Active magnesium oxide suspension calcination system and method

Abstract

The invention provides an active magnesium oxide suspension calcination system and method, and belongs to the technical field of magnesium oxide calcination, the active magnesium oxide suspension calcination system comprises a primary suspension calcination kiln, a closed air discharger, a secondary decomposition rotary furnace, a sealing channel, a rotary heat conversion furnace, a cold air inlet, an unloader and a combustion-supporting hot air pipeline; the primary suspension calcining furnace is provided with a feed port, a discharge port, a flue gas outlet and a fuel gas inlet, the flue gas outlet is communicated with a dust removal system, and a smoke outlet of the dust removal system is connected with a chimney through an induced draft fan; the first-stage suspension calcining kiln, the second-stage decomposition rotary furnace and the rotary heat conversion furnace are used in cooperation, the high decomposition rate and the high chemical activity of magnesium oxide are achieved at the same time, and therefore the produced active magnesium oxide has the excellent chemical activity and the high magnesium oxide content; and a traditional air cooling system is changed into reverse heat exchange slow cooling, so that reversible reaction of carbon dioxide and magnesium oxide is prevented, and the purity of magnesium oxide is guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of magnesium oxide calcination technology, specifically relating to an active magnesium oxide suspension calcination system and method. Background Technology

[0002] Suspension calcination technology has become an important process for producing active magnesium oxide from calcined magnesite powder due to its advantages such as low investment, low energy consumption, and high degree of automation. The magnesite powder after flotation and silica removal has a particle size of 200 mesh or larger, with a small portion of coarser particles ≥150 mesh.

[0003] For example, the patent with announcement number CN110204226B proposes a high-temperature suspension fluidization rapid calcination process and system for powder materials, which overcomes the drawback of the inability of powder to be calcined at high temperatures in the traditional processing technology of magnesite. It adopts a horizontal rolling suspension calcination device to realize the suspension fluidization of powder materials, and at the same time uses the hot flue gas after calcination to dehydrate and dry the magnesite powder and produce steam, so that the heat recovery utilization rate of the system reaches more than 90%.

[0004] However, in existing technologies, due to the short calcination time in suspension kilns, a small portion of larger magnesite particles cannot be completely decomposed. Increasing the calcination temperature can ensure complete decomposition of the calcined magnesium oxide, but it reduces chemical activity, affecting the product's application. Therefore, it is impossible to simultaneously achieve high decomposition rate and high chemical activity of magnesium oxide. Furthermore, in existing technologies, incompletely decomposed magnesite particles, along with the calcined product, are removed from the calcination zone and rapidly cooled to recover heat from the calcined magnesium oxide. During this rapid cooling, carbon dioxide released from the magnesium oxide reacts with the calcined magnesium oxide to form magnesium carbonate, leading to a decrease in magnesium oxide content. This phenomenon is widespread and represents a common technical shortcoming of suspension calcination. Summary of the Invention

[0005] Based on the above-mentioned technical problems, the purpose of this invention is to provide an active magnesium oxide suspension calcination system and method. By using a primary suspension calcination kiln, a secondary decomposition rotary furnace, and a reversible heat exchange furnace in combination, a high decomposition rate and high chemical activity of magnesium oxide are achieved simultaneously, resulting in active magnesium oxide with excellent chemical activity and high magnesium oxide content. Furthermore, the traditional air-cooling system is replaced with reverse heat exchange for slow cooling, preventing the reversible reaction between carbon dioxide and magnesium oxide, thereby ensuring the purity of magnesium oxide.

[0006] The specific technical solution is as follows: An active magnesium oxide suspension calcination system includes: a primary suspension calcination kiln, a closed-loop discharge device, a secondary decomposition rotary furnace, a sealed channel, a regenerative thermal calcination furnace, a cold air inlet, a discharge machine, and a combustion-supporting hot air pipeline. The primary suspension calcination furnace has a feed inlet, a discharge outlet, a flue gas outlet, and a fuel gas inlet. The flue gas outlet is connected to a dust removal system, and the exhaust outlet of the dust removal system is connected to a chimney via an induced draft fan. The feed inlet and discharge outlet of the closed-loop discharge device are respectively connected to the discharge outlet of the primary suspension calcination kiln and the feed inlet of the secondary decomposition rotary furnace. The two ends of the sealed channel are respectively connected to the discharge outlet of the secondary decomposition rotary furnace and the feed inlet of the regenerative thermal calcination furnace. The discharge machine is connected to the discharge outlet of the regenerative thermal calcination furnace. The cold air inlet is connected to the end of the regenerative thermal calcination furnace. The two ends of the combustion-supporting hot air pipeline are respectively connected to the secondary decomposition rotary furnace and the primary suspension calcination furnace.

[0007] In addition, the active magnesium oxide suspension calcination system provided by the present invention may also have the following additional technical features: In the above technical solution, the dust removal system includes a dryer and a pulse dust collector. The inlet of the dryer is connected to the flue gas outlet of the primary suspension calcining kiln, the outlet of the dryer is connected to the inlet of the pulse dust collector, and the outlet of the pulse dust collector is connected to the induced draft fan.

[0008] A method for calcining active magnesium oxide in suspension includes the following steps: S1: Magnesite powder is fed into a primary suspension calcining kiln and rapidly suspended calcined at a temperature of 750℃-850℃ to obtain a mixed hot feed containing active magnesium oxide and incompletely decomposed coarse particles. S2: The mixture is sealed and fed into the secondary decomposition rotary furnace through the closed-air unloader. The furnace speed and inclination are controlled so that the hot material passes through the furnace slowly over a period of 1-4 hours. The temperature of the hot material is slowly reduced from 750℃ to 500℃ to ensure that the coarse particles that are not completely decomposed are decomposed. S3: The completely decomposed magnesium oxide is fed into the rotary kiln; cold air enters from the end of the rotary kiln under the negative pressure of the induced draft fan, and exchanges heat with the magnesium oxide powder moving forward in the furnace in a counter-current contact; after the cold air is gradually heated to above 300°C, it enters the secondary decomposition rotary kiln and continues to exchange heat with the powder at a higher temperature in a counter-current contact, and is finally heated to above 500°C to form high-temperature combustion air; at the same time, during the counter-current heat exchange process, when the powder is lifted and falls by the rolling action of the rotary kiln and the secondary decomposition rotary kiln, the carbon dioxide in the powder is released and is carried away by the counter-current air in time; S4: High-temperature combustion air is introduced into the primary suspension calcining furnace and mixed with the fuel gas for combustion, providing a heat source for the primary suspension calcining kiln in step S1. S5: The material discharged after being cooled by the regenerative thermal annealing furnace is discharged through the unloading machine, thereby obtaining a highly active and high-purity active magnesium oxide product.

[0009] The active magnesium oxide suspension calcination system and method of the present invention have the following advantages compared with the prior art: 1. The magnesite powder is initially decomposed in a primary suspension calcination kiln, and the secondary decomposition rotary kiln provides sufficient reaction time for the incompletely decomposed coarse particles, ensuring the complete decomposition of the incompletely decomposed coarse particles of magnesite powder. This ensures a high decomposition rate and maintains high chemical activity, resulting in active magnesium oxide with excellent chemical activity and high magnesium oxide content.

[0010] 2. By eliminating rapid air cooling and adopting a closed, insulated two-stage decomposition rotary kiln and a regenerative thermal conversion furnace for slow cooling, a channel and time are provided for the carbon dioxide produced during decomposition to escape. Simultaneously, under the negative pressure created by the induced draft fan, cold air is drawn in from the end of the regenerative thermal conversion furnace in a counter-current manner. During the heat exchange with the material, on the one hand, the escaping carbon dioxide is promptly carried away, reducing the risk of reversible side reactions between carbon dioxide and active magnesium oxide and ensuring product purity; on the other hand, the cold air is heated by the material in stages, eventually transforming into high-temperature combustion-supporting hot air which enters the primary suspension calcining kiln, thus constructing a heat energy recovery and utilization system and reducing energy consumption. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the structure of an active magnesium oxide suspension calcination system according to the present invention; in, Figure 1 The correspondence between the reference numerals and component names in the attached drawings is as follows: 10 Primary suspension calcining kiln, 11 Closed-loop discharge device, 12 Secondary decomposition rotary furnace, 13 Sealed channel, 14 Regenerative heat exchange furnace, 15 Cold air inlet, 16 Unloader, 17 Combustion hot air duct, 18 Flue gas outlet, 19 Gas inlet, 20 Dryer, 21 Pulse dust collector, 22 Exhaust fan, 23 Chimney. Detailed Implementation

[0012] The following are specific implementation cases and appendices. Figure 1 The present invention will be further described, but the present invention is not limited to these embodiments.

[0013] An active magnesium oxide suspension calcination system, such as Figure 1As shown, it includes: a primary suspension calcining kiln 10, a closed-loop discharge device 11, a secondary decomposition rotary kiln 12, a sealed channel 13, a regenerative heat exchange furnace 14, a cold air inlet 15, a discharge machine 16, and a combustion-supporting hot air pipeline 17; the primary suspension calcining kiln is equipped with a feed inlet, a discharge outlet, a flue gas outlet 18, and a gas inlet 19. The flue gas outlet 18 is connected to a dust removal system, and the exhaust port of the dust removal system is connected to a chimney 23 via an induced draft fan 22; the closed-loop discharge device 11 has a feed inlet and a discharge outlet... The outlets of the two-stage suspension calcining kiln 10 and the inlet of the secondary decomposition rotary kiln 12 are respectively connected; the two ends of the sealed channel 13 are respectively connected to the outlet of the secondary decomposition rotary kiln 12 and the inlet of the regenerative heat exchanger 14; the unloading machine 16 is connected to the outlet of the regenerative heat exchanger 14; the cold air inlet 15 is connected to the end of the regenerative heat exchanger 14; and the two ends of the combustion-supporting hot air pipe 17 are respectively connected to the secondary decomposition rotary kiln 12 and the primary suspension calcining kiln.

[0014] Using the above structure, the magnesite powder is initially decomposed in the primary suspension calcining kiln 10, and the secondary decomposition rotary kiln 12 provides sufficient reaction time for the incompletely decomposed coarse particles, ensuring complete decomposition of the incompletely decomposed coarse particles. This guarantees a high decomposition rate and maintains high chemical activity, resulting in active magnesium oxide with excellent chemical activity and high magnesium oxide content. The calcined active magnesium oxide is slowly cooled in the recirculation furnace 14. Simultaneously, under the negative pressure created by the induced draft fan 22, cold air is drawn in counter-currently from the end of the recirculation furnace 14, exchanging heat with the materials rising and falling within the recirculation furnace 14 and the secondary decomposition rotary kiln 12. This process not only promptly removes the escaping carbon dioxide, reducing the risk of reversible side reactions between carbon dioxide and active magnesium oxide and ensuring product purity, but also gradually heats the cold air through the materials, ultimately converting it into high-temperature combustion air which enters the primary suspension calcining kiln 10, thus constructing a heat recovery and utilization system and reducing energy consumption.

[0015] Specifically, the material inlets and outlets of the primary suspension calcining kiln 10, the closed-loop discharge device 11, the secondary decomposition rotary kiln 12, the sealed channel 13, the regenerative thermal annealing furnace 14, and the unloading machine 16 are all sealed together via pipelines, forming a continuous, closed material and hot air channel throughout the system. Furthermore, the cold air inlet 15 of the regenerative thermal annealing furnace 14 is open to the atmosphere, and the combustion air outlet of the secondary decomposition rotary kiln 12 is connected to the combustion air inlet of the primary suspension calcining kiln 10 via a combustion air pipeline 17, thus forming a complete and closed hot air circulation path.

[0016] Specifically, the material cooling time in the rotary kiln 14 is 1-4 hours, and the material decomposition time in the secondary decomposition rotary kiln 12 is 1-4 hours.

[0017] Specifically, both the secondary decomposition rotary furnace 12 and the rotary heat exchange furnace 14 are sealed rotary calcining furnaces with insulation.

[0018] In an embodiment of the present invention, the dust removal system includes a dryer 20 and a pulse dust collector 21. The inlet of the dryer 20 is connected to the flue gas outlet 18 of the primary suspension calcining kiln 10, the outlet of the dryer 20 is connected to the inlet of the pulse dust collector 21, and the outlet of the pulse dust collector 21 is connected to the induced draft fan 22.

[0019] The flue gas from the primary suspension calcining kiln 10 is discharged into the dryer 20 for drying and then enters the pulse dust collector 21 for dust removal. After dust removal, it is discharged through the chimney 23.

[0020] By setting up an induced draft fan 22, cold air from the outside enters the rotary kiln 14 under negative pressure, flows counter-currently with the material moving forward in the furnace, and completes a heat exchange. Then, it flows sequentially through the sealed channel 13 and the secondary decomposition rotary kiln 12, where it comes into counter-current contact with the material at a higher temperature, completing a secondary heat exchange. Finally, it enters the primary suspension calcining kiln 10 through the combustion hot air pipe 17 and mixes with the fuel gas to provide a heat source for the primary suspension calcining kiln 10.

[0021] A method for calcining active magnesium oxide in suspension includes the following steps: S1: Magnesite powder is fed into a primary suspension calcining kiln 10 and rapidly suspended calcined at a temperature of 750℃-850℃ to obtain a mixed hot feed containing active magnesium oxide and incompletely decomposed coarse particles. S2: The mixed hot material is sealed and fed into the secondary decomposition rotary furnace 12 through the closed air unloader. The furnace speed and inclination are controlled so that the hot material passes through the furnace slowly in a 1-4 hour travel time. The temperature of the hot material is slowly reduced from 750℃ to 500℃ to ensure that the coarse particles that are not completely decomposed are decomposed. S3: The completely decomposed magnesium oxide is fed into the regenerative thermal converter 14; cold air enters from the end of the regenerative thermal converter 14 under the negative pressure of the induced draft fan 22, and exchanges heat with the magnesium oxide powder moving forward in the furnace in a counter-current contact; after the cold air is gradually heated to above 300°C, it enters the secondary decomposition rotary furnace 12, and continues to exchange heat with the powder at a higher temperature in a counter-current contact, and is finally heated to above 500°C to form high-temperature combustion air; at the same time, during the counter-current heat exchange process, when the powder is lifted and falls under the rolling action of the regenerative thermal converter 14 and the secondary decomposition rotary furnace 12, the carbon dioxide in the powder is released and is carried away by the counter-current air in time; S4: High-temperature combustion air is introduced into the primary suspension calcining furnace and mixed with the fuel gas for combustion, providing a heat source for the primary suspension calcining kiln 10 in step S1. S5: The material discharged after being cooled by the regenerative thermal furnace 14 is discharged through the unloading machine 16, thereby obtaining a highly active and high-purity active magnesium oxide product.

[0022] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An active magnesium oxide suspension calcination system, characterized in that, include: The system comprises a primary suspension calcining kiln, a closed-loop discharge device, a secondary decomposition rotary kiln, a sealed channel, a regenerative thermal annealing furnace, a cold air inlet, a discharge machine, and a combustion-supporting hot air pipeline. The primary suspension calcining kiln has a feed inlet, a discharge outlet, a flue gas outlet, and a fuel gas inlet. The flue gas outlet is connected to a dust removal system, and the dust removal system's exhaust outlet is connected to a chimney via an induced draft fan. The feed inlet and discharge outlet of the closed-loop discharge device are respectively connected to the discharge outlet of the primary suspension calcining kiln and the feed inlet of the secondary decomposition rotary kiln. Both ends of the sealed channel are respectively connected to the discharge outlet of the secondary decomposition rotary kiln and the feed inlet of the regenerative thermal annealing furnace. The discharge machine is connected to the discharge outlet of the regenerative thermal annealing furnace. The cold air inlet is connected to the end of the regenerative thermal annealing furnace. Both ends of the combustion-supporting hot air pipeline are respectively connected to the secondary decomposition rotary kiln and the primary suspension calcining kiln.

2. The active magnesium oxide suspension calcination system according to claim 1, characterized in that, The dust removal system includes a dryer and a pulse dust collector. The inlet of the dryer is connected to the flue gas outlet of the primary suspension calcining kiln, the outlet of the dryer is connected to the inlet of the pulse dust collector, and the outlet of the pulse dust collector is connected to an induced draft fan.

3. A method for calcining activated magnesium oxide in suspension, based on the activated magnesium oxide in suspension calcination system according to any one of claims 1-2, characterized in that, Includes the following steps: S1: Magnesite powder is fed into a primary suspension calcining kiln and rapidly suspended calcined at a temperature of 750℃-850℃ to obtain a mixed hot feed containing active magnesium oxide and incompletely decomposed coarse particles. S2: The mixture is sealed and fed into the secondary decomposition rotary furnace through the closed-air unloader. The furnace speed and inclination are controlled so that the hot material passes through the furnace slowly over a period of 1-4 hours. The temperature of the hot material is slowly reduced from 750℃ to 500℃ to ensure that the coarse particles that are not completely decomposed are decomposed. S3: The completely decomposed magnesium oxide is fed into the rotary kiln; cold air enters from the end of the rotary kiln under the negative pressure of the induced draft fan, and exchanges heat with the magnesium oxide powder moving forward in the furnace in a counter-current contact; after the cold air is gradually heated to above 300°C, it enters the secondary decomposition rotary kiln and continues to exchange heat with the powder at a higher temperature in a counter-current contact, and is finally heated to above 500°C to form high-temperature combustion air; at the same time, during the counter-current heat exchange process, when the powder is lifted and falls by the rolling action of the rotary kiln and the secondary decomposition rotary kiln, the carbon dioxide in the powder is released and is carried away by the counter-current air in time; S4: High-temperature combustion air is introduced into the primary suspension calcining furnace and mixed with the fuel gas for combustion, providing a heat source for the primary suspension calcining kiln in step S1. S5: The material discharged after being cooled by the regenerative thermal annealing furnace is discharged through the unloading machine, thereby obtaining a highly active and high-purity active magnesium oxide product.

Images