A multi-stage flash ammonia removal system and process

Abstract

The present application relates to wastewater deamination technical field, especially to a kind of multistage flash evaporation deamination system and process.The multistage flash evaporation deamination system includes multistage flash evaporation deamination tower, and the multistage flash evaporation deamination tower is connected with venturi water ejector by pipeline, and condenser is equipped on the pipeline between the multistage flash evaporation deamination tower and venturi water ejector.The present application can realize wastewater deamination and preparation of ammonium sulfate process, based on existing multistage flash evaporation heat pump rectification deamination, and multiple flash steam condensers are additionally arranged, which can be condensed before flash steam enters venturi water ejector, reduces the required injection water amount of venturi water ejector, reduces circulating pump power, improves the pumping capacity of venturi water ejector, thereby further improves the flash evaporation capacity of flash evaporation section, improves deamination effect, and simultaneously can greatly reduce the operating energy consumption of deamination process.

Description

Technical Field

[0001] This invention relates to the field of wastewater ammonia removal technology, and in particular to a multi-stage flash ammonia removal system and process. Background Technology

[0002] An ammonia stripping tower is a device used in wastewater treatment, primarily for removing nitrogen compounds, especially ammonia nitrogen, from wastewater. It effectively evaporates ammonia gas from wastewater and produces high-concentration ammonia water through absorption, thereby reducing the impact on the aquatic environment. During operation, the ammonia stripping tower requires a large amount of low-pressure steam as a heat source to evaporate the ammonia gas. The ammonia stripping effect corresponds directly to the steam consumption; the higher the steam flow rate, the better the ammonia stripping effect. Therefore, the entire ammonia stripping process is energy-intensive, and it is necessary to consider how to reduce operating energy consumption while ensuring the ammonia stripping effect.

[0003] The conventional ammonia removal process is achieved using an ammonia removal tower, which can be a packed tower or a plate tower. The ammonia-containing wastewater is first adjusted to a pH above 10. Then, the ammonia gas in the wastewater is evaporated by direct or indirect heating with low-pressure steam. The evaporated ammonia gas, along with water vapor, enters a condenser for condensation. A portion of the vapor phase water (containing a small amount of ammonia) from the evaporation process condenses and returns as reflux to the top of the ammonia removal tower. The uncondensed vapor phase, mainly ammonia gas, can enter the subsequent ammonia absorption system to prepare high-concentration ammonia water or ammonium sulfate. Ammonia-free wastewater is discharged from the bottom of the ammonia removal tower. This wastewater exchanges heat with the ammonia-containing wastewater and is then cooled by cooling water before being sent to the wastewater treatment system.

[0004] In the multi-stage flash heat pump deammoniation process, the steam consumption is about 40 kg of steam per ton of ammonia-containing wastewater and the electricity consumption is about 10 kWh per ton of wastewater. In contrast, the conventional ordinary distillation deammoniation technology consumes about 150 kg of steam per ton of wastewater and about 1 kWh per ton of wastewater.

[0005] Based on a steam price of 300 yuan / ton and an electricity cost of 0.8 yuan / kWh, the cost of ammonia removal using conventional distillation technology is approximately 45.8 yuan / ton of wastewater, while the cost of ammonia removal using a multi-stage flash heat pump process is approximately 20 yuan / ton of wastewater, which is only 44% of the cost of conventional ammonia removal technology, demonstrating a significant cost advantage.

[0006] In the existing multi-stage flash heat pump deammoniation process, the vacuum flash process of the first-stage and second-stage flash stages is achieved through a Venturi water ejector. However, since the flash vapor is directly drawn into the Venturi water ejector, the pumping capacity of the Venturi water ejector is greatly limited, resulting in a low vacuum degree in the first-stage and second-stage flash stages, which affects the deammoniation effect of wastewater. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide a multi-stage flash deammoniation system and process.

[0008] To achieve the above objectives, the technical solution adopted is:

[0009] One of the objectives of this invention is to provide a multi-stage flash ammonia removal system, including a multi-stage flash ammonia removal tower, wherein the multi-stage flash ammonia removal tower is connected to a Venturi water ejector via a pipeline, and a condenser is provided on the pipeline between the multi-stage flash ammonia removal tower and the Venturi water ejector.

[0010] Furthermore, the multi-stage flash ammonia removal system also includes an ammonia absorption tower and a tail gas absorption tower. The multi-stage flash ammonia removal tower includes, from top to bottom, a stripping section, a primary flash section, a secondary flash section, a primary mixing section, and a secondary mixing section. The Venturi water ejector includes a primary Venturi water ejector, a secondary Venturi water ejector, and a tertiary Venturi water ejector. The condenser includes a primary condenser, a secondary condenser, and a tertiary condenser. The primary Venturi water ejector is connected to the inlet of the pretreated ammonia-containing wastewater and is connected to the secondary flash section through the primary condenser. The primary Venturi water ejector and the primary condenser are connected to the primary mixing section. The secondary Venturi water ejector is connected to the primary mixing section and is connected to the primary flash section through the secondary condenser. The tertiary Venturi water ejector is connected to the secondary mixing section and is connected to the secondary flash section through the tertiary condenser. The tertiary Venturi water ejector and the tertiary condenser are connected to the primary mixing section.

[0011] Furthermore, the secondary mixing section is connected to the top inlet of the multi-stage flash ammonia removal tower at the top of the stripping section, and the concentrated ammonia outlet at the top of the multi-stage flash ammonia removal tower and the waste gas outlet of the primary mixing section are connected to the bottom of the ammonia absorption tower.

[0012] Furthermore, the outlet of the stripping section is connected to the inlet of the first-stage flash section via a pipeline. The first-stage flash section is connected to the second-stage flash tank. The second-stage flash tank is connected to a heat exchanger and is connected to the inlet of the heat exchanger for the ammonia removal wastewater to be heat-exchanged. The heat exchanger is correspondingly provided with an outlet for the ammonia removal wastewater after heat exchange. The heat exchanger is connected to the inlet of the pretreated ammonia-containing wastewater and the first-stage Venturi water ejector.

[0013] Furthermore, the secondary mixing section is connected to the primary mixing section.

[0014] Furthermore, the stripping section is connected to a Venturi steam ejector, which is also equipped with a low-pressure steam inlet and a secondary ammonia removal steam inlet. The secondary ammonia removal steam inlet is connected to the secondary ammonia removal steam outlet at the top of the tail gas absorption tower.

[0015] Furthermore, the ammonia absorption tower has a deammoniation-removed water vapor outlet at the top, which is connected to the deammoniation-removed water vapor inlet at the bottom of the tail gas absorption tower.

[0016] Furthermore, the tail gas absorption tower is provided with a sulfuric acid inlet and a sulfuric acid-ammonium sulfate solution outlet. The sulfuric acid-ammonium sulfate solution outlet is connected to the sulfuric acid-ammonium sulfate solution inlet of the ammonia absorption tower. The ammonia absorption tower is also provided with an ammonium sulfate solution outlet, which is connected to an ammonium sulfate storage tank.

[0017] Furthermore, the first circulating transfer pump is located on the pipeline between the inlet of the pretreated ammonia-containing wastewater and the heat exchanger; the second circulating transfer pump is located on the pipeline between the first outlet of the secondary mixing section and the first inlet of the tertiary venturi water ejector; the third circulating transfer pump is located on the pipeline between the first outlet of the primary mixing section and the first inlet of the secondary venturi water ejector; the fourth circulating transfer pump is located on the pipeline between the third outlet of the secondary mixing section and the top of the multi-stage flash ammonia removal tower; and the fifth circulating transfer pump is located on the pipeline between the second outlet of the secondary flash section and the heat exchanger. A water ring vacuum pump is located on the second outlet pipeline of the primary mixing section. A steam circulation heat pump is installed between the top of the multi-stage flash ammonia removal tower and the ammonia absorption tower.

[0018] The second objective of this invention is to provide a multi-stage flash ammonia removal process, employing the aforementioned multi-stage flash ammonia removal system, comprising the following steps:

[0019] The ammonia-containing wastewater to be treated undergoes alkali adjustment, sedimentation, and filtration to obtain pretreated ammonia-containing wastewater. This pretreated wastewater then passes through a heat exchanger, where it exchanges heat with the ammonia-removing wastewater from the secondary flash evaporation section before entering the primary Venturi water ejector. The ejection generates negative pressure, drawing out the flash vapor from the secondary flash evaporation section of the multi-stage flash ammonia removal tower. After condensation in the primary condenser, the vapor mixes with the heat-exchanged ammonia-containing wastewater. The liquid from the primary mixing section, after gas-liquid separation, enters the secondary Venturi water ejector. The negative pressure generated by the ejection draws out the vapor from the primary flash evaporation section. The flash vapor, after condensation in the secondary condenser, mixes with the liquid from the primary mixing section and is continuously fed into the secondary mixing section of the multi-stage flash ammonia removal tower for gas-liquid separation. The exhaust gases from the primary and secondary mixing sections are directed to the ammonia absorption tower. The liquid from the secondary mixing section enters the tertiary Venturi water ejector. The negative pressure generated by the ejection draws out the flash vapor from the secondary flash evaporation section. After condensation in the tertiary condenser, the vapor mixes with the liquid from the secondary mixing section and enters the primary mixing section.

[0020] The liquid from the secondary mixing section is transferred to the top of the multi-stage flash deammoniation tower at the top of the stripping section. Low-pressure steam and water vapor from the tail gas absorption tower after secondary deammoniation are introduced from the top of the stripping section through a Venturi steam ejector. Heat transfer occurs on the packing material above the stripping section. Ammonia gas escapes from the wastewater and, together with the concentrated ammonia gas and the waste gas from the primary and secondary mixing sections, enters the ammonia absorption tower for primary deammoniation. The ammonia gas then enters the tail gas absorption tower from the top of the ammonia absorption tower through the bottom of the tail gas absorption tower for secondary deammoniation. The remaining water vapor after secondary deammoniation returns from the top of the tail gas absorption tower to the stripping section of the multi-stage flash deammoniation tower as a heat source for stripping deammoniation.

[0021] Control the outlet valve in the stripping section to allow the stripped liquid to enter the first-stage flash section. The stripped liquid undergoes negative pressure flashing in the first-stage flash section. The flashed liquid then enters the second-stage flash section and undergoes second-stage flashing under higher vacuum conditions. The liquid after second-stage flashing is transferred out of the second-stage flash section as qualified ammonia removal wastewater and exchanges heat with the ammonia-containing wastewater to be heat-exchanged in a heat exchanger to obtain heat-exchanged ammonia removal wastewater.

[0022] Sulfuric acid enters the tail gas absorption tower, where it is circulated and sprayed to absorb ammonia. The resulting sulfuric acid-ammonium sulfate solution is transferred to the ammonia absorption tower for secondary absorption via circulated spraying. The resulting ammonium sulfate aqueous solution is then transferred from the ammonia absorption tower to the ammonium sulfate storage tank.

[0023] Furthermore, the multi-stage flash deammoniation process includes the following specific steps:

[0024] The ammonia-containing wastewater to be treated undergoes alkali adjustment, sedimentation, and filtration to obtain pretreated ammonia-containing wastewater. Driven by the first circulating transfer pump, the pretreated ammonia-containing wastewater enters the pipeline through the pretreated ammonia-containing wastewater inlet and then enters the heat exchanger through the heat exchanger's heat exchanger inlet. It exchanges heat with the heat-exchangeable ammonia-removing wastewater from the second outlet of the secondary flash evaporation section. The heat-exchangeable wastewater then enters the primary Venturi water ejector through the heat-exchangeable ammonia-containing wastewater outlet and the first inlet of the primary Venturi water ejector. The primary Venturi water ejector generates negative pressure, drawing the flash vapor from the secondary flash evaporation section of the multi-stage flash ammonia removal tower out from the first outlet of the secondary flash evaporation section. The flash vapor is condensed by the primary condenser and then exchanges heat with the heat-exchangeable ammonia-containing wastewater from the outlet of the primary Venturi water ejector. Wastewater is mixed and enters the multi-stage flash ammonia removal tower from the first inlet of the primary mixing section. After gas-liquid separation in the primary mixing section, the liquid from the primary mixing section enters the secondary venturi water ejector through the first outlet, driven by the third circulating transfer pump. The negative pressure generated by the secondary venturi water ejector draws the steam from the primary flash section out from its first outlet. The flash steam is condensed by the secondary condenser and mixed with the liquid from the primary mixing section before being continuously fed into the secondary mixing section of the multi-stage flash ammonia removal tower for gas-liquid separation. The primary and secondary mixing sections are connected by pipelines to ensure identical vacuum. The primary mixing section is evacuated by a water ring vacuum pump. The waste gas from both the primary and secondary mixing sections... The liquid from the secondary mixing section is pumped through a water ring vacuum pump to the ammonia absorption tower. Driven by the second circulating transfer pump, the liquid from the secondary mixing section enters the third-stage Venturi water ejector through the first outlet of the secondary mixing section and the first inlet of the third-stage Venturi water ejector. The negative pressure generated by the jet from the third-stage Venturi water ejector draws the flash steam from the secondary flash section out from the first outlet of the secondary flash section. After being condensed by the third-stage condenser, it mixes with the liquid from the secondary mixing section and then enters the first-stage mixing section through the outlet of the third-stage Venturi water ejector and the first inlet of the first-stage mixing section. Under the action of the fourth circulating transfer pump, the liquid from the secondary mixing section is transferred through the third outlet of the secondary mixing section to the top of the multi-stage flash ammonia stripping tower at the top of the stripping section. Low-pressure steam and exhaust gas are then transferred to the top of the multi-stage flash ammonia stripping tower. After secondary ammonia removal, the steam from the top of the absorption tower is introduced from the top of the stripping section through a Venturi steam ejector. Heat transfer occurs on the packing material above the stripping section, and ammonia gas escapes from the wastewater. The concentrated ammonia gas, along with the steam and waste gas from the primary and secondary mixing sections, passes through a steam circulation heat pump and enters the ammonia absorption tower from the bottom for ammonia removal, resulting in steam after primary ammonia removal. The ammonia-containing steam from the primary ammonia removal enters the tail gas absorption tower from the top of the absorption tower and from the bottom of the tail gas absorption tower for further ammonia removal. The remaining steam after secondary ammonia removal returns from the top of the tail gas absorption tower to the stripping section of the multi-stage flash ammonia removal tower as a heat source for stripping ammonia removal. The operating pressure of the ammonia absorption tower and the tail gas absorption tower is atmospheric pressure.The liquid outlet valve in the stripping section is controlled to allow the stripped liquid to enter the first-stage flash section at a certain flow rate. The stripped liquid undergoes negative pressure flash evaporation in the first-stage flash section. The flashed liquid then enters the second-stage flash section at a certain flow rate from the second outlet of the first-stage flash section, where it undergoes secondary flash evaporation under higher vacuum conditions. The liquid after secondary flash evaporation, as qualified ammonia-removing wastewater, is discharged from the second outlet of the second-stage flash section via the fifth circulating transfer pump. After heat exchange with the ammonia-containing wastewater to be heat-exchanged in a heat exchanger, the heat-exchanged ammonia-removing wastewater is obtained and transferred to the next process. Sulfuric acid enters the tail gas absorption tower through the sulfuric acid inlet. Ammonia gas is absorbed by circulating spray spray within the tower via a circulating transfer pump. The tail gas absorption tower has a high sulfuric acid content, and the resulting sulfuric acid-ammonium sulfate solution is transferred to the ammonia absorption tower through the sulfuric acid-ammonium sulfate solution outlet. It then undergoes secondary absorption by circulating spray spray spray via a circulating transfer pump. The resulting ammonium sulfate aqueous solution is transferred from the ammonia absorption tower to the ammonium sulfate storage tank via a circulating transfer pump.

[0025] Furthermore, the multi-stage flash deammoniation process can be extended to three-stage flash evaporation, achieving even better deammoniation results.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] This invention proposes a multi-stage flash ammonia removal system and process, which can realize wastewater ammonia removal and ammonium sulfate preparation. Based on the existing multi-stage flash heat pump distillation ammonia removal, this invention adds multiple flash vapor condensers. These condensers can condense the flash vapor before it enters the Venturi water jet pump, without affecting the pumping capacity of the water jet pump. This avoids the reduction in vacuum in the flash section caused by flash vapor entering the Venturi water jet pump. It can greatly improve the vacuum of the first-stage and second-stage flash sections without increasing the water jet volume of the Venturi water jet pump, reduce the amount of water jet required by the Venturi water jet pump, reduce the power of the circulating pump, and improve the pumping capacity of the Venturi water jet pump, thereby further improving the flash evaporation capacity of the flash section and improving the ammonia removal effect. At the same time, it can significantly reduce the operating energy consumption of the ammonia removal process. Attached Figure Description

[0028] Figure 1 This is a structural and process flow diagram of the multi-stage flash ammonia removal tower of the present invention;

[0029] Figure 2 This is a structural and process flow diagram of the ammonia absorption tower of the present invention;

[0030] Figure 3 This is a structural and process flow diagram of the tail gas absorption tower of the present invention;

[0031] Figure 4 The results of the simulation of the multi-stage flash ammonia removal process for treating ammonia-containing wastewater according to the present invention are as follows;

[0032] The attached diagram is labeled as follows: T1, multi-stage flash ammonia removal tower; T2, ammonia absorption tower; T3, tail gas absorption tower;

[0033] Q1, Stripping section; Q2, First-stage flash section; Q3, Second-stage flash section; Q4, First-stage mixing section; Q5, Second-stage mixing section;

[0034] F1, heat exchanger; E1, primary condenser; E2, secondary condenser; E3, tertiary condenser;

[0035] M1, primary Venturi water ejector; M2, secondary Venturi water ejector; M3, tertiary Venturi water ejector; M4, Venturi steam ejector; M5, steam circulation heat pump;

[0036] P1, First circulating transfer pump; P2, Second circulating transfer pump; P3, Third circulating transfer pump; P4, Fourth circulating transfer pump; P5, Fifth circulating transfer pump; P6, Water ring vacuum pump; P7, Seventh circulating transfer pump; P8, Eighth circulating transfer pump. Detailed Implementation

[0037] The present invention will be described below with reference to examples. These examples are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0038] Reference Figures 1-3 A multi-stage flash ammonia removal system includes a multi-stage flash ammonia removal tower T1, which is connected to a Venturi water ejector via a pipeline. A condenser is installed on the pipeline between the multi-stage flash ammonia removal tower T1 and the Venturi water ejector.

[0039] In a preferred embodiment, the multi-stage flash ammonia removal system further includes an ammonia absorption tower T2 and a tail gas absorption tower T3. The multi-stage flash ammonia removal tower T1, from top to bottom, includes a stripping section Q1, a primary flash section Q2, a secondary flash section Q3, a primary mixing section Q4, and a secondary mixing section Q5. The Venturi water ejector M1 includes a primary Venturi water ejector M1, a secondary Venturi water ejector M2, and a tertiary Venturi water ejector M3. The condenser includes a primary condenser E1, a secondary condenser E2, and a tertiary condenser E3. The first inlet of the primary Venturi water ejector M1 is connected to the inlet of the pretreated ammonia-containing wastewater, and the second inlet of the primary Venturi water ejector M1 is connected to the first outlet of the secondary flash section Q3 through the primary condenser E1. The outlet of the first-stage condenser E1 is connected to the first inlet of the first-stage mixing section Q4; the first inlet of the second-stage Venturi water ejector M2 is connected to the first outlet of the first-stage mixing section Q4; the second inlet of the second-stage Venturi water ejector M2 is connected to the first outlet of the first-stage flash section Q2 via the second-stage condenser E2; the outlet of the second-stage Venturi water ejector M2 is connected to the outlet of the second-stage condenser E2; the first inlet of the third-stage Venturi water ejector M3 is connected to the first outlet of the second-stage mixing section Q5; the second inlet of the third-stage Venturi water ejector M3 is connected to the first outlet of the second-stage flash section Q3 via the third-stage condenser E3; and the outlets of the third-stage Venturi water ejector M3 and the third-stage condenser E3 are connected to the first inlet of the first-stage mixing section Q4.

[0040] In this embodiment, the secondary mixing section Q5 is provided with a third outlet, and is connected to the top inlet of the stripping section Q1 via the third outlet and the fourth circulating transfer pump P4. The concentrated ammonia outlet at the top of the multi-stage flash ammonia removal tower T1 and the waste gas outlet of the primary mixing section Q4 are connected to the bottom of the ammonia absorption tower T2 via pipelines.

[0041] In an optional embodiment, the outlet of the stripping section Q1 is connected to the inlet of the first-stage flash section Q2 via a pipeline. The first-stage flash section Q2 is connected to the inlet of the second-stage flash tank via a second outlet. The second-stage flash tank is provided with a second outlet, and a heat exchanger F1 is connected to the inlet of the heat exchanger F1 for ammonia removal wastewater to be heat-exchanged. The heat exchanger F1 is provided with a corresponding outlet for ammonia removal wastewater after heat exchange. The inlet of the heat exchanger F1 for ammonia-containing wastewater to be heat-exchanged is connected to the inlet of the pretreated ammonia-containing wastewater. The outlet of the heat exchanger F1 for ammonia-containing wastewater after heat exchange is connected to the first inlet of the first-stage Venturi water ejector M1.

[0042] In an optional embodiment, the secondary mixing section Q5 is provided with a second outlet and is connected to the second inlet of the primary mixing section Q4 through the second outlet.

[0043] In a preferred embodiment, the stripping section Q1 is further provided with an inlet, which is connected to the outlet of the Venturi steam ejector M4. The Venturi steam ejector M4 is further provided with a low-pressure steam inlet and a secondary ammonia removal steam inlet, which is connected to the secondary ammonia removal steam outlet at the top of the tail gas absorption tower T3.

[0044] In this embodiment, the top of the ammonia absorption tower T2 is provided with a deammoniation-removed water vapor outlet, which is connected to the deammoniation-removed water vapor inlet at the bottom of the tail gas absorption tower T3.

[0045] In a preferred embodiment, the tail gas absorption tower T3 is provided with a sulfuric acid inlet and a sulfuric acid-ammonium sulfate solution outlet. The sulfuric acid-ammonium sulfate solution outlet is connected to the sulfuric acid-ammonium sulfate solution inlet of the ammonia absorption tower T2. The ammonia absorption tower T2 is also provided with an ammonium sulfate solution outlet and is connected to an ammonium sulfate storage tank.

[0046] The first circulating transfer pump P1 is located on the pipeline between the inlet of the pretreated ammonia-containing wastewater and the heat exchanger F1. The second circulating transfer pump P2 is located on the pipeline between the first outlet of the secondary mixing section Q5 and the first inlet of the tertiary venturi water ejector M3. The third circulating transfer pump P3 is located on the pipeline between the first outlet of the primary mixing section Q4 and the first inlet of the secondary venturi water ejector M2. The fourth circulating transfer pump P4 is located on the pipeline between the third outlet of the secondary mixing section Q5 and the top of the multi-stage flash ammonia removal tower T1. The fifth circulating transfer pump P5 is located on the pipeline between the second outlet of the secondary flash section Q3 and the heat exchanger F1. The water ring vacuum pump P6 is located on the second outlet pipeline of the primary mixing section Q4. A steam circulation heat pump M5 is installed between the top of the multi-stage flash ammonia removal tower and the ammonia absorption tower.

[0047] This invention also provides a multi-stage flash ammonia removal process, employing the aforementioned multi-stage flash ammonia removal system, comprising the following steps: The ammonia-containing wastewater to be treated undergoes alkali adjustment, sedimentation, and filtration to obtain pretreated ammonia-containing wastewater. Driven by the first circulating transfer pump P1, the pretreated ammonia-containing wastewater enters the pipeline through the pretreated ammonia-containing wastewater inlet, and then enters heat exchanger F1 through the ammonia-containing wastewater to be heat-exchanged inlet. After heat exchange with the ammonia-removed wastewater from the second outlet of the secondary flash section Q3, the wastewater enters the heat exchanger from the ammonia-containing wastewater outlet and the first inlet of the primary Venturi water ejector M1. The first-stage Venturi water ejector M1 generates negative pressure, drawing the flash vapor from the second-stage flash section Q3 of the multi-stage flash deammoniation tower T1 out through the first outlet of Q3. After condensation by the first-stage condenser E1, the flash vapor mixes with the ammonia-containing wastewater after heat exchange at the outlet of the first-stage Venturi water ejector M1. This mixture then enters the multi-stage flash deammoniation tower T1 through the first inlet of the first-stage mixing section Q4. The liquid from the first-stage mixing section Q4, after gas-liquid separation, exits through the first outlet and, driven by the third circulating transfer pump P3, enters the second-stage Venturi water ejector M2 through the first inlet. The secondary Venturi water ejector M2 generates negative pressure, drawing the steam from the first outlet of the primary flash section Q2. The flash steam, after condensation by the secondary condenser E2, mixes with the liquid in the primary mixing section Q4 and is continuously fed into the secondary mixing section Q5 of the multi-stage flash ammonia removal tower T1 for gas-liquid separation. The primary mixing section Q4 and the secondary mixing section Q5 are connected by pipelines to ensure identical vacuum. The primary mixing section Q4 is evacuated by a water ring vacuum pump P6. The exhaust gases from both sections are then pumped through the water ring vacuum pump to the ammonia adsorption section. The liquid in the secondary mixing section Q5, driven by the second circulating transfer pump P2, enters the tertiary venturi water ejector M3 through the first outlet of the secondary mixing section Q5 and the first inlet of the tertiary venturi water ejector M3. The negative pressure generated by the jet of the tertiary venturi water ejector M3 draws the flash steam of the secondary flash section Q3 out from the first outlet of the secondary flash section Q3. After being condensed by the tertiary condenser E3, it mixes with the liquid in the secondary mixing section Q5 and then enters the primary mixing section Q4 through the outlet of the tertiary venturi water ejector M3 and the first inlet of the primary mixing section Q4, and continues to circulate.

[0048] Under the action of the fourth circulating transfer pump P4, part of the liquid in the secondary mixing section Q5 is transferred to the top of the multi-stage flash deammoniation tower T1 at the top of the stripping section Q1 through the third outlet of the secondary mixing section Q5. Low-pressure steam and water vapor from the top of the tail gas absorption tower T3 after secondary deammoniation are introduced from the top of the stripping section Q1 through the Venturi steam ejector M4, and heat transfer occurs on the packing above the stripping section Q1. Ammonia gas in the wastewater escapes, along with concentrated ammonia gas from the primary mixing section Q4 and the secondary mixing section Q5. The waste gas passes through the steam circulation heat pump M5 and enters the ammonia absorption tower T2 from the bottom of the tower for ammonia removal, resulting in water vapor after primary ammonia removal. The ammonia water vapor after primary ammonia removal enters the tail gas absorption tower T3 from the top of the tower and the bottom of the tower for further ammonia removal. The remaining water vapor after secondary ammonia removal returns from the top of the tail gas absorption tower T3 to the stripping section Q1 of the multi-stage flash ammonia removal tower T1 as a heat source for stripping ammonia removal. The operating pressure of the ammonia absorption tower T2 and the tail gas absorption tower T3 is atmospheric pressure.

[0049] Control the liquid outlet valve in the stripping section Q1 to allow the stripped liquid to enter the first-stage flash section Q2 at a certain flow rate. The stripped liquid undergoes negative pressure flashing in the first-stage flash section Q2. The flashed liquid then enters the second-stage flash section Q3 at a certain flow rate from the second outlet of the first-stage flash section Q2, where it undergoes second-stage flashing under higher vacuum conditions. The liquid after second-stage flashing, as qualified deammoniation wastewater, is transferred out from the second outlet of the second-stage flash section Q3 through the fifth circulating transfer pump P5. After heat exchange with the ammonia-containing wastewater to be heat-exchanged in the heat exchanger F1, the heat-exchanged deammoniation wastewater is obtained and transferred to the next process.

[0050] Sulfuric acid enters the tail gas absorption tower T3 through the sulfuric acid inlet. Ammonia gas is absorbed by the seventh circulating transfer pump P7 through circulating spray within the tower. The tail gas absorption tower T3 has a high sulfuric acid content, and the resulting sulfuric acid-ammonium sulfate solution is transferred to the ammonia absorption tower T2 through the sulfuric acid-ammonium sulfate solution outlet. It then undergoes secondary absorption through the eighth circulating transfer pump P8 through circulating spray. The resulting ammonium sulfate aqueous solution is transferred from the ammonia absorption tower T2 to the ammonium sulfate storage tank through the eighth circulating transfer pump P8.

[0051] As a preferred embodiment, the multi-stage flash deammoniation process can be extended to three-stage flash evaporation, and can achieve better deammoniation results.

[0052] Figure 4 This is a simulation result of the multi-stage flash evaporation ammonia removal process of the present invention for treating ammonia-containing wastewater; the volume of ammonia-containing wastewater treated is 40 m³. 3 / h, the ammonia content in the wastewater is 0.5%, and the ammonia content in the treated wastewater is less than 20ppm.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A multi-stage flash ammonia removal system, characterized in that, The system includes a multi-stage flash ammonia removal tower, which is connected to a Venturi water ejector via pipeline. A condenser is installed on the pipeline between the multi-stage flash ammonia removal tower and the Venturi water ejector. From top to bottom, the multi-stage flash ammonia removal tower includes a stripping section, a first-stage flash section, a second-stage flash section, a first-stage mixing section, and a second-stage mixing section. The condenser is used to condense the flash vapor from the flash section. It also includes an ammonia absorption tower and a tail gas absorption tower. The Venturi water ejector includes a primary Venturi water ejector, a secondary Venturi water ejector, and a tertiary Venturi water ejector. The condenser includes a primary condenser, a secondary condenser, and a tertiary condenser. The primary Venturi water ejector is connected to the inlet of the pretreated ammonia-containing wastewater and is connected to the secondary flash evaporation section through the primary condenser. The primary Venturi water ejector and the primary condenser are connected to the primary mixing section. The secondary Venturi water ejector is connected to the primary mixing section and is connected to the primary flash evaporation section through the secondary condenser. The tertiary Venturi water ejector is connected to the secondary mixing section and is connected to the secondary flash evaporation section through the tertiary condenser. The tertiary Venturi water ejector and the tertiary condenser are connected to the primary mixing section.

2. The multi-stage flash ammonia removal system according to claim 1, characterized in that, The secondary mixing section is connected to the top inlet of the multi-stage flash ammonia removal tower at the top of the stripping section, and the concentrated ammonia outlet at the top of the multi-stage flash ammonia removal tower and the waste gas outlet of the primary mixing section are connected to the bottom of the ammonia absorption tower.

3. The multi-stage flash ammonia removal system according to claim 1, characterized in that, The outlet of the stripping section is connected to the inlet of the first-stage flash section via a pipeline. The first-stage flash section is connected to the second-stage flash section. The second-stage flash section is connected to a heat exchanger and is connected to the inlet of the heat exchanger for ammonia removal wastewater to be heat-exchanged. The heat exchanger is correspondingly provided with an outlet for ammonia removal wastewater after heat exchange. The heat exchanger is connected to the inlet of the pretreated ammonia-containing wastewater and the first-stage Venturi water ejector.

4. The multi-stage flash ammonia removal system according to claim 1, characterized in that, The secondary mixing section is connected to the primary mixing section.

5. The multi-stage flash ammonia removal system according to claim 4, characterized in that, The stripping section is connected to a Venturi steam ejector, which is also equipped with a low-pressure steam inlet and a secondary ammonia removal steam inlet. The secondary ammonia removal steam inlet is connected to the secondary ammonia removal steam outlet at the top of the tail gas absorption tower.

6. The multi-stage flash ammonia removal system according to claim 5, characterized in that, The ammonia absorption tower has a deammoniation-removed water vapor outlet at the top, which is connected to the deammoniation-removed water vapor inlet at the bottom of the tail gas absorption tower.

7. The multi-stage flash ammonia removal system according to claim 6, characterized in that, The tail gas absorption tower is provided with a sulfuric acid inlet and a sulfuric acid-ammonium sulfate solution outlet. The sulfuric acid-ammonium sulfate solution outlet is connected to the sulfuric acid-ammonium sulfate solution inlet of the ammonia absorption tower. The ammonia absorption tower is also provided with an ammonium sulfate solution outlet, which is connected to an ammonium sulfate storage tank.

8. A multi-stage flash evaporation ammonia removal process, characterized in that, The multi-stage flash ammonia removal system as described in any one of claims 1 to 7 includes the following steps: The ammonia-containing wastewater to be treated undergoes alkali adjustment, sedimentation, and filtration to obtain pretreated ammonia-containing wastewater. This pretreated wastewater then passes through a heat exchanger, where it exchanges heat with the ammonia-removing wastewater from the secondary flash evaporation section before entering the primary Venturi water ejector. The ejector generates negative pressure, drawing out the flash vapor from the secondary flash evaporation section of the multi-stage flash ammonia removal tower. After condensation in the primary condenser, the vapor mixes with the heat-exchanged ammonia-containing wastewater. The liquid from the primary mixing section, after gas-liquid separation, enters the secondary Venturi water ejector. The ejector generates negative pressure, drawing out the flash vapor from the primary flash evaporation section. This flash vapor, after condensation in the secondary condenser, mixes with the liquid from the primary mixing section and is continuously fed into the secondary mixing section of the multi-stage flash ammonia removal tower for gas-liquid separation. The exhaust gases from both the primary and secondary mixing sections are directed to the ammonia absorption tower. The liquid from the secondary mixing section enters the tertiary Venturi water ejector. The ejector generates negative pressure, drawing out the flash vapor from the secondary flash evaporation section. After condensation in the tertiary condenser, the vapor mixes with the liquid from the secondary mixing section and enters the primary mixing section. The liquid from the secondary mixing section is transferred to the top of the multi-stage flash deammoniation tower at the top of the stripping section. Low-pressure steam and water vapor from the tail gas absorption tower after secondary deammoniation are introduced from the top of the stripping section through a Venturi steam ejector. Heat transfer occurs on the packing material above the stripping section. Ammonia gas escapes from the wastewater and, together with the concentrated ammonia gas and the waste gas from the primary and secondary mixing sections, enters the ammonia absorption tower for primary deammoniation. The ammonia gas then enters the tail gas absorption tower from the top of the ammonia absorption tower through the bottom of the tail gas absorption tower for secondary deammoniation. The remaining water vapor after secondary deammoniation returns from the top of the tail gas absorption tower to the stripping section of the multi-stage flash deammoniation tower as a heat source for stripping deammoniation. Control the outlet valve in the stripping section to allow the stripped liquid to enter the first-stage flash section. The stripped liquid undergoes negative pressure flashing in the first-stage flash section. The flashed liquid then enters the second-stage flash section and undergoes second-stage flashing under higher vacuum conditions. The liquid after second-stage flashing is transferred out of the second-stage flash section as qualified ammonia removal wastewater and exchanges heat with the ammonia-containing wastewater to be heat-exchanged in a heat exchanger to obtain heat-exchanged ammonia removal wastewater. Sulfuric acid enters the tail gas absorption tower, where it is circulated and sprayed to absorb ammonia. The resulting sulfuric acid-ammonium sulfate solution is transferred to the ammonia absorption tower for secondary absorption via circulated spraying. The resulting ammonium sulfate aqueous solution is then transferred from the ammonia absorption tower to the ammonium sulfate storage tank.

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