Method for dissolving gibbsite out without flash evaporation

Abstract

The invention discloses a gibbsite flash evaporation-free dissolving-out method which comprises the following steps: pre-desiliconized ore pulp at 92-95 DEG C enters a heat exchanger A, in the heat exchanger A, high-temperature dissolved-out slurry and the pre-desiliconized ore pulp are subjected to heat exchange, so that the temperature of the pre-desiliconized ore pulp is gradually increased to 110-115 DEG C, then the pre-desiliconized ore pulp enters a heat exchanger B, in the heat exchanger B, through new steam condensate water, the temperature of the pre-desiliconized ore pulp is increased to 110-115 DEG C; the pre-desiliconized ore pulp is continuously heated, the temperature of the pre-desiliconized ore pulp is increased to about 120 DEG C, then the pre-desiliconized ore pulp enters a heat exchanger C, in the heat exchanger C, the pre-desiliconized ore pulp is further heated through new steam till the temperature of the pre-desiliconized ore pulp reaches the dissolution temperature of 155-160 DEG C, then the pre-desiliconized ore pulp enters a heat preservation staying system to stay for 30-60 min, and a dissolution reaction is conducted; the slurry subjected to heat preservation dissolution enters a heat exchanger A to be subjected to liquid-liquid phase-free heat exchange, and the temperature of the slurry subjected to heat exchange is reduced to 109 DEG C or below. The method simplifies the process flow, saves the investment and land occupation, and improves the economic benefit of alumina production.

Description

Technical Field

[0001] The present invention relates to a method for dissolving gibbsite without flash evaporation, belonging to the technical field of alumina production. Background Art

[0002] In the alumina industry in China, for the treatment of gibbsite-type bauxite, the pipe flash evaporation dissolution technology is generally adopted. The specific technological process is as follows: First, the pre-desiliconized pulp at a temperature of about 92 - 95 °C enters the shell-and-tube heat exchanger of the dissolution system. In this heat exchanger, using the secondary steam generated during the step-by-step cooling and pressure reduction flash evaporation process of the dissolved pulp as the heat source, through the way of heat exchange with the low-temperature pulp, the pulp temperature is gradually increased to about 115 - 120 °C. Subsequently, using new steam as the heat source, the pulp is further heated until the pulp temperature reaches the dissolution temperature of about 155 - 160 °C. At this time, the pulp is kept at the dissolution temperature for a heat preservation residence dissolution reaction for 30 - 60 minutes to ensure sufficient reaction and achieve effective dissolution. After the heat preservation dissolution, the pulp enters the flash evaporation link. After flash evaporation, the pulp temperature drops to about 110 °C, and then enters the post-dissolution tank, and the pulp is transported to the next process by the power of the pump.

[0003] From a thermodynamic perspective, full flash evaporation utilizes the heat transfer form of secondary steam heating from gas phase to liquid phase, with sensible heat and latent heat (latent heat accounts for ≥70%), and its heat transfer coefficient is 3 - 6 times that of liquid-liquid heat transfer under the same conditions, and the heat exchange equipment is compact. However, the flash evaporation process causes the alkali concentration in the system to increase, which leads to a relatively high increase in the boiling point of the solution, and the temperature of the discharged pulp from dissolution is relatively high (above 110 °C), and the secondary utilization of system heat is relatively reduced, and the steam consumption of the dissolution system will increase.

[0004] The scaling mechanism of secondary steam on the heat exchange side belongs to silicate deposition. The secondary steam carries micron-sized silicon slag particles (≤50 μm), and due to the sudden drop in temperature (such as 152 °C → 140 °C) on the condensation surface, the supersaturation suddenly rises, triggering heterogeneous nucleation, and it is easy to form amorphous SiO2 scale on the condensation surface.

[0005] It is worth mentioning that during the flash evaporation process of the dissolved pulp, although the high-efficiency recovery and utilization of system heat are achieved, the multi-stage flash evaporator, secondary steam condensate tank, water cooler and supporting vacuum system, etc. supporting the flash evaporation process are not only cumbersome in technology, but also increase equipment investment, power consumption and operation and maintenance costs, etc. A large number of equipment, pipelines, etc. also increase the heat dissipation loss of the system. Simplifying the process flow and improving the system energy efficiency are very necessary. Summary of the Invention

[0006] The present invention aims to provide a flash-free dissolution method for gibbsite, which overcomes the shortcomings of the prior art while simplifying the process, saving investment and land, and improving the economic benefits of alumina production.

[0007] The technical solution of the present invention is as follows: a flash-free dissolution method for gibbsite, wherein a pre-desiliconized slurry with a temperature of 92 to 95°C enters a heat exchanger A, and in heat exchanger A, the temperature of the pre-desiliconized slurry is gradually increased to 110 to 115°C by heat exchange with the high-temperature dissolution slurry and the pre-desiliconized slurry. The pre-desiliconized slurry then enters a heat exchanger B, and in heat exchanger B, the pre-desiliconized slurry is further heated by new steam condensing water, so that the temperature of the pre-desiliconized slurry is increased to about 120°C, and then enters a heat exchanger C, and in heat exchanger C, the pre-desiliconized slurry is further heated by new steam until the temperature of the pre-desiliconized slurry reaches the dissolution temperature of 155 to 160°C, and then the pre-desiliconized slurry enters a heat preservation retention system and stays for 30 to 60 minutes for dissolution reaction. After the heat preservation and dissolution are completed, the slurry enters a heat exchanger A for liquid-liquid phase-free heat exchange, so that the temperature of the slurry after heat exchange is reduced to below 109°C.

[0008] In the aforementioned flash-free dissolution method for gibbsite, the temperature of the slurry after heat exchange is reduced to below 109° C., and then enters the dissolution post-tank, where the slurry is transported to the next process by the power of pump A.

[0009] In the aforementioned flash-free evaporation method for gibbsite, the fresh steam condensate generated after the fresh steam heat exchange eventually enters the fresh steam condenser and is transported to other processes via pump B.

[0010] In the aforementioned flash-free dissolution method for gibbsite, the new steam first enters the heat exchanger C. After heat exchange, the new steam generates new steam condensate which enters the heat exchanger B. After completing heat exchange again in the heat exchanger B, the new steam enters the new steam condenser.

[0011] In the aforementioned flash-free dissolution method for gibbsite, the heat preservation and retention system is composed of a plurality of heat preservation and retention devices connected in series.

[0012] The present invention has the following beneficial effects: Compared with existing technologies, the flash-free evaporation method eliminates the multi-stage flash evaporator, secondary steam condensate tank, water cooler, and supporting vacuum system, as well as the associated piping and accessories connecting these devices and systems. This reduces equipment power consumption and the corresponding investment and operation and maintenance costs, while also eliminating the system heat dissipation losses caused by these links. This not only improves energy utilization efficiency and reduces new steam consumption, but also enhances the economic and environmental benefits of the entire dissolution process to a certain extent, in line with the development concept of energy conservation and emission reduction in modern industrial production.

[0013] From a thermodynamic perspective, without the flash evaporation process, it is a liquid-liquid heat exchange process without phase change where the high-temperature slurry directly corresponds to the low-temperature slurry step by step. The non-flash digestion method of the present invention has a simple process flow, involving fewer types and quantities of digestion unit equipment, and eliminating complex pipeline processes. At the same time, the non-flash evaporation process has no impact on the alkali concentration of the system, the boiling point elevation of the solution is relatively low, and the temperature of the discharged slurry after digestion can also be relatively low (below 109°C), reducing the heat carried out of the digestion system by the slurry, and slightly reducing the steam consumption of the system.

[0014] The scaling mechanism of the high-temperature slurry on the heat exchange side is driven by the temperature gradient. The scale precipitates slowly under mild temperature drops and is mainly inhibited by the flow rate. The slurry is prone to deposition in the low-flow rate area (<0.5 m / s). The temperature difference between the slurries is small, reducing the supersaturation, and the scaling rate slows down. Among them, the fluid flow rate has a shearing effect. When the flow rate ≥ 1.2 m / s, the scaling rate significantly slows down, effectively extending the cleaning cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is the process flow diagram of the present invention.

[0016] Reference numerals: 1 - Heat exchanger A, 2 - Heat exchanger B, 3 - Heat exchanger C, 4 - Insulation residence tank, 5 - Post-digestion tank, 6 - Pump A, 7 - New steam condenser, 8 - Pump B. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be further described below in conjunction with the drawings and embodiments, but it shall not be used as a basis for limiting the present invention.

[0018] Embodiment of the present invention: A non-flash digestion method for gibbsite. The pre-desilication slurry with a temperature of 92 - 95°C enters Heat exchanger A1. In Heat exchanger A1, by using the heat exchange method between the high-temperature digested slurry and the pre-desilication slurry, the temperature of the pre-desilication slurry is gradually increased to 110 - 115°C. Subsequently, the pre-desilication slurry enters Heat exchanger B2. In Heat exchanger B2, through the new steam condensate, the pre-desilication slurry is further heated to raise the temperature of the pre-desilication slurry to about 120°C. Then it enters Heat exchanger C3. In Heat exchanger C3, the pre-desilication slurry is further heated by the new steam until the temperature of the pre-desilication slurry reaches the digestion temperature of 155 - 160°C. Then the pre-desilication slurry enters the insulation residence system and stays for 30 - 60 minutes for the digestion reaction. After the insulation digestion, the slurry enters Heat exchanger A1 for liquid-liquid phase change heat exchange, so that the temperature of the heat-exchanged slurry drops below 109°C.

[0019] In the method of the present invention, heat exchangers A1, B2, and C3 are used to preheat and heat the pre-desilicated pulp to reach the temperature required for digestion. The heat preservation and residence system is used to carry out heat preservation and digestion residence on the pulp that has reached the digestion temperature. After digestion, the slurry exchanges heat indirectly with the low-temperature pulp fed into the cold side on the hot side of heat exchanger 1. The pre-desilicated pulp enters the heat preservation and residence system and stays for 30 to 60 minutes for the digestion reaction. The so-called residence does not mean that the pulp stops moving. The pulp is in a continuous flowing process in the heat preservation and residence system. It takes 30 to 60 minutes for the pulp to enter from the inlet of the heat preservation and residence system and discharge from the outlet.

[0020] The temperature of the heat-exchanged slurry drops below 109 °C, and then it enters the post-digestion tank 5. The post-digestion tank 5 and pump A6 are used to store the digested slurry and transport it to the next process.

[0021] When the heat source used in heat exchanger C3 is new steam, the new steam condensate generated after the new steam exchanges heat finally enters the new steam condenser 7, and the pump B8 transports the new steam condensate to other processes. The new steam condenser 7 and pump 8 are used to store the new steam condensate and transport it to the next process.

[0022] The heat sources used in the whole method include but are not limited to new steam. It is also possible to further explore the coupling with renewable energy (such as solar heating, etc.) to promote the green transformation of the industry. If other heat sources are used, no new steam condensate is generated, and the process can be further simplified by combining heat exchanger B2 and heat exchanger C3 into one. At this time, the new steam condenser 7 and pump B8 can be cancelled in the whole system.

[0023] The new steam first enters heat exchanger C3 from the heat source inlet for the first heat exchange. The new steam condensate generated after the new steam exchanges heat then enters the heat source inlet of heat exchanger B2 from the heat source outlet of heat exchanger C3, and undergoes the second heat exchange in heat exchanger B2. After being discharged from the heat source outlet of heat exchanger B2, it enters the new steam condenser 7 for storage.

[0024] The heat preservation and residence system is composed of multiple heat preservation and residence vessels 4 connected in series. The number of heat preservation and residence vessels 4 is determined according to the digestion residence time and the volume of the heat preservation and residence vessels. The number of equipment such as the post-digestion tank 5, pump A6, new steam condenser 7, and pump B8 is determined according to the actual design conditions. No specific quantity is restricted here.

[0025] The number of heat exchange stages of heat exchangers A1, B2, and C3 is formulated according to the digestion heat balance. Moreover, heat exchangers A1, B2, and C3 include but are not limited to various types of heat exchanger forms suitable for the digestion working conditions, as well as all measures to enhance heat transfer.

[0026] The equipment of the entire dissolution system includes, but is not limited to, a series of materials and measures that are corrosion-resistant and scale-resistant.

[0027] In the composition of the entire system, the heat exchanger A1, heat exchanger B2, heat exchanger C3, heat preservation residence 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 pulp passes through the heat exchanger A1, heat exchanger B2, heat exchanger C3, and heat preservation residence tank 4 in sequence for heating and heat preservation residence dissolution treatment, and finally is transported to the next process by pump A6 through the post-dissolution tank 5. The multi-stage countercurrent or cocurrent heat exchange system of the present invention uses the high-temperature pulp after dissolution to preheat the desilicated pulp entering the dissolution system, realizing the cascade recovery of heat.

[0028] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for non-flash digestion of gibbsite, characterized in that: The pre-desiliconized slurry with a temperature of 92-95°C enters the heat exchanger A (1). In the heat exchanger A (1), the temperature of the pre-desiliconized slurry is gradually increased to 110-115°C by heat exchange between the high-temperature dissolution slurry and the pre-desiliconized slurry. The pre-desiliconized slurry then enters the heat exchanger B (2). In the heat exchanger B (2), the pre-desiliconized slurry is further heated by new steam condensing water, and the temperature of the pre-desiliconized slurry is increased to about 120°C. The pre-desiliconized slurry then enters the heat exchanger C (3). In the heat exchanger C (3), the pre-desiliconized slurry is further heated by new steam until the temperature of the pre-desiliconized slurry reaches the dissolution temperature of 155-160°C. The pre-desiliconized slurry then enters the heat preservation retention system and stays for 30-60 minutes for dissolution reaction. After the heat preservation and dissolution, the slurry enters the heat exchanger A (1) for liquid-liquid phase-free heat transfer, so that the temperature of the slurry after heat exchange is reduced to below 109°C.

2. The flashless digestion method of gibbsite according to claim 1, characterized in that: The temperature of the slurry after heat exchange drops to below 109° C., and then enters the post-dissolution tank (5), and is transported to the next process with the help of the power of pump A (6).

3. A gibbsite non-flash digestion method according to claim 1, characterized in that: The new steam condensate generated after the new steam heat exchange finally enters the new steam condenser (7), and is transported to other processes via pump B (8).

4. A gibbsite non-flash digestion method according to claim 3, characterized in that: The new steam first enters the heat exchanger C (3), and after heat exchange, the new steam generates new steam condensate, which enters the heat exchanger B (2), and then completes heat exchange again in the heat exchanger B (2) and enters the new steam condensate (7).

5. A method for non-flash digestion of gibbsite according to claim 1, characterized in that: The heat preservation retention system is composed of a plurality of heat preservation retention devices (4) connected in series.

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