Open evaporation absorption type feed liquid concentration system

Abstract

The invention provides an open evaporation absorption type feed liquid concentration system, and relates to the technical field of concentration equipment. The system comprises a multi-effect concentration evaporator, a mother liquor concentration tower, a concentrated mother liquor heater, a circulating mother liquor heater, a dead steam heat collector and a roasting furnace sensible heat recoverer, the mother liquor concentration tower is independently arranged outside the multi-effect concentration evaporator, part of mother liquor is concentrated through the mother liquor concentration tower, the roasting furnace sensible heat recoverer is used for providing heat source heat exchange for the concentrated mother liquor heater, and the dead steam heat collector is used for providing heat source heat exchange for the circulating mother liquor heater. As heat required by concentration of the mother liquor concentration tower is provided by the roasting furnace sensible heat recoverer and the dead steam heat collector, additional heat is not needed, the amount of mother liquor introduced into the multi-effect concentration evaporator is reduced, the treatment energy consumption and scaling risk of the multi-effect concentration evaporator are reduced, and meanwhile, recycling of low-grade waste heat is realized; the energy utilization rate is obviously improved, and the system is flexible.

Description

Technical Field

[0001] This invention relates to the field of concentration equipment technology, and more specifically, to an open-type evaporation-absorption type liquid concentration system. Background Technology

[0002] Against the backdrop of the deepening "dual-carbon" strategy and the rigid constraints of industrial energy efficiency improvement, the alumina industry, as a high-energy-consuming sector, faces the dual challenges of energy conservation and carbon reduction, and green transformation. In the alumina production process, mother liquor concentration is a crucial step, accounting for approximately 15% of the company's total energy consumption, directly impacting the overall product cost and environmental compliance. The Bayer process for alumina production involves dissolving aluminum ore in alkaline mother liquor. The mother liquor undergoes sedimentation, filtration, and decomposition to produce aluminum hydroxide, which is then calcined in a roasting furnace to produce alumina. The decomposed mother liquor needs to be evaporated and concentrated before being reused for ore dissolution.

[0003] The current mainstream mother liquor concentration technology in the alumina industry is the multi-effect evaporation method. Although this technology can meet basic concentration requirements, it has significant bottlenecks in practical applications: First, energy consumption is high, requiring 0.195-0.22 tons of steam to evaporate 1 ton of water, which is far higher than the international advanced level and falls short of the industry's energy efficiency benchmark requirements. Second, scaling is a prominent problem, as components such as sodium carbonate and sodium sulfate in the mother liquor are easily precipitated during the concentration process, causing blockages in heat exchangers and pipelines, requiring frequent shutdowns for cleaning, increasing operation and maintenance costs and downtime losses. Third, low-grade waste heat is wasted seriously, as waste heat resources at temperatures of 58-130℃, such as flue gas from the calcining furnace and exhaust steam from the tail end of the six-effect evaporator, are not effectively utilized and are directly dissipated through cooling water, resulting in low energy utilization. Fourth, the concentration adaptability is limited, making it difficult to match fluctuations in waste heat resources and changes in mother liquor composition, resulting in insufficient system flexibility.

[0004] Therefore, addressing the aforementioned technical challenges has become a core research direction and key focus of industrial development in the field of alumina mother liquor treatment.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The present invention aims to provide an open-loop evaporation-absorption type liquid concentration system.

[0007] The embodiments of the present invention can be implemented as follows: In a first aspect, the present invention provides an open-type evaporation-absorption liquid concentration system, including a multi-effect evaporator, a mother liquor concentration tower, a concentrated mother liquor heater, a circulating mother liquor heater, a waste steam heat exchanger, and a sensible heat recovery unit for a calcining furnace. The multi-effect concentrator is equipped with a first mother liquor inlet, a first mother liquor outlet, and a multi-effect exhaust steam outlet. The mother liquor concentration tower is provided with a second mother liquor inlet and a circulating mother liquor inlet at the top, and a fresh air inlet, a concentrated mother liquor outlet, and a circulating mother liquor outlet at the bottom. The concentrated mother liquor heater is provided with a second mother liquor outlet. The concentrated mother liquor outlet is connected to the concentrated mother liquor heater for heating the concentrated mother liquor. The sensible heat recovery unit of the roasting furnace is used to provide a heat source for heat exchange to the concentrated mother liquor heater. The first mother liquor outlet and the second mother liquor outlet are discharged after merging. The circulating mother liquor outlet is connected to the circulating mother liquor heater for heating the circulating mother liquor. The circulating mother liquor heater is connected to the circulating mother liquor inlet for returning the heated circulating mother liquor to the mother liquor concentration tower. The waste steam heat exchanger is used to provide a heat source for the circulating mother liquor heater and is connected to the multi-effect waste steam outlet.

[0008] In an optional embodiment, the sensible heat recovery unit of the roasting furnace is provided with a flue gas inlet of the roasting furnace. The sensible heat recovery unit of the roasting furnace and the concentrated mother liquor heater exchange heat through the circulation of a first intermediate water. After exchanging heat with the roasting flue gas, the first intermediate water is discharged from the sensible heat recovery unit of the roasting furnace and enters the concentrated mother liquor heater to heat the concentrated mother liquor. Subsequently, it is discharged from the concentrated mother liquor heater and returns to the sensible heat recovery unit of the roasting furnace to exchange heat with the flue gas of the roasting furnace again to form a cycle.

[0009] In an optional embodiment, the waste steam heat exchanger and the circulating mother liquor heater exchange heat using a second intermediate water circulation. After exchanging heat with the multi-effect waste steam, the second intermediate water is discharged from the waste steam heat exchanger and enters the circulating mother liquor heater to heat the circulating mother liquor. Subsequently, it is discharged from the circulating mother liquor heater and returned to the waste steam heat exchanger to exchange heat with the multi-effect waste steam again to form a cycle.

[0010] In an optional embodiment, the open-type evaporation absorption liquid concentration system further includes a calcining furnace waste heat recovery tower and a spray water heat exchanger. The calcining furnace waste heat recovery tower is connected to the flue gas outlet of the sensible heat recovery unit of the calcining furnace for recovering the waste heat of the flue gas. The spray water heat exchanger is connected to the circulating mother liquor heater and uses the circulation of a second intermediate water for heat exchange. A spray nozzle is provided at the top of the calcining furnace waste heat recovery tower. The spray water in the calcining furnace waste heat recovery tower is transported from the bottom to the spray water heat exchanger to exchange heat with the second intermediate water and then returned to the calcining furnace waste heat recovery tower from the spray nozzle.

[0011] In an optional embodiment, the mother liquor concentration tower is further provided with a filter press circulation pipeline, and a filter press mechanism is provided on the filter press circulation pipeline. The inlet and outlet of the filter press circulation pipeline are respectively connected to the mother liquor concentration tower.

[0012] In an optional embodiment, a regenerator is further provided between the mother liquor concentration tower and the concentrated mother liquor heater, the regenerator being used to exchange heat between the mother liquor before entering the mother liquor concentration tower and the concentrated mother liquor before entering the concentrated mother liquor heater.

[0013] In an optional embodiment, the open-type evaporation absorption liquid concentration system further includes a purification and scrubbing tower, which is connected to the top of the mother liquor concentration tower for scrubbing the fresh air discharged from the mother liquor concentration tower.

[0014] In an optional embodiment, the open-type evaporation absorption liquid concentration system further includes a waste steam backup cooler, which is connected to the waste steam heat exchanger to cool the multi-effect waste steam after heat exchange to generate waste steam condensate and non-condensable gas. The waste steam backup cooler is connected to the purification and scrubbing tower to use the waste steam condensate as the scrubbing liquid for the fresh air discharged from the mother liquor concentration tower.

[0015] In an optional embodiment, the open-loop evaporation-absorption liquid concentration system further includes a vacuum pump connected to the waste steam standby cooler for pumping out the non-condensable gas.

[0016] In an optional embodiment, the inlet flow rate ratio of the first mother liquor inlet to the second mother liquor inlet is 10-12:2.5-3.5: And / or, the outflow rate ratio of the concentrated mother liquor outlet to the circulating mother liquor outlet is 1:22-24; And / or, the inner wall of the mother liquor concentration tower is provided with an anti-corrosion coating.

[0017] The beneficial effects of the open-loop evaporation-absorption type liquid concentration system provided in this embodiment of the invention include: The open-type evaporation absorption-type liquid concentration system provided by this invention uses a mother liquor concentration tower independently set outside the multi-effect evaporator to concentrate a portion of the mother liquor. This invention fully utilizes the heat from the multi-effect exhaust steam and alumina calcining furnace flue gas, which were originally waste heat. Multiple heat sources work together to construct a low-temperature concentration cycle for the mother liquor, increasing the concentration of the mother liquor and saving steam from the multi-effect evaporator. This invention achieves gradient utilization of heat. For example, the alumina calcining furnace flue gas is divided into latent heat and sensible heat. The sensible heat is recovered as waste heat through a heat exchanger to heat the mother liquor, while the latent heat is recovered as waste heat through a spray tower to heat the circulating mother liquor. Furthermore, the high inlet mother liquor temperature is used for reheating, ensuring that the concentrated mother liquor discharged from the concentration tower undergoes a first temperature rise via a reheater and a second temperature rise via a concentrated mother liquor heater, effectively guaranteeing the temperature of the concentrated mother liquor. Since the heat required for concentration in the mother liquor concentration tower is provided by the sensible heat recovery unit of the calcining furnace and the waste steam heat exchanger, no additional heat is needed. This reduces the amount of mother liquor fed into the multi-effect evaporator, lowers the energy consumption and scaling risk of the multi-effect evaporator, and simultaneously achieves the recovery and utilization of low-grade waste heat, significantly improving energy efficiency and making the system more flexible. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the open-loop evaporation-absorption type liquid concentration system provided in this embodiment; Figure 2 This is a schematic diagram of the process flow of the open-loop evaporation-absorption liquid concentration system provided in this embodiment, with parameters for each step.

[0020] Icons: 100 - Open-type evaporation-absorption liquid concentration system; 110 - Multi-effect concentrator evaporator; 111 - First mother liquor inlet; 112 - First mother liquor outlet; 113 - Multi-effect exhaust steam outlet; 120 - Mother liquor concentration tower; 121 - Second mother liquor inlet; 122 - Circulating mother liquor inlet; 123 - Fresh air inlet; 124 - Concentrated mother liquor outlet; 125 - Circulating mother liquor outlet; 126 - Filter press circulation pipeline; 127 - Filter press mechanism; 1 28-Purification and scrubbing tower; 130-Concentrated mother liquor heater; 131-Second mother liquor outlet; 132-First intermediate water; 140-Circulating mother liquor heater; 141-Second intermediate water; 150-Waste steam heat exchanger; 151-Waste steam standby cooler; 152-Vacuum pump; 160-Roasting furnace sensible heat recovery unit; 161-Roasting furnace flue gas inlet; 170-Roasting furnace waste heat recovery tower; 180-Spray water heat exchanger; 190-Regenerator. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0022] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0023] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0024] In the description of this invention, it should be noted that if terms such as "upper," "lower," "inner," or "outer" are used to indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed, they are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0025] Furthermore, the terms "first" and "second" are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0026] It should be noted that, where there is no conflict, the features in the embodiments of the present invention can be combined with each other.

[0027] The following detailed description of the overall structure, working principle, and technical effects of the open-type evaporation-absorption liquid concentration system 100 provided by the present invention, through embodiments and in conjunction with the accompanying drawings, is a practical example.

[0028] Please see Figure 1 The present invention provides an open evaporation absorption type liquid concentration system 100, including a multi-effect evaporator 110, a mother liquor concentration tower 120, a concentrated mother liquor heater 130, a circulating mother liquor heater 140, a waste steam heat exchanger 150, and a sensible heat recovery unit for a calcining furnace 160. The multi-effect evaporator 110 is equipped with a first mother liquor inlet 111, a first mother liquor outlet 112, and a multi-effect exhaust steam outlet 113. The mother liquor enters the multi-effect evaporator 110 through the first mother liquor inlet 111 for concentration and evaporation, forming concentrated mother liquor which is then discharged through the first mother liquor outlet 112. The multi-effect evaporator 110 is a conventional evaporator. During the evaporation and concentration process, multi-effect exhaust steam is discharged through the multi-effect exhaust steam outlet 113. "Multi-effect exhaust steam" refers to the low-grade steam generated in the previous effect (i.e., the "exhaust steam" of that effect), which is sequentially introduced into subsequent effects as a heating source and utilized in a cascade manner before being finally discharged. In other words, it is the final low-grade steam discharged from the last effect after multi-effect recycling.

[0029] The mother liquor concentration tower 120 is equipped with a second mother liquor inlet 121 and a circulating mother liquor inlet 122 at the top of the tower, and a fresh air inlet 123, a concentrated mother liquor outlet 124 and a circulating mother liquor outlet 125 at the bottom of the tower. The concentrated mother liquor heater 130 is equipped with a second mother liquor outlet 131. The concentrated mother liquor outlet 124 is connected to the concentrated mother liquor heater 130 for heating the concentrated mother liquor. The sensible heat recovery unit 160 of the roasting furnace is used to provide a heat source for the concentrated mother liquor heater 130. The first mother liquor outlet 112 and the second mother liquor outlet 131 are discharged after merging. The circulating mother liquor outlet 125 is connected to the circulating mother liquor heater 140 for heating the circulating mother liquor. The circulating mother liquor heater 140 is connected to the circulating mother liquor inlet 122 for returning the heated circulating mother liquor to the mother liquor concentration tower 120. The waste steam heat exchanger 150 is used to provide a heat source for the circulating mother liquor heater 140. The waste steam heat exchanger 150 is connected to the multi-effect waste steam outlet 113.

[0030] In this invention, a mother liquor concentration tower 120 is independently set outside the multi-effect evaporator 110. The mother liquor concentration tower 120 is used to concentrate part of the mother liquor. That is, the mother liquor originally intended to be processed is divided into two paths. One path enters the multi-effect evaporator 110 from the first mother liquor inlet 111 for conventional evaporation and concentration, while the other path enters the mother liquor concentration tower 120 from the second mother liquor inlet 121 for concentration.

[0031] The ratio of the flow rates of the first mother liquor inlet 111 to the second mother liquor inlet 121 is 10-12:2.5-3.5. It can be seen that most of the mother liquor is still fed into the multi-effect evaporator 110 for conventional evaporation and concentration. In this invention, the amount of mother liquor that can be fed into the second mother liquor inlet is calculated by calculating the heat of the multi-effect exhaust steam generated in the multi-effect evaporator 110, ensuring that the amount of mother liquor entering the multi-effect evaporator 110 is reduced. Since the heat required for concentration in the mother liquor concentration tower 120 is provided by the sensible heat recovery unit 160 of the calcining furnace and the exhaust steam heat exchanger 150, no additional heat is required. This reduces the amount of mother liquor fed into the multi-effect evaporator 110, reduces the processing energy consumption and scaling risk of the multi-effect evaporator 110, and at the same time realizes the recovery and utilization of low-grade waste heat, significantly improving the energy utilization rate and making the system more flexible.

[0032] Meanwhile, the outflow velocity ratio of concentrated mother liquor outlet 124 and circulating mother liquor outlet 125 is 1:22-24. It can be seen that the liquid discharged from the mother liquor concentration tower 120 is also divided into two parts: one part is discharged from concentrated mother liquor outlet 124 and the other part is discharged from circulating mother liquor outlet 125. From the above outflow velocity ratio, it can be seen that only a small part is discharged as concentrated mother liquor and merges with the first mother liquor outlet 112 after being heated by concentrated mother liquor heater 130. Most of the solution is self-circulated as circulating mother liquor and is heated by exhaust steam heat exchanger 150 to ensure full utilization of the heat of exhaust steam heat exchanger 150.

[0033] The mother liquor concentration tower 120 is also equipped with a filter press circulation pipeline 126, on which a filter press mechanism 127 is installed. The inlet and outlet of the filter press circulation pipeline 126 are connected to the mother liquor concentration tower 120, respectively. The filter press circulation pipeline 126 enables continuous filtration of the mother liquor in the mother liquor concentration tower 120 to separate solid impurities, reducing the risk of clogging the mother liquor concentration tower 120.

[0034] Furthermore, the inner wall of the mother liquor concentration tower 120 is provided with an anti-corrosion coating, which can effectively prevent scale formation in the mother liquor within the tower. In addition, the circulating mother liquor within the mother liquor concentration tower 120 is sprayed out through high-flow nozzles, and the tower is also equipped with large-pore packing to prevent clogging.

[0035] In this invention, the sensible heat recovery unit 160 of the roasting furnace is used to recover and utilize the heat of the flue gas generated by the roasting furnace. The sensible heat recovery unit 160 of the roasting furnace is provided with a flue gas inlet 161 of the roasting furnace. The sensible heat recovery unit 160 of the roasting furnace and the concentrated mother liquor heater 130 exchange heat through the circulation of a first intermediate water 132. After exchanging heat with the roasting flue gas, the first intermediate water 132 is discharged from the sensible heat recovery unit 160 of the roasting furnace and enters the concentrated mother liquor heater 130 to heat the concentrated mother liquor. Then it is discharged from the concentrated mother liquor heater 130 and returned to the sensible heat recovery unit 160 of the roasting furnace to exchange heat with the flue gas of the roasting furnace again to form a cycle. The reason for using the circulation of the first intermediate water 132 for heat exchange is that the roasting furnace area and the mother liquor concentration area are too far apart. If the flue gas from the roasting furnace is led to the mother liquor concentration area, a long flue needs to be built, resulting in high investment. If the mother liquor is led to the roasting furnace area, the pipes will be too long and easily clogged. Therefore, using intermediate circulating water to transfer heat can reduce equipment investment and reduce the possibility of clogging.

[0036] The waste steam heat exchanger 150 is used to recover and utilize the heat from the multi-effect waste steam generated by the multi-effect evaporator 110. The waste steam heat exchanger 150 is connected to the multi-effect waste steam outlet 113. The waste steam heat exchanger 150 and the circulating mother liquor heater 140 exchange heat through the circulation of a second intermediate water 141. After exchanging heat with the multi-effect waste steam, the second intermediate water 141 is discharged from the waste steam heat exchanger 150 and enters the circulating mother liquor heater 140 to heat the circulating mother liquor. Subsequently, it is discharged from the circulating mother liquor heater 140 and returns to the waste steam heat exchanger 150 to exchange heat with the multi-effect waste steam again, forming a cycle. The reason for using the circulation of the second intermediate water 141 for heat exchange is that the heat exchange between water and mother liquor is a liquid-liquid heat exchange, with a higher mother liquor flow rate, making it less prone to clogging. If the heat exchange between mother liquor and waste steam were a steam-water heat exchange, the mother liquor flow rate would be lower, making it more prone to clogging.

[0037] This invention simultaneously realizes the heat recovery and utilization of calcination furnace flue gas and multi-effect exhaust steam, and separately realizes the heating of concentrated mother liquor and circulating mother liquor, thus achieving efficient utilization of low-grade waste heat.

[0038] The open-type evaporation absorption liquid concentration system 100 also includes a calcining furnace waste heat recovery tower 170 and a spray water heat exchanger 180. The calcining furnace waste heat recovery tower 170 is connected to the flue gas outlet of the calcining furnace sensible heat recovery unit 160 to recover the waste heat of the flue gas. The spray water heat exchanger 180 is connected to the circulating mother liquor heater 140 and uses the circulation of the second intermediate water 141 for heat exchange. The top of the calcining furnace waste heat recovery tower 170 is provided with a spray nozzle. The spray water in the calcining furnace waste heat recovery tower 170 is transported from the bottom to the spray water heat exchanger 180 to exchange heat with the second intermediate water 141 and then returns to the calcining furnace waste heat recovery tower 170 from the spray nozzle.

[0039] That is, part of the second intermediate water 141 discharged from the circulating mother liquor heater 140 after heat exchange enters the waste steam heat exchanger 150 to exchange heat with the multi-effect waste steam, and the other part enters the spray water heat exchanger 180 to exchange heat with the spray water. After the heat exchange is completed, it is discharged from the waste steam heat exchanger 150 and the spray water heat exchanger 180 respectively and flows into the circulating mother liquor heater 140 to continue heat exchange. In this invention, the waste steam heat exchanger 150 and the spray water heat exchanger 180 are used to exchange heat with the second intermediate water 141, thereby heating the circulating mother liquor and increasing its temperature, so that it can be concentrated by the low temperature and low humidity fresh air in the mother liquor concentration tower 120.

[0040] Furthermore, a regenerator 190 is installed between the mother liquor concentration tower 120 and the concentrated mother liquor heater 130. The regenerator 190 is used to exchange heat between the mother liquor entering the mother liquor concentration tower 120 and the concentrated mother liquor entering the concentrated mother liquor heater 130. The regenerator 190 can achieve heat exchange between the mother liquor and the concentrated mother liquor, thereby lowering the temperature of the mother liquor entering the mother liquor concentration tower 120 and simultaneously raising the temperature of the concentrated mother liquor entering the concentrated mother liquor heater 130. This facilitates heat exchange in the concentrated mother liquor heater 130 to reach the required temperature, which is consistent with the temperature of the mother liquor at the first mother liquor outlet 112, and they are discharged together.

[0041] In addition, the open-type evaporation absorption liquid concentration system 100 also includes a purification and scrubbing tower 128, which is connected to the top of the mother liquor concentration tower 120 for scrubbing the fresh air discharged from the mother liquor concentration tower 120.

[0042] The open-loop evaporation absorption-type liquid concentration system 100 also includes a waste steam backup cooler 151 and a vacuum pump 152. The waste steam backup cooler 151 is connected to the waste steam heat exchanger 150 to cool the multi-effect waste steam after heat exchange, generating waste steam condensate and non-condensable gases. The waste steam backup cooler 151 is connected to the purification scrubbing tower 128 to use the waste steam condensate as the scrubbing liquid for the fresh air discharged from the mother liquor concentration tower 120. The vacuum pump 152 is connected to the waste steam backup cooler 151 to pump out the non-condensable gases.

[0043] Next, the present invention will describe the process flow of the above-mentioned open-type evaporation absorption liquid concentration system 100: (1) Mother liquor entry and preliminary treatment The mother liquor is divided into two streams. One stream goes directly into the multi-effect evaporator 110 for concentration, while the other stream is cooled by heat exchange through the regenerator 190 and then enters the top of the mother liquor concentration tower 120. Low-temperature and low-humidity fresh air enters from the bottom of the mother liquor concentration tower 120. The fresh air and mother liquor come into countercurrent contact and achieve concentration.

[0044] (2) Process in Mother Liquor Concentrator 120 The mother liquor undergoes concentration by contacting fresh air within the mother liquor concentration tower 120. The majority of the concentrated mother liquor produced is recycled back into the concentration tower 120 as circulating mother liquor, while the remainder is discharged as the concentrated product (concentrated mother liquor). Simultaneously, the circulating mother liquor heater 140 heats the circulating mother liquor, providing heat for the concentration process. During this process, due to the very low dew point of the fresh air, the entire cycle can be carried out at a low temperature of 40-60°C.

[0045] (3) Waste heat recovery from roasting furnace flue gas The flue gas from the roasting furnace first enters the sensible heat recovery unit 160 of the roasting furnace. After recovering part of the sensible heat, it then enters the waste heat recovery tower 170 of the roasting furnace.

[0046] In this process, the concentrated mother liquor discharged from the concentrated mother liquor outlet 124 of the mother liquor concentration tower 120 first exchanges heat with the mother liquor entering the mother liquor concentration tower 120 through the regenerator 190, thereby increasing the temperature of the concentrated mother liquor and decreasing the temperature of the mother liquor entering the mother liquor concentration tower 120. Subsequently, the concentrated mother liquor continues to be fed into the concentrated mother liquor heater 130 for secondary heat exchange.

[0047] The heat source of the concentrated mother liquor heater 130 comes from the sensible heat recovery unit 160 of the roasting furnace. The sensible heat recovery unit 160 exchanges heat with the high-temperature flue gas of the roasting furnace and the first intermediate water 132, and uses the first intermediate water 132 to exchange heat with the concentrated mother liquor in the concentrated mother liquor heater 130, so as to realize the secondary heating of the concentrated mother liquor. The temperature of the concentrated mother liquor can be adjusted by the flow rate of the first intermediate water 132 to match the temperature of the concentrated mother liquor discharged from the multi-effect concentrated evaporator 110.

[0048] In the calciner waste heat recovery tower 170, heat from the flue gas is transferred to the spray water via the spray water heat exchanger 180, and then to the second intermediate water 141 for heating the circulating mother liquor, thus achieving effective utilization of the waste heat from the calciner flue gas. The flue gas condensate generated in the calciner waste heat recovery tower 170 can be recycled.

[0049] (4) Multi-effect exhaust steam utilization The circulating mother liquor discharged from the mother liquor concentration tower 120 undergoes heat exchange through the circulating mother liquor heater 140. The heat source for the circulating mother liquor heater 140 comes from the waste steam heat exchanger 150 and the spray water heat exchanger 180. The waste steam heat exchanger 150 uses the multi-effect waste steam generated during the concentration process of the multi-effect evaporator 110 for heat exchange, while the spray water heat exchanger 180 uses the spray water in the calcining furnace waste heat recovery tower 170 for heat exchange.

[0050] (5) Exhaust steam treatment and purification The exhaust steam generated during the concentration process first passes through the exhaust steam heat exchanger 150 to recover heat, and then enters the exhaust steam standby cooler 151. During normal system operation, the exhaust steam standby cooler 151 does not need to be turned on. It is turned on during system fluctuations or maintenance to ensure the exhaust steam is cooled and to maintain the normal operation of the multi-effect system. In the exhaust steam heat exchanger 150 or the exhaust steam standby cooler 151, the exhaust steam is cooled into exhaust steam condensate. The exhaust steam condensate is then used to spray and scrub the fresh air exiting the tower, thoroughly washing away any entrained droplets. This condensate can then be reused within the plant, while the non-condensable gas is discharged through the vacuum pump 152.

[0051] (6) Output of concentrated mother liquor The concentrated mother liquor is discharged from the concentrated mother liquor outlet 124, reheated by the regenerator 190 and the mother liquor heater, and then discharged from the second mother liquor outlet 131. It is then combined with the concentrated mother liquor discharged from the first mother liquor outlet 112 of the multi-effect evaporator 110 and discharged. The two-stage heating is to ensure that the outlet concentrated mother liquor temperature is consistent with the multi-effect outlet temperature, so that no additional steam is needed in the subsequent process.

[0052] The open-type evaporation absorption-type liquid concentration system 100 provided by this invention fully utilizes the heat from the multi-effect exhaust steam and alumina calcining furnace flue gas, which were originally waste heat. Multiple heat sources work together to construct a low-temperature concentration cycle for the mother liquor, increasing the concentration of the mother liquor and saving steam in the multi-effect evaporator. Specifically, the low-temperature mother liquor concentration cycle involves the circulating mother liquor discharged from the mother liquor concentration tower 120 passing through the circulating mother liquor heater 140 and the mother liquor concentration tower 120, eliminating the need for the multi-effect evaporator 110 and effectively alleviating problems such as mother liquor precipitation and blockage in the multi-effect evaporator 110. This invention achieves gradient utilization of heat. For example, the alumina calcining furnace flue gas is divided into latent heat and sensible heat. The sensible heat is recovered as waste heat through a heat exchanger to heat the mother liquor, while the latent heat is recovered as waste heat through a spray tower to heat the circulating mother liquor. Furthermore, the higher inlet mother liquor temperature is used for reheating, ensuring that the concentrated mother liquor discharged from the mother liquor concentration tower 120 undergoes a first temperature increase via the reheater 190 and a second temperature increase via the concentrated mother liquor heater 130, effectively guaranteeing the temperature of the concentrated mother liquor. Taking a six-effect evaporator as an example, one part of steam evaporates about five parts of water. If the temperature of the inlet mother liquor is used for its own evaporation in the tower, one part of heat will save 0.2 parts of steam. However, if the temperature of the outlet concentrated mother liquor is insufficient, steam heating is required. One part of the missing heat requires one part of steam. Therefore, the temperature of the outlet concentrated mother liquor should be prioritized.

[0053] The above solution will be further illustrated by a specific embodiment below: Example 1 - Concentration of mother liquor from alumina production decomposition (1) Feed composition (mass fraction / key indicators) Main components of mother liquor: Caustic soda content (Na2O) k 165g / L, carbon-alkali content (Na2O)c 4.5 g / L, containing easily precipitated components such as sodium carbonate and sodium sulfate; Feed status: ambient temperature liquid phase (75-85℃), feed flow rate 1400t / h, density 1.26kg / L, of which 300t / h is fed into the mother liquor concentration tower through the regenerator, and 1100t / h enters the multi-effect concentration system; Waste heat medium parameters: 250,000 Nm³ / h of flue gas from the calcining furnace at 130℃, and 70t / h of exhaust steam from the sixth-effect furnace at 64℃ (pressure -77kPa.g).

[0054] (2) Control of operating parameters Please see Figure 2 , Figure 2 The process parameters for each stage are shown in detail: The mother liquor (85℃) is fed at a rate of 1400t / h and divided into two streams. One stream is fed at a rate of 1100t / h into the multi-effect evaporator 110 for six-effect evaporation, and the other stream is fed at a rate of 300t / h into the regenerator 190 for heat exchange. After being cooled to 65℃, it enters the mother liquor concentration tower 120.

[0055] Fresh air is introduced into the bottom of the mother liquor concentration tower 120 to contact and concentrate the mother liquor at 65°C. The concentrated liquid is divided into two streams: one stream discharges concentrated mother liquor (41.3°C, 200t / h) from the concentrated mother liquor outlet 124, and the other stream discharges circulating mother liquor (41.3°C, 4700t / h) from the circulating mother liquor outlet 125.

[0056] The concentrated mother liquor (41.3℃, 200t / h) enters the regenerator 190 to exchange heat with the mother liquor (85℃), raising its temperature to 72℃, 200t / h. It then continues to flow into the concentrated mother liquor heater 130 to exchange heat with the first intermediate water 132 (99℃, 200t / h), discharging the concentrated mother liquor (82℃, 200t / h). The circulating mother liquor (41.3℃, 4700t / h) enters the circulating mother liquor heater 140 to exchange heat with the second intermediate water 141 (60.2℃, 5600t / h), raising its temperature to 57℃, 4700t / h, and returning to the mother liquor concentration tower 120 for circulation.

[0057] The first intermediate water 132 exchanges heat with the flue gas in the sensible heat recovery unit 160 of the roasting furnace, and the second intermediate water 141 exchanges heat with the exhaust steam heat exchanger 150 and the spray heat exchanger respectively.

[0058] Specifically, the flue gas from the roasting furnace (242,000 Nm³, inlet temperature 130°C, inlet dew point 74°C) is introduced into the sensible heat recovery unit 160 of the roasting furnace, where it exchanges heat with the first intermediate water 132 (90°C, 200 t / h). The temperature of the first intermediate water 132 rises to 99°C. Subsequently, the flue gas (242,000 Nm³, outlet temperature 110°C, outlet dew point 74°C) enters the waste heat recovery tower 170 of the roasting furnace, where it is purified by spray water. The spray water at the bottom (71.4°C, 2000 t / h) exchanges heat with the second intermediate water 141 (48°C, 1800 t / h), cooling it to 57°C. It is then circulated to the top at a flow rate of 2000 t / h for self-circulation. Finally, the flue gas from the roasting furnace (187,000 Nm³, outlet temperature 62°C, outlet dew point 62°C) is discharged from the top.

[0059] When six-effect evaporation is carried out in the multi-effect concentrator evaporator 110, 1 ton of steam is consumed to produce 5 tons of water. During the evaporation process, multi-effect exhaust steam (70t / h, 64℃) is generated at a gauge pressure of -77kPa / absolute pressure of 23kPa, and finally concentrated mother liquor (82℃, 735t / h) is discharged. Among them, the multi-effect exhaust steam enters the exhaust steam heat exchanger 150 to exchange heat with the second intermediate water 141 (48℃, 3800t / h).

[0060] After the multi-effect exhaust steam heat exchange is completed, it enters the exhaust steam standby cooler 151 and is cooled by standby cooling water. The standby cooling water is discharged after being heated. The condensate of the multi-effect exhaust steam is fed into the purification and scrubbing tower 128 to scrub the fresh air discharged from the top of the mother liquor concentration tower 120. The scrubbed exhaust steam condensate is reused in the plant. The non-condensable gas discharged from the exhaust steam standby condenser is led out by the vacuum pump 152 and discharged externally.

[0061] (3) Operational effect Waste heat recovery capacity: Total 80MW (35MW from calciner flue gas and 45MW from exhaust steam from the sixth-effect furnace); Export concentrated mother liquor specifications: temperature 82℃, caustic soda content (Na2O) k 248g / L, carbon-alkali content (Na2O) c 6.8 g / L, density 1.35 g / L; Energy consumption indicators: The system operates at a power of 1800kW, with 8000 hours of operation per year and an annual power consumption of 14.4 million kWh; it saves 156,000 tons of six-effect steam per year. At the same time, since the original cooling circulating water pump can be shut down, the power consumption of the cooling water pump is saved by 800kW (an additional 6.4 million kWh of electricity is saved per year).

[0062] Heat consumption index: This is the core index. The steam consumption is only the steam consumption of the mother liquor multi-effect concentration system, about 73t / h, while the water evaporation rate is 465t / h. Therefore, the heat consumption index is 0.157 tons of steam / ton of evaporation.

[0063] Comparative Example 1 This comparative example uses a multi-effect evaporator 110 (six-effect) to concentrate and evaporate the same amount of mother liquor. At this time, 93t / h of steam is required, and the heat consumption index is 0.2 tons of steam / ton of evaporation.

[0064] Comparative Example 2 In this comparative example, the first intermediate water 132 and the sensible heat recovery unit 160 of the roasting furnace are omitted. If the temperature of the concentrated mother liquor is too low, an additional 3t / h of steam will be consumed in the next stage. At this time, 76t / h of steam will be required, and the energy consumption index is 0.163 tons of steam / ton of evaporation.

[0065] In summary, the open-type evaporation absorption-type liquid concentration system 100 provided by this invention achieves partial concentration of the mother liquor by independently setting up a mother liquor concentration tower 120 outside the multi-effect evaporator 110. This invention fully utilizes the heat from the multi-effect exhaust steam and alumina calcining furnace flue gas, which were originally waste heat. Multiple heat sources work together to construct a low-temperature concentration cycle for the mother liquor, increasing the concentration of the mother liquor and saving steam from the multi-effect evaporator. This invention achieves gradient utilization of heat. For example, the flue gas from the alumina calcining furnace is divided into latent heat and sensible heat. The sensible heat is recovered as waste heat through a heat exchanger to heat the mother liquor, and the latent heat is recovered as waste heat through a spray tower to heat the circulating mother liquor. Furthermore, the high inlet temperature of the mother liquor is used for reheating, ensuring that the concentrated mother liquor discharged from the mother liquor concentration tower 120 undergoes a first temperature increase via a regenerator 190 and a second temperature increase via a concentrated mother liquor heater 130, effectively guaranteeing the temperature of the concentrated mother liquor. Since the heat required for concentration in the mother liquor concentration tower 120 is provided by the sensible heat recovery unit 160 of the calcining furnace and the exhaust steam heat exchanger 150, no additional heat is required. This reduces the amount of mother liquor fed into the multi-effect evaporator 110, thereby reducing the energy consumption and scaling risk of the multi-effect evaporator 110. At the same time, it achieves the recovery and utilization of low-grade waste heat, significantly improving energy utilization and making the system more flexible.

[0066] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. An open-loop evaporation-absorption type liquid concentration system, characterized in that, It includes a multi-effect evaporator, a mother liquor concentration tower, a concentrated mother liquor heater, a circulating mother liquor heater, a waste steam heat exchanger, and a sensible heat recovery unit for a roasting furnace; The multi-effect concentrator is equipped with a first mother liquor inlet, a first mother liquor outlet, and a multi-effect exhaust steam outlet. The mother liquor concentration tower is provided with a second mother liquor inlet and a circulating mother liquor inlet at the top, and a fresh air inlet, a concentrated mother liquor outlet, and a circulating mother liquor outlet at the bottom. The concentrated mother liquor heater is provided with a second mother liquor outlet. The concentrated mother liquor outlet is connected to the concentrated mother liquor heater for heating the concentrated mother liquor. The sensible heat recovery unit of the roasting furnace is used to provide a heat source for heat exchange to the concentrated mother liquor heater. The first mother liquor outlet and the second mother liquor outlet merge and discharge. The circulating mother liquor outlet is connected to the circulating mother liquor heater for heating the circulating mother liquor. The circulating mother liquor heater is connected to the circulating mother liquor inlet for returning the heated circulating mother liquor to the mother liquor concentration tower. The waste steam heat exchanger is used to provide a heat source for the circulating mother liquor heater and is connected to the multi-effect waste steam outlet.

2. The open-type evaporation-absorption liquid concentration system according to claim 1, characterized in that, The sensible heat recovery unit of the roasting furnace is provided with a flue gas inlet. The sensible heat recovery unit of the roasting furnace and the concentrated mother liquor heater exchange heat through the circulation of a first intermediate water. After exchanging heat with the roasting flue gas, the first intermediate water is discharged from the sensible heat recovery unit of the roasting furnace and enters the concentrated mother liquor heater to heat the concentrated mother liquor. Then, it is discharged from the concentrated mother liquor heater and returns to the sensible heat recovery unit of the roasting furnace to exchange heat with the flue gas of the roasting furnace again to form a cycle.

3. The open-type evaporation-absorption liquid concentration system according to claim 1, characterized in that, The waste steam heat exchanger and the circulating mother liquor heater use a second intermediate water circulation for heat exchange. After exchanging heat with the multi-effect waste steam, the second intermediate water is discharged from the waste steam heat exchanger and enters the circulating mother liquor heater to heat the circulating mother liquor. Then it is discharged from the circulating mother liquor heater and returned to the waste steam heat exchanger to exchange heat with the multi-effect waste steam again to form a cycle.

4. The open-type evaporation-absorption liquid concentration system according to claim 3, characterized in that, The open-type evaporation absorption-type liquid concentration system also includes a calcining furnace waste heat recovery tower and a spray water heat exchanger. The calcining furnace waste heat recovery tower is connected to the flue gas outlet of the sensible heat recovery unit of the calcining furnace for recovering the waste heat of the flue gas. The spray water heat exchanger is connected to the circulating mother liquor heater and uses the circulation of a second intermediate water for heat exchange. The top of the calcining furnace waste heat recovery tower is provided with a spray nozzle. The spray water in the calcining furnace waste heat recovery tower is transported from the bottom to the spray water heat exchanger to exchange heat with the second intermediate water and then returned to the calcining furnace waste heat recovery tower from the spray nozzle.

5. The open-type evaporation-absorption liquid concentration system according to claim 1, characterized in that, The mother liquor concentration tower is also equipped with a filter press circulation pipeline, and a filter press mechanism is installed on the filter press circulation pipeline. The inlet and outlet of the filter press circulation pipeline are respectively connected to the mother liquor concentration tower.

6. The open-type evaporation-absorption liquid concentration system according to claim 1, characterized in that, A regenerator is also provided between the mother liquor concentration tower and the concentrated mother liquor heater. The regenerator is used to exchange heat between the mother liquor before entering the mother liquor concentration tower and the concentrated mother liquor before entering the concentrated mother liquor heater.

7. The open-type evaporation-absorption liquid concentration system according to claim 1, characterized in that, The open-type evaporation absorption liquid concentration system also includes a purification and washing tower, which is connected to the top of the mother liquor concentration tower for washing the fresh air discharged from the mother liquor concentration tower.

8. The open-type evaporation-absorption liquid concentration system according to claim 7, characterized in that, The open-type evaporation absorption-type liquid concentration system also includes a waste steam backup cooler, which is connected to the waste steam heat exchanger to cool the multi-effect waste steam after heat exchange to generate waste steam condensate and non-condensable gas. The waste steam backup cooler is connected to the purification and scrubbing tower to use the waste steam condensate as the scrubbing liquid for the fresh air discharged from the mother liquor concentration tower.

9. The open-type evaporation-absorption liquid concentration system according to claim 8, characterized in that, The open-type evaporation absorption liquid concentration system also includes a vacuum pump, which is connected to the waste steam standby cooler for pumping out the non-condensable gas.

10. The open-type evaporation-absorption liquid concentration system according to claim 1, characterized in that, The inlet flow rate ratio of the first mother liquor inlet to the second mother liquor inlet is 10-12: 2.5-3.5： And / or, the outflow rate ratio of the concentrated mother liquor outlet to the circulating mother liquor outlet is 1:22-24; And / or, the inner wall of the mother liquor concentration tower is provided with an anti-corrosion coating.

Images