A high-salt wastewater step crystallization system and method

Abstract

The invention discloses a high-salt wastewater step-by-step crystallization system and method, which includes a multi-effect step-by-step crystallization device, a single-effect crystallization device and a cooling crystallization device; the multi-effect step-by-step crystallization device includes a first-effect separator and a first-effect evaporator that are interconnected, at least one group of second-effect separators and second-effect evaporators that are interconnected, a three-effect crystallizer and a three-effect evaporator that are interconnected, a 1# centrifuge and a 1# mother liquid tank, and the 1# mother liquid tank is respectively connected to the three-effect evaporator, the single-effect crystallization device and the cooling crystallization device; the cooling crystallization device also includes a cooler, a cooling crystallizer, a 2# centrifuge and a 2# mother liquid tank, and the 2# mother liquid tank is respectively connected to the single-effect crystallization device and the multi-effect step-by-step crystallization device; the single-effect crystallization device also includes a single-effect evaporator, a single-effect crystallizer, a 3# centrifuge and a 3# mother liquid tank, and the 3# mother liquid tank is also connected to the single-effect evaporator. Automatic interlocking control of the whole process of salt separation crystallization can be realized, and the quality and recovery rate of finished salt are guaranteed under low-cost conditions.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a high-salt wastewater step crystallization system and method. Background Art

[0002] According to incomplete statistics, the coal chemical industry emits about 600,000 to 700,000 tons of industrial salt as a by-product each year; the pesticide industry produces more than 600,000 tons of industrial salt as a by-product each year; and the epoxy resin production industry produces more than 200,000 tons of industrial salt as a by-product each year... and every year a large amount of high-salt wastewater or high-salt mother liquor produced through evaporation and crystallization of industrial salt as a by-product can only be treated as hazardous waste or solid waste, causing great environmental risks and waste of resources.

[0003] There are two salt separation processes in China, namely thermal salt separation and membrane salt separation. These two salt separation processes have their own advantages and disadvantages: the advantage of thermal salt separation is that the process is simple, the operation reliability is strong, and the investment and operation costs are low. The disadvantage is that the quality of the crystallized salt is slightly low; the advantage of membrane salt separation is that the quality of sodium chloride salt is slightly higher, which is more suitable for wastewater with sodium chloride as the main component. The disadvantage is that the investment and operation costs are high, the membrane operation reliability is not as good as the thermal method, and the separation efficiency gradually decreases with the extension of operation time.

[0004] The salt content in high-salt wastewater from chemical industries such as coal chemical industry and petrochemical industry is mainly sodium chloride and sodium sulfate, and the concentration of chloride ions and sulfate ions in high-salt wastewater is constantly changing. How to ensure the quality of sodium chloride and sodium sulfate during the evaporation and crystallization process and maximize the recovery rate of crystallized salt at a reasonable cost is a technical problem that needs to be overcome urgently. Summary of the invention

[0005] In view of the above problems, the present invention is proposed to provide a high-salt wastewater step crystallization system and method that overcomes or solves the above problems, which can realize automatic interlocking control of the whole process of salt separation and crystallization, and ensure the quality and recovery rate of finished salt under low cost conditions.

[0006] In a first aspect, an embodiment of the present invention provides a high-salt wastewater step crystallization system, including a multi-effect step crystallization device, a single-effect crystallization device and a cooling crystallization device;

[0007] The multi-effect fractional crystallization device comprises: a feed tank for allowing high-salt wastewater to flow in, a group of interconnected first-effect separators and first-effect evaporators, at least one group of interconnected second-effect separators and second-effect evaporators, a group of interconnected three-effect crystallizers and three-effect evaporators, and a 1# centrifuge connected to the three-effect crystallizer, the 1# centrifuge is used to separate the 1# finished salt and the 1# mother liquor flowing into the 1# mother liquor tank, and the 1# mother liquor tank is respectively connected to the three-effect evaporator, the single-effect evaporator of the single-effect crystallization device and the cooler of the cooling crystallization device;

[0008] The cooling crystallization device further comprises a cooling crystallizer interconnected with the cooler, a 2# centrifuge and a 2# mother liquid tank connected in sequence to the cooling crystallizer, the 2# centrifuge is used to separate the 1# impurities and the 2# mother liquid flowing into the 2# mother liquid tank, and the 2# mother liquid tank is respectively connected to the single-effect evaporator of the single-effect crystallization device and the triple-effect evaporator of the multi-effect fractional crystallization device;

[0009] The single-effect crystallization device also includes a single-effect crystallizer interconnected with the single-effect evaporator, a 3# centrifuge and a 3# mother liquor tank connected to the single-effect crystallizer in sequence, the 3# centrifuge is used to separate the 2# finished salt or 2# impurity salt and the 3# mother liquor flowing into the 3# mother liquor tank, and the 3# mother liquor tank is also connected to the single-effect evaporator.

[0010] In a second aspect, an embodiment of the present invention provides a method for stepwise crystallization of high-salt wastewater, comprising:

[0011] The finished salt is precipitated from the high-salt wastewater by using a high-salt wastewater stepwise crystallization system, wherein the high-salt wastewater stepwise crystallization system is the high-salt wastewater stepwise crystallization system mentioned above.

[0012] The beneficial effects of the above technical solution provided by the embodiment of the present invention include at least:

[0013] The high-salt wastewater step-by-step crystallization system provided by the embodiment of the present invention includes a multi-effect step-by-step crystallization device, a single-effect crystallization device and a cooling crystallization device; the 1# mother liquor tank of the multi-effect step-by-step crystallization device is respectively connected to the triple-effect evaporator of the multi-effect step-by-step crystallization device, the single-effect evaporator of the single-effect crystallization device and the cooler of the cooling crystallization device; the 2# mother liquor tank of the cooling crystallization device is respectively connected to the single-effect evaporator of the single-effect crystallization device and the triple-effect evaporator of the multi-effect step-by-step crystallization device; the 3# mother liquor tank of the single-effect crystallization device is also connected to the single-effect evaporator of the single-effect crystallization device. Through the arrangement of various types of crystallization devices and the connection between each other and the circulation connection within each device, different process routes and matching full-automatic linkage control systems can be adopted for different types of high-salt wastewater and changes in the concentration of chloride ions and sulfate ions, thereby improving the purity and recovery rate of crystallized salt, reducing the output of impure salt and processing costs, and ensuring the quality of finished salt at low cost.

[0014] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0016] Figure 1This is a schematic diagram of the structure of the high-salinity wastewater stepwise crystallization system in Example 1 of the present invention;

[0017] Figure 2 This is a schematic diagram of the specific structure of the high-salinity wastewater stepwise crystallization system in Example 1 of the present invention;

[0018] Figure 3A The H2O-NaCl-Na2SO4 ternary phase diagram at 0°C and 75°C in the embodiment of the present invention;

[0019] Figure 3B It is an application diagram of the H2O-NaCl-Na2SO4 ternary phase diagram at 0°C and 75°C in the embodiment of the present invention;

[0020] Figure 4 This is a schematic diagram of a first interlocking control system in Embodiment 1 of the present invention;

[0021] Figure 5 Schematic diagram of a second interlocking control system in Embodiment 1 of the present invention;

[0022] Figure 6 This is a schematic diagram of a third interlocking control system in Embodiment 1 of the present invention;

[0023] Figure 7 This is a flow chart of the stepwise crystallization method of high-salt wastewater in Example 2 of the present invention;

[0024] Figure 8 This is a flow chart of the stepwise crystallization method of high-salt wastewater in Example 3 of the present invention;

[0025] Fig. 9 This is a flow chart of the stepwise crystallization method for high-salt wastewater in Example 4 of the present invention. DETAILED DESCRIPTION

[0026] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0027] In order to ensure the quality and recovery rate of finished salt from salt fractionation crystallization of high-salt wastewater under low-cost conditions, an embodiment of the present invention provides a high-salt wastewater stepwise crystallization system and method, which can realize automatic interlocking control of the entire process of salt fractionation crystallization and ensure the quality and recovery rate of finished salt under low-cost conditions.

[0028] Embodiment 1

[0029] Embodiment 1 of the present invention provides a high-salt wastewater step crystallization system, the structure of which is as follows: Figure 1 As shown, it includes a multi-effect step-by-step crystallization device, a single-effect crystallization device and a cooling crystallization device.

[0030] The multi-effect step-by-step crystallization device includes: a feed tank 1 for allowing high-salt wastewater to flow in, a group of interconnected first-effect separators 3 and first-effect evaporators 4, at least one group of interconnected second-effect separators 6 and second-effect evaporators 7, a group of interconnected triple-effect crystallizers 9 and triple-effect evaporators 10, and also includes a 1# centrifuge 12 connected to the triple-effect crystallizer 9, the 1# centrifuge 12 is used to centrifugally separate the 1# finished salt and the 1# mother liquor flowing into the 1# mother liquor tank 13, and the 1# mother liquor tank 13 is respectively connected to the triple-effect evaporator 10, the single-effect evaporator 29 of the single-effect crystallization device and the cooler 19 of the cooling crystallization device.

[0031] The cooling crystallization device also includes a cooling crystallizer 18 interconnected with the cooler 19, a 2# centrifuge 22 and a 2# mother liquor tank 23 connected to the cooling crystallizer 18 in sequence, the 2# centrifuge 22 is used to centrifugally separate the 1# miscellaneous salt or sodium sulfate decahydrate and the 2# mother liquor flowing into the 2# mother liquor tank 23, and the 2# mother liquor tank 23 is respectively connected to the single-effect evaporator 29 of the single-effect crystallization device and the triple-effect evaporator 10 of the multi-effect step-by-step crystallization device.

[0032] The single-effect crystallization device also includes a single-effect crystallizer 28 interconnected with the single-effect evaporator 29, a 3# centrifuge 31 and a 3# mother liquor tank 32 connected to the single-effect crystallizer 28 in sequence, the 3# centrifuge 31 is used to centrifugally separate the 2# finished salt or 2# impure salt and the 3# mother liquor flowing into the 3# mother liquor tank 32, and the 3# mother liquor tank 32 is also connected to the single-effect evaporator 29.

[0033] The high-salt wastewater step-by-step crystallization system provided in the first embodiment of the present invention includes a multi-effect step-by-step crystallization device, a single-effect crystallization device and a cooling crystallization device; the 1# mother liquor tank of the multi-effect step-by-step crystallization device is respectively connected to the triple-effect evaporator of the multi-effect step-by-step crystallization device, the single-effect evaporator of the single-effect crystallization device and the cooler of the cooling crystallization device; the 2# mother liquor tank of the cooling crystallization device is respectively connected to the single-effect evaporator of the single-effect crystallization device and the triple-effect evaporator of the multi-effect step-by-step crystallization device; the 3# mother liquor tank of the single-effect crystallization device is also connected to the single-effect evaporator of the single-effect crystallization device. Through the arrangement of various types of crystallization devices and the connection between each other and the circulation connection within each device, different process routes and matching full-automatic linkage control systems can be adopted for different types of high-salt wastewater and changes in the concentration of chloride ions and sulfate ions, thereby improving the purity and recovery rate of crystallized salt, reducing the output of impure salt and processing costs, and ensuring the quality of finished salt at low cost.

[0034] The multi-effect step-by-step crystallization device includes: a group of interconnected first-effect separators and first-effect evaporators, at least one group of interconnected second-effect separators and second-effect evaporators, and a group of interconnected third-effect crystallizers and third-effect evaporators, the hot steam separated by the first-effect separator enters the second-effect evaporator and continues to serve as the heat source of the second-effect evaporator; the hot steam separated by the second-effect separator enters the third-effect evaporator and continues to serve as the heat source of the third-effect evaporator. The energy required in the secondary evaporation and crystallization process is saved, and the energy required for steam cooling is saved, further reducing the crystallization cost of finished salt.

[0035] For details, see Figure 2 As shown, the multi-effect fractional crystallization device also includes a 1# heat source supply device connected to the first-effect evaporator 4, and a 1# pressure gauge 110 and a 6# control valve 206 are provided on the steam pipeline between the first-effect evaporator 4 and the 1# heat source supply device.

[0036] The 1# heat source supply device can provide a heat source for the first-effect evaporator 4 by providing low-pressure hot steam.

[0037] A chloride ion analyzer 101 , a sulfate ion analyzer 102 , a salinity analyzer 103 and a No. 1 flow meter 104 are provided on the pipeline between the feed tank 1 and the first-effect separator 3 .

[0038] The first-effect separator 3 is provided with a 1# thermometer 106 , and the third-effect crystallizer 9 is provided with a 3# liquid level meter 108 and a 1# density meter 109 .

[0039] 1#densitometer 109, 1#thermometer 106, 1#pressure gauge 110 and 6#control valve 206 are interlocked and controlled. Figure 2 Signal chain 1 in.

[0040] A 2# flow meter 111 and a 4# control valve 204 are provided on the pipeline between the triple-effect crystallizer 9 and the 1# centrifuge 12. The 4# control valve 204 is interlocked with the 2# flow meter 111 for control.

[0041] The 1# mother liquid tank 13 is provided with a 4# liquid level meter 112, which is respectively connected to the cooler 19 and the single-effect evaporator 29 through a pipeline provided with a 5# control valve 205, and the 4# liquid level meter 112 and the 5# control valve 205 are interlocked and controlled.

[0042] A 4# flow meter 121 is provided on the pipeline between the 1# mother liquid tank 13 and the triple effect evaporator 10. The chloride ion analyzer 101, the sulfate ion analyzer 102, the 1# flow meter 104, the 4# flow meter 121 and the 2# flow meter 111 are interlocked and controlled. Figure 2 In the signal link 2, the 4# flow meter 121 is also interlocked with the 5# control valve 205 for control.

[0043] See also Figure 4As shown, the above-mentioned chloride ion analyzer 101, sulfate ion analyzer 102, 1# flow meter 104, 1# density meter 109, 2# flow meter 111, 4# control valve 204, 4# flow meter 121, 1# pressure gauge 110, 1# thermometer 106 and 6# control valve 206 are combined into a first interlocking control system for controlling the crystallization point in the first set crystallization zone.

[0044] For example, the crystallization point of high-halogen, low-nitrate high-salt wastewater can be controlled in the sodium chloride crystallization region in the H2O-NaCl-Na2SO4 ternary phase diagram (see Figure 3A and Figure 3B As shown), a finished sodium chloride salt with a purity of ≥98.5% is produced; the crystallization point of the low-halogen medium-high nitrate or low-halogen high-nitrate high-salt wastewater is controlled in the sodium sulfate crystallization region in the H2O-NaCl-Na2SO4 ternary phase diagram, and a finished sodium sulfate salt with a purity of ≥98% is produced.

[0045] The classification standards of high-salinity wastewater into high-halogen and low-nitrate type, low-halogen and medium-high-nitrate type, and low-halogen and high-nitrate type can be referred to as follows:

[0046] When the sodium chloride content in high-salt wastewater is ≥91.5% and the rest is sodium sulfate, it is high-halogen, low-nitrate wastewater; when the sodium sulfate content in high-salt wastewater is 88%>64% and the rest is sodium chloride, it is low-halogen, medium-high-nitrate wastewater; when the sodium sulfate content in high-salt wastewater is ≥88% and the rest is sodium chloride, it is low-halogen, high-nitrate wastewater.

[0047] In some embodiments, a 1# pump 2 is provided between the feed tank 1 and the first-effect separator 3, a 1# control valve 201 is provided on the pipeline therebetween, and the first-effect separator 3 is also provided with a 1# liquid level meter 105, and the 1# control valve 201 is interlocked with the 1# liquid level meter 105. The high-salt wastewater in the feed tank 1 is transported to the first-effect separator 3 through the 1# pump 2.

[0048] The interlocking control of the control valve and the liquid level gauge can ensure that the liquid level in the separator is within a reasonable range, so that the liquid level in the separator will not be too high so that effective separation can be achieved, and at the same time, the liquid level will not be too low, thereby taking into account the separation efficiency while providing good protection for the pump.

[0049] In some embodiments, the first-effect separator 3 is connected to the first-effect evaporator 4 and the second-effect separator 6 respectively through the 2# pump 5, a 2# control valve 202 is provided on the pipeline between the first-effect separator 3 and the second-effect separator 6, the second-effect separator 6 is provided with a 2# liquid level gauge 107, and the 2# control valve 202 is interlocked with the 2# liquid level gauge 107; the second-effect separator 6 is connected to the second-effect evaporator 7 and the triple-effect crystallizer 9 respectively through the 3# pump 8, a 3# control valve 203 is provided on the pipeline between the second-effect separator 6 and the triple-effect crystallizer 9, the triple-effect crystallizer 9 is provided with a 3# liquid level gauge 108, and the 3# control valve 203 is interlocked with the 3# liquid level gauge 108; the triple-effect crystallizer 9 is connected to the triple-effect evaporator 10 and the 1# centrifuge 12 respectively through the 4# pump 11.

[0050] The high-salt wastewater in the feed tank 1 is transported to the first-effect separator 3 through the 1# pump 2, and then heated and evaporated into a gas-liquid mixture by the first-effect evaporator 4. After the separation action of the first-effect separator 3, the separated secondary steam enters the second-effect evaporator and is used as a secondary heat source; the separated liquid part enters the first-effect evaporator for circulating evaporation, and part enters the second-effect separator.

[0051] Similarly, after the heating evaporation in the second-effect evaporator 7 and the separation in the second-effect separator 6, the separated secondary steam enters the third-effect evaporator 10 and is used as a secondary heat source; part of the separated liquid enters the second-effect evaporator 7 for cyclic evaporation, and part enters the third-effect crystallizer 9.

[0052] In some embodiments, the multi-effect fractional crystallization device further includes a condensed water tank 16, the second-effect evaporator 7 and the third-effect evaporator 10 are respectively connected to the condensed water tank 16, and the condensed water tank 16 is used to temporarily store 1# finished water.

[0053] In some embodiments, the multi-effect step-by-step crystallization device also includes an indirect condenser 15 connected to the triple-effect crystallizer 9. The indirect condenser 15 is also connected to the condensed water tank 16, respectively, and is connected to the atmosphere, that is, connected to the external environment.

[0054] After the separation action of the triple-effect crystallizer 9 , the separated secondary steam enters the indirect condenser 15 ; the separated liquid portion enters the triple-effect evaporator 10 for cyclic evaporation and crystallization, and the solid-liquid portion enters the 1# centrifuge 12 .

[0055] The separated gas after condensation in the indirect condenser 15 enters the outside atmosphere, and the separated water enters the condensed water tank 16 .

[0056] The above system achieves zero discharge of high-salt wastewater, and all finished water is recycled for replenishment of circulating water devices or desalination stations, saving a large amount of fresh water. This not only helps solve the problem of water shortage, but also reduces pollution and damage to the environment and ecology.

[0057] In some embodiments, the condensate tank 16 is provided with a 5# liquid level meter 115; the condensate tank 16 is connected to the finished water pipeline of the circulating water device, a 6# pump 17 is provided on the finished water pipeline between the condensate tank 16 and the circulating water device, and a 2# salinity analyzer 113, a 3# flow meter 114 and a 7# control valve 207 are provided on the pipeline between them, and the 5# liquid level meter 115 is interlocked with the 7# control valve 207.

[0058] In some embodiments, the 1# mother liquid tank 13 is connected to the triple-effect evaporator 10, the cooler 19 of the cooling crystallization device and the single-effect evaporator 29 of the single-effect crystallization device respectively through the 5# pump 14.

[0059] The 1# mother liquor can be returned to the multi-effect step-by-step crystallization device, or can be transported to the single-effect crystallization device for single-effect crystallization, or can be transported to the cooling crystallization device for cooling crystallization.

[0060] In some embodiments, the cooling crystallizer 18 is provided with a 2# thermometer 116, a 2# density meter 118 and a 6# liquid level meter 117; the cooling crystallizer 18 is interconnected with the cooler 19, and the cooler 19 is interconnected with the refrigerator 21; the 2# thermometer 116 is interlocked with the 2# density meter 118 and the refrigerator 21, see Figure 2 The signal link 3 in the figure; a 7# pump 20 is provided between the cooling crystallizer 18 and the cooler 19; an 8# control valve 208 is provided on the pipeline between the cooling crystallizer 18 and the 2# centrifuge 22, and the 8# control valve 208 is interlocked with the 6# liquid level meter 117 for control.

[0061] See also Figure 5 As shown, the 2# thermometer 116, the 2# density meter 118, the refrigerator 21, the 6# liquid level meter 117 and the 8# control valve 208 are combined into a second interlocking control system for controlling the crystallization point in the second set crystallization zone.

[0062] For example, if the high-salt wastewater is of high-halogen and low-nitrate type or low-halogen and medium-high-nitrate type, the crystallization point of the 1# mother liquor can be controlled in the sodium sulfate decahydrate crystallization zone through the second interlocking control system to obtain sodium sulfate decahydrate and 2# mother liquor.

[0063] In some embodiments, the 2# mother liquor tank 23 is connected to the single-effect evaporator 29 of the single-effect crystallization device and the triple-effect evaporator 10 of the multi-effect step-by-step crystallization device through the 8# pump 24 and the 9# control valve 209 respectively; the 2# mother liquor tank 23 is provided with a 7# liquid level meter 119, and the 9# control valve 209 is interlocked with the 7# liquid level meter 119 for control.

[0064] In some embodiments, the 2# centrifuge 22 of the cooling crystallization device is also connected to the screw conveyor 25 and the dissolving tank 26 in sequence, and the dissolving tank 26 is connected to the triple-effect evaporator 10 of the multi-effect fractional crystallization device; the dissolving tank 26 and the 1# mother liquor tank 13 of the multi-effect fractional crystallization device are connected to the triple-effect evaporator 10 through a pipeline provided with a 4# flowmeter 121.

[0065] For example, high-salt wastewater is of low-halogen and medium-high-nitrate type. First, the crystallization point is controlled in the sodium sulfate crystallization zone through the first interlocking control system of the multi-effect step-by-step crystallization device to precipitate Na2SO4 crystals; the generated 1# mother liquor passes through the second interlocking control system of the cooling crystallization device to control the crystallization point in the sodium sulfate decahydrate crystallization zone, and the sodium sulfate decahydrate crystal salt and high-purity sodium chloride mother liquor are precipitated after cooling; the sodium sulfate decahydrate is redissolved in the dissolving tank and then returned to the three-effect step-by-step crystallization device to continue evaporation and crystallization to increase the recovery rate of sodium sulfate finished salt.

[0066] In some embodiments, the dissolving tank 26 is provided with an 8# liquid level meter 120, a 9# pump 27 is provided between the dissolving tank 26 and the triple-effect evaporator 10, and a 10# control valve 210 is provided on the pipeline therebetween, and the 10# control valve 210 is interlocked with the 8# liquid level meter 120 for control.

[0067] In some embodiments, the single-effect crystallization device further includes a 2# heat source supply device connected to the single-effect evaporator 29, and a 2# pressure gauge 125 and a 12# control valve 212 are provided on the steam pipeline between the single-effect evaporator 29 and the 2# heat source supply device; the single-effect crystallizer 28 is provided with a 3# thermometer 122, a 3# density meter 124 and a 9# liquid level meter 123, and the 3# density meter 122, the 3# thermometer 124, the 2# pressure gauge 125 and the 12# control valve 212 are interlocked for control, see Figure 2 Signal chain 4 in.

[0068] A 11# control valve 211 is provided on the pipeline between the single-effect crystallizer 28 and the 3# centrifuge 31 , and the 11# control valve 211 is interlocked with the 9# liquid level meter 123 for control.

[0069] See also Figure 6 As shown, the 2# pressure gauge 125, the 3# temperature gauge 124, the 12# control valve 212, the 3# density meter 122, the 9# liquid level gauge 123 and the 11# control valve 211 are combined into a third interlocking control system for controlling the crystallization point in the third set crystallization zone.

[0070] For example, the crystallization point is controlled in the sodium chloride crystallization region or the sodium chloride-sodium sulfate crystallization region to obtain sodium chloride finished salt or sodium chloride impure salt.

[0071] In some embodiments, a 10# pump 30 is provided between the single-effect crystallizer 28 and the single-effect evaporator 29 .

[0072] In some embodiments, the single-effect crystallization device further includes a single-effect condenser 34, which is connected to the single-effect crystallizer 28 and the atmosphere, and is used to precipitate 2# finished water.

[0073] In some embodiments, the 3# mother liquid tank 32 of the single-effect crystallization device is provided with a 10# liquid level meter 126; an 11# pump 33 is provided between the 3# mother liquid tank 32 and the single-effect evaporator 29, and a 13# control valve 213 is provided on the pipeline therebetween, and the 13# control valve 213 is interlocked with the 10# liquid level meter 126 for control.

[0074] Based on the inventive concept of the present invention, an embodiment of the present invention further provides a high-salt wastewater stepwise crystallization method, comprising:

[0075] The high-salt wastewater step crystallization system is used to crystallize finished salt from the high-salt wastewater step by step. The high-salt wastewater step crystallization system is the high-salt wastewater step crystallization system in the above-mentioned embodiment 1.

[0076] Specifically, it can include: using a high-salt wastewater stepwise crystallization system to control the crystallization point of high-halogen and low-nitrate high-salt wastewater in the sodium chloride crystallization zone in the H2O-NaCl-Na2SO4 ternary phase diagram, and produce sodium chloride finished salt with a purity of ≥98.5%; controlling the crystallization point of low-halogen medium-high-nitrate or low-halogen high-nitrate high-salt wastewater in the sodium sulfate crystallization zone in the H2O-NaCl-Na2SO4 ternary phase diagram, and producing sodium sulfate finished salt with a purity of ≥98%; controlling the crystallization point of the cold mother liquor in the sodium sulfate decahydrate crystallization zone in the H2O-NaCl-Na2SO4 ternary phase diagram, to obtain high-purity sodium chloride mother liquor and sodium sulfate decahydrate; the single-effect crystallization device controls the crystallization point in the sodium chloride crystallization zone in the H2O-NaCl-Na2SO4 ternary phase diagram, and produces sodium chloride finished salt with a purity of ≥98.5%.

[0077] Depending on the type of high-salt wastewater, the method of fractional crystallization and the flow route in the high-salt wastewater fractional crystallization system are also different. The following Examples 2 to 4 introduce the fractional crystallization methods for typical high-salt wastewater types.

[0078] Embodiment 2

[0079] Embodiment 2 of the present invention provides a stepwise crystallization method for high-salt wastewater, specifically for high-halogen and low-nitrate high-salt wastewater, and the process is as follows: Figure 7 As shown, the following steps are included:

[0080] Step S71: The crystallization point of the high-salt wastewater is controlled in the sodium chloride crystallization zone through a multi-effect step-by-step crystallization device to obtain sodium chloride finished salt and 1# mother liquor.

[0081] As the water of high-halogen and low-nitrate high-salt wastewater evaporates during the evaporation and crystallization process, it will first enter the sodium chloride crystallization zone and precipitate NaCl crystals. When the solution evaporates and concentrates to a higher multiple, exceeding point B (refer to Figure 3B As shown), the solution enters the sodium chloride-sodium sulfate mixed salt crystallization zone and precipitates NaCl-Na2SO4 mixed crystals.

[0082] Figure 3A and Figure 3B The three vertices in the middle represent pure H2O, pure NaCl and pure Na2SO4 respectively; the dotted line in the area is the saturated solubility line at 75℃, and the solid line is the saturated solubility line at 0℃. Figure 3B In the figure, line ① represents the material line of high-halogen and low-nitrate high-salt wastewater, line ② represents the material line of low-halogen and medium-high-nitrate high-salt wastewater, and line ③ represents the material line of low-halogen and high-nitrate high-salt wastewater. At different temperatures, the crystallization zones at that temperature can be divided according to the saturated solubility line, for example, the NaCl crystallization zone, Na2SO4 crystallization zone, and NaCl+Na2SO4 crystallization zone at 75°C; the NaCl crystallization zone, Na2SO4﹒10H2O crystallization zone, and NaCl+Na2SO4﹒10H2O crystallization zone at 0°C.

[0083] Figure 3B Point A in the figure is the vertex of pure H2O, and points B, C, and D are the change points of different crystallization regions.

[0084] Generally, the crystallization control in the multi-effect step crystallization device and the single-effect crystallization device refers to the H2O-NaCl-Na2SO4 ternary phase diagram at 75°C; the crystallization control in the cooling crystallization device refers to the H2O-NaCl-Na2SO4 ternary phase diagram at 0°C.

[0085] In order to obtain high-purity finished sodium chloride salt, it is necessary to control the evaporation amount. First, the crystallization point is controlled in the sodium chloride crystallization zone through the first interlocking control system of the multi-effect step-by-step crystallization device to precipitate NaCl crystals; the finished sodium chloride salt and the 1# mother liquor are separated by the 1# centrifuge 12, and the purity of the finished sodium chloride salt is ≥98.5%.

[0086] More specifically, in order to produce finished sodium chloride salt with a purity of ≥98.5%, the crystallization point is controlled in the sodium chloride crystallization zone, and the chloride ion analyzer 101, the sulfate ion analyzer 102, the 1# thermometer 106, the 1# pressure gauge 110, the 6# control valve 206 and the 1# density meter 109 are interlocked and controlled; that is, the setting value of the 1# density meter 109 comes from the indication values ​​of the chloride ion analyzer 101 and the sulfate ion analyzer 102 in the high-salinity wastewater, according to Figure 3BThe ternary phase diagram data of H2O-NaCl-Na2SO4 at 75°C shown in the figure is calculated, and the evaporation amount of the system is controlled through the interlocking control of 1# thermometer 106, 1# pressure gauge 110 and 6# control valve 206, so that the indication value of 1# density meter 109 is stabilized within the set value range; the set value of 2# flowmeter 111 is calculated from the indication value of 4# flowmeter 121 of sulfate ion analyzer 102, 1# flowmeter 104 and returned cold mother liquor (2# mother liquor) in high-salt wastewater; through the interlocking control of 4# control valve 204 and 2# flowmeter 111, high-purity sodium chloride slurry is discharged to 1# centrifuge 12 in time, and the crystallization point is always controlled in the sodium chloride crystallization zone.

[0087] Step S72: Through the cooling crystallization device, the crystallization point of the 1# mother liquor is controlled in the sodium sulfate decahydrate crystallization region to obtain sodium sulfate decahydrate impure salt and the 2# mother liquor.

[0088] The 1# mother liquor is a supersaturated mother liquor, which is cooled and crystallized by a cooling crystallization device. The crystallization point is controlled in the sodium sulfate decahydrate crystallization zone by the second interlocking control system, and a small amount of sodium sulfate decahydrate impurity salt and high-purity sodium chloride mother liquor (2# mother liquor) are precipitated by cooling.

[0089] More specifically, in order to improve the recovery rate of sodium chloride and obtain high-purity sodium chloride mother liquor, the crystallization point of the cold mother liquor (1# mother liquor) is controlled in the sodium sulfate decahydrate crystallization zone, the refrigerator 21 is interlocked with the 2# thermometer 115 and the 2# density meter 117, and the sodium sulfate decahydrate slurry is discharged to the 2# centrifuge 22 in time through the 8# control valve 208 and the 6# liquid level meter 117 to obtain high-purity sodium chloride mother liquor, and the cooling crystallization point is always controlled in the sodium sulfate decahydrate crystallization zone.

[0090] Step S73: Return the 2# mother liquor to the multi-effect step-by-step crystallization device, control the crystallization point in the sodium chloride crystallization zone, and continue to produce sodium chloride finished salt.

[0091] The 2# mother liquor is returned from the 2# mother liquor tank 23 of the cooling crystallization device to the triple-effect evaporator 10 of the triple-effect step-by-step crystallization device, and continues to evaporate and crystallize to obtain the finished sodium chloride salt, thereby improving the recovery rate of the finished sodium chloride.

[0092] Embodiment 3

[0093] Embodiment 3 of the present invention provides a stepwise crystallization method for high-salt wastewater, specifically for low-halogen medium-high-nitrate high-salt wastewater, and the process is as follows: Figure 8 As shown, the following steps are included:

[0094] Step S81: The crystallization point of the high-salt wastewater is controlled in the sodium sulfate crystallization zone through a multi-effect step-by-step crystallization device to obtain sodium sulfate finished salt and 1# mother liquor.

[0095] As the water of low-halogen, medium-high-nitrate high-salt wastewater evaporates continuously during the evaporation and crystallization process, when it is concentrated to a supersaturated solution, the solution first enters the sodium sulfate crystallization zone and precipitates Na2SO4 crystals. When the solution continues to be concentrated to a higher multiple, exceeding point C, the solution enters the sodium chloride-sodium sulfate mixed salt crystallization zone and precipitates NaCl-Na2SO4 mixed crystals.

[0096] In order to obtain high-purity sodium sulfate crystal salt, it is necessary to control the evaporation amount. First, the crystallization point is controlled in the sodium sulfate crystallization zone through the first interlocking control system of the multi-effect step-by-step crystallization device to precipitate Na2SO4 crystals; the sodium sulfate finished salt and the 1# mother liquor are separated by the 1# centrifuge 12, and the purity of the sodium sulfate finished salt is ≥98%.

[0097] More specifically, in order to produce finished sodium sulfate salt with a purity of ≥98%, the crystallization point is controlled in the sodium sulfate crystallization zone, and the chloride ion analyzer 101, the sulfate ion analyzer 102, the 1# thermometer 106, the 1# pressure gauge 110, the 6# control valve 206 and the 1# density meter 109 are interlocked and controlled; that is, the setting value of the 1# density meter 109 comes from the indication values ​​of the chloride ion analyzer 101 and the sulfate ion analyzer 102 in the high-salinity wastewater, according to Figure 3B The ternary phase diagram data of H2O-NaCl-Na2SO4 at 75°C shown in the figure is calculated, and the evaporation amount of the system is controlled through the interlocking control of 1# thermometer 106, 1# pressure gauge 110 and 6# control valve 206, so that the indication value of 1# density meter 109 is stabilized within the set value range; the set value of 2# flowmeter 111 is calculated from the indication value of chloride ion analyzer 101, 1# flowmeter 104 and redissolved sodium sulfate decahydrate solution 4# flowmeter 121 in high-salinity wastewater; through the interlocking control of 4# control valve 204 and 2# flowmeter 111, high-purity sodium sulfate slurry is discharged to 1# centrifuge 12 in time, and the crystallization point is always controlled in the sodium sulfate crystallization zone.

[0098] Step S82: Through the cooling crystallization device, the crystallization point of the 1# mother liquor is controlled in the sodium sulfate decahydrate crystallization zone to obtain sodium sulfate decahydrate and 2# mother liquor; the sodium sulfate decahydrate is sent to the dissolving tank to be dissolved into a high-purity sodium sulfate mother liquor and returned to the multi-effect step-by-step crystallization device.

[0099] The 1# mother liquor obtained by separation in the 1# centrifuge 12 is a supersaturated mother liquor. The crystallization point is controlled in the sodium sulfate decahydrate crystallization zone by the second interlocking control system, and sodium sulfate decahydrate and high-purity sodium chloride mother liquor (2# mother liquor) are precipitated by cooling.

[0100] More specifically, in order to improve the recovery rate of sodium sulfate and obtain high-purity sodium sulfate decahydrate and sodium chloride mother liquor, the crystallization point of the 1# mother liquor is controlled in the sodium sulfate decahydrate crystallization zone through the second interlocking control system of the cooling crystallization device, the refrigerator 21 is interlocked with the 2# thermometer 116 and the 2# density meter 118, and the sodium sulfate decahydrate slurry is discharged to the 2# centrifuge 22 in time through the 8# control valve 208 and the 6# liquid level meter 117 interlocking control, so as to always control the cooling crystallization point in the sodium sulfate decahydrate crystallization zone.

[0101] Step S83: The 2# mother liquor is passed to a single-effect crystallization device, and the crystallization point is controlled in the sodium chloride crystallization zone to obtain sodium chloride finished salt.

[0102] The 2# mother liquor is led to a single-effect crystallization device, through which the crystallization point of the 2# mother liquor is controlled in the sodium chloride crystallization zone, and a sodium chloride finished salt with a purity of ≥98.5% is crystallized.

[0103] More specifically, in order to evaporate and crystallize high-purity sodium chloride mother liquor to produce sodium chloride finished salt with a purity of ≥98.5%, the crystallization point is controlled in the sodium chloride crystallization zone through the third interlocking control system of the single-effect crystallization device, and the evaporation amount of the system is controlled through the interlocking control of the 3# thermometer 121, the 2# pressure gauge 125 and the 12# control valve 212, so that the indication value of the 3# density meter 123 is stabilized within the set value range, and the high-purity sodium chloride slurry is discharged to the 3# centrifuge 31 in time through the interlocking control of the 11# control valve 211 and the 9# liquid level gauge 123, so that the crystallization point is always controlled in the sodium chloride crystallization zone.

[0104] In some embodiments, sodium sulfate decahydrate can be transported to the dissolution tank 26 via the screw conveyor 25, and the sodium sulfate decahydrate solution obtained by redissolution is returned to the three-effect step-by-step crystallization device to continue evaporation and crystallization to improve the recovery rate of the finished sodium sulfate salt.

[0105] Embodiment 4

[0106] Embodiment 4 of the present invention provides a stepwise crystallization method for high-salt wastewater, specifically for low-halogen high-nitrate high-salt wastewater, and the process is as follows: Fig. 9 As shown, the following steps are included:

[0107] Step S91: The crystallization point of the high-salt wastewater is controlled in the sodium sulfate crystallization zone through a multi-effect step-by-step crystallization device to obtain sodium sulfate finished salt and 1# mother liquor.

[0108] As the water of low-halogen, high-nitrate high-salt wastewater evaporates continuously during the evaporation and crystallization process, when it is concentrated to a supersaturated solution, the solution first enters the sodium sulfate crystallization zone and precipitates Na2SO4 crystals. When the solution continues to be concentrated to a higher multiple, exceeding point D, the solution enters the sodium chloride-sodium sulfate mixed salt crystallization zone and precipitates NaCl-Na2SO4 mixed crystals.

[0109] In order to obtain high-purity sodium sulfate crystal salt, it is necessary to control the evaporation amount. First, the crystallization point is controlled in the sodium sulfate crystallization zone through the first interlocking control system of the multi-effect step-by-step crystallization device to precipitate Na2SO4 crystals; the sodium sulfate finished salt and the 1# mother liquor are separated by the 1# centrifuge 12, and the purity of the sodium sulfate finished salt is ≥98%.

[0110] More specifically, in order to produce finished sodium sulfate salt with a purity of ≥98%, the crystallization point is controlled in the sodium sulfate crystallization zone, and the chloride ion analyzer 101, the sulfate ion analyzer 102, the 1# thermometer 106, the 1# pressure gauge 110, the 6# control valve 206 and the 1# density meter 109 are interlocked and controlled; that is, the setting value of the 1# density meter 109 comes from the indication values ​​of the chloride ion analyzer 101 and the sulfate ion analyzer 102 in the high-salinity wastewater, according to Figure 3B The ternary phase diagram data of H2O-NaCl-Na2SO4 at 75°C shown in the figure is calculated, and the evaporation amount of the system is controlled through the interlocking control of 1# thermometer 106, 1# pressure gauge 110 and 6# control valve 206, so that the indication value of 1# density meter 109 is stabilized within the set value range; the set value of 2# flowmeter 111 is calculated from the indication values ​​of chloride ion analyzer 101, 1# flowmeter 104 and 4# flowmeter 121 of the returned 1# mother liquor in the high-salt wastewater; through the interlocking control of 4# control valve 204 and 2# flowmeter 111, the high-purity sodium sulfate slurry is discharged to 1# centrifuge 12 in time, and the crystallization point is always controlled in the sodium sulfate crystallization zone.

[0111] Step S92: Determine whether the sodium chloride concentration of 1# mother liquor is greater than the set value.

[0112] If yes, execute step S94. When the sodium chloride content in the mother liquor reaches a certain concentration, it enters the single-effect crystallization device to crystallize into impure salt.

[0113] If not, execute step S93, and the mother liquor after centrifugal separation is returned to the three-effect fractional crystallization device to improve the recovery rate of finished sodium sulfate salt.

[0114] That is, in order to improve the recovery rate of sodium sulfate, the 5# control valve 205 is interlocked with the 4# flow meter 121. At this time, the set value of the 4# flow meter 121 is calculated from the indication values ​​of the chloride ion analyzer 101 and the 1# flow meter 104 in the high-salt wastewater, so that the indication value of the 4# flow meter 121 is stabilized within the set value range, and a large amount of mother liquor returns to the three-effect evaporator 10 to continue evaporation and crystallization, and the remaining small amount of impure salt mother liquor is discharged to the single-effect crystallization device to crystallize into 2# impure salt.

[0115] Step S93: Return the 1# mother liquor to the multi-effect step-by-step crystallization device, control the crystallization point in the sodium sulfate crystallization zone, and continue to produce sodium sulfate finished salt and 1# mother liquor.

[0116] Step S94: Using a single-effect crystallization device, the crystallization point of the 1# mother liquor is controlled in the sodium chloride-sodium sulfate crystallization region to obtain a sodium chloride-sodium sulfate impure salt.

[0117] Through the third interlocking control system of the single-effect crystallization device, the crystallization point of the 1# mother liquor is controlled in the sodium chloride-sodium sulfate crystallization zone to obtain 2# impure salt.

[0118] It should be understood that the specific order or hierarchy of steps in the disclosed process is an example of an exemplary method. Based on design preferences, it should be understood that the specific order or hierarchy of steps in the process can be rearranged without departing from the scope of protection of the present disclosure. The attached method claims present the elements of the various steps in an exemplary order and are not intended to be limited to the specific order or hierarchy described.

[0119] In the above detailed description, various features are grouped together in a single embodiment to simplify the disclosure. This method of disclosure should not be interpreted as reflecting an intention that the embodiments of the claimed subject matter require more features than are clearly stated in each claim. On the contrary, as reflected in the appended claims, the invention is in a state of having less than all the features of the disclosed individual embodiments. Therefore, the appended claims are hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.

[0120] The above description includes examples of one or more embodiments. Of course, it is impossible to describe all possible combinations of components or methods for the purpose of describing the above embodiments, but it should be recognized by those skilled in the art that the various embodiments may be further combined and arranged. Therefore, the embodiments described herein are intended to cover all such changes, modifications and variations that fall within the scope of protection of the appended claims. In addition, with respect to the term "comprising" used in the specification or claims, the word is covered in a manner similar to the term "including", as explained by "including" used as a transitional word in the claims. In addition, any term "or" used in the specification of the claims is intended to mean "non-exclusive or".

[0121] In addition, the terms "1#", "2#" and "3#" etc. are used for descriptive purposes only and are not to be understood as indicating or implying relative importance.

Claims

1. A high-salt wastewater step crystallization system, characterized in that: It includes a multi-effect step-by-step crystallization device, a single-effect crystallization device and a cooling crystallization device; The multi-effect fractional crystallization device comprises: a feed tank for allowing high-salt wastewater to flow in, a group of interconnected first-effect separators and first-effect evaporators, at least one group of interconnected second-effect separators and second-effect evaporators, a group of interconnected three-effect crystallizers and three-effect evaporators, and a 1# centrifuge connected to the three-effect crystallizer, the 1# centrifuge is used to separate the 1# finished salt and the 1# mother liquor flowing into the 1# mother liquor tank, and the 1# mother liquor tank is respectively connected to the three-effect evaporator, the single-effect evaporator of the single-effect crystallization device and the cooler of the cooling crystallization device; The multi-effect fractional crystallization device also includes a 1# heat source supply device connected to the first-effect evaporator, and a 1# pressure gauge and a 6# control valve are provided on the steam pipeline between the first-effect evaporator and the 1# heat source supply device; a chloride ion analyzer, a sulfate ion analyzer, a salinity analyzer and a 1# flow meter are provided on the pipeline between the feed tank and the first-effect separator; the first-effect separator is provided with a 1# thermometer, and the triple-effect crystallizer is provided with a 1# density meter; the 1# density meter, the 1# thermometer, the 1# pressure gauge and the 6# control valve are interlocked and controlled; a 2# flow meter and a 4# control valve are provided on the pipeline between the triple-effect crystallizer and the 1# centrifuge, and the 4# control valve is interlocked and controlled with the 2# flow meter; The 1# mother liquid tank is provided with a 4# liquid level meter, which is respectively connected to the cooler and the single-effect evaporator through a pipeline provided with a 5# control valve, and the 4# liquid level meter and the 5# control valve are interlocked and controlled; a 4# flow meter is provided on the pipeline between the 1# mother liquid tank and the triple-effect evaporator, and the chloride ion analyzer, sulfate ion analyzer, 1# flow meter, 4# flow meter and 2# flow meter are interlocked and controlled; the 4# flow meter is also interlocked and controlled with the 5# control valve; the chloride ion analyzer, sulfate ion analyzer, 1# flow meter, 1# density meter, 2# flow meter, 4# control valve, 4# flow meter, 1# pressure gauge, 1# thermometer and 6# control valve are combined into a first interlock control system for controlling the crystallization point in the first set crystallization zone; The cooling crystallization device further comprises a cooling crystallizer interconnected with the cooler, a 2# centrifuge and a 2# mother liquid tank connected in sequence to the cooling crystallizer, the 2# centrifuge is used to separate the 1# impurities and the 2# mother liquid flowing into the 2# mother liquid tank, and the 2# mother liquid tank is respectively connected to the single-effect evaporator of the single-effect crystallization device and the triple-effect evaporator of the multi-effect fractional crystallization device; The single-effect crystallization device further comprises a single-effect crystallizer interconnected with the single-effect evaporator, a 3# centrifuge and a 3# mother liquid tank connected in sequence to the single-effect crystallizer, the 3# centrifuge is used to separate the 2# finished salt or the 2# impurity salt and the 3# mother liquid flowing into the 3# mother liquid tank, and the 3# mother liquid tank is also connected to the single-effect evaporator; The cooling crystallizer is provided with a 2# thermometer, a 2# density meter and a 6# liquid level meter; the cooling crystallizer is interconnected with the cooler, the cooler is interconnected with the refrigerator, and the 2# density meter, the 2# thermometer and the refrigerator are interlocked; a 7# pump is provided between the cooling crystallizer and the cooler; an 8# control valve is provided on the pipeline between the cooling crystallizer and the 2# centrifuge, and the 8# control valve is interlocked with the 6# liquid level meter; the 2# thermometer, the 2# density meter, the refrigerator, the 6# liquid level meter and the 8# control valve are combined into a second interlocking control system for controlling the crystallization point in the second set crystallization zone; The single-effect crystallization device also includes a 2# heat source supply device connected to the single-effect evaporator, and a 2# pressure gauge and a 12# control valve are provided on the steam pipeline between the single-effect evaporator and the 2# heat source supply device; the single-effect crystallizer is provided with a 3# thermometer, a 3# density meter and a 9# liquid level gauge, and the 3# density meter, the 3# thermometer, the 2# pressure gauge and the 12# control valve are interlocked and controlled; an 11# control valve is provided on the pipeline between the single-effect crystallizer and the 3# centrifuge, and the 11# control valve is interlocked and controlled with the 9# liquid level gauge; the 2# pressure gauge, the 3# thermometer, the 12# control valve, the 3# density meter, the 9# liquid level gauge and the 11# control valve are combined into a third interlock control system for controlling the crystallization point in the third set crystallization zone.

2. The system according to claim 1, characterized in that A 1# pump is provided between the feed tank and the first-effect separator, a 1# control valve is provided on the pipeline between them, and the first-effect separator is also provided with a 1# liquid level gauge, and the 1# control valve is interlocked with the 1# liquid level gauge for control; The first-effect separator is connected to the first-effect evaporator and the second-effect separator respectively through a 2# pump, a 2# control valve is provided on the pipeline between the first-effect separator and the second-effect separator, the second-effect separator is provided with a 2# liquid level gauge, and the 2# control valve is interlocked with the 2# liquid level gauge for control; The second-effect separator is connected to the second-effect evaporator and the third-effect crystallizer respectively through the 3# pump, a 3# control valve is provided on the pipeline between the second-effect separator and the third-effect crystallizer, the third-effect crystallizer is provided with a 3# liquid level gauge, and the 3# control valve is interlocked with the 3# liquid level gauge for control; The triple-effect crystallizer is connected to the triple-effect evaporator and the 1# centrifuge respectively through the 4# pump.

3. The system according to claim 1, characterized in that The multi-effect step-by-step crystallization device also includes a condensed water tank, the second-effect evaporator and the third-effect evaporator are respectively connected to the condensed water tank, and the condensed water tank is used to temporarily store 1# finished water.

4. The system according to claim 3, characterized in that The multi-effect fractional crystallization device also includes an indirect condenser connected to the triple-effect crystallizer. The indirect condenser is also connected to the condensed water tank and communicated with the atmosphere.

5. The system according to claim 3 or 4, characterized in that The condensate tank is provided with a 5# liquid level gauge; The condensate tank is connected to the circulating water device. A 6# pump, a 2# salinity analyzer, a 3# flow meter and a 7# control valve are arranged on the finished water pipeline between the condensate tank and the circulating water device. The 5# liquid level meter is interlocked with the 7# control valve for control.

6. The system according to any one of claims 1 to 4, characterized in that: The 1# mother liquid tank is connected to the triple-effect evaporator, the cooler of the cooling crystallization device and the single-effect evaporator of the single-effect crystallization device respectively through the 5# pump.

7. The system according to claim 1, characterized in that The 2# mother liquid tank is connected to the single-effect evaporator of the single-effect crystallization device and the triple-effect evaporator of the multi-effect fractional crystallization device respectively through the 8# pump and the 9# control valve; The 2# mother liquid tank is provided with a 7# liquid level gauge, and the 9# control valve is interlocked with the 7# liquid level gauge for control.

8. The system of claim 1, wherein: The 2# centrifuge of the cooling crystallization device is also connected to the screw conveyor and the dissolving tank in sequence, and the dissolving tank is connected to the triple-effect evaporator of the multi-effect step-by-step crystallization device; The dissolving tank and the 1# mother liquid tank of the multi-effect fractional crystallization device are connected to the three-effect evaporator through a pipeline provided with a 4# flow meter.

9. The system according to claim 8, characterized in that The dissolving tank is provided with a 8# liquid level gauge, a 9# pump is provided between the dissolving tank and the triple-effect evaporator, a 10# control valve is provided on the pipeline therebetween, and the 10# control valve is interlocked with the 8# liquid level gauge for control.

10. The system according to claim 1, wherein: The single-effect crystallization device also includes a single-effect condenser, which is connected to the single-effect crystallizer and the atmosphere, and is used to produce 2# finished water.

11. The system according to claim 1, characterized in that The 3# mother liquid tank of the single-effect crystallization device is provided with a 10# liquid level gauge; A 11# pump is provided between the 3# mother liquid tank and the single-effect evaporator, and a 13# control valve is provided on the pipeline therebetween. The 13# control valve is interlocked with the 10# liquid level meter for control.

12. A high-salt wastewater stepwise crystallization method, characterized in that: include: The finished salt is precipitated from the high-salt wastewater by step-by-step crystallization using a high-salt wastewater step-by-step crystallization system, wherein the high-salt wastewater step-by-step crystallization system is the high-salt wastewater step-by-step crystallization system according to any one of claims 1 to 11.

13. The method according to claim 12, characterized in that If the high-salt wastewater is of high-halogen and low-nitrate type, the method of using the high-salt wastewater stepwise crystallization system to crystallize finished salt from the high-salt wastewater specifically includes: Through the multi-effect step-by-step crystallization device, the crystallization point of high-salt wastewater is controlled in the sodium chloride crystallization zone to obtain sodium chloride finished salt and 1# mother liquor; The crystallization point of the 1# mother liquor is controlled in the sodium sulfate decahydrate crystallization region by a cooling crystallization device to obtain sodium sulfate decahydrate impure salt and the 2# mother liquor; The 2# mother liquor is returned to the multi-effect step-by-step crystallization device, the crystallization point is controlled in the sodium chloride crystallization zone, and the sodium chloride finished salt is continuously produced.

14. The method according to claim 12, characterized in that If the high-salt wastewater is of low-halogen and medium-high-nitrate type, the method of using the high-salt wastewater stepwise crystallization system to precipitate finished salt from the high-salt wastewater specifically includes: Through the multi-effect step-by-step crystallization device, the crystallization point of high-salt wastewater is controlled in the sodium sulfate crystallization zone to obtain sodium sulfate finished salt and 1# mother liquor; The crystallization point of the 1# mother liquor is controlled in the sodium sulfate decahydrate crystallization zone by a cooling crystallization device to obtain sodium sulfate decahydrate and 2# mother liquor; the sodium sulfate decahydrate is sent to a dissolving tank to be dissolved into sodium sulfate mother liquor and returned to the multi-effect step-by-step crystallization device; the 2# mother liquor is sent to a single-effect crystallization device to control the crystallization point in the sodium chloride crystallization zone to obtain sodium chloride finished salt.

15. The method according to claim 12, characterized in that If the high-salt wastewater is of low-halogen and high-nitrate type, the method of using the high-salt wastewater stepwise crystallization system to precipitate finished salt from the high-salt wastewater specifically includes: Through the multi-effect step-by-step crystallization device, the crystallization point of high-salt wastewater is controlled in the sodium sulfate crystallization zone to obtain sodium sulfate finished salt and 1# mother liquor; Determine whether the sodium chloride concentration of the 1# mother liquor is greater than a set value; If not, return the 1# mother liquor to the multi-effect step-by-step crystallization device, control the crystallization point in the sodium sulfate crystallization zone, and continue to produce sodium sulfate finished salt and 1# mother liquor; If so, the crystallization point of the 1# mother liquor is controlled in the sodium chloride-sodium sulfate crystallization zone through a single-effect crystallization device to obtain a sodium chloride-sodium sulfate mixed salt.

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