HK1221017B - Method and measuring apparatus for determining specific quantities for gas quality - Google Patents

Description

Method and measuring device for determining specific quantity values for gas quality

Technical Field

The invention relates to a method and a measuring device for determining specific quantities for gas quality and/or energy consumption in the domestic and industrial sectors.

Background Art

In the future, (natural) gas composition, and therefore gas quality, will fluctuate more frequently and more dramatically due to new sources (biogas, liquefied gas from around the world, hydrogen produced using excess current from alternative energy sources). This will have varying effects on gas application processes, potentially including negative ones. Directly measuring specific gas quality variables on-site can help adjust these processes to fluctuating gas quality to ensure optimal and safe operation. These include, for example, the Wobbe index for burner control units, the air-fuel ratio in power generation systems (industrial furnaces, fuel cells, etc.), the methane number for gas engines, or the calorific value for billing purchased energy. However, the latter requires measuring the purchased gas volume, which is currently performed using volumetric flow measurement using diaphragm gas meters (for domestic use) or, with limited exceptions, rotary displacement flowmeters, turbine flowmeters, or ultrasonic flowmeters for purchasing large volumes (industrial use). All of these measurement methods are only suitable for determining the operating volume. In order to draw conclusions about the billable energy purchased from this data, conversion to standard volumes is necessary, and information on the calorific value of the various supplied gases is also necessary. Both are implemented imprecisely: standard volume is usually calculated using average temperature and average pressure, and calorific value is also averaged over the billing period.

Summary of the Invention

The object of the present invention is to provide a method and a measuring device which can determine specific values of gas quality and/or power consumption in real time.

Patent application EP 14001767 discloses a method in which a flow is generated through a critical nozzle in order to determine a specific value for the gas quality using a downstream microthermal sensor. This method requires that critical pressure conditions always prevail at the nozzle, which is achieved by supplying the nozzle with upstream pressure or by generating a vacuum downstream of the nozzle. Therefore, this method is not directly suitable for determining specific values for the gas quality at the end user, as the supply network rarely has the required upstream pressure and installing a vacuum pump downstream of the nozzle is simply not possible.

EP 2 574 918 A1 discloses a method in which a volume flow measurement device is modified with a microthermal sensor to determine the thermal diffusivity, which, given a known thermal conductivity, allows the gas to be classified as L (low calorific value) or H (high calorific value) gas. However, it is not possible to draw sufficiently precise conclusions about the calorific value and energy flow from the volume flow, thermal diffusivity, and thermal conductivity.

The object of the present invention is to remedy the disadvantages of the above-mentioned methods and to provide a method and a measuring device which are suitable for low-pressure gas networks and which can be used, in addition to classifying the gas as L or H gas, to determine the calorific value and energy consumption.

This object is achieved by a method according to claim 1 and by a measuring device according to claim 7 .

The invention is based on the concept of combining an ultrasonic flow sensor with a microthermal sensor in order to determine specific quantities of gas quality and/or energy consumption as follows.

Measurement of sound velocity and volume flow with ultrasonic flow sensors :

To determine the volume flow, an ultrasonic signal is usually injected into the flowing medium at a certain angle transverse to the flow direction, and the difference in the travel time of the ultrasonic signal is measured in the flow direction and against the flow direction (Figure 1b). The difference in the travel time of the two ultrasonic signals is then a measure of the average flow velocity, from which the volume flow can be calculated using the known line cross-section:

(1)

in

vx is _the average flow velocity,

c _s refers to the speed of sound,

L is the length of the measured distance,

t12 is the running time in the flow direction, _and

t21 is _the time running in the opposite direction of flow.

The sum of the run times contains information about the sound velocity _cs of the medium, which is usually not used further in ultrasonic flow meters.

When combined with a microthermal sensor such as that described in patent application EP 14001767, this sound velocity information makes it possible to omit the critical nozzle, as it also provides the first-order sound velocity. This has the advantage that the critical pressure condition is unnecessary, meaning that measurement can be performed at a given pressure. Consequently, compressors and vacuum pumps are no longer required in low-pressure gas networks.

Determine mass flow :

The density can be determined by correlation from the speed of sound, which for most gases is well correlated. To further improve the correlation of density, thermal conductivity can additionally be measured at one or several temperatures and included in the correlation.

The mass flow rate is proportional to the product of density ρ and flow velocity v x, ρ· _{v x :}

, (2)

Where A is the cross-sectional area of the flow channel.

Measuring thermal conductivity with the help of microthermal sensors :

An integrated CMOS hot-wire anemometer enables microthermal thermal conductivity measurement as well as mass flow measurement. For more information on this technology, see D. Matter, B. Kramer, T. Kleiner, B. Sabbattini, and T. Suter, “Mikroelektronischer Haushaltsgaszähler mit neuer Technologie” [Microelectronic domestic gas meter with new technology], Technisches Messen 71, 3 (2004), pp. 137-146.

To describe the microthermal measurements, the one-dimensional heat conduction equation describing the microthermal system is used (Kerson Huang: Statistical Mechanics , 2nd edition, John Wiley & Sons, New York 1987, ISBN 0-471-85913-3):

, (3)

in

vx refers to the average flow velocity (velocity vector) _component in the X direction, that is, along the gas flow direction,

T is the temperature,

is the temperature gradient,

cp refers to the heat capacity _of gas at constant pressure.

ρ is the density,

λ is the thermal conductivity of the gas, and

is the Laplace operator applicable to temperature T , where

.

Since the gas (gas flow) flows only in the X direction, the components of the average velocity in the Y and Z directions _, vy and vz _, are assumed to be zero. The source term, expressed in Watt/ ^m³ , describes the heating element. In microthermal methods, this source term originates from the heating wire of a miniaturized integrated hot-wire anemometer that supplies thermal energy to the system.

It must be noted that the thermal conductivity λ contributes solely to the solution of Equation (3) due to the source term. In contrast, the thermal conductivity can be determined when using a microthermal sensor without applying a mass flow ( v _x = 0 and = 0). The relevant differential equation for the temperature distribution is then simply

(4).

Furthermore, the temperature distribution can be changed by varying the source term, which enables the determination of the thermal conductivity at different temperatures.

Determine heat capacity with the help of a microthermal sensor :

The solution of equation (3) describing the temperature distribution in the microthermal system enables the flow factor to be determined by measuring said temperature distribution,

, (5)

Where A is the cross-sectional area of the flow channel on the micro-thermal sensor and is the mass flow rate. Finally, the heat capacity can be determined using the known mass flow rate and the known thermal conductivity.

Specific values related to gas quality :

From the speed of sound _cs , the thermal conductivity λ and the heat capacity _cp, three independently measured quantities are obtained, _which can now be correlated with specific quantities of the gas quality, such as the calorific value, using the correlation function fcorr :

(6).

The “sensor output” S _out is a function of the output magnitude c _s , λ, and c _p :

(7).

For example, the following correlation function is obtained for the dependence of the density ratio Q = ρ/ρ _ref at 0° C. and 1013.25 mbar shown in FIG2 a:

(8a)

where the coefficients a ₀ = 36, a ₁ = -65 and a ₂ = 30 and methane (G20) is used as a reference. _{S out} is simply the speed of sound c _s :

(9a).

Figure 2b shows an improved correlation of the density ratio Q = ρ/ρ _ref at 0 °C and 1013.25 mbar based on the sound velocity and thermal conductivity measured at two different temperatures.

In the case of the dependence of certain quantities of the gas quality in FIG3 a , equation (8a) for the calorific value example is interpreted as follows:

(8b)

The coefficients a ₀ = 8.1, a ₁ = -11 and a ₂ = 4.7 and methane (G20) remain as the reference value. _{S out} is now a function of all three output values:

(9b).

It is easy to understand from the results in Figures 2 and 3a that the Wobbe index W defined as follows as a measure of burner power is

, (10)

As a further gas quality, the density equation (8a) and the calorific value equation (9b) can be combined with one another using c _s , c _p and λ.

As another example, the three independent quantities of speed of sound _cs , thermal conductivity λ, and heat capacity _cp can be related to the gas quality Z or real gas factor, which describes the deviation of the behavior of a real gas from the ideal gas law:

(11).

Real gas behavior deviates significantly from ideal gas behavior, especially at higher pressures—thus requiring particular consideration—such as those found in large gas pipelines. Of interest in this application is the fact that the determination of the individual quantities need not be performed at the same high pressure, but can also be performed, for example, at ambient pressure, where the various measuring devices can be configured much more simply. Figure 3b shows a possible correlation of the Z factor at 50 bar with the following basic parameters:

(8c)

The coefficients a ₀ = 1.1, a ₁ = 0.15, a ₂ = -0.29 and a ₃ = 0.05 are used, and methane (G20) is used as a reference. _{S out} is again a function of all three output quantities (at ambient pressure):

(9c).

Another example to mention is the relationship between kinematic viscosity η/ρ (viscosity/density). This quantity is in turn found in the Reynolds number Re, which is used in fluid mechanics and can be understood as the ratio of inertial forces to viscous forces:

, (12)

where ρ is the density, v is the velocity of the gas relative to the body in the fluid, and d is the characteristic length of the body. This shows that similar objects behave identically in turbulence at the same Reynolds number. Knowing the kinematic viscosity allows us to estimate when turbulence occurs in, for example, the gas in a pipeline system. This is an important input for configuring such a gas distribution network, as in the case of a gas distribution network. Figure 3c shows the correlation between the kinematic viscosity η/ρ and the sensor output S _out :

(8d)

The coefficients a ₀ = 0.15 and a ₁ = 0.85 are used and methane (G20) is used as a reference. _{S out} is again a function of all three output values:

(9d).

It must be noted that the choice of S _out on the one hand and f _corr on the other hand is by no means predetermined, but is freely chosen so that the resulting correlation error becomes as small as possible. The polynomial functions mentioned in equations (8a) to (8d) are typical choices that are usually successful, while equations (9a) to (9d) attempt to describe the physical interrelationships.

In order to demonstrate that the method of the present invention is not limited to the examples described above, further examples of specific values of the gas quality which can be determined using the method are mentioned below:

The methane number is an important indicator of the knock tendency of gaseous fuels in gas engine drives, which can be used in a stationary manner (for example in combined heat and power plants) or in the power sector (for example in gas vehicles, ships, etc.).

The "air-fuel ratio" and therefore the amount of air supplied to the process. Knowledge of the "air-fuel ratio" is important, for example, in combustion processes that are stoichiometric (e.g. in combustion plants) or with excess air (e.g. in lean-burn engines), open-ignition or catalytic (e.g. in retrofit processes in high-temperature fuel cells), in order to optimize the efficiency of the combustion process and the exhaust gas behavior.

The methane content, whose monitoring is important, is crucial in the process industry. In biogas plants, the methane content is usually monitored in the crude biogas (e.g., as a measure of fermenter efficiency) and/or in the fuel gas supplied to the natural gas grid (e.g., for quality control) and/or in the residual gas released into the air (primarily carbon dioxide and, to a lesser extent, methane, as the latter has a high greenhouse effect).

Method steps in a typical embodiment

1. Measure the pressure p and temperature T of the gas.

2. Ultrasound determines the volume flow rate, which is proportional to the flow velocity _vx , and the speed of sound _cs , which for most gases is well related to the standard density ρ _norm .

3. The thermal conductivity λ _Ti measured with a microthermal sensor (at one or several temperatures _Ti ) is added to further improve the correlation of the standard density ρ _norm .

4. Calculate the density under operating conditions using the following formula:

(13).

5. Use this information (v _x ,ρ) to determine the mass flow rate, which is proportional to ρ·v _x , and use it together with the thermal conductivity λ measured with the microthermal sensor and the flow factor to determine the heat capacity c _p .

6. Correlate the required specific values of gas quality, in particular the calorific value CV, from the speed of sound _cs , thermal conductivity λ and heat capacity _cp .

7. If necessary, the energy consumption _En can be determined by multiplying the mass or volume flow rate by the calorific value CV (in J/kg or J/ ^m3 respectively).

The above-mentioned standard density ρ _norm is to be understood in this specification as the density at a specified temperature T _norm and a specified pressure p _norm . The standard density is usually specified at 0°C and 1013.25 mbar. Other values of temperature T _norm and pressure p _norm can also be determined, for which the correlation between density and sound speed is known.

Method and measuring device of the present invention

In the method of the present invention for determining a specific quantity value of gas quality,

- The gas or gas mixture flows through the ultrasonic flow sensor and through the microthermal sensor, wherein

- detecting the temperature and pressure of the gas or gas mixture;

- determining the flow rate or volume flow and the speed of sound of the gas or gas mixture by means of an ultrasonic flow sensor;

- Correlation between the speed of sound and the density of the gas or gas mixture;

- Use density information together with flow velocity to calculate mass flow rate;

- determination of the thermal conductivity of the gas or gas mixture at one or several temperatures by means of a microthermal sensor;

- calculating a flow factor from the flow signal of the microthermal sensor in order to determine from it, together with information on the mass flow and thermal conductivity, the heat capacity or a quantity of the gas or gas mixture that depends on the heat capacity;

Finally, the speed of sound, the heat capacity at one or several temperatures and the heat capacity or quantities dependent on the heat capacity are used to correlate certain quantities with the gas quality, in particular the calorific value.

If necessary, the sound velocity determined by the ultrasonic flow sensor can be converted to the sound velocity at standard temperature.

In an advantageous embodiment, the thermal conductivity determined at one or several temperatures by means of the microthermal sensor is used together with the speed of sound to more accurately correlate the density.

The density correlated by the speed of sound or by the speed of sound and the thermal conductivity can be, for example, a standard density. The density correlated by the speed of sound or by the speed of sound and the thermal conductivity or the standard density is advantageously converted to a density under operating conditions using the temperature and pressure of the gas or gas mixture.

In an advantageous embodiment of the method, the speed of sound, the thermal conductivity at one or several temperatures and the heat capacity or a quantity dependent on the heat capacity are used to correlate the calorific value or the Wobbe index (W) or the Z factor or the kinematic viscosity.

In a further advantageous embodiment of the method, the energy consumption is calculated from the calorific value together with the volume or mass flow, for example wherein the product of the volume or mass flow and the calorific value is integrated over time.

The above-described method and the above-described embodiments and variants are suitable for both continuous and intermittent determination of specific quantities for gas quality and/or energy consumption.

The measuring device according to the invention for determining specific quantities of gas quality and/or energy consumption comprises an evaluation unit equipped for carrying out a method according to one of the above-described embodiments and variants and an ultrasonic flow sensor for measuring the sound velocity and the flow velocity, a pressure sensor for measuring the pressure, a temperature sensor for measuring the temperature, and a microthermal sensor for measuring the thermal conductivity and heat capacity or quantities of the gas or gas mixture that are dependent on the heat capacity.

In a first embodiment of the measuring device, an ultrasonic flow sensor and a microthermal sensor are arranged in the gas line and can provide the same mass flow.

In a second embodiment of the measuring device, an ultrasonic flow sensor is arranged in the main gas line and a microthermal sensor is arranged in a bypass gas line of the main gas line, wherein an element generating a pressure drop is provided in the main gas line to generate a mass flow in the bypass gas line.

In the first and second embodiments, the ultrasonic flow sensor is advantageously placed non-invasively on the gas line or main gas line.

In a third embodiment of the measuring device, an ultrasonic flow sensor and a microthermal sensor are arranged in a bypass gas line of the main gas line, wherein an element generating a pressure drop is provided in the main gas line to generate a mass flow in the bypass gas line.

The split ratio between the mass flows in the bypass gas line and the main gas line is advantageously known in the second and third embodiments, for example by calibration with a known gas.

Regardless of the embodiment and variant, the measuring device may further comprise a section of a gas line or a main gas line and/or a bypass gas line in which at least one sensor of the measuring device is located, and/or an element generating a pressure drop in the main gas line.

The evaluation unit advantageously forms a modular unit together with the rest of the measuring device. Depending on the application, the measuring device can form a modular unit even without the evaluation unit, wherein the evaluation unit can be formed in a separate or higher-level computing unit.

The advantage of the inventive method and measuring device for determining specific quantities of gas quality and/or energy consumption is that they can also be used in low-pressure gas networks without requiring an additional compressor or an additional vacuum pump as provided in the measuring device described in patent application EP 14001767.

It is also advantageous that the thermal conductivity of the gas or gas mixture at one or several temperatures determined by means of the microthermal sensor can be used together with the speed of sound to more accurately correlate the density, which leads to more accurate mass flow values.

The association of specific quantities of the gas quality from the three independent variables of sound velocity, thermal conductivity and heat capacity furthermore enables a higher degree of accuracy in determining the calorific value and energy consumption than is possible with the initially described method according to EP 2 574 918 A1.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be explained in more detail below with reference to the accompanying drawings, in which:

FIG1 a shows a schematic configuration of one embodiment of a microthermal anemometer;

FIG1 b shows a schematic diagram of an ultrasonic flow sensor;

Figure 2a shows an example of density determination (correlation) based on the speed of sound;

FIG2 b shows an example of an improved density determination (correlation) based on the speed of sound and thermal conductivity;

FIG3 a shows an example of calorific value determination (correlation) based on heat capacity, thermal conductivity, and sound velocity;

Figure 3b shows an example of Z-factor determination (correlation) based on heat capacity, thermal conductivity, and sound velocity;

Figure 3c shows an example of kinematic viscosity determination (correlation) based on heat capacity, thermal conductivity, and sound speed;

FIG4 shows an embodiment of a schematic construction of a measuring device according to the invention in a main gas line;

FIG5 shows a second embodiment of a schematic construction of a measuring device according to the invention with a microthermal sensor in a bypass gas line of a main gas line, and

FIG. 6 shows a third embodiment of a schematic configuration of a measuring device according to the invention in a bypass gas line.

DETAILED DESCRIPTION

FIG1a shows one embodiment of a microthermal sensor 7 for use in the measuring device according to the present invention. As shown in FIG1a , the microthermal sensor can be an integrated microthermal CMOS hot-wire anemometer, which, during operation, is placed in a bypass gas line and supplied with a gas or gas mixture flow 2a. The microthermal CMOS hot-wire anemometer comprises a substrate 13, which typically contains a membrane 14 a few micrometers thick. The CMOS hot-wire anemometer further comprises two thermocouples 15.1 and 15.2 and a heating element 16 that can be positioned in the flow direction between the two thermocouples. The thermocouples 15.1 and 15.2 can be used to detect the temperature, which is obtained as a result of heat exchange 15.1a and 15.2a with the gas or gas mixture flow 2a.

For further details on the functionality of the integrated microthermal CMOS hot wire anemometer, reference is made to D. Matter, B. Kramer, T. Kleiner, B. Sabbattini, T. Suter, “Mikroelektronischer Haushaltsgaszähler mit neuer Technologie” [Microelectronic domestic gas meter with new technology], Technisches Messen 71, 3 (2004), pp. 137-146.

FIG1B shows one embodiment of an ultrasonic flow sensor 4 for use in a measuring device according to the present invention. For example, two units 17 and 18 are positioned at obliquely opposite locations on the measuring line, both generating and receiving sound (e.g., piezoelectric actuators or receivers). The sound pulses emitted by actuator 17 arrive at receiver 18 more quickly than the sound pulses emitted simultaneously by actuator 18. The sound velocity _cs and the flow velocity _vx can both be calculated from the operating times _t12 and _t21, along with the geometric factors of the device.

For further details on the functioning of ultrasonic sensors, reference is hereby made to L.C. Lynnwortha, Yi Liub, “Ultrasonic flowmeters: Half-century progress report, 1955–2005” in Ultrasonics, 44, Supplement (2006), pp. e1371–e1378.

FIG4 shows one embodiment of a schematic configuration of a measuring device according to the present invention. In this embodiment, a measuring device 11 comprises an evaluation unit 10 equipped for carrying out the method according to the present invention, an ultrasonic flow sensor 4, a microthermal sensor 7, as well as a pressure sensor 8 and a temperature sensor 9, which can be arranged in the gas line 1. Some or all of these components can be combined into a modular unit, of which the evaluation unit 10 can be a component (variant 11a), or the evaluation unit can be connected separately (variant 11b), for example, in a higher-level computing unit.

The configuration of the embodiment shown in FIG. 4 is particularly suitable for determining specific quantities of gas quality in small and minute gas flows as are present in the field of gas analysis and where information on the gas quality is of significance.

The measuring device in the embodiment shown in FIG4 can be used, for example, as an analysis unit or as a separate analysis device. The analysis unit or analysis device advantageously comprises a gas line 1 in which the sensors 4, 7, 8, 9 of the measuring device are located. Gas samples can be taken and analyzed using the analysis unit or analysis device. The necessary connections and valves for this purpose are not shown in FIG4.

An embodiment of the method according to the present invention for determining specific quantitative values of the gas quality of gas and gas mixtures is described below with reference to FIG4 . In this method, the gas or gas mixture flows through an ultrasonic flow sensor 4 and a microthermal sensor 7 in a gas pipeline 1. Pressure and temperature sensors 8 and 9, additionally installed in the gas pipeline, are used to determine the pressure and temperature of the gas or gas mixture, i.e., the operating conditions. The ultrasonic sensors also measure the speed of sound and the flow velocity or volume flow. The density is then correlated based on the speed of sound, with the density determined using this correlation being appropriately converted to the density at a given temperature and pressure (operating conditions).

In addition, the thermal conductivity of the gas at one or several temperatures is measured using a microthermal sensor 7, while varying the heating power of the heating wire. If necessary, the results of this measurement can also be included in the density correlation. The mass flow rate is then calculated from the density and volume flow values. The ratio between the heat capacity and thermal conductivity of the gas is calculated using the flow factor, also measured using the microthermal sensor, and combined with the known thermal conductivity to calculate the heat capacity value. The speed of sound, thermal conductivity, and heat capacity are then correlated to specific quantities of gas quality, such as the calorific value, Wobbe index (W), Z factor, or kinematic viscosity. If necessary, the energy consumption can be determined by multiplying the mass flow rate by the calorific value.

5 shows a second embodiment of a schematic design of a measuring device 11 according to the invention with a microthermal sensor 7 in a bypass gas line 6 of a main gas line 1. In this case, a pressure drop-generating element 5 is provided in the main gas line to generate a pressure drop via the bypass gas line during operation, which results in a gas flow 2 in the bypass gas line, wherein a characteristic split ratio 3 is achieved between the main gas line and the bypass gas line.

In the illustrated embodiment, the measuring device comprises, in addition to the microthermal sensor 7, an evaluation unit 10 equipped for carrying out the method according to the invention, as well as an ultrasonic flow sensor 4, a pressure sensor 8, and a temperature sensor 9, which are typically arranged in the main gas line 1. Some or all of these components can be combined into a modular unit, of which the evaluation unit 10 can be a component (variant 11a), or the evaluation unit can be connected separately (variant 11b), for example in a higher-level computing unit.

5 is suitable both for determining specific quantities for gas quality and, using calorific value as gas quality, for measuring the energy consumption of medium to large gas flows, such as are found in the domestic sector, industry or custody transfer.

The ultrasonic flow sensor 4 does not necessarily have to be installed in the gas line or main gas line 1, but can also be connected to the gas line or main gas line from the outside as a so-called "clamp-on device." On the other hand, the microthermal sensor 7 only requires minute flow quantities and is therefore preferably placed in the bypass gas line 6.

A second embodiment of the method for determining specific values of the gas quality of gas and gas mixtures according to the present invention will now be described with reference to FIG5 . In this method, the gas or gas mixture flows through a main gas line 1 or through a pressure drop-generating element 5. A bypass gas line 6 branches off before the pressure drop-generating element 5 and rejoins the main gas line after the element. The pressure drop-generating element 5 forces a portion of the gas or gas mixture 2 to flow through the bypass gas line 6 and past a microthermal sensor 7 positioned therein. The main gas flow is supplied to an ultrasonic flow sensor 4.

The pressure and temperature of the gas or gas mixture, i.e., the operating conditions, are determined using a pressure sensor 8 and a temperature sensor 9, which are also installed in the main gas line. Ultrasonic sensors also measure the speed of sound and the flow velocity or volume flow. The density is then correlated based on the speed of sound. The density determined using this correlation is then appropriately converted to the density at the given temperature and pressure (operating conditions).

Furthermore, the thermal conductivity of the gas at one or several temperatures is measured using a microthermal sensor 7, while varying the heating power of the heating wire. If necessary, the results of this measurement can also be included in the density correlation. The mass flow through the main gas line 1 is then calculated from the density and volume flow values. The mass flow in the bypass gas line is then calculated using the appropriate split ratio between the mass flows of the main and bypass gas lines. This split ratio can be predetermined, for example, using calibration measurements with known gases.

The ratio between the heat capacity and thermal conductivity of the gas or gas mixture is calculated from the flow factor, also measured by the microthermal sensor, and combined with the known thermal conductivity to calculate the heat capacity value. The speed of sound, thermal conductivity, and heat capacity are then used to correlate specific values for gas quality. In the case of calorific value as the gas quality, the mass flow in the main gas line multiplied by the calorific value also provides an indication of energy consumption.

6 shows a third embodiment of a schematic configuration of a measuring device 11 according to the invention in a bypass gas line 6 of a main gas line 1. In this case, a pressure drop-generating element 5 is provided in the main gas line to produce a pressure drop via the bypass gas line during operation, which results in a gas flow 2 in the bypass gas line, wherein a characteristic split ratio 3 is formed between the main gas line and the bypass gas line.

In the illustrated embodiment, the measuring device comprises an evaluation unit 10 equipped for carrying out the method according to the invention, as well as an ultrasonic flow sensor 4 and a microthermal sensor 7 arranged in the bypass gas line 6. The measuring device also comprises a pressure sensor 8 and a temperature sensor 9, which are usually also arranged in the bypass gas line 1. Some or all of these components can be combined into a modular unit, wherein the evaluation unit 10 can be a component of the modular unit (variant 11a), or the evaluation unit can be connected separately (variant 11b), for example, in a higher-level computing unit.

6 is preferably obtained when the ultrasonic sensor 4 is formed in microtechnology and only microflow values are required for said sensor, like the microthermal sensor 7 . Both sensors are then advantageously arranged in the bypass gas line 6 .

A third embodiment of the method according to the present invention for determining specific values of gas quality for gas and gas mixtures is described below with reference to FIG6 . This method is suitable for both continuous and intermittent determination of specific values of gas quality and/or energy consumption. Optional connections and valves are not shown in FIG6 .

In a third embodiment of the method, the gas or gas mixture flows through or through a pressure drop-generating element 5 in the main gas line 1. A bypass gas line 6 branches off before the pressure drop-generating element 5 and rejoins the main gas line after the element. The pressure drop-generating element 5 forces a portion of the gas or gas mixture 2 to flow through the bypass gas line 6 and past an ultrasonic flow sensor 4 and a microthermal sensor 7 positioned within the bypass gas line. The ultrasonic flow sensor 4 and the microthermal sensor 7 are supplied with the same gas flow.

The pressure and temperature of the gas or gas mixture, i.e., the operating conditions, are determined using a pressure sensor 8 and a temperature sensor 9, which are also installed in the bypass gas line. Ultrasonic sensors are also used to measure the speed of sound and the flow velocity or volume flow. The density is then correlated based on the speed of sound. The density determined using this correlation is then appropriately converted to the density at the given temperature and pressure (operating conditions).

Furthermore, a microthermal sensor 7 measures the thermal conductivity of the gas at one or several temperatures, varying the heating power of the heating wire. If necessary, the results of these measurements can also be incorporated into the density correlation. The mass flow through the bypass gas line 6 is then calculated from the density and volume flow values.

The ratio between the heat capacity and thermal conductivity of the gas is calculated from the flow factor, also measured with the microthermal sensor, and combined with the known thermal conductivity to calculate the heat capacity value. The speed of sound, thermal conductivity, and heat capacity are then used to correlate specific values for the gas quality.

Since the above measurements and calculations involve the bypass gas line, the mass flow in the main gas line is calculated using the split ratio of the mass flow between the main gas line and the bypass gas line. The split ratio can be predetermined, for example, using a known gas in a calibration measurement. If the calorific value is determined as a specific measure of gas quality, the multiplication of the mass flow in the main gas line by the calorific value also provides the energy consumption.

The method and the measuring device for determining specific quantities of gas quality and/or energy consumption according to the invention and the above-described embodiments and variants can be used in high-pressure and low-pressure gas networks and provide a relatively high degree of accuracy in the determination of the above-mentioned quantities due to the correlation of the three independent variables, namely the speed of sound, the thermal conductivity and the heat capacity.

Claims (14)

1. A method for determining a specific value of gas quality, wherein - allowing the gas or gas mixture to flow through the ultrasonic flow sensor and the microthermal sensor, and detecting the temperature (T) and pressure (p) of the gas or gas mixture; - determining the flow velocity (v _x ) or volume flow and the speed of sound (c _s ) of the gas or gas mixture by means of the ultrasonic flow sensor; - Correlating the density of the gas or gas mixture to the speed of sound (c _s ); - using said density information together with the flow velocity to calculate the mass flow rate; - determining the thermal conductivity (λ) of the gas or gas mixture at one or several temperatures using the microthermal sensor; - calculating a flow factor ( ) from the flow signal of the microthermal sensor in order to determine therefrom, together with the information on the mass flow and thermal conductivity, the heat capacity ( c _p ) or a quantity of the gas or gas mixture dependent on the heat capacity; Finally, the speed of sound, the thermal conductivity at one or several temperatures and the heat capacity or a quantity dependent on the heat capacity are used to correlate a specific quantity to the gas quality. 2 . The method according to claim 1 , wherein the sound velocity (c _s ) determined by the ultrasonic flow sensor is converted into a sound velocity at a standard temperature (T _norm ). 3. The method according to claim 1, wherein the thermal conductivity (λ) determined by the microthermal sensor at one or several temperatures is used together with the speed of sound to more accurately correlate the density. 4. The method according to claim 1 , wherein the density determined by means of the correlation is a standard density and/or wherein the density determined by means of the correlation is converted into a density under operating conditions (ρ) using the temperature (T) and pressure (p) of the gas or gas mixture. 5. The method according to claim 1 , wherein the sound velocity, the thermal conductivity at one or several temperatures and the heat capacity or a quantity dependent on the heat capacity are used to correlate the calorific value or the Wobbe index (W) or the Z factor or the kinematic viscosity. 6. Method according to claim 5, wherein the energy consumption ( _EN ) is calculated from the calorific value together with the volume flow or mass flow. 7. A measuring device for determining specific quantities of gas quality and/or energy consumption, comprising an evaluation unit (10) equipped for carrying out the method according to one of claims 1 to 6 and comprising an ultrasonic flow sensor (4) for measuring the speed of sound and the flow velocity, a pressure sensor (8) for measuring the pressure, a temperature sensor (9) for measuring the temperature, and a microthermal sensor (7) for measuring the thermal conductivity and heat capacity or quantities of the gas or gas mixture that are dependent on the heat capacity. 8. The measuring device according to claim 7, wherein the ultrasonic flow sensor (4) and the microthermal sensor (7) are arranged in the gas line (1) and can provide the same mass flow. 9. The measuring device according to claim 7, wherein an ultrasonic flow sensor (4) is arranged in a main gas line (1) and a microthermal sensor (7) is arranged in a bypass gas line (6) of the main gas line, and an element (5) generating a pressure drop is provided in the main gas line to generate a mass flow in the bypass gas line. 10. The measuring device according to claim 8, wherein an ultrasonic flow sensor (4) is placed non-invasively on the gas line or main gas line (1). 11. The measuring device according to claim 7, wherein the ultrasonic flow sensor (4) and the microthermal sensor (7) are arranged in a bypass gas line (6) of the main gas line (1), and an element (5) that generates a pressure drop is provided in the main gas line to generate a mass flow in the bypass gas line. 12. The measuring device according to claim 9, wherein the split ratio between the mass flows in the bypass gas line and the main gas line is known. 13. The measuring device according to claim 7 , wherein the measuring device further comprises a section of the main gas line ( 1 ) and/or the bypass gas line ( 6 ) in which at least one of the sensors ( 4 , 7 , 8 , 9 ) of the measuring device ( 11 ) is arranged, and/or an element ( 5 ) for generating a pressure drop in the main gas line ( 1 ). 14. Measuring device according to one of claims 7 to 9 or 11, wherein the evaluation unit (10) forms a modular unit together with the rest of the measuring device, or wherein the measuring device forms a modular unit without the evaluation unit (10) and the evaluation unit is formed in a separate or higher-level computing unit.