Regeneration process for adsorbent for nitrogen oxides in combustion exhaust gas

Abstract

A regeneration process for an adsorbent for nitrogen oxides in combustion exhaust gas. The treatment flow comprises: heating a regeneration gas flow, then introducing same into an adsorption-saturated nitrogen oxide adsorber (7, 15) to desorb an adsorbent, and upon desorption, enabling the gas flow containing a high concentration of nitrogen oxides to be mixed with air suctioned into an internal combustion engine (4) and then undergo a combustion reaction with fuel, so that the nitrogen oxides in the gas flow are reduced into nitrogen in the fuel combustion process. Thus, the purposes of desorption and regeneration of nitrogen oxide adsorbents and gas treatment after desorption are achieved.

Description

A regeneration process for combustion tail gas nitrogen oxide adsorbent Technical Field

[0001] The invention relates to a regeneration process for a combustion tail gas nitrogen oxide adsorbent, belonging to the technical field of air pollution control and environmental protection. Background Art

[0002] Harmful nitrogen oxide gases (NO x Nitrogen oxides (NO) are primarily composed of NO and NO₂. Nitric oxide (NO) typically accounts for over 95% of the total gas, with concentrations ranging from several hundred to several thousand ppm. Exhaust from internal combustion engines in vehicles and ships is also a major source of NOx emissions. Nitrogen oxides are toxic to humans, and large amounts are a major cause of photochemical smog and acid rain.

[0003] Currently, Selective Catalytic Reduction (SCR) is the primary method for controlling NOx in fossil fuel flue gas or exhaust. However, the catalyst has stringent operating conditions and requires a reducing agent such as ammonia or urea. Sulfides, chlorides, and dust in the airstream significantly impact the catalyst's effectiveness. In particular, controlling nitrogen oxides (NOx) emissions from diesel engines is particularly challenging, requiring a reducing agent such as urea, resulting in complex and expensive systems. Technical issues

[0004] Solid adsorption can also remove nitrogen oxides from airflow, but the adsorbent needs to be regenerated after saturation. Building on the adsorbent (purifier) ​​already developed by the inventors (CN109715269A), this present invention provides a regeneration process for exhaust nitrogen oxide adsorbents used in internal combustion engines, such as automobiles and ships. Technical Solutions

[0005] The present invention solves the above-mentioned technical problems by employing a technical solution: a process for regenerating a nitrogen oxide adsorbent from exhaust gas from internal combustion engines. The regeneration process involves heating a regeneration gas flow and introducing it into a saturated nitrogen oxide adsorber to desorb the adsorbent. The desorbed gas flow, containing a high concentration of nitrogen oxides, is then mixed with the engine's intake air and returned to the burner. During fuel combustion, the nitrogen oxides in the gas flow are reduced to nitrogen, thereby achieving desorption and regeneration of the nitrogen oxide adsorbent and post-desorption gas treatment. The regeneration gas flow can be a portion of the exhaust gas from the internal combustion engine.

[0006] The present invention relates to a nitrogen oxide adsorption system for exhaust gas from an internal combustion engine, comprising an air inlet, an air valve, an internal combustion engine gas inlet, an internal combustion engine, an exhaust gas outlet, a first exhaust gas heater, a first nitrogen oxide adsorber, a first return air pipe valve, a first exhaust gas discharge valve, an exhaust gas outlet, a second exhaust gas discharge valve, a second return air pipe, a second return air pipe valve, a second nitrogen oxide adsorber, and a second exhaust gas heater. The air inlet communicates with the internal combustion engine gas inlet via the air valve. The internal combustion engine exhaust gas outlet communicates with the first nitrogen oxide adsorber via the first exhaust gas heater, and with the second nitrogen oxide adsorber via the second exhaust gas heater. The first nitrogen oxide adsorber communicates with the internal combustion engine gas inlet via the first return air pipe and the first return air pipe valve, and with the exhaust gas outlet via the first exhaust gas discharge valve. The second nitrogen oxide adsorber communicates with the internal combustion engine gas inlet via the second return air pipe and the second return air pipe valve, and with the exhaust gas outlet via the second exhaust gas discharge valve.

[0007] Among them, the function of the air valve is to adjust the air intake volume, the function of the return pipe valve is to adjust the air volume of the regeneration circuit, and the function of the exhaust gas discharge valve is to adjust the exhaust gas volume.

[0008] Adsorption process flow: The internal combustion engine operates normally, the air valve is opened according to the normal air supply, the first and second return air pipe valves are closed, and air is introduced into the internal combustion engine combustion chamber through the air inlet and the internal combustion engine gas inlet for combustion. After combustion, the exhaust gas discharged by the internal combustion engine enters the first or second nitrogen oxide adsorber (either one) through the exhaust gas outlet. The nitrogen oxides in the air flow are adsorbed and removed by the solid adsorbent in the adsorber. The purified air flow passes through the exhaust gas outlet valve after the adsorber and is discharged from the exhaust gas outlet.

[0009] When the adsorber is saturated (assuming the first nitrogen oxide adsorber is working), it enters the adsorbent regeneration mode:

[0010] Step 1: Close the first exhaust gas discharge valve and keep the second return air pipe valve closed.

[0011] Step 2: According to the set air volume relationship, the openings of the air valve, the first return air pipe valve and the second exhaust gas discharge valve are adjusted respectively, so that a part of the exhaust gas discharged from the exhaust outlet of the internal combustion engine is heated by the first exhaust heater and then introduced into the first nitrogen oxide adsorber, so that the nitrogen oxides adsorbed by the adsorbent in the adsorber are desorbed. After desorption, the nitrogen oxide-containing gas flow passes through the first return air pipe and is mixed with the fresh air after passing through the air valve, and then is introduced into the combustion chamber of the internal combustion engine through the gas inlet of the internal combustion engine, where a combustion reaction occurs, so that the nitrogen oxides in the exhaust gas are reduced to nitrogen. The other part of the exhaust gas discharged from the exhaust outlet of the internal combustion engine is adsorbed by the second nitrogen oxide adsorber to remove the nitrogen oxides contained therein, and then discharged through the second exhaust gas discharge valve and the exhaust outlet.

[0012] Step 3: After the adsorbent in the first nitrogen oxide adsorber is regenerated, the first return air pipe valve is closed, the first exhaust gas discharge valve and the second return air pipe valve are kept closed, and the internal combustion engine is restored to normal working state. At this time, the second nitrogen oxide adsorber is in operation.

[0013] According to the above steps, the first nitrogen oxide adsorber and the second nitrogen oxide adsorber are operated alternately.

[0014] The nitrogen oxide adsorbent described in the present invention is a solid compound or a mixed compound composed of at least one element of iron, cobalt, manganese or copper, at least one element of sodium, potassium, lithium, calcium, barium or magnesium, and at least one component of sulfate, chlorine or carbonate. The specific preparation method, adsorption and operating parameters, etc. have been described in detail in the aforementioned documents disclosed by the inventors and will not be described again here.

[0015] The adsorbent can also be an active ingredient containing at least one metal oxide of iron, cobalt, manganese, copper, cerium, or zirconium. Alumina and kaolin can be used as a matrix, with carbonates such as calcium carbonate and barium carbonate as additives. The regeneration performance is generally comparable to the aforementioned adsorbents. The preparation method generally involves mixing a metal nitrate solution of the aforementioned oxide with the relevant matrix and additive (aluminum oxide and calcium carbonate, for example) in a specific proportion. The mixture is then granulated, dried (at approximately 60-95°C), and activated (at approximately 500-700°C) to produce the granular adsorbent. The active metal oxide content is generally no more than 90%, while the matrix and additive content is generally above 10%.

[0016] The adsorbent described herein generally operates at a temperature above 100°C, preferably between 200°C and 400°C. Adsorbents containing iron or cobalt as primary active ingredients may operate at higher temperatures, while those containing manganese or copper may operate at lower temperatures (for details, see the aforementioned related patents). The adsorption capacity of nitrogen oxides by the adsorbent is approximately 0.1% to 1% of the adsorbent's mass, which can be determined through simulation experiments.

[0017] The nitrogen oxide adsorber described in the present invention is generally a fixed bed adsorber, and the adsorbent can be formed into a spherical, flat or honeycomb shape. The adsorbent loading capacity can be designed based on the continuous adsorption working time of the adsorbent under the standard working conditions of the internal combustion engine, preferably 80 to 120 hours. The regeneration temperature of the adsorbent is generally above 350°C, preferably 450-650°C, and varies according to the composition of the adsorbent. The regeneration temperature of the adsorbent with iron and cobalt as the main components can be higher, and the adsorbent with manganese and copper as the main components can be lower. The residence time of the desorbed gas in the adsorber is generally above 0.5s, preferably 2-5s. The exhaust gas heater can adopt a variety of heating means such as electric furnace, heat conducting medium, electromagnetic or microwave, etc., with comparable effects.

[0018] The gas volume used for adsorbent regeneration is generally 50% or less of the total exhaust gas emitted by the internal combustion engine, preferably 5-10%. The specific amount is selected based on needs, with no special requirements. Generally, a large amount of regenerated exhaust gas, after mixing with air, reduces the oxygen content in the gas entering the internal combustion engine, which is beneficial for the reduction of nitrogen oxides. However, too low a concentration may lead to an increase in carbon monoxide concentration in the exhaust gas. The average concentration of nitrogen oxides in the regenerated gas is generally 3000-9000 ppm. After reacting with the fuel during the internal combustion engine combustion process, it can be reduced by approximately 80%. This is mainly related to the equilibrium constant of the relevant reaction, and the main influencing factors are oxygen content and combustion temperature. During adsorbent regeneration, the oxygen content in the exhaust gas is preferably below 12%, and the optimal range is 5-10%. Under regeneration conditions, the concentration of nitrogen oxides in the exhaust gas outlet of the internal combustion engine increases slightly compared to standard conditions, generally within 30%.

[0019] During regeneration of the nitrogen oxide adsorbent described herein, in addition to using a portion of the exhaust gas from fuel combustion, inert gases such as nitrogen, argon, and carbon dioxide can also be used as the regeneration gas stream, with comparable effectiveness. A certain concentration of reducing gases, such as hydrogen, ammonia, methane, and formaldehyde, can also be added to the regeneration gas stream to assist in the reduction process. The concentration should generally be roughly equivalent to the nitrogen oxide concentration in the regeneration gas stream and can be added as needed.

[0020] The combustion exhaust gas mentioned in the present invention is mainly the combustion exhaust gas of various internal combustion engines (including mobile sources such as vehicles and ships), and can also be related airflows generated by other industrial processes, including thermal power generation, building materials and smelting, etc., which are generated by fossil fuel combustion or other processes containing nitrogen oxides. Beneficial effects

[0021] Compared with the existing technology, the advantages of the present invention are: partially combusted exhaust gas is heated and introduced into the nitrogen oxide adsorber, so that the nitrogen oxides adsorbed by the adsorbent are desorbed and released, and then the desorbed airflow containing high concentrations of nitrogen oxides is mixed with air and returned to the combustion chamber of the internal combustion engine, so that the nitrogen oxides in the airflow are reduced to nitrogen during the fuel combustion process, thereby achieving the purpose of regenerating the nitrogen oxide adsorbent. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG1 is a schematic diagram of a combustion exhaust nitrogen oxide adsorption system.

[0023] In the figure: 1; air inlet; 2 air duct valve; 3 internal combustion engine gas inlet; 4 internal combustion engine; 5 internal combustion engine exhaust outlet; 6 first exhaust gas heater; 7 first nitrogen oxide adsorber; 8 first return air pipe valve; 9 first return air pipe; 10 first exhaust gas discharge valve; 11 exhaust gas outlet; 12 second exhaust gas discharge valve; 13 second return air pipe; 14 second return air pipe valve; 15 second nitrogen oxide adsorber; 16 second exhaust gas heater. Best Mode for Carrying Out the Invention

[0024] The best mode for carrying out the present invention is described in detail in Example 1. Modes for Carrying Out the Invention

[0025] The present invention is further described in detail below with reference to the accompanying drawings and examples.

[0026] Example 1: A combustion exhaust nitrogen oxide adsorption system is shown in FIG1 . It mainly comprises an air inlet (1), an air valve (2), an internal combustion engine gas inlet (3), an internal combustion engine (4), an exhaust gas outlet (5), a first exhaust gas heater (6), a first nitrogen oxide adsorber (7), a first return air pipe valve (8), a first return air pipe (9), a first exhaust gas discharge valve (10), an exhaust gas outlet (11), a second exhaust gas discharge valve (12), a second return air pipe (13), a second return air pipe valve (14), a second nitrogen oxide adsorber (15), and a second exhaust gas heater (16).

[0027] The air inlet (1) is connected to the gas inlet (3) of the internal combustion engine through the air valve (2). The exhaust gas outlet (5) of the internal combustion engine (4) is connected to the first nitrogen oxide adsorber (7) through the first exhaust gas heater (6), and is connected to the second nitrogen oxide adsorber (15) through the second exhaust gas heater (16). The first nitrogen oxide adsorber (7) is connected to the gas inlet (3) of the internal combustion engine through the first return gas pipe (9) and the first return gas pipe valve (8), and is connected to the exhaust gas outlet (11) through the first exhaust gas discharge valve (10). The second nitrogen oxide adsorber (15) is connected to the gas inlet (3) of the internal combustion engine through the second return gas pipe (13) and the second return gas pipe valve (14), and is connected to the exhaust gas outlet (11) through the second exhaust gas discharge valve (12).

[0028] Among them, the function of the air valve (2) is to adjust the air intake volume, the function of the return pipe valves (8) and (11) is to adjust the regeneration circuit air volume, and the function of the exhaust gas discharge valves (10) and (12) is to adjust the exhaust gas volume.

[0029] Adsorption process flow: The internal combustion engine operates normally, the air valve (2) is fully opened according to the normal air supply, and the return air pipe valves (8) and (14) are closed. Air is introduced into the internal combustion engine from the air inlet (1) and the internal combustion engine gas inlet (3) to burn the fuel. The exhaust gas discharged by the internal combustion engine (4) is introduced into any nitrogen oxide adsorber (5) or (12) through the exhaust gas outlet (5). The nitrogen oxides in the air flow are removed by the adsorbent in the adsorber through a gas-solid adsorption reaction. The purified air flow is discharged through the exhaust gas outlet (11) corresponding to the adsorber through the exhaust gas outlet valve (10) or (12) (one open and one closed).

[0030] When the adsorber is saturated (assuming the first nitrogen oxide adsorber), it enters the adsorbent regeneration mode:

[0031] Step 1: Close the first tail gas discharge valve (10) and keep the second return gas pipe valve (14) closed.

[0032] Step 2: According to the set gas volume relationship, the openings of the air valve (2), the first air return pipe valve (8) and the second exhaust gas discharge valve (12) are respectively adjusted, so that a part of the exhaust gas discharged from the exhaust outlet (5) of the internal combustion engine (5) (regenerated exhaust gas) is heated by the first exhaust heater (6) and then introduced into the first nitrogen oxide adsorber (7), so that the nitrogen oxides adsorbed by the adsorbent filling layer of the adsorber are desorbed. The nitrogen oxide-containing gas flow after desorption passes through the first air return pipe (9) and is mixed with the air after passing through the air valve (2) and then introduced into the internal combustion engine (4) through the internal combustion engine gas inlet (3) to react with the fuel, so that the nitrogen oxides in the exhaust gas are reduced to nitrogen. The other part of the exhaust gas discharged from the exhaust outlet (5) of the internal combustion engine is adsorbed by the second nitrogen oxide adsorber (15) to remove the nitrogen oxides contained therein, and then discharged through the second exhaust gas discharge valve (12) and the exhaust outlet (11).

[0033] Step 3: When the adsorbent in the first nitrogen oxide adsorber (7) is regenerated, the first air return pipe valve (8) is closed, the first exhaust gas discharge valve (10) and the second air return pipe valve (14) are kept closed, and the internal combustion engine is restored to a normal working state (the second nitrogen oxide adsorber is working).

[0034] The first nitrogen oxide adsorber (5) and the second nitrogen oxide adsorber (12) are operated alternately according to the above steps.

[0035] The internal combustion engine described in this embodiment has a power of approximately 60 kW, a diesel fuel consumption of approximately 15 L / h, an excess air coefficient for fuel combustion of approximately 2.3, and a flue gas concentration of nitrogen oxides (including 95% nitric oxide) of approximately 500 ppm under standard operating conditions, oxygen of approximately 12% (volume, the same below), a moisture content of approximately 5%, carbon dioxide of approximately 5%, and the remainder being nitrogen.

[0036] The nitrogen oxide adsorber measures approximately 300mm x 550mm in diameter, has an insulated outer wall, and is filled with a granular adsorbent approximately 5mm in diameter. The adsorbent is prepared by mixing manganese carbonate, calcium hydroxide, sodium sulfate, and water in a molar ratio of approximately 1:2:1:6. The mixture is pelletized, dried at 65°C, and activated at approximately 600°C. The operating temperature of the adsorbent is approximately 250-300°C. The bulk density of the adsorbent is approximately 1500kg / m 3 The filling length is about 300 mm, the adsorption capacity is about 0.5% of the adsorbent mass, and the adsorption working time of the adsorbent under standard working conditions is about 80 to 100 hours, followed by desorption and regeneration. The regeneration exhaust heater uses a sleeve electric heater with a power of about 3kW. The regeneration exhaust gas volume is about 20Nm 3 / h, and at adsorbent regeneration temperatures of 450, 500, 550, 600, and 650°C, the regeneration times for complete adsorbent desorption (desorption rate ≥ 95%) were approximately 150, 120, 90, 60, and 50 minutes, respectively. Under these regeneration conditions, the average nitrogen oxide concentration in the engine exhaust outlet was approximately 900-1200 ppm. After the regeneration process was complete, the engine resumed normal operation.

[0037] Example 2: The regeneration temperature is 550°C, and the first return air valve (8) is adjusted to make the regeneration tail gas volume approximately 30, 60, 90 and 120 Nm 3 / h, and other conditions were the same as in Example 1. The regeneration times for complete desorption of the adsorbent were approximately 80 min, 60 min, 40 min, and 30 min, respectively. Under the regeneration conditions, the average concentration of nitrogen oxides in the exhaust outlet gas of the internal combustion engine was approximately 600-800 ppm.

[0038] Example 3: The adsorbent is prepared by mixing copper oxide, aluminum hydroxide, and calcium carbonate in a molar ratio of approximately 1:3:2. The preparation method is to mix copper nitrate solution (50% by mass, equivalent to copper oxide) with aluminum hydroxide and calcium carbonate powders in corresponding proportions, granulate, dry at 65°C, and activate at approximately 500°C. The regenerated tail gas volume is approximately 15 Nm 3 / h, the regeneration temperature was 500°C, and other conditions were the same as in Example 1. The adsorbent desorption regeneration time was approximately 180 min. The average concentration of nitrogen oxides in the exhaust outlet gas of the internal combustion engine under regeneration conditions was approximately 1200 ppm.

[0039] Example 4: Approximately 1% by volume of methane gas was added to the regeneration gas stream in Example 3. Other conditions were the same as in Example 3. The adsorbent desorption and regeneration time was substantially the same. Under regeneration conditions, the average nitrogen oxide concentration in the exhaust gas outlet of the internal combustion engine was approximately 800-900 ppm.

[0040] Example 5: Approximately 1% (volume) ammonia was added to the regeneration gas stream in Example 3. Other conditions were the same as in Example 3. The adsorbent desorption regeneration time was approximately 150 minutes. Under regeneration conditions, the average nitrogen oxide concentration in the exhaust gas outlet of the internal combustion engine was approximately 400-500 ppm. Industrial Applicability

[0041] The combustion exhaust gas discussed in this invention primarily refers to exhaust from various internal combustion engines (including mobile sources such as vehicles and ships), but can also be related airflows generated by other industrial processes, including fossil fuel combustion from thermal power generation, building materials production, smelting, and other processes containing nitrogen oxides. The alternating operation of the nitrogen oxide adsorbers offers a simple and reliable process with high efficiency and low operating costs.

Claims

1. A regeneration process for a combustion tail gas nitrogen oxide adsorbent, characterized in that The regeneration process is to heat the regeneration gas flow and then introduce it into the saturated nitrogen oxide adsorber to desorb the adsorbent. After desorption, the gas flow containing high concentration of nitrogen oxides is mixed with the intake gas flow of the internal combustion engine and then enters the burner. During the fuel combustion process, the nitrogen oxides in the gas flow are reduced to nitrogen, thereby achieving the purpose of desorption and regeneration of the nitrogen oxide adsorbent and post-desorption gas treatment; the composition of the nitrogen oxide adsorbent is a compound or mixture containing at least one element of the components of iron, cobalt, manganese or copper, at least one element of the components of sodium, potassium, lithium, calcium, barium or magnesium, and at least one component of the components of sulfate, chlorine or carbonate.

2. A regeneration process for a combustion tail gas nitrogen oxide adsorbent according to claim 1, characterized in that The combustion exhaust gas includes various internal combustion engine combustion exhaust gases, fossil fuel combustion, or other processes that generate nitrogen oxide-containing related gas flows.

3. The regeneration process of a combustion exhaust nitrogen oxide adsorbent according to claim 1, characterized in that The nitrogen oxide adsorbent is an adsorbent containing at least one of the oxides of metal iron, cobalt, manganese, copper, cerium or zirconium as an active ingredient.

4. The regeneration process of a combustion tail gas nitrogen oxide adsorbent according to claim 1, characterized in that The regeneration gas flow is tail gas after combustion of an internal combustion engine, or inert gas such as nitrogen, argon and carbon dioxide.

5. The regeneration process of a combustion tail gas nitrogen oxide adsorbent according to claim 1, characterized in that The regeneration gas stream contains reducing gases such as hydrogen, ammonia, methane or formaldehyde.

6. The regeneration process of a combustion tail gas nitrogen oxide adsorbent according to claim 1, characterized in that The working temperature of the nitrogen oxide adsorbent under adsorption conditions is 100-400°C.

7. The regeneration process of a combustion tail gas nitrogen oxide adsorbent according to claim 1, characterized in that The working temperature of the desorption and regeneration condition of the nitrogen oxide adsorber adsorbent is above 350°C.

8. The combustion tail gas nitrogen oxide adsorbent regeneration process according to claim 1, characterized in that The process comprises an air inlet (1), an air valve (2), an internal combustion engine gas inlet (3), an internal combustion engine (4), an exhaust gas outlet (5), a first exhaust gas heater (6), a first nitrogen oxide adsorber (7), a first return air pipe valve (8), a first return air pipe (9), a first exhaust gas discharge valve (10), an exhaust gas discharge outlet (11), a second exhaust gas discharge valve (12), a second return air pipe (13), a second return air pipe valve (14), a second nitrogen oxide adsorber (15) and a second exhaust gas heater (16), wherein the air inlet (1) is connected to the internal combustion engine gas inlet (3) via the air valve (2); the exhaust gas outlet (5) of the internal combustion engine is connected to the first nitrogen oxide adsorber (7) via the first exhaust gas heater (6), and is connected to the second nitrogen oxide adsorber (15) via the second exhaust gas heater (16); the first nitrogen oxide adsorber (7) is connected to the first return air pipe (9) and the first return air pipe valve (11). The first exhaust gas outlet (11) is connected to the exhaust gas outlet (11) via the first exhaust gas outlet valve (10); the second nitrogen oxide adsorber (15) is connected to the internal combustion engine gas inlet (3) via the second return gas pipe (13) and the second return gas pipe valve (14), and is connected to the exhaust gas outlet (11) via the second exhaust gas outlet valve (12).

9. A process for regenerating a combustion exhaust nitrogen oxide adsorbent according to claim 1 or 9, characterized in that After the adsorber is saturated with adsorption (assuming the first nitrogen oxide adsorber), it enters the adsorbent regeneration mode: Step 1: close the first exhaust gas discharge valve (10) and keep the second gas return pipe valve (14) closed; Step 2: adjusting the openings of the air valve (2), the first air return pipe valve (8) and the second exhaust gas discharge valve (12) according to the set gas volume relationship, so that a part of the exhaust gas (regeneration exhaust gas) discharged from the exhaust gas outlet (5) of the internal combustion engine is heated by the first exhaust gas heater (6) and then introduced into the first nitrogen oxide adsorber (7), so that the nitrogen oxide adsorbed by the adsorbent filling layer of the adsorber is desorbed, and the nitrogen oxide-containing gas flow after desorption passes through the first air return pipe (9) and the air mixture after passing through the air valve (2) and then introduced into the internal combustion engine (4) through the internal combustion engine gas inlet (3) to react with the fuel, so that the nitrogen oxide in the exhaust gas is reduced to nitrogen, and another part of the exhaust gas discharged from the exhaust gas outlet (5) of the internal combustion engine is adsorbed by the second nitrogen oxide adsorber (15) to remove the nitrogen oxide contained therein, and then discharged through the second exhaust gas discharge valve (12) and the exhaust gas outlet (11); Step 3: When the adsorbent in the first nitrogen oxide adsorber (7) is regenerated, the first return air pipe valve (8) is closed, the first exhaust gas discharge valve (10) and the second return air pipe valve (14) are kept closed, and the internal combustion engine is restored to a normal working state (the second nitrogen oxide adsorber is working); According to the above steps, the first nitrogen oxide adsorber (5) and the second nitrogen oxide adsorber (12) are alternately performed.

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