A system for the production of valuable products by means of the fluidized roasting of gypsum in stages and a method therefor

Abstract

The application relates to a system for preparing valuable products by sectional fluid roasting of gypsum and a method thereof, and belongs to the field of comprehensive utilization of gypsum. The system comprises a feeding-dedusting system, a first roasting system, a second roasting system and a gas-solid separation-treatment system; the feeding-dedusting system, the first roasting system, the second roasting system and the gas-solid separation-treatment system are sequentially connected. The system is suitable for three different processes of gypsum -> beta-hemihydrate gypsum -> anhydrite, gypsum -> anhydrite -> calcium oxide + sulfur dioxide and gypsum -> anhydrite -> calcium sulfide by roasting different gases. Compared with traditional rotary kiln and shaft furnace roasting, the system realizes efficient mass and heat transfer of gas and solid. In the roasting process, sectional roasting technology is adopted, the roasting atmosphere (air, coal gas and hydrogen), the gas amount and the roasting temperature of the second roasting system are finely controlled, and the phase transformation of gypsum is accurately controlled. Compared with other roasting furnaces, the system has the advantages of low energy consumption, small floor area and high running rate.

Description

Technical Field

[0001] This invention relates to the field of gypsum comprehensive utilization technology, specifically to a system and method for preparing valuable products by segmented fluid calcination of gypsum. Background Technology

[0002] The stockpiles of chemical byproducts such as phosphogypsum, fluorogypsum, and borosilicate are increasing. Most are simply piled up or landfilled, with harmful impurities seeping into soil and water bodies with rainwater, causing serious environmental pollution. Gypsum's main component is CaSO4·2H2O, typically exceeding 85%. Under specific thermodynamic conditions, CaSO4·2H2O can be converted into anhydrous gypsum, calcium oxide, and other products, which is one way to achieve the resource utilization of gypsum.

[0003] High-temperature calcination can remove phosphorus and fluorine impurities from gypsum and is the only effective way to remove eutectic phosphorus, but this process is costly and energy-intensive. After calcination at 800℃, the content of soluble phosphorus and soluble fluorine is reduced to 0%, and the content of eutectic phosphorus is reduced by 90%; after calcination at 500℃, the content of soluble phosphorus and soluble fluorine is reduced by 82% and 98%, respectively.

[0004] However, current gypsum equipment mainly consists of traditional roasting equipment such as rotary kilns, calcining furnaces, and fluidized bed furnaces. These devices all involve a two-step dehydration reaction within a single roasting furnace, making it impossible to precisely control the crystal transformation process of gypsum into β-hemihydrate gypsum and then into anhydrite. They also cannot provide a reducing atmosphere, thus failing to achieve the two-step oxidation and reduction roasting of gypsum. These traditional roasting devices suffer from high energy consumption, large footprint, and low operating rates, which are inconsistent with industry trends.

[0005] In addition, the current system has relatively poor adaptability and cannot achieve the preparation of anhydrous gypsum, calcium oxide and sulfur dioxide in a single system. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a system and method for preparing valuable products by segmented fluid calcination of gypsum: a two-stage fluid calcination system is used to realize the first-stage calcination (air atmosphere) and the second-stage calcination process (air / hydrogen / coal gas atmosphere) in two separate reactors.

[0007] This invention provides a system applicable to three gypsum calcination processes:

[0008] The first process: Gypsum → β-hemihydrate gypsum → anhydrite: The system first removes some of the water of crystallization from phosphogypsum to obtain β-hemihydrate gypsum, then forms anhydrous gypsum, and then performs a second-stage high-temperature calcination in air atmosphere to produce anhydrite products.

[0009] The second process: Gypsum → Anhydrous Gypsum → Calcium Oxide + Sulfur Dioxide: The system first removes the water of crystallization from phosphogypsum to obtain anhydrous gypsum; further, the anhydrous gypsum is reduced to SO2 and CaO through a two-stage high-temperature reduction decomposition process in a mixed atmosphere of coal gas and air, ultimately producing SO2 and CaO products.

[0010] The third process: gypsum → anhydrous gypsum → calcium sulfide: The system first removes the water of crystallization from phosphogypsum to obtain anhydrous gypsum; further, the anhydrous gypsum is reduced to calcium sulfide through a two-stage reduction decomposition process under a mixed atmosphere of hydrogen and nitrogen, and finally produces calcium sulfide product.

[0011] This invention applies segmented fluid roasting technology to gypsum roasting and adjusts the roasting equipment according to different roasting requirements of gypsum. Compared with the original rotary kiln and vertical shaft furnace roasting technologies, this technology achieves highly efficient gas-solid mass and heat transfer. Furthermore, the segmented roasting process, through precise control of the roasting atmosphere (air, coal gas, hydrogen), gas flow rate, and roasting temperature in both stages, achieves accurate regulation of the gypsum phase transformation. Compared with other roasting furnaces, the fluid roasting furnace has the advantages of low energy consumption, small footprint, and high operating rate. Ultimately, this technology achieves the goal of treating waste with waste and utilizing gypsum resources.

[0012] This invention provides a system for preparing valuable products by staged fluid calcination of gypsum, which mainly includes a feeding-dust removal system, a primary calcination system, a secondary calcination system, and a gas-solid separation-treatment system. The feeding-dust removal system, the primary calcination system, the secondary calcination system, and the gas-solid separation-treatment system are connected sequentially.

[0013] The feeding-dust removal system includes a silo, a screw feeder, a first cyclone separator, a first dust collector, a first ash hopper, a first fan, and a chimney;

[0014] The silo is connected to the first cyclone separator via a screw feeder. The flue gas outlet of the first cyclone separator is connected in sequence to the first dust collector and the first fan. Furthermore, the dust outlet of the first dust collector is connected to the first ash hopper. Furthermore, the first fan is connected to the chimney.

[0015] The aforementioned calcination system includes a fluid calcination reactor, a first airlock valve, and a second blower;

[0016] The material outlet of the first cyclone separator is connected to the material inlet of the first-stage fluid roasting reactor, the second blower is connected to the lower air inlet of the first-stage fluid roasting reactor, and the material outlet of the first-stage fluid roasting reactor is connected to the first airlock valve.

[0017] The two-stage roasting system includes a two-stage fluid roasting reactor, a second cyclone separator, a second airlock valve, a high-temperature hot air generator, a third fan, and a flow valve.

[0018] The first airlock valve of the first-stage roasting system is connected to the second-stage fluid roasting reactor of the second-stage roasting system. The material outlet of the second-stage fluid roasting reactor is connected to the second airlock valve. The bottom of the second-stage fluid roasting reactor is connected to a high-temperature hot air generator, which is equipped with an air inlet and a fuel gas inlet. Furthermore, a third fan is installed on the pipe connected to the air inlet. The fluid roasting gas inlet is located at the bottom of the second-stage fluid roasting reactor, and a flow valve is installed on the pipe.

[0019] Furthermore, the flue gas outlet of the two-stage fluid roasting reactor is connected to the second cyclone separator, the material outlet separated by the second cyclone separator is connected to the two-stage fluid roasting reactor, and the flue gas outlet separated by the second cyclone separator is connected to the second dust collector.

[0020] Furthermore, one or more of hydrogen, air, coal gas, and nitrogen are introduced into the fluid roasting gas inlet, with the specific gas introduced depending on the product being prepared.

[0021] The gas-solid separation and treatment system includes a second dust collector, a gas scrubbing tower, a ball mill, and a vibrating screen.

[0022] The second airlock valve of the two-stage roasting system is connected to the second dust collector of the gas-solid separation and treatment system. The flue gas outlet of the second dust collector is connected to the scrubbing tower. The exhaust port of the scrubbing tower is not connected to the chimney; it can directly collect the tail gas or discharge the gas into the chimney. The discharge outlet of the second dust collector is connected to the feed port of the ball mill. The discharge port of the ball mill is connected to the vibrating screen. The product on the vibrating screen is connected to the feed port of the ball mill, forming a closed-loop grinding and screening cycle. Further, the solid roasting product is obtained from the discharge port at the bottom of the vibrating screen, and the roasting gas is obtained after being scrubbed in the scrubbing tower. If the roasting gas is a useful product, it needs to be collected; otherwise, it will be discharged into the chimney.

[0023] Furthermore, the internal structures of the single-stage and two-stage fluid roasting reactors are identical. A central baffle divides the fluid roasting reactor into two chambers, with a channel for material flow located beneath the baffle. The feed inlet is connected to the top of the first chamber, and the discharge outlet is connected to the upper-middle part of the outer side of the second chamber. An air distribution plate and an air inlet are located at the bottom of the reactor.

[0024] One section of the fluid roasting reactor is equipped with electric heating devices on all four sides of the furnace wall.

[0025] The method for preparing valuable products by segmented fluid calcination of gypsum according to the present invention, using the above-mentioned system for preparing valuable products by segmented fluid calcination of gypsum, includes the following steps:

[0026] Step 1: Feeding and Dust Removal

[0027] The gypsum is fed from the silo into the first cyclone separator via a screw feeder. After separation, it enters the first-stage fluid roasting reactor.

[0028] The gypsum is preferably one or more of phosphogypsum, fluorogypsum, and borosilicate.

[0029] Furthermore, the flue gas in the gypsum is separated by the first cyclone separator and then collected and treated by the first dust collector, the first ash hopper and the first fan; wherein, the dust collected in the first dust collector enters the first ash hopper, the separated flue gas enters the first fan and is discharged through the chimney.

[0030] Step 2, First-stage roasting

[0031] Gypsum enters a first-stage fluid calcination reactor and undergoes fluidized calcination in an air atmosphere, resulting in first-stage calcined gypsum material that enters the first airlock valve.

[0032] Furthermore, the gypsum enters the first chamber of the first-stage fluid roasting reactor. Air supplied by the second blower is blown in from the bottom of the reactor, passing through the air distribution plate to keep the gypsum in a fluid state, while simultaneously providing an air atmosphere for the first-stage roasting. The four walls of the first-stage fluid roasting reactor are equipped with electric heating devices to heat the furnace chamber. The roasting flue gas enters the first cyclone separator, while the gypsum material passes through a channel into the second chamber. In its fluid state, the gypsum material from the first-stage roasting enters the first airlock valve.

[0033] The first airlock valve is used to prevent gas leakage between the first-stage fluid roasting reactor and the second-stage fluid roasting reactor.

[0034] Step 3, Second-stage roasting

[0035] After initial roasting, the gypsum material is fed into the second-stage fluid roasting reactor via the first airlock valve. Fuel gas and air enter the high-temperature hot air generator for combustion, generating high temperatures. The required fluid roasting gas enters the bottom of the second-stage fluid roasting reactor via a flow valve, fluidizing the material while simultaneously subjecting it to second-stage roasting. The flue gas is separated by the second cyclone separator and then fed into the second dust collector. The second-stage roasted gypsum material enters the second airlock valve to prevent cross-contamination between the second-stage fluid roasting reactor and the second dust collector.

[0036] Step 4: Gas-solid separation and treatment system

[0037] The gypsum material from the second stage of calcination enters the second dust collector of the gas-solid separation and treatment system after passing through the second airlock valve. The discharge from the second dust collector is fed into a ball mill for fine grinding. The ball mill and vibrating screen form a closed circuit, with the product over the vibrating screen fed back into the ball mill. Furthermore, the product under the vibrating screen is the finely ground calcined product. Further, the flue gas from the second dust collector is discharged after being scrubbed in a gas scrubbing tower. Depending on the process, if the gas contains a useful product, it is collected; otherwise, it is discharged into the chimney.

[0038] The material flow path of this system is as follows: silo, screw feeder, first-stage fluid roasting reactor, first airlock valve, second-stage fluid roasting reactor, second airlock valve, second dust collector, ball mill, vibrating screen.

[0039] Furthermore, when this system is used to produce anhydrite:

[0040] In step two, the temperature in the fluid roasting reactor is 180–200℃, and the roasting time is 30–50 min. Adsorbed water and some crystal water in the raw ore are removed, and the gypsum's crystal structure is transformed into β-hemihydrate gypsum (CaSO4·2H2O—CaSO4·1 / 2H2O+3 / 2H2O), yielding a β-hemihydrate gypsum product with uniform and stable properties.

[0041] In step three, the fuel gas is selected from natural gas, coal gas, or coke oven gas. Air enters the bottom of the two-stage fluid roasting reactor through a flow valve, controlling the temperature inside the reactor to 780℃~820℃, and the roasting time to 50min~80min, while the gypsum layer remains in a fluid state. During this process, the water of crystallization in the β-hemihydrate gypsum lattice is further removed to form anhydrite (CaSO4·1 / 2H2O——CaSO4+1 / 2H2O). Furthermore, roasting removes water-soluble phosphorus from the phosphogypsum, reduces the eutectic phosphorus content, significantly reduces the fluorine content, and converts most of the impurities and organic matter into gaseous volatilization.

[0042] In step four, the flue gas from the second dust collector is washed by the gas scrubbing tower and then discharged through the chimney.

[0043] Furthermore, when this system is used to produce calcium oxide and sulfur dioxide:

[0044] In step two, the temperature in the fluid roasting reactor is 380–410°C, and the roasting time is 20–35 minutes. Most of the adsorbed water and crystal water in the raw ore are removed, and the crystal structure of the gypsum is transformed into anhydrous gypsum (CaSO4·2H2O—CaSO4+2H2O). Subsequently, the anhydrous gypsum is fed into the reduction decomposition process.

[0045] In step three, the fuel gas is selected from natural gas, blast furnace gas, or coke oven gas. The fuel gas or hydrogen enters the bottom of the two-stage fluid roasting reactor through a flow valve, controlling the temperature inside the reactor at 950–1050°C and the roasting time at 50–80 minutes. Anhydrous gypsum is reduced and decomposed into CaO and SO2 products under a reducing atmosphere (CaSO4+H2 → CaO+SO2+H2O, CaSO4+CO → CaO+SO2+CO2).

[0046] In step four, the flue gas from the second dust collector is washed by a gas scrubbing tower to obtain SO2 product.

[0047] Furthermore, when this system is used to produce calcium sulfide:

[0048] In step two, the temperature in the first-stage fluid roasting reactor is 380-400℃, and the roasting time is 40-60 minutes. Most of the adsorbed water and crystal water in the raw ore are removed, and the lattice structure of gypsum is transformed into anhydrous gypsum. Subsequently, the anhydrous gypsum is fed into the reduction and decomposition process.

[0049] And / or, in step three, the fuel gas is selected from natural gas, blast furnace gas or coke oven gas; the mixture of hydrogen and nitrogen enters the bottom of the two-stage fluid roasting reactor through a flow valve, and the temperature inside the two-stage fluid roasting reactor is controlled at 390-410℃, and the roasting time is 20-40 minutes; anhydrous gypsum is reduced and decomposed into calcium sulfide product under a reducing atmosphere;

[0050] And / or, in step four, the flue gas from the second dust collector is washed by the gas scrubbing tower and then discharged through the chimney.

[0051] Compared with existing technologies, the system and method for preparing valuable products by segmented fluid calcination of gypsum according to the present invention have the following advantages:

[0052] 1. This invention employs a segmented roasting technology in the gypsum roasting process. By precisely controlling the roasting atmosphere (air, coal gas, hydrogen), gas volume, and roasting temperature in the two stages, the phase transformation of gypsum is accurately regulated.

[0053] 2. This segmented fluid calcination system is suitable for three gypsum processing processes: gypsum → β-hemihydrate gypsum → anhydrite, gypsum → anhydrous gypsum → calcium oxide + sulfur dioxide, and gypsum → anhydrous gypsum → calcium sulfide.

[0054] 3. This invention provides a segmented fluid roasting technology applied to gypsum roasting. Compared to traditional rotary kiln and vertical shaft furnace roasting technologies, this technology achieves highly efficient gas-solid mass and heat transfer. Compared to other roasting furnaces, the fluid roasting furnace has advantages such as significantly reduced energy consumption, smaller flue gas volume, lower flue gas temperature, compact structure, and lower carbon emissions.

[0055] 4. In this invention, the two-stage fluid roasting process uses a high-temperature hot air generator as a separate heat source to achieve high-temperature oxidation roasting by heating the air entering the furnace. This solves the problem of insufficient temperature in the original equipment's two-stage fluid roasting reactor, which required electric heating assistance. Furthermore, the high-temperature hot air generator has high heat transfer efficiency for air, provides thorough heating, precise temperature control, and is relatively low in cost. Attached Figure Description

[0056] Figure 1 A schematic diagram of a system for preparing valuable products by segmented fluid calcination of gypsum;

[0057] In the diagram above, 1 is the silo, 2 is the screw feeder, 3 is the first cyclone separator, 4 is the first-stage fluid roasting reactor, 5 is the first dust collector, 6 is the first ash hopper, 7 is the first blower, 8 is the chimney, 9 is the first airlock valve, 10 is the second cyclone separator, 11 is the second-stage fluid roasting reactor, 12 is the second airlock valve, 13 is the third blower, 14 is the high-temperature hot air generator, 15 is the flow valve, 16 is the second dust collector, 17 is the air scrubbing tower, 18 is the ball mill, 19 is the vibrating screen, and 20 is the second blower. Detailed Implementation

[0058] Combined with appendix Figure 1 This invention provides a clear and complete description of the technical solutions implemented in this patent. It should be noted that the examples described in this invention are for further explanation and illustration only, and not for limiting its scope of application. All other embodiments obtained by those skilled in the art based on this invention without inventive effort are within the protection scope of this patent.

[0059] Example 1:

[0060] A schematic diagram of the system for preparing valuable products using segmented fluid calcination of gypsum is shown below. Figure 1 It mainly includes a feeding-dust removal system, a first-stage roasting system, a second-stage roasting system, and a gas-solid separation-treatment system.

[0061] The feeding-dust removal system includes a silo 1, a screw feeder 2, a first cyclone separator 3, a first dust collector 5, a first ash hopper 6, a first fan 7, and a chimney 8.

[0062] The aforementioned calcination system includes a fluid calcination reactor 4, a first airlock valve 9, and a second blower 20;

[0063] The two-stage roasting system includes a two-stage fluid roasting reactor 11, a second cyclone separator 10, a second airlock valve 12, a high-temperature hot air generator 14, a third fan 13, and a flow valve 15.

[0064] The gas-solid separation and treatment system includes a second dust collector 16, a gas scrubbing tower 17, a ball mill 18, and a vibrating screen 19.

[0065] The silo 1 is connected to the first cyclone separator 3 via the screw feeder 2. The flue gas outlet of the first cyclone separator 3 is connected to the first dust collector 5 and the first fan 7 in sequence. The dust outlet of the first dust collector 5 is connected to the first ash hopper 6. The first fan 7 is connected to the chimney 8.

[0066] The material outlet of the first cyclone separator 3 is connected to the material inlet of the first-stage fluid roasting reactor 4, the second blower 20 is connected to the lower air inlet of the first-stage fluid roasting reactor 4, and the material outlet of the first-stage fluid roasting reactor 4 is connected to the first airlock valve 9.

[0067] The first airlock valve 9 of the first-stage roasting system is connected to the second-stage fluid roasting reactor 11 of the second-stage roasting system. The material outlet of the second-stage fluid roasting reactor 11 is connected to the second airlock valve 12. The bottom of the second-stage fluid roasting reactor 11 is connected to the high-temperature hot air generator 14, which is equipped with an air inlet and a fuel gas inlet. A third fan 13 is installed on the pipe connected to the air inlet. The fluid roasting gas inlet is located at the bottom of the second-stage fluid roasting reactor 11, and a flow valve 15 is installed on the pipe.

[0068] The flue gas outlet of the two-stage fluid roasting reactor 11 is connected to the second cyclone separator 10. The material outlet separated by the second cyclone separator 10 is connected to the two-stage fluid roasting reactor 11. The flue gas outlet separated by the second cyclone separator 10 is connected to the second dust collector 16.

[0069] The second airlock valve 12 of the two-stage roasting system is connected to the second dust collector 16 of the gas-solid separation and treatment system. The flue gas outlet of the second dust collector 16 is connected to the scrubbing tower 17. The exhaust port of the scrubbing tower is not connected to the chimney and can directly collect the tail gas, or it can discharge the gas into the chimney. The discharge outlet of the second dust collector 16 is connected to the feed port of the ball mill 18. The discharge port of the ball mill 18 is connected to the vibrating screen 19. The product on the screen of the vibrating screen 19 is connected to the feed port of the ball mill 18, forming a closed-loop grinding and screening cycle. Furthermore, the solid roasting product is obtained from the discharge port at the bottom of the vibrating screen 19, and the roasting gas is obtained after being scrubbed by the scrubbing tower 17. If the roasting gas is a useful product, it needs to be collected; otherwise, it will be discharged into the chimney.

[0070] The internal structure of the single-stage and two-stage fluid roasting reactors is identical. A central baffle separates the fluid roasting reactor into two chambers, with a channel for material flow located below the baffle. The feed inlet is connected to the top of the first chamber, and the discharge outlet is connected to the upper-middle part of the outer side of the second chamber. An air distribution plate and an air inlet are located at the bottom of the reactor.

[0071] One section of the fluid roasting reactor is equipped with electric heating devices on all four sides of the furnace wall.

[0072] The system described above for preparing valuable products by segmented fluid calcination of gypsum was used to prepare anhydrite products by fluid calcination of a certain phosphogypsum in Jiangxi Province.

[0073] (1) The phosphogypsum ore in the silo 1 enters the first cyclone separator 3 through the screw feeder 2. After separation, it enters the first-stage fluid roasting reactor 4 for first-stage roasting.

[0074] After the flue gas in the gypsum is separated by the first cyclone separator 3, it is collected and treated by the first dust collector 5, the first ash hopper 6 and the first fan 7. The dust collected in the first dust collector 5 enters the first ash hopper 6, the separated flue gas enters the first fan 7 and is discharged through the chimney 8.

[0075] (2) The temperature inside the furnace chamber of the first-stage fluid calcination reactor 4 is set to 190℃ by electric heating. Air is blown into the bottom of the first-stage fluid calcination reactor 4 by the second blower 20, so that the gypsum inside the first-stage fluid calcination reactor 4 is in a fluid state, and at the same time, an air atmosphere is provided for the first-stage calcination. The gypsum reacts in the first-stage fluid calcination reactor 4 for 30 minutes. The crystal structure of the first-stage calcined gypsum is transformed into β-hemihydrate gypsum, and a β-hemihydrate gypsum product with uniform and stable properties is obtained. At the same time, the gypsum bed is kept in a fluidized state, and the obtained first-stage calcined gypsum material enters the first airlock valve 9.

[0076] (3) The gypsum material from the first stage of calcination enters the second-stage fluid calcination reactor 11 through the first airlock valve 9. Natural gas enters the high-temperature hot air generator 14 and is burned to generate high temperature. Air is blown into the high-temperature hot air generator 14 by the third blower 13 and is heated. The hot air enters the bottom of the second-stage fluid calcination reactor 11, heating the material in the reactor to 790°C for 50 minutes. At this time, the water of crystallization in the β-hemihydrate gypsum lattice is further removed to form anhydrite.

[0077] (4) The material after two-stage roasting enters the second dust collector 16 through the second airlock valve 12. The discharge from the second dust collector is fed into the ball mill 18 for fine grinding, and the ball mill 18 and the vibrating screen 19 form a closed circuit. The undersize product of the vibrating screen 19 is qualified anhydrite (CaSO4) product. The flue gas from the second dust collector 16 is scrubbed by the gas scrubbing tower and then discharged through the chimney 8.

[0078] Example 2:

[0079] Anhydrite products were prepared by staged fluid calcination using phosphogypsum from Sichuan as raw material.

[0080] (1) After being separated by the first cyclone separator 3 through the screw feeder 2, the phosphogypsum ore enters the first-stage fluid roasting reactor 4 for first-stage roasting.

[0081] (2) The temperature inside the furnace chamber of the first-stage fluid calcination reactor 4 is set to 180℃. Air is blown into the bottom of the first-stage fluid calcination reactor 4 by the second blower 20, so that the gypsum inside the first-stage fluid calcination reactor 4 is in a fluid state, and at the same time, an air atmosphere is provided for the first-stage calcination. The gypsum reacts in the first-stage fluid calcination reactor 4 for 30 minutes. After calcination, the crystal structure of the gypsum is transformed into β-hemihydrate gypsum, and a β-hemihydrate gypsum product with uniform and stable properties is obtained. At the same time, the gypsum bed is kept in a fluidized state, and the obtained first-stage calcined gypsum material enters the first airlock valve 9.

[0082] (3) The gypsum material from the first stage of calcination enters the second-stage fluid calcination reactor 11 through the first airlock valve 9. Natural gas enters the high-temperature hot air generator 14 and is burned to generate high temperature. Air is blown into the high-temperature hot air generator 14 by the third blower 13 and is heated. The hot air enters the bottom of the second-stage fluid calcination reactor 11, heating the material in the reactor to 790.4℃ for 68.5 minutes. At this time, the water of crystallization in the β-hemihydrate gypsum lattice is further removed to form anhydrite.

[0083] Furthermore, after the flue gas generated in the two-stage fluid roasting reactor 11 is separated by the second cyclone separator 10, part of it returns to the two-stage fluid roasting reactor 11, while the other part of the flue gas directly enters the second dust collector 16.

[0084] (4) The material after two-stage roasting enters the second dust collector 16 through the second airlock valve 12. The discharge from the second dust collector is fed into the ball mill 18 for fine grinding, and the ball mill 18 and the vibrating screen 19 form a closed circuit. The undersize product of the vibrating screen 19 is qualified anhydrite (CaSO4) product. The flue gas from the second dust collector 16 is scrubbed by the gas scrubbing tower and then discharged through the chimney 8.

[0085] Example 3:

[0086] Anhydrite products were prepared by staged fluid calcination using desulfurized gypsum from Chongqing as raw material.

[0087] (1) After being separated by the first cyclone separator 3 via the screw feeder 2, the desulfurized gypsum ore enters the first-stage fluid roasting reactor 4 for first-stage roasting.

[0088] (2) The temperature inside the furnace chamber of the first-stage fluid calcination reactor 4 is set to 200℃. Air is blown into the bottom of the first-stage fluid calcination reactor 4 by the second blower 20, so that the gypsum inside the first-stage fluid calcination reactor 4 is in a fluid state, while providing an air atmosphere for the first-stage calcination. The gypsum reacts in the first-stage fluid calcination reactor 4 for 45 minutes. The crystal structure of the gypsum in the first-stage calcination is transformed into β-hemihydrate gypsum.

[0089] (3) The gypsum material from the first stage of roasting enters the second-stage fluid roasting reactor 11 through the first airlock valve 9. Blast furnace gas enters the high-temperature hot air generator 14 and is burned to generate high temperature. Air is blown into the high-temperature hot air generator 14 by the third blower 13 and is heated. The hot air enters the bottom of the second-stage fluid roasting reactor 11, heating the material in the reactor to 818.6℃ for a roasting time of 67.2 min. At this time, the water of crystallization in the β-hemihydrate gypsum lattice is further removed to form anhydrite.

[0090] (4) The material after two-stage roasting enters the second dust collector 16 through the second airlock valve 12. The discharge from the second dust collector is fed into the ball mill 18 for fine grinding, and the ball mill 18 and the vibrating screen 19 form a closed circuit. The undersize product of the vibrating screen 19 is qualified anhydrite (CaSO4) product. The flue gas from the second dust collector 16 is scrubbed by the gas scrubbing tower and then discharged through the chimney 8.

[0091] Example 4:

[0092] Using the above-mentioned system for preparing valuable products by segmented fluid calcination of gypsum, sulfur dioxide and calcium oxide products were prepared by fluid calcination of a phosphogypsum in Guangdong.

[0093] (1) After being separated by the first cyclone separator 3 through the screw feeder 2, the phosphogypsum ore enters the first-stage fluid roasting reactor 4 for first-stage roasting.

[0094] (2) The temperature inside the furnace chamber of the first-stage fluid roasting reactor 4 is set at 390℃. Air is blown into the bottom of the first-stage fluid roasting reactor 4 by the second blower 20, so that the gypsum inside the first-stage fluid roasting reactor 4 is in a fluid state, and at the same time, an air atmosphere is provided for the first-stage roasting. The gypsum reacts in the first-stage fluid roasting reactor 4 for 30 minutes. Under the air atmosphere, the gypsum bed is kept in a fluidized state. The crystal water in the raw ore is gradually removed, and the crystal lattice structure of phosphogypsum is transformed into hemihydrate gypsum, and then into anhydrous gypsum. The gypsum material from the first-stage roasting enters the first airlock valve 9.

[0095] (3) The gypsum material from the first stage of roasting enters the second-stage fluid roasting reactor 11 through the first airlock valve 9. Coke oven gas enters the high-temperature hot air generator 14 and burns to generate high temperature. The mixture of gas and air (by volume, gas:air = 6:1) enters the bottom of the second-stage fluid roasting reactor 11 through the flow valve 15, heating the material in the second-stage fluid roasting reactor to 950℃ for 22 minutes. At this time, the anhydrous gypsum undergoes a reduction reaction under a hydrogen atmosphere to stably generate SO2 and CaO.

[0096] (4) The material after two-stage roasting enters the second dust collector 16 through the second airlock valve 12. The CaO discharge from the second dust collector is fed into the ball mill 18 for fine grinding, and the ball mill 18 and the vibrating screen 19 form a closed circuit. The undersize product of the vibrating screen 19 is a qualified CaO product. The flue gas from the second dust collector 16 is washed by the gas scrubbing tower to obtain a qualified SO2 gas product.

[0097] Example 5

[0098] Using the above-mentioned system for preparing valuable products by segmented fluid calcination of gypsum, sulfur dioxide and calcium oxide products were prepared by fluid calcination of a certain phosphogypsum in Fujian.

[0099] (1) After the phosphogypsum ore is separated by the first cyclone separator 3 through the screw feeder 2, it enters the first-stage fluid roasting reactor 4 for first-stage roasting.

[0100] (2) The temperature inside the furnace chamber of the first-stage fluid roasting reactor 4 is set at 410℃. Air is blown into the bottom of the first-stage fluid roasting reactor 4 by the second blower 20, so that the gypsum inside the first-stage fluid roasting reactor 4 is in a fluid state, and at the same time, an air atmosphere is provided for the first-stage roasting. The gypsum reacts in the first-stage fluid roasting reactor 4 for 35 minutes. Under the air atmosphere, the gypsum bed is kept in a fluidized state. The crystal water in the raw ore is gradually removed, and the crystal lattice structure of phosphogypsum is transformed into hemihydrate gypsum, and then into anhydrous gypsum. The first-stage roasting product enters the first airlock valve 9.

[0101] (3) The material from the first stage of roasting enters the second-stage fluid roasting reactor 11 through the first airlock valve 9. Blast furnace gas enters the high-temperature hot air generator 14 and burns to generate high temperature. The mixture of gas and air (by volume, gas:air = 8:1) enters the bottom of the second-stage fluid roasting reactor 11 through the flow valve 15, heating the material in the second-stage fluid roasting reactor to 990℃ for 32 minutes. At this time, anhydrous gypsum undergoes a reduction reaction under a hydrogen atmosphere to stably generate SO2 and CaO.

[0102] (4) The material after two-stage roasting enters the second dust collector 16 through the second airlock valve 12. The CaO discharge from the second dust collector is fed into the ball mill 18 for fine grinding, and the ball mill 18 and the vibrating screen 19 form a closed circuit. The undersize product of the vibrating screen 19 is a qualified CaO product. The flue gas from the second dust collector 16 is washed by the gas scrubbing tower to obtain a qualified SO2 gas product.

[0103] Example 6

[0104] Sulfur dioxide and calcium oxide products were prepared by fluid roasting of phosphogypsum from Shaanxi Province.

[0105] (1) After being separated by the first cyclone separator 3 through the screw feeder 2, the phosphogypsum ore enters the first-stage fluid roasting reactor 4 for first-stage roasting.

[0106] (2) The temperature inside the furnace chamber of the first-stage fluid roasting reactor 4 is set to 405℃. Air is blown into the bottom of the first-stage fluid roasting reactor 4 by the second blower 20, so that the gypsum inside the first-stage fluid roasting reactor 4 is in a fluid state, and at the same time, an air atmosphere is provided for the first-stage roasting. The gypsum reacts in the first-stage fluid roasting reactor 4 for 31 minutes. Under the air atmosphere, the gypsum bed is kept in a fluidized state. The gypsum material product from the first-stage roasting enters the first airlock valve 9.

[0107] (3) Two-stage fluid roasting reactor 11 for gypsum material in the first stage of roasting. Natural gas enters the high-temperature hot air generator 14 and is burned to generate high temperature. A mixture of hydrogen and nitrogen (by volume, H2:N2 = 0.4:1) enters the bottom of the two-stage fluid roasting reactor 11 through the flow valve 15, heating the material in the reactor to 390°C for 18 minutes. At this time, anhydrous gypsum undergoes a reduction reaction under a hydrogen atmosphere to stably generate calcium sulfide.

[0108] (4) The material after two-stage roasting enters the second dust collector 16 through the second airlock valve 12. The calcium sulfide discharge from the second dust collector is fed into the ball mill 18 for fine grinding, and the ball mill 18 and the vibrating screen 19 form a closed circuit. The undersize product of the vibrating screen 19 is a qualified calcium sulfide product. The flue gas from the second dust collector 16 is scrubbed by the gas scrubbing tower and then discharged into the air through the chimney.

[0109] Example 7

[0110] Same as Example 1, except that the temperature inside the two-stage fluid calcination reactor is 820°C, while other conditions remain unchanged. After crushing and screening, qualified anhydrite products are obtained.

[0111] Example 8

[0112] Similar to Example 4, except that the temperature in the first-stage fluid roasting reactor is 400°C, and the temperature in the second-stage fluid roasting reactor is 1050°C, while other conditions remain unchanged. Finally, qualified calcium oxide and sulfur dioxide gas products are obtained.

[0113] Comparative Example 1

[0114] A system and method for preparing valuable products by segmented fluid calcination of gypsum is described below. The difference between this system and the system of the present invention is that without a segmented fluid calcination system, the quality of the calcined product is poor, and it is impossible to stably produce qualified anhydrite products.

[0115] Comparative Example 2

[0116] A system and method for preparing valuable products by segmented fluid calcination of gypsum is described in Example 3. The difference between the system and the system of the present invention is that without a segmented fluid calcination system, the phosphogypsum reacts directly with the reducing gas, resulting in extremely poor performance and an inability to stably produce qualified sulfur dioxide and calcium oxide products.

Claims

1. A method for preparing valuable products by staged fluid calcination of gypsum, characterized in that, Includes the following steps: Step 1: Feeding and Dust Removal Gypsum is fed from the silo into the first cyclone separator via a screw feeder. After separation, it enters the first-stage fluid calcination reactor. Step 2, First-stage roasting Gypsum enters a first-stage fluid calcination reactor and undergoes fluidized calcination in an air atmosphere, resulting in first-stage calcined gypsum material that enters the first airlock valve. Step 3, Second-stage roasting After the first stage of calcination, the gypsum material is fed into the second stage fluid calcination reactor through the first airlock valve. The fuel gas and air enter the high-temperature hot air generator for combustion to generate high temperature. The calcination gas required for calcination enters the bottom of the second stage fluid calcination reactor through the flow valve, so that the material is fluidized and calcined in the second stage. The flue gas is separated by the second cyclone separator and fed into the second dust collector; the gypsum material from the second stage of roasting enters the second airlock valve; Step 4: Gas-solid separation and treatment system The gypsum material from the second stage of calcination enters the second dust collector of the gas-solid separation-treatment system after passing through the second airlock valve. The discharge from the second dust collector is fed into a ball mill for fine grinding. The ball mill and the vibrating screen form a closed circuit. The product on the vibrating screen is fed into the ball mill. The product under the vibrating screen is the finely ground calcined product. The flue gas from the second dust collector is discharged after being scrubbed by a gas scrubbing tower. Depending on the process, it can be collected or vented. The preparation of anhydrite, calcium oxide, and calcium sulfide is achieved within a single system. Precise control of the calcination atmosphere, gas flow, and calcination temperature during the two-stage calcination process allows for precise regulation of the gypsum phase transformation. When the product is anhydrite: In step two, the first-stage roasting temperature is 180℃~200℃, and the time is 30min~50min, resulting in β-hemihydrate gypsum; In step three, air enters the bottom of the second-stage fluid roasting reactor through a flow valve, and the second-stage roasting temperature is 780℃~820℃, and the time is 50min~80min, converting β-hemihydrate gypsum into anhydrite; In step four, the finely ground roasted product is the anhydrite product, and the flue gas is discharged after being scrubbed by a gas scrubbing tower. When the products are calcium oxide and sulfur dioxide: In step two, the first-stage roasting temperature is 380℃~410℃, and the time is 20min~35min, resulting in anhydrous gypsum; In step three, the mixture of coal gas and air enters the bottom of the second-stage fluid roasting reactor through a flow valve, and the second-stage roasting temperature is 950℃~1050℃, and the time is 50min~80min, during which the anhydrous gypsum decomposes into CaO and SO2; In step four, the finely ground roasted product is CaO, and the flue gas is scrubbed through a gas scrubbing tower to obtain SO2. When the product is calcium sulfide: In step two, the temperature of the first-stage roasting is 380℃~400℃, and the time is 40min~60min, and anhydrous gypsum is obtained from the first-stage roasting; In step three, the mixed gas of hydrogen and nitrogen enters the bottom of the second-stage fluid roasting reactor through the flow valve, and the temperature of the second-stage roasting is 390℃~410℃, and the time is 20min~40min, and anhydrous gypsum decomposes into calcium sulfide; In step four, the finely ground roasted product is the calcium sulfide product, and the flue gas is discharged after being scrubbed by the gas scrubbing tower.

2. The method for preparing valuable products by segmented fluid calcination of gypsum according to claim 1, characterized in that, It includes a feeding-dust removal system, a primary roasting system, a secondary roasting system, and a gas-solid separation-treatment system; the feeding-dust removal system, the primary roasting system, the secondary roasting system, and the gas-solid separation-treatment system are connected in sequence.

3. The method for preparing valuable products by segmented fluid calcination of gypsum according to claim 2, characterized in that, The feeding-dust removal system includes a silo, a screw feeder, a first cyclone separator, a first dust collector, a first ash hopper, a first fan, and a chimney; The silo is connected to the first cyclone separator via a screw feeder. The flue gas outlet of the first cyclone separator is connected to the first dust collector and the first fan in sequence. The dust outlet of the first dust collector is connected to the first ash hopper. The first fan is connected to the chimney.

4. The method for preparing valuable products by segmented fluid calcination of gypsum according to claim 3, characterized in that, The aforementioned calcination system includes a fluid calcination reactor, a first airlock valve, and a second blower; The material outlet of the first cyclone separator is connected to the material inlet of the first-stage fluid roasting reactor, the second blower is connected to the lower air inlet of the first-stage fluid roasting reactor, and the material outlet of the first-stage fluid roasting reactor is connected to the first airlock valve.

5. The method for preparing valuable products by segmented fluid calcination of gypsum according to claim 4, characterized in that, The two-stage roasting system includes a two-stage fluid roasting reactor, a second cyclone separator, a second airlock valve, a high-temperature hot air generator, a third fan, and a flow valve. The first airlock valve of the first-stage roasting system is connected to the second-stage fluid roasting reactor of the second-stage roasting system. The material outlet of the second-stage fluid roasting reactor is connected to the second airlock valve. The bottom of the second-stage fluid roasting reactor is connected to a high-temperature hot air generator, which is equipped with an air inlet and a fuel gas inlet. A third fan is installed on the pipe connected to the air inlet. The fluid roasting gas inlet is located at the bottom of the second-stage fluid roasting reactor, and a flow valve is installed on the pipe. One or more of hydrogen, air, coal gas, and nitrogen are introduced into the fluid roasting gas inlet, and the specific gas introduced is determined according to the product being prepared.

6. The method for preparing valuable products by segmented fluid calcination of gypsum according to claim 5, characterized in that, The flue gas outlet of the two-stage fluid roasting reactor is connected to the second cyclone separator. The material outlet separated by the second cyclone separator is connected to the two-stage fluid roasting reactor. The flue gas outlet separated by the second cyclone separator is connected to the second dust collector.

7. The method for preparing valuable products by segmented fluid calcination of gypsum according to claim 5, characterized in that, The gas-solid separation and treatment system includes a second dust collector, a gas scrubbing tower, a ball mill, and a vibrating screen. The second airlock valve of the two-stage roasting system is connected to the second dust collector of the gas-solid separation-treatment system. The flue gas outlet of the second dust collector is connected to the scrubbing tower. The discharge outlet of the second dust collector is connected to the feed port of the ball mill. The discharge port of the ball mill is connected to the vibrating screen. The product on the vibrating screen is connected to the feed port of the ball mill, forming a closed-loop grinding and screening cycle. The solid roasting product is obtained from the discharge port at the bottom of the vibrating screen, and the roasting gas is obtained after being scrubbed by the scrubbing tower.

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