Aluminum oxide evaporation system last-effect secondary steam waste heat recycling device

Abstract

The utility model relates to a last-effect secondary steam waste heat recycling device of an aluminum oxide evaporation system, which comprises a plurality of evaporators arranged in sequence, a steam outlet of the evaporator at the front position is connected with a steam inlet of the evaporator at the rear position along the steam trend, the evaporator at the closest position is named as a last-effect evaporator, and the evaporator at the closest position is named as a second-effect evaporator. A steam outlet of the last-effect evaporator is connected with a waste heat recovery pipeline, at least one steam compressor is arranged on the waste heat recovery pipeline, a heat source inlet of the heat exchanger is connected with the waste heat recovery pipeline, the heat exchanger is located on the downstream of the steam compressor, and the heat exchanger is further provided with a cold source water inlet and a cold source water outlet. The utility model provides a waste heat recycling device capable of recycling waste heat of last-effect secondary steam of an aluminum oxide evaporation system.

Description

Technical Field

[0001] This utility model relates to energy-saving equipment for evaporation systems in the field of metallurgical and chemical technology, and in particular to a device for recovering and utilizing waste heat from the final-effect secondary steam in an alumina evaporation system. Background Technology

[0002] Mother liquor evaporation is a crucial process in alumina production, responsible for maintaining the liquid balance of the alumina production system, providing a suitable concentration of alkali solution for leaching or raw slurry preparation, and removing carbon and alkali accumulated during production. Evaporation is a major energy-consuming unit in alumina production and a vital step in maintaining liquid balance.

[0003] Currently, multi-effect evaporators are used for mother liquor evaporation in alumina production, with the number of effects ranging from 3 to 7. The more effects, the more energy-efficient the evaporator. The steam produced at the last effect of a multi-effect evaporator is called the last-effect secondary steam. The use of this last-effect secondary steam in existing alumina production evaporation systems is as follows: Figure 1 As shown, the secondary steam from the last effect evaporator (2) of the multi-effect evaporator enters the water cooler (also called the atmospheric condenser). The multi-effect evaporator consists of multiple evaporators (1) connected sequentially. Inside the water cooler (3), the steam directly contacts the low-temperature circulating water for heat exchange, condensing it and entering the circulating water system through the water tank (4). The circulating water absorbs the steam from the last effect evaporator, increasing its temperature, and then returns to the circulating cooling tower (5) for further cooling. Due to the continuous influx of condensate from the last effect evaporator, the circulating water system needs to discharge a portion of its circulating water to maintain a water balance. Item 6 in the diagram represents the vacuum pump.

[0004] The secondary steam in the final effect of an alumina evaporation system accounts for about 30% of the total steam volume. Under current evaporation process conditions, the temperature of this final secondary steam is generally between 50 and 60°C. Due to its low temperature and pressure, its energy quality is poor, making recovery and utilization difficult. However, the volume of this final secondary steam is large, and it contains a significant amount of latent heat, accounting for 30% to 40% of the evaporator's heat recovery. The heat carried away by one ton of alumina secondary steam is as high as 1813.7 MJ, equivalent to 62 kg of standard coal. In existing technology, the energy of the final secondary steam is absorbed by the evaporation circulating water. To maintain system energy balance, the evaporation circulating water system uses a cooling tower to discharge this energy, consuming a large portion of energy during the cooling tower's operation. According to relevant calculations, 10-15 m³ of circulating water needs to be injected into the water cooler to absorb 1 ton of final secondary steam. For a current mainstream 1 million-ton oxygen production line, the required circulating water volume is as high as 5000-7000 m³ / h, and the transportation of this circulating water consumes a significant amount of energy.

[0005] The heat balance calculation for a seven-effect falling film evaporator at an alumina production plant is shown in the table below:

[0006] Evaporation heat balance table (based on 1.0t alumina)

[0007]

[0008] Based on my country's alumina production capacity of nearly 100 million tons per year, the energy lost annually through secondary steam evaporation amounts to as much as 62 million tons of standard coal equivalent. Therefore, it is of great significance to recover the energy from the final secondary steam in the evaporation system. Utility Model Content

[0009] The purpose of this invention is to provide a waste heat recovery and utilization device that can recover and utilize the waste heat of the secondary steam at the end of the alumina evaporation system.

[0010] To solve the above-mentioned technical problems, the present invention provides a waste heat recovery and utilization device capable of recovering and utilizing the waste heat of the final-effect secondary steam of an alumina evaporation system, as follows:

[0011] A waste heat recovery and utilization device for the last-effect secondary steam of an alumina evaporation system includes multiple evaporators arranged in sequence along the steam direction. The steam outlet of the evaporator located at the front is connected to the steam inlet of the evaporator located at the rear. The evaporator located at the front is called the last-effect evaporator. The steam outlet of the last-effect evaporator is connected to a waste heat recovery pipeline. At least one steam compressor is installed on the waste heat recovery pipeline. The waste heat recovery and utilization device also includes a heat exchanger connected to the waste heat recovery pipeline with a heat source inlet. The heat exchanger is located downstream of the steam compressor and also has a cold source inlet and a cold source outlet.

[0012] Furthermore, a vacuum pump is connected to the upper end of the heat exchanger shell to discharge the non-condensable secondary steam in the heat exchanger.

[0013] Furthermore, there may be one steam compressor; or there may be multiple steam compressors connected in series.

[0014] Furthermore, the heat exchanger can be a direct heat exchanger or an indirect heat exchanger.

[0015] Furthermore, after entering the heat exchanger shell via the heat source inlet, the final-effect secondary steam directly contacts and exchanges heat with the cold source between the cold source inlet and outlet.

[0016] Furthermore, it also includes a heating heat exchanger for the living area, with the inlet of the heating heat exchanger connected to the outlet of the cold source, and the outlet of the heating heat exchanger for the living area connected to the inlet of the cold source.

[0017] Furthermore, a domestic water supply pipeline is also connected to the cold source outlet.

[0018] The beneficial effects of this invention are as follows: In this invention, the secondary steam discharged from the final-effect evaporator is heated and pressurized by a steam compressor, converting low-quality steam into high-quality steam with higher waste heat that is easier to recover and utilize. During the use of the upgraded secondary steam, its latent heat is recovered and utilized. The cold source water outlet produced after heat exchange with the secondary steam has a higher temperature and better water quality, which can be recycled back into the alumina production process. Compared with existing processes, the circulating water system can be eliminated, reducing the investment and operating costs of the circulating water system. Attached Figure Description

[0019] The above and other objects, features, and advantages of this disclosure will become readily apparent from the following detailed description of exemplary embodiments with reference to the accompanying drawings. In the drawings, several embodiments of this disclosure are illustrated by way of example and not limitation, and like or corresponding reference numerals denote like or corresponding portions, wherein:

[0020] Figure 1 This is a schematic diagram of the structure of the prior art secondary steam waste heat recovery and utilization device in this utility model;

[0021] Figure 2 This is a structural schematic diagram of Embodiment 1 of this utility model;

[0022] Figure 3 This is a structural schematic diagram of Embodiment 2 of this utility model;

[0023] 1. Evaporator; 2. Last-effect evaporator; 3. Water cooler; 4. Water tank; 5. Cooling tower; 6. Vacuum pump; 7. Steam compressor; 8. Waste heat recovery pipeline; 9. Heat source inlet; 10. Cold source inlet; 11. Cold source outlet; 12. Heat exchanger; 13. Water pump; 14. Heating heat exchanger for residential area; 15. Domestic water supply pipeline; 16. Condensate outlet. Detailed Implementation

[0024] To facilitate understanding of this utility model, a more detailed description is provided below with reference to the accompanying drawings and specific embodiments. The accompanying drawings show preferred embodiments of this utility model. However, this utility model can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this utility model.

[0025] It should be noted that, unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of the invention.

[0026] Example 1 of the waste heat recovery and utilization device for the final effect secondary steam in an alumina evaporation system of this utility model is as follows: Figure 2 As shown:

[0027] The system includes multiple evaporators 1 arranged in sequence. In this embodiment, the number of evaporators 1 is not less than three. Along the steam direction, the steam outlet of the evaporator located at the front is connected to the steam inlet of the evaporator located at the rear. The evaporator located closest to the inlet is called the last-effect evaporator 2, and the steam discharged from the last-effect evaporator 2 is called the last-effect secondary steam.

[0028] The steam outlet of the final-effect evaporator 2 is connected to a waste heat recovery pipeline 8. At least one steam compressor 7 is installed on the waste heat recovery pipeline 8. The waste heat recovery and utilization device also includes a heat exchanger 12 connected to the waste heat recovery pipeline via a heat source inlet 9. The heat exchanger 12 is located downstream of the steam compressor 7. The heat exchanger 12 also has a cold source inlet 10 and a cold source outlet 11.

[0029] In this embodiment, the heat exchanger is a direct heat exchanger, which includes a vertically arranged heat exchanger shell, a cold source inlet 10 located at the top of the heat exchanger shell, a cold source outlet 11 located at the bottom of the heat exchanger shell, and a heat source inlet 9 located on the side wall of the heat exchanger shell. After the last-effect secondary steam enters the heat exchanger shell through the heat source inlet, it directly contacts and exchanges heat with the cold source between the cold source inlet and the cold source outlet.

[0030] A vacuum pump 6 is connected to the upper end of the heat exchanger shell to discharge the non-condensable secondary steam in the last effect of the heat exchanger.

[0031] The final-effect secondary steam waste heat recovery and utilization device also includes a residential heating heat exchanger 14. The inlet of the residential heating heat exchanger 14 is connected to the cold source outlet, and the outlet of the residential heating heat exchanger is connected to the cold source inlet. The residential heating heat exchanger can be a radiator or underfloor heating. A domestic water supply pipeline 15 is also connected to the cold source outlet. Water pumps 13 are installed on both the domestic water supply pipeline and the pipeline where the residential heating heat exchanger is located.

[0032] In this invention, the use of a steam compressor can raise the temperature of the final-effect secondary steam to over 80°C and the pressure from 0.015MPa to over 0.05MPa, converting low-quality steam into high-quality steam, thereby facilitating the recovery and utilization of waste heat from the final-effect secondary steam.

[0033] Taking a six-effect falling film evaporator in an alumina plant as an example, the final effect secondary steam flow rate of the six-effect falling film evaporator is 20 t / h, the steam temperature is 58℃, and the steam pressure is 0.018 MPa. The existing production process requires the use of approximately 2000 m³ / h of secondary steam. 3 A circulating water supply of / h is used to absorb this portion of the steam.

[0034] The proposed solution is as follows: The final-effect secondary steam is compressed using a single-stage high-speed centrifugal steam compressor (single-stage compressor motor power 1250kW). Each stage of the compressor can increase the steam temperature by 20℃. After compression and upgrading, the temperature of the final-effect secondary steam is increased to 78℃, and the pressure is 0.044MPa. The upgraded steam is then directly exchanged with the heating return water (temperature around 60℃) used in residential areas.

[0035] (1) The temperature of the heating return water for a heating capacity of 740t / h can be increased from 60℃ to 75℃;

[0036] (2) The amount of heat supplied to the heating system is 46.153 GJ / h. The energy consumed by the steam compressor is 4.5 GJ / h.

[0037] (3) To reduce the evaporation circulation water volume by 2000t / h, one 280kW circulating water pump can be shut down.

[0038] (4) Achieved a water supply capacity of 20t / h for the heating system;

[0039]

[0040] Example 2 of a waste heat recovery and utilization device for the last-effect secondary steam of an alumina evaporation system: Figure 3 As shown:

[0041] The difference between Example 2 and Example 1 is that the heat exchanger is an indirect heat exchanger. The heat exchanger includes a vertically arranged heat exchanger shell, inside which heat exchange tubes are installed. A cold source inlet 10 communicates with the upper end of the heat exchange tubes, and a cold source outlet 11 communicates with the lower end of the heat exchange tubes. A heat source inlet 9 is located on the heat exchanger shell and communicates with the inner cavity of the heat exchanger shell. The final-effect secondary steam enters the inner cavity of the heat exchanger shell through the heat source inlet and exchanges heat with the cold source inside the heat exchange tubes through contact with them. During the heat exchange process, the final-effect secondary steam is pre-cooled to produce condensate. A condensate outlet 16 is provided at the bottom of the heat exchanger shell, and a condensate discharge pump (not shown in the figure) is installed at the condensate outlet.

[0042] Taking a six-effect falling film evaporator in an alumina plant as an example, the final effect secondary steam flow rate of the six-effect falling film evaporator is 20 t / h, the steam temperature is 58℃, and the steam pressure is 0.018 MPa. The existing production process requires the use of approximately 2000 m³ / h of secondary steam. 3 A circulating water supply of / h is used to absorb this portion of the steam.

[0043] The proposed solution is as follows: The final-effect secondary steam is compressed using a two-stage single-stage high-speed centrifuge (single-stage compressor motor power 1250kW). Each stage of the compressor increases the steam temperature by 20°C. After compression and upgrading, the final-effect secondary steam temperature is raised to 98°C. The upgraded steam is then sent to a heater to heat the demineralized water in a thermal power plant. The following effects can be achieved:

[0044] (1) The final-effect secondary steam compression increases the installed power by 2500kW.

[0045] (2) To reduce the evaporation circulation water volume by 2000t / h, one 280kW circulating water pump can be shut down.

[0046] (3) Steam condensation produces 20t / h of 95℃ condensate, which is of good quality and can be returned to the alumina production process.

[0047] (4) The temperature of the demineralized water in a 200t / h power plant can be increased from 30℃ to 84.11℃, which can reduce the steam used for heating the demineralized water by 18.86t / h.

[0048]

[0049] Based on an electricity price of 0.56 yuan / ton, a steam price of 120 yuan / ton, an evaporation condensate price of 8 yuan / ton, and an annual operating time of 8000 hours, the annual cost reduction is 9.44 million yuan / year.

[0050] In the foregoing description of this specification, unless otherwise expressly specified and limited, the terms "fixed," "installed," "connected," or "joined" should be interpreted broadly. For example, the term "joined" can refer to a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; or it can refer to the internal communication of two components or the interaction between two components. Therefore, unless otherwise expressly limited in this specification, those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0051] Based on the above description in this specification, those skilled in the art will also understand that terms used, such as "upper," "lower," "front," "rear," "left," "right," "length," "width," "thickness," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," "circumferential," "center," "longitudinal," "transverse," "clockwise," or "counterclockwise," are terms indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings of this specification. They are only for the purpose of facilitating the explanation of the present invention and simplifying the description, and do not imply that the device or element involved must have the specific orientation, or be constructed and operated in a specific orientation. Therefore, the above-mentioned orientation or positional relationship terms should not be understood or interpreted as limitations on the present invention.

[0052] Furthermore, the terms "first" or "second," etc., used in this specification to refer to numbers or ordinal numbers are for descriptive purposes only and should not be construed as indicating, explicitly or implicitly, relative importance or specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this specification, "a plurality of" means at least two, such as two, three, or more, unless otherwise explicitly specified.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this utility model, and not to limit it. Although this utility model 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. Such 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 this utility model.

Claims

1. A device for recovering and utilizing waste heat from secondary steam in the final effect of an alumina evaporation system, comprising multiple evaporators arranged sequentially along the steam direction, wherein the steam outlet of the evaporator located at the front is connected to the steam inlet of the evaporator located at the rear, and the evaporator located closest to the inlet is called the final effect evaporator, characterized in that: The steam outlet of the final-effect evaporator is connected to a waste heat recovery pipeline, and at least one steam compressor is installed on the waste heat recovery pipeline. The waste heat recovery and utilization device also includes a heat exchanger connected to the waste heat recovery pipeline via a heat source inlet. The heat exchanger is located downstream of the steam compressor and also has a cold source inlet and a cold source outlet.

2. The waste heat recovery and utilization device for the final-effect secondary steam of the alumina evaporation system according to claim 1, characterized in that: A vacuum pump is connected to the upper end of the heat exchanger shell to discharge the non-condensable secondary steam in the heat exchanger.

3. The waste heat recovery and utilization device for the final-effect secondary steam of the alumina evaporation system according to claim 1, characterized in that: There is one steam compressor; or there are multiple steam compressors connected in series.

4. The waste heat recovery and utilization device for the final-effect secondary steam of the alumina evaporation system according to claim 1, characterized in that: The heat exchanger can be a direct heat exchanger or an indirect heat exchanger.

5. The waste heat recovery and utilization device for the final-effect secondary steam of the alumina evaporation system according to claim 1, characterized in that: The heat exchanger includes a vertically arranged heat exchanger shell, a cold source inlet located at the top of the heat exchanger shell, a cold source outlet located at the bottom of the heat exchanger shell, and a heat source inlet located on the side wall of the heat exchanger shell. After the final-effect secondary steam enters the heat exchanger shell through the heat source inlet, it directly contacts and exchanges heat with the cold source between the cold source inlet and the cold source outlet.

6. The waste heat recovery and utilization device for the final-effect secondary steam of the alumina evaporation system according to any one of claims 1 to 4, characterized in that: It also includes a heating heat exchanger for the living area, with the inlet of the heating heat exchanger connected to the outlet of the cold source and the outlet of the heating heat exchanger connected to the inlet of the cold source.

7. The waste heat recovery and utilization device for the final-effect secondary steam of the alumina evaporation system according to claim 5, characterized in that: The cold water outlet is also connected to a domestic water supply pipeline.

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