Tail gas treatment system for nitric acid production

Abstract

This utility model discloses a tail gas treatment system for nitric acid production, relating to the field of nitric acid production technology. The technical solution includes an evaporator and a mixer, a catalytic reduction reactor, a turbine expander, and a tail gas detector connected sequentially via pipelines. The outlet of the tail gas detector is connected to an exhaust pipeline. The tail gas detector is equipped with a nitric oxide detector, a nitrogen dioxide detector, and an ammonia detector. The evaporator is connected to a liquid ammonia pipeline and then to the mixer via an ammonia pipeline. A flow meter and a regulating valve are installed on the ammonia pipeline. The mixer is connected to a heat exchanger via a preheating tail gas pipeline, and the heat exchanger is connected to the tail gas pipeline. This utility model effectively removes nitrogen oxides from the tail gas through a catalytic reduction reaction and regulates the ammonia flow rate, combined with real-time monitoring by the tail gas detector, ensuring that the tail gas meets emission standards and completely solving the problem of yellow smoke from nitric acid tail gas.

Description

Technical Field

[0001] This utility model relates to the field of nitric acid production technology, specifically to a tail gas treatment system for nitric acid production. Background Technology

[0002] Nitrogen oxides (NO) x Nitric acid (NOx) is one of the major air pollutants. When emitted into the air, it forms yellow or brown smog, causing severe air pollution, acid rain, and ozone layer depletion. In industrial production, the nitric acid industry is a major source of NOx. x One of the main sources of emissions, its exhaust pollution problem has long plagued most nitric acid production enterprises.

[0003] The production of nitric acid mainly involves two steps: first, the oxidation of ammonia to produce NO, primarily NO2. x Gases; secondly, these NOs x After being pressurized and cooled, the gas reacts with water in the nitric acid absorption system to produce nitric acid. The nitric acid absorption system typically consists of one or two plate towers connected in series. The liquid phase inside the absorption tower is maintained at a low temperature thanks to the heat exchange system on the plates. The operating conditions of the absorption tower significantly affect the NO concentration in the exhaust gas. x The concentration of NO has a significant impact; even a slight deviation in operation can lead to an increase in NO concentration in the exhaust gas from the absorption system. x If the content exceeds the standard, yellow smoke will be emitted, and it must be treated before it can be discharged.

[0004] Currently, there are two main methods for treating nitric acid industrial tail gas: one is to improve the absorption effect by pressurizing the absorption tower and introducing low-temperature water, thereby reducing the nitrogen oxide content in the tail gas; the other is to add hydrogen peroxide to the top of the nitric acid absorption tower, allowing it to react with nitrogen oxides to produce nitric acid. However, both methods are not only difficult to control, but also have poor treatment effects and cannot completely solve the problem of yellow smoke from nitric acid tail gas. Utility Model Content

[0005] The technical problem to be solved by this utility model is to overcome the shortcomings of the existing technology and provide a tail gas treatment system for nitric acid production. It effectively removes nitrogen oxides from the tail gas through catalytic reduction reaction, regulates ammonia flow rate, and combines tail gas detectors for real-time monitoring to ensure that the tail gas meets emission standards, thus completely solving the problem of yellow smoke from nitric acid tail gas.

[0006] The technical solution of this utility model is as follows: The tail gas treatment system for nitric acid production includes an evaporator and a mixer, a catalytic reduction reactor, a turbine expander, and a tail gas detector connected in sequence by pipelines. The outlet of the tail gas detector is connected to an exhaust pipeline. The tail gas detector is equipped with a nitric oxide detector, a nitrogen dioxide detector, and an ammonia detector. The evaporator is connected to a liquid ammonia pipeline and to the mixer via an ammonia pipeline. A flow meter and a regulating valve are installed on the ammonia pipeline. The mixer is connected to a heat exchanger via a preheating tail gas pipeline, and the heat exchanger is connected to the tail gas pipeline.

[0007] Preferably, the exhaust gas detector's outlet is connected to an alkaline absorption tower via an emergency treatment bypass pipeline, and valves are installed on both the exhaust pipeline and the emergency treatment bypass pipeline.

[0008] Preferably, the emergency treatment bypass pipeline is connected to the bottom of the alkali absorption tower, and several alkali spray heads are installed at the top of the alkali absorption tower, with each spray head connected to an alkali pipeline; the alkali absorption tower is connected to an exhaust pipeline and a drain pipeline.

[0009] Preferably, exhaust pipe one and exhaust pipe two are respectively connected to the chimney.

[0010] Preferably, a temperature sensor is installed on the preheated exhaust gas pipeline, the heat exchanger is connected to a heat exchange medium inlet pipeline and a heat exchange medium outlet pipeline, and a regulating valve is installed on the heat exchange medium inlet pipeline.

[0011] Preferably, the catalytic reduction reactor is equipped with a nitrogen purging line.

[0012] Compared with the prior art, this utility model has the following advantages: 1. This utility model discloses a tail gas treatment system for nitric acid production, which can efficiently remove nitrogen oxides from the tail gas, completely solve the problem of yellow smoke from the tail gas, and ensure that emissions meet standards. The system uses a mixer to fully mix the tail gas with ammonia before sending it into a catalytic reduction reactor, where nitrogen oxides (nitric oxide and nitrogen dioxide) are reduced and removed under the action of a catalyst. Compared with existing methods that are difficult to control and have poor treatment effects, such as pressurizing the absorption tower, introducing low-temperature water, or adding hydrogen peroxide, the nitric oxide detector, nitrogen dioxide detector, and ammonia detector in this system can monitor the content of relevant components in real time. Combined with the flow meter and regulating valve on the ammonia pipeline, the ammonia flow rate can be precisely controlled to ensure that the reaction proceeds fully, effectively reduce the nitrogen oxide content in the tail gas, avoid yellow smoke, and ensure that the tail gas meets the standards when discharged through the exhaust pipeline.

[0013] 2. This utility model's tail gas treatment system for nitric acid production possesses emergency response capabilities, further ensuring the tail gas treatment effect and improving treatment reliability: When the tail gas detector detects that the tail gas continuously fails to meet standards, the tail gas can enter the alkaline absorption tower through the emergency treatment bypass pipeline, where the alkaline solution absorbs the remaining nitrogen oxides and other harmful gases in the tail gas. This emergency mechanism effectively addresses occasional tail gas exceedances caused by the difficulty in controlling existing treatment methods, enhancing the system's reliability in treating tail gas and ensuring stable compliance with tail gas emission standards. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the tail gas treatment system for nitric acid production according to this utility model.

[0015] In the diagram, 1. Evaporator; 2. Mixer; 3. Catalytic reduction reactor; 4. Turbine expander; 5. Tail gas detector; 501. Nitric oxide detector; 502. Nitrogen dioxide detector; 503. Ammonia detector; 6. Exhaust line one; 7. Liquid ammonia line; 8. Ammonia line; 801. Flow meter; 802. Regulating valve one; 9. Preheating tail gas line; 901. Temperature sensor; 10. Heat exchanger; 1001. Heat exchange medium feed line; 10011. Regulating valve two; 1002. Heat exchange medium discharge line; 11. Tail gas line; 12. Emergency treatment bypass line; 13. Alkali absorption tower; 1301. Alkali spray head; 14. Valve; 15. Alkali line; 16. Exhaust line two; 17. Drainage line; 18. Chimney; 19. Nitrogen purging line. Detailed Implementation

[0016] To enable those skilled in the art to better understand the technical solutions of this utility model, the technical solutions of this utility model will be clearly and completely described below in conjunction with the embodiments of this utility model.

[0017] Example 1 like Figure 1As shown, this embodiment provides a tail gas treatment system for nitric acid production, including an evaporator 1 and a mixer 2, a catalytic reduction reactor 3, a turbine expander 4, and a tail gas detector 5 connected in sequence by pipelines. The outlet of the tail gas detector 5 is connected to an exhaust pipeline 6, which is connected to a chimney 18. A nitric oxide detector 501, a nitrogen dioxide detector 502, and an ammonia detector 503 are installed in the tail gas detector 5. The evaporator 1 is connected to a liquid ammonia pipeline 7 and to the mixer 2 via an ammonia pipeline 8. A flow meter 801 and a regulating valve 802 are installed on the ammonia pipeline 8. The mixer 2 is connected to a heat exchanger 10 via a preheating tail gas pipeline 9, and the heat exchanger 10 is connected to a tail gas pipeline 11. The nitric oxide detector 501, nitrogen dioxide detector 502, ammonia detector 503, flow meter 801, and regulating valve 802 are electrically connected to the control system.

[0018] Working principle: The tail gas from nitric acid production enters heat exchanger 10 via tail gas pipeline 11. After being preheated in heat exchanger 10, it enters mixer 2 via preheated tail gas pipeline 9. Evaporator 1 receives liquid ammonia via liquid ammonia pipeline 7. The liquid ammonia evaporates into ammonia gas in evaporator 1 and is then transported to mixer 2 via ammonia gas pipeline 8. The ammonia gas and the preheated tail gas are thoroughly mixed in mixer 2 and then enter catalytic reduction reactor 3, where a reduction reaction occurs under the action of a catalyst to remove nitrogen oxides (nitric oxide and nitrogen dioxide) from the tail gas. The catalyst can be a conventional catalyst in the art, such as a vanadium-titanium catalyst. The gas after the reaction enters turbine expander 4 for energy recovery and then enters tail gas detector 5. Nitric oxide detector 501, nitrogen dioxide detector 502, and ammonia detector 503 in tail gas detector 5 detect the content of the corresponding gases, respectively. These detectors are electrically connected to the control system, which facilitates real-time monitoring of the content of the corresponding components in the tail gas. The control system can preset high-limit values ​​for the concentrations of each gas. When the concentrations of nitric oxide and nitrogen dioxide are detected to be higher than the preset high-limit values, the flow rate of ammonia is increased by flow meter 801 and regulating valve 802, allowing the nitric oxide and nitrogen dioxide in the exhaust gas to react fully with the ammonia. This ensures that the concentrations of nitric oxide and nitrogen dioxide detected by nitric oxide detectors 501 and 502 in the exhaust gas detector 5 are both below the preset high-limit values. When the ammonia concentration is detected to be higher than the preset high-limit value, the flow rate of ammonia is reduced by flow meter 801 and regulating valve 802, until the ammonia concentration detected by ammonia detector 503 in the exhaust gas detector 5 is below the preset high-limit value. After the exhaust gas treatment meets the standards, it is discharged through exhaust pipeline 6, which is connected to chimney 18, for high-altitude emission.

[0019] Example 2 Based on Example 1, such as Figure 1As shown, the outlet of the exhaust gas detector 5 is connected to the alkaline absorption tower 13 via the emergency treatment bypass pipeline 12. Valves 14 are installed on the exhaust pipeline 6 and the emergency treatment bypass pipeline 12, and the valves 14 are electrically connected to the control system. Specifically, the emergency treatment bypass pipeline 12 is connected to the bottom of the alkaline absorption tower 13. Several alkaline spray heads 1301 are installed at the top of the alkaline absorption tower 13, and the alkaline spray heads 1301 are connected to the alkaline pipeline 15. The alkaline absorption tower 13 is connected to the exhaust pipeline 16 and the drain pipeline 17, and the exhaust pipeline 16 is connected to the chimney 18.

[0020] When the exhaust gas detector 5 detects that the concentrations of nitric oxide and nitrogen dioxide in the post-reaction gas continue to exceed the standard (e.g., exceeding the preset high limit by 1.2 times), the control system closes valve 14 on exhaust pipeline 6 and opens valve 14 on emergency treatment bypass pipeline 12, allowing the exhaust gas to enter the alkaline absorption tower 13 for further treatment via the emergency treatment bypass pipeline 12. The exhaust gas enters the tower from the bottom, and the alkaline solution is transported to the alkaline spray head 1301 at the top of the tower via alkaline solution pipeline 15. The alkaline spray head 1301 sprays the alkaline solution downwards, ensuring full contact with the rising exhaust gas and absorbing any remaining harmful gases (such as unreacted ammonia, nitrogen oxides, etc.). The treated exhaust gas is discharged through exhaust pipeline 16, which is connected to chimney 18, allowing the exhaust gas to be discharged at high altitude. The alkaline solution that has absorbed the harmful gases is discharged outside the tower via drain pipeline 17, achieving emergency treatment of the exhaust gas. After the main system returns to normal operation, the system switches back to the main process.

[0021] Example 3 Based on Example 1, such as Figure 1 As shown, a temperature sensor 901 is installed on the preheating exhaust gas pipeline 9. The heat exchanger 10 is connected to a heat exchange medium inlet pipeline 1001 and a heat exchange medium outlet pipeline 1002. A regulating valve 10011 is installed on the heat exchange medium inlet pipeline 1001. The regulating valve 10011 is electrically connected to the control system.

[0022] A temperature sensor 901 installed on the preheating exhaust gas pipeline 9 can monitor the preheating temperature of the exhaust gas entering the mixer 2 in real time and transmit the temperature data to the control system. Based on the temperature data detected by the temperature sensor 901, the control system adjusts the opening of the regulating valve 10011 to change the feed rate of the heat exchange medium, thereby regulating the preheating temperature of the exhaust gas by the heat exchanger 10. This ensures that the temperature of the exhaust gas entering the mixer 2 is within a suitable reaction range, improving the efficiency of the subsequent catalytic reduction reaction.

[0023] Example 4 Based on Example 1, such as Figure 1 As shown, the catalytic reduction reactor 3 is equipped with a nitrogen purging line 19.

[0024] Nitrogen purging line 19 allows nitrogen to be introduced during system shutdown, maintenance, or when the catalytic reduction reactor 3 needs cleaning. Nitrogen purges residual gases (such as unreacted ammonia, harmful gases in the tail gas, etc.) from the catalytic reduction reactor 3, preventing adverse reactions from residual gases within the reactor 3, or corrosion and blockage caused by residual substances during equipment shutdown, thus ensuring equipment safety and subsequent normal operation.

Claims

1. A tail gas treatment system for nitric acid production, characterized in that, It includes an evaporator (1) and a mixer (2), a catalytic reduction reactor (3), a turbine expander (4) and a tail gas detector (5) connected in sequence by pipelines. The outlet of the tail gas detector (5) is connected to an exhaust pipeline (6). The tail gas detector (5) is equipped with a nitric oxide detector (501), a nitrogen dioxide detector (502) and an ammonia detector (503). The evaporator (1) is connected to a liquid ammonia pipeline (7) and is connected to the mixer (2) through an ammonia pipeline (8). A flow meter (801) and a regulating valve (802) are installed on the ammonia pipeline (8). The mixer (2) is connected to a heat exchanger (10) through a preheating tail gas pipeline (9). The heat exchanger (10) is connected to a tail gas pipeline (11).

2. The tail gas treatment system for nitric acid production as described in claim 1, characterized in that, The outlet of the exhaust gas detector (5) is connected to the alkaline absorption tower (13) via the emergency treatment bypass pipeline (12), and valves (14) are installed on the exhaust pipeline (6) and the emergency treatment bypass pipeline (12).

3. The tail gas treatment system for nitric acid production as described in claim 2, characterized in that, The emergency treatment bypass pipeline (12) is connected to the bottom of the alkaline absorption tower (13). Several alkaline spray heads (1301) are installed at the top of the alkaline absorption tower (13). The alkaline spray heads (1301) are connected to the alkaline pipeline (15). The alkaline absorption tower (13) is connected to the exhaust pipeline (16) and the drain pipeline (17).

4. The tail gas treatment system for nitric acid production as described in claim 3, characterized in that, The exhaust pipe one (6) and exhaust pipe two (16) are respectively connected to the chimney (18).

5. The tail gas treatment system for nitric acid production as described in claim 1, characterized in that, A temperature sensor (901) is installed on the preheating exhaust gas pipeline (9). The heat exchanger (10) is connected to a heat exchange medium feed pipeline (1001) and a heat exchange medium discharge pipeline (1002). A regulating valve (10011) is installed on the heat exchange medium feed pipeline (1001).

6. The tail gas treatment system for nitric acid production as described in claim 1, characterized in that, The catalytic reduction reactor (3) is equipped with a nitrogen purging line (19).

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