Method and device for measuring fusion characteristics of high-alkali metal fuel ash

Abstract

The present invention provides a method and apparatus for measuring the melting characteristics of high-alkali metal fuel ash. The method comprises the following steps: preparing sample ash from the high-alkali metal fuel to be measured using a low-temperature ashing method; preparing a measurement sample from the sample ash; and measuring the measurement sample using a pressure differential method to obtain the initial sintering temperature of the measurement sample. The method and apparatus of the present invention can be widely used to measure the melting characteristics of high-alkali metal fuels, providing more accurate results.

Description

Technical Field

[0001] The present invention relates to the technical field of measuring fuel ash fusion characteristics, and in particular to the technical field of measuring ash fusion characteristics of fuel with a high alkali metal content. Background Art

[0002] Efficient energy utilization is undoubtedly a critical technological area in achieving carbon peak and carbon neutrality goals. Among my country's proven coal resources, the Zhundong Coalfield in Xinjiang boasts extremely rich reserves. It is currently the country's largest unassembled coalfield, with estimated reserves of 390 billion tons, which is of great significance in alleviating the nation's tight coal supply. Zhundong coal has medium-to-high moisture content, low ash content, high calorific value, high spontaneous combustion, and easy breakage, making it an excellent power coal. Biomass energy is my country's fourth largest energy source. It is abundant in resources and features renewable energy, high combustion efficiency, and low pollution emissions. Biomass energy, when utilized, can also contribute to the supply of clean energy, control environmental pollution, and address climate change, making it an effective measure to achieve carbon neutrality. my country currently has considerable potential for the use of biomass energy for power generation, and the biomass power generation industry is continuously expanding.

[0003] The common feature of the above energy sources is that the alkali metal content in their fuel ash is high, which can easily cause ash and slagging on the boiler heating surface during the combustion process, causing the boiler to be contaminated or even corroded, affecting the safe and economical operation of the boiler.

[0004] The melting characteristics of fuel ash are used to describe the process of fuel ash gradually changing from solid to liquid when heated. It is an important indicator to guide boiler design and operation, so that the occurrence of problems such as slagging can be avoided or reduced during boiler operation.

[0005] Currently, the domestic industry generally uses the four characteristic temperatures in GB / T 219-2008, "Determination of Ash Fusibility," to characterize fuel ash melting properties. The American National Standard ASTM D 1857-17, similar to the Chinese standard, uses the initial deformation temperature, softening temperature, hemispherical temperature, and flow temperature of the ash cone to characterize ash melting properties. For biomass fuels, China has developed a dedicated standard, GB / T 30726-2014, "Determination of Ash Fusibility of Solid Biomass Fuels."

[0006] The aforementioned standard measurement method has significant errors when measuring fuels with high alkali metal content. For example, rice husks, a biomass energy source, have a softening temperature as high as 1500°C when measured using the national standard method. However, in practice, slagging occurs when the temperature of rice husks used in circulating fluidized bed boilers is below 800°C. Summary of the Invention

[0007] To address the problem of large errors in existing methods for measuring the ash fusion characteristics of high-alkali metal fuels, the present invention provides a method for measuring the ash fusion characteristics of high-alkali metal fuels and a device for measuring the ash fusion characteristics of high-alkali metal fuels.

[0008] The technical solutions of the present invention are as follows:

[0009] A method for measuring the fusion characteristics of high alkali metal fuel ash comprises the following steps:

[0010] S1. Prepare sample ash by low-temperature ashing method for the high-alkali metal fuel to be measured;

[0011] S2. preparing the sample ash into a measurement sample;

[0012] S3. Measure the measurement sample using a pressure difference method to obtain an initial sintering temperature of the measurement sample.

[0013] Optionally, step S1 includes the following steps: the low-temperature ashing method is performed using a low-temperature ashing instrument; during the process of preparing the sample ash, the temperature setting range in the cavity of the low-temperature ashing instrument is 180°C to 220°C.

[0014] Optionally, step S2 includes the following step: preparing the sample ash into the measurement sample by a physical pressing method.

[0015] Optionally, in step S2, at least two measurement samples are prepared using the sample ash from the same batch.

[0016] Optionally, step S3 includes the following steps: placing the two measurement samples in a first sample chamber and a second sample chamber, respectively; the two measurement samples have the same shape and size, and the shape and size of the measurement samples match the internal space of the first sample chamber and the second sample chamber; and connecting the first sample chamber and the second sample chamber in series.

[0017] Optionally, the first sample chamber is provided with an air inlet channel; step S3 includes the following steps: introducing gas into the first sample chamber; and measuring the air pressure difference between the two ends of the measurement sample in the second sample chamber.

[0018] Optionally, step S3 includes the following steps: placing the two sample chambers in a heating furnace; and introducing the gas into the first sample chamber after the temperature in the heating furnace rises to a predetermined temperature.

[0019] Optionally, step S3 includes the following steps: after the gas is introduced into the first sample chamber, the heating furnace is continued to be heated until an inflection point appears in the value of the gas pressure difference at both ends of the measurement sample in the second sample chamber, and the temperature corresponding to the inflection point is the initial sintering temperature of the measurement sample.

[0020] A device for measuring the melting characteristics of high-alkali metal fuel ash comprises a first sample chamber and a second sample chamber for implementing a pressure differential method; the shape and size of the first sample chamber are the same as the shape and size of the second sample chamber;

[0021] The first sample chamber is provided with a first air inlet channel and a first exhaust channel. When a first sample to be measured is set in the first sample chamber, the first air inlet channel and the first exhaust channel are respectively arranged on both sides of the sample to be measured; the second sample chamber is provided with a second air inlet channel and a second exhaust channel. When a second sample to be measured is set in the second sample chamber, the second air inlet channel and the second exhaust channel are respectively arranged on both sides of the sample to be measured; the first exhaust channel is connected to the second air inlet channel;

[0022] The first air intake passage is communicated with an air source; and a pressure sensor is provided for measuring the difference between the pressure at the second air intake passage and the pressure at the second exhaust passage.

[0023] Optionally, the pressure sensor includes a pressure sensor arranged at the second intake passage; and the second exhaust passage is connected to the atmosphere.

[0024] Optionally, the shape of the first sample chamber includes a cylinder.

[0025] Optionally, the first air inlet channel and the first exhaust channel are respectively arranged at two ends of the cylinder; the second air inlet channel and the second exhaust channel are respectively arranged at two ends of the second sample chamber.

[0026] The technical effects of the present invention are as follows:

[0027] In the existing national standard method for measuring the ash melting characteristics of fuels, the final ash temperature of the ash cone is set relatively high. Before reaching the final ash temperature, a large amount of alkali metals in the high-alkali metal fuel will precipitate, resulting in a reduction in low-melting-point compounds in the ash cone, and a large deviation between the composition of the ash cone and the composition of the original fuel. During the ash heating process, the skeleton effect of the high-melting-point substance masks the ash melting phenomenon at low temperatures, thereby exacerbating the final measurement deviation. The method for measuring the ash melting characteristics of high-alkali metal fuels of the present invention adopts a low-temperature ash ash method to prepare sample ash, which can effectively reduce the loss of alkali / alkaline earth metals in the sample ash, so that the composition of the measured sample can be consistent with that of the original fuel, thereby improving the accuracy of the final measurement results.

[0028] The present invention's method for measuring the melting characteristics of high-alkali metal fuel ash utilizes a pressure drop method to measure the sample. The basic principle of the pressure drop method is to introduce a certain flow rate of gas into one end of the sample and monitor the pressure drop across the sample during the heating process. As the gas continues to be introduced, the pressure drop across the sample increases. When the sample reaches its initial sintering temperature, the sample begins to sinter. Consequently, large-scale airflow channels appear in the sample, increasing the amount of air flowing through the sample and causing the pressure drop across the sample to suddenly decrease. Therefore, the pressure drop measurement can determine whether the sample has sintered, and the temperature at which sintering occurs can be determined as the sample's initial sintering temperature. This demonstrates that the pressure drop method employed in the present invention is highly sensitive and can accurately detect changes in the sample's volume, thereby determining the initial sintering temperature of the fuel ash. Existing national standard methods, however, require observing the deformation of the ash cone to determine the characteristic temperature, which results in significant measurement errors due to observational errors.

[0029] The high-alkali metal fuel ash melting property measuring device of the present invention can effectively implement the high-alkali metal fuel ash melting property measuring method of the present invention, has a simple system structure, is easy to measure, and is applicable to a wide range of fuel types.

[0030] In summary, the technical solution of the present invention achieves the purpose of the present invention.

[0031] Further effects of the above optional manner will be described below in conjunction with specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a flow chart of an embodiment of a method for measuring the fusion characteristics of high-alkali metal fuel ash according to the present invention.

[0033] Figure 2 This is a structural principle diagram of an embodiment of a device for measuring the melting characteristics of high-alkali metal fuel ash according to the present invention.

[0034] Figure 3 This is a physical picture of the device for measuring the melting characteristics of high-alkali metal fuel ash according to the present invention.

[0035] Figure 4 for Figure 1 Experimental results of the illustrated embodiments.

[0036] The symbols in the figure are explained as follows:

[0037] 201. Differential pressure gauge; 202. Recorder; 203. Temperature sensor; 204. Second exhaust channel; 205. Second sample chamber; 206. Second air inlet channel; 207. Muffle furnace; 208. First exhaust channel; 209. First sample chamber; 210. First air inlet channel; 211. Flow controller; 212. Gas source. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is described in detail below with reference to the embodiments shown in the accompanying drawings.

[0039] Figure 1 An embodiment of the present invention's method for measuring the ash melting characteristics of a high-alkali metal fuel is shown. The high-alkali metal fuel used in this embodiment is rice husk. The method for measuring the ash melting characteristics of a high-alkali metal fuel includes the following steps:

[0040] First, the sample ash was prepared by low-temperature ashing method.

[0041] In this step, the high alkali metal fuel to be measured is subjected to a low-temperature ashing method to prepare sample ash.

[0042] In this embodiment, a low-temperature ashing instrument is used to prepare sample ash. The specific process is: crush the rice husk, screen out about 2 grams of particles with a particle size of less than 0.075 mm and spread them evenly on a tray. Place the tray in the cavity of the low-temperature ashing instrument. Turn on the low-temperature ashing instrument switch and the vacuum pump switch, set the ashing instrument power to 250W, the cavity temperature to 180-220°C, turn on the oxygen, and introduce oxygen into the cavity of the low-temperature ashing instrument at 80-120 mL / min. Set the low-temperature ashing time to 2 hours and start ashing. After 2 hours, open the low-temperature ashing instrument, take out the tray, mix and stir the sample on the tray, and then spread it evenly on the tray again. Then, place the tray back into the cavity of the low-temperature ashing instrument and repeat the above-mentioned low-temperature ashing instrument operation. After repeated many times, when the low-temperature ashing time accumulates to 24 hours, the low-temperature ashing process is completed to obtain 0.4 grams of sample ash.

[0043] The low-temperature ashing instrument used in this example is a PT-5S plasma cleaning machine manufactured by Shenzhen Fenghe Boda Electromechanical Equipment Co., Ltd. It operates based on the principle of plasma low-temperature ashing. Plasma low-temperature ashing involves excitation of oxygen molecules into a plasma through an electrodeless, high-frequency electric field discharge in a low-pressure environment (130-670 Pa). The highly reactive oxygen atoms in these plasmas are capable of oxidizing the organic matter in the high-alkali metal fuel being measured. During this oxidation process, the mineral components of the high-alkali metal fuel being measured remain largely unaffected.

[0044] The main purpose of low-temperature ashing is to obtain completely ashed sample ash at low temperature. However, the existing technology uses a muffle furnace for high-temperature ashing. During the high-temperature ashing process, the alkali metals in the high-alkali metal fuel escape to varying degrees. The loss of this alkali metal component causes a reduction in low-melting point compounds in the ash cone, which results in a large deviation in the final measurement result. Taking wheat straw as an example, the changes in the alkali metal content in its low-temperature ash, medium-temperature ash and high-temperature ash (low-temperature ash is prepared by a low-temperature ashing instrument, and medium-temperature ash and high-temperature ash are prepared by a muffle furnace) are shown in Table 1. As can be seen from Table 1, compared with its medium-temperature ash and high-temperature ash, the low-temperature ash of wheat straw has less alkali metal precipitation, and a relatively complete original mineral substance in the high-alkali metal fuel can be obtained. Therefore, the low-temperature ash can reduce the precipitation of alkali metals and thus reduce the impact on the initial sintering temperature measurement results.

[0045] Table 1

[0046]

[0047] Second, prepare the measurement sample.

[0048] In this step, the sample ash prepared in the first step is prepared into a measurement sample.

[0049] In this example, a physical pressing method is used to compress the sample ash prepared in the first step into a cylindrical measurement sample. Specifically, 3 grams of the sample ash is placed in an acrylic test tube container. A pressing rod that can be inserted into the container is used to compress the sample ash into a cylindrical measurement sample with a height of 30 mm and a diameter of 22 mm. During the pressing process, weights are successively applied to the pressing rod, and the weights' gravity is used to compress the sample ash. This ensures that properties such as density of the measurement samples prepared multiple times remain consistent, which helps reduce final measurement errors.

[0050] The "physical compression" method described in this step refers to the complete use of pressure to compress the sample ash into a measurement sample, without the use of any other shaped preparations mixed with the sample ash. For example, in the prior art, the preparation of ash cones requires mixing a dextrin solution into the sample ash to moisten it, thereby imparting plasticity to the sample ash before extrusion. However, the inclusion of such a shaped preparation may adversely affect measurement results during subsequent heating. Therefore, the "physical compression" method employed in the present invention avoids errors introduced by shaped preparations.

[0051] In the second step, two or more measurement samples can be prepared from the same batch of sample ash for use in subsequent experiments. The same batch of sample ash refers to high-alkali metal fuel from the same source (e.g., rice husks from the same origin and year) processed in the same low-temperature ashing instrument. Using the same batch of sample ash can avoid inaccurate measurement results due to differences in sample ash composition and other aspects from different batches.

[0052] Third, use the pressure difference method to measure.

[0053] In this step, the pressure difference method is used to measure the measurement sample obtained in the second step to obtain the initial sintering temperature of the measurement sample.

[0054] The schematic diagram of the measuring device for realizing the pressure difference measurement in this step is as follows Figure 2 As shown. Figure 2The high-alkali metal fuel ash melting characteristics measurement device shown in the present invention includes a first sample chamber 209 and a second sample chamber 205, both of identical internal shape and size. The walls of the first sample chamber 209 and the second sample chamber 205 are both constructed from an airtight material. In this embodiment, the walls of the first and second sample chambers are constructed from 316L steel. This airtight material prevents gas from escaping through the walls of the first and second sample chambers 209 and 205. The first sample chamber 209 is provided with a first air inlet channel 210 and a first air outlet channel 208; the second sample chamber 205 is provided with a second air inlet channel 206 and a second air outlet channel 204. The first sample chamber 209 has a cylindrical internal profile, with the first air inlet channel 210 and the first air outlet channel 208 located at either end of the cylinder. The second sample chamber 205 also has a cylindrical internal profile, with the second air inlet channel 206 and the second air outlet channel 204 located at either end of the cylinder. The high-alkali metal fuel ash melting characteristics measurement device also includes a gas source 212. The gas source 212 is a gas cylinder storing high-pressure nitrogen. The gas source 212 is connected to the first air inlet channel 210, and a flow controller 211 is provided on the channel connecting the gas source 212 and the first air inlet channel 210. The first exhaust channel 208 is connected to the second air inlet channel 206. The first sample chamber 209, the second sample chamber 205, and the pipeline connecting the first exhaust channel 208 and the second air inlet channel 206 are all disposed within the muffle furnace 207. In this embodiment, the muffle furnace 207 is a model YX-1212 muffle furnace manufactured by Shanghai Yuzhi Technology Co., Ltd. The second exhaust channel 204 is connected to the atmosphere outside the muffle furnace 207. A temperature sensor 203 is provided within the second exhaust channel 204. The temperature sensor 203 is electrically connected to the recorder 202. A branch pipeline is provided on the pipeline connecting the first exhaust channel 208 and the second air inlet channel 206, and a pressure sensor electrically connected to the differential pressure gauge 201 is provided in the branch pipeline. Figure 3 An example of main components of a high alkali metal fuel ash melting property measuring device including a first sample chamber, a second sample chamber, and a passage communicating with the two sample chambers is shown.

[0055] In this step, the two cylindrical measurement samples of the same size obtained in the second step are placed in the first sample chamber 209 and the second sample chamber 205 respectively, and the two sample chambers are assembled and sealed respectively. The shape and size of the cylindrical measurement sample match the internal contour of the first sample chamber 209; the shape and size of the cylindrical measurement sample match the internal contour of the second sample chamber 205. The shape matching mentioned here means that the end of the cylindrical contour inside the sample chamber (the first sample chamber or the second sample chamber) is arranged adjacent to the end of the cylindrical measurement sample, and the side wall of the internal cylindrical contour is close to the side wall of the cylindrical measurement sample. The size matching mentioned here means that the distance between the measurement sample and the inner wall of the sample chamber should be set to avoid forming an airflow channel with low resistance, and the side wall of the measurement sample needs to be as close as possible to the side wall of the sample chamber. When the cylindrical measurement sample is placed in the first sample chamber 209, the first air inlet channel 210 and the first exhaust channel 208 are respectively arranged on both sides of the measurement sample; when the cylindrical measurement sample is placed in the second sample chamber 205, the second air inlet channel 206 and the second exhaust channel 204 are respectively arranged on both sides of the measurement sample.

[0056] The specific experimental process of this step is described as follows.

[0057] The temperature inside the muffle furnace 207 is raised at a rate of 10°C / min. After reaching a predetermined temperature (400°C in this embodiment), the flow controller 211 is activated, and nitrogen gas is introduced into the first sample chamber 209 through the first air inlet channel 210. The nitrogen gas passes through the measurement sample placed in the first sample chamber 209 and then enters the second sample chamber 205 via the first exhaust channel 208 and the second air inlet channel 206. After passing through the measurement sample in the second sample chamber 205, the nitrogen gas is discharged from the second sample chamber 205 through the second exhaust channel 204. The predetermined temperature is set based on a pre-estimated initial sintering temperature of the fuel being measured and should be lower than the estimated initial sintering temperature. Since the introduction of gas can exacerbate the precipitation of alkali / alkaline earth metals, introducing gas after heating to a certain temperature can reduce the time for gas introduction, thereby reducing alkali / alkaline earth metal precipitation and avoiding the adverse effects of prolonged gas introduction on the measurement results.

[0058] After nitrogen is introduced, the temperature continues to rise. A heating rate of 7°C / min can be set to facilitate observing changes in the result curve. Nitrogen enters the first sample chamber 209. Due to the mismatch between the sample and the interior space of the first sample chamber 209, the nitrogen can only flow through the microscopic structural gaps within the sample and cannot bypass the sample. After passing through the first sample chamber 209, the nitrogen enters the second sample chamber 205. As previously mentioned, nitrogen in the second sample chamber 205 cannot bypass the sample and can only flow through the microscopic structural gaps within the sample. As the temperature within the muffle furnace 207 increases, a certain amount of alkali / alkaline earth metals precipitate from both the sample in the first sample chamber 209 and the sample in the second sample chamber 205. Since the sample in the first sample chamber 209 and the sample in the second sample chamber 205 are from the same batch and have the same shape and size, the amount of alkali / alkaline earth metals precipitated from the sample in the first sample chamber 209 and the sample in the second sample chamber 205 is equal. Driven by the airflow, the alkali / alkaline earth metals precipitated from the measurement sample in the second sample chamber 205 are discharged from the second sample chamber 205. However, an equal amount of alkali / alkaline earth metals precipitated from the measurement sample in the first sample chamber 209 enters the second sample chamber 205 and is captured by the measurement sample in the second sample chamber 205. Therefore, the dual-sample chamber configuration of the high-alkali metal fuel ash melting characteristics measurement device of the present invention compensates for the alkali / alkaline earth metals precipitated from the measurement sample in the second sample chamber 205 during the temperature increase measurement process, allowing the measurement sample in the second sample chamber 205 to retain its original composition, resulting in more accurate measurement results.

[0059] The temperature sensor 203 records the temperature value in the second sample chamber 205 at a certain frequency and transmits it to the recorder 202 for recording. The differential pressure gauge 201 records the pressure difference between the second air inlet channel 206 and the second air outlet channel 204. The two records are combined to form Figure 4 The experimental result curve is shown in Figure 2. Figure 4 The experimental results show that when the pressure difference across the second sample chamber 205 increases with the temperature, an inflection point appears ( Figure 4 The temperature corresponding to the inflection point is the initial sintering temperature. Specifically, the temperature corresponding to the pressure differential across second sample chamber 205 before it begins to decrease is recorded as the initial sintering temperature of the measured sample. The inflection point occurs when the measured sample begins to sinter, forming a larger airflow channel within it, causing the pressure differential across second sample chamber 205 to begin to decrease. Therefore, the temperature corresponding to the inflection point is considered the initial sintering temperature. Figure 4The initial sintering temperature of rice husks shown is 695°C, while the softening temperature of rice husks measured using the national standard method is as high as 1500°C. In production practice, slagging occurs when the temperature of rice husks during combustion in a circulating fluidized bed boiler system is below 800°C. In comparison, the initial sintering temperature of rice husks measured by this invention is more realistic.

[0060] It is worth noting that the above description is merely a preferred embodiment of the present invention and does not limit the scope of patent protection of the present invention. The present invention may also be replaced by equivalent technologies. Therefore, any equivalent changes made by applying the description and illustrations of the present invention, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.

Claims

1. A method for measuring the melting characteristics of high-alkali metal fuel ash, characterized by: The steps include: S1. A low-temperature ashing method is used to prepare sample ash of the high-alkali metal fuel to be measured; the low-temperature ashing method is performed using a low-temperature ashing instrument; during the preparation of the sample ash, the temperature in the chamber of the low-temperature ashing instrument is set in a range of 180° C. to 220° C.; S2. preparing the sample ash into a measurement sample; Using the sample ash from the same batch to prepare at least two measurement samples; S3. measuring the measurement sample using a pressure difference method to obtain an initial sintering temperature of the measurement sample; placing the two measurement samples in a first sample chamber and a second sample chamber respectively; The two measurement samples have the same shape and size, and the shape and size of the measurement samples match the internal spaces of the first sample chamber and the second sample chamber; the first sample chamber and the second sample chamber are connected in series; The first sample chamber is provided with an air inlet channel; gas is introduced into the first sample chamber; and the air pressure difference between the two ends of the measurement sample in the second sample chamber is measured; The two sample chambers are placed in a heating furnace; after the temperature in the heating furnace rises to a predetermined temperature, the gas is introduced into the first sample chamber.

2. The method for measuring the fusion characteristics of high-alkali metal fuel ash according to claim 1, characterized in that: Step S2 includes the following steps: preparing the sample ash into the measurement sample by a physical pressing method.

3. The method for measuring the fusion characteristics of high-alkali metal fuel ash according to claim 1, characterized in that: Step S3 includes the following steps: after the gas is introduced into the first sample chamber, the heating furnace is continuously heated until an inflection point is detected in the pressure difference between the two ends of the measurement sample in the second sample chamber, and the temperature corresponding to the inflection point is the initial sintering temperature of the measurement sample.

4. High alkali metal fuel ash melting characteristics measuring device, characterized by: It includes a first sample chamber and a second sample chamber used to implement the pressure differential method; the shape and size of the first sample chamber are the same as the shape and size of the second sample chamber; The first sample chamber is provided with a first air inlet channel and a first exhaust channel. When a first sample to be measured is set in the first sample chamber, the first air inlet channel and the first exhaust channel are respectively arranged on both sides of the sample to be measured; the second sample chamber is provided with a second air inlet channel and a second exhaust channel. When a second sample to be measured is set in the second sample chamber, the second air inlet channel and the second exhaust channel are respectively arranged on both sides of the sample to be measured; the first exhaust channel is connected to the second air inlet channel; The first air intake passage is communicated with an air source; and a pressure sensor is provided for measuring the difference between the pressure at the second air intake passage and the pressure at the second exhaust passage.

5. The high alkali metal fuel ash melting characteristic measuring device according to claim 4, characterized in that: The pressure sensor includes a pressure sensor provided at the second intake passage; the second exhaust passage is in communication with the atmosphere.

6. The high alkali metal fuel ash melting characteristic measuring device according to claim 4, characterized in that: The shape of the first sample chamber includes a cylindrical shape.

7. The high alkali metal fuel ash melting characteristic measuring device according to claim 6, characterized in that: The first air inlet channel and the first exhaust channel are respectively arranged at two ends of the cylinder; the second air inlet channel and the second exhaust channel are respectively arranged at two ends of the second sample chamber.

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