A high thermal efficiency aluminum hydroxide calcination process and equipment

Abstract

A high-efficiency aluminum hydroxide roasting process and equipment, comprising: a cooling process, a drying process, a feeding process, a preheating process, a roasting process, and a tail gas treatment process. This invention adds a drying process to the traditional aluminum hydroxide roasting process. The residual heat from part of the high-temperature air output from the cooling process is used as the drying heat source to dry the wet aluminum hydroxide raw material, thereby removing free water and reducing the heat consumption of aluminum hydroxide roasting. The cyclone preheater and cyclone cooler of this invention are both high-efficiency cyclones, improving the separation efficiency of the preheating and cooling systems. The high-temperature air discharged from the cooling process is divided into two paths: one path provides sufficient oxygen and some heat for fuel combustion in the furnace; the other path utilizes the heat in the high-temperature air as the heat source for drying the wet aluminum hydroxide raw material, achieving full utilization of the heat carried by the high-temperature alumina, thereby further reducing the roasting heat consumption.

Description

Technical Field

[0001] This invention relates to the field of alumina production technology, specifically to a high thermal efficiency aluminum hydroxide roasting process and equipment. Background Technology

[0002] Aluminum hydroxide roasting is the final step in the production of metallurgical-grade alumina. The main process unit for converting aluminum hydroxide into alumina is the aluminum hydroxide roasting furnace. Wet aluminum hydroxide raw material from the upstream process is metered and fed into the furnace. Inside, relying on the heat provided by fuel combustion, the wet aluminum hydroxide undergoes a series of reactions during the heating process, including the removal of all free water, almost all water of crystallization, and partial crystal transformation, ultimately yielding a qualified metallurgical-grade alumina product. The reactions occurring sequentially during this process are as follows:

[0003] 1) Removal of free water

[0004] H₂O(l) = H₂O↑ (100~120℃)

[0005] 2) Removal of water of crystallization

[0006] Al2O3·3H2O=Al2O3·H2O+2H2O↑ (268~308℃)

[0007] Al2O3·H2O=γ-Al2O3+H2O↑ (473~548℃)

[0008] 3) Alumina crystal transformation

[0009] γ-Al2O3=α-Al2O3(>900℃)

[0010] Traditionally, aluminum hydroxide roasting is done in a roasting kiln. In modern times, with the widespread adoption of fluidized bed technology, fluidized bed roasting technology for aluminum hydroxide has also been continuously developing, improving, and maturing, and is now widely used both domestically and internationally. The fluidized bed roasting process suspends preheated material in an airflow, greatly increasing the surface area of ​​contact between the hot airflow and the particles, resulting in a highly vigorous heat exchange process. The suspended material can be heated in a very short time. Therefore, compared to a roasting kiln, the fluidized bed roasting furnace for aluminum hydroxide exhibits a series of advantages, including higher output, lower investment per unit product, lower roasting heat consumption, and lower pollutant emissions.

[0011] Currently, widely used fluidized bed roasting equipment for aluminum hydroxide includes Alcoa's fluidized bed flash roaster (flash furnace), Lurgi's circulating fluidized bed roaster (circulating furnace), and Smith's gaseous suspension roaster (suspension furnace), among others. In China, Smith's gaseous suspension roaster is the most widely used. Taking Smith's gaseous suspension roaster as an example, its process flow can be divided into three parts: the main roasting furnace, the preheating system, and the cooling system. All combustion enters the main roasting furnace, and the released heat is used to complete part of the removal of crystal water and almost all crystal transformation. The high-temperature flue gas exiting the main roasting furnace enters the preheating system to preheat the material, and completes the removal of all free water and part of the crystal water during the preheating process. The high-temperature product exiting the main roasting furnace enters the cooling system and undergoes staged cooling with the ambient air entering the cooling system before entering the downstream process. The heated air then enters the main roasting furnace as fuel.

[0012] The main drawbacks of current fluidized bed calcining furnaces for aluminum hydroxide are:

[0013] 1) Low thermal efficiency

[0014] In alumina calcination systems, approximately 30% of the heat consumed is lost as flue gas heat exiting the preheating system and product heat exiting the cooling system. To optimize the utilization of this flue gas heat and product heat, an oxygen concentration meter is installed at the preheating system outlet, and the system's airflow is controlled based on the air process coefficient. When the oxygen concentration is too high, the amount of air entering the cooling system increases, leading to a significant reduction in the product temperature exiting the cooling system and a corresponding decrease in product heat. However, this also increases the amount of flue gas exiting the preheating system. Conversely, the reduction in product temperature in the cooling system is smaller. Therefore, current alumina calcination systems cannot simultaneously achieve relatively low levels of flue gas heat exiting the preheating system and product heat exiting the cooling system, making it difficult to effectively improve thermal efficiency.

[0015] 2) Inefficient material flow

[0016] Currently, the alumina products in the roasting process come from two sources: one is the material entering the cooling system after passing through the roasting furnace; the other is fly ash collected by bag filters from the flue gas exiting the preheating system. The fly ash contains a significant amount of unroasted aluminum hydroxide raw material, which, when mixed into the product, easily increases the aluminum hydroxide impurities and leads to a higher loss on ignition, thus affecting product quality. Therefore, the current production measure is to increase the temperature inside the roasting furnace to minimize the aluminum hydroxide content in the material exiting the furnace, thereby ensuring product quality even after fly ash is incorporated. However, increasing the temperature inside the roasting furnace also causes a rise in the temperature of the flue gas exiting the preheating system, increasing roasting heat consumption.

[0017] Alumina production plays a vital role in my country's metallurgical industry, consuming significant amounts of energy. Although the heat consumption of fluidized bed roasting furnaces has been greatly reduced compared to traditional processes like roasting kilns, the current system heat consumption of fluidized bed roasting furnaces is approximately 2.9–3.2 GJ / t-Al₂O₃. Of the heat released during combustion, about 60% is used to complete the roasting reaction, while the remaining 40% is dissipated into the environment through heat dissipation from the system surface, flue gas heat from the preheating system, and product heat from the cooling system, resulting in low system thermal efficiency. With the introduction of "dual carbon" targets, the alumina industry still faces considerable pressure to save energy and reduce consumption. Therefore, improving existing fluidized bed roasting processes and equipment for aluminum hydroxide is of great significance. Summary of the Invention

[0018] Based on the technical problems mentioned above, the present invention provides a high thermal efficiency aluminum hydroxide roasting process and equipment to improve the thermal efficiency utilization rate in the fluidized bed roasting process of aluminum hydroxide, thereby achieving energy saving and consumption reduction.

[0019] To achieve the above objectives, the present invention provides a high thermal efficiency aluminum hydroxide calcination process, comprising the following steps:

[0020] 1) Cooling process:

[0021] The high-temperature alumina output after calcination is mixed with ambient air input from the outside for heat exchange. Then, after gas-solid separation, the alumina product with reduced temperature and the high-temperature air are output. The high-temperature air is divided into two streams for output so that the recovered heat can be fully utilized in the subsequent process. The high-temperature alumina output after calcination refers to the high-temperature alumina product produced and output by the subsequent calcination process.

[0022] 2) Drying process:

[0023] The wet aluminum hydroxide raw material is mixed with one of the high-temperature air streams output from the cooling process. This high-temperature air stream is used as a drying heat source to remove free water from the aluminum hydroxide raw material. Then, dust-containing flue gas and dried aluminum hydroxide are output through gas-solid separation.

[0024] 3) Feeding process:

[0025] The aluminum hydroxide output from the drying process is stored and then output according to a metering method.

[0026] 4) Preheating process:

[0027] The high-temperature flue gas output after roasting is mixed with the aluminum hydroxide material output by metering in the feeding process for heat exchange, so that some of the crystal water in the aluminum hydroxide material is removed. Then, the preheated aluminum hydroxide material and the flue gas with reduced temperature are output through gas-solid separation. The high-temperature flue gas output after roasting refers to the high-temperature flue gas generated and output after roasting in the roasting process.

[0028] 5) Roasting process:

[0029] Another stream of high-temperature air output from the cooling process is mixed with the preheated aluminum hydroxide material output from the preheating process, and roasted using gas as fuel. The roasting product is then separated into the above-mentioned high-temperature flue gas and the above-mentioned high-temperature aluminum oxide.

[0030] 6) Exhaust gas treatment process:

[0031] The preheated flue gas from the preheating process and the dust-laden flue gas from the drying process are separated into gas and ash. The collected fly ash is then transported to the feeding process and stored together with the aluminum hydroxide from the drying process.

[0032] According to another aspect of the present invention, the present invention also provides a high thermal efficiency aluminum hydroxide calcination apparatus, which employs the above-described high thermal efficiency aluminum hydroxide calcination process, the apparatus comprising:

[0033] The suspension cooling system is used to mix the high-temperature alumina output after calcination with ambient air input from the outside for heat exchange, and then output the alumina product with reduced temperature and the high-temperature air through gas-solid separation, and then split the high-temperature air into two streams for output.

[0034] The conveyor bed drying system is used to mix wet aluminum hydroxide raw material with one of the high-temperature air output from the suspension cooling system, using the high-temperature air as a drying heat source to remove free water from the aluminum hydroxide raw material, and then output dust-containing flue gas and dried aluminum hydroxide through gas-solid separation.

[0035] A storage and feeding system is used to store the aluminum hydroxide output from the conveyor bed drying system and then output it by metering.

[0036] The suspension preheating system is used to mix the high-temperature flue gas output after roasting with the aluminum hydroxide material output by the storage and feeding system according to the metering for heat exchange, so that some of the crystal water in the aluminum hydroxide material is removed, and then the preheated aluminum hydroxide material and the cooled flue gas are output through gas-solid separation.

[0037] A calcination system is used to mix another stream of high-temperature air output from the suspension cooling system with preheated aluminum hydroxide material output from the suspension preheating system, and to calcine using fuel gas. The calcination products are then separated into high-temperature flue gas and high-temperature alumina as output.

[0038] The exhaust gas treatment system is used to separate the cooled flue gas output from the suspension preheating system and the dust-laden flue gas output from the conveying bed drying system. The collected fly ash is transported to the storage and feeding system and stored together with the aluminum hydroxide output from the conveying bed drying system. The separated gas is then discharged.

[0039] As a further preferred technical solution of the present invention, the suspension cooling system includes at least one cyclone cooler, in which the high-temperature alumina output after calcination is mixed with ambient air input from the outside and undergoes heat exchange, and then gas-solid separation is performed; when there are two or more cyclone coolers, the two or more cyclone coolers are cascaded in series or in parallel.

[0040] As a further preferred technical solution of the present invention, the conveying bed drying system includes a conveying bed drying tower and a cyclone dust collector. The wet aluminum hydroxide raw material is mixed with one of the high-temperature air output from the suspension cooling system in the conveying bed drying tower. The high-temperature air is used as the drying heat source for the wet aluminum hydroxide raw material. The cyclone dust collector is connected to the discharge end of the conveying bed drying tower. The cyclone dust collector outputs dust-containing flue gas and dried aluminum hydroxide through gas-solid separation.

[0041] As a further preferred technical solution of the present invention, the storage and feeding system includes a silo and a metering and conveying mechanism. The aluminum hydroxide output by the conveying bed drying system and the fly ash collected by the exhaust gas treatment system are mixed and stored in the silo. The metering and conveying mechanism is set at the output end of the silo to meter the aluminum hydroxide material in the silo to the suspension preheating system.

[0042] As a further preferred technical solution of the present invention, the suspension preheating system includes at least one cyclone preheater. The high-temperature flue gas output after calcination is mixed with the aluminum hydroxide material output by the storage and feeding system according to the metering and is transported into the cyclone preheater for mixing and heat exchange, and then gas-solid separation is performed. When there are two or more cyclone preheaters, the two or more cyclone preheaters are cascaded in series or in parallel.

[0043] As a further preferred technical solution of the present invention, the roasting system includes a roasting main furnace and a cyclone separator. Another stream of high-temperature air output from the suspension cooling system, along with the preheated aluminum hydroxide material output from the suspension preheating system and the fuel gas, are roasted in the roasting main furnace. The cyclone separator is connected to the discharge end of the roasting main furnace for outputting the aforementioned high-temperature flue gas and the aforementioned high-temperature alumina through gas-solid separation.

[0044] As a further preferred technical solution of the present invention, the exhaust gas treatment system includes a bag filter dust collector, wherein the flue gas with reduced temperature output from the suspension preheating system and the dust-laden flue gas output from the conveying bed drying system are separated into gas and ash by the bag filter dust collector.

[0045] As a further preferred technical solution of the present invention, the conveyor bed drying system is provided with a first induced draft fan, which is used to provide power to introduce one of the high-temperature air output from the suspension cooling system into the conveyor bed drying system; the exhaust gas treatment system is provided with a second induced draft fan, which is used to provide power to introduce the dust-laden flue gas output from the conveyor bed drying system and the cooled flue gas output from the suspension preheating system into the exhaust gas treatment system.

[0046] As a further preferred embodiment of the present invention, the roasting temperature in the roasting system is 800-1000℃, and the reaction time is 0.01-20 seconds; the temperature of the preheated aluminum hydroxide material output by the suspension preheating system is 300-500℃, the temperature of the cooled flue gas output by the suspension preheating system is 80-180℃, and the temperature of the alumina product output by the suspension cooling system is 60-150℃.

[0047] This invention optimizes the material flow, fully utilizing the waste heat during aluminum hydroxide roasting, and offers advantages such as high thermal efficiency, low heat consumption during alumina roasting, and high output. Compared with existing technologies, it has the following beneficial effects:

[0048] 1) In this invention, the volume of cold air entering the cooling process can be adjusted according to the calcination output and the temperature of the high-temperature alumina. This allows for a larger volume of cold air compared to existing processes, resulting in more thorough heat exchange between the high-temperature alumina and the cold air during the cooling process. Consequently, the temperature of the alumina product exiting the cooling process is lower, thereby reducing heat loss carried out of the system with the alumina product and lowering calcination heat consumption. The high-temperature air discharged from the cooling process is divided into two paths: one path goes to the calcination process, providing sufficient oxygen and some heat for fuel combustion in the furnace; the other path goes to the drying process, utilizing the heat in the high-temperature air as a heat source for drying the wet alumina raw material. This achieves full utilization of the heat carried by the high-temperature alumina and rational distribution of the high-temperature air, thereby further reducing calcination heat consumption.

[0049] 2) The drying process of this invention adopts a conveyor bed drying tower, which has a large temperature gradient and concentration gradient between the wet material and the high temperature air in the tower, resulting in high transmission power, high drying efficiency, fast removal of free water, and high thermal efficiency.

[0050] 3) In existing aluminum hydroxide roasting processes, high-loss-on-ignition fly ash from the flue gas is collected and then fed into the cooling process along with the high-temperature alumina discharged from the roasting furnace. To ensure that the product meets the loss on ignition requirements, the temperature inside the roasting furnace needs to be increased to minimize the loss on ignition of the material exiting the furnace. This invention collects the high-loss-on-ignition fly ash from the flue gas output from the preheating process and sends it to a raw material storage bin. After metering, it is reintroduced into the roasting system, thereby ensuring that the alumina material entering the cooling process is all high-temperature alumina discharged from the roasting furnace. Using this process, the temperature inside the roasting furnace can be lowered compared to existing processes, effectively reducing roasting heat consumption; simultaneously, the furnace heat load is reduced, and alumina production can be increased. Attached Figure Description

[0051] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0052] Figure 1 This is a schematic diagram of the system frame of the high thermal efficiency aluminum hydroxide calcination equipment of the present invention, as well as the flow direction of materials (aluminum hydroxide, alumina or fly ash) and gases (clean air or dust-laden gas) between the systems, wherein dust-laden gas refers to flue gas containing the above-mentioned materials.

[0053] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0054] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Terms such as "upper," "lower," "left," "right," "middle," and "one" used in the preferred embodiments are merely for clarity of description and are not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0055] The high thermal efficiency aluminum hydroxide calcination process of the present invention is an improvement on the existing fluidized bed calcination process for aluminum hydroxide, and includes the following steps:

[0056] 1) Cooling process:

[0057] The high-temperature alumina output after calcination is mixed with ambient air from the outside for heat exchange. Then, the cooled alumina product and the high-temperature air are output through gas-solid separation, and the high-temperature air is split into two streams for output.

[0058] This cooling process cools the high-temperature alumina output after calcination, while simultaneously recovering waste heat for subsequent use. To achieve this, the high-temperature alumina is thoroughly mixed with room-temperature air, and heat exchange occurs during the flow process. The alumina remains suspended in the airflow, significantly improving heat exchange efficiency. More preferably, the high-temperature alumina and room-temperature air flow macroscopically in opposite directions; that is, the high-temperature alumina output after calcination flows downwards under gravity, while the room-temperature air flows upwards, achieving mixing and heat exchange between the two.

[0059] 2) Drying process:

[0060] The wet aluminum hydroxide raw material is mixed with one of the high-temperature air streams output from the cooling process. This high-temperature air stream is used as a drying heat source to remove free water from the aluminum hydroxide raw material. Then, dusty flue gas and dried aluminum hydroxide are output through gas-solid separation.

[0061] The purpose of this drying process is to remove free water from the wet aluminum hydroxide raw material. This is achieved by ensuring that the high-temperature aluminum oxide output after calcination is fully cooled by a sufficient amount of ambient temperature air in the cooling process. This ensures that the high-temperature air output from the cooling process meets the reasonable air requirements for calcination, while the excess high-temperature air is used for drying and dehydrating the wet aluminum hydroxide raw material, reducing the heat consumption required for subsequent preheating. At the same time, the high-temperature air is rationally allocated to effectively utilize the recovered heat energy.

[0062] 3) Feeding process:

[0063] The aluminum hydroxide produced after the drying process is stored and then metered out.

[0064] The purpose of this feeding process is to centrally buffer the materials to be preheated, and at the same time output aluminum hydroxide material to the subsequent preheating process according to the preset metering.

[0065] 4) Preheating process:

[0066] The high-temperature flue gas output after roasting is mixed with the aluminum hydroxide material output by metering in the feeding process for heat exchange, so that some of the crystal water in the aluminum hydroxide material is removed. Then, the preheated aluminum hydroxide material and the cooled flue gas are output through gas-solid separation.

[0067] The purpose of this preheating process is to remove some of the water of crystallization from the aluminum hydroxide material before roasting by mixing it with the high-temperature flue gas output after roasting for heat exchange. Simultaneously, it preheats the aluminum hydroxide material to a certain temperature, thereby reducing the energy consumption required for subsequent roasting and achieving energy saving. To this end, by thoroughly mixing the high-temperature flue gas with the aluminum hydroxide material, the aluminum hydroxide material remains suspended in the airflow during the flow heat exchange process, greatly improving heat exchange efficiency. More preferably, the aluminum hydroxide material and the high-temperature flue gas flow in opposite directions macroscopically; that is, the high-temperature flue gas output after roasting flows from bottom to top, while the aluminum hydroxide material flows from top to bottom under gravity, achieving mixing and heat exchange between the two.

[0068] 5) Roasting process:

[0069] Another stream of high-temperature air output from the cooling process is mixed with the preheated aluminum hydroxide material output from the preheating process, and roasted using gas as fuel to remove the remaining water of crystallization and partially transform the crystal form of the material. The roasting product is then separated into the aforementioned high-temperature flue gas and the aforementioned high-temperature aluminum oxide through gas-solid separation.

[0070] The air and aluminum hydroxide material used in the roasting process absorb heat through heat exchange before roasting, which can effectively reduce the energy consumption of roasting.

[0071] 6) Exhaust gas treatment process:

[0072] The preheated flue gas from the preheating process and the dust-laden flue gas from the drying process are separated into gas and ash. The collected fly ash is transported to the feeding process and stored together with the aluminum hydroxide from the drying process. The separated gas is then discharged.

[0073] The purpose of exhaust gas treatment is to collect the material components contained in the flue gas through gas-ash separation, so that the flue gas (also known as exhaust gas) can be emitted in compliance with standards.

[0074] In actual production, the processes described in 1)-6) above are carried out simultaneously.

[0075] like Figure 1 As shown, the high thermal efficiency aluminum hydroxide calcination equipment using the above-described process provided by the present invention specifically includes the following systems:

[0076] The suspension cooling system is used to mix the high-temperature alumina output after calcination with ambient air for heat exchange. The cooled alumina product and the high-temperature air are then separated by gas-solid separation and output as two separate airflows. Specifically, the suspension cooling system uses cyclone coolers as the mixing and heat exchange and gas-solid separation devices. The high-temperature alumina output after calcination is input from above the cyclone cooler and flows downwards under gravity, while the ambient air is input from below and flows upwards, achieving mixing and heat exchange. The high-temperature alumina and ambient air flow macroscopically in opposite directions. The cooled alumina product and high-temperature air after gas-solid separation are output from below and above the cyclone cooler, respectively. To improve heat exchange efficiency, the suspension cooling system uses 2 to 5 cascaded cyclone coolers, either in series or in parallel. When two cyclone coolers are cascaded in series and arranged vertically, the high-temperature alumina output after calcination is input from the top of the upper cyclone cooler, and the ambient air is input from the bottom of the lower cyclone cooler, thus achieving macroscopic countercurrent flow between the two.

[0077] The conveyor bed drying system is used to mix wet aluminum hydroxide raw material with one of the streams of high-temperature air output from the suspension cooling system. This high-temperature air serves as the drying heat source to remove free water from the aluminum hydroxide raw material. The resulting product is then separated into dusty flue gas and dried aluminum hydroxide. The conveyor bed drying system includes a conveyor bed drying tower and a cyclone dust collector. The wet aluminum hydroxide raw material is mixed with one of the streams of high-temperature air output from the suspension cooling system in the conveyor bed drying tower. This high-temperature air serves as the drying heat source for removing free water from the wet aluminum hydroxide raw material. The cyclone dust collector is connected to the discharge end of the conveyor bed drying tower. The airflow output from the conveyor bed drying tower undergoes gas-solid separation in the cyclone dust collector, finally outputting dusty flue gas and dried (free water removed) aluminum hydroxide.

[0078] A storage and feeding system is used to store aluminum hydroxide output from the conveyor bed drying system and then output it by metering. Specifically, the storage and feeding system includes a silo and a metering conveying mechanism. The aluminum hydroxide output from the conveyor bed drying system and the fly ash collected by the subsequent exhaust gas treatment system are mixed and stored in the silo. The metering conveying mechanism is located at the output end of the silo to meter the material in the silo to the subsequent suspension preheating system. The metering conveying mechanism consists of a weighing unit and a conveying unit. The weighing unit can be an electronic scale, and the conveying unit can be a belt conveyor assembly, a funnel conveyor assembly, or a combination of both.

[0079] The suspension preheating system is used to mix the high-temperature flue gas output after calcination with the metered aluminum hydroxide material output from the storage and feeding system for heat exchange. This process removes some of the water of crystallization from the aluminum hydroxide material, and then the preheated aluminum hydroxide material and the cooled flue gas are output after gas-solid separation. Specifically, the suspension preheating system uses a cyclone preheater as the mixing heat exchange and gas-solid separation device. The aluminum hydroxide material is fed into the cyclone preheater from above and flows downward under gravity, while the high-temperature flue gas after calcination is fed into the cyclone preheater from below and flows upward to achieve mixing and heat exchange. The high-temperature flue gas and aluminum hydroxide material in the mixed state flow in opposite directions macroscopically. After gas-solid separation, the preheated aluminum hydroxide material and the cooled flue gas are output from the bottom and top of the cyclone preheater, respectively. To improve heat exchange efficiency, the suspension cooling system uses 2 to 3 cascaded cyclone preheaters, which can be connected in series or in parallel. When two cyclone preheaters are cascaded in series and arranged vertically, aluminum hydroxide material is input from the top of the upper cyclone preheater, and high-temperature flue gas is input from the bottom of the lower cyclone preheater, thus achieving macroscopic counter-flow between the two.

[0080] The roasting system is used to mix another stream of high-temperature air from the suspension cooling system with preheated aluminum hydroxide material from the suspension preheating system, and uses fuel gas for roasting. This process removes residual water of crystallization and partially transforms the crystal structure of the material. The roasting product is then separated into high-temperature flue gas and high-temperature alumina via gas-solid separation. Specifically, the roasting system includes a main roasting furnace and a cyclone separator. The high-temperature air from the suspension cooling system, the preheated aluminum hydroxide material from the suspension preheating system, and the fuel gas are all fed into the main roasting furnace for roasting. The cyclone separator is connected to the discharge end of the main roasting furnace to separate high-temperature flue gas and high-temperature alumina via gas-solid separation.

[0081] The exhaust gas treatment system is used to separate the cooled flue gas from the suspension preheating system and the dust-laden flue gas from the conveyor bed drying system. The collected fly ash is recycled (also known as ash return) to a storage and feeding system and stored together with the aluminum hydroxide output from the conveyor bed drying system. The separated gas is then discharged. Specifically, the exhaust gas treatment system includes a baghouse dust collector, through which the cooled flue gas from the suspension preheating system and the dust-laden flue gas from the conveyor bed drying system undergo gas-ash separation.

[0082] In one specific embodiment, the conveyor bed drying system is equipped with a first induced draft fan, which provides power to introduce one of the high-temperature air outputs from the suspension cooling system into the conveyor bed drying tower. The amount of high-temperature air introduced into the conveyor bed drying tower can be controlled by the first induced draft fan. The exhaust gas treatment system is equipped with a second induced draft fan, which provides power to introduce the dust-laden flue gas output from the conveyor bed drying system and the cooled flue gas output from the suspension preheating system into the exhaust gas treatment system.

[0083] In another specific embodiment, the high thermal efficiency aluminum hydroxide roasting equipment using the above-described process has the following characteristics during the roasting process: the temperature inside the main roasting furnace of the roasting system is 800–1000°C, and the reaction time is 0.01–20 seconds; the temperature of the preheated aluminum hydroxide material output by the suspension preheating system is 300–500°C, the temperature of the cooled flue gas output by the suspension preheating system is 80–180°C, and the temperature of the alumina product output by the suspension cooling system is 60–150°C.

[0084] It should be noted that the cyclone preheater, cyclone cooler, cyclone dust collector, and cyclone separator used in the equipment of this invention are all existing conventional equipment, also known as cyclone tubes. Their working principle is based on the cyclone principle to process the mixing and heat exchange of powder materials and gases, as well as the separation of the two. Their specific structure and detailed working mechanism will not be elaborated here.

[0085] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is defined only by the appended claims.

Claims

1. A high-thermal-efficiency aluminum hydroxide calcination process, characterized in that, Includes the following steps: 1) Cooling process: The high-temperature alumina output after calcination is mixed with ambient air from the outside for heat exchange, and then the cooled alumina product and high-temperature air are output through gas-solid separation. The high-temperature air is then split into two streams for output. 2) Drying process: The wet aluminum hydroxide raw material is mixed with one of the high-temperature air streams output from the cooling process. This high-temperature air stream is used as a drying heat source to remove free water from the aluminum hydroxide raw material. Then, dust-containing flue gas and dried aluminum hydroxide are output through gas-solid separation. 3) Feeding process: The aluminum hydroxide output from the drying process is stored and then output according to a metering method. 4) Preheating process: The high-temperature flue gas output after roasting is mixed with the aluminum hydroxide material output by metering in the feeding process for heat exchange, so that some of the crystal water in the aluminum hydroxide material is removed. Then, the preheated aluminum hydroxide material and the flue gas with reduced temperature are output through gas-solid separation. 5) Roasting process: Another stream of high-temperature air output from the cooling process is mixed with the preheated aluminum hydroxide material output from the preheating process, and roasted using gas as fuel. The roasting product is then separated into the above-mentioned high-temperature flue gas and the above-mentioned high-temperature aluminum oxide. 6) Exhaust gas treatment process: The preheated flue gas from the preheating process and the dust-laden flue gas from the drying process are separated into gas and ash. The collected fly ash is then transported to the feeding process and stored together with the aluminum hydroxide from the drying process.

2. A high-thermal-efficiency aluminum hydroxide calcination device, characterized in that, The equipment used to perform the high thermal efficiency aluminum hydroxide calcination process of claim 1 includes: The suspension cooling system is used to mix the high-temperature alumina output after calcination with ambient air input from the outside for heat exchange, and then output the alumina product with reduced temperature and the high-temperature air through gas-solid separation, and then split the high-temperature air into two streams for output. The conveyor bed drying system is used to mix wet aluminum hydroxide raw material with one of the high-temperature air output from the suspension cooling system, using the high-temperature air as a drying heat source to remove free water from the aluminum hydroxide raw material, and then output dust-containing flue gas and dried aluminum hydroxide through gas-solid separation. A storage and feeding system is used to store the aluminum hydroxide output from the conveyor bed drying system and then output it by metering. The suspension preheating system is used to mix the high-temperature flue gas output after roasting with the aluminum hydroxide material output by the storage and feeding system according to the metering for heat exchange, so that some of the crystal water in the aluminum hydroxide material is removed, and then the preheated aluminum hydroxide material and the cooled flue gas are output through gas-solid separation. A calcination system is used to mix another stream of high-temperature air output from the suspension cooling system with preheated aluminum hydroxide material output from the suspension preheating system, and to calcine using fuel gas. The calcination products are then separated into high-temperature flue gas and high-temperature alumina as output. The exhaust gas treatment system is used to separate the cooled flue gas output from the suspension preheating system and the dust-laden flue gas output from the conveying bed drying system. The collected fly ash is transported to the storage and feeding system and stored together with the aluminum hydroxide output from the conveying bed drying system. The separated gas is then discharged.

3. The high thermal efficiency aluminum hydroxide calcination equipment according to claim 2, characterized in that, The suspension cooling system includes at least one cyclone cooler. The high-temperature alumina output after calcination is mixed with ambient air input from the outside and undergoes heat exchange in the cyclone cooler, followed by gas-solid separation. When there are two or more cyclone coolers, the two or more cyclone coolers are cascaded in series or in parallel.

4. The high thermal efficiency aluminum hydroxide calcination equipment according to claim 2, characterized in that, The conveyor bed drying system includes a conveyor bed drying tower and a cyclone dust collector. The wet aluminum hydroxide raw material is mixed with one of the high-temperature air output from the suspension cooling system in the conveyor bed drying tower. The high-temperature air is used as the heat source for drying the wet aluminum hydroxide raw material. The cyclone dust collector is connected to the discharge end of the conveyor bed drying tower. The cyclone dust collector outputs dust-containing flue gas and dried aluminum hydroxide through gas-solid separation.

5. The high thermal efficiency aluminum hydroxide calcination equipment according to claim 2, characterized in that, The storage and feeding system includes a silo and a metering conveying mechanism. Aluminum hydroxide output from the conveying bed drying system and fly ash collected by the exhaust gas treatment system are mixed and stored in the silo. The metering conveying mechanism is located at the output end of the silo to meter the aluminum hydroxide material in the silo to the suspension preheating system.

6. The high thermal efficiency aluminum hydroxide calcination equipment according to claim 2, characterized in that, The suspension preheating system includes at least one cyclone preheater. The high-temperature flue gas output after calcination is mixed with the aluminum hydroxide material output by the storage and feeding system according to the metering and is transported into the cyclone preheater for heat exchange, and then gas-solid separation is performed. When there are two or more cyclone preheaters, the two or more cyclone preheaters are cascaded in series or in parallel.

7. The high thermal efficiency aluminum hydroxide calcination equipment according to claim 2, characterized in that, The roasting system includes a main roasting furnace and a cyclone separator. Another stream of high-temperature air output from the suspension cooling system, along with preheated aluminum hydroxide material output from the suspension preheating system and fuel gas, are roasted in the main roasting furnace. The cyclone separator is connected to the discharge end of the main roasting furnace to output the aforementioned high-temperature flue gas and the aforementioned high-temperature alumina through gas-solid separation.

8. The high thermal efficiency aluminum hydroxide calcination equipment according to claim 2, characterized in that, The exhaust gas treatment system includes a bag filter dust collector, through which the cooled flue gas output from the suspension preheating system and the dust-laden flue gas output from the conveying bed drying system are separated into gas and ash.

9. The high thermal efficiency aluminum hydroxide calcination equipment according to claim 2, characterized in that, The conveyor bed drying system is equipped with a first induced draft fan, which provides power to introduce one of the high-temperature air outputs from the suspension cooling system into the conveyor bed drying system; the exhaust gas treatment system is equipped with a second induced draft fan, which provides power to introduce the dust-laden flue gas output from the conveyor bed drying system and the cooled flue gas output from the suspension preheating system into the exhaust gas treatment system.

10. The high thermal efficiency aluminum hydroxide calcination equipment according to any one of claims 2-9, characterized in that, The roasting temperature in the roasting system is 800–1000℃, and the reaction time is 0.01–20 seconds; the temperature of the preheated aluminum hydroxide material output by the suspension preheating system is 300–500℃, and the temperature of the cooled flue gas output by the suspension preheating system is 80–180℃; the temperature of the alumina product output by the suspension cooling system is 60–150℃.

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