Process and device for removing nitrogen oxides from exhaust gases by oxidation absorption coupled catalytic reduction

Abstract

The application discloses a process and a treatment device for denitration of nitrogen oxide waste gas by oxidation absorption coupling catalytic reduction, which comprises the following steps: S1, adjusting a valve assembly of an SCR treatment assembly, and preheating a catalyst to 220-300 DEG C; S2, blowing the waste gas and air into an oxidation tower, and stopping for 20-150 s, and opening a first circulating assembly, so that NO2 is quickly absorbed into dilute nitric acid by water and re-releases 1 / 3 amount of NO; S3, delivering the gas in the oxidation tower into an oxidation two tower, controlling the temperature to be 10-25 DEG C, stopping for 20-150 s, and opening a second circulating pump, so that NO2 is quickly absorbed into dilute nitric acid by water and re-releases 1 / 3 amount of NO; S4, mixing the reacted waste gas in the oxidation two tower and the qualified exhaust gas outside into a mixer to form mixed gas, heating the mixed gas to 180-300 DEG C, and then entering a catalytic reaction layer of an SCR furnace; S5, opening a liquid ammonia steel cylinder, inputting the gasified ammonia gas into the SCR catalytic reaction piece and reacting with the heated gas, and discharging the reaction qualified gas after heat exchange and heat recovery with the new SCR furnace waste gas.

Description

Technical Field

[0001] This invention relates to the field of nitrogen oxide treatment technology, and in particular to a process and treatment device for denitrifying nitrogen oxide waste gas by oxidation absorption coupled with catalytic reduction. Background Technology

[0002] In industries such as thermal power and metallurgy, the flow rate of nitrogen oxide exhaust gas ranges from tens of thousands to hundreds of thousands of cubic meters per hour, and its NO... X The content is generally between 200-2000 mg / m³ 3 Non-selective catalytic reduction (SCR) is generally used for treatment, employing ammonia gas converted from ammonia water, urea, or liquid ammonia as the reducing agent. For nitrogen oxide waste gas from thermal power / metallurgical industries with relatively stable concentrations / flow rates, the SCR process achieves a treatment efficiency of 80-90%, resulting in concentrations <200 mg / m³. 3 The emission standards and processes are very mature. The key technology lies in how to minimize maintenance work and extend catalyst life.

[0003] In industrial processes such as aluminum oxidation, electroplating, and metal plate pickling, the flow rate of nitrogen oxide exhaust gas is typically less than 10,000 cubic meters per hour, and its NO... X Concentration between 1000-20000 mg / m³ 3 The concentrations fluctuate drastically between these values. The SCR process has significant limitations when treating small volumes of nitrogen oxide exhaust gas with highly variable concentrations: either NO... X Excessive emissions resulting in yellow smoke indicate either severe ammonia escape. Few manufacturers are capable of operating SCR technology to treat unsteady nitrogen oxide emissions. Most companies still use traditional multi-stage alkaline washing with sodium sulfide or sodium thiosulfate reduction washing. The alkaline reduction washing process is very costly, requiring the treatment of large amounts of secondary saline wastewater. Furthermore, it often leads to excessive emissions due to insufficient time to increase the amount of reducing agent caused by drastic fluctuations in exhaust gas concentration. In addition, numerous serious incidents of hydrogen sulfide poisoning have resulted in environmental protection departments in some regions banning the use of sodium sulfide alkaline reduction washing technology for nitrogen oxide emissions treatment.

[0004] Therefore, it is necessary to develop a special process and equipment for treating high-concentration, low-volume nitrogen oxide waste gas from small and medium-sized factories. Summary of the Invention

[0005] This invention provides a process and treatment device for denitrifying nitrogen oxide waste gas by oxidation absorption coupled with catalytic reduction to solve the above problems.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] The first aspect discloses a treatment process for denitrifying nitrogen oxide waste gas through oxidation absorption coupled with catalytic reduction, including:

[0008] S1: Adjust the valve assembly, fan, and electric heater of the SCR treatment unit to preheat the catalyst to 220-300℃;

[0009] S2: After preheating, the waste gas and air are blown into the oxidation tower. The residence time in the tower is 20-150s, and the first circulation component is turned on, so that NO2 is quickly absorbed by water into dilute nitric acid and 1 / 3 of the NO is released again, and NO is oxidized into NO2.

[0010] S3: Transfer the gas in oxidation tower 1 to oxidation tower 2, control the temperature in the tower to 10-25℃, and the residence time in the tower to 20-150s. Start the second circulation pump and circulate the following reaction in the tower: NO2 is absorbed by water to form dilute nitric acid and releases 1 / 3 of the amount of NO. NO is slowly oxidized to NO2.

[0011] S4: The concentrated waste gas in the second oxidation tower and the qualified exhaust gas are mixed in the mixer to form a mixed gas. The mixed gas exchanges heat with the qualified exhaust gas in the heat exchanger in the SCR treatment component and is then heated to 180-300℃ in the electric heater.

[0012] S5: Open the liquid ammonia cylinder to output liquid ammonia. The liquid ammonia is vaporized through the vaporizer and mixed with the waste gas that has been heated to 180-300℃. It passes through the three-stage catalyst layer of the SCR furnace and undergoes a reduction reaction to generate N2. Then it is discharged to the heat exchanger to exchange heat with the new waste gas. Part of it is discharged and part of it is returned to the front of the device to mix with the new waste gas.

[0013] In one embodiment, S2 includes:

[0014] S21: Blow the waste gas and air into the oxidation tower;

[0015] S22: Ensure that the residence time in the oxidation tower is 20-150 seconds, and at the same time, use circulating water to absorb the generated NO2 into dilute nitric acid;

[0016] S23: Collect 15-22% concentration dilute nitric acid by pumping it out continuously or intermittently.

[0017] In one embodiment, S3 includes:

[0018] S31: The gas discharged from the first oxidation tower is blown into the second oxidation tower;

[0019] S32: Ensure that the gas residence time in the second oxidation tower is 20-150 seconds and the temperature inside the tower is 10-25℃. At the same time, use circulating water to absorb the generated NO2 and turn it into dilute nitric acid.

[0020] S33: Send part of the dilute nitric acid produced in the second oxidation tower into the first oxidation tower, and add fresh pure water to the tower.

[0021] In one embodiment, S5 further includes:

[0022] S6: When the temperature of the catalytic reactor is >420℃, the high-temperature gas will be directly discharged without recovering heat through a heat exchanger.

[0023] In one embodiment, the NOx content in the qualified gas discharged by S5 is less than 50 mg / m³. 3 The oxygen content is between 6% and 15%.

[0024] On the other hand, a treatment device for denitrifying nitrogen oxide waste gas by oxidation absorption coupled with catalytic reduction is provided, including: an oxidation tower, an oxidation tower, and an SCR treatment component;

[0025] The first oxidation tower has a waste gas inlet for inputting waste gas. The top of the first oxidation tower is connected to the second oxidation tower via a pipeline for inputting the reacted waste gas into the second oxidation tower. The top of the second oxidation tower is connected to a mixing tank via a pipeline, and the SCR treatment unit is connected through the mixing tank.

[0026] In one embodiment, the oxidation tower is further connected to a first circulation assembly, which includes a tower circulation pump and a tower spray system. The tower circulation pump is connected to the tower spray system at the bottom and top of the oxidation tower via pipelines, respectively, for circulating spray water to absorb NO2 and form dilute nitric acid.

[0027] The second oxidation tower is also connected to a first circulation component. The second circulation component includes a second tower circulation pump and a second tower spray component. The second tower circulation pump is connected to the second tower spray component at the bottom and top of the second oxidation tower respectively through pipelines, and is used to circulate spray water to absorb NO2 to form dilute nitric acid.

[0028] In one embodiment, both the first oxidation tower and the second oxidation tower are connected to a recovery pipeline, which is used to indirectly or continuously recover the generated 15-22% concentration dilute nitric acid.

[0029] It also includes an oxidation pipeline that connects the second oxidation tower and the first oxidation tower, and is used to spray the generated dilute nitric acid into the first oxidation tower through the second tower circulation pump.

[0030] In one embodiment, the SCR treatment assembly includes: a fan, a heat exchanger, an electric heater, and a catalytic reactor connected sequentially via pipelines. The catalytic reactor contains three catalyst layers in the channel for the flow of exhaust gas. The mixing tank mixes the gas treated by the second oxidation tower with the qualified exhaust gas, and the mixed gas is driven by the fan to the heat exchanger and electric heater for heating. The heated mixed gas then reacts with the catalyst in the catalytic reactor to absorb NO. XAfter passing the emission test, the gas enters the heat exchanger and exchanges heat with the newly added gas. Part of the mixed gas after heat exchange enters the mixing tank and mixes with the gas output from the second oxidation tower. The other part of the mixed gas after heat exchange is discharged to the outside.

[0031] It also includes a liquid ammonia storage tank, which is connected to the catalytic reaction unit via a pipeline.

[0032] In one embodiment, it further includes: a water supply valve, an oxygen control valve, an ammonia regulating valve, a temperature sensor, a high-temperature regulating valve, an exhaust stack CEMS detector, and a controller;

[0033] The oxygen control valve is connected to the air inlet of the oxidation tower and electrically connected to the controller. The exhaust stack CEMS detector is connected to the pipeline through which the mixed gas is discharged to the outside and electrically connected to the controller. The ammonia regulating valve is connected to the pipeline between the liquid ammonia storage tank and the catalytic reactor.

[0034] The water supply valve is connected to the water supply pipeline of the second oxidation tower and is electrically connected to the controller;

[0035] The temperature sensor is electrically connected to the controller and is used to detect the temperature of the catalytic reaction module;

[0036] One end of the high-temperature regulating valve is connected to the pipeline between the heat exchanger and the catalytic reaction module, and the other end is connected to the pipeline that discharges the mixed gas to the outside.

[0037] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0038] Before the SCR treatment components, the waste gas is first passed through the first oxidation tower. Under uncontrolled temperature conditions, circulating spray water absorbs some of the NO2, and the NO will slowly oxidize into NO2 for 20-150 seconds, initially absorbing the nitrogen oxides in the waste gas. Then, the remaining waste gas is fed into the second oxidation tower. Under the controlled temperature of 10-25℃ in the second tower, the circulating spray lasts for 20-150 seconds. Using a two-stage oxidation absorption process can smooth out the peak and valley of NOx content in the waste gas. This can buffer and balance the inlet concentration of the waste gas to prevent the subsequent SCR furnace or reduction scrubbing tower from overheating, emitting yellow smoke, or requiring frequent electric heating for reheating. It can also recover nitric acid and significantly reduce the cost of reagents required for operation.

[0039] On the other hand, the controller is electrically connected to and controls the liquid level filling and temperature in the secondary oxidation absorption unit, achieving full automation and reducing factors caused by improper operation. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the structure of the multifunctional portable pressurization device according to an embodiment of the present invention. Figure 1 .

[0041] In the diagram: 1. Oxidation Tower 1; 11. Tower 1 spray system; 12. Tower 1 circulating pump; 2. Oxidation Tower 2; 21. Tower 2 spray system; 22. Tower 2 circulating pump; 4. Fan; 5. Heat exchanger; 6. Electric heater; 7. Catalytic reactor; 8. Mixing tank; a. Water supply valve; b. Oxygen control valve; c. Ammonia regulating valve; e. High temperature regulating valve; f. Exhaust stack CEMS detector; g. Safety valve; h. Loop valve; i. Emergency valve. Detailed Implementation

[0042] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided to make the invention more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and therefore repeated descriptions of them will be omitted.

[0043] The terms used to express position and direction in this invention are illustrated with reference to the accompanying drawings, but changes can be made as needed, and all such changes are included within the scope of protection of this invention.

[0044] Reference Figure 1 This invention provides a process for treating nitrogen oxide waste gas by oxidation absorption coupled with catalytic reduction, comprising:

[0045] S1: Adjust the valves, fan 4, and electric heater of the SCR treatment component to preheat the catalyst to 220-300℃. Preheating the SCR section completes the preheating of the catalyst, ensuring its activity meets catalytic requirements.

[0046] The valve assembly includes a safety valve g, a high-temperature regulating valve e, and a loop valve h. The emergency valve i, safety valve g, high-temperature regulating valve e, and furnace inlet valve are closed. Loop valve h and furnace inlet valve are opened, blower 4 is turned on and operates at low frequency, and electric heater 6 is turned on to preheat the catalyst to its ignition temperature of 180-300℃. Using loop preheating can shorten the preheating time and improve the subsequent SCR effect on waste gas treatment.

[0047] S2: The waste gas and air are blown into oxidation tower 1, where they stay for 20-150 seconds. The first circulation component is then activated, allowing NO2 to be quickly absorbed by water into dilute nitric acid and 1 / 3 of the NO to be released again.

[0048] In one embodiment, S2 includes:

[0049] S21: The waste gas and air are blown into oxidation tower 1.

[0050] S22: Ensure that the residence time in oxidation tower 1 is 20-150 seconds, while circulating water absorbs the generated NO2 and turns it into dilute nitric acid.

[0051] S23: Collect 15-22% concentration dilute nitric acid by pumping it out continuously or intermittently.

[0052] After preheating, the waste gas and air are fed into oxidation tower 1 together to absorb nitrogen oxides in the waste gas and reduce the nitrogen oxide peak. A circulating spray system absorbs NO2 from the water to generate dilute nitric acid. This 15-22% concentration dilute nitric acid is continuously or intermittently pumped out and collected for supply to the workshop, saving production costs.

[0053] S3: Transfer the gas in oxidation tower 1 to oxidation tower 2, control the temperature in oxidation tower 2 to 10-25℃, and keep it in the tower for 20-150s. Start the second circulation pump and circulate the following reaction in the tower: NO2 is absorbed by water to form dilute nitric acid and releases 1 / 3 of the amount of NO. NO is slowly oxidized to NO2.

[0054] In one embodiment, S3 includes:

[0055] S31: The gas discharged from oxidation tower 1 is blown into oxidation tower 2;

[0056] S32: Ensure that the residence time of the gas in the second oxidation tower 2 is 20-150 seconds and that the temperature inside the tower is 10-25℃. At the same time, use circulating water to absorb the generated NO2 and turn it into dilute nitric acid.

[0057] S33: Send part of the dilute nitric acid produced in oxidation tower 2 into oxidation tower 1, and add fresh pure water to the tower.

[0058] NO is absorbed and pre-treated through secondary oxidation. X This reduces the peak value of nitrogen oxides in the exhaust gas. In the example, when it exceeds 3000 mg / m³, 3 When ultra-high concentration waste gas passes through a secondary oxidation process, NO can be reduced. X The content was reduced to 1000 mg / m³ by peak reduction and valley leveling. 3 The following can both buffer and balance the inlet concentration of exhaust gas to prevent overheating, yellow smoke emission, or frequent electric heating supplementation of SCR treatment components or reduction scrubbing tower, and can also recover 20% concentration of nitric acid.

[0059] S4: The waste gas after concentration in the second oxidation tower 2 and the qualified exhaust gas are mixed in the mixer to form a mixed gas. The mixed gas exchanges heat with the qualified exhaust gas in the heat exchanger 5 in the SCR treatment component and is then heated to 180-300℃ in the electric heater 6.

[0060] The qualified exhaust gas is mixed with the waste gas that has undergone secondary oxidation treatment, so that the NO in the mixed gas is reduced.X The content is reduced, thus reducing the NO content in the exhaust gas input to the SCR unit. X The content should be controlled to prevent subsequent SCR treatment components from failing to remove NO from the exhaust gas. X Absorption to below 50 mg / m 3 Ultra-low emission standards.

[0061] S5: Outputs liquid ammonia. The liquid ammonia is vaporized through a vaporizer and mixed with the waste gas that has been heated to 180-300℃. The mixed ammonia and heated waste gas pass through the three-stage catalyst layer of the SCR furnace, where a reduction reaction is carried out to generate N2. Then, it is discharged to heat exchanger 5 to exchange heat with the new waste gas entering the SCR furnace. Part of it is discharged and part is returned to the front of the device to mix with the new waste gas. The ammonia is then input into the catalytic reaction element 7 to react with the heated gas, and the qualified gas is discharged.

[0062] Liquid ammonia can be heated externally via a 20-45℃ water bath coil to evaporate the liquid ammonia flowing through the coil. The vaporized ammonia is then introduced into the catalytic reactor 7 and mixed with NO in the exhaust gas after passing through the mixing tank 8. X reaction.

[0063] In a preferred embodiment, S5 further includes:

[0064] S6: When the temperature of the catalytic reaction element 7 is >420℃, the high-temperature gas is directly discharged without recovering heat through the heat exchanger 5.

[0065] When the reaction temperature inside the catalytic reactor 7 is greater than 420°C, it is not necessary to exchange heat between the waste gas after the reaction and the newly added waste gas to raise the temperature of the newly added waste gas. Instead, it can be directly discharged, which can ensure that the temperature of the waste gas entering the catalytic reactor 7 is always kept within an effective range and avoid overheating that could lead to danger.

[0066] The NOx content in the qualified gas discharged from S5 is less than 50 mg / m³. 3 The oxygen content is between 6% and 15%.

[0067] Another aspect of the present invention discloses a treatment device for denitrifying nitrogen oxide waste gas by oxidation absorption coupled with catalytic reduction, comprising: an oxidation tower 1, an oxidation tower 2, and an SCR treatment component.

[0068] The oxidation tower 1 has a waste gas inlet and an oxygen inlet for oxygen to enter. The top of the oxidation tower 1 is connected to the oxidation tower 2 via a pipeline for inputting the waste gas after the reaction into the oxidation tower 2. The top of the oxidation tower 2 is connected to the mixing tank 8 via a pipeline, and the SCR treatment component is connected through the mixing tank 8.

[0069] The waste gas and oxygen from the air are introduced into oxidation tower 1. Inside oxidation tower 1, water is circulated and sprayed for 20-150 seconds without temperature control, absorbing some of the NO2. The remaining gas is transported through pipelines to oxidation tower 2, where it is circulated and sprayed for 20-150 seconds at 10-25℃ to remove NO2 from the waste gas. X The reabsorption removes NO from the exhaust gas. X The concentration peak.

[0070] In one embodiment, the oxidation tower 1 is further connected to a first circulation assembly, which includes a tower circulation pump 12 and a tower spray element 11. The tower circulation pump 12 is connected to the tower spray element 11 at the bottom and top of the oxidation tower 1 respectively through pipelines, and is used to circulate spray water to absorb NO2 to form dilute nitric acid.

[0071] The second oxidation tower 2 is also connected to a first circulation assembly. The second circulation assembly includes a second tower circulation pump 22 and a second tower spray component 21. The second tower circulation pump 22 is connected to the second tower spray component 21 at the bottom and top of the second oxidation tower 2 respectively through pipelines, and is used to circulate spray water to absorb NO2 to form dilute nitric acid.

[0072] Under the action of circulating pump 12 and circulating pump 22, water is fully sprayed into oxidation tower 1 and oxidation tower 2, thereby removing NO from the waste gas. X It is fully absorbed and converted into dilute nitric acid.

[0073] In a preferred embodiment, both oxidation tower 1 and oxidation tower 2 are connected to recovery pipelines, which are used to indirectly or continuously recover the generated dilute nitric acid with a concentration of 15-22%. The concentration of dilute nitric acid in oxidation tower 1 is monitored in real time. When the concentration threshold of 15-22% is reached, the recovery pipeline is activated. During operation, a corrosion-resistant nitric acid pump can be used to drive the recovery pipeline to draw out the dilute nitric acid from oxidation tower 1, so that the drawn-out nitric acid can be supplied to the production workshop for later use.

[0074] It also includes an oxidation pipeline connecting the second oxidation tower 2 and the first oxidation tower 1, for spraying the generated dilute nitric acid into the first oxidation tower 1 via the second tower circulation pump 22. The oxidation pipeline can also return the dilute nitric acid generated in the second oxidation tower 2 to the first oxidation tower 1.

[0075] In one embodiment, the SCR treatment assembly includes: a fan 4, a heat exchanger 5, an electric heater 6, and a catalytic reactor 7 connected sequentially by pipelines. The mixing tank 8 mixes the gas absorbed and treated by the oxidation tower 2 with the qualified exhaust gas, and drives the mixed gas through the fan 4 to the heat exchanger 5 and the electric heater 6 for heating. The heated mixed gas then reacts with the catalyst in the catalytic reactor 7 to absorb NO. XAfter passing the emission test, the gas enters heat exchanger 5 and exchanges heat with the newly added gas in heat exchanger 5. Part of the mixed gas after heat exchange enters the mixing tank 8 and the gas output from the oxidation tower 2 for mixing. The other part of the mixed gas after heat exchange is discharged to the outside.

[0076] After secondary oxidation, the waste gas and qualified exhaust gas are mixed in the mixing tank 8, and then driven by the fan 4 into the heat exchanger 5 to initially raise the temperature. After being heated by the electric heater 6, the temperature is raised again to the reaction temperature of the waste gas, 180-360℃, and then the waste gas is introduced into the catalytic reaction unit 7.

[0077] It also includes a liquid ammonia storage tank, which is connected to the catalytic reactor 7 via a pipeline. The liquid ammonia is vaporized by heating in a water bath at 20-45°C and enters the catalytic reactor 7 to react and absorb the waste gas.

[0078] In one embodiment, it further includes: a water supply valve a, an oxygen control valve b, an ammonia regulating valve c, a temperature sensor, a high-temperature regulating valve e, an exhaust stack CEMS detector f, and a controller.

[0079] The oxygen control valve b is connected to the air inlet of the oxidation tower 1 and electrically connected to the controller. The exhaust stack CEMS detector f is connected to the pipeline from which the mixed gas is discharged to the outside and electrically connected to the controller. The ammonia regulating valve c is connected to the pipeline between the liquid ammonia storage tank and the catalytic reactor 7. During operation, the exhaust stack CEMS detector f is installed on the exhaust pipeline to detect the content of nitrogen oxides and oxygen in the exhaust gas. When the content of nitrogen oxides and oxygen in the emitted gas is lower than a preset range, the controller controls the oxygen control valve b and the ammonia regulating valve c to control the emission of oxygen and liquid ammonia in the entire system, thereby automating the control and preventing ammonia escape and new pollution. Through the controller's automated control coordination, the amount of oxygen and ammonia input can be controlled in real time based on the nitrogen oxide content in the exhaust gas, improving the flexibility and controllability of the entire system and preventing accidents.

[0080] The water supply valve a is connected to the water supply pipelines of oxidation tower 2 and oxidation tower 1 respectively, and is electrically connected to the controller.

[0081] In addition, level sensors are installed in oxidation tower 2 and oxidation tower 1. The level sensors transmit the level information to the controller, which controls the water level in oxidation tower 2 and oxidation tower 1 to maintain the water level, thereby achieving automated control and avoiding the danger of manual water addition.

[0082] The temperature sensor is electrically connected to the controller and is used to detect the temperature of the catalytic reaction module.

[0083] One end of the high-temperature regulating valve e is connected to the pipeline between the heat exchanger 5 and the catalytic reaction module, and the other end is connected to the pipeline that discharges the mixed gas to the outside. When the temperature inside the catalytic reaction module is too high, the high-temperature regulating valve e opens, preventing the exhaust gas after the reaction from further increasing the temperature of the newly added exhaust gas through heat conduction. This avoids the temperature on the catalytic reaction module from continuing to rise. Both the first-tower circulation pump 12 and the second-tower circulation pump 22 are electrically connected to the controller.

[0084] Example 1 of this application:

[0085] The processing apparatus and processing method provided in this application are used.

[0086] 500m³ of exhaust gas inlet 3 / h, NO concentration 32000 mg / m 3 Temperature 30-45℃, oxygen content 0, and 150-300m 3 Air enters an oxidation tower (4m long, 3m wide, 2m high) along with other air. 6000L of pure water is added to the tower's bottom, and the gas is continuously circulated and sprayed for washing. Oxidation is exothermic, and the exhaust gas temperature inside the tower can reach 50-60℃. When the concentration of recovered nitric acid in the bottom of the tower is sampled and found to be >20%, most of the recovered nitric acid is pumped out and returned to the workshop for the preparation of 40% nitric acid (1800kg of 20% nitric acid can be recovered daily, valued at 900 yuan / day). After primary oxidation washing, the exhaust gas enters a... In oxidation tower 2, the dilute acid pumped from the bottom is cooled to 5-10℃ using an online cooler before being sprayed for washing. After nitric acid is recovered in tower 1, the dilute acid from oxidation tower 2 is pumped into oxidation tower 1. Fresh pure water is added from the top of the demister layer in oxidation tower 2 to wash the demister packing. The entire water replacement process is fully automated by PLC control. After two-stage oxidation and washing, the NO concentration in the exhaust gas is <1000mg / m³. 3 The gas enters the mixing tank 8 of the SCR unit at a temperature of 10-20℃ and mixes with part of the returned SCR exhaust gas. The power consumption of the circulation pump is <7 kWh / h, and the power consumption is about 150 yuan / day.

[0087] Fan 4 sends the waste gas mixture into the SCR treatment unit (designed treatment load 2000 m3 / h), where it exchanges heat with the 280℃ external exhaust gas through heat exchanger 5 and is further heated by electric heating to 180-260℃ (if the NOx concentration in the initial waste gas entering the SCR unit exceeds 1500 mg / m3). 3 (Electrically heated, requiring almost no additional heating) Ammonia gas is introduced from the top of the catalyst. After reacting through three layers of catalyst, part of the gas is discharged externally, and part is returned to the SCR unit inlet. The NOx content detected by the CEMS in the exhaust chimney is used to control the ammonia gas regulating valve, and the concentration of nitrogen oxides in the emitted gas is 35 mg / m³. 3It meets ultra-low emission standards. Ammonia consumption is 2-5 kg / h, electricity consumption is 10 kWh / h, and the cost is 450 yuan / day. Including catalyst replacement, instrument maintenance, etc., the total operating cost of the entire unit is 200 yuan / day.

[0088] Comparative Example 1:

[0089] The equipment uses a traditional four-stage reduction scrubbing system with an inlet exhaust gas volume of 500 m³ / h. 3 / h, NO concentration 32000 mg / m 3 The temperature is 30-45℃, and the product passes through a four-stage alkaline washing and reduction tower in sequence. The system automatically adds 30% liquid alkali to control the pH of the washing solution to 8-12, and automatically adds 20% sodium thiosulfate solution to control the ORP value of the washing solution to <-500. The concentration of nitrogen oxides in the output exhaust gas is 200-500 mg / m³. 3 It consumes 1 ton of 30% liquid alkali and 1 ton of 98% sodium thiosulfate every day, producing 7,000 kg of wastewater containing 20% ​​salt. Including electricity consumption and wastewater treatment fees, the daily operating cost is 3,250 yuan.

[0090] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the invention without departing from the principles and spirit of the invention, and all such changes should fall within the protection scope of the claims of the present invention.

Claims

1. A treatment process for denitrifying nitrogen oxide waste gas using oxidation absorption coupled with catalytic reduction, characterized in that, include: S1: Adjust the valves, fans, and electric heaters of the SCR treatment components to preheat the catalyst to 220-300℃; S2: Blow the waste gas and air into the oxidation tower one. Under uncontrolled temperature conditions, the residence time in the tower is 20-150s. Start the first circulation component and continuously repeat the following reaction in the tower: NO2 is absorbed by water to form dilute nitric acid and 1 / 3 of the NO is released again; NO is oxidized to NO2; S3: Transfer the gas in the oxidation tower one to the oxidation tower two. Control the temperature in the oxidation tower two to 10-25℃. The residence time in the tower is 20-150s. Start the second circulation pump and circulate the following reaction in the tower: NO2 is absorbed by water to form dilute nitric acid and 1 / 3 of the NO is released again; NO is slowly oxidized to NO2; S4: The concentrated waste gas from the second oxidation tower enters the SCR system. In the mixer of the SCR system, it mixes with the qualified exhaust gas to form a mixed gas. The mixed gas exchanges heat with the qualified exhaust gas in the heat exchanger of the SCR treatment component and is then heated to 180-300℃ in the electric heater. S5: The liquid ammonia cylinder is opened to output liquid ammonia. The liquid ammonia is vaporized through the vaporizer and mixed with the waste gas that has been heated to 180-300℃. The mixed ammonia and the heated waste gas pass through the three-stage catalyst layer of the SCR furnace and undergo a reduction reaction to generate N2. Then, it is discharged to the heat exchanger to exchange heat with the new waste gas entering the SCR furnace. Part of it is discharged and part is returned to the front of the device to mix with the new waste gas.

2. The processing technology according to claim 1, characterized in that, S2 includes: S21: blowing waste gas and air into the oxidation tower; S22: ensuring the residence time in the oxidation tower is 20-150 seconds, while circulating water absorbs the generated NO2 to become dilute nitric acid; S23: continuously or intermittently pumping out and collecting dilute nitric acid with a concentration of 15-22%.

3. The processing technology according to claim 2, characterized in that, The S3 The process includes: S31: blowing the gas discharged from the first oxidation tower into the second oxidation tower; S32: ensuring that the gas residence time in the second oxidation tower is 20-150 seconds and that the temperature inside the tower is 10-25℃, while circulating water absorbs the generated NO2 to become dilute nitric acid; S33: sending part of the dilute nitric acid generated in the second oxidation tower back into the first oxidation tower and adding fresh pure water to the tower.

4. The processing technology according to claim 3, characterized in that, S5 further includes: S6: When the temperature of the catalytic reaction element is >420°C, the high-temperature gas is directly discharged without recovering heat through a heat exchanger.

5. The processing technology according to claim 4, characterized in that, The qualified gas discharged from S5 has a NOx content of less than 50 mg / m3 and an oxygen content of 6-15%.

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