A method and apparatus for oxidative roasting of high-sulfur bauxite using a multi-stage countercurrent cyclone separator

Abstract

A method and apparatus for oxidative roasting of high-sulfur bauxite using a multi-stage countercurrent cyclone separator, belonging to the field of comprehensive utilization technology of high-sulfur bauxite, the method includes: (1) using high-sulfur bauxite as raw material, and using high-temperature carbon dioxide and oxygen generated by combustion of a gas-fired boiler as heat source and oxidant respectively; (2) oxidative roasting is carried out in a multi-stage countercurrent cyclone separator, and the pyrite phase in the high-sulfur bauxite is converted into iron oxide and sulfur dioxide; (3) the multi-stage countercurrent cyclone separator is composed of 1 to N cyclone heat exchangers, and the solid phase and gas phase complete the oxidation reaction of the pyrite phase in the heat exchange process in a countercurrent manner; (4) the temperature of the flue gas obtained after the reaction drops to below 200℃, and the heat utilization rate of the system reaches more than 80%; (5) after the flue gas is desulfurized and denitrified, the sulfur component is used to prepare sulfuric acid, and the carbon dioxide is absorbed by a calcium-containing solution to prepare light calcium carbonate products; the present invention is an efficient and pollution-free method for utilizing high-sulfur bauxite.

Description

Technical Field

[0001] This invention belongs to the field of comprehensive utilization technology of high-sulfur bauxite, specifically relating to a method and apparatus for oxidative roasting of high-sulfur bauxite using a multi-stage countercurrent cyclone separator. Background Technology

[0002] High-sulfur bauxite generally refers to bauxite with a sulfur content higher than 0.7 wt.%, where sulfur is mainly found in pyrite, accompanied by pyrrhotite, marcasite, and sulfates. High-sulfur bauxite cannot be directly used in alumina production because sulfur causes increased alkali consumption, container scaling, deterioration of product quality, and equipment corrosion during the leaching process. Therefore, developing and utilizing complex bauxite deposits, such as high-sulfur bauxite, can greatly alleviate my country's bauxite shortage.

[0003] Patent CN201910738682.9 discloses an apparatus and method for desulfurization through suspension roasting of high-sulfur bauxite. The apparatus includes a silo, a screw feeder, a primary cyclone separator, a suspension roasting furnace, a secondary cyclone separator, and dust removal and desulfurization equipment. The method is as follows: (1) High-sulfur bauxite is crushed, dried, and placed in the silo; (2) The induced draft fan is turned on to create a negative pressure in the system; (3) Natural gas and air are introduced into the burner, and after ignition, a high-temperature oxidizing gas is formed; (4) High-sulfur bauxite powder is fed into the primary cyclone separator, and the resulting primary solid material enters the suspension roasting furnace; (5) The primary solid material undergoes an oxidation roasting reaction, and the reacted material enters the secondary cyclone separator; (6) The secondary solid material is discharged through the discharge pipe. The method of this invention has a simple process flow, low overall energy consumption, high gas-solid mass and heat transfer efficiency, stable product properties, and high production efficiency.

[0004] Patent CN201510362694.8 discloses a method for producing alumina from low-grade, high-sulfur bauxite, comprising the following steps: (1) adding a mineralizing agent to the low-grade, high-sulfur bauxite, and converting SiO2 in the bauxite into active silicon under roasting, followed by desulfurization of the flue gas before emission; (2) treating the roasted bauxite with sodium hydroxide solution to desiliconize it, thereby increasing the A / S ratio of the bauxite to 6-14; (3) obtaining sodium silicate solution and high-grade bauxite after solid-liquid separation of the desiliconized slurry; (4) using the Bayer process to produce metallurgical-grade alumina from the high-grade bauxite obtained by solid-liquid separation; (5) directly evaporating the sodium silicate solution obtained by solid-liquid separation to obtain sodium metasilicate product or adding lime milk to produce active calcium silicate product and sodium hydroxide solution, with the sodium hydroxide solution returned to the desiliconization process. This invention achieves roasting desulfurization of low-grade, high-sulfur bauxite, activation of silicon minerals, and chemical desiliconization, resulting in low cost and good economic benefits.

[0005] Patent CN201210399209.0 discloses a method for activating high-sulfur bauxite using a low-temperature roasting desulfurization process. The method involves oxidative desulfurization roasting of bauxite with a sulfur content of 1-5 wt% to make it suitable as a raw material for Bayer process alumina production. The key feature is controlling the oxidative desulfurization temperature within the range of 500-600℃. Specifically, the ground ore powder is heated with hot air at 650-900℃ in a fluidized bed furnace or rotary kiln. After treatment, the sulfur content of the ore powder is reduced to below 0.5%, and the organic matter in the ore is completely oxidized and decomposed. Simultaneously, the low roasting temperature avoids the transformation of activated alumina, preventing excessive stability. When the roasted bauxite is used for Bayer process leaching, the leaching performance is improved, with an alumina leaching rate greater than 93%. For the SO2-containing tail gas generated by oxidative desulfurization, treatment with limestone suspension circulating spray desulfurization or red mud suspension spray desulfurization can reduce the SO2 content to 300 mg / m³. 3 The following meet the emission standards.

[0006] In summary, most existing methods for utilizing high-sulfur bauxite involve desulfurization through oxidative roasting. However, the traditional roasting method has low heat exchange efficiency between the high-sulfur bauxite and oxygen or oxygen-enriched air, resulting in low desulfurization efficiency. Suspension roasting oxidative desulfurization requires finer mineral powder particles and a larger gas-solid two-phase reaction area, leading to a higher desulfurization rate. However, it requires a higher roasting temperature, which is not conducive to energy conservation. Microwave roasting has the advantages of low roasting temperature, fast heating speed, uniform heating, and short-time high efficiency, but its cost is high and the desulfurization effect is difficult to guarantee under large-scale production conditions. Summary of the Invention

[0007] This invention provides a method for oxidative roasting of high-sulfur bauxite using a multi-stage countercurrent cyclone separator, comprising the following steps:

[0008] (1) Using high-sulfur bauxite as raw material, high-temperature carbon dioxide and oxygen generated by "oxygen-enriched and oxygen-excessive" combustion in a gas-fired boiler are used as heat source and oxidant, respectively.

[0009] (2) High-sulfur bauxite is oxidized and roasted in a multi-stage countercurrent cyclone, and the pyrite phase in the high-sulfur bauxite is transformed into iron oxide and sulfur dioxide.

[0010] (3) The multi-stage countercurrent cyclone separator consists of 1 to N cyclone heat exchangers, in which the solid phase and the gas phase adopt a countercurrent method to complete the oxidation reaction of the pyrite phase during the heat exchange process;

[0011] (4) The temperature of the flue gas obtained after the reaction of the multi-stage countercurrent cyclone separator drops to below 200℃, and the heat utilization rate of the system reaches more than 80%.

[0012] (5) After the flue gas is desulfurized and denitrified, the sulfur component is used to prepare sulfuric acid, and the remaining carbon dioxide is absorbed by a calcium-containing solution to prepare light calcium carbonate products.

[0013] The high-sulfur bauxite mentioned in step (1) refers to bauxite with a sulfur content higher than 0.5 wt.%.

[0014] The "oxygen-enriched and oxygen-peroxidized" combustion of carbon and oxygen described in step (1) involves the reaction of carbon monoxide and oxygen in a gas-fired boiler to produce high-temperature flue gas containing carbon dioxide and oxygen, which serves as the heat source and oxidant for the oxidation reaction. The reaction stoichiometric formula is as follows:

[0015] mC + (m + n)O₂ = mCO₂ + nO₂

[0016] The reaction temperature for the oxidation roasting process of high-sulfur bauxite in step (2) is 300–900℃, and the mass ratio of oxygen in the flue gas to high-sulfur bauxite is (0.1–1):1, with a reaction time of 1–120 seconds. The oxidation efficiency of the pyrite phase in the high-sulfur bauxite is >99.9%, S 2- Content ≤0.1%.

[0017] The multi-stage countercurrent cyclone separators described in steps (2)-(3) can be 1-N multi-stage countercurrent cyclone separators according to the actual needs of the pyrite phase oxidation reaction process in high-sulfur bauxite. In the multi-stage countercurrent cyclone separator, the solid phase and the gas phase undergo oxidation reaction in a countercurrent manner during the heat exchange process.

[0018] A multi-stage counter-current cyclone oven-roasting device for high-sulfur bauxite includes: 1-N stage cyclone heat exchangers; the flue gas outlet of the first stage cyclone heat exchanger is connected to a flue gas purification device via a gas pipeline; and the air inlet of the Nth stage cyclone heat exchanger is connected to the air outlet of a gas-fired boiler via a gas pipeline. Preferably, the multi-stage counter-current cyclone oven-roasting device consists of 1-5 stage cyclone heat exchangers.

[0019] Taking a three-stage counter-current cyclone separator as an example, the high-temperature flue gas generated by the two-stage counter-current cyclone heat exchanger is fed into the first-stage counter-current cyclone heat exchanger, where heat exchange and oxidation reactions occur. The flue gas discharged from the first-stage counter-current cyclone heat exchanger undergoes flue gas purification treatment, where sulfur dioxide is used to produce sulfuric acid and carbon dioxide is mineralized to produce light calcium carbonate. The slag produced by the first-stage counter-current cyclone heat exchanger is fed into the second-stage counter-current cyclone heat exchanger using the high-temperature flue gas generated by the third-stage counter-current cyclone heat exchanger, where heat exchange and oxidation reactions occur. The slag produced by the second-stage counter-current cyclone heat exchanger is fed into the third-stage counter-current cyclone heat exchanger using high-temperature carbon dioxide and oxygen generated by the gas-fired boiler, where heat exchange and oxidation reactions occur. The slag produced by the third-stage counter-current cyclone heat exchanger is discharged after heat exchange and enters the subsequent Bayer process to extract alumina.

[0020] The multi-stage countercurrent cyclone oxidative roasting method and apparatus for high-sulfur bauxite of the present invention have the following advantages compared with the prior art:

[0021] (1) High desulfurization efficiency and high heat utilization efficiency. Using a multi-stage counter-current cyclone heat exchanger as the reactor results in high heat exchange efficiency; the oxidation efficiency of the pyrite phase in high-sulfur bauxite is >99.9%, S 2- The content is ≤0.1%. Compared with conventional fluidized bed reactors, the heat utilization rate of the three-stage or higher countercurrent cyclone separator reaches over 80%, and the temperature of the resulting flue gas is reduced to below 200℃.

[0022] (2) High-temperature carbon dioxide and oxygen generated by "oxygen-enriched and oxygen-excessive" combustion in a gas-fired boiler are used as the heat source and oxidant, respectively. No additional heating is required, the process is zero-emission, clean production, and the product has high added value. The residual carbon dioxide in the tail gas is passed into a calcium-containing aqueous solution to prepare light calcium carbonate, which increases the added value of carbon dioxide utilization without releasing carbon dioxide. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a method and apparatus for the oxidation roasting of high-sulfur bauxite using a three-stage countercurrent cyclone separator. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the embodiments.

[0025] The main components of the high-sulfur bauxite used in the embodiments of the present invention are Al2O3-63.85%, SiO2-15.84%, TiO2-2.93%, FeS2-4.64%, with the remainder being impurities.

[0026] Example 1

[0027] (1) Carbon monoxide and oxygen are "oxygen-enriched and oxygen-excessive" in the gas boiler to produce high-temperature flue gas containing carbon dioxide and oxygen, which serves as the heat source and oxidant for the oxidation reaction. The ratio of oxygen to high-sulfur bauxite in the flue gas is 0.1:1.

[0028] (2) Figure 1 As shown, high-sulfur bauxite and oxygen are subjected to an oxidative roasting reaction in a three-stage countercurrent cyclone heat exchanger, which converts the lutetite phase in the high-sulfur bauxite into iron oxide and sulfur into sulfur dioxide. The reaction temperature of the oxidative roasting process is 900℃ and the reaction time is 10s.

[0029] (3) Alumina concentrate obtained by cooling the high-temperature desulfurized mineral powder. The resulting concentrate contains S 2- With a content of 0.06%, compared with conventional fluidized bed reactors, the heat utilization rate of the three-stage or higher countercurrent cyclone separator reaches more than 80%, and the temperature of the resulting flue gas is reduced to below 200℃;

[0030] (4) SO2-containing flue gas is treated by denitrification, and then sulfuric acid is prepared by absorption liquid. The remaining carbon dioxide in the tail gas is passed into a calcium-containing aqueous solution to prepare light calcium carbonate.

[0031] Example 2

[0032] (1) Carbon monoxide and oxygen are "oxygen-enriched and oxygen-excessive" in the gas boiler to produce high-temperature flue gas containing carbon dioxide and oxygen, which serves as the heat source and oxidant for the oxidation reaction. The ratio of oxygen to high-sulfur bauxite in the flue gas is 1:1.

[0033] (2) High-sulfur bauxite and oxygen-enriched air are subjected to an oxidative roasting reaction in a two-stage counter-current cyclone heat exchanger to convert the lutetite phase in the high-sulfur bauxite into iron oxide and sulfur into sulfur dioxide. The reaction temperature of the oxidative roasting process is 700℃ and the reaction time is 30s.

[0034] (3) Alumina concentrate obtained by cooling the high-temperature desulfurized mineral powder. The resulting concentrate contains S 2- The content is 0.07%;

[0035] (4) SO2-containing flue gas is treated by denitrification, and then sulfuric acid is prepared by absorption liquid. The remaining carbon dioxide in the tail gas is passed into a calcium-containing aqueous solution to prepare light calcium carbonate.

[0036] Example 3

[0037] (1) Carbon monoxide and oxygen are "oxygen-enriched and oxygen-excessive" in the gas-fired boiler to produce high-temperature flue gas containing carbon dioxide and oxygen, which serves as the heat source and oxidant for the oxidation reaction. The ratio of oxygen to high-sulfur bauxite in the flue gas is 0.2:1.

[0038] (2) High-sulfur bauxite and oxygen are oxidized and roasted in a first-stage counter-current cyclone heat exchanger to convert the yellow body phase in the high-sulfur bauxite into iron oxide and sulfur into sulfur dioxide. The reaction temperature of the oxidative roasting process is 600℃ and the reaction time is 120s.

[0039] (3) Alumina concentrate obtained by cooling the high-temperature desulfurized mineral powder. The resulting concentrate contains S 2- The content is 0.09%;

[0040] (4) SO2-containing flue gas is treated by denitrification, and then sulfuric acid is prepared by absorption liquid. The remaining carbon dioxide in the tail gas is passed into a calcium-containing aqueous solution to prepare light calcium carbonate.

[0041] Example 4

[0042] (1) Carbon monoxide and oxygen are "oxygen-enriched and oxygen-excessive" in the gas boiler to produce high-temperature flue gas containing carbon dioxide and oxygen, which serves as the heat source and oxidant for the oxidation reaction. The ratio of oxygen to high-sulfur bauxite in the flue gas is 0.8:1.

[0043] (2) High-sulfur bauxite and oxygen are oxidized and roasted in a four-stage countercurrent cyclone heat exchanger to convert the yellow body phase in the high-sulfur bauxite into iron oxide and sulfur into sulfur dioxide. The reaction temperature of the oxidative roasting process is 850℃ and the reaction time is 15s.

[0044] (3) Alumina concentrate obtained by cooling the high-temperature desulfurized mineral powder. The resulting concentrate contains S 2- With a content of 0.1%, the resulting flue gas temperature drops below 200℃, and the system's heat utilization rate reaches over 80%.

[0045] (4) SO2-containing flue gas is treated by denitrification, and then sulfuric acid is prepared by absorption liquid. The remaining carbon dioxide in the tail gas is passed into a calcium-containing aqueous solution to prepare light calcium carbonate.

[0046] Example 5

[0047] (1) Carbon monoxide and oxygen are "oxygen-enriched and oxygen-excessive" in the gas boiler to produce high-temperature flue gas containing carbon dioxide and oxygen, which serves as the heat source and oxidant for the oxidation reaction. The ratio of oxygen to high-sulfur bauxite in the flue gas is 0.6:1.

[0048] (2) High-sulfur bauxite and oxygen are oxidized and roasted in a three-stage counter-current cyclone heat exchanger to convert the yellow body phase in the high-sulfur bauxite into iron oxide and sulfur into sulfur dioxide. The reaction temperature of the oxidative roasting process is 750℃ and the reaction time is 20min.

[0049] (3) Alumina concentrate obtained by cooling the high-temperature desulfurized mineral powder. The resulting concentrate contains S 2- With a content of 0.07%, the resulting flue gas temperature drops below 200℃, and the system's heat utilization rate reaches over 80%.

[0050] (4) SO2-containing flue gas is treated by denitrification, and then sulfuric acid is prepared by absorption liquid. The remaining carbon dioxide in the tail gas is passed into a calcium-containing aqueous solution to prepare light calcium carbonate.

Claims

1. A method for oxidative roasting of high-sulfur bauxite using a multi-stage countercurrent cyclone separator, characterized in that, The multi-stage counter-current cyclone separator is a five-stage cyclone heat exchanger. The flue gas outlet of the first-stage cyclone heat exchanger is connected to the flue gas purification device via a gas pipeline, and the air inlet of the fifth-stage cyclone heat exchanger is connected to the gas outlet of the gas boiler via a gas pipeline. The specific method includes the following steps: (1) High-sulfur bauxite with a sulfur content higher than 0.5 wt.% is used as raw material, and high-temperature carbon dioxide and oxygen generated by combustion in a gas-fired boiler are used as heat source and oxidant, respectively; (2) The high-sulfur bauxite is oxidized and roasted in a five-stage cyclone heat exchanger at a reaction temperature of 300-900℃. The mass ratio of oxygen in the flue gas to high-sulfur bauxite is (0.1-1):

1. The reaction time is 1-120 seconds. The pyrite phase in the high-sulfur bauxite is converted into iron oxide and sulfur dioxide. (3) The oxidation reaction of the pyrite phase is completed in the heat exchange process by the solid phase and the gas phase in a countercurrent manner; (4) The temperature of the flue gas obtained after the reaction in the five-stage cyclone heat exchanger drops to below 200℃, and the heat utilization rate of the system reaches more than 80%. (5) After the flue gas is desulfurized and denitrified, the sulfur component is used to prepare sulfuric acid, and the remaining carbon dioxide is absorbed by a calcium-containing solution to prepare light calcium carbonate products.

2. The method for oxidative roasting of high-sulfur bauxite using a multi-stage countercurrent cyclone separator according to claim 1, characterized in that, In step (2) of the oxidative roasting of high-sulfur bauxite, the oxidation efficiency of the pyrite phase in the high-sulfur bauxite is >99.9%, S 2- Content ≤0.1%.

3. The method for oxidative roasting of high-sulfur bauxite using a multi-stage countercurrent cyclone separator according to claim 1, characterized in that, Compared with conventional fluidized bed reactors, the five-stage cyclone heat exchanger achieves a heat utilization rate of over 80% and a hydrogen utilization efficiency of over 99%.

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