A method and device for treating ammonia nitrogen wastewater and recovering ammonia

Abstract

The present invention relates to a method and device for treating ammonia nitrogen wastewater and recovering ammonia, belonging to the technical field of industrial wastewater treatment, including a deammonification tower, a heat pump reboiler, a heat pump condenser and a heat pump compressor; an ammonia nitrogen wastewater feed port is provided between the rectifying section and the stripping section of the deammonification tower, the rectifying section is provided with an ammonia-containing steam discharge port and a dilute ammonia water reflux port, and the stripping section is provided with a deammonified water discharge port and a stripping steam feed port; the deammonified water discharge port and the stripping steam feed port are circulated and connected to the heat pump reboiler; the ammonia-containing steam discharge port and the dilute ammonia water reflux port are circulated and connected to the heat pump condenser; the heat pump condenser and the heat pump reboiler are circulated and connected via a heat pump compressor to form a heat pump cycle. Heat pump working fluid steam is used to heat the heat pump reboiler, replacing the use of raw steam, saving energy and reducing consumption; the heat pump compressor pressurizes the non-toxic and harmless heat pump working fluid steam, solving the safety hazard problem of directly pressurizing ammonia-containing steam in the prior art.

Description

Technical Field

[0001] The invention belongs to the technical field of industrial wastewater treatment and relates to a method and a device for treating ammonia nitrogen wastewater and recovering ammonia. Background Art

[0002] Chemical, fertilizer, pesticide, printing and dyeing, battery and other industries produce a lot of ammonia nitrogen wastewater in the production process, in which ammonia nitrogen is in the form of free ammonia (NH 3 ) and ammonium ions (NH 4 + ) exists in the form of. After sewage containing ammonia nitrogen is discharged into the water body, it is toxic to aquatic organisms due to its high oxygen consumption. Under the action of nitrifying bacteria, it is oxidized into nitrite and nitrate, which is also toxic to the human body. The state has strict regulations and restrictions on the content of ammonia nitrogen in discharged wastewater.

[0003] At present, the main methods for treating ammonia nitrogen wastewater are biological, chemical and physical methods. Biological methods include nitrification and algae cultivation, chemical methods include ion exchange, chemical precipitation, breakpoint chlorination, and physical methods include membrane separation and air stripping. Biological methods have good treatment effects and no secondary pollution, but bacterial culture is difficult and has weak load resistance, and is only suitable for low-concentration ammonia nitrogen wastewater; some chemical methods have high operating costs, and some may cause secondary pollution; membrane separation in the physical method has problems of membrane leakage and membrane pollution, and equipment investment and operating costs are high.

[0004] The stripping method is divided into air stripping and steam stripping. Air stripping or water vapor stripping is used under alkaline conditions to continuously transfer volatile substances such as ammonia nitrogen in the wastewater from the liquid phase to the gas phase, thereby achieving the purpose of removing ammonia nitrogen in the wastewater. The air stripping method is suitable for treating ammonia nitrogen wastewater at room temperature. The ammonia nitrogen transferred to the air is easy to cause secondary pollution of the atmosphere, and requires a large amount of air and high power consumption. In contrast, the steam stripping method can increase the water temperature of the wastewater and has a higher ammonia nitrogen removal rate. The ammonia-containing vapor obtained by stripping is then prepared into ammonia gas, ammonia water or ammonium salt by distillation / condensation / absorption / chemical treatment, which can be reused as a resource and avoid secondary pollution. It has become the main method for treating ammonia nitrogen wastewater.

[0005] The traditional process of using a single tower for steam stripping to treat ammonia nitrogen wastewater usually has a steam consumption of up to 250-300kg / t of wastewater, which is energy-intensive. Although double-effect steam stripping can reduce steam consumption, it is often complex, requires a large number of equipment, and requires high investment. The existing schemes for energy saving and consumption reduction using heat pump technology all use compressors to directly pressurize and heat the ammonia-containing steam obtained by stripping to provide heat for the reboiler. However, ammonia-containing steam is flammable, toxic, and has a strong irritating odor, which can burn the skin, eyes, and mucous membranes of the respiratory organs. Directly pressurizing ammonia-containing steam has certain safety hazards. At the same time, the compressor is a dynamic device, and leakage may occur after the seal is worn during long-term operation, which is harmful to the operator. When the ammonia concentration is within the explosion limit, there is also a risk of combustion or even explosion. Therefore, the existing technology lacks ammonia nitrogen wastewater treatment scheme that can take into account good safety performance, low energy consumption, small equipment investment, simple process, high recycling rate, and no secondary pollution. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a method and device for treating ammonia nitrogen wastewater and recovering ammonia, utilizing heat pump technology to save energy and reduce consumption, and the heat pump compressor pressurizes non-toxic and harmless heat pump working fluid steam rather than ammonia-containing steam obtained from a deammonification tower, thereby ensuring safety and solving the problem of potential safety hazards in directly pressurizing ammonia-containing steam in the prior art.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for treating ammonia nitrogen wastewater and recovering ammonia, comprising the following steps:

[0009] Ammonia nitrogen wastewater is passed into a deammoniation tower for deammoniation, and ammonia-containing steam is obtained from the ammonia-containing steam outlet of the deammoniation tower rectification section. The ammonia-containing steam enters the hot side of the heat pump condenser and exchanges heat with the heat pump working fluid on the cold side of the heat pump condenser. Part of the water vapor and ammonia in the ammonia-containing steam condense to form dilute ammonia water and leave the hot side of the heat pump condenser, and part or all of it is sent to the deammoniation tower as reflux liquid; the uncondensed water vapor and ammonia in the ammonia-containing steam form concentrated ammonia vapor and leave the hot side of the heat pump condenser to become a recovered ammonia resource;

[0010] The heat pump working fluid on the cold side of the heat pump condenser exchanges heat with the ammonia-containing steam to generate heat pump working fluid steam, which is pressurized by the heat pump compressor and enters the hot side of the heat pump reboiler, exchanges heat with the deammonified water from the deammonification tower on the cold side of the heat pump reboiler, condenses to form heat pump working fluid and leaves the hot side of the heat pump reboiler; the deammonified water on the cold side of the heat pump reboiler exchanges heat to generate steam that returns to the deammonification tower and serves as stripping steam for the stripping section of the deammonification tower.

[0011] Furthermore, the concentrated ammonia vapor leaving the hot side of the heat pump condenser enters the hot side of the spray condenser, exchanges heat with the cooling medium on the cold side of the spray condenser, and condenses to form concentrated ammonia water; a part of the concentrated ammonia water returns to the hot side of the spray condenser as spray liquid, and the other part is produced as ammonia water product.

[0012] Furthermore, the concentrated ammonia water used as the spray liquid is first cooled by the spray liquid cooler and then enters the spray condenser.

[0013] Furthermore, when part of the dilute ammonia water in the heat pump condenser is sent to the deamination tower, the remaining part is passed into the hot side of the spray condenser as a spray liquid.

[0014] Furthermore, the ammonia nitrogen wastewater is heated by heat exchange with deammonified water from a deammonification tower in a wastewater preheater, and then introduced into the deammonification tower for deammonification; the deammonified water after heat exchange and heat energy recovery in the wastewater preheater is discharged to subsequent processes.

[0015] Furthermore, the heat pump working fluid is water, and the corresponding heat pump working fluid vapor is heat pump working fluid water vapor.

[0016] Further, the heat pump working fluid leaving the hot side of the heat pump reboiler is circulated to the cold side of the heat pump condenser.

[0017] Furthermore, other reboilers besides the heat pump reboiler are added, and heating medium is introduced into the hot side of other reboilers. The heating medium is extracted after heat exchange with the deammoniation water from the deammoniation tower on the cold side of other reboilers, and the deammoniation water is converted into steam after heat exchange and returns to the deammoniation tower.

[0018] Furthermore, the raw steam and the heat pump working fluid water vapor are mixed and passed into the hot side of the heat pump reboiler to provide heat for the heat pump reboiler; the raw steam and the heat pump working fluid water vapor are heat exchanged to form condensed water, part of which is returned to the cold side of the heat pump condenser as the heat pump working fluid, and the other part is extracted.

[0019] A device for treating ammonia nitrogen wastewater and recovering ammonia, comprising a deammonification tower, a heat pump reboiler, a heat pump condenser and a heat pump compressor;

[0020] The deamination tower comprises a rectifying section and a stripping section, an ammonia nitrogen wastewater feed port is arranged between the two sections, the rectifying section is provided with an ammonia steam discharge port and a dilute ammonia water reflux port, and the stripping section is provided with a deammoniation water discharge port and a stripping steam feed port;

[0021] The deammoniation water outlet and the stripping steam feed port are circulated and connected to the cold side of the heat pump reboiler; the ammonia-containing steam outlet and the dilute ammonia water reflux port are circulated and connected to the hot side of the heat pump condenser; and a heat pump compressor is connected between the cold side of the heat pump condenser and the hot side of the heat pump reboiler.

[0022] Furthermore, a heat pump working fluid return pipeline is connected from the hot side of the heat pump reboiler to the cold side of the heat pump condenser, forming a heat pump cycle.

[0023] Furthermore, it also includes a spray condenser, wherein a concentrated ammonia steam pipeline is connected between the hot side of the spray condenser and the hot side of the heat pump condenser; a concentrated ammonia water production pipeline and a concentrated ammonia water spray pipeline are connected to the hot side of the spray condenser, and a cooling medium introduction pipeline and a cooling medium production pipeline are connected to the cold side of the spray condenser.

[0024] Furthermore, the concentrated ammonia water spray pipeline is connected to a spray liquid cooler.

[0025] Furthermore, a dilute ammonia water pipeline is connected between the hot side of the heat pump condenser and the hot side of the spray liquid cooler.

[0026] Furthermore, it also includes other reboilers, the hot side of which is connected with a heating medium introduction pipeline and a heating medium extraction pipeline, and the cold side of which is connected with the deamination tower through a deammoniation water introduction pipeline and a steam outlet pipeline.

[0027] Furthermore, the heat pump compressor consists of one stage or multiple stages.

[0028] Furthermore, a steam mixer is connected between the heat pump compressor and the hot side of the heat pump reboiler.

[0029] Furthermore, the deamination tower includes a rectifying tower as a rectifying section and a stripping tower as a stripping section; or the deamination tower is formed by arranging a plurality of super gravity towers in series or in parallel.

[0030] The beneficial effects of the present invention are:

[0031] (1) In the method and device for treating ammonia nitrogen wastewater and recovering ammonia disclosed in the present invention, the heat pump working fluid liquid forms heat pump working fluid vapor after heat exchange in the heat pump condenser, and enters the heat pump compressor for pressurization and temperature increase. The heat pump compressor pressurizes and treats non-toxic and harmless heat pump working fluid vapor (such as heat pump working fluid water vapor) rather than ammonia-containing vapor with toxic characteristics, thereby avoiding the safety hazards of directly pressurizing ammonia-containing vapor and improving safety performance.

[0032] (2) The method and device for treating ammonia nitrogen wastewater and recovering ammonia disclosed in the present invention form a heat pump cycle between the heat pump condenser, the heat pump compressor and the heat pump reboiler, which converts the low-grade thermal energy of the ammonia steam in the deammonification tower into high-grade thermal energy to provide heat for the heat pump reboiler, replacing the use of a large amount of raw steam. At the same time, it reduces the condensation load of the ammonia steam in the deammonification tower, and significantly reduces the overall energy consumption.

[0033] (3) The method and device for treating ammonia nitrogen wastewater and recovering ammonia disclosed in the present invention adopt a step-by-step condensation method. Ammonia-containing vapor enters a heat pump condenser for primary condensation to obtain dilute ammonia water and concentrated ammonia vapor. The concentrated ammonia vapor enters a spray condenser for secondary condensation to obtain concentrated ammonia water. The cooled concentrated ammonia water or a mixture of concentrated ammonia water and part of the dilute ammonia water is used as a spray liquid for secondary condensation in the spray condenser to absorb ammonia in the uncondensed concentrated ammonia vapor, thereby completely condensing the concentrated ammonia vapor to obtain a high-concentration (≥20%) ammonia water product with a high recovery rate, which is convenient for resource recycling and avoids secondary pollution.

[0034] (4) The method and device for treating ammonia nitrogen wastewater and recovering ammonia disclosed in the present invention only require one distillation tower (deammoniation tower) to make the deammonified water meet the national first-level emission standard (ammonia nitrogen content ≤ 15 mg / L), and at the same time recover a high-concentration ammonia water product. The process is simple, the number of equipment is small, the equipment investment is small, and the footprint is small.

[0035] (5) Compared with the device using live steam to heat the reboiler, the method and device for treating ammonia nitrogen wastewater and recovering ammonia disclosed in the present invention do not change the load and discharge rate of the deammonification tower. It can be used not only for the design of new devices but also for energy-saving transformation of existing devices, and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to make the purpose, technical solution and advantages of the present invention more clear, the present invention provides the following drawings for illustration:

[0037] Figure 1 This is a schematic diagram of the process of Example 1 of the present invention;

[0038] Figure 2 This is a schematic diagram of the process of Embodiment 2 of the present invention;

[0039] Figure 3 This is a schematic diagram of the process of Example 3 of the present invention.

[0040] Figure numerals: wastewater preheater 1, deamination tower 2, heat pump condenser 3, heat pump compressor 4, heat pump reboiler 5, spray liquid cooler 6, spray condenser 7, raw steam reboiler 8, steam mixer 9. DETAILED DESCRIPTION

[0041] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0042] Embodiment 1:

[0043] like Figure 1 As shown, this embodiment provides a device for treating ammonia nitrogen wastewater and recovering ammonia, including a wastewater preheater 1, a deammonification tower 2, a heat pump condenser 3, a heat pump compressor 4, a heat pump reboiler 5, a spray liquid cooler 6 and a spray condenser 7.

[0044] The deammoniation tower 2 is a vertical single tower body, including a rectifying section and a stripping section, wherein the rectifying section is located above the stripping section. An ammonia nitrogen wastewater feed port is provided between the rectifying section and the stripping section, an ammonia steam discharge port and a dilute ammonia water reflux port are provided in the rectifying section, and a deammoniation post-water discharge port and a stripping steam feed port are provided in the stripping section.

[0045] The wastewater preheater 1 is connected with the ammonia nitrogen wastewater feed port and the deammoniation water discharge port of the deammoniation tower 2. The wastewater preheater 1 is connected with an ammonia nitrogen wastewater feed pipe and a deammoniation water discharge pipe.

[0046] The deammoniation water outlet and the stripping steam feed port are circulated to the cold side of the heat pump reboiler 5; the ammonia-containing steam outlet and the dilute ammonia water reflux port are circulated to the hot side of the heat pump condenser 3; and a heat pump compressor 4 is connected between the cold side of the heat pump condenser 3 and the hot side of the heat pump reboiler 5.

[0047] A heat pump working fluid return pipeline is connected from the hot side of the heat pump reboiler 5 to the cold side of the heat pump condenser 3, forming a heat pump cycle.

[0048] A concentrated ammonia steam pipeline is connected between the hot side of the spray condenser 7 and the hot side of the heat pump condenser 3; a concentrated ammonia water extraction pipeline and a concentrated ammonia water spray pipeline are connected to the hot side of the spray condenser 7, and a cooling medium introduction pipeline and a cooling medium extraction pipeline are connected to the cold side of the spray condenser 7. The concentrated ammonia water spray pipeline is connected to a spray liquid cooler 6.

[0049] In this embodiment, the heat pump compressor 4 is one stage. In other embodiments, the heat pump compressor 4 can be arranged in series in multiple stages according to actual needs, and heat pump working fluid steam desuperheaters are connected between adjacent stages of the heat pump compressors 4 .

[0050] This embodiment also provides a method for treating ammonia nitrogen wastewater and recovering ammonia, comprising the following steps:

[0051] First, the ammonia nitrogen wastewater is mixed with an alkali solution (the alkali solution can be a sodium hydroxide aqueous solution) for alkalization treatment, so that the pH value of the discharged deammonified water reaches 9.5-12; then the alkalized ammonia nitrogen wastewater is heated by heat exchange with the deammonified water from the deammonification tower 2 through the wastewater preheater 1, and then passed into the deammonification tower 2 for deammonification; the deammonified water after heat exchange and heat energy recovery in the wastewater preheater 1 is discharged to the subsequent process;

[0052] Ammonia-containing steam is obtained from the ammonia-containing steam outlet of the deamination tower 2, and the ammonia-containing steam enters the hot side of the heat pump condenser 3, and exchanges heat with the heat pump working fluid (the heat pump working fluid in this embodiment is water) on the cold side of the heat pump condenser 3. Part of the water vapor and ammonia in the ammonia-containing steam condense to form dilute ammonia water and leave the hot side of the heat pump condenser 3, and all of them are sent to the deamination tower as reflux liquid; the uncondensed water vapor and ammonia in the ammonia-containing steam form concentrated ammonia vapor and leave the hot side of the heat pump condenser 3 to become a recovered ammonia resource;

[0053] The heat pump working fluid on the cold side of the heat pump condenser 3 exchanges heat with the ammonia-containing steam to generate heat pump working fluid steam (the heat pump working fluid steam in this embodiment is heat pump working fluid water vapor), which enters the hot side of the heat pump reboiler 5 after being pressurized by the heat pump compressor 4, exchanges heat with the deaminated water from the deammoniation tower 2 on the cold side of the heat pump reboiler 5, condenses to form heat pump working fluid and leaves the hot side of the heat pump reboiler 5; the deaminated water on the cold side of the heat pump reboiler 5 is partially vaporized after heat exchange, and the generated steam returns to the deammoniation tower 2 as the stripping steam of the stripping section of the deammoniation tower 2, and the unvaporized part can return to the deammoniation tower 2 through the stripping steam feed port, or can be directly extracted;

[0054] The heat pump working fluid leaving the hot side of the heat pump reboiler 5 is circulated and passed to the cold side of the heat pump condenser 3 to form a heat pump cycle;

[0055] The concentrated ammonia vapor leaving the hot side of the heat pump condenser 3 enters the hot side of the spray condenser 7, exchanges heat with the cooling medium (circulating cooling water is used as the cooling medium in this embodiment) on the cold side of the spray condenser 7, and condenses to form concentrated ammonia water; a part of the concentrated ammonia water is cooled by the spray liquid cooler 6 and returned to the hot side of the spray condenser 7 as spray liquid, and the other part is produced as ammonia water product.

[0056] In other embodiments, a dilute ammonia water pipeline can be connected between the hot side of the heat pump condenser 3 and the hot side of the spray liquid cooler 6 to send part of the dilute ammonia water in the heat pump condenser 3 to the deammonification tower 2, and the remaining part is cooled by the spray liquid cooler 6 and passed into the hot side of the spray condenser 7 as spray liquid.

[0057] In this embodiment, the ammonia nitrogen wastewater flow rate is 80m 3 / h, the ammonia nitrogen content is 3000mg / L. After treatment, the ammonia nitrogen content in the deammonified water is 5.2mg / L, reaching the national first-level emission standard, with a high ammonia removal rate.

[0058] In the heat pump condenser 3, since the saturated vapor pressure of water is lower than that of ammonia at the same temperature, water vapor is easier to condense than ammonia, so the condensation fraction of water vapor in the ammonia-containing vapor is higher than the condensation fraction of ammonia, so that the ammonia content in the ammonia-containing vapor that has not yet condensed increases, and the uncondensed ammonia-containing vapor becomes concentrated ammonia vapor; the dew point of the ammonia-containing vapor decreases, so that it is lower than the lowest condensation temperature that the heat pump condenser 3 can provide, resulting in part of the ammonia cannot be completely condensed, and only dilute ammonia water with a lower concentration can be obtained. This embodiment introduces a spray condenser 7, and the uncondensed concentrated ammonia vapor in the heat pump condenser 3 enters the hot side of the spray condenser 7, condenses to form concentrated ammonia water after heat exchange, and part of the concentrated ammonia water is cooled and passed into the hot side of the spray condenser 7 as a spray liquid, so as to achieve the effect of absorbing ammonia in the uncondensed concentrated ammonia vapor, thereby completely condensing the concentrated ammonia vapor. The concentration of the concentrated ammonia water reaches 20.5%, which improves the ammonia recovery rate, is conducive to the recovery of ammonia resources for reuse, and prevents secondary pollution.

[0059] In other embodiments, part of the dilute ammonia water in the heat pump condenser 3 may be introduced into the hot side of the spray condenser 7 to be sprayed as a spray liquid.

[0060] A heat pump cycle is formed between the heat pump condenser 3, the heat pump compressor 4 and the heat pump reboiler 5, which replaces the use of a large amount of raw steam. The power consumption for treating each ton of ammonia nitrogen wastewater is 13.9 degrees (the efficiency of the heat pump compressor 4 is 83%), and the comprehensive energy consumption is significantly reduced.

[0061] The heat pump working fluid forms heat pump working fluid vapor after heat exchange in the heat pump condenser 3, and enters the heat pump compressor for pressurization and temperature increase. The heat pump compressor pressurizes non-toxic and harmless heat pump working fluid vapor (such as heat pump working fluid water vapor in this embodiment, or other media), rather than ammonia-containing vapor with toxic properties, thereby avoiding the safety hazards of directly pressurizing ammonia-containing vapor and improving safety performance.

[0062] In this embodiment, only one deamination tower 2 is configured to make the deammoniation water meet the national first-level emission standards and obtain a high-concentration ammonia product. The process is simple, the number of equipment is small, the equipment investment is small, and the floor space is small. Of course, in other embodiments, the deamination tower 2 can be split into a distillation tower as a distillation section and a stripping tower as a stripping section; or the deamination tower 2 is composed of a plurality of supergravity towers arranged in series or in parallel. Through the combination configuration of multiple towers, the basic functions of the deamination tower 2 in the present invention are realized, and the basic effects of the deamination tower 2 in the present invention are achieved. This combination configuration also falls within the protection scope of the present invention.

[0063] Embodiment 2:

[0064] The difference between Example 2 and Example 1 in terms of the device is that a steam mixer 9 is connected between the heat pump compressor 4 and the hot side of the heat pump reboiler 5 , and a condensate extraction pipeline is connected between the heat pump reboiler 5 and the heat pump condenser 3 .

[0065] The difference in method is that the raw steam and the heat pump working medium water vapor are mixed through the steam mixer 9 and passed into the hot side of the heat pump reboiler 5 to provide heat for the heat pump reboiler 5; the raw steam and the heat pump working medium water vapor are heat exchanged to form condensed water, a part of which is returned to the cold side of the heat pump condenser 3 as the heat pump working medium liquid, and the other part is extracted to keep the total amount of the heat pump working medium liquid in a circulating state balanced.

[0066] In this embodiment, the ammonia nitrogen wastewater flow rate is 30m 3 / h, the ammonia nitrogen content is 20000mg / L. After treatment, the ammonia nitrogen content of the deammonified water is 12.5mg / L, the concentration of ammonia product is 22.0%, the steam consumption per ton of wastewater is 48.2kg, and the power consumption is 2.6 degrees (the efficiency of heat pump compressor 4 is 83%).

[0067] The technical solution disclosed in this embodiment can be used for the construction of new devices, and is also suitable for energy-saving transformation of the original device that uses live steam to supply heat to the reboiler. The original reboiler that uses live steam to supply heat is replaced with a reboiler with a larger heat exchange area, which is equivalent to the heat pump reboiler 5 in this embodiment. Since water is used as the working fluid of the heat pump, the live steam and pressurized steam can be mixed to supply heat to the heat pump reboiler 5.

[0068] After the transformation, the consumption of raw steam is greatly reduced compared with the original device. During operation, the reduction in raw steam can be adjusted according to the changes in raw steam and electricity prices to minimize production costs.

[0069] Embodiment 3:

[0070] The difference between Example 3 and Example 1 in terms of the device is that it further includes a live steam reboiler 8, using live steam as the heating medium. The hot side of the live steam reboiler 8 is connected with a heating medium introduction pipeline and a heating medium extraction pipeline, and the cold side of the live steam reboiler 8 is connected with the deammoniation tower 2 through a deammoniation water introduction pipeline and a steam outlet pipeline, the deammoniation water introduction pipeline is connected with the deammoniation water discharge port of the deammoniation tower 2, and the steam outlet pipeline is connected with another stripping steam feed port provided in the stripping section of the deammoniation tower 2.

[0071] The difference in method lies in that a live steam reboiler 8 is added in addition to the heat pump reboiler 5, and live steam is used as the heating medium to provide stripping steam to the deamination tower 2. Specifically, the deammoniated water at the bottom of the deamination tower 2 is divided into three parts, one part enters the cold side of the heat pump reboiler 5, another part enters the hot side of the wastewater preheater 1 and is discharged after heat exchange with ammonia nitrogen wastewater, and another part enters the cold side of the live steam reboiler 8 and is heat exchanged with the live steam entering the hot side of the live steam reboiler 8. After the heat exchange, the live steam forms condensed water for extraction, and the deammoniated water part is vaporized to form stripping steam and returned to the deamination tower 2. The unvaporized part can be returned to the deamination tower 2 through the stripping steam feed port, or can be directly extracted.

[0072] In this embodiment, the ammonia nitrogen wastewater flow rate is 60m 3 / h, the ammonia nitrogen content is 7000mg / L. After treatment, the ammonia nitrogen content of the deammonified water is 9.8mg / L, the concentration of ammonia product is 21.2%, the steam consumption per ton of wastewater is 37.6kg, and the power consumption is 2.5 degrees (the efficiency of heat pump compressor 4 is 83%).

[0073] The technical solution disclosed in this embodiment can be used for the construction of new devices, and is also suitable for energy-saving transformation of existing devices that use live steam to supply heat to the reboiler. The reboiler in the original device is equivalent to the live steam reboiler 8 in this embodiment, on this basis, a heat pump reboiler 5 is added.

[0074] After the transformation, the consumption of raw steam is greatly reduced compared with the original device. During operation, the reduction in raw steam can be adjusted according to the changes in raw steam and electricity prices to minimize production costs.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A method for treating ammonia nitrogen wastewater and recovering ammonia, characterized in that: The following steps are involved: The ammonia nitrogen wastewater is passed into a deamination tower for deamination. The deamination tower comprises a distillation section and a stripping section. An ammonia nitrogen wastewater feed port is provided between the two sections. Ammonia-containing steam is obtained from the ammonia-containing steam discharge port of the distillation section of the deamination tower. The ammonia-containing steam enters the hot side of the heat pump condenser and exchanges heat with the heat pump working fluid on the cold side of the heat pump condenser. Part of the water vapor and ammonia in the ammonia-containing steam condense to form dilute ammonia water, which leaves the hot side of the heat pump condenser and is partially or completely sent to the deamination tower as reflux liquid. The uncondensed water vapor and ammonia in the ammonia-containing steam form concentrated ammonia vapor and leave the hot side of the heat pump condenser to become a recovered ammonia resource; The heat pump working fluid on the cold side of the heat pump condenser exchanges heat with the ammonia-containing steam to generate heat pump working fluid steam, which is pressurized by the heat pump compressor and enters the hot side of the heat pump reboiler, exchanges heat with the deammonified water from the deammonification tower on the cold side of the heat pump reboiler, condenses to form heat pump working fluid and leaves the hot side of the heat pump reboiler; the deammonified water on the cold side of the heat pump reboiler exchanges heat to generate steam that returns to the deammonification tower as the stripping steam for the stripping section of the deammonification tower. The concentrated ammonia vapor leaving the hot side of the heat pump condenser enters the hot side of the spray condenser, exchanges heat with the cooling medium on the cold side of the spray condenser, and condenses to form concentrated ammonia water; part of the concentrated ammonia water returns to the hot side of the spray condenser as spray liquid, and the other part is produced as ammonia water product. The concentrated ammonia water used as the spray liquid is first cooled in the spray liquid cooler before entering the spray condenser. The step-by-step condensation method is adopted. The ammonia-containing vapor enters the heat pump condenser for primary condensation to obtain dilute ammonia water and concentrated ammonia vapor. The concentrated ammonia vapor enters the spray condenser for secondary condensation to obtain concentrated ammonia water. The cooled concentrated ammonia water is used as spray liquid for secondary condensation in the spray condenser, thereby completely condensing the concentrated ammonia vapor. Other reboilers besides the heat pump reboiler are added, and heating medium is introduced into the hot side of other reboilers. The heating medium is extracted after heat exchange with the deammoniation water from the deammoniation tower on the cold side of other reboilers. The deammoniation water is converted into steam after heat exchange and returns to the deammoniation tower. Or the heat pump working fluid is water, and the corresponding heat pump working fluid steam is heat pump working fluid water vapor. The raw steam and the heat pump working fluid water vapor are mixed and passed into the hot side of the heat pump reboiler to supply heat to the heat pump reboiler; condensed water is formed after heat exchange between the raw steam and the heat pump working fluid water vapor, a part of which is returned to the cold side of the heat pump condenser as the heat pump working fluid, and the other part is extracted.

2. The method for treating ammonia nitrogen wastewater and recovering ammonia according to claim 1, characterized in that: When the dilute ammonia water in the heat pump condenser is sent to the deamination tower, the remaining part is passed into the hot side of the spray condenser as spray liquid. The mixture of the cooled concentrated ammonia water and part of the diluted ammonia water is used as the spray liquid for the secondary condensation of the spray condenser.

3. The method for treating ammonia nitrogen wastewater and recovering ammonia according to claim 1, characterized in that: The ammonia nitrogen wastewater is heated by heat exchange with the deammonified water from the deammonification tower in the wastewater preheater, and then passed into the deammonification tower for deammonification; the deammonified water after heat exchange and heat energy recovery in the wastewater preheater is discharged to the subsequent process.

4. The method for treating ammonia nitrogen wastewater and recovering ammonia according to claim 1, characterized in that: The heat pump working fluid leaving the hot side of the heat pump reboiler is circulated to the cold side of the heat pump condenser.

5. A device for treating ammonia nitrogen wastewater and recovering ammonia, characterized in that: It includes a deamination tower, a heat pump reboiler, a heat pump condenser and a heat pump compressor; The deamination tower comprises a rectifying section and a stripping section, an ammonia nitrogen wastewater feed port is arranged between the two sections, the rectifying section is provided with an ammonia steam discharge port and a dilute ammonia water reflux port, and the stripping section is provided with a deammoniation water discharge port and a stripping steam feed port; The outlet of deammoniation water and the feed inlet of stripping steam are circulated to the cold side of the heat pump reboiler; the outlet of ammonia-containing steam and the reflux port of dilute ammonia water are circulated to the hot side of the heat pump condenser; a heat pump compressor is connected between the cold side of the heat pump condenser and the hot side of the heat pump reboiler. It also includes a spray condenser, wherein a concentrated ammonia steam pipeline is connected between the hot side of the spray condenser and the hot side of the heat pump condenser; a concentrated ammonia water extraction pipeline and a concentrated ammonia water spray pipeline are connected to the hot side of the spray condenser, and a cooling medium introduction pipeline and a cooling medium extraction pipeline are connected to the cold side of the spray condenser. The concentrated ammonia water spray pipeline is connected to a spray liquid cooler. The device also includes another reboiler, the hot side of the other reboiler is connected with a heating medium introduction pipeline and a heating medium extraction pipeline, and the cold side of the other reboiler is connected with a deamination tower through a deammoniation water introduction pipeline and a steam outlet pipeline. Alternatively, a steam mixer is connected between the heat pump compressor and the hot side of the heat pump reboiler.

6. The device for treating ammonia nitrogen wastewater and recovering ammonia according to claim 5, characterized in that: A heat pump working fluid return pipeline is connected from the hot side of the heat pump reboiler to the cold side of the heat pump condenser, forming a heat pump cycle.

7. The device for treating ammonia nitrogen wastewater and recovering ammonia according to claim 5, characterized in that: A dilute ammonia water pipeline is connected between the hot side of the heat pump condenser and the hot side of the spray liquid cooler.

8. The device for treating ammonia nitrogen wastewater and recovering ammonia according to claim 5, characterized in that: The heat pump compressor consists of one stage or multiple stages.

9. The device for treating ammonia nitrogen wastewater and recovering ammonia according to claim 5, characterized in that: The deamination tower includes a rectifying tower as a rectifying section and a stripping tower as a stripping section; or the deamination tower is formed by arranging a plurality of super gravity towers in series or in parallel.

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