Continuous desulfurization method and device for bauxite under suspension fluidized bed pressure relief atmosphere regulation

Abstract

The application discloses a kind of based on suspension fluidized bed pressure relief atmosphere regulation and control bauxite continuous desulfurization method and device, belong to mineral processing field.The present application aims at solving the problem of slow gas-solid interface update in existing fluidized bed desulfurization technology, sulfide oxidation is limited by diffusion.The technical scheme is as follows: after grinding, high-sulfur bauxite is continuously added to the suspension fluidized bed reactor, and pressurized oxidizing atmosphere is used as fluidizing medium;During the operation of the fluidized bed, the surface of the particles experiences instantaneous pressure drop by periodically changing the bed pressure (pressure is rapidly cycled between 0.1-1.5 MPa) or using the Venturi-type hood / inner member throttle on the distribution plate;The pressure relief effect destroys the reaction product film on the surface of pyrite, enhances the mass transfer of oxygen and the oxidation reaction of sulfide, and the reaction temperature is controlled at 400-650℃.The present application realizes continuous desulfurization, and the desulfurization rate can reach more than 85%, the aluminum recovery rate loss is less than 3%, and the device structure is simple, the energy consumption is low, suitable for industrial pretreatment of high-sulfur bauxite.

Description

Technical Field

[0001] This invention belongs to the field of mineral processing and alumina production technology, specifically relating to a desulfurization method for high-sulfur bauxite, and more particularly to a method and dedicated device for continuous desulfurization of bauxite by using periodic or local rapid pressure changes to regulate the reaction atmosphere in a suspended fluidized bed reactor. Background Technology

[0002] Sulfur in high-sulfur bauxite exists primarily in the form of pyrite, posing a serious hazard in the Bayer process. Suspension fluidized bed technology is widely used in mineral roasting due to its advantages such as high gas-solid contact efficiency, uniform bed temperature, and adjustable solid residence time. However, traditional bauxite fluidized bed desulfurization typically operates under constant or slightly negative pressure, with reaction interface renewal relying on bubble breakage and particle movement, lacking active, forced "pressure fluctuations" to enhance mass transfer. Introducing periodic pressure relief disturbances into the fluidized bed could potentially overcome diffusion limitations and achieve efficient, selective desulfurization, but no such technology has yet been publicly disclosed. Summary of the Invention

[0003] This invention aims to provide a continuous desulfurization method and apparatus for bauxite based on a suspended fluidized bed with controlled depressurization atmosphere, to address the problems of insufficient gas-solid interface renewal efficiency and sulfide oxidation limited by the diffusion layer in existing fluidized bed desulfurization technologies. By dynamically creating pressure drop zones or periodic depressurization cycles in the fluidized bed reactor, the microenvironmental disturbance on the surface of pyrite particles is enhanced, thereby improving the desulfurization rate and protecting the aluminum-containing minerals.

[0004] A continuous desulfurization method for bauxite using a suspended fluidized bed with depressurized atmosphere control is characterized by: placing bauxite powder in a fluidized bed reactor, using a pressurized oxidizing atmosphere as the fluidizing medium, and during the operation of the fluidized bed, periodically changing the bed pressure or using the throttling effect of the distribution plate / internal components to cause the particles in the bed to undergo one or more rapid pressure drop processes, thereby utilizing this depressurization effect to enhance the oxidative desulfurization reaction of bauxite.

[0005] The continuous desulfurization method for bauxite using a suspended fluidized bed depressurization atmosphere control, as described above, is characterized by:

[0006] The specific implementation steps are as follows:

[0007] (1) Material preparation: crush and grind the high-sulfur bauxite to -30 mesh to -400 mesh, of which more than 70% should be of -200 mesh to facilitate fluidization;

[0008] (2) Fluidized bed feeding and atmosphere establishment: The powder is continuously fed into the suspended fluidized bed reactor, and an oxidizing atmosphere pressurized to 0.1-1.5 MPa, including air, oxygen-enriched air or oxygen-inert gas mixture, is introduced from the bottom; the apparent gas velocity is controlled at 0.5-5.0 m / s to ensure that it is higher than the minimum fluidization velocity, so as to form a stable fluidized bed and maintain the bed temperature at 400-650℃;

[0009] (3) Pressure relief regulation enhances desulfurization;

[0010] (4) Continuous discharge and gas-solid separation: The desulfurized bauxite is continuously discharged through the overflow pipe or the bottom discharge valve; the gas carrying fine powder is recovered by the cyclone separator and the solid is returned to the bed, while the gas is purified and partially recycled.

[0011] Furthermore, in step (2), the oxygen volume fraction in the oxidizing atmosphere is 21%-100%, and the total pressure is 0.1-1.5 MPa.

[0012] Furthermore, the "pressure relief" effect of the pressure relief regulation to enhance desulfurization described in step (3) is divided into three types;

[0013] Method I, Periodic Total Pressure Fluctuation: Utilizing a rapid pressure regulating valve on the intake system to maintain the bed pressure at a high value P H Maintain pressure at 0.5-1.5 MPa for 10-120 seconds, then rapidly depressurize to a low value P. L The pressure is 0.1-0.3 MPa, the depressurization time is ≤5 seconds, and the pressure is increased again after 10-60 seconds. This cycle is repeated. Each time the pressure is depressurized, the gas adsorbed on the surface of the particles in the bed expands rapidly and peels off the reaction product film.

[0014] Method II, distribution plate throttling and pressure relief: A distribution plate with a Venturi-shaped wind cap is used. When the airflow passes through the throat of the wind cap, the velocity increases sharply and the pressure drops sharply: ΔP≥0.05 MPa. Micro-zone pressure relief is formed around the outlet of the wind cap, continuously renewing the particle interface; multiple micro-pressure reliefs can be achieved by connecting multiple rows of wind caps in series.

[0015] Method III, Local Pressure Relief within the Bed: A horizontal porous plate internal component with throttling holes is installed inside the fluidized bed to divide the bed into upper and lower zones. When the airflow passes through the orifice plate, a pressure drop is generated, and the particles experience a sudden pressure change when passing through the orifice plate.

[0016] Furthermore, in step (3) of method I, the pressure cycle frequency is 0.5-5 times / minute, and the total number of depressurization times is set to 1-20 times based on the average residence time according to the desulfurization rate requirements.

[0017] Furthermore, the method of throttling through the distribution plate in step (3) is as follows: a venturi-type or nozzle-type wind cap is used, and a local pressure drop of ≥0.05 MPa is generated when the airflow passes through the throat of the wind cap.

[0018] A continuous desulfurization device used in the method described above, characterized in that it comprises:

[0019] (1) Fluidized bed reactor body: It has a bed section and an expansion section, and a gas distribution plate is installed inside;

[0020] (2) Gas-solid separation and circulation system: including cyclone separator and return valve, used to return the fine powder separated to the bed to achieve continuous operation;

[0021] (3) Pressurized atmosphere supply system: including gas compressor, pressure stabilizing tank and fast pressure regulating valve, used to provide oxidizing gas whose pressure can be changed quickly;

[0022] (4) Pressure relief regulation unit.

[0023] Furthermore, the fluidized bed reactor is equipped with 1 to 3 orifice plates as internal components, which divide the bed into multiple pressure zones. Particles undergo pressure relief when passing through the orifice plates. The ratio of the bed height to the diameter of the fluidized bed is 1:1 to 5:1, and the gas velocity in the expansion section is reduced to 0.1-0.5 m / s to facilitate the settling of fine powder.

[0024] Furthermore, the fluidized bed reactor is also equipped with a side air inlet for injecting water vapor or CO2 to adjust the oxidation selectivity.

[0025] Furthermore, the pressure relief regulation unit includes at least one of the following structures:

[0026] (a) A pulse pressure relief valve assembly located below the gas distribution plate can periodically and rapidly release the pressure at the bottom of the bed;

[0027] (b) Throttling nozzles or Venturi-type air caps installed on the distribution plate create a local pressure drop in the airflow entering the bed;

[0028] (c) Bypass quick discharge system: connected to the upper or middle part of the reactor, and periodically discharges part of the gas through a quick-opening valve, causing the bed pressure to drop instantaneously.

[0029] The specific method of using the device described in this invention is as follows:

[0030] (1) Start-up of the device and establishment of the fluidized bed

[0031] Start the gas compressor to pressurize the oxidizing atmosphere (air, oxygen-enriched air, or oxygen-inert gas mixture) to 0.1-1.5 MPa. After buffering in a pressure stabilizing tank, the atmosphere is continuously introduced into the fluidized bed reactor through a gas distribution plate. Simultaneously, start the reactor heating system to raise and stabilize the bed temperature at 400-650℃. Once the bed temperature reaches the set value, pre-ground high-sulfur bauxite powder (pre-ground to -30 mesh to -400 mesh, with -200 mesh accounting for more than 70%) is continuously added from the reactor side wall feed inlet using a screw feeder or pneumatic conveying device.

[0032] Adjust the inlet air flow rate to control the apparent gas velocity in the bed at 0.5-5.0 m / s (higher than the minimum fluidization velocity of the material), allowing the material to form a stable fluidized bed within the reactor. Maintain the bed height to diameter ratio between 1:1 and 5:1. At this point, the oxidizing atmosphere comes into full contact with the bauxite particles, and the pyrite begins to undergo an oxidative desulfurization reaction.

[0033] (2) Pressure relief regulation to enhance desulfurization

[0034] During stable operation of the fluidized bed, based on ore characteristics and desulfurization targets, one or more combinations of the following three pressure relief control methods are selected to apply periodic or localized rapid pressure reduction (pressure relief) treatment to the particles in the bed:

[0035] Method I (Periodic Total Pressure Fluctuation): The controller drives the rapid pressure regulating valve according to a preset sequence. Specifically: the exhaust valve is closed, maintaining the bed pressure at a high value P_H (0.5-1.5 MPa) for 10-120 seconds; then the exhaust valve is quickly opened, releasing the bed pressure to a low value P_L (0.1-0.3 MPa) within ≤5 seconds, maintaining this pressure for 10-60 seconds before closing the exhaust valve, and the system is pressurized again. This cycle is repeated 0.5-5 times / minute, with the total number of depressurization cycles set to 1-20 times based on the target desulfurization rate (based on the average residence time of the material). During each depressurization, the adsorbed gas on the particle surface expands rapidly, peeling off the reaction product film.

[0036] Method II (Distribution Plate Throttling and Pressure Relief): A Venturi or nozzle-type air cap distribution plate is used. As the airflow passes through the throat of the air cap, its velocity increases sharply and its static pressure decreases significantly (ΔP ≥ 0.05 MPa), creating a micro-zone pressure relief environment around the air cap outlet. The particle interface is continuously renewed as it passes through this micro-zone. For multi-stage enhancement, multiple rows of air caps can be connected in series, allowing the particles to undergo multiple micro-pressure relief processes.

[0037] Method III (Local Pressure Relief within the Bed): One to three layers of horizontal porous plates with throttling holes are installed inside the fluidized bed as internal components, dividing the bed into multiple pressure zones along its height. When the gas-solid two-phase flow passes through the porous plates, the airflow experiences a pressure drop (ΔP≥0.05 MPa) due to the throttling effect. The particles experience a sudden pressure change as they pass through the porous plates, achieving enhanced local pressure relief.

[0038] During the depressurization process, water vapor or CO2 can be injected into the upper part of the bed or the expanded section through the side air supply port as needed to control the reaction selectivity or absorb part of SO2.

[0039] (3) Gas-solid separation and continuous solid discharge

[0040] After the reaction, the gas-solid mixture rises to the upper expansion section of the reactor. Due to the reduced gas velocity (down to 0.1-0.5 m / s), some coarse particles naturally settle back into the bed. The gas carrying fine powder leaves the reactor and enters a cyclone separator. The recovered fine powder is returned to the bed through a return valve to continue participating in the reaction. Part of the purified gas is discharged into the subsequent tail gas treatment system, while the other part is pressurized by a circulating fan, mixed with fresh oxidizing atmosphere, and returned to the bottom of the reactor for recycling.

[0041] The desulfurized bauxite concentrate is continuously discharged through the overflow pipe or bottom discharge valve at the bottom of the bed, and after cooling, it is sent to the Bayer process leaching process.

[0042] (4) System control and parameter adjustment

[0043] The entire unit's inlet pressure, flow rate, temperature, depressurization cycle, and discharge rate are automatically monitored and regulated by a control system (PLC or DCS) to ensure stable and continuous operation of the reactor under set conditions. Operators can adjust key parameters such as depressurization frequency, pressure amplitude, and residence time online based on real-time feedback signals such as desulfurization rate, bed pressure drop, and product sulfur content to achieve optimized desulfurization treatment for different high-sulfur bauxite ores.

[0044] Beneficial effects of the invention

[0045] 1. High reaction efficiency: The fluidized bed itself has excellent gas-solid contact, and with the added pressure relief disturbance, the sulfate passivation layer on the surface of pyrite is further destroyed, and the desulfurization rate can reach more than 88%.

[0046] 2. Continuous and stable production: It avoids the frequent loading and unloading of batch reactors, making it suitable for large-scale industrial production; the solid residence time can be independently adjusted (by bed height and discharge rate), decoupled from gas velocity.

[0047] 3. Low aluminum loss: The decompression process is mainly physical disturbance, which does not significantly increase the local temperature or oxidation intensity. The phase of gibbsite remains intact, and the aluminum recovery rate loss is less than 3%.

[0048] 4. Recyclable atmosphere: Some of the gas after the reaction is desulfurized and then pressurized for reuse, reducing oxygen consumption and exhaust gas treatment costs. Attached Figure Description

[0049] Figure 1 : A schematic diagram of the suspended fluidized bed desulfurization device in this embodiment of the invention (labeled with pressure circulation system, distribution plate, cyclone separator, etc.).

[0050] Figure 2 Bed pressure-time curve under periodic total pressure fluctuation mode (showing rapid pressure relief peak).

[0051] Figure 3 Curves showing the change in desulfurization rate at different depressurization frequencies.

[0052] Figure 1 In this system, the components are: 1. Gas source; 2. Pressure stabilizing tank; 3. Controller; 4. Quick pressure regulating valve; 5. Distribution plate with Venturi-type air cap; 6. Feed inlet; 7. Furnace chamber; 8. Horizontal perforated plate internal component with throttling orifice; 9. Cyclone separator; 10. Return valve; 11. Return pipe. Detailed Implementation

[0053] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the invention.

[0054] Example 1 (Periodic Total Pressure Fluctuation)

[0055] High-sulfur bauxite (total sulfur 4.5%, Al2O3 55%) was selected and ground to -320 mesh (85% purity). A fluidized bed reactor with an inner diameter of 150 mm and an initial bed height of 200 mm was used. Air was used as the fluidizing medium, with a compressor providing pressure and a fast exhaust valve.

[0056] Operating parameters: Pressurize to 1.0 MPa and hold for 60 seconds; quickly open the exhaust valve, depressurize to atmospheric pressure within 5.0 seconds, and hold for 40 seconds; pressurize to 1.0 MPa within 5.0 seconds; repeat the cycle. Bed temperature is controlled at 450℃. Average residence time is controlled to 20 minutes through continuous feeding and discharging (equivalent to approximately 12 pressure cycles).

[0057] Analysis of the solids continuously discharged after the reaction: total sulfur content 0.52%, desulfurization rate 88.4%. Samples were taken for Bayer process leaching (260℃, 180g / L alkali solution, 30min), with a relative leaching rate of 97.2%.

[0058] Example 2 (Distribution Plate Throttling and Pressure Relief)

[0059] A Venturi-type air cap distribution plate (throat diameter 3mm, contraction angle 30°, diffusion angle 15°) is used. The air cap pressure drop is designed to be 0.08 MPa. Oxygen-enriched air (O2 40%, N2 60%) is used, with a total inlet pressure of 0.6 MPa and a bed operating pressure of approximately 0.52 MPa. No periodic total pressure fluctuations are implemented; the reaction is enhanced solely by the localized pressure drop as the airflow passes through the air cap. The temperature is 500℃, the apparent gas velocity is 1.2 m / s, and the feed and discharge are continuous with a residence time of 15 minutes.

[0060] The sulfur content after desulfurization is 0.69%, and the desulfurization rate is 84.7%. The aluminum dissolution rate is 96.5%.

[0061] Comparative Example 1 (Conventional atmospheric pressure fluidized bed, without pressure relief control)

[0062] Using the same ore, fluidized bed desulfurization was performed at atmospheric pressure (0.1 MPa), 450℃, and in air atmosphere, with a residence time of 20 minutes and no pressure fluctuations. The final sulfur content was 1.68%, the desulfurization rate was 62.7%, and the aluminum leaching rate was 95.8%.

[0063] As can be seen in the comparison, by introducing pressure relief regulation (periodic total pressure fluctuation or distribution plate throttling), the present invention significantly increases the desulfurization rate from 62.7% to 84-88% within a similar residence time, without significantly impairing the aluminum recovery rate.

[0064] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of the claims of the present invention pending approval.

Claims

1. A continuous desulfurization method for bauxite based on suspended fluidized bed depressurization atmosphere control, characterized in that: Bauxite powder is placed in a fluidized bed reactor, with a pressurized oxidizing atmosphere as the fluidizing medium. During the operation of the fluidized bed, the particles in the bed undergo one or more rapid pressure drop processes by periodically changing the bed pressure or by the throttling effect of the distribution plate / internal components. This pressure relief effect is used to enhance the oxidative desulfurization reaction of bauxite.

2. The continuous desulfurization method for bauxite using a suspended fluidized bed depressurization atmosphere control according to claim 1, characterized in that: The specific implementation steps are as follows: (1) Material preparation: crush and grind the high-sulfur bauxite to -30 mesh to -400 mesh, of which more than 70% should be of -200 mesh to facilitate fluidization; (2) Fluidized bed feeding and atmosphere establishment: The powder is continuously fed into the suspended fluidized bed reactor, and an oxidizing atmosphere pressurized to 0.1-1.5 MPa, including air, oxygen-enriched air or oxygen-inert gas mixture, is introduced from the bottom; the apparent gas velocity is controlled at 0.5-5.0 m / s to ensure that it is higher than the minimum fluidization velocity, so as to form a stable fluidized bed and maintain the bed temperature at 400-650℃; (3) Pressure relief regulation enhances desulfurization; (4) Continuous discharge and gas-solid separation: The desulfurized bauxite is continuously discharged through the overflow pipe or the bottom discharge valve; the gas carrying fine powder is recovered by the cyclone separator and the solid is returned to the bed, while the gas is purified and partially recycled.

3. The continuous desulfurization method for bauxite using a suspended fluidized bed depressurization atmosphere control according to claim 2, characterized in that: In step (2), the oxygen volume fraction in the oxidizing atmosphere is 21%-100%, and the total pressure is 0.1-1.5 MPa.

4. The continuous desulfurization method for bauxite using a suspended fluidized bed depressurization atmosphere control according to claim 2, characterized in that: The "pressure relief" effect of the pressure relief regulation to enhance desulfurization described in step (3) is divided into three types; Method I, Periodic Total Pressure Fluctuation: Utilizing a rapid pressure regulating valve on the intake system to maintain the bed pressure at a high value P H Maintain pressure at 0.5-1.5 MPa for 10-120 seconds, then rapidly depressurize to a low value P. L 0.1-0.3 MPa, depressurization time ≤5 seconds, maintain for 10-60 seconds and then pressurize again, repeat this cycle; each time the pressure is released, the gas adsorbed on the surface of the particles in the bed expands rapidly and peels off the reaction product film; Method II, distribution plate throttling and pressure relief: A distribution plate with a Venturi-shaped wind cap is used. When the airflow passes through the throat of the wind cap, the velocity increases sharply and the pressure drops sharply: ΔP≥0.05 MPa, forming a micro-zone pressure relief around the outlet of the wind cap, continuously renewing the particle interface; multiple micro-pressure reliefs can be achieved by connecting multiple rows of wind caps in series. Method III, Local Pressure Relief within the Bed: A horizontal porous plate internal component with throttling holes is installed inside the fluidized bed to divide the bed into upper and lower zones. When the airflow passes through the orifice plate, a pressure drop is generated, and the particles experience a sudden pressure change when passing through the orifice plate.

5. The continuous desulfurization method for bauxite using a suspended fluidized bed depressurization atmosphere control according to claim 4, characterized in that: In step (3) of method I, the pressure cycle frequency is 0.5-5 times / minute, and the total number of depressurization times is set to 1-20 times based on the average residence time according to the desulfurization rate requirements.

6. The continuous desulfurization method for bauxite using a suspended fluidized bed depressurization atmosphere control according to claim 4, characterized in that: The method of throttling through the distribution plate in step (3) is as follows: a Venturi or nozzle type wind cap is used, and a local pressure drop of ≥0.05 MPa is generated when the airflow passes through the throat of the wind cap.

7. A continuous desulfurization apparatus for use in the method as described in claim 1 or 2, characterized in that: include: (1) Fluidized bed reactor body: It has a bed section and an expansion section, and a gas distribution plate is installed inside; (2) Gas-solid separation and circulation system: including cyclone separator and return valve, used to return the fine powder separated to the bed to achieve continuous operation; (3) Pressurized atmosphere supply system: including gas compressor, pressure stabilizing tank and fast pressure regulating valve, used to provide oxidizing gas whose pressure can be changed quickly; (4) Pressure relief regulation unit.

8. The continuous desulfurization device according to claim 7, characterized in that: The fluidized bed reactor is equipped with 1 to 3 orifice plates as internal components, which divide the bed into multiple pressure zones. Particles undergo pressure relief when passing through the orifice plates. The ratio of the bed height to the diameter of the fluidized bed is 1:1 to 5:1, and the gas velocity in the expansion section is reduced to 0.1-0.5 m / s to facilitate the settling of fine powder.

9. The continuous desulfurization device according to claim 7, characterized in that: The fluidized bed reactor is also equipped with a side air inlet for injecting water vapor or CO2 to adjust the oxidation selectivity.

10. The continuous desulfurization device according to claim 7, characterized in that: The pressure relief regulation unit includes at least one of the following structures: (a) A pulse pressure relief valve assembly located below the gas distribution plate can periodically and rapidly release the pressure at the bottom of the bed; (b) Throttling nozzles or Venturi-type air caps installed on the distribution plate create a local pressure drop in the airflow entering the bed; (c) Bypass quick discharge system: connected to the upper or middle part of the reactor, and periodically discharges part of the gas through a quick-opening valve, causing the bed pressure to drop instantaneously.

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