Tail gas waste heat utilization system and process of mixed acid waste liquid treatment system

Abstract

The invention relates to the technical field of acid pickling waste liquid resourceful treatment and regeneration, in particular to a tail gas waste heat utilization system and process of a mixed acid waste liquid treatment system.The mixed acid waste liquid treatment system is used for treating mixed acid waste liquid and discharging high-temperature tail gas, and the tail gas waste heat utilization system comprises a first heat exchanger, a second heat exchanger and a refrigeration mechanism; a first heat exchange circulating water path is arranged between the first heat exchanger and the refrigerating mechanism; the first heat exchanger provides a heat source for the refrigerating mechanism by using tail gas heat and reduces the water temperature of the first heat exchange circulating water path by means of the refrigerating mechanism; a second heat exchange circulating water path is arranged between the second heat exchanger and the refrigerating mechanism. The second heat exchanger is further connected to a circulating pipeline of the mixed acid waste liquid treatment system so as to reduce the temperature of circulating liquid. Through the tail gas waste heat utilization system, flue gas waste heat of the mixed acid waste liquid treatment system is effectively recycled, and energy waste is reduced; and the second heat exchanger reduces the circulating liquid temperature of the mixed acid waste liquid treatment system and improves the oxidation efficiency of the flue gas.

Description

Technical Field

[0001] The invention relates to the technical field of resource treatment and regeneration of pickling waste liquid, and in particular to a tail gas waste heat utilization system and process of a mixed acid waste liquid treatment system. Background Art

[0002] The pickling process in the metallurgical industry is an indispensable step in metal surface treatment, especially in the pretreatment of materials such as plates, rods and wires. Although this process improves the processing performance of metal materials, it is also accompanied by the generation of a large amount of pickling waste liquid. The waste acid and heavy metals contained in these waste liquids pose a serious threat to the environment and have become pollutants that metallurgical enterprises urgently need to solve.

[0003] These pickling waste liquids are classified as important substances in the national hazardous waste list because of the harmful substances they contain. In the prior art, there is a mixed acid waste liquid resource regeneration system that realizes the resource regeneration of mixed acid waste liquid through concentration, decomposition, acid absorption, oxidation, denitrification and other steps. However, the exhaust gas discharged by this treatment method has a high temperature and is directly discharged into the air, causing a large amount of energy waste. Therefore, an effective heat utilization system is urgently needed to recycle the large amount of heat discharged by the mixed acid waste liquid resource regeneration system. Summary of the invention

[0004] The object of the present invention is to provide a system and process for utilizing waste heat of tail gas in a mixed acid waste liquid treatment system, so as to solve the problem of energy waste in the above-mentioned mixed acid waste liquid treatment process.

[0005] To achieve the above-mentioned purpose, the technical solution of the present invention includes: a tail gas waste heat utilization system of a mixed acid waste liquid treatment system, the mixed acid waste liquid treatment system is used to treat mixed acid waste liquid and discharge high-temperature tail gas, the tail gas waste heat utilization system includes a first heat exchanger, a second heat exchanger and a refrigeration mechanism, a first heat exchange circulation water circuit is provided between the first heat exchanger and the refrigeration mechanism, the first heat exchanger is also connected to the tail gas discharge end of the mixed acid waste liquid treatment system, so as to use the heat of the tail gas to provide a heat source to the refrigeration mechanism and reduce the water temperature of the first heat exchange circulation water circuit with the help of the refrigeration mechanism; a second heat exchange circulation water circuit is provided between the second heat exchanger and the refrigeration mechanism, and the water temperature of the second heat exchange circulation water circuit is reduced with the help of the refrigeration mechanism, and the second heat exchanger is also connected to the circulation pipeline of the circulating liquid of the mixed acid waste liquid treatment system to reduce the temperature of the circulating liquid.

[0006] In one embodiment, the first heat exchanger is provided with a first heat exchange water inlet and a first heat exchange water outlet, the first heat exchange water inlet is connected to the first refrigeration water outlet of the refrigeration mechanism, the first heat exchange water outlet is connected to the first refrigeration water inlet of the refrigeration mechanism, the first heat exchanger is used to heat the first low-temperature water from the refrigeration mechanism into the first high-temperature water with the help of the tail gas discharged from the mixed acid waste liquid treatment system, thereby using the heat of the tail gas to provide a heat source to the refrigeration mechanism, and the refrigeration mechanism uses the heat source to cool the first high-temperature water to the first low-temperature water, thereby reducing the water temperature of the first heat exchange circulation water circuit with the help of the refrigeration mechanism.

[0007] In one embodiment, the second heat exchanger is provided with a second heat exchange water inlet and a second heat exchange water outlet, the second heat exchange water inlet is connected to the second refrigeration water outlet of the refrigeration mechanism, the second heat exchange water outlet is connected to the second refrigeration water inlet of the refrigeration mechanism, and the refrigeration mechanism reduces the water temperature of the second heat exchange circulation water circuit by cooling the second high-temperature water from the second heat exchanger to second low-temperature water.

[0008] In one embodiment, the refrigeration mechanism is a lithium bromide refrigeration mechanism, wherein the concentration of lithium bromide ranges from 40% to 60%.

[0009] In one embodiment, it also includes a first water-driven pump group and a second water-driven pump group, the first water-driven pump group is used to realize water circulation transportation in the first heat exchange circulation water circuit, and the second water-driven pump group is used to realize water circulation transportation in the second heat exchange circulation water circuit.

[0010] In one embodiment, the mixed acid waste liquid treatment system includes a decomposition furnace, a pre-concentration mechanism, an absorption mechanism, a cooling mechanism, an oxidation mechanism, a denitrification mechanism and a flue gas duct connecting the mechanisms. The circulation pipeline is connected to a cooler, an oxidation mechanism and the second heat exchanger. The cooler is used to cool the circulating liquid from the oxidation mechanism for the first time, and the second heat exchanger is used to cool the circulating liquid for the second time. The circulation pipeline is also provided with a branch connected to the flue gas duct, and the second heat exchanger is used to provide the circulating liquid after the second cooling to the oxidation mechanism or the oxidation mechanism and the flue gas duct.

[0011] The technical solution of the present invention also includes: a tail gas waste heat utilization process of a mixed acid waste liquid treatment system, characterized in that: the process is based on the tail gas waste heat utilization system of the mixed acid waste liquid treatment system, and the process at least includes two parts: tail gas waste heat recovery and circulating liquid cooling, wherein:

[0012] The steps of exhaust gas waste heat recovery include:

[0013] a) introducing tail gas into the first heat exchanger;

[0014] b) the refrigeration mechanism provides first low-temperature water to the first heat exchanger, and the first heat exchanger uses the heat of the exhaust gas to heat the first low-temperature water into first high-temperature water;

[0015] c) supplying the first high-temperature water to the refrigeration mechanism, so as to use the heated first high-temperature water as a heat source to drive the refrigeration mechanism;

[0016] d) the refrigeration mechanism cools the water in the first heat exchange circulation water circuit;

[0017] The steps for cooling the circulating fluid include:

[0018] 1) The refrigeration mechanism delivers second low-temperature water to the second heat exchanger;

[0019] 2) In the second heat exchanger, the second low-temperature water exchanges heat with the circulating fluid to reduce the temperature of the circulating fluid, and the temperature of the second low-temperature water increases to form second high-temperature water;

[0020] 3) The second high-temperature water formed by heating the second low-temperature water flows back to the refrigeration mechanism, thereby forming a second heat exchange circulation water path between the second heat exchanger and the refrigeration mechanism.

[0021] In one embodiment, the temperature of the first low-temperature water is 70-85°C, and the temperature of the first high-temperature water is 90-105°C.

[0022] In one embodiment, the temperature of the second low-temperature water is 7-17°C, and the temperature of the second high-temperature water is 12-22°C.

[0023] In one embodiment, the temperature of the circulating fluid after passing through the second heat exchanger is 15-37°C.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) Through the tail gas waste heat utilization system, the waste heat of the low-grade flue gas at the end of the mixed acid waste liquid treatment system is effectively recovered, reducing energy waste.

[0026] (2) Through the heat exchange process of the second heat exchanger, the temperature of the circulating liquid in the mixed acid waste liquid treatment system is reduced, thereby improving the oxidation efficiency of nitrogen oxides in the flue gas in the mixed acid waste liquid treatment system and realizing efficient regeneration and utilization of the waste acid liquid.

[0027] (3) Effectively utilize the flue gas heat as a heat source to promote the operation of the refrigeration mechanism, so that the refrigeration mechanism outputs low-temperature water. The low-temperature water reduces the temperature of the flue gas on the one hand and the temperature of the circulating fluid on the other hand, thus realizing the recovery and utilization of heat. In turn, the heat is used to reduce the temperature of the circulating fluid and improve the oxidation efficiency, thus realizing the effective circulation of heat.

[0028] (4) It has achieved multiple improvements in production efficiency, energy efficiency and economic benefits, and has high economic value. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the overall structure of an embodiment of the present invention.

[0030] Figure 2 It is a partial structural diagram of an embodiment of the present invention.

[0031] Figure 3 It is a partial structural diagram of another embodiment of the present invention. DETAILED DESCRIPTION

[0032] To further illustrate the various embodiments, the present invention provides drawings. These drawings are part of the disclosure of the present invention, which are mainly used to illustrate the embodiments and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these contents, a person of ordinary skill in the art should be able to understand other possible implementations and advantages of the present invention. The components in the figures are not drawn to scale, and similar component symbols are generally used to represent similar components.

[0033] See also Figure 1 and Figure 2 As shown, the present invention discloses a tail gas waste heat utilization system of a mixed acid waste liquid treatment system. The mixed acid waste liquid treatment system 10 is used to treat mixed acid waste liquid and discharge high-temperature tail gas. The tail gas waste heat utilization system 20 includes a first heat exchanger 21, a second heat exchanger 22 and a refrigeration mechanism 23. A first heat exchange circulation waterway 201 is provided between the first heat exchanger 21 and the refrigeration mechanism 23. The first heat exchanger 21 is also connected to the tail gas discharge end of the mixed acid waste liquid treatment system 10 to provide a heat source to the refrigeration mechanism 23 using the heat of the tail gas and reduce the water temperature of the first heat exchange circulation waterway 201 by means of the refrigeration mechanism 23. A second heat exchange circulation waterway 202 is provided between the second heat exchanger 22 and the refrigeration mechanism 23. The water temperature of the second heat exchange circulation waterway 202 is reduced by means of the refrigeration mechanism 23. The second heat exchanger 22 is also connected to the circulation pipeline of the circulating liquid of the mixed acid waste liquid treatment system 10 to reduce the temperature of the circulating liquid.

[0034] The mixed acid waste liquid treatment system 10 includes a decomposition furnace 11, a pre-concentration mechanism 12, an absorption mechanism 13, a cooling mechanism 14, an oxidation mechanism 15, a denitration mechanism 16, and a flue gas pipeline connecting each mechanism to realize the resource recycling of the mixed acid waste liquid. In the mixed acid waste liquid treatment system 10, the mixed acid waste liquid is first concentrated by the pre-concentration mechanism 12, and then injected into the decomposition furnace 11 for decomposition. The hot flue gas generated during the decomposition process enters the pre-concentration mechanism 12 through the flue gas pipeline for cooling and dust removal. The cooled flue gas then enters the absorption mechanism 13 through the flue gas pipeline to realize the recovery of the regenerated acid. The cooling mechanism 14 further reduces the flue gas temperature, providing conditions for the efficient operation of the oxidation mechanism 15. The oxidation mechanism 15 oxidizes the nitrogen oxides in the flue gas to further improve the recovery rate of the regenerated acid. The working temperature of the oxidation mechanism 15 has a great influence on the oxidation efficiency. The lower the temperature, the higher the oxidation efficiency. Therefore, the mixed acid waste liquid treatment system 10 is provided with a circulation pipeline 101. The cooler 17 in the circulation pipeline 101 is used to cool the circulating liquid, thereby reducing the working temperature of the oxidation mechanism 15. Finally, the denitrification mechanism 16 denitrifies the flue gas to ensure that the nitrogen oxide content in the flue gas meets the emission standard. At the same time, the catalytic reaction during denitrification may require heating of the flue gas, so that the flue gas temperature finally discharged by the mixed acid waste liquid treatment system 10 is higher. In the mixed acid waste liquid treatment system 10 of this embodiment, the flue gas temperature discharged from the tail gas discharge end is between 180 and 250°C. The flue gas temperature is relatively high. If it is directly discharged into the air, there will be a large amount of heat loss, and the ambient temperature around the tail gas discharge outlet will be too high, which is not conducive to the heat dissipation of the mixed acid waste liquid treatment system 10.

[0035] The present invention reduces the temperature of the exhaust flue gas by setting a first heat exchanger 21, converts the temperature of the flue gas into the temperature of the first heat exchange circulation water circuit 201, and uses the heat as the heat source of the refrigeration mechanism 23, thereby driving the refrigeration mechanism 23 to work, so that the heat is recycled and utilized, the energy utilization rate is improved, and the surrounding air is prevented from being excessively heated. Secondly, since the oxidation mechanism 15 of the mixed acid waste liquid treatment system 10 needs to be cooled during operation, the present invention adds a second heat exchanger 22 to the circulation pipeline 101 of its circulating liquid, and uses the second heat exchange circulation water circuit 202 between the refrigeration mechanism 23 and the second heat exchanger 22 to reduce the temperature of the circulating liquid of the mixed acid waste liquid treatment system 10, so as to improve the cooling effect on the oxidation mechanism 15, thereby improving the oxidation efficiency and improving the oxidation efficiency. The present invention can reduce the flue gas temperature discharged from the mixed acid waste liquid treatment system 10 and reduce the impact of the flue gas temperature on the environment through water circulation between the first heat exchanger 21, the second heat exchanger 22 and the refrigeration mechanism 23; secondly, the flue gas temperature can be used as the heat source of the refrigeration mechanism 23 to drive the refrigeration mechanism 23 to work, thereby realizing heat recovery and reuse and improving energy utilization; thirdly, the refrigeration mechanism 23 can also use the heat from the flue gas to achieve heat conversion and reduce the temperature of the second heat exchange circulation water circuit 202, so as to achieve the purpose of cooling the circulating liquid and improving the oxidation efficiency; finally, the refrigeration mechanism 23 can reduce the water temperature of the first heat exchange circulation water circuit 201 and the second heat exchange circulation water circuit 202 only by the heat of the exhaust gas, thereby providing low-temperature water for the first heat exchanger 21 and the second heat exchanger 22, and then use the low-temperature water to reduce the flue gas and circulating liquid temperatures in turn, without inputting energy and making full use of heat conversion to optimize the treatment effect of the mixed acid waste liquid treatment system 10.

[0036] The first heat exchanger 21 is provided with a first heat exchange water inlet and a first heat exchange water outlet. The first heat exchange water inlet is connected to the first refrigeration water outlet of the refrigeration mechanism 23, and the first heat exchange water outlet is connected to the first refrigeration water inlet of the refrigeration mechanism 23. The first heat exchanger 21 is used to heat the first low-temperature water from the refrigeration mechanism 23 into the first high-temperature water with the help of the exhaust gas discharged from the mixed acid waste liquid treatment system 10, thereby using the heat of the exhaust gas to provide a heat source to the refrigeration mechanism 23. The refrigeration mechanism 23 uses the heat source to cool the first high-temperature water to the first low-temperature water, thereby reducing the water temperature of the first heat exchange circulation water circuit 201 with the help of the refrigeration mechanism 23.

[0037] The second heat exchanger 22 is provided with a second heat exchange water inlet and a second heat exchange water outlet, the second heat exchange water inlet is connected to the second refrigeration water outlet of the refrigeration mechanism 23, the second heat exchange water outlet is connected to the second refrigeration water inlet of the refrigeration mechanism 23, and the refrigeration mechanism 23 reduces the water temperature of the second heat exchange circulation water circuit 202 by cooling the second high temperature water from the second heat exchanger 22 to second low temperature water.

[0038] The first heat exchanger 21 and the second heat exchanger 22 are respectively provided with independent heat exchange circulation water circuits to realize heat exchange with the refrigeration mechanism 23, which can not only reduce the water temperature of each heat exchange circulation water circuit, but also provide water of different temperatures to the first heat exchanger 21 and the second heat exchanger 22 as needed.

[0039] The second heat exchanger 22 participates in the circulating liquid flow direction of the circulating pipeline 101 of the mixed acid waste liquid treatment system 10 as follows: Figure 2 As shown, the circulating liquid flows out of the oxidation mechanism 15 and enters the cooler 17 through a one-way valve for the first cooling. The circulation pipeline is provided with two branches so that the circulating liquid leaving the cooler 17 is divided into two branches. In this embodiment, the circulating liquid is split before leaving the cooler 17 and entering the second heat exchanger 22. One branch is split into the flue gas pipe and the other branch enters the second heat exchanger 22 for the second cooling. Thus, the second heat exchanger 22 provides the oxidation mechanism 15 with the circulating liquid after two-stage cooling, so that the temperature of the circulating liquid is further reduced, ensuring that the oxidation mechanism 15 can work at a lower temperature and improve the oxidation efficiency. Each branch is provided with a valve to control the on-off and flow rate of the circulating liquid. The part of the circulating liquid that enters the flue gas pipe cools the flue gas in the mixed acid waste liquid treatment system 10. The circulating liquid is split before entering the second heat exchanger 22 so that less circulating liquid enters the second heat exchanger 22, so that the cooling effect of the second heat exchanger 22 on this part of the circulating liquid is more obvious. In another embodiment, refer to Figure 3 As shown, the circulating liquid is cooled twice by the cooler 17 and the second heat exchanger 22 and then split. One path enters the flue gas duct to cool the flue gas, and the other path enters the oxidation mechanism 15, so that the second heat exchanger supplies the circulating liquid that has been cooled twice to the flue gas duct and the oxidation mechanism respectively. This design allows the circulating liquid to enter the flue gas duct at a lower temperature, and the cooling effect on the flue gas is more obvious.

[0040] The refrigeration mechanism 23 of this embodiment is a lithium bromide refrigeration mechanism, wherein the concentration of lithium bromide ranges from 40% to 60%. It uses the input heat source to reduce the water temperature of the first heat exchange circulation water circuit 201 and the second heat exchange circulation water circuit 202, thereby achieving the purpose of refrigeration. The working principle of the lithium bromide refrigeration mechanism is prior art and will not be repeated here.

[0041] See also Figure 1 As shown, the first water-driven pump group and the second water-driven pump group are also included. The first water-driven pump group is used to realize the water circulation transportation of the first heat exchange circulation waterway 201, and the second water-driven pump group is used to realize the water circulation transportation of the second heat exchange circulation waterway 202. The first water-driven pump group and the second water-driven pump group can ensure the normal circulation transportation of water in the first heat exchange circulation waterway 201 and the second heat exchange circulation waterway 202, so that the heat exchange is carried out normally, thereby achieving the required heat exchange effect.

[0042] The refrigeration mechanism 23 is also connected to a cooling water circuit 203, which is used to cool the refrigeration mechanism 23 to prevent the refrigeration mechanism 23 from being overheated during operation. The first heat exchange circulation water circuit 201 and the second heat exchange circulation water circuit 202 are respectively provided with a water supply water circuit 204, so that water can circulate in the first heat exchange circulation water circuit 201 and the second heat exchange circulation water circuit 202 when starting to work. When the first heat exchange circulation water circuit 201 and the second heat exchange circulation water circuit 202 are performing normal water circulation, the water supply water circuit 204 may no longer supply water to the first heat exchange circulation water circuit 201 and the second heat exchange circulation water circuit 202. In addition, the temperature of the water supplied by the water supply water circuit 204 should match the water temperature of the corresponding heat exchange circulation water circuit to ensure that the water temperature of the heat exchange circulation water circuit meets the requirements.

[0043] The present invention also discloses a tail gas waste heat utilization process of a mixed acid waste liquid treatment system. The process is based on the tail gas waste heat utilization system of the mixed acid waste liquid treatment system. The process includes at least two parts: tail gas waste heat recovery and circulating liquid cooling. The tail gas waste heat recovery step includes:

[0044] a) introducing the tail gas into the first heat exchanger 21;

[0045] b) The refrigeration mechanism 23 provides the first low-temperature water to the first heat exchanger 21, and the first heat exchanger 21 uses the exhaust gas heat to heat the first low-temperature water into first high-temperature water;

[0046] c) supplying the first high temperature water to the refrigeration mechanism 23, so that the heated first high temperature water is used as a heat source to drive the refrigeration mechanism 23;

[0047] d) The refrigeration mechanism 23 cools the water in the first heat exchange circulation water path 201 .

[0048] The steps for cooling the circulating fluid include:

[0049] 1) The refrigeration mechanism 23 delivers the second low-temperature water to the second heat exchanger 22;

[0050] 2) In the second heat exchanger 22, the second low-temperature water exchanges heat with the circulating fluid to reduce the temperature of the circulating fluid, and the temperature of the second low-temperature water increases to form second high-temperature water;

[0051] 3) The second high-temperature water formed by the second low-temperature water being heated flows back to the refrigeration mechanism 23 , thereby forming a second heat exchange circulation water path 202 between the second heat exchanger 22 and the refrigeration mechanism 23 .

[0052] The second heat exchanger 22 is respectively Figure 2 or Figure 3 One of the embodiments shown cools the circulating fluid. The two cooling methods have been described in detail in the above content and will not be repeated here.

[0053] The temperature of the first low-temperature water is 70-85°C, and in this embodiment, it is more preferably 75-80°C. The temperature of the first high-temperature water is 90-105°C, and in this embodiment, it is more preferably 95-100°C.

[0054] The temperature of the second low-temperature water is 7-17°C, and in this embodiment, it is more preferably 7-12°C. The temperature of the second high-temperature water is 12-22°C, and in this embodiment, it is more preferably 12-18°C.

[0055] The temperature of the circulating fluid after passing through the second heat exchanger 22 is 15-37°C, and in this embodiment, it is further preferably 20-30°C. The flow rate range of the circulating fluid is 60-160m 3 / h.

[0056] Although the present invention has been specifically shown and described in conjunction with the preferred embodiments, those skilled in the art should understand that the remaining undescribed portions are prior art, and that various changes made to the present invention in form and detail without departing from the spirit and scope of the present invention as defined in the appended claims shall fall within the scope of protection of the present invention.

Claims

1. A tail gas waste heat utilization system of a mixed acid waste liquid treatment system, characterized in that: The mixed acid waste liquid treatment system is used to treat mixed acid waste liquid and discharge high-temperature exhaust gas. The exhaust gas waste heat utilization system includes a first heat exchanger, a second heat exchanger and a refrigeration mechanism. A first heat exchange circulation water circuit is provided between the first heat exchanger and the refrigeration mechanism. The first heat exchanger is also connected to the exhaust gas discharge end of the mixed acid waste liquid treatment system to utilize the heat of the exhaust gas to provide a heat source to the refrigeration mechanism and reduce the water temperature of the first heat exchange circulation water circuit with the help of the refrigeration mechanism; a second heat exchange circulation water circuit is provided between the second heat exchanger and the refrigeration mechanism, and the water temperature of the second heat exchange circulation water circuit is reduced with the help of the refrigeration mechanism. The second heat exchanger is also connected to the circulation pipeline of the circulating liquid of the mixed acid waste liquid treatment system to reduce the temperature of the circulating liquid.

2. The tail gas waste heat utilization system of the mixed acid waste liquid treatment system according to claim 1 is characterized by: The first heat exchanger is provided with a first heat exchange water inlet and a first heat exchange water outlet, the first heat exchange water inlet is connected to the first refrigeration water outlet of the refrigeration mechanism, the first heat exchange water outlet is connected to the first refrigeration water inlet of the refrigeration mechanism, the first heat exchanger is used to heat the first low-temperature water from the refrigeration mechanism into the first high-temperature water with the help of the tail gas discharged from the mixed acid waste liquid treatment system, thereby using the heat of the tail gas to provide a heat source to the refrigeration mechanism, and the refrigeration mechanism uses the heat source to cool the first high-temperature water to the first low-temperature water, thereby reducing the water temperature of the first heat exchange circulation water circuit with the help of the refrigeration mechanism.

3. The tail gas waste heat utilization system of the mixed acid waste liquid treatment system according to claim 1, characterized in that: The second heat exchanger is provided with a second heat exchange water inlet and a second heat exchange water outlet, the second heat exchange water inlet is connected to the second refrigeration water outlet of the refrigeration mechanism, the second heat exchange water outlet is connected to the second refrigeration water inlet of the refrigeration mechanism, and the refrigeration mechanism reduces the water temperature of the second heat exchange circulation water circuit by cooling the second high-temperature water from the second heat exchanger to second low-temperature water.

4. The tail gas waste heat utilization system of the mixed acid waste liquid treatment system according to claim 1, characterized in that: The refrigeration mechanism is a lithium bromide refrigeration mechanism, wherein the concentration of lithium bromide ranges from 40 to 60%.

5. The tail gas waste heat utilization system of the mixed acid waste liquid treatment system according to claim 1, characterized in that: It also includes a first water-driven pump group and a second water-driven pump group. The first water-driven pump group is used to realize water circulation and transportation in the first heat exchange circulation water circuit, and the second water-driven pump group is used to realize water circulation and transportation in the second heat exchange circulation water circuit.

6. The tail gas waste heat utilization system of the mixed acid waste liquid treatment system according to claim 1, characterized in that: The mixed acid waste liquid treatment system includes a decomposition furnace, a pre-concentration mechanism, an absorption mechanism, a cooling mechanism, an oxidation mechanism, a denitrification mechanism and a flue gas pipeline connecting the mechanisms. The circulation pipeline is connected to a cooler, an oxidation mechanism and the second heat exchanger. The cooler is used to cool the circulating liquid from the oxidation mechanism for the first time, and the second heat exchanger is used to cool the circulating liquid for the second time. The circulation pipeline is also provided with a branch connected to the flue gas pipeline. The second heat exchanger is used to provide the circulating liquid after the second cooling to the oxidation mechanism or the oxidation mechanism and the flue gas pipeline.

7. A process for utilizing waste heat from tail gas of a mixed acid waste liquid treatment system, characterized in that: The process is a tail gas waste heat utilization system based on any one of claims 1 to 6 of the mixed acid waste liquid treatment system. The process includes at least two parts: tail gas waste heat recovery and circulating liquid cooling. The tail gas waste heat recovery step includes: a) introducing tail gas into the first heat exchanger; b) the refrigeration mechanism provides first low-temperature water to the first heat exchanger, and the first heat exchanger uses the heat of the exhaust gas to heat the first low-temperature water into first high-temperature water; c) supplying the first high-temperature water to the refrigeration mechanism, so as to use the heated first high-temperature water as a heat source to drive the refrigeration mechanism; d) the refrigeration mechanism cools the water in the first heat exchange circulation water circuit; The steps for cooling the circulating fluid include: 1) The refrigeration mechanism delivers second low-temperature water to the second heat exchanger; 2) In the second heat exchanger, the second low-temperature water exchanges heat with the circulating fluid to reduce the temperature of the circulating fluid, and the temperature of the second low-temperature water increases to form second high-temperature water; 3) The second high-temperature water formed by heating the second low-temperature water flows back to the refrigeration mechanism, thereby forming a second heat exchange circulation water path between the second heat exchanger and the refrigeration mechanism.

8. The process for utilizing waste heat from tail gas of a mixed acid waste liquid treatment system according to claim 7, characterized in that: The temperature of the first low-temperature water is 70-85°C, and the temperature of the first high-temperature water is 90-105°C.

9. The process for utilizing waste heat from tail gas of a mixed acid waste liquid treatment system according to claim 7, characterized in that: The temperature of the second low-temperature water is 7-17°C, and the temperature of the second high-temperature water is 12-22°C.

10. The process for utilizing waste heat from tail gas of a mixed acid waste liquid treatment system according to claim 7, characterized in that: The temperature of the circulating fluid after passing through the second heat exchanger is 15-37°C.

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