A continuous dehydration preheating calcination process for pre-treating raw materials for brown corundum smelting

Abstract

The application discloses a kind of brown corundum smelting raw material pretreatment continuous dehydration preheating calcination process, first, bauxite raw material is coarsely broken, and is sent into countercurrent rotary preheating machine, and heat exchange dehydration is completed using calcining machine flue gas waste heat;Bauxite after dehydration is uniformly mixed with sieve under product coke powder, iron powder according to proportion, and mixed material is sent into rotary calcining machine and is indirectly heated calcination, while adding reducing agent in high temperature section to carry out impurity pre-reduction reaction, and generate fusible silicon iron phase;Hot material after calcination is directly hot sent to electric furnace charging bin through closed device with heat preservation and inert gas protection, and realizes continuous operation in whole process.The application realizes the cascade utilization of flue gas waste heat, effectively reduces the comprehensive energy consumption of brown corundum smelting, greatly reduces the smelting load of electric furnace, improves the raw material processing efficiency and product quality stability, and realizes the resource utilization of industrial solid waste, and the process has strong adaptability and practicality.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical raw material pretreatment technology, specifically relating to a continuous dehydration, preheating and calcination process for raw materials used in brown fused alumina smelting, which is particularly suitable for a continuous treatment method that adds iron powder and reducing agent coke powder in the high-temperature calcination section for impurity pre-reduction. Background Technology

[0002] Brown fused alumina (Al2O3≥95%) is an important refractory material and abrasive, widely used in high-temperature industries such as steel, cement, glass, and chemicals. Its quality directly affects the wear resistance, high-temperature resistance, and service life of end products. With the continuous development of global high-temperature industries and the increasing demand for high-quality refractory materials, the market has placed higher demands on the output, chemical composition stability, and production cost control of brown fused alumina. However, existing brown fused alumina raw material pretreatment and smelting processes suffer from numerous technical bottlenecks, severely restricting the industry's energy efficiency improvement and green development.

[0003] Currently, most brown fused alumina producers use the traditional rotary kiln roasting process for pretreatment of bauxite: the bauxite raw material is fed into a rotary kiln and roasted at 900-1200℃ through direct heating (direct contact between flame and high-temperature flue gas), causing dehydration, crystal transformation, and decomposition of some impurities. After roasting, the material is cooled to room temperature and then transferred to the smelting workshop for melting in an electric furnace. While this process can remove moisture from the raw material and improve some physicochemical properties, it has the following significant drawbacks:

[0004] (1) Heat is not utilized in a tiered manner, resulting in high energy consumption.

[0005] Rotary kiln roasting requires a large amount of fuel (pulverized coal, natural gas or electricity). After roasting, the material needs to be cooled to room temperature before it can be put into the furnace. As a result, the sensible heat generated during the roasting process is not utilized and is directly lost, causing serious energy waste.

[0006] (2) Intermittent or quasi-continuous operation makes it difficult to achieve full-process continuity.

[0007] Rotary kilns typically operate intermittently or quasi-continuously, with the roasting and cooling processes being disconnected from each other. This prevents the continuous flow of raw materials from pretreatment to smelting, affecting production rhythm and limiting the improvement of automation levels.

[0008] (3) Single function, insufficient impurity removal and pre-reduction.

[0009] Rotary kiln roasting is mainly for removing crystal water. It is not possible to introduce reducing agents during the roasting stage to pre-reduce impurities such as SiO2 and Fe2O3. The task of impurity reduction is all concentrated in the smelting furnace, which increases the smelting power consumption and the difficulty of furnace condition control.

[0010] (4) Long production cycle and low efficiency

[0011] The roasting-cooling-furnace loading process involves waiting time, resulting in a long overall processing cycle, limited production efficiency, and an inability to meet the requirements of modern high-temperature industries for rapid and stable raw material supply. Furthermore, the separation of raw material pretreatment and smelting processes prevents continuous operation throughout the entire process, leading to low automation and high labor and material handling costs.

[0012] In summary, the existing brown fused alumina raw material processing route, which is based on rotary kiln roasting, cooling, and furnace feeding, suffers from problems such as high energy consumption, heat waste, discontinuity, single function, and low resource utilization. It is difficult to meet the needs of high-end refractory material production for energy-saving, efficient, continuous, and green raw material pretreatment.

[0013] Therefore, developing a new method for pretreatment of brown fused alumina raw materials that features a compact process flow, high dehydration efficiency, the ability to utilize high-temperature pre-reduction, low energy consumption, deep impurity removal, and full utilization of waste materials has become a pressing technical challenge in this field.

[0014] This application addresses the shortcomings of existing processes by proposing a continuous dehydration preheating and calcination process. This process utilizes a counter-current rotary preheater connected in series with a rotary calciner, directly preheating with waste heat from the calciner flue gas, employing indirect heating (heat transfer via a heating drum) in the calcination section, and adding iron powder and reducing agent coke powder in the high-temperature calcination section for impurity pre-reduction. This method eliminates the need for ultrafine grinding of all raw materials, allowing the preparation of a mixture from waste materials. Through continuous counter-current heat exchange and high-temperature pre-reduction reaction, it achieves rapid dehydration, partial impurity pre-reduction, and stable component output. Simultaneously, it significantly reduces smelting power consumption and equipment investment, effectively solving the bottleneck problems of existing technologies and possessing outstanding energy-saving, cost-reducing, and environmental advantages. Summary of the Invention

[0015] This invention addresses the shortcomings of existing brown fused alumina raw material pretreatment processes by providing a continuous dehydration, preheating, and calcination process. This process enables efficient utilization of waste heat from raw material pretreatment, early removal of impurities, and continuous direct delivery of hot materials, thereby reducing the overall energy consumption of brown fused alumina smelting and improving product quality stability.

[0016] In this invention, the high-temperature flue gas from the calciner is introduced into the preheater as a dehydration heat source, achieving cascade recovery and utilization of flue gas waste heat. The preheating section adopts a combination of direct countercurrent heat exchange and indirect heating in the calcination section, ensuring dehydration efficiency and calcination effect while avoiding contamination of raw materials by combustion gas impurities and improving raw material purity. The reduction reaction of SiO2 and Fe2O3 is moved forward to the pretreatment calcination section, and impurities are pre-reduced through the synergistic effect of fine powder reducing agent to generate fusible ferrosilicon phase, reducing the reduction load of electric furnace smelting. After calcination, the hot material does not need to be cooled and is directly fed into the furnace through a sealed protective conveying system, achieving continuous flow of heat and material throughout the entire process and avoiding double energy loss from cooling and reheating.

[0017] This invention provides a continuous dehydration, preheating, and calcination process for the pretreatment of brown fused alumina raw materials, comprising the following steps:

[0018] (1) The bauxite raw material is crushed to obtain crushed material;

[0019] (2) The crushed material is fed into a counter-current rotary preheater, and the high-temperature flue gas discharged from the rotary calciner is used as a heat source. The raw material is preheated and dehydrated by direct counter-current heat exchange.

[0020] (3) The dehydrated bauxite, coke powder, and iron powder are fed into a screw conveyor mixer to mix and obtain a uniform mixture. The coke powder is industrial screened coke powder, and the iron powder is reduced iron powder or smelting by-product iron powder.

[0021] (4) The mixture is fed into a rotary calciner and calcined to remove impurities by indirect heating. Iron powder and coke powder are added as reducing agents in the high-temperature calcination section to complete the pre-reduction reaction of impurities in the raw materials and generate fusible ferrosilicon phase.

[0022] (5) The calcined hot material is directly delivered to the electric furnace feeding hopper through a closed heat-resistant conveying device to complete the continuous pretreatment.

[0023] As a further preferred option, in step (1), a combination of jaw crusher and vertical mill is used for crushing. The particle size of the bauxite raw material after crushing is limited to ≤3mm, and scrap or powdery waste can be added to the bauxite raw material.

[0024] As a further preferred option, in step (2), the counter-current rotary preheater has a cylinder inclination angle of 3° and a rotation speed of 3-5 r / min. The preheating and dehydration temperature is controlled at 250-350℃. The high-temperature flue gas used for heat exchange is taken from the 600-700℃ flue gas discharged from the rotary calciner. After dehydration, the natural water content of the raw material drops to ≤0.5%, and the total moisture content is ≤0.4%.

[0025] As a further preferred option, in step (3), the coke powder particle size is ≤1mm, the dry basis mass ratio of coke powder, iron powder and dehydrated bauxite is 515% and 420% respectively, the speed of the ribbon mixer is 20-40r / min, and the mixing time is 10-15min.

[0026] As a further preferred option, in step (4), the rotary calciner cylinder has an inclination angle of 2° and a rotation speed of 2-4 r / min. It uses a heating drum for indirect heating, and the calcination temperature is controlled at 700-900℃. The combustion gas does not come into direct contact with the mixture, and the crystal water of the raw material is removed to ≤0.2% after calcination.

[0027] As a further preferred option, in step (4), iron powder and coke powder are quantitatively added in the high-temperature calcination section by a screw feeder. The impurity pre-reduction is carried out on silicon dioxide and ferric oxide in the raw materials, and the reaction generates elemental silicon and elemental iron, which are further combined to form a fusible ferrosilicon phase.

[0028] As a further preferred option, in step (5), the closed heat-resistant conveying device is equipped with a heat insulation cover and an inert gas protection structure. The inert gas is nitrogen, and the temperature of the hot material is kept at ≥500℃ during the conveying process.

[0029] Below, we will provide a more detailed explanation of each step in the continuous dehydration, preheating, and calcination process for brown fused alumina raw materials, based on practical operation.

[0030] For the raw material crushing step, a combination of jaw crusher and vertical mill can be used to crush bauxite raw materials to a particle size ≤3mm. 10-15% of production scraps or powdery waste can be added to the bauxite raw materials. This crushing method can efficiently and quickly crush raw materials to the set particle size, ensuring uniform particle size and avoiding problems of excessively large or small particle sizes. Controlling the particle size to ≤3mm during coarse crushing is the foundation for efficient operation of subsequent processes. The addition of a small amount of production scraps or powdery waste enables the resource utilization of solid waste from production.

[0031] For the preheating and dehydration step, a counter-current rotary preheater with a cylinder inclination angle of 3° and a rotation speed of 3-5 r / min is preferred. This utilizes the high-temperature flue gas discharged during the operation of the rotary calciner for direct counter-current heat exchange and dehydration, reducing the natural water content from approximately 15% to ≤10%. The high-temperature flue gas discharged from the rotary calciner is a process by-product heat energy; introducing it into the preheater as a dehydration heat source achieves efficient recovery and resource utilization of flue gas waste heat. Precise control of the total moisture content of the dehydrated raw material further reduces the heat energy required for moisture evaporation in subsequent calcination processes, improving the stability of subsequent smelting processes. The inclined preheater cylinder allows the crushed bauxite raw material to move slowly and evenly within the cylinder, significantly extending the contact time between the raw material and the high-temperature flue gas, ensuring more thorough heat exchange and more complete dehydration.

[0032] For the material mixing step, dehydrated bauxite is mixed with coke powder and iron powder in a ribbon mixer. The coke powder is undersize coke powder (particle size ≤ 1 mm), or it can be an undersize by-product from the coking or smelting process. The iron powder is reduced iron powder or by-product iron powder. The fine powder form of coke powder and iron powder can significantly increase the contact surface area with bauxite particles, creating favorable kinetic conditions for the subsequent high-temperature pre-reduction reaction. The ribbon mixer enables uniform mixing of the three materials, allowing the fine powder form of reducing agent to fully contact the bauxite particles, significantly improving the mass and heat transfer rate between the solid phases, avoiding the problem of too much or too little reducing agent in some areas, and ensuring that the subsequent pre-reduction reaction can fully occur in all parts of the mixture.

[0033] For the calcination pre-reduction step, the mixture is fed into a rotary calciner and calcined at 700-900℃ using a heated drum-type indirect heating structure to remove impurities. The combustion gases do not directly contact the mixture, removing the water of crystallization from the raw material after calcination. In the high-temperature calcination section, iron powder and reducing agent coke powder are added for impurity pre-reduction, generating a fusible ferrosilicon phase. This heating method achieves uniform and stable control of the calcination temperature, avoiding localized overheating or insufficient heating, ensuring complete removal of the water of crystallization from the raw material, and completely eliminating the adverse effects of the water of crystallization on subsequent electric furnace smelting. In the high-temperature calcination section, iron powder and reducing agent coke powder (or undersize coke powder) are added via a screw feeder to promote impurity pre-reduction. Due to the large specific surface area of ​​coke powder and iron powder, the contact between reactants is more thorough, and the reduction reaction of impurities (such as SiO2, Fe2O3) with carbon can achieve a high conversion rate at a lower temperature and in a shorter time, generating a low-melting-point ferrosilicon phase, which facilitates slag-iron separation in subsequent smelting.

[0034] For the direct hot material conveying step, the calcined hot material is directly conveyed to the electric furnace charging hopper via a sealed, heat-resistant conveying device equipped with an insulation cover and a nitrogen inert gas protection structure. The temperature of the hot material is maintained at ≥500℃ during the conveying process. The insulation cover effectively reduces heat loss during conveying, preventing heat exchange between the hot material and the external low-temperature environment, ensuring that the temperature of the hot material remains within the set range. The nitrogen inert gas protection structure isolates the high-temperature hot material from oxygen in the air, preventing oxidation reactions during conveying.

[0035] This invention, through the collaborative design of multiple process stages and the precise matching of process parameters and equipment selection, achieves significant technical benefits compared to existing traditional processes, resulting in a substantial reduction in overall energy consumption. The preheating section utilizes the waste heat from the flue gas of the rotary kiln for dehydration, replacing the traditional independent fuel heating mode and completely eliminating fuel energy input for the dehydration process. Simultaneously, the design of directly feeding hot materials into the furnace without cooling fully utilizes the sensible heat of the materials, significantly reducing the heating energy consumption of electric furnace smelting. Furthermore, the continuous operation of the entire process avoids heat loss during the start-up and shutdown processes of traditional intermittent processes, comprehensively improving the overall thermal energy utilization rate of the process and resulting in a significant reduction in overall energy consumption compared to traditional processes.

[0036] The electric furnace smelting load and production risks are effectively reduced, and production stability is significantly improved. This invention moves the reduction reaction of impurities such as SiO2 and Fe2O3 to the pretreatment calcination section, which greatly reduces the amount of reduction reaction in the electric furnace, fundamentally reducing the smelting load of the electric furnace, and avoiding problems such as sudden pressure increase and splashing caused by a large amount of violent reduction reaction in the electric furnace.

[0037] This invention features a tightly integrated process from crushing, dewatering, mixing, calcination to direct hot material delivery, achieving continuous feeding and discharging. This eliminates material waiting time between processes in traditional methods, improving raw material processing efficiency per unit time. Furthermore, it only requires coarse crushing of the raw material to ≤3mm, eliminating the need for ultrafine grinding as in traditional processes. This significantly reduces the difficulty of equipment operation and maintenance, decreases energy consumption and equipment wear in the grinding process, further enhancing overall production efficiency. The continuous design of the entire process also facilitates higher levels of automation.

[0038] After pretreatment, the moisture content of the raw materials is precisely controlled at an extremely low level, and uniform mixing makes the raw material composition more uniform. At the same time, the indirect heating method avoids the contamination of the raw materials by combustion gases, effectively ensuring the purity of the raw materials. The improvement of raw material quality makes the electric furnace smelting furnace condition more stable, avoiding the deviation of smelting effect caused by the fluctuation of raw material moisture and composition. This makes the main Al2O3 content index of brown fused alumina products more stable, the fluctuation range of impurity index is greatly reduced, and the uniformity of product quality is significantly improved.

[0039] This invention directly utilizes the coke powder and by-product iron powder produced in the coking and smelting processes as reducing agents. It can also add scraps and powdered waste from the production process to the bauxite raw materials, transforming various industrial solid wastes into production resources, improving resource utilization, and reducing raw material procurement costs to a certain extent.

[0040] The process of this invention can process bauxite raw materials of different grades. The addition ratio of coke powder and iron powder can be flexibly adjusted according to the differences in SiO2 and Fe2O3 content in raw materials of different grades to ensure the effect of pre-reduction reaction. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the process flow for the continuous dehydration, preheating, and calcination process of brown fused alumina raw material pretreatment according to the present invention. Detailed Implementation

[0042] The technical effects of the present invention are illustrated below through data comparison using two embodiments and a comparative example.

[0043] General experimental equipment parameters

[0044] Equipment parameters Counter-flow rotary preheater The cylinder is 6m long, with an inclination angle of 3° and a rotation speed of 3~5 r / min. Equipment parameters Rotary calciner Indirect heating type (heating drum gas / electric heating, combustion gas does not contact the material), cylinder length 8m, inclination angle 2°, rotation speed 2~4r / min Equipment parameters Ribbon mixer Volume 1 cubic meter, rotation speed 20~40 r / min Basic indicators of raw materials bauxite raw materials Al2O3 content 80%, initial moisture 15% Basic indicators of raw materials Caramel powder Initial moisture content 1%, particle size ≤1mm Basic indicators of raw materials Iron powder Essentially dry (moisture content is negligible)

[0045] Example 1

[0046] Step (1): Crushing

[0047] Take 1 ton of bauxite scraps and powdery waste, and crush them to a particle size of ≤3 mm using a jaw crusher and a vertical mill.

[0048] Step (2): Preheating and dehydration (direct heating to remove natural water)

[0049] The crushed material is fed into a counter-current rotary preheater, where it undergoes direct counter-current heat exchange using the high-temperature flue gas (600-700℃) discharged from the calciner. The preheating section temperature is controlled at 250-350℃, reducing the natural water content in the raw material from 5% to ≤0.5%, while retaining almost all the water of crystallization. At this point, the total moisture content of the raw material is approximately 10.5% (10% water of crystallization + 0.5% residual natural water).

[0050] Step (3): Mixing

[0051] Dehydrated bauxite, coke powder (1% moisture), and iron powder are added to a ribbon mixer in a set ratio and mixed evenly. The coke powder is selected from undersize coke powder (particle size ≤1mm), and the iron powder is reduced iron powder (particle size ≤0.5mm). Both are fine powders, which significantly increase the contact surface area with bauxite particles, shorten the reaction distance, and improve the kinetic conditions of the pre-reduction reaction of impurities during the calcination stage. This is beneficial for rapidly completing the pre-reduction of SiO2 and Fe2O3 at 700~900℃. The ratio (based on the dry weight of bauxite): coke powder 15%, iron powder 4%. The moisture content of the mixture after mixing is approximately:

[0052] 10.5%×(1−0.19)+1%×0.15≈8.96%

[0053] Step (4): Calcination and pre-reduction (indirect heating, removal of water of crystallization and pre-reduction)

[0054] The mixture is fed into a rotary calciner and calcined at 700-900℃ using indirect heating (heat transfer via a heating drum, without direct contact with combustion gases). During calcination, the water of crystallization is reduced from approximately 10% to ≤0.2%, while some volatile matter is also removed. In the high-temperature calcination section, iron powder and coke powder (or undersize coke powder) are added via a screw feeder for impurity pre-reduction, generating a fusible ferrosilicon phase. After calcination, the total moisture content of the material is ≤0.2%, meeting the requirements for furnace feeding. Due to the large specific surface area of ​​coke powder and iron powder, the reactants are in full contact, and the impurity reduction reaction can proceed efficiently within the set calcination temperature and time range, generating a ferrosilicon alloy phase that is easily separated in subsequent smelting, reducing the reduction load in the smelting furnace.

[0055] Step (5): Hot material is delivered directly

[0056] The calcined and pre-reduced hot material (temperature ≥500℃) is directly conveyed to the electric furnace charging hopper via a closed heat-resistant conveying device, utilizing sensible heat to participate in the smelting reaction, saving about 10%~15% of the electrical energy required for heating the electric furnace.

[0057] Test results:

[0058] (1) The smelting power consumption is 1760 kWh / t, which is about 20% lower than the traditional direct heating rotary kiln process.

[0059] (2) Splash rate decreased by 85%.

[0060] (3) The moisture content of the raw materials entering the furnace is ≤0.2%, the composition is uniform, and the smelting process is stable.

[0061] Example 2

[0062] Step (1): Crushing

[0063] Take 1 ton of bauxite raw material (with 15% of production powder waste), crush it to a particle size of ≤3mm using a jaw crusher and vertical mill, and ensure that the raw material has a uniform particle size distribution and no large particles remain.

[0064] Step (2): Preheating and dehydration (direct heating to remove natural water)

[0065] The crushed material is fed into a counter-current rotary preheater, where 700°C high-temperature flue gas discharged from the rotary calciner is introduced for direct counter-current heat exchange. The temperature of the preheating section is precisely controlled at 320~350°C, extending the contact time between the material and the flue gas. This reduces the natural water content in the raw material from 5% to 0.3%, retains 9.8% crystal water, and reduces the total moisture content of the raw material to 10.1%. After heat exchange, the flue gas temperature drops below 200°C, meeting emission standards.

[0066] Step (3): Mixing

[0067] Dehydrated bauxite, coke powder (particle size ≤1mm, moisture 1%), and iron powder (by-product of smelting) are added to a ribbon mixer in a specific ratio. The mixer is operated at 40 rpm for 10 minutes to achieve uniform dispersion of the materials. The proportions (based on dry bauxite weight) are: 8% coke powder and 15% iron powder. The fine powder reducing agent ensures thorough contact with the bauxite particles, resulting in a final mixture with approximately 9.2% moisture content.

[0068] Step (4): Calcination and pre-reduction (indirect heating, removal of water of crystallization and pre-reduction)

[0069] The mixture was fed into a rotary calciner and indirectly heated by a heating drum. The calcination temperature was controlled at 850~900℃, and the drum speed was adjusted to 3r / min. During the calcination process, the water of crystallization was removed from 9.8% to 0.1%, and the total moisture content was reduced to below 0.1%. In the high-temperature calcination section, coke powder and iron powder were quantitatively added by a screw feeder to allow SiO2 and Fe2O3 to undergo a full pre-reduction reaction, generating a fusible ferrosilicon phase. The impurity reduction conversion rate was increased by 5% compared with Example 1.

[0070] Step (5): Hot material is delivered directly

[0071] After calcination and pre-reduction, the hot material temperature rises to 650℃ and is directly conveyed to the electric furnace charging hopper via a closed chain conveyor equipped with nitrogen protection and a heat insulation cover. During the conveying process, the hot material temperature is maintained above 600℃, and the high-temperature sensible heat is used to participate in the smelting reaction, saving about 18-20% of the electricity required for heating the electric furnace.

[0072] Test results:

[0073] (1) The smelting power consumption is 1650 kWh / t, which is about 25% lower than the traditional direct heating rotary kiln process.

[0074] (2) The splashing rate decreased by 92%, and the smelting furnace condition remained stable.

[0075] (3) The moisture content of the raw materials entering the furnace is ≤0.1%, the uniformity of the composition is improved, and the Al2O3 content of the brown fused alumina product reaches 95.8%.

[0076] Comparative example (traditional rotary kiln process)

[0077] Step (1): Crushing and grinding

[0078] Take 1 ton of bauxite of the same grade (without waste added), crush it with a jaw crusher and then grind it into ultrafine powder with a particle size of ≤0.1mm with a ball mill. The grinding process takes 2 hours and consumes 120kWh of electricity.

[0079] Step (2): Rotary kiln firing

[0080] The powder is fed into a direct-heating rotary kiln and directly heated to 1000℃ by natural gas for roasting and dehydration. The roasting time is 3 hours, consuming 15m³ / t of natural gas. After roasting, the total moisture content of the raw material is reduced to 0.5%.

[0081] Step (3): Cooling at room temperature

[0082] After roasting, the material is cooled to room temperature (25℃) by a water-cooled cooler. During the cooling process, the sensible heat of the material is completely dissipated. After cooling, the material is left to stand naturally for 1 hour to prevent it from absorbing moisture.

[0083] Step (4): Cold material transfer

[0084] Normal temperature materials are transferred to the electric furnace feeding hopper via ordinary belt conveyor. During the transfer process, the materials are prone to dust generation, and manual inspection is required to control the amount of materials being transported.

[0085] Step (5): Electric furnace smelting

[0086] After the cold material is fed into the furnace, the electric furnace needs to use electricity to heat the material to the smelting temperature, and complete the reduction reaction of all SiO2 and Fe2O3 impurities in the furnace. During the smelting process, the violent reduction reaction can easily cause splashing.

[0087] Test results:

[0088] (1) The smelting power consumption is 2200 kWh / t, and the combined energy consumption of grinding + roasting + smelting is much higher than that of the process of this invention.

[0089] (2) The splashing rate during the smelting process reaches 10%, and the furnace condition fluctuates frequently, requiring frequent adjustment of electric furnace parameters.

[0090] (3) The moisture content of the raw material entering the furnace is 0.5%, and the composition is prone to local unevenness. The Al2O3 content of the brown fused alumina product is 94.0%±1.0%, and the quality stability is poor.

[0091] (4) The raw material processing efficiency is 0.7t / h, the entire process takes more than 6 hours, and there is no solid waste resource utilization.

[0092] Comparison Table of Examples 1-2 and Comparative Examples

[0093] Total moisture content of raw materials after pretreatment ≤0.2% ≤0.1% 0.5% Power consumption per ton of brown fused alumina smelting 1760kWh / t 1650kWh / t 2200kWh / t Smelting power consumption reduction rate 20% 25% - Splashing rate during smelting 1.5% 0.8% 10.0% Splash rate reduction rate 85% 92% - Raw material processing efficiency 1.0t / h 1.3t / h 0.7t / h <![CDATA[Brown corundum Al2O3 content]]> 95.2% 95.8% 94.0%±1.0% Solid waste utilization rate 20% 25% 0% Overall process time 3h 2.5h ≥6h

[0094] As can be seen from the above comparative data, the process of the present invention has achieved significant technical improvements in energy consumption control, production efficiency, product quality, and resource utilization compared with the traditional rotary kiln process. Example 2 achieved even better technical results due to the optimized matching of process parameters and the reasonable adjustment of the solid waste addition ratio, which fully demonstrates the feasibility, advancement and flexibility of the process of the present invention.

[0095] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0096] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A continuous dehydration, preheating, and calcination process for pretreatment of brown fused alumina raw materials, characterized in that, Includes the following steps: (1) The bauxite raw material is crushed to obtain crushed material; (2) The crushed material is fed into a counter-current rotary preheater, and the high-temperature flue gas discharged from the rotary calciner is used as a heat source. The raw material is preheated and dehydrated by direct counter-current heat exchange. (3) The dehydrated bauxite, coke powder, and iron powder are fed into a screw conveyor mixer to mix and obtain a uniform mixture. The coke powder is industrial screened coke powder, and the iron powder is reduced iron powder or smelting by-product iron powder. (4) The mixture is fed into a rotary calciner and calcined to remove impurities by indirect heating. Iron powder and coke powder are added as reducing agents in the high-temperature calcination section to complete the pre-reduction reaction of impurities in the raw materials and generate fusible ferrosilicon phase. (5) The calcined hot material is directly delivered to the electric furnace feeding hopper through a closed heat-resistant conveying device to complete the continuous pretreatment.

2. The continuous dehydration, preheating, and calcination process for brown fused alumina raw material pretreatment according to claim 1, characterized in that, In step (1), a combination of jaw crusher and vertical mill is used for crushing. The particle size of the bauxite raw material after crushing is limited to ≤3mm, and scrap or powdery waste can be added to the bauxite raw material.

3. The continuous dehydration, preheating, and calcination process for brown fused alumina raw material pretreatment according to claim 1, characterized in that, In step (2), the counter-current rotary preheater has a cylinder inclination angle of 3° and a rotation speed of 3~5 r / min. The preheating and dehydration temperature is controlled at 250~350℃. The high-temperature flue gas used for heat exchange is taken from the 600~700℃ flue gas discharged from the rotary calciner. After dehydration, the natural water content of the raw material drops to ≤0.5%, and the total moisture content is ≤0.4%.

4. The continuous dehydration, preheating, and calcination process for brown fused alumina raw material pretreatment according to claim 1, characterized in that, In step (3), the coke powder particle size is ≤1mm, the dry basis mass ratio of coke powder, iron powder and dehydrated bauxite is 5~15% and 4~20% respectively, the speed of the ribbon mixer is 20~40r / min, and the mixing time is 10~15min.

5. The continuous dehydration, preheating, and calcination process for brown fused alumina raw material pretreatment according to claim 1, characterized in that, In step (4), the rotary calciner cylinder has an inclination angle of 2° and a rotation speed of 2~4 r / min. It uses a heating drum for indirect heating, and the calcination temperature is controlled at 700~900℃. The combustion gas does not come into direct contact with the mixture. After calcination, the crystal water of the raw material is removed to ≤0.2%.

6. The continuous dehydration, preheating, and calcination process for brown fused alumina raw material pretreatment according to claim 1, characterized in that, In step (4), iron powder and coke powder are added quantitatively through a screw feeder in the high-temperature calcination section, reacting to generate elemental silicon and elemental iron, which then combine to form a fusible ferrosilicon phase.

7. The continuous dehydration, preheating, and calcination process for brown fused alumina raw material pretreatment according to claim 1, characterized in that, In step (5), the sealed heat-resistant conveying device is equipped with a heat insulation cover and an inert gas protection structure. Nitrogen is selected as the inert gas, and the temperature of the hot material is maintained at ≥500℃ during the conveying process.

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