A device and measurement method for online monitoring of supercritical carbon dioxide working fluid purity

Abstract

The present invention discloses a device and a measuring method for online monitoring of the purity of supercritical carbon dioxide working fluid. The device utilizes the characteristic that the density of supercritical fluid fluctuates greatly due to the influence of purity, and compares the measured real-time density of CO2 working fluid with the density values ​​of CO2 of different purities pre-stored in a digital display calculation module, thereby obtaining the purity of the supercritical CO2 working fluid of the measured sample gas. The device has a simple and reasonable structure, occupies a small volume, can effectively reduce the working fluid purity measurement cost, and realizes online real-time monitoring of the purity of supercritical carbon dioxide working fluid.

Description

Technical Field

[0001] The present invention relates to the field of instrumentation measurement technology used in the fields of thermal power, nuclear power, chemical industry, refrigeration, aviation and aerospace, and in particular to a device and a measuring method for online monitoring of the purity of supercritical carbon dioxide working fluid. Background Art

[0002] The supercritical carbon dioxide Brayton cycle can achieve the efficiency of the steam Rankine cycle at 700℃ at a temperature level of 620℃. As a new advanced power cycle, it has inherent advantages such as high energy density, high heat transfer efficiency, and simple system. It can greatly improve the heat-to-work conversion efficiency, reduce the size of the equipment, and has high economy. In recent years, new power systems based on supercritical carbon dioxide power cycles have received widespread attention from domestic and foreign academic and industrial circles, and have gradually been put into use.

[0003] As a circulating working fluid, the physical properties of supercritical carbon dioxide are important factors affecting the thermal efficiency of the system cycle, and the influence of the purity of carbon dioxide in the supercritical state on the physical properties is very obvious. At present, the main method for measuring purity is gas chromatography analysis, which uses the difference in molecular forces to bring the test sample gas into the chromatographic column and observe the time for each component of the sample gas to flow out of the chromatographic column to determine the composition of the sample gas. Although this method has a wide range of applications and a fast analysis speed, it cannot directly detect the concentration of carbon dioxide for high-purity carbon dioxide samples. It can only detect the content of impurity gases and use the difference to obtain the concentration of carbon dioxide, which makes the result very prone to errors. In actual pipeline sampling, CO2 working fluid is very likely to generate dry ice in the sampling pipeline, which interferes with the detection accuracy. At the same time, the gas chromatography analysis equipment is relatively complex, with many components, heavy and difficult to move. The cost is high when analyzing impurity gases with a content of more than ten parts per million, and it is only suitable for analysis in the laboratory, which brings great difficulties to the work of online monitoring of the purity of supercritical carbon dioxide working fluid.

[0004] Since a purity difference of one ten-thousandth in the supercritical state will result in a maximum difference of five percent in the density of carbon dioxide, this characteristic of supercritical carbon dioxide can be used to analyze the purity of the sample gas being measured. This method has high accuracy, good sensitivity and low cost. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing purity measurement technology and provide a device and a measurement method for online monitoring of the purity of supercritical carbon dioxide working fluid with the characteristics of convenient measurement, high accuracy, sensitivity and reliability. The device utilizes the characteristic that the density of supercritical fluid fluctuates greatly due to the influence of purity to reversely realize high-precision measurement of the purity of supercritical carbon dioxide circulating working fluid.

[0006] In order to achieve the above technical effects, the specific technical solutions of the present invention are as follows:

[0007] A device for online monitoring of the purity of supercritical carbon dioxide working fluid comprises a digital display calculation module 1, a temperature transmitter 2, a pressure transmitter 3, a main body bracket 4, a piezoresistive sensor 5, a sealing filler 6, a connecting rod 7, a CO2 membrane box 8, a guide pipe sleeve 9 and an outer pipeline 10; the outer pipeline 10 is connected to the CO2 sample gas pipeline to be measured, the main body bracket 4 is fixed in the outer pipeline 10, the CO2 membrane box 8 is fixedly placed on the main body bracket 4, the barrel of the CO2 membrane box 8 is made of rigid material, the top cover is a compressible top cover, and the CO2 membrane box 8 encapsulates a preset mass of CO2 at normal temperature and pressure. O2 gas, the connecting rod 7 is made of rigid material, and its bottom is fixedly connected to the compressible top cover of the CO2 membrane box 8. The connecting rod 7 passes through the guide sleeve 9. There is a sealing filler 6 in the guide sleeve 9 to seal. The piezoresistive sensor 5 is arranged on the top of the guide sleeve 9. The top of the connecting rod 7 is pressed on the piezoresistive sensor 5. The connecting rod 7 can move axially without constraint in the guide sleeve 9; the temperature transmitter 2 and the pressure transmitter 3 pass through the wall of the outer pipe 10 and are inserted into the main bracket 4; the digital display calculation module 1 is connected with the temperature transmitter 2, the pressure transmitter 3 and the piezoresistive sensor 5.

[0008] A pressure transmitter 3 is arranged upstream of the CO2 sample gas to be measured in the main support 4, and a temperature transmitter 2 is arranged downstream of the CO2 sample gas to be measured in the main support 4, so as to avoid interference of the movement of the connecting rod 7 on the pressure value measured by the pressure transmitter 3, and at the same time avoid interference of the temperature transmitter 2 on the pressure value measured by the pressure transmitter 3.

[0009] When the connecting rod 7 is installed, a certain pre-tightening pressure is applied to the contact surface between the top of the connecting rod 7 and the piezoresistive sensor 5 .

[0010] The compressible top cover of the CO2 membrane box 8 is a corrugated cover that can produce axial deformation under pressure, and the cylinder material is a hard alloy metal material that is rigid under preset temperature and pressure; after the CO2 membrane box is packaged, the corresponding relationship between the axial deformation of the corrugated cover and the volume inside the CO2 membrane box is debugged and recorded.

[0011] The sealing filler 6 is made of carbon fiber or flexible graphite sealing material, and is tightly connected to the guide sleeve 9 by pre-tightening or self-tightening of the pressure of the measured sample gas, while not affecting the axial displacement of the free end of the connecting rod 7.

[0012] The connecting rod 7 is made of a hard alloy metal material that is rigid under a preset temperature and pressure. The bottom of the connecting rod 7 is fixedly connected to the compressible top cover of the CO2 membrane box, and can produce axial displacement along with the axial deformation of the compressible top cover. The top of the connecting rod is umbrella-shaped. During installation, the umbrella-shaped top of the connecting rod covers the piezoresistive sensor 5. After installation, the corresponding relationship between the axial displacement of the connecting rod 7, the internal volume of the CO2 membrane box 8 and the piezoresistive sensor 5 is debugged and recorded, and stored in the digital display calculation module 1.

[0013] The digital display calculation module 1 pre-stores the density values ​​of CO2 of different purities under a series of pressure and temperature conditions calculated by commercial physical property software. The digital display calculation module 1 has a communication interface to output the supercritical CO2 purity of the sample gas to the PLC or DCS computer control system.

[0014] The purity measurement method of the device for online monitoring of the purity of supercritical carbon dioxide working fluid is described. The outer pipeline 10 of the device is connected to the CO2 sample gas pipeline to be measured, and the CO2 membrane box 8 is placed in the atmosphere of the CO2 sample gas to be measured. Since there is a density difference between the CO2 working fluid inside and outside the CO2 membrane box 8 and the cylinder of the CO2 membrane box 8 is a rigid material, the CO2 working fluid outside the CO2 membrane box 8, that is, the CO2 sample gas to be measured, will drive the compressible top cover of the CO2 membrane box 8 to produce axial deformation. Since the compressible top cover of the CO2 membrane box 8 is fixedly connected to the bottom of the connecting rod 7, and the connecting rod 7 has no other constraints, and the connecting rod 7 is made of a rigid metal material, the axial deformation of the compressible top cover of the CO2 membrane box 8 will drive the axial displacement of the connecting rod 7; since the top of the connecting rod 7 covers the piezoresistive sensor 5, the contact surface between the top of the connecting rod 7 and the piezoresistive sensor 5 has a certain pre-tightening pressure when installing, and the axial displacement of the connecting rod 7 will change the pressure between the top of the connecting rod 7 and the piezoresistive sensor 5, and the piezoresistive sensor 5 transmits the pressure change to the digital display computer Module 1, and the temperature transmitter 2 and the pressure transmitter 3 also transmit the real-time temperature and pressure information to the digital display calculation module 1. The digital display calculation module 1 calculates the axial displacement of the connecting rod 7 and the axial deformation of the compressible top cover of the CO2 membrane box 8 according to the pressure signal transmitted by the piezoresistive sensor 5. Since the cylinder of the CO2 membrane box 8 is a rigid material and will not be deformed due to the change of the working fluid pressure, the volume change of the CO2 membrane box 8 can be calculated according to the axial deformation of the compressible top cover of the CO2 membrane box 8, and the volume of the CO2 membrane box 8 under this working condition can be obtained. At the same time, the mass of the CO2 working fluid encapsulated in the CO2 membrane box 8 is known. Since the CO2 density inside and outside the CO2 membrane box 8 is the same at this time, the density of the sample gas being measured at this time is calculated. At the same time, the digital display calculation module 1 queries the density table of CO2 of different purities under this temperature and pressure according to the real-time temperature and pressure information transmitted by the temperature transmitter 2 and the pressure transmitter 3, and compares the real-time density of the sample gas being measured with the data in the density table to obtain the purity of the sample gas being measured at this time.

[0015] The present invention has the following beneficial effects:

[0016] The present invention utilizes the characteristic that the density of supercritical fluid fluctuates greatly due to the influence of purity, places a CO2 membrane box encapsulating a certain mass of CO2 working fluid in the environment of the sample gas to be measured, and compares the measured real-time density of CO2 working fluid with the density values ​​of CO2 of different purities pre-stored in the digital display calculation module to obtain the supercritical CO2 purity of the sample gas to be measured. Users can monitor the supercritical CO2 purity of the sample gas to be measured online through the digital display calculation module.

[0017] Furthermore, compared with existing purity measurement technologies such as gas chromatography, the technical method adopted by the present invention has high detection accuracy and can significantly reduce investment and maintenance costs. At the same time, the device has a simple and reasonable structure, a small footprint, and is easy to install, and can achieve online real-time monitoring of the supercritical CO2 purity of the sample gas being measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of the present invention.

[0019] Figure 2 Schematic diagram of the structure of the connecting rod and the piezoresistive sensor.

[0020] Figure 3 It is the appearance structure diagram of the present invention.

[0021] Among them, 1 is a digital display calculation module, 2 is a temperature transmitter, 3 is a pressure transmitter, 4 is a main body bracket, 5 is a piezoresistive sensor, 6 is a sealing filler, 7 is a connecting rod, 8 is a CO2 membrane box, 9 is a guide pipe sleeve, and 10 is an external pipeline. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0023] like Figure 1 , Figure 2 and Figure 3 As shown, the device for online monitoring of the purity of supercritical carbon dioxide working fluid described in the present invention includes a digital display calculation module 1, a temperature transmitter 2, a pressure transmitter 3, a main body bracket 4, a piezoresistive sensor 5, a sealing filler 6, a connecting rod 7, a CO2 membrane box 8, a guide pipe sleeve 9, and an external pipeline 10.

[0024] A certain mass of CO2 working fluid at normal temperature and pressure is encapsulated in the CO2 membrane box 8. During the experiment, the outer pipe 10 of the device is connected to the pipe of the CO2 sample gas to be measured by welding, and the CO2 membrane box 8 is placed in the atmosphere of the CO2 sample gas to be measured. Since there is a density difference between the CO2 working fluid inside and outside the CO2 membrane box 8 and the cylinder of the CO2 membrane box 8 is a rigid material, the CO2 working fluid outside the CO2 membrane box 8, i.e. the CO2 sample gas to be measured, will drive the corrugated cover of the CO2 membrane box 8 to produce axial deformation. Since the corrugated cover of the CO2 membrane box 8 is fixedly connected to the bottom of the connecting rod 7, and the connecting rod 7 has no other constraints, and the connecting rod 7 is made of a rigid metal material, the axial deformation of the corrugated cover of the CO2 membrane box 8 will drive the axial displacement of the connecting rod 7. Since the top of the connecting rod 7 is umbrella-shaped and covers the piezoresistive sensor 5, there is a certain pre-tightening pressure on the contact surface between the top of the connecting rod 7 and the piezoresistive sensor 5 when the connecting rod 7 is installed. The axial displacement of the connecting rod 7 will change the pressure between the top of the connecting rod 7 and the piezoresistive sensor 5. The piezoresistive sensor 5 transmits the pressure change to the digital display calculation module 1. At the same time, the temperature transmitter 2 and the pressure transmitter 3 also transmit the real-time temperature and pressure information to the digital display calculation module 1. The digital display calculation module 1 can calculate the axial displacement of the connecting rod 7 and the axial deformation of the compressible top cover of the CO2 membrane box 8 according to the pressure signal from the piezoresistive sensor 5. Since the cylinder of the CO2 membrane box 8 is made of rigid material, it will not be affected by the working fluid. Pressure changes cause deformation, so the volume change of the CO2 membrane box 8 can be calculated based on the axial deformation of the compressible top cover of the CO2 membrane box 8, and the volume of the CO2 membrane box 8 under this working condition can be obtained. At the same time, the mass of the CO2 working fluid encapsulated in the CO2 membrane box 8 is known. Since the CO2 densities inside and outside the CO2 membrane box 8 are the same at this time, the density of the sample gas being measured at this time can be calculated. At the same time, the digital display calculation module 1 queries the density table of CO2 of different purities under this temperature and pressure based on the real-time temperature and pressure information transmitted by the temperature transmitter 2 and the pressure transmitter 3, and compares the real-time density of the sample gas being measured with the data in the density table to obtain the purity of the sample gas being measured at this time.

[0025] The implementation methods of the present invention are not limited to the above-mentioned embodiments, and any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention shall be equivalent replacement methods and shall be included in the protection scope of the present invention.

Claims

1. A device for online monitoring of the purity of supercritical carbon dioxide working fluid, characterized in that: The device comprises a digital display calculation module (1), a temperature transmitter (2), a pressure transmitter (3), a main body bracket (4), a piezoresistive sensor (5), a sealing filler (6), a connecting rod (7), a CO2 membrane box (8), a guide tube sleeve (9) and an external pipeline (10); the external pipeline (10) is connected to the CO2 sample gas pipeline to be measured, the main body bracket (4) is fixed in the external pipeline (10), the CO2 membrane box (8) is fixedly placed on the main body bracket (4), the cylinder of the CO2 membrane box (8) is made of rigid material, the top cover is a compressible top cover, the CO2 membrane box (8) encapsulates CO2 gas of preset mass at normal temperature and pressure, the connecting rod (7) is rigid The material has a bottom which is fixedly connected to a compressible top cover of a CO2 membrane box (8); a connecting rod (7) passes through a guide sleeve (9); a sealing filler (6) is arranged in the guide sleeve (9) to perform a sealing function; a piezoresistive sensor (5) is arranged at the top of the guide sleeve (9); the top of the connecting rod (7) is pressed on the piezoresistive sensor (5); the connecting rod (7) can move axially without constraint in the guide sleeve (9); a temperature transmitter (2) and a pressure transmitter (3) pass through the wall of an outer pipe (10) and are inserted into a main body bracket (4); the digital display calculation module (1) is connected to the temperature transmitter (2), the pressure transmitter (3) and the piezoresistive sensor (5); The compressible top cover of the CO2 membrane box (8) is a corrugated cover that can produce axial deformation under pressure, and the cylinder body is made of a hard alloy metal material that is rigid under a preset temperature and pressure; after the CO2 membrane box is packaged, the corresponding relationship between the axial deformation of the corrugated cover and the volume inside the CO2 membrane box is debugged and recorded; The connecting rod (7) is made of a hard alloy metal material that is rigid under a preset temperature and pressure, and the bottom of the connecting rod (7) is fixedly connected to the compressible top cover of the CO2 membrane box and can generate axial displacement along with the axial deformation of the compressible top cover; The digital display calculation module (1) pre-stores density values ​​of CO2 with different purities under a series of pressure and temperature conditions. The digital display calculation module (1) is provided with a communication interface for outputting the supercritical CO2 purity of the sample gas to be measured to a PLC or DCS computer control system.

2. The device for online monitoring of supercritical carbon dioxide working medium purity according to claim 1, characterized in that: A pressure transmitter (3) is arranged upstream of the CO2 sample gas to be measured in the main body bracket (4), and a temperature transmitter (2) is arranged downstream of the CO2 sample gas to be measured in the main body bracket (4), so as to avoid interference of the movement of the connecting rod (7) on the pressure value measured by the pressure transmitter (3), and at the same time avoid interference of the temperature transmitter (2) on the pressure value measured by the pressure transmitter (3).

3. The device for online monitoring of supercritical carbon dioxide working medium purity according to claim 1, characterized in that: When the connecting rod (7) is installed, a certain pre-tightening pressure is applied to the contact surface between the top of the connecting rod (7) and the piezoresistive sensor (5).

4. The device for online monitoring of supercritical carbon dioxide working medium purity according to claim 1, characterized in that: The sealing filler (6) is made of carbon fiber or flexible graphite sealing material, and is tightly connected to the guide sleeve (9) through pre-tightening or self-tightening of the pressure of the sample gas being measured, while not affecting the axial displacement of the free end of the connecting rod (7).

5. The device for online monitoring of supercritical carbon dioxide working medium purity according to claim 1, characterized in that: The top of the connecting rod (7) is in an umbrella shape. When installed, the umbrella-shaped top of the connecting rod covers the piezoresistive sensor (5). After installation, the corresponding relationship between the axial displacement of the connecting rod (7), the internal volume of the CO2 membrane box (8) and the piezoresistive sensor (5) is debugged and recorded, and stored in the digital display calculation module (1).

6. The purity measurement method of the device for online monitoring the purity of supercritical carbon dioxide working medium according to any one of claims 1 to 5, characterized in that: The outer pipe (10) of the device is connected to the pipe of the CO2 sample gas to be measured, and the CO2 membrane box (8) is placed in the atmosphere of the CO2 sample gas to be measured. Since there is a density difference between the CO2 working medium inside and outside the CO2 membrane box (8) and the cylinder of the CO2 membrane box (8) is made of rigid material, the CO2 working medium outside the CO2 membrane box (8), i.e., the CO2 sample gas to be measured, will drive the compressible top cover of the CO2 membrane box (8) to produce axial deformation. Since the compressible top cover of the CO2 membrane box (8) is fixedly connected to the bottom of the connecting rod (7), and the connecting rod (7) has no other fixed connection, the CO2 membrane box (8) is not deformed. The connecting rod (7) is made of a rigid metal material. The axial deformation of the compressible top cover of the CO2 membrane box (8) will drive the axial displacement of the connecting rod (7). Since the top of the connecting rod (7) covers the piezoresistive sensor (5), the contact surface between the top of the connecting rod (7) and the piezoresistive sensor (5) has a certain pre-tightening pressure when the connecting rod (7) is installed. The axial displacement of the connecting rod (7) will change the pressure between the top of the connecting rod (7) and the piezoresistive sensor (5). The piezoresistive sensor (5) transmits the pressure change to the digital display calculation module (1). At the same time, the temperature transmitter The device (2) and the pressure transmitter (3) also transmit the real-time temperature and pressure information to the digital display calculation module (1). The digital display calculation module (1) calculates the axial displacement of the connecting rod (7) and the axial deformation of the compressible top cover of the CO2 membrane box (8) according to the pressure signal transmitted by the piezoresistive sensor (5). Since the cylinder of the CO2 membrane box (8) is made of rigid material and will not be deformed due to the change of the working fluid pressure, the volume change of the CO2 membrane box (8) can be calculated according to the axial deformation of the compressible top cover of the CO2 membrane box (8), and the working fluid pressure can be obtained. The volume of the CO2 diaphragm box (8) under the given conditions and the mass of the CO2 working fluid encapsulated in the CO2 diaphragm box (8) are known. Since the density of CO2 inside and outside the CO2 diaphragm box (8) is the same at this time, the density of the sample gas being measured at this time is calculated. At the same time, the digital display calculation module (1) queries the density table of CO2 of different purities under the temperature and pressure according to the real-time temperature and pressure information transmitted by the temperature transmitter (2) and the pressure transmitter (3), compares the real-time density of the sample gas being measured with the data in the density table, and obtains the purity of the sample gas being measured at this time.

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