Flash-evaporation-free digestion system for gibbsite

Abstract

The utility model discloses a gibbsite flash-evaporation-free dissolution system which comprises a heat exchanger A1, a cold source outlet of the heat exchanger A1 is connected with a cold source inlet of a heat exchanger B2 through a pipeline, a cold source outlet of the heat exchanger B2 is connected with a cold source inlet of a heat exchanger C3 through a pipeline, and a cold source outlet of the heat exchanger C3 is connected with an inlet of a heat preservation staying system through a pipeline. An outlet of the heat preservation staying system is connected with a heat source inlet of the heat exchanger A1 through a pipeline, and heat source inlets of the heat exchanger B2 and the heat exchanger C3 are further connected with a heat source. According to the flash-free system disclosed by the utility model, a multi-stage flash evaporator, a secondary steam condensate water tank, a water cooler, a matched vacuum system and the like as well as related pipelines and accessories for connecting the equipment and the system are omitted, so that the power consumption of the equipment and the corresponding investment and operation and maintenance cost are reduced, and meanwhile, the heat dissipation loss of the system caused by the links is also eliminated. Therefore, the energy utilization efficiency is improved, the consumption of fresh steam is reduced, and the economic benefits and environmental protection benefits of the whole dissolution process are improved to a certain extent.

Description

Technical Field

[0001] This utility model relates to a flash-free leaching system for gibbsite, belonging to the field of alumina production technology. Background Technology

[0002] In my country's alumina industry, pipeline flash leaching technology is commonly used for processing gibbsite-type bauxite. The specific process is as follows: First, pre-desiliconized slurry at approximately 92-95℃ enters the shell-and-tube heat exchanger of the leaching system. Inside this heat exchanger, secondary steam generated during the staged cooling and depressurization flash leaching process is used as a heat source. Through heat exchange with the low-temperature slurry, the slurry temperature is gradually increased to approximately 115-120℃. Then, fresh steam is used as a heat source to further heat the slurry until it reaches the leaching temperature of approximately 155-160℃. At this point, the slurry is held at the leaching temperature for 30-60 minutes to ensure a complete reaction and effective leaching. After the holding leaching process, the slurry enters the flash leaching stage. After flash leaching, the slurry temperature drops to approximately 110℃, and then it enters the post-leaching tank, where a pump transports the slurry to the next process.

[0003] From a thermodynamic perspective, flash evaporation utilizes secondary steam heating to transfer heat from the gas phase to the liquid phase, combining sensible and latent heat (latent heat accounting for ≥70%). Its heat transfer coefficient is 3 to 6 times that of liquid-liquid heat exchange under the same conditions, and the heat exchange equipment is compact. However, the evaporation process increases the alkali concentration in the system, leading to a relatively higher boiling point of the solution and a relatively higher temperature (above 110℃) of the leached slurry. This reduces the secondary utilization of heat in the system and increases the steam consumption of the leaching system.

[0004] The scaling mechanism of secondary steam on the heat exchange side is silicate deposition. The secondary steam carries micron-sized silicon slag particles (≤50μm). Due to the sudden drop in temperature (e.g., 152℃→140℃), the supersaturation on the condensation surface increases sharply, triggering heterogeneous nucleation. Amorphous SiO2 scales are easily formed on the condensation surface.

[0005] It is worth mentioning that although the flash evaporation process of the leaching slurry achieves efficient heat recovery and utilization, the multi-stage flash evaporators, secondary steam condensate tanks, water coolers, and associated vacuum systems involved in the flash evaporation process are not only cumbersome but also increase equipment investment, power consumption, and operation and maintenance costs. The large amount of equipment and piping also increases the system's heat loss. Therefore, simplifying the process flow and improving system energy efficiency is essential. Summary of the Invention

[0006] The purpose of this invention is to provide a flash-free leaching system for gibbsite. This system overcomes the shortcomings of existing technologies while simplifying the process, saving investment and land area, and improving the economic efficiency of alumina production.

[0007] The technical solution of this utility model is as follows: a trihydrate gibbsite flash-free leaching system, comprising a heat exchanger A, the cold source outlet of heat exchanger A being connected to the cold source inlet of heat exchanger B via a pipe, the cold source outlet of heat exchanger B being connected to the cold source inlet of heat exchanger C via a pipe, the cold source outlet of heat exchanger C being connected to the inlet of a heat insulation system via a pipe, the outlet of the heat insulation system being connected to the heat source inlet of heat exchanger A, and heat sources being connected to the heat source inlets of heat exchangers B and C.

[0008] In the aforementioned trihydrate gibbsite flash-free leaching system, the heat source is connected to the heat source inlet of heat exchanger C via a pipeline, and the heat source outlet of heat exchanger C is connected to the heat source inlet of heat exchanger B via a pipeline.

[0009] In the aforementioned trihydrate gibbsite flash-free leaching system, the heat source outlet of heat exchanger B is connected to the inlet of a new steam condenser, and the outlet of the new steam condenser is connected to pump B.

[0010] In the aforementioned gibbsite flashless leaching system, the heat source outlet of heat exchanger A is connected to the leaching tank, and pump A is also connected to the leaching tank.

[0011] In the aforementioned gibbsite flash-free leaching system, the heat preservation and retention system consists of multiple heat preservation and retention devices connected in series.

[0012] The beneficial effects of this invention are as follows: Compared with existing technologies, the flashless system of this invention eliminates multi-stage flash evaporators, secondary steam condensate tanks, water coolers, and supporting vacuum systems, as well as the pipes and accessories connecting these devices and systems. This reduces equipment power consumption and corresponding investment and maintenance costs, while also eliminating system heat loss caused by these components. This not only improves energy utilization efficiency and reduces the consumption of new steam, but also enhances the economic and environmental benefits of the entire leaching process to a certain extent, aligning with the development concept of energy conservation and emission reduction in modern industrial production.

[0013] From a thermodynamic perspective, the flash-free process involves a direct, one-to-one correspondence between the high-temperature slurry and the low-temperature slurry, eliminating phase change liquid-liquid heat exchange. Using this system simplifies the entire leaching process, reducing the number and types of leaching unit equipment and eliminating complex piping. Furthermore, the flash-free process does not affect the system's alkali concentration; the alkali concentration is relatively lower than after flash leaching, resulting in a lower boiling point elevation and a lower outlet slurry temperature (below 109°C). This reduces the heat carried out of the leaching system by the slurry, slightly decreasing the system's steam consumption.

[0014] The scaling mechanism of high-temperature slurry on the heat exchange side is driven by temperature gradient. Scaling occurs slowly under moderate temperature drop and is mainly suppressed by flow rate. In the low flow rate region (<0.5m / s), slurry is easy to deposit. The small temperature difference between slurries reduces supersaturation and slows down the scaling rate. The fluid flow rate has a shearing effect. When the flow rate is ≥1.2m / s, the scaling rate slows down significantly, effectively extending the cleaning cycle. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of this utility model.

[0016] Figure reference numerals: 1-Heat exchanger A, 2-Heat exchanger B, 3-Heat exchanger C, 4-Insulation retention tank, 5-Dissolution tank, 6-Pump A, 7-New steam condensate, 8-Pump B. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention.

[0018] An embodiment of this utility model: A gibbsite flash-free leaching system includes a heat exchanger A1. The cold source outlet of heat exchanger A1 is connected to the cold source inlet of heat exchanger B2 via a pipe. The cold source outlet of heat exchanger B2 is connected to the cold source inlet of heat exchanger C3 via a pipe. The cold source outlet of heat exchanger C3 is connected to the inlet of a heat insulation system via a pipe. The outlet of the heat insulation system is connected to the heat source inlet of heat exchanger A1 via a pipe. The heat source inlets of heat exchangers B2 and C3 are also connected to heat sources.

[0019] In use, the pre-desilicon slurry, with a temperature of 92-95℃, enters heat exchanger A1 through the cold source inlet. Inside heat exchanger A1, the high-temperature leaching slurry flowing from the heat-insulating retention system exchanges heat with the pre-desilicon slurry, gradually raising its temperature to 110-115℃. The pre-desilicon slurry then enters heat exchanger B2, where it is further heated by high-temperature fresh steam condensate, raising its temperature to 120℃. At approximately ℃, the pre-desilicated slurry then enters heat exchanger C3. Inside C3, fresh steam further heats the slurry until it reaches the dissolution temperature of 155–160℃. The slurry then enters a heat-insulating retention system and remains there for 30–60 minutes for the dissolution reaction. This "retention" does not mean the slurry stops moving; it is a continuously flowing process within the system, taking 30–60 minutes from entry to exit. After the heat-insulating dissolution process, the slurry enters heat exchanger 1 and undergoes a liquid-liquid phase-change reaction with the pre-desilicated slurry (at 92–95℃) entering from the cold source inlet. This process lowers the temperature of the heat-exchanged, dissolved slurry to below 109℃.

[0020] In this invention, heat exchangers A1, B2, and C3 are used to preheat and heat the pre-desiliconized slurry to reach the temperature required for leaching. A heat-preservation and retention system is used to maintain the slurry at the leaching temperature. After leaching, the slurry indirectly exchanges heat with the low-temperature slurry fed to the cold side of heat exchanger A1.

[0021] The heat source is connected to the heat source inlet of heat exchanger C3 via a pipeline, and the heat source outlet of heat exchanger C3 is connected to the heat source inlet of heat exchanger B2 via a pipeline, thus realizing the reuse of the heat source, namely fresh steam. The condensate from the fresh steam generated by its phase change can be used to reheat the pre-desiliconized slurry.

[0022] The heat source outlet of heat exchanger B2 is connected to the inlet of new steam condenser 7. Pump B8 is connected to the outlet of new steam condenser 7. High-temperature new steam enters heat exchanger C3 for the first heat exchange. The new steam condensate generated after the heat exchange then enters heat exchanger B2 for the second heat exchange. The new steam condensate after the heat exchange finally enters new steam condenser 7, and is then transported to other processes by pump B8.

[0023] The heat source outlet of the heat exchanger A1 is connected to the dissolution tank 5. The dissolution tank 5 is also connected to the pump A6. After the heat exchange is completed, the temperature of the dissolution slurry drops to below 109°C and then enters the dissolution tank 5. The dissolution tank 5 and the pump A6 are used to store the dissolution slurry and transport it to the next process.

[0024] The heat preservation and residence system consists of multiple heat preservation and residence units 4 connected in series to correspond to different dissolution residence times. The number of heat preservation and residence units 4 is determined according to the dissolution residence time and the volume of the heat preservation and residence units. The number of equipment such as the dissolution tank 5, pump A6, new steam condenser 7, and pump B8 is determined according to the actual design conditions, and no specific constraints are imposed here.

[0025] When the heat source is fresh steam, the condensate produced after heat exchange ultimately enters the fresh steam condenser 7, and is then transported to other processes via pump B8. The fresh steam condenser 7 and pump B8 are used to store the fresh steam condensate and transport it to the next process stage. The heat sources used in the entire system include, but are not limited to, fresh steam. Further exploration of coupling with renewable energy sources (such as solar heating) can also be undertaken to promote the industry's green transformation. If other heat sources are used, no fresh steam condensate is generated, allowing for further process simplification. Heat exchangers B2 and C3 can be combined into one, eliminating the need for the fresh steam condenser 7 and pump B8.

[0026] The number of heat exchange stages of heat exchangers A1, B2, and C3 is determined based on the dissolution heat balance. Furthermore, heat exchangers A1, B2, and C3 include, but are not limited to, various types of heat exchangers applicable to dissolution conditions, as well as all measures to enhance heat transfer.

[0027] The equipment for the entire leaching system includes, but is not limited to, a series of materials and measures that are corrosion-resistant and anti-scaling.

[0028] In the entire system, heat exchangers A1, B2, C3, heat-insulating retention tank 4, post-dissolution tank 5, pump A6, fresh steam condenser 7, and pump B8 are connected by pipelines to form a continuous production line. The slurry sequentially passes through heat exchangers A1, B2, C3, and heat-insulating retention tank 4 for heating, heat preservation, and dissolution treatment. Finally, it is transported to the next process stage by pump A6 via post-dissolution tank 5. This multi-stage countercurrent or cocurrent heat exchange system utilizes the high-temperature slurry after dissolution to preheat the desilication slurry entering the dissolution system, achieving cascaded heat recovery.

[0029] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A flash-free leaching system for gibbsite, characterized in that: It includes heat exchanger A (1), the cold source outlet of heat exchanger A (1) is connected to the cold source inlet of heat exchanger B (2) via a pipe, the cold source outlet of heat exchanger B (2) is connected to the cold source inlet of heat exchanger C (3) via a pipe, the cold source outlet of heat exchanger C (3) is connected to the inlet of the heat insulation system via a pipe, the outlet of the heat insulation system is connected to the heat source inlet of heat exchanger A (1), and the heat source inlets of heat exchanger B (2) and heat exchanger C (3) are also connected to heat sources.

2. The gibbsite flash-free leaching system according to claim 1, characterized in that: The heat source is connected to the heat source inlet of heat exchanger C (3) via a pipeline, and the heat source outlet of heat exchanger C (3) is connected to the heat source inlet of heat exchanger B (2) via a pipeline.

3. The gibbsite flash-free leaching system according to claim 2, characterized in that: The heat source outlet of the heat exchanger B (2) is connected to the inlet of the new steam condenser (7), and the outlet of the new steam condenser (7) is connected to the pump B (8).

4. The gibbsite flash-free leaching system according to claim 1, characterized in that: The heat source outlet of the heat exchanger A (1) is connected to the dissolution tank (5), and the dissolution tank (5) is also connected to the pump A (6).

5. The gibbsite flash-free leaching system according to claim 1, characterized in that: The heat preservation system consists of multiple heat preservation devices (4) connected in series.

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