Fluidized bed waste heat recovery device of aluminum oxide roasting furnace

Abstract

The utility model discloses a fluidized bed waste heat recovery device of an aluminum oxide roasting furnace, which belongs to the technical field of aluminum oxide production and comprises an upper flow cavity and a lower flow cavity which are separated from each other through a dividing wall. The heat pipes fixedly penetrate through the dividing wall, and the two ends of each heat pipe are located in the upper flow cavity and the lower flow cavity respectively. According to the waste heat recovery device, the heat pipe is arranged in the fluidized bed to serve as a heat exchange medium between the upper flow cavity and the lower flow cavity, even if the heat pipe is damaged, aluminum oxide cannot make direct contact with cooling water, and then the situation that aluminum oxide solid powder is hardened when meeting water and consequently a cooling unit fails is avoided; and therefore, energy conservation and emission reduction are realized.

Description

Technical Field

[0001] This utility model belongs to the field of alumina production technology, specifically a fluidized bed waste heat recovery device for alumina calcining furnace. Background Technology

[0002] Aluminum hydroxide roasting is the final step in alumina production, accounting for approximately 10% of the energy consumption in the alumina production process. Alumina production generally employs gas suspension roasting furnace technology. After roasting in the gas suspension roaster, the alumina (Al₂O₃) material exits the roaster's cyclone separator at a temperature of 260–350°C. It then enters a fluidized bed cooler to lower the temperature to below 80°C before entering the conveying and packaging system. The fluidized bed cooler uses circulating cooling water to cool the alumina, but the residual heat of the alumina is carried away by the circulating cooling water and eventually dissipated into the atmosphere through a cooling tower, resulting in a significant waste of heat. Furthermore, the cooling water system also consumes some electricity, representing a waste of energy.

[0003] Patent CN201795687U discloses a system for recovering heat from alumina in a fluidized bed cooler of a calcining furnace. The cooling unit consists of a heat exchange tube bundle made of multiple steel pipes. The outer side of the heat exchange tubes is in direct contact with the fluidized high-temperature alumina powder. Compressed air drives the alumina particles to form a turbulent state within the fluidized bed to enhance heat transfer. Cooling water flows through the inner side of the heat exchange tubes, and heat exchange occurs through the tube walls to cool the alumina. Patent CN207600225U discloses a waste heat recovery device for alumina in a calcining furnace, which also recovers waste heat by exchanging heat between cooling water flowing in a coiled tubular heat exchanger and alumina.

[0004] However, this type of waste heat recovery structure has significant drawbacks. First, during long-term operation, the high-speed flowing alumina particles continuously erode the outer wall of the heat exchange tubes. Combined with the high hardness of alumina itself, this leads to severe erosion and wear on the outer wall of the steel heat exchange tubes, especially in stress-concentrated areas such as welded joints and elbows, easily resulting in localized thinning or even perforation. Second, if the heat exchange tubes are damaged, internal cooling water will leak into the fluidized bed and come into contact with the alumina. Upon contact with water, the alumina rapidly undergoes a hydration reaction, causing the material to clump together, severely disrupting the fluidization state of the fluidized bed and causing a sharp drop in cooling efficiency. Utility Model Content

[0005] The purpose of this invention is to provide a fluidized bed waste heat recovery device for alumina calcining furnace to solve the problems mentioned in the prior art.

[0006] A fluidized bed waste heat recovery device for an alumina calcining furnace is provided, comprising:

[0007] The upper and lower flow cavities are separated from each other by partitions;

[0008] Several heat pipes are fixedly inserted through the partition wall, with the two ends of the heat pipes located in the upper flow cavity and the lower flow cavity, respectively.

[0009] Furthermore, the heat pipe comprises, from the outside to the inside, a pipe wall, a capillary layer, and a hollow cavity, and the heat pipe is filled with a working fluid.

[0010] The heat pipe consists of an evaporation section and a condensation section. The liquid working fluid is heated and evaporated in the evaporation section, and the vapor flows through a hollow cavity to the condensation section for cooling and condensation. A capillary layer generates capillary force through its microporous structure, driving the condensed working fluid back to the evaporation section, maintaining the phase change cycle. This capillary force-driven working fluid circulation eliminates the need for external pumping devices, reducing energy consumption.

[0011] Furthermore, the outer wall of the heat pipe is provided with several fins. The fins are used to increase the contact area between the heat pipe and the alumina particles, enhance convective heat transfer, and improve waste heat recovery efficiency. The fins can disperse the impact force of the particles and reduce the wear per unit area of ​​the heat pipe wall.

[0012] Furthermore, the fins are formed extending on the radial plane of the heat pipe, and a plurality of the fins are arranged along the length of the heat pipe. The fin extension surfaces are parallel to the alumina flow direction, reducing disturbance to the alumina particle flow and avoiding dead zones caused by particle accumulation. The fins are spaced apart along the length of the heat pipe to avoid local thermal stress concentration and reduce the risk of local damage to the heat pipe.

[0013] Furthermore, the fins and heat pipes are integrally formed. This integral forming method eliminates weak points caused by welding and avoids wear and cracking at the connection between the fins and heat pipes due to alumina particle erosion.

[0014] Furthermore, the upper flow cavity is provided with an alumina inlet and an alumina outlet at both ends. The inlet and outlet are located at both ends of the upper flow cavity to ensure that the alumina particles flow uniformly along the length of the heat pipe.

[0015] Furthermore, a cooling water outlet is provided at one end of the downstream cavity near the alumina inlet, and a cooling water inlet is provided at the other end of the downstream cavity near the alumina outlet. The cooling water flows in the opposite direction to the alumina, ensuring that a certain temperature gradient is always maintained between the alumina and the cooling water, thus ensuring directional heat transfer.

[0016] Furthermore, the sidewall of the upper flow cavity is provided with several compressed air inlets along its length. Compressed air is injected from multiple points on the sidewall to drive the fluidization of alumina particles, avoiding the power attenuation caused by single-point air intake and improving the fluidization quality of the particles.

[0017] Furthermore, the heat pipe is positioned to avoid the output extension space of the compressed air inlet. The heat pipe installation location avoids the core area of ​​the compressed air jet, preventing direct exposure to particle impact carried by the high-speed airflow, extending its service life, and reducing fluidized bed pressure drop losses.

[0018] Furthermore, several guide vanes are provided within the downstream cavity to form a labyrinthine channel. The guide vanes force the cooling water to flow along a serpentine path, increasing the residence time and fully absorbing the heat transferred by the heat pipe.

[0019] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0020] This waste heat recovery device uses heat pipes inside the fluidized bed as the heat exchange medium between the upper and lower flow chambers. Even if the heat pipes are damaged, the alumina will not come into direct contact with the cooling water. This avoids the alumina solid powder from caking when it comes into contact with water, which would cause the cooling unit to fail and lead to a reduction in the load of the calcining furnace or even a shutdown. This achieves energy saving and emission reduction. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this drawing or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this drawing. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0022] Figure 1 This is a side structural diagram of the fluidized bed waste heat recovery device for an alumina calcining furnace;

[0023] Figure 2 A top view of the fluidized bed waste heat recovery device for an alumina calcining furnace;

[0024] Figure 3 A schematic diagram of the heat pipe provided by this utility model.

[0025] In the diagram: 1. Partition wall; 2. Upper flow chamber; 21. Alumina inlet; 22. Alumina outlet; 23. Compressed air inlet; 3. Lower flow chamber; 31. Cooling water inlet; 32. Cooling water outlet; 33. Baffle plate; 4. Heat pipe; 41. Pipe wall; 42. Capillary layer; 43. Hollow cavity; 44. Fin. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this application clearer, the application is described and illustrated below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0027] Obviously, the accompanying drawings described below are merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios based on these drawings without any inventive effort. Furthermore, it is understood that although the efforts made in this development process may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0028] However, there may be instances where unnecessary detailed descriptions are omitted. For example, detailed descriptions of well-known matters or repetitive descriptions of essentially the same structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0029] Please see Figure 1-2 As shown, in this embodiment of the present invention, there are an upper flow cavity 2 and a lower flow cavity 3 that are isolated from each other by a partition wall 1; and a plurality of heat pipes 4 that are fixedly inserted through the partition wall 1, with the two ends of the heat pipes 4 located in the upper flow cavity 2 and the lower flow cavity 3 respectively.

[0030] The fluidized bed is divided into upper and lower chambers by a partition wall 1. The upper chamber 2 contains high-temperature alumina particles, while the lower chamber 3 is vented with cooling water. The two chambers are physically isolated to prevent direct contact. A heat pipe 4 runs through the partition wall 1, efficiently transferring heat through the phase change cycle of the working fluid inside the heat pipe 4. The heat from the high-temperature alumina in the upper chamber 2 is rapidly transferred to the cooling water in the lower chamber 3 via the heat pipe 4. Even if one of the heat pipes 4 is damaged, the cooling water will not directly contact the alumina due to the isolation between the upper and lower chambers, completely avoiding the caking problem caused by hydration reaction.

[0031] Furthermore, since the partition wall 1 does not directly bear the impact of alumina particles, its structural state is stable, ensuring that cooling water will not leak into the upper flow chamber 2. Because the lower flow chamber 3 is located at the bottom, even if the partition wall 1 is damaged, it will not cause a large amount of cooling water to flow in and come into contact with the alumina.

[0032] In one embodiment, the heat pipe 4 is completely filled with a liquid working fluid, and heat and cold flow exchange is achieved through the self-driving effect of the liquid working fluid under the temperature gradient. However, this structure has a high liquid working fluid filling volume, which can still cause local caking problems if leakage occurs, and the heat conduction efficiency is relatively low.

[0033] In one embodiment, the heat pipe 4 is integrally formed from a metal material, and heat exchange between the alumina and the cooling water is achieved through the thermal conduction of the material itself. This structure can effectively prevent liquid leakage, but the thermal conduction efficiency is relatively low.

[0034] In one embodiment, see Figure 1 and Figure 3 As shown, the heat pipe 4 comprises, from the outside to the inside, a pipe wall 41, a capillary structure layer 42, and a hollow cavity 43, and is filled with a working fluid. The heat pipe 4 includes an evaporation section located in the upper flow cavity 2 and in contact with alumina, and a condensation section located in the lower flow cavity 3 and in contact with cooling water.

[0035] The working fluid within the capillary layer 42 of the evaporation section is in direct contact with the tube wall 41. The working fluid absorbs heat and vaporizes in the evaporation section. Under pressure, the vapor is forced into the hollow cavity 43, and then flows through the hollow cavity 43 to the condensation section. In the condensation section, the vapor releases heat and liquefies. The capillary layer 42, through micropore capillary force, drives the liquid working fluid back to the evaporation section. This phase change circulation system requires no external pumping, reducing system energy consumption. This system also boasts high latent heat exchange heat transfer efficiency.

[0036] The outer wall of the heat pipe 4 is provided with several fins 44. The fins 44 increase the heat transfer efficiency by increasing the contact area between the heat pipe 4 and the alumina. The fins 44 are formed by extending in the radial plane of the heat pipe 4, and the extension direction of the fins 44 is parallel to the flow direction of the alumina, which reduces the flow resistance of alumina and air and reduces the pressure drop of the fluidized bed. The continuous arrangement of the fins 44 along the length of the heat pipe 4 avoids the concentration of local temperature gradients, reduces the peak thermal stress, and reduces the probability of heat pipe 4 failure.

[0037] The fin 44 and the heat pipe 4 can be welded together, but the weld may have a weak point due to thermal stress, and there is a risk of damage under the impact of alumina particles.

[0038] Furthermore, the fins 44 and heat pipe 4 are integrally formed, achieving an integrated structure through extrusion, casting, or 3D printing. This integrally formed structure eliminates weak weld points at the joints, extending its lifespan and resistance to particle erosion, while also eliminating the risk of deformation and cracking caused by differences in thermal expansion between dissimilar materials.

[0039] The upper flow chamber 2 has an alumina inlet 21 and an alumina outlet 22 at its two ends, with alumina flowing from the alumina inlet 21 to the alumina outlet 22. The lower flow chamber 3 has a cooling water outlet 32 ​​at the end near the alumina inlet 21 and a cooling water inlet 31 at the end near the alumina outlet 22. Cooling water flows in from the low-temperature end (near the alumina outlet 22) and flows out from the high-temperature end (near the alumina inlet 21), creating a balanced temperature gradient along the length of the fluidized bed to ensure continuous heat exchange.

[0040] The sidewall of the upper flow chamber 2 is provided with several compressed air inlets 23 along its length. Compressed air enters the upper flow chamber 2 through the compressed air inlets 23, carrying alumina solid powder from the alumina inlet 21 to the alumina outlet 22. After transferring heat to the heat pipe 4, the temperature gradually decreases, thus completing the waste heat recovery.

[0041] Furthermore, the heat pipes 4 are positioned to avoid the output extension space of the compressed air inlet 23. That is, the heat pipes 4 are arranged in groups of several, with intervals between adjacent groups, providing a continuous and stable flow space for the compressed air inlet 23. The arrangement of the heat pipes 4 avoids the core area of ​​the compressed air jet, preventing direct exposure to particle impacts carried by the high-speed airflow and extending the service life of the heat pipes 4. The heat pipes 4 are staggered from the airflow path, reducing fluidized bed pressure drop losses.

[0042] The lower flow chamber 3 is equipped with several guide plates 33 to form a labyrinth channel. The guide plates 33 force the cooling water to deflect multiple times, extend the flow path, increase the residence time of the cooling water, and enable the cooling water to fully absorb the heat transferred by the heat pipe 4.

[0043] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. An apparatus for recovering waste heat from a fluidized bed of an alumina calciner, characterized by, include: The upper flow cavity (2) and the lower flow cavity (3) are separated from each other by a partition wall (1); A number of heat pipes (4) are fixedly inserted through the partition wall (1), with the two ends of the heat pipes (4) located in the upper flow cavity (2) and the lower flow cavity (3), respectively.

2. The fluidized bed waste heat recovery device for an alumina calcination furnace according to claim 1, characterized by The heat pipe (4) consists of a pipe wall (41), a capillary structure layer (42) and a hollow cavity (43) from the outside to the inside, and the heat pipe (4) is filled with a working fluid.

3. The fluidized bed waste heat recovery device for an alumina calcination furnace according to claim 1, characterized by The outer wall of the heat pipe (4) is provided with several ribs (44).

4. The fluidized bed waste heat recovery device for an alumina calcination furnace according to claim 3, characterized by The ribs (44) are formed extending on the radial plane of the heat pipe (4), and a plurality of the ribs (44) are arranged along the length of the heat pipe (4).

5. The fluidized bed waste heat recovery device for an alumina calcination furnace according to claim 3, characterized by The rib (44) is integrally formed with the heat pipe (4).

6. The fluidized bed waste heat recovery device for an alumina calcination furnace according to claim 1, characterized by The upper flow chamber (2) is provided with an alumina inlet (21) and an alumina outlet (22) at its two ends.

7. The fluidized bed waste heat recovery device for an alumina calcination furnace according to claim 6, characterized by The downstream cavity (3) is provided with a cooling water outlet (32) at one end near the alumina inlet (21), and a cooling water inlet (31) at the other end near the alumina outlet (22).

8. The fluidized bed waste heat recovery device for an alumina calcination furnace according to claim 1, characterized by The sidewall of the upper flow cavity (2) is provided with several compressed air inlets (23) along its length.

9. The fluidized bed waste heat recovery device for an alumina calcination furnace according to claim 8, characterized by The heat pipe (4) is positioned to avoid the output extension space of the compressed air inlet (23).

10. The fluidized bed waste heat recovery device for an alumina calcination furnace according to claim 1, characterized by The downflow cavity (3) is provided with several guide plates (33) to form a maze passage.

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