A system and method for extracting iron from red mud by pyrolysis of biomass

Abstract

The present invention discloses a system and method for extracting iron from red mud by pyrolysis reduction of biomass. Biomass pyrolysis gas is used as a reducing agent, and iron oxide in the red mud is reduced by low-temperature fluidization in a solid-state manner. Ferromagnetic material is then magnetically separated to obtain an iron recovery rate of ≥80%. A variable-diameter fluidized bed with a built-in bottom-extending multi-layer stirring device is used to dry, break up, and transport the red mud. Biomass combustion provides the heat required by the system, and carbon dioxide emissions are zero. The multi-layer fluidized bed allows biomass pyrolysis and red mud reduction to occur in different temperature ranges, facilitating optimization and control. The biomass pyrolysis products are directly used as fuel, and the reduced material is cooled with nitrogen to recover heat for biomass pyrolysis. The reduced tail gas is used to preheat the raw materials, resulting in a high system energy utilization rate. The process and equipment of the present invention are simple, applicable to a wide range of raw materials, and environmentally friendly. It can achieve large-scale, clean, and efficient iron extraction from red mud, with excellent economic and social benefits.

Description

Technical Field

[0001] The present invention belongs to the field of nonferrous metallurgy environmental protection, and in particular relates to a system and method for extracting iron by reducing red mud through biomass pyrolysis. Background Art

[0002] Red mud is an industrial solid waste generated during the alkaline leaching of bauxite to produce alumina. It is characterized by high alkalinity, high moisture content, high viscosity, and radioactivity. Existing disposal methods primarily rely on dry damming and stockpiling, which not only consumes significant land resources but also poses significant safety hazards and harm to surrounding soil and water resources over long periods of storage. Red mud contains a high iron content and can be used as a secondary resource for iron recovery. Separating and recovering the iron in red mud is a key approach to its resource utilization and reduction.

[0003] Chinese patent application CN1300348A discloses a method for recovering iron from red mud. Red mud with a moisture content of 10-20% is mixed with coal and sponge iron powder, extruded, and dried. The mixture is then mixed with industrial coal and fed into a rotary kiln for reduction roasting at 1100-1200°C. The roasted product is cooled and magnetically separated to produce sponge iron powder. Chinese patent application CN102839249A discloses a method for producing iron ore concentrate by direct reduction of high-iron red mud in a rotary hearth furnace. The red mud is dried in a chain grate using preheated air to a moisture content of less than 12%. The mud is then mixed with coke or coal powder and pressed into green pellets. The green pellets are dried, screened, and refined to 8-12mm in size before being fed into a rotary kiln for reduction roasting at 1000-1400°C. The roasted product is cooled, crushed, and magnetically separated to produce iron ore concentrate with an iron grade exceeding 60%. Chinese patent application CN103805726A discloses a method for comprehensively utilizing high-iron red mud using a rotary hearth furnace pelletized iron process. The method involves mixing high-iron red mud, coal powder or coke powder, and a certain amount of additives, forming pellets, and then reducing and roasting them in a rotary hearth furnace at 1350-1450°C. The roasted product is cooled, crushed, and magnetically separated to produce pelletized iron. Chinese patent application CN107254583A discloses a method for comprehensively utilizing red mud based on direct reduction roasting and magnetic separation in a rotary kiln. The method uses red mud as the raw material, coal powder as the reducing agent, titanomagnetite as an additive, and starch and bentonite as binders to form pellets, dry them, and then directly reduce and roast them in a rotary kiln at 1280-1300°C. The roasted product is cooled and magnetically separated to produce direct reduced iron with an iron grade exceeding 92%. All of the above technical solutions achieve the recovery of iron resources in red mud through reduction roasting, but all use coal powder or coke powder as the reducing agent. The roasting process emits large amounts of carbon dioxide and introduces other impurities into the roasted products. In addition, the reduction roasting temperature of each technical solution is above 1000°C, which results in high energy consumption.

[0004] Biomass is an important renewable energy source, derived directly or indirectly from plant photosynthesis, and is environmentally friendly, low-cost, and carbon neutral. Chinese patent application CN107311479A discloses a method for reducing iron oxide in red mud using biomass to simultaneously increase the activity of inorganic components. The method involves uniformly mixing biomass with high-iron Bayer red mud and roasting it at 400-750°C. The roasted product undergoes magnetic separation to yield iron concentrate and inorganic materials with high gelling activity. Compared to pulverized coal reduction, biomass reduction can reduce the reduction temperature by 200°C, saving energy. However, this approach remains at the small-scale laboratory fixed-bed research stage, with no viable production process system or method. Furthermore, the method involves coupling biomass pyrolysis and iron oxide reduction at the same temperature, which hinders optimal reaction control. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the present invention aims to provide a system and method for extracting iron by reducing red mud through biomass pyrolysis.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A system for extracting iron from red mud by pyrolysis reduction of biomass includes a red mud silo, a red mud feeder, a variable-diameter fluidized bed, a bottom-extending multi-layer stirring device, a stirring motor, a first-stage cyclone separator I, a standpipe, a discharge valve I, a second-stage cyclone separator I, a first-stage cyclone preheater, a second-stage cyclone preheater, a first-stage cyclone separator II, a fuel biomass silo, a fuel biomass feeder, a combustion chamber, a multi-layer fluidized bed, a discharge valve II, a pyrolysis biomass silo, a pyrolysis biomass feeder, a first-stage cyclone separator III, a second-stage cyclone separator II, a cyclone separator discharge valve I, a fluidized bed cooler, a first-stage cyclone separator VI, a second-stage cyclone separator III, a cyclone separator discharge valve II, a discharge valve III, and a magnetic separation system.

[0008] The red mud silo, red mud feeder, and variable diameter fluidized bed are connected in sequence along the direction of material flow; the air inlet, air outlet, and material outlet of the variable diameter fluidized bed are respectively connected to the air outlet of the first-stage cyclone separator II, the air inlet of the first-stage cyclone separator I, and the material inlet at the upper end of the standpipe;

[0009] The air inlet, air outlet and material outlet of the secondary cyclone separator I are respectively connected to the air outlet of the primary cyclone separator I, the tail gas treatment system and the material inlet of the primary cyclone preheater;

[0010] The feed port, discharge port and air inlet of the discharge valve I are respectively connected to the discharge port at the lower end of the riser, the feed port of the first-stage cyclone preheater and the air pipeline.

[0011] The discharge port and air outlet of the first-stage cyclone preheater are respectively connected to the air outlet of the combustion chamber and the air inlet of the first-stage cyclone separator II; the air inlet of the first-stage cyclone preheater is connected to the air outlet of the second-stage cyclone preheater, and the air inlet of the second-stage cyclone preheater is connected to the air outlet of the combustion chamber; the discharge port of the fuel biomass silo is connected to the feed port of the fuel biomass feeder, and the discharge port of the fuel biomass feeder is connected to the feed port of the combustion chamber;

[0012] The middle part of the multi-layer fluidized bed is divided into a tertiary biomass layer, a secondary red mud particle layer and a primary red mud particle layer from bottom to top, and gas can pass between the tertiary biomass layer, the secondary red mud particle layer and the primary red mud particle layer; the discharge port and the feed port of the tertiary biomass layer are respectively connected to the feed port of the fuel biomass feeder and the discharge port of the pyrolysis biomass feeder, the discharge port of the secondary red mud particle layer is connected to the feed port of the discharge valve II, the discharge port of the primary cyclone separator II and the discharge port of the secondary cyclone preheater are both connected to the feed port of the primary red mud particle layer; an overflow pipe is also provided in the multi-layer fluidized bed, the feed port at the upper end of the overflow pipe is communicated with the primary red mud particle layer, and the secondary red mud particle layer is communicated with the discharge port at the lower end of the overflow pipe; the feed port of the pyrolysis biomass feeder is connected to the discharge port of the pyrolysis biomass silo;

[0013] The air inlet and air outlet of the multi-layer fluidized bed are respectively connected to the air outlet of the secondary cyclone separator III and the air inlet of the primary cyclone separator III; the air outlet of the primary cyclone separator III is connected to the air inlet of the secondary cyclone separator II, the discharge port of the primary cyclone separator III and the discharge port of the secondary cyclone separator II are both connected to the feed port of the cyclone separator discharge I, and the air outlet of the secondary cyclone separator II is connected to the air inlet of the secondary cyclone preheater; the discharge port of the discharge valve II and the discharge port of the cyclone separator discharge I are both connected to the feed port of the fluidized bed cooler, the air inlet of the discharge valve II is connected to the nitrogen pipeline, and the air inlet of the cyclone separator discharge I is connected to the nitrogen pipeline;

[0014] The air inlet of the fluidized bed cooler is connected to the nitrogen pipeline, the air outlet of the fluidized bed cooler is connected to the air inlet of the first-level cyclone separator VI, the air outlet of the first-level cyclone separator VI is connected to the air inlet of the second-level cyclone separator III, the discharge port of the first-level cyclone separator VI is connected to the feed port of the cyclone separator discharge valve II, the discharge port of the second-level cyclone separator III is connected to the feed port of the cyclone separator discharge valve II, the discharge port of the fluidized bed cooler is connected to the feed port of the discharge valve III, the air inlet of the discharge valve III is connected to the nitrogen pipeline, and the air inlet of the cyclone separator discharge valve II is connected to the nitrogen pipeline;

[0015] The discharge port of the cyclone separator discharge valve II is connected to the inlet of the magnetic separation system, and the air inlet of the discharge valve III is connected to the nitrogen pipeline.

[0016] Furthermore, in the above system, the diameter of the lower part of the variable diameter fluidized bed is larger than the diameter of the upper part, and the lower part of the variable diameter fluidized bed is provided with a bottom-extending multi-layer stirring device, and the bottom-extending multi-layer stirring device is driven by a stirring motor.

[0017] Furthermore, in the above system, the stirring center axis of the bottom-extending multi-layer stirring device extends from the bottom center of the variable diameter fluidized bed, and the stirring paddles of the bottom-extending multi-layer stirring device are multi-layer stirring paddles, the number of layers of the multi-layer stirring paddles is more than 3 layers, and the stirring paddles of each layer are evenly distributed along the axial direction of the stirring shaft.

[0018] The present invention also provides a working method of the above-mentioned system for extracting iron by reducing red mud through biomass pyrolysis, the specific process of which is as follows:

[0019] The red mud is stored in a red mud silo and enters a variable diameter fluidized bed through a red mud feeder. In the variable diameter fluidized bed, the red mud material is dried by the residual heat of the flue gas from the primary cyclone separator II and is dispersed by the stirring and shearing action of a bottom-extending multi-layer stirring device with more than three layers of stirring paddles. The dried and dispersed red mud material enters the primary cyclone separator I for gas-solid separation. The separated red mud material passes through a riser and a discharge valve I in sequence and enters the primary cyclone preheater. The separated tail gas enters the tail gas treatment system and is discharged after being treated to meet the standards.

[0020] After primary preheating in the primary cyclone preheater, the red mud material is discharged from the discharge port of the primary cyclone preheater and enters the secondary cyclone preheater along with the flue gas output from the combustion chamber for secondary preheating. The heat required for preheating in the secondary cyclone preheater is provided by the flue gas output from the combustion chamber. After heat exchange in the secondary cyclone preheater, the flue gas enters the primary cyclone preheater, and the residual heat in the flue gas continues to provide the required heat for preheating in the primary cyclone preheater. The flue gas after heat exchange in the primary cyclone preheater enters the primary cyclone separator II. After gas-solid separation, the flue gas obtained enters the variable diameter fluidized bed, causing the red mud material in the variable diameter fluidized bed to be rapidly fluidized under the action of the flue gas and dried by the residual heat of the flue gas.

[0021] The red mud material separated by the primary cyclone separator II and the red mud material preheated by the secondary cyclone preheater both enter the primary red mud particle layer of the multi-layer fluidized bed. When the height of the red mud material in the primary red mud particle layer reaches the height of the feed port of the overflow pipe, it enters the secondary red mud particle layer through the overflow pipe.

[0022] The pyrolysis biomass enters the tertiary biomass layer from the pyrolysis biomass silo through the pyrolysis biomass feeder, and is roasted to complete pyrolysis under the action of hot nitrogen from the secondary cyclone separator III. The pyrolysis biomass product enters the combustion chamber through the fuel biomass feeder; the fuel biomass enters the combustion chamber from the fuel biomass silo through the fuel biomass feeder, and air enters the combustion chamber from the air pipeline. The fuel biomass and the pyrolysis biomass product are burned in the air of the combustion chamber to form high-temperature flue gas, which is sent to the secondary cyclone preheater; the pyrolysis gas from the tertiary biomass layer passes upward through the secondary red mud particle layer and the primary red mud particle layer in sequence, and the red mud materials in the secondary red mud particle layer and the primary red mud particle layer are reduced and roasted, and low-temperature fluidized solid-state reduction is completed under the action of the pyrolysis gas. The reduced tail gas passes through the primary cyclone separator III and the secondary cyclone separator II in sequence to separate the solid and then enters the secondary cyclone preheater;

[0023] The material after low-temperature fluidized solid-state reduction enters the fluidized bed cooler through the discharge valve II. Nitrogen enters the fluidized bed cooler through the nitrogen pipeline and exchanges heat with the material in the fluidized bed cooler. The material after heat exchange and cooling enters the magnetic separation system through the discharge valve III. Ferromagnetic material and aluminum-containing slag are obtained through magnetic separation.

[0024] The hot nitrogen after heat exchange passes through the gas outlet of the fluidized bed cooler in sequence through the first-stage cyclone separator VI and the second-stage cyclone separator III for gas-solid separation and then enters the third-stage biomass layer of the multi-layer fluidized bed to provide heat for the pyrolysis of the pyrolysis biomass.

[0025] Furthermore, in the above method, the materials in the primary red mud particle layer, the secondary red mud particle layer and the tertiary biomass layer of the multi-layer fluidized bed are in bubbling fluidization or turbulent fluidization.

[0026] Furthermore, in the above method, the solid mass content of the red mud is 30%-80%.

[0027] Furthermore, in the above method, the water content of the fuel biomass and the pyrolysis biomass is ≤5%, and the fuel biomass and the pyrolysis biomass are both a combination of one or more of lignin, sawdust, rice husks, and straw.

[0028] Furthermore, in the above method, the rotation speed of the bottom-extending multi-layer stirring device is 100-2000 rpm.

[0029] Furthermore, in the above method, the reduction roasting temperature of the primary red mud particle layer and the secondary red mud particle layer of the multi-layer fluidized bed is 400-500°C, and the reduction time is 0.5-1h; the pyrolysis temperature of the tertiary biomass layer of the multi-layer fluidized bed is 200-400°C, and the reduction time is 0.5-1h.

[0030] Furthermore, in the above method, the recovery rate of iron is ≥80%.

[0031] The beneficial effects of the present invention are:

[0032] 1. This invention uses biomass pyrolysis gas as the fluidized reducing gas to reduce iron oxide in red mud at a relatively low temperature, eliminating the mixing, pelletizing, and pellet drying steps, resulting in a simple process flow. The fluidized bed provides good mixing and contact between the gas and solid phases, rapid mass and heat transfer, and high reduction efficiency.

[0033] 2. The present invention uses a multi-layer fluidized bed to decouple biomass pyrolysis and iron oxide reduction in red mud, allowing the two to proceed at different temperatures, which is beneficial to system optimization and regulation and reduces energy consumption.

[0034] 3. This invention utilizes a high-speed, variable-diameter fluidized bed with a built-in, bottom-extending, multi-layered agitator to efficiently dry, dehydrate, break up, and transport red mud. This high-speed, bottom-extending, multi-layered agitator efficiently shears and disperses high-moisture, high-viscosity red mud, enhancing mass and heat transfer, strengthening the drying and dehydration process, and effectively breaking up the dried material. The equipment is simple and easy to operate.

[0035] 4. In the present invention, the solid phase processing processes of red mud drying, breaking up, conveying and reduction of iron oxide in red mud all adopt a gas-solid fluidized bed, which is convenient for continuous operation and large-scale treatment.

[0036] In summary, the present invention provides an advanced, complete and controllable system and method for extracting iron from red mud by pyrolysis of biomass, which can realize large-scale, efficient and clean utilization of iron resources in red mud. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic diagram of the system structure in Example 1 of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be further described below in conjunction with the accompanying drawings. It should be noted that this embodiment is based on the technical solution and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to this embodiment.

[0039] Example 1

[0040] This embodiment provides a system for extracting iron from red mud by pyrolysis of biomass. Figure 1As shown, it includes a red mud silo 1, a red mud feeder 2, a variable diameter fluidized bed 3, a bottom-extending multi-layer stirring device 31, a stirring motor 32, a primary cyclone separator I4, a vertical pipe 5, a discharge valve I6, a secondary cyclone separator I7, a primary cyclone preheater 8, a secondary cyclone preheater 9, a primary cyclone separator II 10, a fuel biomass silo 11, a fuel biomass feeder 12, a combustion chamber 13, a multi-layer fluidized bed 14, a primary red mud particle layer 141, a secondary red mud particle layer 142, a tertiary biomass layer 143, an overflow pipe 144, a discharge valve II 15, a pyrolysis biomass silo 16, a pyrolysis biomass feeder 17, a primary cyclone separator III 18, a secondary cyclone separator II 19, and a cyclone separator discharge valve I 20, fluidized bed cooler 21, primary cyclone separator VI 22, secondary cyclone separator III 23, cyclone separator discharge valve II 24, discharge valve III 25 and magnetic separation system 26;

[0041] The red mud silo 1, the red mud feeder 2, and the variable diameter fluidized bed 3 are connected in sequence along the direction of material flow; the air inlet, air outlet, and material outlet of the variable diameter fluidized bed 3 are respectively connected to the air outlet of the first-stage cyclone separator II 10, the air inlet of the first-stage cyclone separator I 4, and the material inlet at the upper end of the standpipe 5; the air inlet, air outlet, and material outlet of the second-stage cyclone separator I 7 are respectively connected to the air outlet of the first-stage cyclone separator I 4, the tail gas treatment system, and the material inlet of the first-stage cyclone preheater 8;

[0042] The feed port, discharge port and air inlet of the discharge valve I 6 are respectively connected to the discharge port at the lower end of the riser 5, the feed port of the first-stage cyclone preheater 8 and the air pipeline.

[0043] The discharge port and air outlet of the first-stage cyclone preheater 8 are respectively connected to the air outlet of the combustion chamber 13 and the air inlet of the first-stage cyclone separator II 10; the air inlet of the first-stage cyclone preheater 8 is connected to the air outlet of the second-stage cyclone preheater 9, and the air inlet of the second-stage cyclone preheater 9 is connected to the air outlet of the combustion chamber 13; the discharge port of the fuel biomass silo 11 is connected to the feed port of the fuel biomass feeder 12, and the discharge port of the fuel biomass feeder 12 is connected to the feed port of the combustion chamber 13;

[0044] The middle part of the multi-layer fluidized bed 14 is divided into a tertiary biomass layer 143, a secondary red mud particle layer 142 and a primary red mud particle layer 141 from bottom to top, and gas can pass between the tertiary biomass layer 143, the secondary red mud particle layer 142 and the primary red mud particle layer 141; the discharge port and the feed port of the tertiary biomass layer 143 are respectively connected to the feed port of the fuel biomass feeder 12 and the discharge port of the pyrolysis biomass feeder 17, the discharge port of the secondary red mud particle layer 142 is connected to the feed port of the discharge valve II 15, and the primary cyclone separator II The discharge port of 10 and the discharge port of the secondary cyclone preheater 9 are both connected to the feed port of the primary red mud particle layer 141; an overflow pipe 144 is further provided in the multi-layer fluidized bed 14, the feed port at the upper end of the overflow pipe 144 is communicated with the primary red mud particle layer 141, and the secondary red mud particle layer 142 is communicated with the discharge port at the lower end of the overflow pipe 144; the feed port of the pyrolysis biomass feeder 17 is connected to the discharge port of the pyrolysis biomass silo 16;

[0045] The air inlet and outlet of the multi-layer fluidized bed 14 are respectively connected to the air outlet of the secondary cyclone separator III 23 and the air inlet of the primary cyclone separator III 18; the air outlet of the primary cyclone separator III 18 is connected to the air inlet of the secondary cyclone separator II 19, the discharge port of the primary cyclone separator III 18 and the discharge port of the secondary cyclone separator II 19 are both connected to the feed port of the cyclone separator discharge valve I 20, and the air outlet of the secondary cyclone separator II 19 is connected to the air inlet of the secondary cyclone preheater 9; the discharge port of the discharge valve II 15 and the discharge port of the cyclone separator discharge valve I 20 are both connected to the feed port of the fluidized bed cooler 21, the air inlet of the discharge valve II 15 is connected to the nitrogen pipeline, and the air inlet of the cyclone separator discharge valve I 20 is connected to the nitrogen pipeline;

[0046] The air inlet of the fluidized bed cooler 21 is connected to the nitrogen pipeline, the air outlet of the fluidized bed cooler 21 is connected to the air inlet of the first-level cyclone separator VI22, the air outlet of the first-level cyclone separator VI22 is connected to the air inlet of the second-level cyclone separator III23, the discharge port of the first-level cyclone separator VI22 is connected to the feed port of the cyclone separator discharge valve II24, the discharge port of the second-level cyclone separator III23 is connected to the feed port of the cyclone separator discharge valve II24, the discharge port of the fluidized bed cooler 21 is connected to the feed port of the discharge valve III25, the air inlet of the discharge valve III25 is connected to the nitrogen pipeline, and the air inlet of the cyclone separator discharge valve II24 is connected to the nitrogen pipeline;

[0047] The discharge port of the cyclone separator discharge valve II 24 is connected to the inlet of the magnetic separation system 26, and the air inlet of the discharge valve III 25 is connected to the nitrogen pipeline.

[0048] In this embodiment, the diameter of the lower part of the variable diameter fluidized bed 3 is larger than the diameter of the upper part. The lower part of the variable diameter fluidized bed 3 is provided with a bottom-extending multi-layer stirring device 31, and the bottom-extending multi-layer stirring device 31 is driven by a stirring motor 32.

[0049] In this embodiment, the stirring center axis of the bottom-extending multi-layer stirring device 31 extends from the bottom center of the variable diameter fluidized bed 3, and the stirring paddles of the bottom-extending multi-layer stirring device 31 are multi-layer stirring paddles. The number of layers of the multi-layer stirring paddles is more than 3 layers, and the stirring paddles of each layer are evenly distributed along the axial direction of the stirring shaft.

[0050] Example 2

[0051] This embodiment provides a method for operating the system for extracting iron from red mud by pyrolysis of biomass as described in Example 1:

[0052] Red mud with a solid content of 30% is stored in a red mud silo 1 and enters a variable diameter fluidized bed 3 through a red mud feeder 2. Within the variable diameter fluidized bed 3, the red mud material is dried by the waste heat of the flue gas from the primary cyclone separator II 10 and is dispersed by the high-speed stirring and shearing action of 2000 rpm in a bottom-extending multi-layer stirring device 31 with three layers of stirring paddles. The dried and dispersed red mud material enters the primary cyclone separator I 4 for gas-solid separation. The separated red mud material passes through a riser 5 and a discharge valve I 6 and enters a primary cyclone preheater 8. The separated exhaust gas enters an exhaust gas treatment system and is discharged after being treated to meet standards.

[0053] After primary preheating in the primary cyclone preheater 8, the red mud material is discharged from the discharge port of the primary cyclone preheater 8 and enters the secondary cyclone preheater 9 along with the flue gas output from the combustion chamber for secondary preheating. The heat required for preheating in the secondary cyclone preheater 9 is provided by the flue gas output from the combustion chamber 13. After heat exchange in the secondary cyclone preheater, the flue gas enters the primary cyclone preheater 8, where the residual heat in the flue gas continues to provide the required heat for preheating in the primary cyclone preheater 8. The flue gas after heat exchange in the primary cyclone preheater 8 enters the primary cyclone separator II 10. After gas-solid separation, the resulting flue gas enters the variable diameter fluidized bed 3, causing the red mud material in the variable diameter fluidized bed 3 to be rapidly fluidized by the flue gas and dried by the residual heat of the flue gas.

[0054] The red mud separated by the primary cyclone separator II 10 and the red mud preheated by the secondary cyclone preheater 9 both enter the primary red mud particle layer 141 of the multi-layer fluidized bed 14. When the red mud in the primary red mud particle layer 141 reaches the height of the feed port of the overflow pipe 144, the red mud enters the secondary red mud particle layer 142 through the overflow pipe 144.

[0055] The straw pyrolysis biomass with a moisture content of 5% enters the third-stage biomass layer 143 from the pyrolysis biomass silo 16 via the pyrolysis biomass feeder 17. Under the action of the hot nitrogen from the secondary cyclone separator III 23, it is roasted at 200°C for 1 hour to complete pyrolysis. The pyrolysis biomass product enters the combustion chamber 13 via the fuel biomass feeder 12. Sawdust fuel biomass with a moisture content of 3% enters the combustion chamber 13 from the fuel biomass silo 11 through the fuel biomass feeder 12. Air enters the combustion chamber 13 from the air pipeline. The fuel biomass and pyrolysis biomass products are burned in the air of the combustion chamber 13 to form high-temperature flue gas, which is then fed into the secondary cyclone preheater 9. The pyrolysis gas from the tertiary biomass layer passes upward through the secondary red mud particle layer 142 and the primary red mud particle layer 141. The red mud materials in the secondary red mud particle layer 142 and the primary red mud particle layer 141 are roasted at 400°C for 1 hour. Under the action of the pyrolysis gas, low-temperature fluidized solid-state reduction is completed. The reduced tail gas passes through the primary cyclone separator III 18 and the secondary cyclone separator II 19 in sequence to separate the solids and then enter the secondary cyclone preheater 9.

[0056] The material after low-temperature fluidized solid-state reduction enters the fluidized bed cooler 21 through the discharge valve II 15. Nitrogen enters the fluidized bed cooler 21 through the nitrogen pipeline and exchanges heat with the material in the fluidized bed cooler 21. The material after heat exchange and cooling enters the magnetic separation system 26 through the discharge valve III 25. Magnetic separation is performed to obtain ferromagnetic material and aluminum-containing slag. The iron recovery rate in the ferromagnetic material is 83%.

[0057] The hot nitrogen after heat exchange passes through the gas outlet of the fluidized bed cooler 21, passes through the first cyclone separator VI 22 and the second cyclone separator III 23 for gas-solid separation, and then enters the third biomass layer 143 of the multi-layer fluidized bed 14 to provide heat for the pyrolysis of the pyrolysis biomass.

[0058] In this embodiment, the materials in the primary red mud particle layer 141 , the secondary red mud particle layer 142 and the tertiary biomass layer 143 of the multi-layer fluidized bed 14 are in bubbling fluidization or turbulent fluidization.

[0059] Example 3

[0060] This example is essentially the same as Example 2, and the similarities are not described here. The differences are: the red mud solids content is 80%, the bottom-extending multi-layer stirring device 31 has five layers of stirring paddles, and the rotation speed is 100 rpm. The red mud is roasted at 500°C for 0.5 h in the primary and secondary red mud particle layers 141, 142 of the multi-layer fluidized bed 14. The fuel biomass is lignin fuel biomass with a moisture content of 2%, and the pyrolysis biomass is rice husk pyrolysis biomass with a moisture content of 3%. The rice husk pyrolysis biomass is roasted at 400°C for 0.5 h in the tertiary biomass layer 143. The material after low-temperature fluidized solid-state reduction is cooled and magnetically separated to obtain a ferromagnetic material with an iron recovery rate of 85%.

[0061] Example 4

[0062] This example is essentially the same as Example 2, and the similarities are not reiterated. The differences are: the red mud solids content is 50%, the bottom-extending multi-layer stirring device 31 has four layers of stirring paddles, and the rotation speed is 1000 rpm. The red mud is roasted at 450°C for 0.7 h in the primary red mud particle layer 141 and the secondary red mud particle layer 142 of the multi-layer fluidized bed 14. The fuel biomass is rice husk fuel biomass with a moisture content of 3%, and the pyrolysis biomass is straw pyrolysis biomass with a moisture content of 4%. The rice husk pyrolysis biomass is roasted at 300°C for 0.7 h in the tertiary biomass layer 143. The material after low-temperature fluidized solid-state reduction is cooled and magnetically separated to obtain a ferromagnetic material with an iron recovery rate of 87%.

[0063] In the above embodiments, all % without explanation are percentage by mass.

[0064] Those skilled in the art can make various corresponding changes and modifications based on the above technical solutions and concepts, and all of these changes and modifications should be included in the scope of protection of the claims of the present invention.

Claims

1. A system for extracting iron by reducing red mud using biomass pyrolysis, characterized in that: It includes a red mud silo, a red mud feeder, a variable diameter fluidized bed, a bottom-extending multi-layer stirring device, a stirring motor, a first-stage cyclone separator I, a riser, a discharge valve I, a second-stage cyclone separator I, a first-stage cyclone preheater, a second-stage cyclone preheater, a first-stage cyclone separator II, a fuel biomass silo, a fuel biomass feeder, a combustion chamber, a multi-layer fluidized bed, a discharge valve II, a pyrolysis biomass silo, a pyrolysis biomass feeder, a first-stage cyclone separator III, a second-stage cyclone separator II, a cyclone separator discharge valve I, a fluidized bed cooler, a first-stage cyclone separator VI, a second-stage cyclone separator III, a cyclone separator discharge valve II, a discharge valve III, and a magnetic separation system; The red mud silo, red mud feeder, and variable diameter fluidized bed are connected in sequence along the direction of material flow; the air inlet, air outlet, and material outlet of the variable diameter fluidized bed are respectively connected to the air outlet of the first-stage cyclone separator II, the air inlet of the first-stage cyclone separator I, and the material inlet at the upper end of the standpipe; The air inlet, air outlet and material outlet of the secondary cyclone separator I are respectively connected to the air outlet of the primary cyclone separator I, the tail gas treatment system and the material inlet of the primary cyclone preheater; The feed port, discharge port and air inlet of the discharge valve I are respectively connected to the discharge port at the lower end of the standpipe, the feed port of the first-stage cyclone preheater and the air pipeline; The discharge port and air outlet of the first-stage cyclone preheater are respectively connected to the air outlet of the combustion chamber and the air inlet of the first-stage cyclone separator II; the air inlet of the first-stage cyclone preheater is connected to the air outlet of the second-stage cyclone preheater, and the air inlet of the second-stage cyclone preheater is connected to the air outlet of the combustion chamber; the discharge port of the fuel biomass silo is connected to the feed port of the fuel biomass feeder, and the discharge port of the fuel biomass feeder is connected to the feed port of the combustion chamber; The middle part of the multi-layer fluidized bed is divided into a tertiary biomass layer, a secondary red mud particle layer and a primary red mud particle layer from bottom to top, and gas can pass between the tertiary biomass layer, the secondary red mud particle layer and the primary red mud particle layer; the discharge port and the feed port of the tertiary biomass layer are respectively connected to the feed port of the fuel biomass feeder and the discharge port of the pyrolysis biomass feeder, the discharge port of the secondary red mud particle layer is connected to the feed port of the discharge valve II, the discharge port of the primary cyclone separator II and the discharge port of the secondary cyclone preheater are both connected to the feed port of the primary red mud particle layer; an overflow pipe is also provided in the multi-layer fluidized bed, the feed port at the upper end of the overflow pipe is communicated with the primary red mud particle layer, and the secondary red mud particle layer is communicated with the discharge port at the lower end of the overflow pipe; the feed port of the pyrolysis biomass feeder is connected to the discharge port of the pyrolysis biomass silo; The air inlet and air outlet of the multi-layer fluidized bed are respectively connected to the air outlet of the secondary cyclone separator III and the air inlet of the primary cyclone separator III; the air outlet of the primary cyclone separator III is connected to the air inlet of the secondary cyclone separator II, the discharge port of the primary cyclone separator III and the discharge port of the secondary cyclone separator II are both connected to the feed port of the cyclone separator discharge I, and the air outlet of the secondary cyclone separator II is connected to the air inlet of the secondary cyclone preheater; the discharge port of the discharge valve II and the discharge port of the cyclone separator discharge I are both connected to the feed port of the fluidized bed cooler, the air inlet of the discharge valve II is connected to the nitrogen pipeline, and the air inlet of the cyclone separator discharge I is connected to the nitrogen pipeline; The air inlet of the fluidized bed cooler is connected to the nitrogen pipeline, the air outlet of the fluidized bed cooler is connected to the air inlet of the first-level cyclone separator VI, the air outlet of the first-level cyclone separator VI is connected to the air inlet of the second-level cyclone separator III, the discharge port of the first-level cyclone separator VI is connected to the feed port of the cyclone separator discharge valve II, the discharge port of the second-level cyclone separator III is connected to the feed port of the cyclone separator discharge valve II, the discharge port of the fluidized bed cooler is connected to the feed port of the discharge valve III, the air inlet of the discharge valve III is connected to the nitrogen pipeline, and the air inlet of the cyclone separator discharge valve II is connected to the nitrogen pipeline; The discharge port of the cyclone separator discharge valve II is connected to the inlet of the magnetic separation system, and the discharge port of the discharge valve III is connected to the inlet of the magnetic separation system.

2. The system according to claim 1, wherein: The diameter of the lower part of the variable diameter fluidized bed is greater than the diameter of the upper part. The lower part of the variable diameter fluidized bed is provided with a bottom-extending multi-layer stirring device, and the bottom-extending multi-layer stirring device is driven by a stirring motor.

3. The system according to claim 2, characterized in that The stirring center axis of the bottom-extending multi-layer stirring device extends from the bottom center of the variable diameter fluidized bed. The stirring paddles of the bottom-extending multi-layer stirring device are multi-layer stirring paddles. The number of layers of the multi-layer stirring paddles is more than 3 layers, and the stirring paddles of each layer are evenly distributed along the axial direction of the stirring shaft.

4. A method for operating a system for extracting iron from red mud by pyrolysis of biomass according to any one of claims 1 to 3, characterized in that: The specific process is: The red mud is stored in a red mud silo and enters a variable diameter fluidized bed through a red mud feeder. In the variable diameter fluidized bed, the red mud material is dried by the residual heat of the flue gas from the primary cyclone separator II and is dispersed by the stirring and shearing action of a bottom-extending multi-layer stirring device with more than three layers of stirring paddles. The dried and dispersed red mud material enters the primary cyclone separator I for gas-solid separation. The separated red mud material passes through a riser and a discharge valve I in sequence and enters the primary cyclone preheater. The separated tail gas enters the tail gas treatment system and is discharged after being treated to meet the standards. After primary preheating in the primary cyclone preheater, the red mud material is discharged from the discharge port of the primary cyclone preheater and enters the secondary cyclone preheater along with the flue gas output from the combustion chamber for secondary preheating. The heat required for preheating in the secondary cyclone preheater is provided by the flue gas output from the combustion chamber. After heat exchange in the secondary cyclone preheater, the flue gas enters the primary cyclone preheater, and the residual heat in the flue gas continues to provide the required heat for preheating in the primary cyclone preheater. The flue gas after heat exchange in the primary cyclone preheater enters the primary cyclone separator II. After gas-solid separation, the flue gas obtained enters the variable diameter fluidized bed, causing the red mud material in the variable diameter fluidized bed to be rapidly fluidized under the action of the flue gas and dried by the residual heat of the flue gas. The red mud material separated by the primary cyclone separator II and the red mud material preheated by the secondary cyclone preheater both enter the primary red mud particle layer of the multi-layer fluidized bed. When the height of the red mud material in the primary red mud particle layer reaches the height of the feed port of the overflow pipe, it enters the secondary red mud particle layer through the overflow pipe. The pyrolysis biomass enters the third-stage biomass layer from the pyrolysis biomass silo through the pyrolysis biomass feeder, and is roasted under the action of hot nitrogen from the secondary cyclone separator III to complete pyrolysis. The pyrolysis biomass product enters the combustion chamber through the fuel biomass feeder; The fuel biomass enters the combustion chamber from the fuel biomass silo through the fuel biomass feeder, and air enters the combustion chamber from the air pipeline. The fuel biomass and pyrolysis biomass products are burned in the air of the combustion chamber to form high-temperature flue gas, which is sent to the secondary cyclone preheater; The pyrolysis gas from the tertiary biomass layer passes upward through the secondary red mud particle layer and the primary red mud particle layer in sequence. The red mud materials in the secondary red mud particle layer and the primary red mud particle layer are reduced and roasted. Under the action of the pyrolysis gas, low-temperature fluidized solid-state reduction is completed. The reduced tail gas passes through the primary cyclone separator III and the secondary cyclone separator II in sequence to separate the solids and then enters the secondary cyclone preheater. The material after low-temperature fluidized solid-state reduction enters the fluidized bed cooler through the discharge valve II. Nitrogen enters the fluidized bed cooler through the nitrogen pipeline and exchanges heat with the material in the fluidized bed cooler. The material after heat exchange and cooling enters the magnetic separation system through the discharge valve III. Ferromagnetic material and aluminum-containing slag are obtained through magnetic separation. The hot nitrogen after heat exchange passes through the gas outlet of the fluidized bed cooler in sequence through the first-stage cyclone separator VI and the second-stage cyclone separator III for gas-solid separation and then enters the third-stage biomass layer of the multi-layer fluidized bed to provide heat for the pyrolysis of the pyrolysis biomass.

5. The method according to claim 4, characterized in that The materials in the primary red mud particle layer, the secondary red mud particle layer and the tertiary biomass layer of the multi-layer fluidized bed are in bubbling fluidization or turbulent fluidization.

6. The method according to claim 4, characterized in that The solid mass content of the red mud is 30%-80%.

7. The method according to claim 4, characterized in that The water content of the fuel biomass and the pyrolysis biomass is ≤5%, and the fuel biomass and the pyrolysis biomass are a combination of one or more of lignin, sawdust, rice husks, and straw.

8. The method according to claim 4, characterized in that The rotation speed of the bottom-extending multi-layer stirring device is 100-2000 rpm.

9. The method according to claim 4, characterized in that The reduction roasting temperature of the primary and secondary red mud particle layers of the multi-layer fluidized bed is 400-500°C, and the reduction time is 0.5-1h; the pyrolysis temperature of the tertiary biomass layer of the multi-layer fluidized bed is 200-400°C, and the reduction time is 0.5-1h.

10. The method according to claim 4, characterized in that The iron recovery rate is ≥80%.

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