A method for testing ammonia storage capacity

Abstract

This invention provides a method for testing ammonia storage capacity. First, a small sample of catalyst is installed. Then, the catalyst sample is purged with oxygen-containing gas. Next, the temperature of the heating zone in the reactor is lowered until the catalyst inlet temperature reaches the test temperature point, and then maintained at a constant temperature. Based on the FTIR feedback of the concentration of each gas component, the set flow rates of each gas component are adjusted so that the fluctuation range of the measured concentration of each gas component meets the deviation range of the theoretical target value. NH3 is introduced into the reaction gas path, allowing the catalyst surface to fully adsorb NH3. Once NH3 adsorption is saturated, the ammonia supply is stopped. After the physically adsorbed ammonia is released, the temperature is increased to allow the chemically adsorbed ammonia to continue to be released, and the time of the initial heating is recorded. After the test, the ammonia storage capacity is calculated using an integral method. This invention's testing method is more flexible than the engine bench testing method, has better testing accuracy and repeatability, lower testing costs, and is more energy-efficient and environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the technical field of diesel vehicle exhaust aftertreatment performance index testing and evaluation, and in particular relates to a method for testing ammonia storage capacity. Background Technology

[0002] Integrating NH3 selective catalytic reduction (NH3-SCR) devices into the exhaust system is a key technology for NOx removal in diesel vehicles. The NH3-SCR reaction mechanism involves ammonia gas, the reducing agent, entering the carrier channels in the reactor. It is first adsorbed onto the acidic sites on the SCR catalyst surface, and then selectively reacts with NOx in the exhaust gas under the action of the SCR catalyst to produce N2 and H2O. Therefore, the adsorption and desorption rates of NH3 on the SCR catalyst surface, as well as their adsorption and desorption capabilities, are inextricably linked to the transient and steady-state performance of the SCR at different temperatures. Among these, the NH3 storage capability of the SCR at different temperatures is a key focus of its application characteristics. Currently, the only publicly available methods for assessing the ammonia storage capacity of SCR catalysts are those using engine bench testing. However, due to numerous factors such as the physicochemical properties of the urea solution itself, the size and direction of the urea droplets, exhaust temperature, and the design of the exhaust pipe space, the pyrolysis and hydrolysis rates of urea are not 100%. Some incompletely pyrolyzed and hydrolyzed urea solution adheres to the exhaust pipe, forming precipitates, crystals, and byproducts. This is a common and unavoidable problem when testing on traditional engine benches. Therefore, the theoretical ammonia storage capacity calculated using the mass conservation method will be larger than the actual ammonia storage capacity, making it difficult to accurately assess the ammonia storage capacity of the SCR catalyst itself. Existing methods cannot provide a separate quantitative assessment of the ammonia storage capacity of the SCR catalyst and are not suitable for testing and evaluation by SCR catalyst manufacturers during the product development phase. Summary of the Invention

[0003] In view of this, the present invention aims to overcome the defects in the prior art and proposes an ammonia storage capacity testing method to overcome the many shortcomings of testing the ammonia storage capacity of SCR catalysts using the traditional diesel engine bench method. It is also applicable to ammonia slip catalysts (ASCs) installed at the rear end of the SCR catalyst to capture ammonia gas leaking from the rear end of the SCR.

[0004] To achieve the above objectives, the technical solution created by this invention is implemented as follows:

[0005] A method for testing ammonia storage capacity includes the following steps:

[0006] S1. Use a sampling tool to take out a small catalyst sample from the large catalyst sample, manually refine the shape and size of the small sample, measure the size of the small sample, and calculate the volume of the small sample; use compressed air to blow away the floating dust on the outer surface and in the pores of the sample, wrap the small sample with quartz fiber cotton and put it into the reaction zone of the test reaction tube.

[0007] S2. Insert a thermocouple at the gas inlet end of the reaction tube to measure the inlet temperature of the catalyst sample. The thermocouple is located in the reaction zone of the reaction tube at the point where the inlet temperature of the catalyst sample is measured.

[0008] S3. Adjust the temperature of the heating zone of the reactor so that the inlet temperature of the catalyst sample reaches 500℃~600℃; then introduce a mixture of O2 and N2 and purge until the NH3 concentration at the catalyst outlet returns to near zero, then turn off O2.

[0009] S4. Reduce the temperature of the heating zone of the reactor until the catalyst inlet temperature reaches the test temperature point and then maintain a constant temperature. While waiting for the temperature to drop, switch the gas flow to the gas distribution path and set the target flow rate of each gas component based on the theoretical flow rate calculated for each gas component.

[0010] S5. Adjust the set flow rate of each gas component based on the FTIR feedback on the concentration of each gas component, so that the fluctuation range of the measured concentration of each gas component meets the deviation range of the theoretical target value, and record the adjusted set flow rate of each gas component.

[0011] S6. Shut down NH3, keeping other atmospheres unchanged. After the NH3 concentration drops to near zero, adjust the three-way valve in the gas path to switch the gas path back to the reaction gas path;

[0012] S7. Based on the NH3 flow rate determined in the gas mixing process, NH3 is stably introduced and the ammonia introduction time is recorded. When the NH3 outlet concentration is stable at the highest point, it is confirmed that NH3 adsorption is saturated. Maintain this state for more than 3 minutes, change the NH3 introduction concentration to 0, stop the ammonia introduction, and record the time when the ammonia introduction is stopped.

[0013] S8. Keep the catalyst inlet temperature constant and wait for the ammonia physically adsorbed on the catalyst surface to be gradually released. After the physically adsorbed ammonia is completely released, increase the temperature of the heating zone of the reactor in a programmed manner to gradually release the chemically adsorbed ammonia, and record the time when the temperature rise begins.

[0014] When the catalyst inlet temperature reaches 500℃~600℃, if the NH3 outlet concentration has dropped to near zero, stop heating and the test ends; if the NH3 outlet concentration still has a certain concentration, maintain the high temperature until the NH3 outlet concentration drops to near zero, then stop heating and the test ends.

[0015] S9. The ammonia storage capacity is calculated using the integral method. The calculation formula is as follows:

[0016]

[0017]

[0018]

[0019] In the formula:

[0020] NSC i —Ammonia storage capacity (g / L), i = Phy, representing the ammonia storage capacity of the physical adsorption portion; i = Chem, representing the ammonia storage capacity of the chemical adsorption portion; i = Total, representing the total ammonia storage capacity.

[0021] C — Actual sampled value (ppm) of NH3 outlet concentration recorded at a sampling frequency of 1Hz;

[0022] t1 — the time interval (s) from the moment ammonia is stopped to the moment heating begins;

[0023] t2 — the time interval (s) from the start of heating to the end of heating;

[0024] t3—Timeout (s) from the moment ammonia is stopped to the moment heating is stopped;

[0025] Q—The actual measured value of total gas flow rate (mL / min) recorded at a sampling frequency of 1Hz;

[0026] V – Sample volume (L);

[0027] ρ — density of ammonia (771 mg / L).

[0028] Furthermore, the thermocouple is positioned 1 cm upstream of the inlet end face of the catalyst sample at the point where the inlet temperature is measured, and is located at the center line of the sample.

[0029] Furthermore, compressed air is used to blow away the floating dust on the outer surface and inside the pores of the sample, and the distance between the high-pressure air nozzle and the sample is not less than 3 cm when blowing the catalyst sample.

[0030] Furthermore, a sealing gasket is used to wrap the outer surface of the sample, so that the sample is sealed with the tube wall after being loaded into the reaction tube.

[0031] Furthermore, the length of the catalyst sample is 1 to 6 times its diameter.

[0032] Furthermore, the reactor is a segmented heating tubular reactor, including a preheating zone, a constant temperature zone, and a reaction zone.

[0033] Furthermore, the reaction tube is made of quartz, with an inner diameter of 20mm to 30mm.

[0034] Compared with existing technologies, the present invention has the following advantages:

[0035] This invention's testing method offers different handling methods for operational details to meet varying testing speed requirements, satisfying the diverse needs of rapid screening and high-precision evaluation in laboratories. It is more flexible than engine bench testing, offering better accuracy and repeatability. It overcomes the problem of inaccurate supply and overestimation of results caused by using urea-water solution to supply ammonia on an engine bench. Based on feedback from the FTIR exhaust gas analyzer regarding gas component concentrations, the mass flow rate of the gas mixture and the pump speed of the water pump are further finely adjusted, allowing for precise control of gas component concentrations and avoiding the impact of engine exhaust component fluctuations on test results. Thermocouples are used to measure temperature, achieving a temperature control accuracy of ±1℃, overcoming the impact of large engine exhaust temperature fluctuations on test accuracy. Furthermore, compared to the high fuel consumption required by the engine bench method, the main testing costs of this invention lie in gas mixture and electricity, resulting in lower testing costs, better energy efficiency and environmental friendliness, higher safety, and fewer supporting equipment and facilities. Attached Figure Description

[0036] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0037] Figure 1 A schematic diagram of the experimental curves in Example 1 of this invention;

[0038] Figure 2 This is a schematic diagram of the experimental curves in Example 3 of the present invention. Detailed Implementation

[0039] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0040] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0041] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0042] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0043] A method for testing ammonia storage capacity includes the following steps:

[0044] S1. Using a sampling tool, remove a small catalyst sample from the large catalyst sample. Manually refine the sample's dimensions, measuring its length and diameter at different locations (measure at least three times at each location). Calculate the average length and diameter, and then calculate the sample volume using the formula for cylinder volume. Typically, the average diameter and length measured at different locations are used as input values ​​for the sample's dimensions. Use compressed air to blow away any dust from the sample's outer surface and pores. Slowly push the sample into the reaction zone of the test reaction tube; the reaction tube is a quartz tube with a circular opening. It should be noted that when taking the sample, a saw blade or a cylindrical sampling mold (preferably a cylindrical sampling tool) can be used to cut a cylindrical sample from the catalyst carrier. The diameter of the catalyst sample should match the inner diameter of the reaction tube, ideally fitting perfectly inside. The length of the catalyst sample can be 1 to 6 times its diameter, and it is recommended that the aspect ratio of the sample be consistent with the original aspect ratio of the catalyst. Typically, a sealing gasket is used to wrap the outer surface of the sample to ensure a seal between the sample and the tube wall after it is inserted into the reaction tube.

[0045] S2. Insert a thermocouple at the gas inlet end of the reaction tube to measure the inlet temperature of the catalyst sample. The thermocouple should be positioned within the reaction zone of the reaction tube at the inlet temperature measurement point. The sample inlet should be 1 cm away from the inlet of the reaction zone. The inner diameter of the reaction tube is generally 20 mm to 30 mm; however, according to industry practice, a quartz tube inner diameter of 26 mm is recommended. The length of the quartz tube should match that of the tube furnace and should not be too long to prevent water vapor in the reaction tube from condensing outside the tube furnace.

[0046] Before using the reaction tube, thoroughly clean the inner wall with a test tube brush or high-pressure water gun. After cleaning, blow it clean with compressed air to ensure the tube is clean and dry. Before conducting the ammonia storage test, purge the catalyst surface with an oxidizing atmosphere at high temperature to remove NH3 and other impurity gases adhering to the catalyst surface. Testing without purging will result in lower ammonia storage test results, as verified by experiments. Typically, use compressed air to purge the surface of the sample and remove dust from the pores. When purging the catalyst sample, the distance between the compressed air nozzle and the sample should be no less than 3 cm.

[0047] S3. Adjust the temperature of the heating zone of the reactor to bring the inlet temperature of the catalyst sample to 500℃~600℃. Select a higher temperature within the temperature range that the catalyst can tolerate to ensure more thorough and efficient purging. Then, introduce a mixture of O2 and N2. Specifically, the O2 and N2 mixture can be introduced at the same rate as the space velocity under the ammonia storage measurement conditions, with an oxygen concentration of 2%~10%. Within this range, the higher the oxygen concentration, the higher the purging efficiency. After purging until the NH3 concentration at the catalyst outlet returns to near zero, turn off the O2. This process usually takes 5-30 minutes to complete.

[0048] It should be noted that the selected reactor is preferably a tubular reactor with segmented heating. The heater has three zones: a preheating zone, a constant temperature zone, and a reaction zone (low temperature zone). The three zones of the heating zone can be temperature-controlled independently, with a temperature control accuracy of ±1℃. The preheating zone is used to preheat the reaction gas entering the reaction tube; as the gas flow passes through the preheating zone, it absorbs heat and its temperature rises. The constant temperature zone is used to further heat the gas flow; as the gas flow reaches the constant temperature zone, its temperature gradually reaches an equilibrium point. By adjusting the furnace temperatures in the preheating and constant temperature zones, the target catalyst inlet temperature can be achieved. The furnace temperature settings in the preheating and constant temperature zones should be consistent.

[0049] The reaction zone simulates the gas-solid phase reaction of the catalyst sample with hot engine exhaust gas at low ambient temperatures. To prevent condensation of water vapor entering the catalyst, which could reduce the accuracy of FTIR analysis, the reaction zone temperature of the tubular reactor must be appropriately set; a furnace temperature of 120℃ is recommended. Water vapor is supplied by filtered distilled water from a water tank, which is then metered and pumped into the vaporizer via a constant flow pump. The water vapor flow rate control accuracy should be no less than ±2%FS.

[0050] S4. Reduce the temperature of the heating zone of the tubular reactor until the catalyst inlet temperature reaches the test temperature point and then maintain a constant temperature; while waiting for the temperature to drop, switch the gas flow to the gas distribution path and set the target flow rate of each gas component based on the theoretical flow rate calculated for each gas component.

[0051] S5. A flow meter is used to control the gas flow rate. Based on the FTIR feedback of the concentration of each gas component, the set flow rate of each gas component is adjusted to ensure that the fluctuation range of the measured concentration of each gas component meets the deviation range of the theoretical target value. The adjusted set flow rate of each gas component is recorded. The flow meter is preferably a high-speed mass digital flow meter with an accuracy of not less than ±1%FS. During gas preparation, a gas cylinder is used as the gas source. After pressure reduction and filtration, the gas enters the gas flow meter. All gases, including water vapor, are thoroughly mixed by a mixer to prepare a mixed gas with the set concentration and flow rate. Then, based on the gas component concentration feedback from FTIR analysis, the set flow rate of each gas component is adjusted to ultimately ensure that the fluctuation range of the measured concentration of each gas component meets the deviation range of the theoretical target value. The mixed gas is heated by a heater in a tube furnace within a quartz reaction tube.

[0052] S6. Shut down NH3, keeping other atmospheres unchanged. After the NH3 concentration drops to near zero, adjust the three-way valve in the gas path to switch the gas path back to the reaction gas path;

[0053] S7. Based on the NH3 flow rate determined in the gas mixing process, NH3 is stably introduced and the ammonia introduction time is recorded. When the NH3 outlet concentration is stable at the highest point, it is confirmed that NH3 adsorption is saturated. Maintain this state for more than 3 minutes, change the NH3 introduction concentration to 0, stop the ammonia introduction, and record the time of stopping the ammonia introduction (accurate to the second).

[0054] S8. Keep the catalyst inlet temperature constant, and gradually release the ammonia physically adsorbed on the catalyst surface. After the physically adsorbed ammonia has been released, increase the temperature of the heating zone of the reactor in a programmed manner to gradually release the chemically adsorbed ammonia, and record the time when the temperature rise begins.

[0055] Under the desired inlet temperature (since SCRs typically operate within a temperature range of 100℃ to 500℃, one or more temperatures within this range can be selected as the observation points) and NH3 concentration (which can be determined based on the NH3 concentration in the upstream tail gas entering the actual working environment of the SCR, typically the NH3 concentration range for SCR operation is 250ppm to 2000ppm), the NH3 is made to saturate the catalyst surface.

[0056] When the catalyst inlet temperature reaches 500℃~600℃, if the NH3 outlet concentration has dropped to near zero, stop heating and the test ends; if the NH3 outlet concentration still has a certain concentration, maintain the high temperature until the NH3 outlet concentration drops to near zero, then stop heating and the test ends.

[0057] Adsorbed NH3 exists in two states: physical adsorption and acidic site adsorption. The type of adsorption (physical or chemical adsorption) can be determined by the temperature at which ammonia is released. Chemical adsorption is acidic site adsorption. At a constant temperature, ammonia adsorbed at chemical sites will not be released; only ammonia physically adsorbed on the catalyst surface by van der Waals forces will gradually detach from the catalyst surface and be released as the ammonia concentration decreases. As the temperature increases, ammonia adsorbed at chemical sites will gradually detach from the acidic sites and be released, meaning that the adsorbed ammonia is completely released through high temperature. Four ammonia release methods are provided below for different testing speed requirements. These four methods have different requirements for the NH3 outlet concentration at the time of heating and at the time of stopping the ammonia release statistics.

[0058] Method 1: Accurately calculate the ammonia storage capacity based on physical and chemical adsorption.

[0059] By keeping the catalyst inlet temperature constant, the ammonia physically adsorbed on the catalyst surface is gradually released.

[0060] When the NH3 outlet concentration drops to near zero (the physically adsorbed ammonia has been completely released), the heating zone of the tubular reactor is programmed to heat up at a rate of (5-10) °C / min, and the start time of heating is recorded. During this process, the chemically adsorbed ammonia is gradually released.

[0061] When the catalyst inlet temperature reaches (500-600)℃, if the NH3 outlet concentration has dropped to near zero, heating is stopped, and the test ends. If the NH3 outlet concentration still has a certain concentration, the high temperature is maintained until the NH3 outlet concentration drops to near zero, at which point heating is stopped, and the test ends. It should be noted that SCRs typically still have ammonia storage capacity at 450℃, but usually lose this capacity at 500℃. If the temperature is below 500℃, ammonia will be incompletely released; therefore, 500℃ is chosen as the lower limit of the ammonia desorption temperature.

[0062] Normally, ammonia is completely released when the temperature rises to 500℃. However, for some SCRs with extremely strong ammonia storage capacity and high ammonia storage, ammonia may not be completely released when the temperature rises to 500℃. In order to further increase the ammonia desorption rate, the temperature can be further increased to accelerate the release of ammonia. The normal operating temperature of SCR usually does not exceed 600℃. Choosing 600℃ as the upper limit of the ammonia release temperature can ensure that the ammonia is completely released without exceeding the normal operating temperature of the SCR and causing thermal aging of the SCR catalyst.

[0063] Method 2: Rapidly calculate the ammonia storage capacity based on physical adsorption and chemical adsorption.

[0064] The requirement in Method 1, "NH3 outlet concentration drops to near zero," is changed to "NH3 outlet concentration is less than a certain value (this value is 0.5% to 2% of the NH3 inlet concentration, and this value is related to the ammonia concentration during the ammonia storage stage; the higher the ammonia concentration during the ammonia storage stage, the higher this value can be), which can significantly reduce the time required for the ammonia release stage. The reason is that when the NH3 outlet concentration is low, the ammonia release rate is slower, and the amount of ammonia released during this stage is also smaller, accounting for a smaller proportion in the calculated value of the ammonia storage result." The other steps are the same as in Method 1. Compared with Method 1, this method can shorten the ammonia release time by about 20 min to 120 min.

[0065] Method 3: Accurately calculate the total ammonia storage.

[0066] The requirement in clause (2) of Method 1, "NH3 outlet concentration drops to near zero," is changed to "NH3 outlet concentration is less than a certain value (recommended value is 20% to 80% of NH3 inlet concentration)." That is, when it is not necessary to distinguish between the amount of ammonia stored through physical and chemical adsorption, and only the total amount of ammonia stored is calculated, the temperature can be raised after the ammonia supply stops and the ammonia concentration decreases slightly. The amount of ammonia desorbed from the time ammonia supply stops to the time heating stops is calculated as the total amount of ammonia stored. Other steps are the same as in Method 1. This method can shorten the ammonia release time by 20 to 120 minutes compared to Method 1.

[0067] Method 4: Quickly calculate the total ammonia storage.

[0068] The requirement in clause (2) of Method 2, "NH3 outlet concentration drops to near zero," is changed to "NH3 outlet concentration is less than a certain value (recommended value is 20% to 80% of NH3 inlet concentration)." The other steps are the same as in Method 2. This method can shorten the ammonia release time by 10 to 60 minutes compared to Method 2.

[0069] This invention also provides four ammonia removal methods based on different testing requirements (whether to distinguish between physical adsorption and chemical adsorption, and whether to pursue high testing efficiency). The methods have better repeatability and use the amount of ammonia released during the ammonia release stage as the ammonia storage capacity of the sample. Compared with the calculation method of directly calculating the amount of ammonia stored during the ammonia storage stage, this method is more accurate and can eliminate the error introduced by the fluctuation of ammonia concentration during the ammonia storage stage when the ammonia storage is close to saturation.

[0070] S9. The ammonia storage capacity is calculated using the integral method. The calculation formula is as follows:

[0071]

[0072]

[0073]

[0074] In the formula:

[0075] NSC i —Ammonia storage capacity (g / L), i = Phy, representing the ammonia storage capacity of the physical adsorption portion; i = Chem, representing the ammonia storage capacity of the chemical adsorption portion; i = Total, representing the total ammonia storage capacity.

[0076] C — Actual sampled value (ppm) of NH3 outlet concentration recorded at a sampling frequency of 1Hz;

[0077] t1 — the time interval (s) from the moment ammonia is stopped to the moment heating begins;

[0078] t2 — the time interval (s) from the start of heating to the end of heating;

[0079] t3—Timeout (s) from the moment ammonia is stopped to the moment heating is stopped;

[0080] Q—The actual measured value of total gas flow rate (mL / min) recorded at a sampling frequency of 1Hz;

[0081] V – Sample volume (L);

[0082] ρ — density of ammonia (771 mg / L).

[0083] The thermocouple is positioned 1 cm upstream of the catalyst sample inlet temperature measurement point, centered on the sample's centerline. Maintaining a certain distance between the measurement point and the catalyst prevents the catalyst's exothermic or endothermic effects from influencing the inlet temperature measurement results. Industry practice typically involves a 1 cm interval, and this measurement point should be located within the reaction zone of the quartz tube.

[0084] It should be noted that the FTIR of the Fourier Transform Infrared (FTIR) analyzer preferably uses a single-channel sampling head with a resolution of not less than 0.5 cm. -1 This system is used to collect and analyze the concentrations of various components in the gas streams at the catalyst inlet and outlet. The sampling point is located at the intersection of the quartz reaction tube outlet and the gas distribution path outlet. A three-way valve is installed at the intersection of the quartz reaction tube inlet and the gas distribution path inlet to switch the gas stream between the reaction path and the gas distribution path. When the gas stream switches to the gas distribution path, the FTIR analysis data represents the component concentration at the catalyst inlet; when the gas stream switches to the reaction path, the FTIR analysis data represents the component concentration at the catalyst outlet.

[0085] Advantages compared to the traditional diesel engine bench method: First, this method directly introduces ammonia gas into the reaction pipeline, eliminating the interference caused by incomplete pyrolysis and hydrolysis of urea solution in the exhaust pipeline, resulting in precipitation, crystallization, and byproducts that affect the ammonia storage capacity of the SCR catalyst. This significantly improves the correlation between test results and the sample's inherent characteristics, thus greatly enhancing test accuracy. Second, the use of gas cylinders to supply the reaction gas and an electrically heated reactor to provide the heat source allows for accurate and convenient control of test conditions (reaction gas component concentration, reaction gas flow rate, catalyst inlet temperature). Compared to the diesel engine bench method, the control precision of test condition parameters is higher, and the repeatability and reproducibility of the test are greatly improved. Third, the use of a heated tubular simulated reactor replaces the diesel engine bench, eliminating the need for the intake air conditioning, iron floor, fuel inlet pipeline, and other supporting facilities required for a diesel engine bench laboratory; it also eliminates the need for diesel engine dynamometers, fuel consumption meters, and other supporting instruments and equipment; and it avoids the safety hazards posed by the high heat generated during diesel engine operation and the high-speed rotating dynamometer drum. Meanwhile, compared with the diesel engine bench method, this method reduces the equipment footprint, lowers the requirements for supporting facilities, significantly reduces equipment purchase and operating costs, and improves the safety of the test operation.

[0086] Example 1:

[0087] Using SCR catalyst A as the test object, a small sample size was taken. The ammonia storage capacity based on physical and chemical adsorption was accurately calculated using Method 1, with a test space velocity of 40,000 h⁻¹. -1 The test inlet temperature was 250℃, the NH3 concentration was 1200ppm, and the H2O concentration was 8%.

[0088] (1) Oxygen purging: The air velocity setting of the input airflow is 40000 h. -1 The input gas composition is 10% O2 (v / v), with N2 as the balance gas. Oxygen-containing gas is introduced to purge the catalyst and remove NH3 adhering to its surface. 10% O2 and N2 are continuously introduced until the measured NH3 concentration at the catalyst outlet drops below 2 ppm, at which point the O2 is shut off. This process takes approximately 5–15 minutes. Precise control of the O2 concentration is not required in this step; the ultimate goal is to completely purge the catalyst of NH3.

[0089] (2) Gas Distribution: Lower and adjust the furnace temperature setpoints in the preheating and isothermal zones of the tubular furnace to reduce the catalyst inlet temperature to the test temperature point (250±2)℃ and maintain it at a constant temperature. For example, during the cooling process, switch the gas path from the reaction gas path to the distribution gas path, inputting a new gas component with an NH3 concentration of 1200ppm and an H2O concentration of 8%. Based on the NH3 and H2O concentrations fed back by the FTIR analyzer, adjust the setpoints for the NH3 and H2O flow rates until the NH3 and H2O concentrations reach the target control accuracy. Then stop the NH3 flow. When the NH3 outlet concentration is observed to drop below 5ppm, switch the gas path back to the reaction gas path. Once the H2O concentration in the reaction gas path stabilizes, record the various temperature, flow rate, and concentration data.

[0090] (3) Ammonia Storage: Adjust the NH3 flow rate setting value obtained during the gas mixing stage to allow NH3 to flow into the reaction gas path. Manually record the ammonia flow time at this moment. When the NH3 outlet concentration is observed to return to the inlet concentration level and remain stable (for more than 3 minutes), change the NH3 flow rate setting value to 0 again to stop the NH3 flow. Manually record the ammonia shutdown time at this moment (accurate to seconds). The ammonia storage time is approximately (30-50) minutes.

[0091] (4) First stage of ammonia release: The first stage of ammonia release is completed when the NH3 outlet concentration is observed to gradually decrease to below 2 ppm. The ammonia release time in this stage is about 134 min.

[0092] (5) Second stage ammonia release: The furnace temperature rise method of the preheating and constant temperature zones of the tubular furnace was changed to programmed temperature rise, with the preheating and heating zones of the tubular furnace being raised at 10℃ / min. The start time of the temperature rise was manually recorded. When the catalyst inlet temperature reached 600℃, the furnace temperature of the preheating and constant temperature zones of the tubular furnace was set to heat preservation mode, so that the catalyst inlet temperature was maintained at (600±10)℃. During the temperature rise process, secondary desorption of NH3 was observed. Data collection was stopped after the NH3 outlet concentration gradually decreased to below 1ppm. The ammonia release time in this stage was approximately 82 minutes.

[0093] (6) Plot a curve with time (in seconds from the moment NH3 is introduced) on the x-axis and NH3 outlet concentration (ppm) on the y-axis, as shown below. Figure 1 As shown in the figure. In this experiment, the NH3 was introduced for 2440 seconds. It can be observed from the curve that after the ammonia was stopped, the NH3 outlet concentration did not drop immediately, but only began to drop significantly at 2466 seconds. The period from 2441 seconds to 2465 seconds should be considered a system delay.

[0094] (7) The ammonia storage capacity at different desorption stages during the ammonia desorption process was calculated using the area integral method, with time as the integral unit. In this experiment, the integration interval for the first desorption stage (physical desorption) was from 2466 seconds to 8000 seconds, with an ammonia release time of approximately 92 minutes; the integration interval for the second desorption stage (chemical adsorption) was from 8001 seconds (start of heating) to 12925 seconds, with an ammonia release time of approximately 82 minutes; the total ammonia release time was approximately 174 minutes. After the first test, the temperature was lowered back to the test temperature, and the second and third ammonia storage tests were repeated using the same method. The results of the three parallel determinations are shown in the table below. The table shows that the relative standard deviations (RSDs) of the three parallel determinations for physical adsorption, chemical adsorption, and total adsorption (physical adsorption + chemical adsorption) were similar and all less than 1%, indicating that this method has the advantages of high accuracy and good repeatability in assessing the ammonia storage capacity at different desorption stages.

[0095] Table: Results of three parallel determinations of ammonia storage capacity in Example 1

[0096]

[0097] Example 2:

[0098] Using the sample and testing requirements in Example 1, the ammonia storage capacity based on physical adsorption and chemical adsorption was quickly calculated according to Method 2.

[0099] (4) First stage of ammonia release: Change “wait for the NH3 outlet concentration to drop to 2 ppm” to “wait for the NH3 outlet concentration to drop to 10 ppm”. The ammonia release time in this stage is about 40 minutes.

[0100] (5) Second stage of ammonia release: Change "wait for the NH3 at the outlet to drop to 1 ppm" to "wait for the NH3 at the outlet to drop to 10 ppm". The ammonia release time in this stage is about 30 minutes.

[0101] The test was performed in parallel once, and the other steps were the same as in Example 1. The total ammonia release time in Example 2 was approximately 70 min, which was about 104 min shorter than the ammonia release time in Example 1.

[0102] Example 3:

[0103] Using the sample and testing requirements from Example 1, the total ammonia storage was accurately calculated according to Method 3. During the first stage of ammonia release, the phrase "waiting for the NH3 outlet concentration to drop to 2 ppm" was changed to "waiting for the NH3 outlet concentration to drop to approximately 250 ppm". Other steps were the same as in Example 1. In Example 3, ammonia release began at 2597 seconds and ended at 6688 seconds, with a total release time of approximately 68 minutes. The experimental curve is shown below. Figure 2 As shown, the total ammonia release time in Example 3 was shortened by approximately 106 minutes compared to Example 1.

[0104] Example 4:

[0105] Using the sample and testing requirements from Example 1, the total ammonia storage capacity was quickly calculated according to Method 4. During the second stage of ammonia release: the phrase "waiting for the outlet NH3 to drop to 1 ppm" was changed to "waiting for the outlet NH3 to be below 10 ppm." This stage of ammonia release took approximately 50 minutes. Other steps were the same as in Method 3. Example 4 shortened the ammonia release time by approximately 18 minutes compared to Example 3.

[0106] Comparison of ammonia storage capacity measurement results in Examples 1-4 (Table 1)

[0107] Example 5:

[0108] Using SCR catalyst B (SCR catalysts A and B are samples from different manufacturers) as the test object, the NH3 concentration was changed, and different inlet temperatures were selected to verify the method of the present invention. Small sample sizes were taken. The total ammonia storage capacity was quickly calculated using Method 4, with a test space velocity of 100,000 h⁻¹. -1 The NH3 concentration was 500 ppm, the H2O concentration was 10%, and the test inlet temperatures were 100℃, 200℃, 250℃, 350℃, and 450℃.

[0109] (1) Oxygen purging: Increase the catalyst inlet temperature to 500℃ and purge with a space velocity of 100,000 h⁻¹ -1 After purging with 10% O2 / N2 until the NH3 concentration at the catalyst outlet drops below 2 ppm, the O2 is turned off. The process takes about 10 minutes.

[0110] (2) Lower the furnace temperature to the test temperature (±2)℃ and maintain a constant temperature. While waiting for the temperature to drop, switch the gas path to the distribution gas path, adjust the NH3 concentration to (500±5)ppm and the H2O concentration to (10±0.25)%, then shut off the NH3. After the NH3 concentration drops below 2ppm, switch the gas path to the reaction gas path. Once the H2O in the reaction gas path stabilizes, begin data acquisition at a frequency of 1Hz.

[0111] (3) Ammonia storage: Introduce NH3 at the flow rate measured in the gas distribution path and record the ammonia supply time. When the NH3 outlet concentration returns to the inlet concentration level, stop the NH3 supply and record the ammonia shutdown time (starting from whole minutes, accurate to seconds). Ammonia storage time (5-20) min.

[0112] (4) First stage of ammonia release: Under constant temperature, wait for the NH3 outlet concentration to drop to 200ppm.

[0113] (5) Second stage ammonia release: The temperature is increased to 500℃ at a programmed rate of 10℃ / min and then maintained at that temperature. The time when the temperature increases is recorded. When the outlet NH3 drops to 5ppm, the data collection is stopped and the ammonia release ends.

[0114] (6) Plot a curve with time (from the moment NH3 is introduced, s) on the x-axis and NH3 outlet concentration (ppm) on the y-axis. Calculate the amount of desorbed ammonia stored at each temperature point using the area integration method.

[0115] Table 5 Measurement Results

[0116]

[0117] This invention's testing method offers different handling methods for operational details to meet varying testing speed requirements, satisfying the diverse needs of rapid and high-precision evaluation in laboratories. It is more flexible than engine bench testing methods, offering better testing accuracy and repeatability. It overcomes the problem of inaccurate supply and overestimation of results caused by using urea-water solution to supply ammonia on an engine bench, and avoids the influence of engine exhaust composition fluctuations on the test atmosphere. The H2O source is pure water, which is quantitatively and stably pumped into the carburetor using a horizontal flow pump. After thorough vaporization in the carburetor, the water mixes evenly with other gaseous components before entering the reaction gas path. Based on feedback from the FTIR exhaust gas analyzer regarding water vapor concentration, the pump speed is further finely adjusted to precisely control the water vapor flow, avoiding the influence of fluctuations in engine exhaust water content on the test results. Thermocouples are used to measure temperature, with a temperature control accuracy of ±1℃, overcoming the impact of large engine exhaust temperature fluctuations on test accuracy. Furthermore, compared to engine fuel consumption, the main cost of this invention lies in gas distribution and electricity, resulting in lower testing costs and better energy efficiency and environmental friendliness. The above description is merely 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 method for testing ammonia storage capacity, characterized in that, Includes the following steps: S1. Take a small sample of catalyst, refine it, measure its size, and calculate its volume. Use compressed air to blow away the dust from the outer surface and pores of the sample, and slowly push the sample into the reaction zone of the test reaction tube. S2. Insert a thermocouple at the gas inlet end of the reaction tube to measure the inlet temperature of the catalyst sample. The thermocouple is located in the reaction zone of the reaction tube at the point where the inlet temperature of the catalyst sample is measured. S3. Adjust the temperature of the heating zone of the reactor to bring the inlet temperature of the catalyst sample to 500℃~600℃; then introduce... and , purge to catalyst outlet Shut down after the concentration returns to near zero ; S4. Reduce the temperature of the heating zone of the reactor until the catalyst inlet temperature reaches the test temperature point and then maintain a constant temperature. While waiting for the temperature to drop, switch the gas flow to the gas distribution path and set the target flow rate of each gas component based on the theoretical flow rate calculated for each gas component. S5. Adjust the set flow rate of each gas component based on the FTIR feedback on the concentration of each gas component, so that the fluctuation range of the measured concentration of each gas component meets the deviation range of the theoretical target value, and record the adjusted set flow rate of each gas component. S6, Shutdown The rest of the atmosphere remains unchanged, waiting After the concentration drops to near zero, adjust the three-way valve in the gas path to switch the gas path back to the reaction gas path; S7, determined in the valve timing process Stable flow of traffic Record the time of ammonia flow. After the export concentration stabilized at its peak Adsorption saturation, maintain this state for more than 3 minutes, then... Change the ammonia concentration to 0, stop the ammonia flow, and record the time when the ammonia flow was stopped; S8. Keep the catalyst inlet temperature constant and wait for the ammonia physically adsorbed on the catalyst surface to be gradually released. After the physically adsorbed ammonia is completely released, increase the temperature of the heating zone of the reactor in a programmed manner to gradually release the chemically adsorbed ammonia, and record the time when the temperature rise begins. When the catalyst inlet temperature reaches 500℃~600℃, such as The outlet concentration has dropped to near zero; heating has been stopped, and the test is now complete. The outlet concentration remains at a certain level; maintain this high temperature until... When the outlet concentration drops to near zero, heating is stopped, and the experiment ends. S9. The ammonia storage capacity is calculated using the integral method. The calculation formula is as follows: In the formula: —Ammonia storage capacity, This represents the ammonia storage capacity of the physically adsorbed portion; This represents the ammonia storage capacity of the chemisorption portion; This represents the overall ammonia storage capacity. —— Export concentration; —Timekeeping from the moment ammonia is stopped to the moment heating begins; —Timekeeping during the heating process from the start of heating to the end of heating; —Timekeeping from the moment ammonia is stopped to the moment heating is stopped; —Actual measured value of total gas flow rate; —Sample volume; —Ammonia density.

2. The ammonia storage capacity testing method according to claim 1, characterized in that: The thermocouple is positioned 1 cm upstream of the inlet temperature of the catalyst sample, at a point on the sample's inlet face, and is located at the center line of the sample.

3. The ammonia storage capacity testing method according to claim 1, characterized in that: Use compressed air to blow away the dust from the outer surface and pores of the sample, and when blowing away the catalyst sample, the distance between the compressed air nozzle and the sample should be no less than 3 cm.

4. The ammonia storage capacity testing method according to claim 1, characterized in that: The outer surface of the sample is wrapped with a sealing gasket to ensure a seal between the sample and the tube wall after the sample is placed into the reaction tube.

5. The ammonia storage capacity testing method according to claim 1, characterized in that: The length of the catalyst sample is 1 to 6 times its diameter.

6. The ammonia storage capacity testing method according to claim 1, characterized in that: The reactor is a segmented heating tubular reactor, including a preheating zone, a constant temperature zone, and a reaction zone.

7. The ammonia storage capacity testing method according to claim 1, characterized in that: The reaction tube is made of quartz and has an inner diameter of 20mm to 30mm.

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