is used as a product. (6) The 600-700℃ high-temperature flue gas discharged from the feed end of the iron ore rotary kiln enters the waste heat boiler. Through indirect heat exchange with water, while producing high-temperature and high-pressure steam, the temperature of the flue gas can be reduced to 150-180℃. After cooling, the flue gas is then purged by a cyclone dust collector and a bag dust collector, and finally discharged after being pressurized by a smoke extractor. (7) A heating burner is installed at the discharge end of the rotary kiln. When the rotary kiln is in operation, heat preservation, production fluctuations are large, or the temperature is low during normal production, heat is supplied to the rotary kiln through the burner. (8) A baffle ring is installed inside the kiln body at the discharge end, inside the kiln body at 1 / 3 of the total length of the rotary kiln from the discharge end, and inside the kiln body at 2 / 3 of the total length of the rotary kiln from the discharge end, close to the inner wall. As the material moves from the feed end to the discharge end within the kiln, the baffle ring slows down the material flow, increases the rotary kiln filling rate, and expands the contact area between the material and the kiln wall. Simultaneously, by increasing the rotary kiln speed, the high-volatile coal falling onto the feed surface can be quickly rolled into the interior of the material layer, thereby improving the utilization rate of hydrogen reduction in iron ore.

[0009] The present invention features a baffle ring inside the rotary kiln with a height of 12-15% of the inner diameter of the rotary kiln and a bottom width of 20-30% of the inner diameter of the rotary kiln. The outer contour of the baffle ring's cross-section is similar to a parabola. The baffle ring is cast from high-temperature refractory material and is integrally constructed with the refractory material of the kiln body.

[0010] By setting a baffle ring inside the rotary kiln, this invention controls the material filling rate inside the rotary kiln to 20-25%, which can increase the material layer thickness inside the rotary kiln by 40-50%. The thicker material layer can maintain a higher reducing atmosphere inside the high-temperature material. At the same time, the reducing gas generated by the bottom material during the reduction process needs to pass through the thicker material layer as it flows from bottom to top, which increases the contact area between the reducing gas and the iron ore, thereby improving the H2 utilization efficiency in the iron ore reduction process.

[0011] The present invention improves the rotary kiln filling rate, thereby increasing the amount of reducing gas overflowing from the inside of the material layer to the surface of the material. The larger amount of reducing gas on the surface of the material isolates the oxidizing atmosphere in the kiln space from the contact between the reducing material and the reducing material, reducing the secondary oxidation of the reducing material in the rotary kiln and improving the reduction quality of iron ore.

[0012] This invention involves eccentrically displacing the granular coal spray gun mounted on the kiln head hood at the discharge end of a rotary kiln from its central position. The displacement direction is closer to the center of the crescent-shaped material surface, and the movement position is 10-20% of the rotary kiln diameter. By moving the granular coal spray gun towards the material surface, most of the granular coal sprayed by the spray gun falls onto the material surface at the bottom of the rotary kiln. Furthermore, the rotation of the rotary kiln causes even more granular coal to be turned into the material layer.

[0013] By installing a baffle ring inside the rotary kiln, the rotational speed of the rotary kiln can be increased to 0.6-0.8 r / min. With the increased rotational speed, the material flow rate inside the kiln is accelerated, allowing the granular coal injected into the bottom material surface of the rotary kiln by the granular coal spray gun to tumble into the material layer in a shorter time. This reduces the residence time of the granular coal in the high-temperature space inside the kiln, reduces the amount of volatile matter released from the granular coal on the surface of the material layer, and allows more volatile matter from the granular coal to enter the interior of the material, thereby improving the hydrogen utilization rate in the iron ore reduction process.

[0014] To improve the temperature uniformity of iron ore in the reduction section of the rotary kiln and increase the H2 reduction efficiency, the original premixed burners in the rotary kiln were replaced with sleeve burners. The sleeve burners spray fuel and air from their respective channels. The pressure of the combustion air is 16-20 kPa. The fuel and air undergo diffuse combustion while flowing and mixing and preheating in the rotary kiln space. This can increase the flame length of the burner to 15-20 m. The longer flame length reduces the heat load in the burner combustion zone and makes the temperature in the high-temperature zone of the rotary kiln more uniform.

[0015] To reduce the high-temperature heat load in the blowing area of ​​the rotary kiln back fan, this invention increases the air pressure blown into the kiln by the kiln back fan to 6-8 kPa. The higher air pressure allows the air jet to act within a range of 6-7 m inside the kiln, thereby greatly extending the blowing area of ​​the kiln back fan.

[0016] The beneficial effects of the present invention are: (1) Three baffle rings are set at different positions inside the rotary kiln. As the material moves from the feed end to the discharge end, the baffle rings slow down the flow rate of the material, increase the filling rate of the rotary kiln, increase the contact area between the material and the kiln wall, and improve the H2 reduction effect of iron ore.

[0017] (2) By increasing the rotation speed of the rotary kiln, the high volatile coal falling into the material surface in the rotary kiln can be turned into the material layer as quickly as possible, which increases the amount of volatile coal released by thermal release in the material layer and increases the hydrogen reduction rate of iron ore.

[0018] (3) The present invention moves the coal granules spray gun on the kiln head cover at the discharge end of the rotary kiln eccentrically from the center position, so that most of the coal granules sprayed by the coal granules spray gun fall into the material surface at the bottom of the rotary kiln, and the coal granules are turned into the material layer in time by the rapid rotation of the rotary kiln.

[0019] (4) The present invention replaces the original premixed burner of the rotary kiln with a sleeve burner. The fuel and air are diffused and burned in the rotary kiln space, which can increase the flame length of the burner to 15-20m. The longer flame length reduces the heat load of the burner combustion area, makes the temperature of the high temperature zone in the rotary kiln more uniform, and improves the hydrogen reduction effect of iron ore. Attached Figure Description

[0020] Figure 1 A schematic diagram of an existing rotary kiln for direct reduction of iron ore; Figure 2 A schematic diagram of the distribution of roasted materials on the cross-section of a direct reduction iron ore rotary gyratory; Figure 3 Equipment connection diagram for improving hydrogen reduction in rotary kilns for direct reduction of iron ore and coal-based materials; Figure 4 To improve the connection diagram of the rotary kiln hydrogen reduction equipment for direct reduction of iron ore and coal, see section A; Figure 5 This is a process flow diagram for improving the hydrogen reduction method of rotary kiln for direct reduction of iron ore based on coal. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments: A method for improving hydrogen reduction in a rotary kiln for direct reduction of iron ore based on coal, involving equipment including: a rotary kiln body, a kiln back fan, a kiln tail feeding end, a kiln head discharging end, a feed end, a discharge end, a kiln head burner, refractory materials, a granular coal spray gun, a granular coal feeding port, a Roots blower, a waste heat boiler, a cyclone dust collector, a bag filter dust collector, a smoke extractor, an oxygen-free cooling device, a residual carbon separation device, an iron ore reduction furnace, and a baffle ring; involving materials including: roasted materials, high-temperature and high-pressure steam, water, high-volatile coal, iron ore, residual carbon, and high-temperature reducing materials; the implementation method of this invention is as follows: (1) Iron ore and residual carbon are batched and mixed evenly in a weight ratio of 100:32 and then added into the rotary kiln from the feed end of the iron ore rotary kiln. (2) Under the rotation of the rotary kiln, the mixture flows continuously from the feed end to the discharge end during the tumbling and flow process, and exchanges heat with the high-temperature flue gas flowing in the countercurrent in the kiln, causing the temperature of the mixture to rise continuously.

[0022] (3) When the temperature of the mixture rises to 600℃, the iron ore begins to undergo a reduction reaction under the action of carbon in the residual carbon. As the temperature of the mixture rises, the reduction reaction rate of the iron ore accelerates. The metallurgical gas overflowing from the mixture is burned under the action of air blown in by the kiln back fan and heats the rotary kiln. (4) By controlling the reduction temperature of iron ore to 1050℃ and the reduction time to 160min, the iron ore can be fully reduced.

[0023] (5) After the high-temperature reduced material obtained after the reduction of iron ore is discharged from the iron ore rotary kiln, it enters the oxygen-free cooling device for oxygen-free cooling. After being cooled to room temperature, the reduced material enters the residual carbon separation device to separate the reduced material into metallized material and residual carbon. The residual carbon is returned to the batching system of the iron ore rotary kiln for use, and the metallized material is used as a product.

[0024] (6) The 600-700℃ high-temperature flue gas discharged from the feed end of the iron ore rotary kiln enters the waste heat boiler. Through indirect heat exchange with water, while producing high-temperature and high-pressure steam, the temperature of the flue gas can be reduced to 150-180℃. After the flue gas is cooled, it is then removed by a cyclone dust collector and a bag dust collector, and finally discharged after being pressurized by a smoke extractor.

[0025] (7) A baffle ring is installed close to the inner wall of the kiln body at the discharge end, at 1 / 3 of the total length of the kiln body from the discharge end, and at 2 / 3 of the total length of the kiln body from the discharge end. During the process of material moving from the feed end to the discharge end in the kiln, the baffle ring can slow down the material flow speed, increase the filling rate of the rotary kiln, and increase the contact area between the material and the kiln wall. At the same time, by increasing the rotation speed of the rotary kiln, the high volatile coal falling on the material surface can be turned into the material layer as quickly as possible.

[0026] (8) On the kiln head cover at the discharge end of the rotary kiln, the granular coal spray gun is eccentrically displaced. The displacement direction is close to the center of the crescent-shaped material surface, and the moving position is 15% of the diameter of the rotary kiln.

[0027] (9) A sleeve-type burner is provided at the discharge end of the rotary kiln. When the rotary kiln is in the process of opening, heat preservation, production fluctuation, or when the temperature is low during normal production, heat is supplied to the rotary kiln through the burner.

Claims

1. A method for improving hydrogen reduction in a rotary kiln for direct reduction of iron ore based on coal, comprising the following equipment: rotary kiln body, kiln back fan, kiln tail feeding end, kiln head discharging end, feeding end, discharging end, kiln head burner, refractory material, granular coal spray gun, granular coal feeding port, Roots blower, waste heat boiler, cyclone dust collector, bag filter dust collector, smoke extractor, oxygen-free cooling device, residual carbon separation device, iron ore reduction furnace, and baffle ring; and the following materials: roasted materials, high-temperature and high-pressure steam, water, high-volatile coal, iron ore, residual carbon, and high-temperature reducing materials; Its features are: By setting three baffle rings at different positions inside the rotary kiln and eccentrically displacing the granular coal spray gun on the kiln head cover at the discharge end of the rotary kiln, and selecting a sleeve-type burner for the rotary kiln burner, the contact area between the material and the kiln wall can be increased while reducing the material drop difference inside the rotary kiln, thereby improving the rotational speed, material filling rate, and temperature uniformity inside the kiln.

2. The method for improving hydrogen reduction in a rotary kiln for direct reduction of iron ore based on coal, as described in claim 1, is characterized in that: The H2 reduction efficiency of a rotary kiln for direct reduction of iron ore and coal can be improved using the following methods: (1) Iron ore and residual carbon are batched and mixed evenly in a weight ratio of 100:25-35, and then added into the rotary kiln from the feed end of the iron ore rotary kiln. (2) Under the rotation of the rotary kiln, the mixture flows continuously from the feed end to the discharge end during the tumbling and flow process, and exchanges heat with the high-temperature flue gas flowing in the countercurrent in the kiln, causing the temperature of the mixture to rise continuously. (3) When the temperature of the mixture rises to 600℃, the iron ore begins to undergo a reduction reaction under the action of carbon in the residual carbon. As the temperature of the mixture rises, the reduction reaction rate of the iron ore accelerates. The metallurgical gas overflowing from the mixture is burned under the action of air blown in by the kiln back fan and heats the rotary kiln. (4) By controlling the reduction temperature of iron ore to 900-1100℃ and the reduction time to 90-180min, the iron ore can be fully reduced; (5) After the high-temperature reducing material obtained after the reduction of iron ore is discharged from the iron ore rotary kiln, it enters the oxygen-free cooling device for oxygen-free cooling. After being cooled to room temperature, the reducing material enters the residual carbon separation device to separate the reducing material into metallized material and residual carbon. The residual carbon is returned to the batching system of the iron ore rotary kiln for use, and the metallized material is used as a product. (6) The 600-700℃ high-temperature flue gas discharged from the feed end of the iron ore rotary kiln enters the waste heat boiler. Through indirect heat exchange with water, while producing high-temperature and high-pressure steam, the temperature of the flue gas can be reduced to 150-180℃. After the flue gas is cooled, it is then removed by a cyclone dust collector and a bag dust collector, and finally discharged after being pressurized by a smoke extractor. (7) A baffle ring is set in close contact with the inner wall of the kiln body at the discharge end, at the kiln body at 1 / 3 of the total length of the kiln at the discharge end, and at the kiln body at 2 / 3 of the total length of the kiln at the discharge end. During the process of the material in the kiln moving from the feed end to the discharge end, the baffle ring can slow down the flow speed of the material, increase the filling rate of the rotary kiln, and increase the contact area between the material and the kiln wall. At the same time, by increasing the rotation speed of the rotary kiln, the high volatile coal falling into the material surface can be turned into the material layer as quickly as possible. (8) On the kiln head cover at the discharge end of the rotary kiln, the granular coal spray gun is eccentrically moved from the center position, with the displacement direction being closer to the center position of the crescent-shaped material surface, and the moving position being 10-20% of the diameter of the rotary kiln; (9) A sleeve-type burner is provided at the discharge end of the rotary kiln. When the rotary kiln is in the process of opening, heat preservation, production fluctuation, or when the temperature is low during normal production, heat is supplied to the rotary kiln through the burner.

3. A method for improving hydrogen reduction in a rotary kiln for direct reduction of iron ore based on coal, as described in claim 1 or 2, characterized in that: The height of the baffle ring is 12-15% of the inner diameter of the rotary kiln, and the bottom width is 20-30% of the inner diameter of the rotary kiln. The outer contour of the baffle ring cross section is similar to a parabola. The baffle ring is cast from high-temperature refractory material and is constructed integrally with the refractory material of the kiln body.

4. A method for improving hydrogen reduction in a rotary kiln for direct reduction of iron ore based on coal, as described in claim 1 or 2, characterized in that: The material filling rate inside the rotary kiln is 20-25%, and the rotation speed of the rotary kiln is 0.6-0.8 r / min.

5. A method for improving hydrogen reduction in a rotary kiln for direct reduction of iron ore based on coal, as described in claim 1 or 2, characterized in that: The granular coal spray gun on the kiln head cover at the discharge end of the rotary kiln undergoes eccentric displacement, with the displacement direction being closer to the center of the crescent-shaped material surface, and the moving position being 10-20% of the rotary kiln diameter.

6. A method for improving hydrogen reduction in a rotary kiln for direct reduction of iron ore based on coal, as described in claim 1 or 2, characterized in that: The rotary kiln burner adopts a sleeve-type burner, and the pressure of the combustion air is 16-20 kPa. The fuel and air undergo diffuse combustion in the rotary kiln space, and the flame length of the burner is 15-20 m.

7. A method for improving hydrogen reduction in a rotary kiln for direct reduction of iron ore based on coal, as described in claim 1 or 2, characterized in that: The air pressure blown into the rotary kiln by the back fan is 6-8 kPa, and the air jet blown out by the fan acts within a range of 6-7m inside the kiln.

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