A method and device for measuring the exhaust enthalpy of a low-pressure cylinder

Abstract

The present invention relates to the technical field of thermal power generating units, and discloses a method and device for measuring the exhaust enthalpy of a low-pressure cylinder. The measuring device includes a low-pressure cylinder exhaust bypass, a first flowmeter and a second flowmeter connected in series to the low-pressure cylinder exhaust bypass. The measuring method is to measure a first flow value and a second flow value on the low-pressure cylinder exhaust bypass, and measure the pressure difference of the second flowmeter, and calculate the exhaust enthalpy value. The exhaust enthalpy is calculated based on the flow rate and pressure as reference values, which solves the problems of cumbersome process and inaccurate results using other methods.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal power generating units, and particularly to a method and device for measuring the exhaust enthalpy of a low-pressure cylinder. Background Art

[0002] In the on-line monitoring and on-line thermal economy analysis of thermal power generating units, the exhaust enthalpy is a very important parameter. Since the exhaust steam quality of the low-pressure cylinder is low and the exhaust steam point is in the wet steam region, its enthalpy value cannot be directly obtained by measuring instruments. Therefore, accurately obtaining the exhaust enthalpy of a steam turbine has always been a difficult point in realizing on-line diagnosis of the unit.

[0003] However, since the exhaust steam of the steam turbine is in the wet steam region and its enthalpy value cannot be directly obtained by measuring instruments, the existing on-line calculation of the exhaust enthalpy of the steam turbine is mainly based on a theoretical calculation method of a model. Currently, the more commonly used on-line calculation methods for the exhaust enthalpy of the steam turbine mainly include the energy balance method, the curve extrapolation method, the equivalent enthalpy drop method, the Flügel formula method, and the entropy increase calculation method. These methods all have the following limitations to varying degrees:

[0004] (1) When using the energy balance method, it is necessary to comprehensively consider the energy input and output of the system, and almost every time a comprehensive and complex calculation needs to be carried out again;

[0005] (2) The equivalent enthalpy drop method uses the material and energy balance of the steam turbine regenerative heating system, and calculates the exhaust enthalpy using the equivalent enthalpy drop and the inter-stage efficiency. It has a high calculation accuracy under steady-state conditions, and the equivalent enthalpy drop method is not applicable to working conditions with large load changes;

[0006] (3) The curve extrapolation method makes a thermodynamic process first based on the inlet state point and the extraction state point of the steam turbine in the superheated steam region, and smoothly extrapolates to the wet steam region to determine the exhaust enthalpy. The curve extrapolation method has poor calculation accuracy at low loads;

[0007] (4) The Flügel formula method is not applicable to working conditions with changes in the steam passage area;

[0008] (5) The entropy increase calculation method needs to comprehensively consider the distribution of the auxiliary steam and water flow rates in the thermodynamic system, which is not easy to accurately grasp in practice and has poor practicability. Summary of the Invention

[0009] In some embodiments of the present application, to solve the above technical problems, a method and device for measuring the exhaust enthalpy of a low-pressure cylinder are provided. The measuring device includes a bypass for the exhaust steam of the low-pressure cylinder, and a first flowmeter and a second flowmeter connected in series to the bypass for the exhaust steam of the low-pressure cylinder. The measuring method is to measure a first flow value and a second flow value on the bypass for the exhaust steam of the low-pressure cylinder, and measure the pressure difference of the second flowmeter, and calculate the exhaust enthalpy value. The exhaust enthalpy is calculated based on the flow rate and the pressure as reference values, solving the problems of cumbersome process and inaccurate results using other methods.

[0010] In some embodiments of the present application, a method for measuring the exhaust enthalpy of a low-pressure cylinder is disclosed, which is applied to a device for measuring the exhaust enthalpy of a low-pressure cylinder. The measuring device includes: a bypass for the exhaust steam of the low-pressure cylinder, which is a bypass led out from the pipeline from the low-pressure cylinder of the steam turbine to the condenser, i.e., the exhaust steam pipeline of the low-pressure cylinder, for sampling the fluid of the low-pressure cylinder of the steam turbine; a first flowmeter and a second flowmeter, which are connected in series on the bypass of the low-pressure test. The first flowmeter is used to measure the first flow value of the fluid, and the second flowmeter is used to measure the second flow value and the pressure difference value of the fluid. The method includes: obtaining the first flow value, the second flow value and the pressure difference value, and obtaining the exhaust enthalpy value based on the exhaust enthalpy calculation model.

[0011] In some embodiments of the present application, the exhaust enthalpy calculation model is specifically: setting the flow densities at the first flowmeter and the second flow value to be equal; obtaining the first mass flow and the second mass flow according to the first flow value, the second flow value and the flow density; obtaining the actual density based on the equality of the first mass flow and the second mass flow; and calculating the exhaust enthalpy value based on the actual density.

[0012] In some embodiments of the present application, the measuring device includes a steam temperature measuring instrument for measuring the temperature value in the bypass of the exhaust steam of the low-pressure cylinder; and also includes a steam pressure measuring instrument for measuring the pressure value in the bypass of the exhaust steam of the low-pressure cylinder. In the measuring method, calculating the exhaust enthalpy value based on the actual density is specifically: obtaining the temperature value and the pressure value to obtain the saturated steam dry density of the fluid; obtaining the actual dryness of the fluid according to the actual density and the saturated steam dry density of the fluid; obtaining the saturated water enthalpy value and the wet saturated steam enthalpy value; and obtaining the exhaust enthalpy value based on the method for obtaining the dryness of wet steam in the IF-97 equation of water and water vapor.

[0013] In some embodiments of the present application, the formula for the first flow value is:

[0014]

[0015] where Q v1 - the first flow value; f - the vortex frequency; K1 - the calibration coefficient;

[0016] The formula for the second flow value is:

[0017]

[0018] where Q v2 -- the volume flow; ρ2 - the flow density at the second flowmeter; Δp - the differential pressure; ε - the gas expansion coefficient; K2 - a constant;

[0019] The formula for the first mass flow rate is:

[0020]

[0021] The formula for the second mass flow rate is:

[0022]

[0023] Based on Q m1 = Q m2 and the setting ρ1≈ρ2 = ρ; dividing the two equations gives the actual density ρ:

[0024]

[0025] In some embodiments of the present application, the actual density is ρ, the saturated vapor dry density of the fluid is ρ s , and the actual dryness of the fluid is X. The specific calculation formula is:

[0026]

[0027] The saturated water enthalpy value is h'; the wet saturated steam enthalpy value is h''; the formula for calculating the exhaust steam enthalpy value h is:

[0028] h = (1 - X)×h' + X×h''.

[0029] In some embodiments of the present application, a low-pressure cylinder exhaust steam enthalpy measuring device is also proposed, which is applicable to the low-pressure cylinder exhaust steam enthalpy measuring method. The measuring device includes the low-pressure cylinder exhaust steam bypass, a test unit, and a calculation unit; the test unit is composed of the first flowmeter and the second flowmeter, and converts the first flow value and the second flow value into electrical signals and transmits them to the calculation unit; the calculation unit receives the electrical signals and calculates the exhaust steam enthalpy value.

[0030] In some embodiments of the present application, the first flowmeter is a vortex flowmeter, and the second flowmeter is a V-cone flowmeter.

[0031] In some embodiments of the present application, it further includes: a working medium recovery unit and a low-pressure heater drain pump. The working medium recovery unit expands the sampled steam and then converts it into condensate, which is sent back to the condensate system through the low-pressure drain pump.

[0032] In some embodiments of the present application, the low-pressure cylinder exhaust steam bypass is made of metal stainless steel pipe, with a thermal insulation layer added. A check valve is installed on the inlet side of the bypass, and an electric control valve is installed on the outlet side.

[0033] In some embodiments of the present application, the calculation unit is set as a PLC.

[0034] The beneficial effects of the present invention are as follows: The present invention can accurately calculate the exhaust enthalpy value of the low-pressure cylinder of a steam turbine online, directly display the calculation result and transmit it to the unit DCS system, improve the performance index of the unit, send the sampled steam and the working medium used in the measurement process to the regenerative system of the steam turbine for continued utilization, without causing waste of the working medium and energy, and is conducive to the energy-saving and economic operation of the unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic diagram of the exhaust enthalpy measurement device for the low-pressure cylinder in the embodiment of the present invention;

[0036] Figure 2 It is a flowchart of a method for measuring the exhaust enthalpy of the low-pressure cylinder in an embodiment of the present invention;

[0037] Figure 3 It is a flowchart of the exhaust enthalpy calculation model in the embodiment of the present invention.

[0038] In the figure: 100, low-pressure cylinder exhaust pipeline; 200, low-pressure cylinder exhaust bypass; 210, first flowmeter; 220, second flowmeter; 230, low-pressure heater drain pump; 300, condensate system; 400, calculation unit; 500, low-pressure cylinder; 600, condenser. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] The following will further describe in detail the specific embodiments of the present invention in conjunction with the drawings and embodiments. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0040] In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present application.

[0041] The terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present application, unless otherwise stated, the meaning of "a plurality" is two or more.

[0042] In the description of the present application, it should be noted that unless otherwise clearly specified and defined, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0043] In some embodiments of the present application, as Figure 1 shown, a low-pressure cylinder exhaust enthalpy measuring device is proposed. The measuring device includes a low-pressure cylinder exhaust bypass 200, which is a bypass of the low-pressure cylinder exhaust pipeline on the low-pressure cylinder exhaust bypass 200. The low-pressure cylinder exhaust pipeline 100 is a pipeline from the low-pressure cylinder of the steam turbine to the condenser. Fluids flow through the low-pressure cylinder exhaust bypass 200 and the low-pressure cylinder exhaust pipeline. The measuring device and measuring method of the present application measure the enthalpy value of the fluid in the above pipeline. In a specific embodiment, the fluid is water vapor.

[0044] In some embodiments of the present application, the measuring device further includes a test unit and a calculation unit 400. The test unit is used to measure various parameters of the fluid in the pipeline and convert the parameters into electrical signals and transmit them to the calculation unit 400. The calculation unit 400 receives the electrical signals with parameters and calculates the parameters to obtain the exhaust enthalpy value.

[0045] In some embodiments of the present application, the measuring device includes a first flowmeter 210 and a second flowmeter 220. The first flowmeter 210 and the second flowmeter 220 are connected in series. The first flowmeter 210 measures a first flow value, and the second flowmeter 220 measures a second flow value. The second flowmeter 220 can also measure the pressure difference when the fluid flows through the second flowmeter 220.

[0046] In some specific embodiments of the present application, the first flowmeter 210 is a vortex flowmeter, and the second flowmeter 220 is a V-cone flowmeter. The vortex flowmeter measures the flow rate by applying the principle of fluid oscillation. When the fluid passes through the vortex generator, two columns of vortices proportional to the flow velocity are alternately generated. The frequency of the vortices is proportional to the average velocity of the fluid.

[0047] Therefore, based on the characteristics of the vortex flowmeter itself, the calculation formula for the first flow value measured by the vortex flowmeter is:

[0048]

[0049] where, Q v1 - The first flow value; f - The vortex frequency; K1 - The calibration coefficient.

[0050] The V-cone flowmeter is also a differential pressure type instrument. It has the same principle as other general differential pressure flowmeters, both based on Bernoulli's law of energy conversion in a closed pipeline. In a stable flow field, the flow velocity in the pipeline is proportional to the square root of the differential pressure. By using the fluid continuity equation and Bernoulli equation, the mathematical relationship between the measured flow rate and the output differential pressure can be derived.

[0051] Therefore, based on the characteristics of the V-cone flowmeter itself, the calculation formula for the second flow rate value measured by the V-cone flowmeter is:

[0052]

[0053] Where, Q v2 - volumetric flow rate; ρ2 - the flow density at the second flowmeter; Δp - differential pressure; ε - gas expansion coefficient; K2 - constant.

[0054] It should be noted that K2 is related to the discharge coefficient C, throttling ratio β, and equivalent orifice diameter d. Therefore, the value of K2 is a fixed value under various flow rates of the fluid, which is a value preset in the calculation unit. The specific formula representation is:

[0055]

[0056] The measuring device also includes a steam temperature measuring instrument, a steam differential pressure measuring instrument, and a steam pressure measuring instrument; the steam temperature measuring instrument is used to measure the temperature value, and the steam pressure measuring instrument is used to measure the pressure value; specifically, the steam temperature measuring instrument selects a thermal resistance for the measured temperature range of 140°C to 200°C; the steam differential pressure measuring instrument selects a differential pressure transmitter for the measured differential pressure range of -0.05 MPa to 0.05 MPa; the steam pressure measuring instrument selects a pressure transmitter for the measured pressure range of 0 MPa to 0.05 MPa.

[0057] In some embodiments of the present application, the V-cone flowmeter is an integrated temperature and pressure compensated flowmeter, which consists of units such as the steam temperature measuring instrument, the steam differential pressure measuring instrument, and the pressure measuring instrument. The V-cone flowmeter also includes an intelligent integrator unit, a temperature and pressure compensation unit, a steam condensation unit, etc.; the vortex flowmeter is an integrated temperature and pressure compensated flowmeter, and the vortex flowmeter also includes an intelligent integrator unit, a temperature and pressure compensation unit, etc.

[0058] In some embodiments of the present application, the measuring device also includes a working medium recovery unit and a low-pressure heater drain pump 230. The working medium recovery unit and the low-pressure heater drain pump 230 are sequentially connected to the end of the low-pressure cylinder exhaust bypass 200. The fluid passing through the test unit is expanded and then turned into condensate, which is sent back to the condensate system 300 through the low-pressure heater drain pump 230 to realize the closed-loop of the system.

[0059] In some embodiments of the present application, the low-pressure cylinder exhaust steam pipeline 100 is made of metal stainless steel pipe with an additional heat insulation layer. A check valve is installed on the inlet side of the low-pressure cylinder exhaust steam bypass 200, and an electric control valve is installed on the outlet side to ensure the structural stability and temperature stability of the low-pressure cylinder exhaust steam pipeline 100 and the low-pressure cylinder exhaust steam bypass 200.

[0060] In some embodiments of the present application, the calculation unit 400 is set as a PLC, which is convenient for inputting or changing the calculation program.

[0061] In some embodiments of the present application, a method for measuring the enthalpy of low-pressure cylinder exhaust steam is also proposed. As Figure 2 shown, the method includes: Step S101, obtaining the first flow value, the second flow value and the pressure difference value, and obtaining the exhaust steam enthalpy value based on the exhaust steam enthalpy calculation model.

[0062] Specifically, the first flowmeter, i.e., the vortex flowmeter, obtains the first flow value at the vortex flowmeter; the second flowmeter, i.e., the V-cone flowmeter, obtains the second flow value at the V-cone flowmeter. The V-cone flowmeter can also obtain the pressure difference value when the fluid passes through the V-cone flowmeter. According to the formula relationship between the same values and different values between the two flowmeters, the exhaust steam enthalpy value of the low-pressure cylinder exhaust steam bypass is calculated. Only three easily obtainable variable measurement methods need to be detected and the exhaust steam enthalpy value is measured according to the well-known characteristic formula, which simplifies the process of obtaining the exhaust steam enthalpy value and improves the accuracy of obtaining the exhaust steam enthalpy value.

[0063] In order to accurately calculate the exhaust steam enthalpy value, in some embodiments of the present application, as Figure 3 shown, the exhaust steam enthalpy calculation model is specifically: Step S201, setting the flow densities of the first flow value and the second flow value to be equal.

[0064] Since the first flowmeter and the second flowmeter are connected in series on the low-pressure cylinder exhaust steam bypass, and in the actual use process, the positions of the first flowmeter and the second flowmeter are close, it can be directly determined that the flow densities of the fluid passing through the first flowmeter and the second flowmeter are equal to obtain the equivalent value in the calculation process.

[0065] The formula representation is: ρ1≈ρ2 = ρ.

[0066] Step S202, obtaining the first mass flow rate and the first mass flow rate according to the first flow value, the second flow value and the flow density.

[0067] The first flow value and the second flow value are in the velocity unit of flow. The first flow value divided by the flow density is the first mass flow rate, and the second flow value divided by the flow density is the second mass flow rate.

[0068] Step S203, obtaining the actual density based on the equality of the first mass flow rate and the second mass flow rate.

[0069] Since the first flowmeter and the second flowmeter are connected in series on the same pipeline, the first flow mass and the second flow mass are equal in value. Thus, an equation can be established to calculate the specific value of the actual density. Based on the above representation formulas for the first flow value and the second flow value, the specific formula for calculating the actual density is as follows:

[0070] The formula for the first mass flow rate is:

[0071]

[0072] The formula for the second mass flow rate is:

[0073]

[0074] Based on Q m1 = Q m2 and the assumption that ρ1≈ρ2 = ρ; dividing the two equations gives the actual density ρ:

[0075]

[0076] Based on the actual density, the exhaust enthalpy value can be calculated.

[0077] Specifically, the enthalpy value of a gas is related to the gas density, pressure, and temperature. The temperature of the gas is obtained through a steam temperature measuring instrument, the pressure of the gas is obtained through a steam pressure measuring instrument, and the corresponding enthalpy value can be obtained from the calculated actual density.

[0078] In order to accurately calculate the exhaust enthalpy value, in some embodiments of the present application, in step S204, a temperature value and a pressure value are obtained to obtain the saturated steam dry density of the fluid;

[0079] In step S205, based on the actual density and the saturated steam dry density of the fluid, the actual dryness of the fluid is obtained.

[0080] It should be noted that regarding the saturated steam dry density, in the prior art field, the saturated steam temperature-pressure-density table is common knowledge. By using the temperature value and the pressure value obtained through a steam temperature measuring instrument and a steam pressure measuring instrument as known data, the saturated steam dry density can be found. In the case of obtaining the actual density and the saturated steam dry density of the fluid, the ratio of the two is the actual dryness of the fluid. The specific formula is as follows:

[0081]

[0082] where, X - the actual dryness of the fluid; ρ s - the saturated steam dry density.

[0083] In some embodiments of the present application, after obtaining the actual dryness of the steam, in step S206, the enthalpy value of saturated water and the enthalpy value of saturated steam are obtained; in step S207, based on the method for calculating the dryness of wet steam in the water and steam IF-97 equation, the enthalpy value of the exhaust steam is obtained.

[0084] It should be noted that both the enthalpy value of saturated water and the enthalpy value of saturated steam are the inherent characteristics of water and water vapor and are known data. The water and steam IF-97 equation is another way to calculate the dryness of wet steam. Based on the method for obtaining the actual dryness of the fluid proposed in the present application, an equation of the known actual dryness of the fluid and the unknown enthalpy value of the exhaust steam is obtained, and thus the enthalpy value of the exhaust steam is obtained. The specific formula representation is as follows:

[0085] The water and steam IF-97 equation is: x = (h - h') / (h'' - h');

[0086] The formula deformed to obtain the enthalpy value of the exhaust steam is: h = (1 - X)×h' + X×h''

[0087] Where h' is the enthalpy value of saturated water, h'' is the enthalpy value of saturated steam, and h is the enthalpy value of the exhaust steam.

[0088] The present invention can accurately calculate the enthalpy value of the exhaust steam of the low-pressure cylinder of the steam turbine online, directly display the calculation result and transmit it to the unit DCS system, improve the performance index of the unit, send the sampled steam and the working medium used in the measurement process to the regenerative system of the steam turbine for continued utilization, and will not cause waste of the working medium and energy, which is beneficial to the energy-saving and economic operation of the unit.

[0089] Those of ordinary skill in the art can understand that the above description is only the preferred embodiments of the present invention and is not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for measuring the exhaust enthalpy of a low-pressure cylinder, characterized in that, Applied to the exhaust enthalpy measurement device of the low-pressure cylinder, the measurement device includes: A low-pressure cylinder exhaust bypass, which is a bypass led from the pipeline of the low-pressure cylinder of the steam turbine to the condenser, that is, the low-pressure cylinder exhaust pipeline, for sampling the fluid of the low-pressure cylinder of the steam turbine; A first flowmeter and a second flowmeter, the first flowmeter and the second flowmeter are connected in series on the low-pressure test bypass, the first flowmeter is used to measure the first flow value of the fluid, and the second flowmeter is used to measure the second flow value and the pressure difference value of the fluid; The method includes: Obtain the first flow value, the second flow value and the pressure difference value, and obtain the exhaust enthalpy value based on the exhaust enthalpy calculation model; The specific form of the exhaust enthalpy calculation model is: Set the flow densities at the first flowmeter and the second flow value to be equal; According to the first flow value, the second flow value and the flow density, obtain the first mass flow rate and the second mass flow rate; Based on the equality of the first mass flow rate and the second mass flow rate, obtain the actual density; Based on the actual density, calculate and obtain the exhaust enthalpy value.

2. The measuring method according to claim 1, wherein The measurement device includes a steam temperature measuring instrument for measuring the temperature value in the low-pressure cylinder exhaust bypass; and also includes a steam pressure measuring instrument for measuring the pressure value in the low-pressure cylinder exhaust bypass; In the measurement method, based on the actual density, calculating the exhaust enthalpy value specifically includes: Obtain the temperature value and the pressure value to obtain the saturated steam dry density of the fluid; According to the actual density and the saturated steam dry density of the fluid, obtain the actual dryness of the fluid; Obtain the saturated water enthalpy value and the wet saturated steam enthalpy value; Based on the method for obtaining the dryness of wet steam in the IF-97 equation of water and water vapor, obtain the exhaust enthalpy value.

3. The measurement method according to claim 1, characterized in that, The formula for the first flow value is: Among them, Q v1 - The first flow rate value; f - Vortex frequency; K1 - Calibration coefficient; The formula for the second flow value is: where Q v2 — volumetric flow rate; ρ2— flow density at the second flowmeter; Δp— differential pressure; ε— gas expansion coefficient; K2— constant The formula for the first mass flow rate is: The formula for the second mass flow rate is: Based on Q m1 = Q m2 and setting ρ1≈ρ2 = ρ; dividing the two equations gives the actual density ρ:

4. The method according to claim 2, wherein The actual density is ρ, and the saturated vapor dry density of the fluid is ρ s , and the actual dryness of the fluid is X. The specific calculation formula is as follows: The saturated water enthalpy value is h'; the wet saturated steam enthalpy value is h"; the formula for calculating the exhaust enthalpy value h is: h = (1 - X)×h' + X×h".

5. A low-pressure cylinder exhaust enthalpy measurement device, characterized in that, Applicable to the low-pressure cylinder exhaust enthalpy measurement method described in any one of claims 1-4, the measurement device includes the low-pressure cylinder exhaust bypass, a test unit and a calculation unit; The test unit is composed of the first flowmeter and the second flowmeter, and converts the first flow value and the second flow value into electrical signals and transmits them to the calculation unit; The calculation unit receives the electrical signal and calculates and obtains the exhaust enthalpy value.

6. The measuring device according to claim 5, characterized in that, The first flowmeter is a vortex flowmeter, and the second flowmeter is a V-cone flowmeter.

7. The measuring device according to claim 5, characterized in that, It further includes: A working medium recovery unit and a low-pressure heater drain pump, and the working medium recovery unit expands the fluid and then converts it into condensate and sends it back to the condensate system through the low-pressure drain pump.

8. The measuring device according to claim 5, characterized in that The low-pressure cylinder exhaust bypass is made of metal stainless steel pipe with an additional insulation layer, a check valve is installed on the inlet side of the low-pressure cylinder exhaust bypass, and an electric control valve is installed on the outlet side.

9. The measuring device according to claim 5, characterized in that, The calculation unit is set as a PLC.

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