Energy-saving treatment system and process for salt-containing and heavy metal-containing ammonia-nitrogen wastewater

Abstract

An energy-saving treatment system and process for salt-containing and heavy metal-containing ammonia-nitrogen wastewater. The system comprises a wastewater treatment subsystem and a heat pump subsystem. The wastewater treatment subsystem performs treatment on wastewater by means of deammonification, heavy metal removal, and desalination to make the wastewater reach standard, and the heat pump subsystem integrates energy during the deammonification, heavy metal removal, and desalination for use, so that the integration of energy of the process is obviously improved, the energy consumption of the system is greatly reduced, and energy saving during treatment of salt-containing and heavy metal-containing ammonia-nitrogen wastewater is effectively realized.

Description

TECHNICAL FIELD

[0001] The present disclosure belongs to the field of energy-saving techniques for wastewater treatment, and specifically relates to an energy-saving treatment system and process for a salt-containing and heavy metal-containing ammonia-nitrogen wastewater. BACKGROUND

[0002] In production processes such as chemical, metallurgical, electroplating, and material preparation processes, industrial wastewater containing heavy metal ions, inorganic salts, and ammonia nitrogen is often generated. For example, in a preparation process for ternary cathode materials of lithium-ion batteries, a precursor material is synthesized mainly through complex-precipitation as follows: ammonia water is added to a mixed aqueous solution of nickel sulfate, cobalt sulfate, and manganese sulfate, then a NaOH solution is added to adjust the pH such that hydroxide precipitates are produced from nickel, cobalt, and manganese metal ions, and then filtration dewatering and heat aging are conducted to obtain a ternary precursor. Wastewater produced in the above process contains large amounts of ammonium ions (NH4+) and free ammonia (NH3), unprecipitated nickel, cobalt, and manganese ions, and Na+ and SO42' ions. In order to make wastewater meet discharge standards, the wastewater must undergo ammonia removal, heavy metal removal, and desalting.

[0003] Since heavy metal ions are complexed with ammonia in salt-containing and heavy metal-containing ammonia-nitrogen wastewater, the heavy metal ions can only be removed after decomplexation of metal ions through ammonia removal. Only the complete removal of heavy metal ions can make heavy metal ions in inorganic salts obtained by a desalting procedure not exceed corresponding standards. Therefore, a treatment process of salt-containing and heavy metal-containing ammonia-nitrogen wastewater must be ammonia removal-heavy metal removal-desalting. In the patent "Treatment Method and System for Wastewater Generated during Ternary Cathode Material Production" (ZL202010819833.6), a membrane separation / solid-liquid separation / evaporative crystallization combined process is adopted to treat salt-containing and heavy metal-containing ammonia-nitrogen wastewater generated in a ternary cathode material precursor production process. The membrane separation / solid-liquid separation / evaporative crystallization combined process is as follows: 1. With a sulfuric acid solution as an absorbent, ammonia nitrogen in the wastewater is converted into ammonium sulfate through membrane separation to allow ammonia removal. 2. Heavy metal ions in ammonia-removed wastewater are decomplexed and react with an alkali to produce precipitates, and the precipitates are removed through filtration to obtain a supernatant. 3. The supernatant is subjected to evaporative crystallization to obtain sodium sulfate. This process can effectively treat salt-containing and heavy metal-containing ammonia-nitrogen wastewater generated in a ternary cathode material precursor production process. However, the membrane separation cannot allow the complete ammonia nitrogen removal, and is faced with operational problems such as membrane leakage and contamination and secondary environmental problems such as solid waste resulting from failed membranes. Currently, the industrial salt-containing and heavy metal-containing ammonia-nitrogen wastewater is generally treated by the following stripping rectification-based ammonia removal + filtration-based heavy metal removal + evaporative crystallization-based desalting process: The wastewater is first subjected to pH adjustment and then fed into a rectification tower, and a steam is introduced at a bottom of the rectification tower for heating, such that an ammonia water product is produced at the top of the rectification tower and ammonia removed wastewater is produced at the bottom of the rectification tower. The pH of the ammonia removed wastewater is adjusted with an alkali liquor to convert heavy metal ions into hydroxide precipitates, and the hydroxide precipitates are removed through filtration to obtain salt-containing wastewater. The salt-containing wastewater is subjected to evaporative crystallization for desalting. In the above ammonia removal, heavy metal removal, and desalting procedures, the stripping rectification-based ammonia removal and the evaporative crystallization-based desalting both involve very high energy consumption.

[0004] Therefore, the development of a new technique to reduce energy consumption is the key to a technical progress of a salt-containing and heavy metal-containing ammonia-nitrogen wastewater treatment process. In the patent "Method and Device for Treatment and Ammonia Recovery of Ammonia-Nitrogen Wastewater" (application No. 202010819833.6), a closed-loop heat pump technology for vapor compression at the top of an ammonia removal rectification tower is adopted, which involves comprehensive energy consumption reduced by 30% or more compared with the original technology. Currently, the industrial evaporative crystallization-based desalting process also generally adopts mechanical vapor recompression (MVR), which greatly reduces the energy consumption of the industrial evaporative crystallization-based desalting process.

[0005] However, the three procedures of the existing salt-containing and heavy metal-containing ammonia-nitrogen wastewater treatment process are relatively independent, and the existing salt-containing and heavy metal-containing ammonia-nitrogen wastewater treatment process has a poor heat integration degree and is mainly faced with the following problems: 1) Heat pumps of the MVR evaporation-crystallization-based desalting procedure and the heat pump-based ammonia removal procedure are independent of each other, which hinders improvements in compressor efficiency. 2) In the MVR evaporation-crystallization-based desalting procedure, high-temperature condensated water resulting from the condensation of a heating steam in an evaporator is directly discharged, resulting in energy waste. 3) The filtration-based heavy metal removal procedure is conducted at room temperature. Ammonia-removed wastewater needs to be cooled before entering the heavy metal removal procedure, and heavy metal-removed wastewater needs to be reheated after entering the desalting procedure, resulting in energy loss.

[0006] Therefore, in view of the problems such as low heat integration degree and high energy consumption of the existing salt-containing and heavy metal-containing ammonia-nitrogen wastewater treatment process and the major needs of energy saving and carbon reduction in industrial processes of China, it is urgent to develop an energy-saving treatment process for salt-containing and heavy metal-containing ammonia-nitrogen wastewater to contribute to the "Peak Carbon Dioxide Emissions and Carbon Neutrality" goal of China. SUMMARY

[0007] In view of this, an objective of the present disclosure is to provide a heat integration solution in view of the existing salt-containing and heavy metal-containing ammonia-nitrogen wastewater treatment process. The heat integration solution can effectively allow the energy saving for a salt-containing and heavy metal-containing ammonia-nitrogen wastewater treatment.

[0008] To allow the above objective, the present disclosure provides the following technical solutions:

[0009] 1. An energy-saving treatment system for a salt-containing and heavy metal-containing ammonia-nitrogen wastewater is provided, including: a wastewater treatment subsystem and a heat pump subsystem, where the wastewater treatment subsystem includes an ammonia removal tower 01, a reboiler 03, a filter 04, an evaporator 05, and an evaporation separator 06; a bottom of the ammonia removal tower 01 is connected with a cold side of the reboiler 03, the bottom of the ammonia removal tower 01 is connected with the filter 04 and the evaporation separator 06 successively through pipelines, and a cold side of the evaporator 05 is connected with the evaporation separator 06; the heat pump subsystem includes a primary condenser 02 and a compressor 07; and a hot side of the primary condenser 02 is connected with a top of the ammonia removal tower 01, and a cold side of the primary condenser 02, the compressor 07, and a hot side of the reboiler 03 are connected with each other successively through pipelines.

[0010] Preferably, the evaporation separator 06 is connected with an inlet of the compressor 07, and a hot side of the evaporator 05 is connected with an outlet of the compressor 07.

[0011] Preferably, the wastewater treatment subsystem further includes a raw wastewater preheater 10; the raw wastewater preheater 10 is arranged on a raw wastewater inlet pipeline; and a hot side of the raw wastewater preheater is connected with a hot side of the evaporator 05, and a cold side of the raw wastewater preheater is connected with the ammonia removal tower 01.

[0012] Preferably, the wastewater treatment subsystem further includes a secondary condenser 08 and a spray liquid cooler 09; a hot side of the secondary condenser 08 is connected with the hot side of the primary condenser 02, and the hot side of the secondary condenser 08 communicates with an ammonia water discharge pipeline and an ammonia water spray pipeline; and the spray liquid cooler 09 is arranged on the ammonia water spray pipeline.

[0013] Preferably, the wastewater treatment subsystem includes an alkali-feeding device, and the alkali-feeding device is arranged on an inlet pipeline of the filter 04; and the wastewater treatment subsystem includes an acid-feeding device, and the acid-feeding device is arranged on an inlet pipeline of the evaporation separator 06.

[0014] Preferably, the wastewater treatment subsystem includes one or more evaporation separators and corresponding one or more evaporators.

[0015] 2. An energy-saving treatment process for a salt-containing and heavy metal-containing ammonia-nitrogen wastewater is provided, including the following steps:

[0016] (1) feeding the salt-containing and heavy metal-containing ammonia-nitrogen wastewater into an ammonia removal tower for ammonia removal to produce an ammonia-containing steam at a top of the ammonia removal tower; allowing the ammonia-containing steam to enter a primary condenser to undergo a heat exchange with heat pump circulating water, such that the ammonia-containing steam is partially condensated to produce dilute ammonia water and a concentrated ammonia-containing steam; partially or fully returning the dilute ammonia water to the ammonia removal tower; and allowing the concentrated ammonia-containing steam to enter a secondary condenser to undergo condensation and spray absorption to produce an ammonia water product;

[0017] (2) pressurizing, by a compressor, a heat pump circulating steam produced after the heat exchange of the heat pump circulating water in the primary condenser to produce a compressed steam, allowing the compressed steam to enter a reboiler to undergo a heat exchange with ammonia-removed wastewater obtained at a bottom of the ammonia removal tower to produce condensated water, and returning the condensated water to the primary condenser; and

[0018] (3) allowing a part of the ammonia-removed wastewater obtained at the bottom of the ammonia removal tower to enter the reboiler, conducting heating to allow for partial vaporization of the part of the ammonia-removed wastewater, and returning an obtained vapor-liquid mixture to the ammonia removal tower; allowing a remaining part of the ammonia-removed wastewater obtained to enter a filter for separation and removal of heavy metal precipitates to produce heavy metal-removed wastewater; and allowing the heavy metal-removed wastewater to enter an evaporation separator and an evaporator successively for evaporation to produce a water vapor and a crystallized salt.

[0019] Preferably, the heat pump circulating steam from the primary condenser and the water vapor from the evaporation separator are mixed and then pressurized by the compressor to produce a compressed steam; the compressed steam is used as heat sources for the evaporator and the reboiler; the compressed steam is converted into condensated water after undergoing a heat exchange in the evaporator and then is discharged; and the compressed steam is returned to the primary condenser after undergoing a heat exchange for condensation in the reboiler.

[0020] Preferably, after the salt-containing and heavy metal-containing ammonia-nitrogen wastewater undergoes the ammonia removal in the ammonia removal tower, the ammonia-removed wastewater obtained at the bottom of the ammonia removal tower is first subjected to a pH adjustment with an alkali and then enters the filter; and the heavy metal-removed wastewater is first subjected to a pH adjustment with an acid and then enters the evaporation separator.

[0021] Preferably, the condensated water discharged from the evaporator is discharged after undergoing a heat exchange with feed wastewater for a heat recovery.

[0022] Preferably, the evaporation of the heavy metal-removed wastewater is set to single-effect evaporation or multi-effect evaporation according to actual needs.

[0023] Preferably, when the multi-effect evaporation is adopted for the heavy metal-removed wastewater, in a first effect, with a compressed steam as a heat source, the heavy metal-removed wastewater is evaporated step by step; and a steam produced by final-effect evaporation is introduced into the compressor for compression.

[0024] The present disclosure has the following beneficial effects:

[0025] (1) In the energy-saving treatment system for a salt-containing and heavy metal-containing ammonia-nitrogen wastewater disclosed in the present disclosure, heat pumps for ammonia removal and desalting of an ammonia-nitrogen wastewater treatment are integrated into a single heat pump system. Heat pump circulating water undergoes a heat exchange in the primary condenser at a top of the ammonia removal tower to produce a heat pump circulating steam, the heat pump circulating steam, together with a steam produced at a top of the evaporation separator, enters the compressor and is pressurized to produce a compressed steam, and the compressed steam can be used as heat sources for the reboiler and the evaporator, which effectively reduces the energy consumption of the wastewater treatment process. The integration of the heat pumps for ammonia removal and desalting into a single heat pump system can significantly improve the efficiency of the heat-pump compressor to allow energy conservation.

[0026] (2) High-temperature condensated water generated in the evaporator can be used to preheat feed raw wastewater, which allows the utilization of waste heat and improves the utilization efficiency of energy.

[0027] (3) The ammonia-removed wastewater discharged from the ammonia removal tower is directly delivered to the filter for heavy metal removal without cooling, which avoids the energy loss caused by heavy metal removal at room temperature in the existing process, and also solves the problem that the energy consumption increases due to the heating of wastewater required before desalting as the heavy metal removed wastewater is at room temperature.

[0028] (4) In the present disclosure, the energy of ammonia removal, the energy of heavy metal removal, and the energy of desalting are integrated for use, which significantly improves an energy integration degree of the process and greatly reduces the energy consumption of the system.

[0029] Other advantages, objectives, and features of the present disclosure will be illustrated in the subsequent description to some extent, and will be apparent to those skilled in the art to some extent based on the following investigation and research, or teachings may be obtained by practicing the present disclosure. The objectives and other advantages of the present disclosure can be implemented and obtained by the description below. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to make the objectives, technical solutions, and advantages of the present disclosure clear, the present disclosure will be preferably described in detail below with reference to the accompanying drawings.

[0031] FIG. 1 shows the energy-saving treatment system for a salt-containing and heavy metal-containing ammonia-nitrogen wastewater in the present disclosure;

[0032] FIG. 2 shows the energy-saving treatment system for a salt-containing and heavy metal-containing ammonia-nitrogen wastewater in Example 1 of the present disclosure;

[0033] FIG. 3 shows the process flow adopted in Comparative Example 1; and

[0034] FIG. 4 shows the process flow adopted in Comparative Example 2.

[0035] Reference numerals: ammonia removal tower 01, primary condenser 02, reboiler 03, filter 04, evaporator 05, evaporation separator 06, compressor 07, secondary condenser 08, spray liquid cooler 09, raw wastewater preheater 10, compressor 11, crystallizer 12, centrifugal separator 13, and pre-filtration cooler 14. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] The embodiments of the present disclosure are described below through specific examples, and those skilled in the art can easily understand other advantages and effects of the present disclosure from the contents disclosed in this specification. The present disclosure can also be implemented or applied through other different specific implementations. Based on different viewpoints and applications, various modifications or alterations can be made to various details of this specification without departing from the spirit of the present disclosure. It should be noted that the diagrams provided in the following embodiments merely illustrate the basic conception of the present disclosure only schematically, and the following embodiments or features in the embodiments may be combined in a non-conflicting manner.

[0037] In order to facilitate the well understanding of the present disclosure, the present disclosure is illustrated through the following embodiments. These embodiments fall within the protection scope of the present disclosure, but do not limit the protection scope of the present disclosure.

[0038] As shown in FIG. 1, an energy-saving treatment system for a salt-containing and heavy metal-containing ammonia-nitrogen wastewater is provided, including: a wastewater treatment subsystem and a heat pump subsystem. The wastewater treatment subsystem includes an ammonia removal tower 01, a reboiler 03, a filter 04, an evaporator 05, and an evaporation separator 06. A bottom of the ammonia removal tower 01 is connected with a cold side of the reboiler 03, the bottom of the ammonia removal tower 01 is connected with the filter 04 and the evaporation separator 06 successively through pipelines, and a cold side of the evaporator 05 is connected with the evaporation separator 06. The heat pump subsystem includes a primary condenser 02 and a compressor 07. A hot side of the primary condenser 02 is connected with a top of the ammonia removal tower 01, and a cold side of the primary condenser 02, the compressor 07, and a hot side of the reboiler 03 are connected with each other successively through pipelines. The evaporation separator 06 is connected with an inlet of the compressor 07, and a hot side of the evaporator 05 is connected with an outlet of the compressor 07. The wastewater treatment subsystem further includes a raw wastewater preheater 10. The raw wastewater preheater 10 is arranged on a raw wastewater inlet pipeline. A hot side of the raw wastewater preheater is connected with a hot side of the evaporator 05, and a cold side of the raw wastewater preheater is connected with the ammonia removal tower 01. The wastewater treatment subsystem further includes a secondary condenser 08 and a spray liquid cooler 09. A hot side of the secondary condenser 08 is connected with the hot side of the primary condenser 02, and the hot side of the secondary condenser 08 communicates with an ammonia water discharge pipeline and an ammonia water spray pipeline. The spray liquid cooler 09 is arranged on the ammonia water spray pipeline. The wastewater treatment subsystem includes an alkali-feeding device, and the alkali-feeding device is arranged on an inlet pipeline of the filter 04. The wastewater treatment subsystem includes an acid-feeding device, and the acid-feeding device is arranged on an inlet pipeline of the evaporation separator 06. One evaporation separator 06 and one evaporator 05 are provided. A vapor compression process in the heat pump subsystem can be allowed by a single compressor or a combination of a plurality of compressors arranged in series or in parallel according to actual needs.

[0039] An energy-saving treatment process for a salt-containing and heavy metal-containing ammonia-nitrogen wastewater using the energy-saving treatment system for a salt-containing and heavy metal-containing ammonia-nitrogen wastewater is provided, including the following steps:

[0040] (1) The salt-containing and heavy metal-containing ammonia-nitrogen wastewater is fed into the ammonia removal tower 01 for ammonia removal to produce an ammonia-containing steam at a top of the ammonia removal tower. The ammonia-containing steam is allowed to enter the primary condenser 02 to undergo a heat exchange with heat pump circulating water, such that the ammonia-containing steam is partially condensated to produce dilute ammonia water and a concentrated ammonia-containing steam. The dilute ammonia water is partially or fully returned to the ammonia removal tower 01. The concentrated ammonia-containing steam is allowed to enter the secondary condenser 08 to undergo condensation and spray absorption to produce an ammonia water product.

[0041] (2) A heat pump circulating steam produced after the heat exchange of the heat pump circulating water in the primary condenser 02 is pressurized by the compressor 07 to produce a compressed steam. The compressed steam is allowed to enter the reboiler 03 to undergo a heat exchange with ammonia-removed wastewater obtained at a bottom of the ammonia removal tower 01 to produce condensated water, and the condensated water is returned to the primary condenser 02.

[0042] (3) A part of the ammonia-removed wastewater obtained at the bottom of the ammonia removal tower 01 is allowed to enter the reboiler 03, heating is conducted to allow for partial vaporization of the part of the ammonia-removed wastewater, and an obtained vapor-liquid mixture is returned to the ammonia removal tower 01; a remaining part of the ammonia-removed wastewater obtained is allowed to enter the filter 04 for separation and removal of heavy metal precipitates to produce heavy metal-removed wastewater. The heavy metal-removed wastewater is allowed to enter the evaporation separator 06 and the evaporator 05 successively for evaporation to produce a water vapor and a crystallized salt.

[0043] The heat pump circulating steam from the primary condenser 02 and the water vapor from the evaporation separator 06 are mixed and then pressurized by the compressor 07 to produce a compressed steam. The compressed steam is used as heat sources for the evaporator 05 and the reboiler 03. The compressed steam is converted into condensated water after undergoing a heat exchange in the evaporator 05, then undergoes a heat exchange with feed wastewater for a heat recovery, and is discharged. The compressed steam is converted into condensated water after undergoing a heat exchange in the reboiler 03 and then is returned to the primary condenser 02.

[0044] After the salt-containing and heavy metal-containing ammonia-nitrogen wastewater undergoes the ammonia removal in the ammonia removal tower 01, the ammonia-removed wastewater obtained at the bottom of the ammonia removal tower is first subjected to a pH adjustment with an alkali and then enters the filter 04. The heavy metal-removed wastewater is first subjected to a pH adjustment with an acid and then enters the evaporation separator 06.

[0045] Use Example 1

[0046] FIG. 2 shows an optimized energy-saving treatment system for a salt-containing and heavy metal-containing ammonia-nitrogen wastewater. The system shown in FIG. 2 is different from the system shown in FIG. 1 in that: the heat pump subsystem in FIG. 2 further includes a compressor 11, the cold side of the primary condenser 02, the compressor 07, and the hot side of the evaporator 05 are connected with each other successively through pipelines, and the compressor 07, the compressor 11, and the hot side of the reboiler 03 are connected with each other successively through pipelines. The system shown in FIG. 2 is also different from the system shown in FIG. 1 in that: the system shown in FIG. 2 further includes a crystallizer 12 configured to allow further crystallization for an inorganic salt product and a centrifugal separator 13, and the evaporation separator 06, the crystallizer 12, and the centrifugal separator 13 are connected with each other in circulation.

[0047] The difference in the process is as follows: The heat pump circulating water undergoes a heat exchange in the primary condenser 02 to produce a heat pump circulating steam. The heat pump circulating steam and a water vapor from the evaporation separator 06 are mixed and then pressurized by the compressor 07 to produce a compressed steam. A part of the compressed steam is used as a heat source for the evaporator 05. The remaining part of the compressed steam is pressurized by the compressor 11 to produce a secondary compressed steam, and the secondary compressed steam is used as a heat source for the reboiler 03. An inorganic salt product from the evaporation separator 06 is further separated and purified by the crystallizer 12 and the centrifugal separator 13, and a liquid produced accordingly is returned to the evaporation separator 06 for evaporation.

[0048] The system shown in FIG. 2 was used to treat the following salt-containing and heavy metal-containing ammonia-nitrogen wastewater: a salt-containing and heavy metal-containing ammonia-nitrogen wastewater inlet flow rate: 120 m'7h, an ammonia-nitrogen content: 7,005.68 mg / L, a Na+ content: 60,023.20 mg / L, a SO?’ content: 120,004.12 mg / L, and heavy metal ion contents: Ni2+: 315.96 mg / L, Co2+: 78.86 mg / L, and Mn3+: 80.97 mg / L. Water produced after the treatment was as follows: an ammonia-nitrogen content: 7.82 mg / L, aNa+ content: 344.41 mg / L, a SO42' content: 546.71 mg / L, and heavy metal ion contents: Ni2+: 0.53 mg / L, Co2+: 0.72 mg / L, and Mn3+: 1.16 mg / L, which reached the first-grade national discharge standard of China. An ammonia water product produced after the treatment had a mass concentration of 20.28%, which met the concentration requirement of industrial ammonia water.

[0049] The treatment of each ton of ammonia-nitrogen wastewater involved a power consumption of 60.31 kWh and a live steam consumption of 0, which significantly reduced the comprehensive energy consumption.

[0050] Comparative Example 1

[0051] The system shown in FIG. 3 is adopted in Comparative Example 1. The process in Comparative Example 1 is different from the process in Use Example 1 in that: A heat pump circulating steam from the primary condenser 02 is compressed by the compressor 07 to produce a compressed steam and then the compressed steam is directly delivered to the reboiler 03. A water vapor produced at the top of the evaporation separator 06 is pressurized by the compressor 11 and then used as a heat source for the evaporator 05.

[0052] In this comparative example, the system was used to treat the following wastewater from ternary cathode material precursor production: a wastewater inlet flow rate: 120 m3 / h, an ammonia-nitrogen content: 7,005.68 mg / L, a Na+ content: 60,023.20 mg / L, a SOU content: 120,004.12 mg / L, and heavy metal ion contents: Ni2+: 315.96 mg / L, Co2+: 78.86 mg / L, and Mn3+: 80.97 mg / L. Water produced after the treatment was as follows: an ammonia-nitrogen content: 8.12 mg / L, a Na+ content: 352.43 mg / L, a SOU content: 556.78 mg / L, and heavy metal ion contents: Ni2+: 0.51 mg / L, Co2+: 0.72 mg / L, and Mn3+: 1.13 mg / L. An ammonia water product produced after the treatment had a mass concentration of 20.57%, which met the concentration requirement of industrial ammonia water.

[0053] Because the heat pumps for ammonia removal and desalting are not integrated, the efficiency of the steam compressor is reduced and the power consumption of the steam compressor increases compared with Use Example 1. The treatment of each ton of ammonia-nitrogen wastewater involved a power consumption of 81.73 kWh and a live steam consumption of 0.

[0054] Comparative Example 2

[0055] The system shown in FIG. 4 is adopted in Comparative Example 2. The process in Comparative Example 2 is different from the process in Use Example 1 in that: The heavy metal removal is conducted by room-temperature filtration. Ammonia-removed wastewater produced at the bottom of the ammonia removal tower 01 is cooled to about 40°C by the pre-filtration cooler 14, then is subjected to a pH adjustment with an alkali liquor, and then enters the filter 04. A live steam is introduced at the hot side of the evaporator 05 to supplement the heat.

[0056] In this comparative example, the system was used to treat the following wastewater: a wastewater inlet flow rate: 120 m3 / h, an ammonia-nitrogen content: 7,005.68 mg / L, a Na+ content: 60,023.20 mg / L, a SOU content: 120,004.12 mg / L, and heavy metal ion contents: Ni2+: 315.96 mg / L, Co2+: 78.86 mg / L, and Mn3 : 80.97 mg / L. Water produced after the treatment was as follows: an ammonia-nitrogen content: 7.91 mg / L, a Na+ content: 352.38 mg / L, a SOU content: 557.82 mg / L, and heavy metal ion contents: Ni2+: 0.48 mg / L, Co2+: 0.65 mg / L, and io Mn3+: 1.09 mg / L. An ammonia water product produced after the treatment had a mass concentration of 20.16%, which met the concentration requirement of industrial ammonia water.

[0057] Because the low-temperature filtration is adopted, the energy consumption in this comparative example includes a power consumption and a live steam consumption, and increases compared with Use Example 1. The treatment of each ton of wastewater involved a power consumption of 68.14 kWh. Because the heavy metal removal is conducted at a low temperature, the energy consumption of desalting increases, and the steam produced by the heat pump subsystem cannot meet the demand of the entire system. Therefore, during the treatment of each ton of wastewater, 0.07 kg of the additional live steam (0.40 MPa) is required for desalting.

[0058] In summary, in the present disclosure, the energy of ammonia removal, the energy of heavy metal removal, and the energy of desalting are integrated for use, which significantly improves an energy integration degree of the process and greatly reduces the energy consumption of the system.

[0059] It should be noted that the above embodiments are only intended to explain, rather than to limit the technical solutions of the present disclosure. Although the present disclosure is described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that modifications or equivalent substitutions may be made to the technical solutions of the present disclosure without departing from the spirit and scope of the technical solutions of the present disclosure, and such modifications or equivalent substitutions should be included within the scope of the claims of the present disclosure.

Claims

1. An energy-saving treatment system for a salt-containing and heavy metal-containing ammonia-nitrogen wastewater, comprising: a wastewater treatment subsystem and a heat pump subsystem, wherein the wastewater treatment subsystem comprises an ammonia removal tower (01), a reboiler (03), a filter (04), an evaporator (05), and an evaporation separator (06); a bottom of the ammonia removal tower (01) is connected with a cold side of the reboiler (03), the bottom of the ammonia removal tower (01) is connected with the filter (04) and the evaporation separator (06) successively through pipelines, and a cold side of the evaporator (05) is connected with the evaporation separator (06); the heat pump subsystem comprises a primary condenser (02) and a compressor (07); and a hot side of the primary condenser (02) is connected with a top of the ammonia removal tower (01), and a cold side of the primary condenser (02), the compressor (07), and a hot side of the reboiler (03) are connected with each other successively through pipelines.

2. The energy-saving treatment system for a salt-containing and heavy metal-containing ammonia-nitrogen wastewater according to claim 1, wherein the evaporation separator (06) is connected with an inlet of the compressor (07), and a hot side of the evaporator (05) is connected with an outlet of the compressor (07).

3. The energy-saving treatment system for a salt-containing and heavy metal-containing ammonia-nitrogen wastewater according to claim 1, wherein the wastewater treatment subsystem further comprises a raw wastewater preheater (10); the raw wastewater preheater (10) is arranged on a raw wastewater inlet pipeline; and a hot side of the raw wastewater preheater is connected with a hot side of the evaporator (05), and a cold side of the raw wastewater preheater is connected with the ammonia removal tower (01).

4. The energy-saving treatment system for a salt-containing and heavy metal-containing ammonia-nitrogen wastewater according to claim 1, wherein the wastewater treatment subsystem further comprises a secondary condenser (08) and a spray liquid cooler (09); a hot side of the secondary condenser (08) is connected with the hot side of the primary condenser (02), and the hot side of the secondary condenser (08) communicates with an ammonia water discharge pipeline and an ammonia water spray pipeline; and the spray liquid cooler (09) is arranged on the ammonia water spray pipeline.

5. The energy-saving treatment system for a salt-containing and heavy metal-containingammonia-nitrogen wastewater according to claim 1, wherein the wastewater treatment subsystem comprises an alkali-feeding device, and the alkali-feeding device is arranged on an inlet pipeline of the filter (04); and the wastewater treatment subsystem comprises an acid-feeding device, and the acid-feeding device is arranged on an inlet pipeline of the evaporation separator (06).

6. The energy-saving treatment system for a salt-containing and heavy metal-containing ammonia-nitrogen wastewater according to claim 1, wherein the wastewater treatment subsystem comprises one or more evaporation separators and corresponding one or more evaporators.

7. An energy-saving treatment process for a salt-containing and heavy metal-containing ammonia-nitrogen wastewater, comprising the following steps:(1) feeding salt-containing and heavy metal-containing ammonia-nitrogen wastewater into an ammonia removal tower for ammonia removal to produce an ammonia-containing steam at a top of the ammonia removal tower; allowing the ammonia-containing steam to enter a primary condenser to undergo a heat exchange with heat pump circulating water, such that the ammonia-containing steam is partially condensated to produce dilute ammonia water and a concentrated ammonia-containing steam; partially or fully returning the dilute ammonia water to the ammonia removal tower; and allowing the concentrated ammonia-containing steam to enter a secondary condenser to undergo condensation and spray absorption to produce an ammonia water product;(2) pressurizing, by a compressor, a heat pump circulating steam produced after the heat exchange of the heat pump circulating water in the primary condenser to produce a compressed steam, allowing the compressed steam to enter a reboiler to undergo a heat exchange with ammonia-removed wastewater obtained at a bottom of the ammonia removal tower to produce condensated water, and returning the condensated water to the primary condenser; and(3) allowing a part of the ammonia-removed wastewater obtained at the bottom of the ammonia removal tower to enter the reboiler, conducting heating to allow for partial vaporization of the part of the ammonia-removed wastewater, and returning an obtained vapor-liquid mixture to the ammonia removal tower; allowing a remaining part of the ammonia-removed wastewater obtained to enter a filter for separation and removal of heavy metal precipitates to produce heavy metal-removed wastewater; and allowing the heavy metal-removed wastewater to enter an evaporation separator and an evaporator successively for evaporation to produce a water vapor and a crystallized salt.

8. The energy-saving treatment process for a salt-containing and heavy metal-containing ammonia-nitrogen wastewater according to claim 7, wherein the heat pump circulating steamfrom the primary condenser and the water vapor from the evaporation separator are mixed and then pressurized by the compressor to produce a compressed steam; the compressed steam is used as heat sources for the evaporator and the reboiler; the compressed steam is converted into condensated water after undergoing a heat exchange in the evaporator and then is discharged; and the compressed steam is returned to the primary condenser after undergoing a heat exchange for condensation in the reboiler.

9. The energy-saving treatment process for a salt-containing and heavy metal-containing ammonia-nitrogen wastewater according to claim 7, wherein after the salt-containing and heavy metal-containing ammonia-nitrogen wastewater undergoes the ammonia removal in the ammonia removal tower, the ammonia-removed wastewater obtained at the bottom of the ammonia removal tower is first subjected to a pH adjustment with an alkali and then enters the filter; and the heavy metal-removed wastewater is first subjected to a pH adjustment with an acid and then enters the evaporation separator.

10. The energy-saving treatment process for a salt-containing and heavy metal-containing ammonia-nitrogen wastewater according to claim 8, wherein the condensated water discharged from the evaporator is discharged after undergoing a heat exchange with feed wastewater for a heat recovery.

11. The energy-saving treatment process for a salt-containing and heavy metal-containing ammonia-nitrogen wastewater according to claim 7, wherein the evaporation of the heavy metal-removed wastewater is set to single-effect evaporation or multi-effect evaporation according to actual needs.

12. The energy-saving treatment process for a salt-containing and heavy metal-containing ammonia-nitrogen wastewater according to claim 11, wherein when the multi-effect evaporation is adopted for the heavy metal-removed wastewater, in a first effect, with a compressed steam as a heat source, the heavy metal-removed wastewater is evaporated step by step; and a steam produced by final-effect evaporation is introduced into the compressor for compression.

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