Powdery lime slurrying system for Bayer process red mud dealkalization

Abstract

The invention relates to a powdery lime slurrying system aiming at Bayer process red mud dealkalization, which belongs to the technical field of aluminum oxide production and comprises a lime bin, slurrying reaction equipment, a buffer tank, a settling tank and an overflow tank, a discharging pipe of the metering conveying device and a slurrying water inlet pipe are both connected with the feeding end of the slurrying reaction device, the slurrying reaction device is connected with the buffer tank, the buffer tank is connected with the settling tank through a vertical buffer pump arranged on the top, and the settling tank is connected with the overflow tank through an overflow pipe. The method solves the problems that in the Bayer process aluminum oxide production process, after the red mud dealkalization procedure is added, the dosage of lime milk is sharply increased, and the treatment capacity of a traditional ashing system is insufficient, meanwhile, graded utilization of high-concentration lime milk and low-concentration lime milk is achieved, and the production efficiency of lime milk preparation is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of alumina production, and in particular relates to a powdered lime slurry system for dealkalization of Bayer process red mud. Background Art

[0002] Red mud is a waste product in the Bayer process of alumina production. The sodium oxide content in the discharged red mud not only restricts its large-scale comprehensive utilization, but also takes away the alkali circulating in the Bayer process system, increasing the alkali consumption of the alumina plant and affecting the cost and economic indicators of the alumina plant.

[0003] In recent years, in order to recover the alkali in red mud and promote the sustainable development of the alumina industry, a variety of red mud dealkalization technology routes have been developed. At present, most alumina plants adopt the method of adding lime milk to the washing sedimentation tank, using the calcium in the lime milk to react with the sodium in the red mud to generate more insoluble cancryogenite, and replace the alkali in the red mud for recovery, thereby reducing the alkalinity of the discharged red mud and the alkali consumption of the whole plant. In the production process, lime milk is generally added according to the red mud calcium-silicon ratio of 1.0-2.0. When converted to the consumption of dry lime, the ash consumption increases by more than 10 times, and the slurrying process of the traditional drum-type ash machine can no longer meet the production requirements. At the same time, red mud dealkalization has low activity requirements for lime milk and high concentration requirements to ensure that good washing effects are obtained while dealkalization. Therefore, a powdered lime slurrying system for Bayer red mud dealkalization is provided to improve the lime processing capacity, meet the demand for high-concentration lime milk for red mud dealkalization, and achieve efficient utilization of high and low solid content lime milk in the whole plant. Summary of the invention

[0004] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a powdered lime slurrying system for Bayer process red mud dealkalization, which solves the problem of limited production capacity in the lime milk slurrying process in the alumina production process, and at the same time realizes the efficient utilization of lime milk of different concentrations in the Bayer process production process, improves the production efficiency of lime milk preparation, and meets the demand for high-concentration lime milk in red mud dealkalization.

[0005] In order to achieve the above object, the main technical solutions adopted by the present invention include: A powdered lime slurry system for Bayer red mud dealkalization comprises a lime silo for storing powdered lime, a slurrying reaction device, a buffer tank, a sedimentation tank, and an overflow tank. The discharge end of the lime silo is connected to a metering and conveying device via a spiral gate. The discharge end of the metering and conveying device and a slurrying water inlet pipeline are both connected to the feed end of the slurrying reaction device. The lime powder feed amount is matched with the flow rate of the inlet pipe. The slurrying reaction device is used to produce an effective calcium concentration of 160-180 g / l and a density of 1100-1200 kg / m 3The lime milk slurry, the slurry reaction equipment is connected to the buffer tank, the buffer tank is connected to the sedimentation tank through the vertical buffer pump arranged on the top, the overflow layer of the sedimentation tank is connected to the overflow tank through the overflow pipe, and the underflow layer of the sedimentation tank is pumped by the underflow pump to discharge the effective calcium concentration of 180-220g / l and the density of 1200-1300kg / m 3 The underflow lime milk is sent to the red mud dealkalization process, and the overflow tank is pumped with an effective calcium concentration of 120-160g / l and a density of 1000-1100kg / m 3 The overflow lime milk is sent to the fine filtration process.

[0006] Furthermore, the powdered lime has a particle size of 100% ≤ 5 mm and a bulk density of 1.1-1.5 t / m 3 , repose angle 40-50°.

[0007] Furthermore, the lower part of the lime bin is a cone angle, the cone angle is between 50-70 degrees, and an air cannon is provided at the discharge end, and the number of the air cannon is 1-4.

[0008] Furthermore, the metering and conveying equipment is one of a spiral scale, a quantitative feeder, and a belt scale.

[0009] Furthermore, the return material of the buffer tank is connected to the slurry reaction equipment via a vertical buffer pump.

[0010] Furthermore, the pulping reaction equipment is a pulper or a tank digester.

[0011] Furthermore, the sedimentation tank is a cone structure with a bottom facing downward, and the cone angle of the sedimentation tank is 90-120°.

[0012] Furthermore, the sedimentation tank is connected to the overflow trough through an overflow pipe, the overflow port height of the sedimentation tank is higher than the feed port height of the overflow trough, and the slope of the overflow pipe is greater than 3%.

[0013] Furthermore, the sedimentation tank is stirred by a rake.

[0014] The beneficial effects of the present invention are as follows: the powdered lime slurry system of the present invention for the Bayer process red mud dealkalization technology integrates the storage, weighing, slurrying and grading equipment of lime powder into a system, thereby improving the processing capacity and effect of the slurrying system, meeting the demand for the amount of lime milk in the process of red mud dealkalization, and obtaining lime milk with stable composition, realizing the graded utilization of high and low solid concentrations of lime milk in red mud dealkalization and other processes, which is beneficial to the sustainable development of the alumina industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The present invention is a schematic diagram of a powdered lime slurry system for dealkalization of Bayer process red mud.

[0016] In the figure: 1. Lime silo, 2. Air cannon, 3. Screw gate, 4. Measuring and conveying equipment, 5. Slurry water inlet pipeline, 6. Slurry reaction equipment, 7. Buffer tank, 8. Vertical buffer pump, 9. Sedimentation tank, 10. Underflow pump, 11. Overflow tank, 12. Overflow pump. DETAILED DESCRIPTION

[0017] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation modes in conjunction with the accompanying drawings.

[0018] like Figure 1 As shown, the present invention provides a powdered lime slurry system for Bayer red mud dealkalization, including a lime powder storage system, a metering system, a digestion system, and a lime milk sedimentation and grading system. The lime powder storage system includes: a lime silo 1, an air cannon 2, and a spiral gate 3. The metering system includes a metering and conveying device 4 and a slurry water inlet pipeline 5. The digestion system includes a slurry reaction device 6, a buffer tank 7, and a vertical buffer pump 8. The lime milk sedimentation and grading system includes a sedimentation tank 9, an underflow pump 10, an overflow tank 11, and an overflow pump 12.

[0019] The lime powder is transported into the lime silo 1 by pneumatic conveying equipment for storage. The particle size of the powdered lime is 100% ≤ 5 mm, and the bulk density is 1.1-1.5 t / m 3 The repose angle is between 40-50°. The lower part of the lime silo 1 is a cone, and an air cannon 2 is arranged at the bottom of the cone. The air cannon 2 is welded to the steel bracket at the cone of the lower hopper of the lime silo 1. The air pipe of the air cannon 2 is inserted into the lime silo 1. The number of air cannons 2 is 1-4, and the cone angle of the lime silo is 50-70°. The function of the air cannon 2 is to blow air into the silo to help discharge the material when the lime silo 1 is blocked.

[0020] The discharge end of the lime bin 1 is connected to the metering and conveying device 4 through the spiral gate 3. Specifically, the metering and conveying device 4 is one of a spiral scale, a quantitative feeder, and a belt scale. The discharge of the metering and conveying device 4 and the slurry water inlet pipe 5 are both connected to the feed end of the slurry reaction device 6. The lime powder feed amount and the inlet pipe flow are matched through a chain relationship. The slurry reaction device is used to make an effective calcium concentration of 160-180g / l and a density of 1100-1200kg / m 3lime milk slurry. Specifically, the slurrying reaction equipment 6 is a slurrying device or a tank digester. The slurrying reaction equipment 6 is connected to the buffer tank 7, and the buffer tank 7 is connected to the sedimentation tank 9 through the vertical buffer pump 8 arranged on the top, and the sedimentation tank 9 is connected to the overflow tank 11 through an overflow pipe. The conical bottom lime storage tank 9 adopts a rake machine for stirring, which is convenient for the stratification of the lime milk. The lime milk with higher solid content is sent to the red mud dealkalization process through the underflow pump 10 for use, and the lime milk with lower solid content uses the height difference to flow into the overflow tank 11 through the chute. The overflow tank 11 adopts mechanical stirring to ensure that the overflowed lime milk is evenly mixed and sent to fine filtration and other processes through the overflow pump.

[0021] The lower part of the lime bin 1 is the discharge port. Lime powder is stored in the lime bin 1. When it is needed, the spiral gate 3 at the bottom of the lime bin is opened, and the lime powder passes through the metering and conveying equipment 4 and enters the slurry reaction equipment 6 at the same time as the water in the slurry water inlet pipe 5 according to a certain ratio. Through the chain relationship, the amount of lime and digestion water entering the digestion system is matched, and the slurry reaction is carried out to produce an effective calcium concentration of 160-180g / l and a density of 1100-1200kg / m 3 The lime milk slurry. The produced lime milk flows out from the discharge port of the slurrying reaction equipment 6, passes through the chute and enters the buffer tank 7. The buffer tank 7 is arranged underground and is provided with a stirring device to obtain lime milk slurry with uniform composition. A density meter is installed at the discharge port of the buffer tank 7. Whether the lime milk slurry after slurrying is qualified is judged according to the density. The qualified lime milk slurry will be sent to the sedimentation tank 9, and the unqualified lime milk slurry needs to be returned to the slurrying equipment 6 through the return pipeline for re-slurrying reaction. The qualified lime milk is pumped into the sedimentation tank 9 for sedimentation and separation by the vertical buffer pump 8 on the top of the buffer tank 7. The return material of the buffer tank 7 is connected to the slurrying reaction equipment 6 via the vertical buffer pump 8. If the material in the buffer tank 7 is found to be unqualified by manual inspection or density meter, it is returned to the slurrying reaction equipment 6 through the vertical buffer pump 8 for secondary ash treatment. The vertical buffer pump 8 adopts a vertical slurry pump, which is installed on the top of the buffer tank 7, and is used to pump qualified lime milk slurry from the buried buffer tank 7 into the above-ground sedimentation tank 9. The sedimentation tank 9 uses an underflow pump 10 to send the underflow lime milk slurry to the red mud dealkalization process. The overflow of the sedimentation tank 9 is connected to the overflow tank 11 through an overflow pipe. The overflow tank 11 uses an overflow pump 12 to send the lime milk to fine filtration and other processes. The lime powder processing capacity of the present invention is large, which can meet the requirement of dry lime within 100t / h. The effective calcium concentration of the underflow lime milk can reach 180-220g / l, and the underflow density is 1200-1300kg / m 3 The effective calcium concentration of overflow lime milk can reach 120-160g / l, and the overflow density is 1000-1100kg / m 3 , meeting the requirements of red mud dealkalization and other processes in alumina production for effective calcium concentration, solid content and density of lime milk.

[0022] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. Alterations, modifications, substitutions and variations of the above embodiments by a person skilled in the art are all within the scope of the present invention.

Claims

1. A powdered lime slurry system for dealkalization of Bayer red mud, Features: The invention comprises a lime bin (1) for storing powdered lime, a slurry reaction device (6), a buffer tank (7), a sedimentation tank (9), and an overflow tank (11). The discharge end of the lime bin (1) is connected to a metering and conveying device (4) via a spiral gate (3). The discharge end of the metering and conveying device (4) and a slurry water inlet pipe (5) are both connected to the feed end of the slurry reaction device (6). The feed amount of lime powder is matched with the flow rate of the inlet pipe. The slurry reaction device (6) is used to produce a limestone having an effective calcium concentration of 160-180 g / l and a density of 1100-1200 kg / m 3 The lime milk slurry is prepared by mixing the slurry reaction equipment (6) with the buffer tank (7), the buffer tank (7) is connected to the sedimentation tank (9) via a vertical buffer pump (8) arranged at the top, the overflow layer of the sedimentation tank (9) is connected to the overflow tank (11) via an overflow pipe, and the underflow layer of the sedimentation tank (9) is pumped by the underflow pump (10) to reduce the effective calcium concentration of the discharged material to 180-220 g / l and the density to 1200-1300 kg / m 3 The underflow lime milk is sent to the red mud dealkalization process, and the overflow tank (11) transfers the effective calcium concentration of 120-160g / l and the density of 1000-1100kg / m 3 The overflow lime milk is sent to the fine filtration process.

2. A powdered lime slurry system for dealkalization of Bayer red mud according to claim 1, Features: The powdered lime particle size is 100% ≤ 5mm, and the bulk density is 1.1-1.5t / m 3 , repose angle 40-50°.

3. A powdered lime slurry system for dealkalization of Bayer red mud according to claim 1, Features: The lower part of the lime bin (1) is a cone angle, the cone angle is between 50-70 degrees, and an air cannon (2) is provided at the discharge end, the number of the air cannons (2) is 1-4.

4. A powdered lime slurry system for dealkalization of Bayer red mud according to claim 1, Features: The metering and conveying equipment (4) is one of a spiral scale, a quantitative feeder, and a belt scale.

5. A powdered lime slurry system for dealkalization of Bayer red mud according to claim 1, Features: The return material from the buffer tank (7) is connected to the slurry reaction equipment (6) via a vertical buffer pump (8).

6. A powdered lime slurrying system for dealkalization of Bayer red mud according to claim 1 or 4, Features: The pulping reaction equipment (6) is a pulper or a tank digester.

7. A powdered lime slurry system for dealkalization of Bayer red mud according to claim 1, Features: The sedimentation tank (9) is a cone structure with a bottom facing downward, and the cone angle of the sedimentation tank (9) is 90-120°.

8. A powdered lime slurrying system for dealkalization of Bayer red mud according to claim 1 or 6, Features: The sedimentation tank (9) is connected to the overflow tank (11) via an overflow pipe, the overflow port height of the sedimentation tank (9) is higher than the feed port height of the overflow tank (11), and the slope of the overflow pipe is greater than 3%.

9. A powdered lime slurry system for dealkalization of Bayer red mud according to claim 1, Features: The sedimentation tank (9) is stirred by a rake.

Images