DE19823193A1 - Natural gas density determination - Google Patents

Abstract

The density or sound velocity of both the gas and a calibration gas are each measured under standard conditions. The density of the gas under operational conditions is determined from a correlation function. Preferred Features: A large number of correlation functions is presented, each provided as an equation. Quantities interrelated under standard and operational conditions include density, calorific value (unqualified), temperature, carbon dioxide proportion, gas viscosity. A second calibration gas may be involved in addition to methane, e.g. argon, ethylene or nitrogen. Sound velocity equations are provided.

Description

The invention relates to a method for determining the Density of a gas, especially natural gas, under operation conditions, wherein a Be containing a vibrating body drive density sensor calibrated using a calibration gas and a density reading of the gas under operating conditions is measured with the help of the operating density sensor.

Can be used as vibrating bodies in the operating density transducers e.g. B. swing forks or swing cylinders can be used. To measure a density reading, the vibrating body is turned on its surface exposed to the gas to be examined. At Excitation of the vibrating body in the operating density sensor the surrounding gas is also excited to vibrate. It pressure and speed fluctuations in the gas witnesses that reproduce at the speed of sound. There through energy from the vibrating system to the surrounding one Gas released. The energy radiated by the vibrating body is converted into kinetic energy in the gas. Due to the depending on the density of the surrounding gas attenuation of the Vibrating body increases the period of the vibrations and their frequency.

When calibrating an operating density sensor with A calibration gas becomes a relationship between the density of the calibration gas and the frequency of the vibrating body posed.

The density sensor is then used to determine the Density of a gas used under operating conditions, wel a different composition than the calibration gas indicates systematic measurement errors of up to approx. 3% the influence of the gas type.

The object of the present invention is to cost one to provide an inexpensive process to the density  of a gas under operating conditions to determine more precisely can.

This task is carried out in a generic method solved according to the invention in that the density or sound speed of both the gas and the calibration gas is recorded under standard conditions and the density of the Gases under operating conditions from the density reading Help one of the difference in density or sound speeds of the gas and the calibration gas below standard condition-dependent correction function is determined.

An extremely simple correction function is e.g. B. as follows:

ρ _corr = ρ _BDA . [1 + K _{ρ n} .Δρ _n ] (1),

where K _{ρ n is} a constant or a function of ρ _BDA and / or temperature, and

Δρ _n = ρ _{n, meas} - ρ _{n, cal} .

The density of the gas can be determined just as easily with the help of the following correction function:

ρ _corr = ρ _BDA . [1 + K _{c n} .Δc _n ] (2),

where K _{c n is} a constant or a function of ρ _BDA and / or temperature, and

Δc _n = c _{n, meas} - c _{n, cal} .

A further development of the invention, one more thing allows more accurate determination of the density of the gas is there characterized in that also the calorific value of the gas and the calibration gas is detected under standard conditions and that the correction function used to determine the under Be operating density measured is used from Calorific value of the gas and the calibration gas under standard conditions.

In this case, for example, the correction function can have the following form:

ρ _corr = ρ _BDA . [1 + K _{ρ n} .Δρ _n + K _{H n} .ΔH _n ] (3),

where K _{ρ n} and K _{H n are} constants or functions of ρ _BDA and / or temperature, and

Δρ _n = ρ _{n, mess} - ρ _{n, cal} and
ΔH _n = H _{n, meas} - H _{n, cal} .

If sound speed values for the gas and the calibration gas are already available under standard conditions for a special application, the density of the gas can alternatively be determined using the following correction function:

ρ _corr = ρ _BDA . [1 + K _{c n} .Δc _n + K _{H n} .ΔH _n ] (4),

where K _{c n} and K _{H n are} constants or functions of ρ _BDA and / or temperature, and

Δc _n = c _{n, meas} - c _{n, cal} and
ΔH _n = H _{n, meas} - H _{n, cal} .

The accuracy of measurement for determining the density of the gas can be further increased by also detecting the temperature of the gas under operating conditions (T _mess ) and the temperature of the calibration gas during calibration (T _kal ) and that the correction function used to determine the Density measured under operating conditions is dependent on the operating temperature of the gas and the calibration temperature of the calibration gas.

Naturally, the highest accuracy can be achieved by achieving that both the calorific value of the gas and the Calibration gas under standard conditions as well as the operating temperature and the calibration temperature are recorded.

It has been shown that the density of the gas can be determined particularly reliably using the following correction function:

ρ _corr = ρ _BDA . [1 + K _{ρ n} .Δρ _n + K _{H n} .ΔH _n ] + K _T .ΔT (5),

where K _{ρ n} and K _{H n are} constants or functions of ρ _BDA and / or temperature, K _{T is} a constant or function of ρ _BDA , and

Δρ _n = ρ _{n, mess} - ρ _{n, cal} ,
ΔH _n = H _{n, meas} - H _{n, cal} and
ΔT = T _mess - T _kal .

Equally reliable results for density can be determined using the following correction function:

ρ _corr = ρ _BDA . [1 + K _{c n} .Δc _n + K _{H n} .ΔH _n ] + K _T .ΔT (6),

where K _{c n} and K _{H n are} constants or functions of ρ _BDA and / or temperature, K _{T is} a constant or function of ρ _BDA , and

Δc _n = c _{n, meas} - c _{n, cal} ,
ΔH _n = H _{n, meas} - H _{n, cal} and
ΔT = T _mess - T _kal .

A further development of the invention with which the density of the gas can be determined more precisely under operating conditions is characterized in that the carbon dioxide content of the gas and the calibration gas (x _{CO2, measured} , x _{CO2, cal} ) is also detected and that the correction function , which is used to determine the density measured under operating conditions, is dependent on the carbon dioxide part of the gas and the calibration gas.

In a preferred embodiment, the density of the gas is determined using the following correction function:

ρ _corr = ρ _BDA . [1 + K _{ρ n} .Δρ _n + K _{H n} .ΔH _n + K _CO2 .Δx _CO2 ] + K _T .ΔT (7),

where K _{ρ n} , K _{H n} and K _{CO2 are} constants or functions of ρ _BDA and / or temperature, K _{T is} a constant or function of ρ _BDA , and

Δρ _n = ρ _{n, mess} - ρ _{n, cal} ,
ΔH _n = H _{n, mess} - H _{n, cal} ,
ΔT = T _mess - T _kal and
Δx _CO2 = x _{CO2, mess} - x _{CO2, cal} .

Alternatively, the density of the gas can be determined with the following correction function:

ρ _corr = ρ _BDA . [1 + K _{c n} .Δc _n + K _{H n} .ΔH _n + K _CO2 .Δx _CO2 ] + K _T .ΔT (8),

where K _{c n} , K _{H n} and K _{CO2 are} constants or functions of ρ _BDA and / or temperature, K _{T is} a constant or function of ρ _BDA , and

Δc _n = c _{n, meas} - c _{n, cal} ,
ΔH _n = H _{n, mess} - H _{n, cal} ,
ΔT = T _mess - T _kal and
Δx _CO2 = x _{CO2, mess} - x _{CO2, cal} .

The variable K _T is preferably determined using the following simple function: K _T = K _{T 0} + ρ _BDA .K _{T 1} , where K _{T 0} and K _{T 1 are} constants.

The above-mentioned object of the present invention is further achieved by a generic method, which is characterized in that the speed of sound and the viscosity of both the gas and the calibration gas in each case under operating conditions (c _mess , c _kal , η _mess , η _kal ) is determined and the density of the gas under operating conditions is determined from the density measured value with the aid of a correction function dependent on the speed of sound and the viscosity of the gas and the calibration gas.

The speed of sound and the viscosity of the gas and the calibration gas can either be measured immediately are derived or from other known measurands the. The latter option is used in practice Preferred for reasons of cost.

A preferred embodiment of the invention is characterized in that the density of the gas is determined using the following correction function:

where τ: period of the vibrating body,
T: temperature and
K _C , K _η , K _T0 , K _{T1 are} constants.

The reliability that can be achieved with the help of this correction function when determining the density of the gas under operating conditions is considerable. It has proven useful to use K _c ² ethane as the reference gas to determine the sound velocity-dependent constant.

For some applications, e.g. B. in the density determination of natural gas, a correspondingly high accuracy can be achieved with the help of the following simplified correction function:

where τ: period of the vibrating body,
T: temperature and
K _C , K _η , K _T0 , K _{T1 are} constants.

Basically, it is advantageous to determine the operating density calibrate with a calibration gas which is has the same composition as the sample gas, whose density is then to be measured. Should the Density of natural gas can be determined, it is advantageous that Methane is used as the calibration gas. The density of me than is with very high accuracy in the prior art knows. In addition, there is usually at least one natural gas 80% from methane. The natural gas from the CIS states even contains more than 98% methane. So calibration with Me than a good basis for an exact density determination of Natural gas.

K _c ² and K _η are preferably determined by calibration with a second calibration gas in addition to methane, e.g. B. argon, ethene or nitrogen, and are treated as type-specific constants, which depend only on the operating density sensor type.

It has been proven that the speed of sound of the Gases and / or the calibration gas as a function of density under operating conditions and density under standard conditions conditions and / or the temperature and / or the calorific value and / or the carbon dioxide content is determined. Also here the principle applies that the speed of sound is all the more can be determined more precisely, the more measured variables in the radio tion to determine the speed of sound. The  Accuracy in the subsequent determination of the density of the Gases under operating conditions increase accordingly.

A further development of the invention is characterized in that when determining the density of natural gas methane is used as the calibration gas, that the speed of sound of methane (c _{CH 4} ) is calculated according to the following equation:

c _{CH 4} = A ₀ + (A ₁ + A ₂ .T _mess ) .T _mess + (A ₃ + A ₄ .ρ _BDA + A ₅ .ρ ² _BDA ) .ρ _BDA '+ (A ₆ + A ₇ . T _mess ) .T _mess .ρ _BDA (11)

and the speed of sound of the natural gas (c _mess ) is determined according to the following equation:

C _mess = C _{CH 4} + [(B ₁ + B ₂ .Δρ _n + B ₃ .T _mess ) + (B ₄ + B ₅ .T _mess + B ₆ .ρ _BDA + B ₇ .ρ _BDA .Δρ _n ) .ρ _BDA ] .Δ _n
+ [(C ₁ + C ₂ .T _mess ) + (C ₃ + C ₄ .ρ _BDA + C ₅ .T _mess ) .ρ _BDA ] .ΔH _n + [D ₁ .ρ _BDA ] .X _{CO 2} (12 ),

where A ₀ -A ₇ , B ₁ -B ₇ , C ₁ -C ₅ and D _{1 are} constants, X _{CO 2} indicates the carbon dioxide content in natural gas,

Δρ _n = ρ _{n, mess} - ρ _{n, CH 4} and
ΔH _n = H _n , meas - H _n , CH ₄ .

Equations (11) and (12) are very simple builds and sufficiently precise. With them the Schallge speed determined with an error below 0.1% become.

The viscosity of the gas is advantageous and / or the calibration gas as a function of the density below Operating conditions and density under standard conditions and / or the temperature and / or the calorific value. All measured variables go into the function for determining the Vis kosität the gas or the calibration gas, the Determine the viscosity of the gas with the greatest accuracy. The accuracy in determining the density of the gas is correspondingly high.

For example, if methane is used as the calibration gas when determining the density of natural gas, the viscosity of methane is used, the viscosity of methane (η _{CH 4} ) can be calculated using the following equation:

η _{CH 4} = A ₀ + A ₁ .T + (A ₂ + A ₃ .ρ _BDA ) .ρ _BDA (13)

and the viscosity of the natural gas (η _mess ) can be determined according to the following equation:

η _mess = η _{CH 4} + B ₁ (1 - ρ _BDA ) .Δρ _n + B ₂ .ΔH _n (14)

where A ₀ -A ₃ , B ₁ and B _{2 are} constants,

Δρ _n = ρ _{n, mess} - ρ _{n, CH 4} and
ΔH _n = H _{n, meas} - H _{n, CH 4} .

Equations (13) and (14) are also very simple built up. The viscosities determined with them are only with an error well below 5% and so with sufficient accuracy to correct the density reading.

It has proven useful to find the parameters and Constants of suitable functions, especially the correction turfunctions, several measuring cycles with reference gases leads, the compositions of which are known. As Re Reference equation for calculating the speed of sound can e.g. For example, the AGA-8-DC92 equation of state can be used. However, the precondition for their application is the exact one Knowledge of the composition of the reference gases. For reference equation for calculating the viscosity of natural gases e.g. B. the approach of Herning and Zipperer can be chosen. The reference gases should advantageously range from Cover compositions in which the compositions of the later measurement gases are expected to lie.

In the following the invention based on several in the Exemplary embodiments shown in the drawings tert. The drawing shows:

Fig. 1 eight diagrams in which the density measurement error against the density for six pure gases and four different operating density transducers at T = 10 ° C is plotted, namely in the left column using the known method and in the right column for users application of the method according to the invention;

Fig. 2 eight diagrams in which the density measurement error against the density for six natural gases and the four different operational density transducers at T = 10 ° C is plotted, in the left column when using the known method and in the right column when using the method according to the invention;

Fig. 3 eight diagrams in which the density measurement error for Ekofisk natural gas and the four different operating density transducers is plotted against the density at different temperatures, in the left column when using the known method and in the right column when using a second exemplary embodiment of the method according to the invention;

Fig. 4 is six graphs which illustrate the operation of the inventive method according to Fig. 1 and 2;

Fig. 5 six diagrams that illustrate the operation of a third embodiment of the inventive method.

In Fig. 1, the density measurement error against the density for six pure gases at T = 10 ° C is plotted, among each other for four different types of operating density. The left-hand column shows the density measurement errors in the density measurement according to the prior art and the right-hand column shows the remaining residual errors when using the method according to the invention. In the illustrated embodiment, the density was determined using the following correction function:

The operating density transducers were calibrated with methane at 10 ° C before the measurement. The pure gases (N ₂ , CO ₂ , C ₂ H ₆ , C ₂ H ₄ , Ar, Ne) were then examined, since they each have characteristic properties and cover a wide range of speeds of sound and viscosity. As can clearly be seen, the method according to the invention succeeds in reducing the systematic density measurement error from up to 3% to less than 0.1%. With the new method, the density measurement error can thus be effectively reduced to approximately 1/30 of the original measurement error.

Fig. 2 differs only from Fig. 1 in that the diagrams show the measured values for six natural gases at T = 10 ° C. The operating density sensors were calibrated with methane at 10 ° C as in Fig. 1. As can be clearly seen in the diagrams, the systematic measurement error for natural gases can be reduced by up to approx. + 0.5% from less than 0.05%, i.e. to less than 1/10 of the original measurement error. The method according to the invention is therefore also very effective for natural gases.

The operating density sensors are usually only at a constant temperature, e.g. B. 10 ° C, calibrated. If the operating temperature deviates from the calibration temperature, additional density measurement errors due to the temperature difference occur. With the embodiment of the invention illustrated in FIG. 3, these additional density measurement errors can also be eliminated. In Fig. 3, the systematic density measurement errors for Ekofisk natural gas at the three temperatures, T = 0 ° C, 10 ° C and 20 ° C for four different types of operating density sensors are plotted on the left. In the diagrams on the right side, the residual errors are drawn using the method according to the invention. In this embodiment, the correction function (10) was used:

where τ: period of the vibrating body,
T: temperature and
K _C , K _η , K _T0 , K _{T1 are} constants.

As can be seen, the density can also in this case Measurement errors reduced from around + 0.5% to less than 0.05% become.

FIG. 4 illustrates the mode of operation of the exemplary embodiments according to FIGS. 1 and 2.

The correction function (9) can simply be brought into the following form:

where c * is a sound velocity parameter, namely

and η * is a viscosity parameter, namely

Here K _c ² and K _{η are} type-specific transducer constants.

Diagram 1 of FIG. 4 plots the density measurement error against the density for six pure gases. Diagram 2 differs from Diagram 1 in that the density measurement error is plotted against the sound velocity parameter c * instead of against the density. As this diagram confirms, the density measurement error depends linearly on the sound velocity parameter c *. The straight line drawn was adapted with the aid of the various measured values and provides the type-specific transducer constant K _c ² as the slope.

Diagram 3 of FIG. 4 plots the residual error in density that results when the correction with respect to the sound velocity parameter has already been carried out. This residual error is plotted against the sound velocity parameter c *. While the values for ethylene, argon and ethane already have only minor residual errors, the density values of nitrogen, carbon dioxide and neon are still subject to relatively high errors. As can be seen in diagrams 4 to 6, these residual errors can be significantly reduced using the viscosity parameter η *.

The residual error is plotted against the viscosity parameter η * in diagram 4 in FIG. 4. As can be expected on the basis of the functional equation, the residual errors in this diagram can also be approximated well by a straight line. The slope of the straight line provides the type-specific transducer constant K _η .

In diagram 5 the residual error of the density after correction of the viscosity effect is plotted against the viscosity parameter η * using the 2nd term of equation (16). After both the speed of sound effect and the viscosity effect have been corrected, the densities of the six pure gases are only affected by residual errors below 0.1%. This extremely small residual error of density is finally plotted against the density in diagram 6 of FIG. 4 in order to enable a better comparison with the density measurement error according to diagram 1.

For natural gases, the density can be determined according to the following simplified embodiment of the invention. It has been found that the speed of sound of natural gas and the viscosity of natural gas can be surprisingly determined using the following two equations:

c _E = c _CH4 (T, ρ) + Δc _E (T, ρ, ρ _n ) + Δc _E (T, ρ, H _n ) + Δc _E (ρ, x _CO2 ) (19),

η _E = η _CH4 (T, ρ) + Δη _E (ρ, ρ _n ) + Δη (H _n ) (20),

where the Δc _E and Δη _E only denote correction terms that are dependent on the measured variables given in brackets.

If these approximate terms for the speed of sound and the viscosity of the natural gas are used in equation (10), this approximately results in the function according to equation (8):

ρ _corr = ρ _BDA . [1 + K _{ρ n} .Δρ _n + K _{H n} .ΔH _n + K _CO2 .Δx _CO2 ] + K _T .ΔT,

where K _{ρ n} , K _{H n} and K _{CO2 are} constants, functions of ρ _BDA and / or temperature,
K _{T is} a constant or a function of ρ _BDA ,

Δρ _n = ρ _{n, mess} - ρ _{n, cal} ,
ΔH _n = H _{n, mess} - H _{n, cal} ,
ΔT = T _mess - T _kal and Δx _CO2 = x _{CO2, mess} - x _{CO2, kal} .

In the particularly simple exemplary embodiment shown in FIG. 5, K _CO2 = 0 and K _{ρ n} and K _{H n} are constants and for K _{T the} following applies: K _T = K _{T 0} + ρ _BDA .K _{T 1} , where K _{T 0} and K _{T 1 are} constants.

In FIG. 5, the operation of this simplified process is shown for determining the density of natural gas for six natural gases. In diagram 1, the density measurement error is plotted against the density without using the method according to the invention. As can be seen in the diagram, the density is subject to an error of up to 0.5%.

In diagram 2 of FIG. 5, the density measurement error is plotted against the density of the natural gas under standard conditions. As can be expected on the basis of the correction function, the measured values in this representation can be approximated by a straight line. The slope of the straight line gives the constant K _{ρ n} .

Diagram 3 shows the residual error of the density after correction of the density values using the second term of equation (8). The residual error for all six examined natural gases is only less than 0.1%. This residual error of density against the calorific value of the respective natural gas is shown in diagram 4 under standard conditions. Here too, the measured values already corrected with regard to the standard density can be approximated well by a straight line. The constant K _{H n can} be read off the slope of the straight line.

In diagram 5, the residual error of density is corrected with the help of the third term according to equation (8) Darge poses. The remaining residual error is only less than 0.05%.

In diagram 6, this residual error of the fiction method against density shown to a particular comparison with the previous measurement error according to the diagram 1 to enable.

A correction regarding the temperature (4th term of the Equation 8) was not necessary in this case because the Measuring temperature coincided with the calibration temperature.

With the help of the method according to the invention Density depending on the application with the desired accuracy be determined. The one for correcting the density reading required constants and parameters of the correction functions only need to be used once for each type of operational density sensor with the help of reference gases of known composition be true.

Numerous further developments are within the scope of the invention possible. For example, nitrogen can also be used as a calibration gas can be used. The calibration should be in are in the middle of the usual operating temperature range, however, other calibration temperatures can also be selected the. The ex needed to determine the density measurement error Actual measured values for the density can be obtained with a known combination either be calculated or with an equivalent correspondingly expensive, high-precision operational density transducers be measured.

Claims (23)

1. A method for determining the density of a gas, in particular natural gas, under operating conditions, an operating density sensor containing a vibrating body being calibrated using a calibration gas, and a measured density value of the gas under operating conditions (ρ _BDA ) being measured using the operating density sensor , characterized in that
the density or speed of sound of both the gas and the calibration gas is recorded under standard conditions (ρ _{n, mess} , ρ _{n, kal} , c _{n, mess} , c _{n, kal} ) and
the density of the gas under operating conditions is determined from the measured density value with the aid of a correction function which is dependent on the difference in the densities or the sound velocities of the gas and the calibration gas under standard conditions. 2. The method according to claim 1, characterized in that the density of the gas is determined using the following correction function:
ρ _corr = ρ _BDA . [1 + K _{ρ n} .Δρ _n ],
where K _{ρ n is} a constant or a function of ρ _BDA and / or temperature, and
Δρ _n = ρ _{n, meas} - ρ _{n, cal} . 3. The method according to claim 1, characterized in that the density of the gas is determined using the following correction function:
ρ _corr = ρ _BDA . [1 + K _{c n} .Δc _n ],
where K _{c n is} a constant or a function of ρ _BDA and / or temperature, and
Δc _n = c _{n, meas} - c _{n, cal} . 4. The method according to claim 1, characterized in that in addition the calorific value of the gas and the calibration gas under standard conditions (H _{n, measurement} , H _{n, kal} ) is detected and that the correction function which is used to determine the density measured under operating conditions, depends on the calorific value of the gas and the calibration gas under standard conditions. 5. The method according to claim 4, characterized in that the density of the gas is determined using the following correction function:
ρ _corr = ρ _BDA . [1 + K _{ρ n} .Δρ _n + K _{H n} .ΔH _n ],
where K _{ρ n} and K _{H n are} constants or functions of ρ _BDA and / or temperature, and
Δρ _n = ρ _{n, mess} - ρ _{n, cal} and
ΔH _n = H _{n, meas} - H _{n, cal} . 6. The method according to claim 4, characterized in that the density of the gas is determined using the following correction function:
ρ _corr = ρ _BDA . [1 + K _{c n} .Δc _n + K _{H n} .ΔH _n ],
where K _{c n} and K _{H n are} constants or functions of ρ _BDA and / or temperature, and
Δc _n = c _{n, meas} - c _{n, cal} and
ΔH _n = H _{n, meas} - H _{n, cal} . 7. The method according to claim 1 or 4, characterized in that also the temperature of the gas under operating conditions (T _mess ) and the temperature of the calibration gas during calibration (T _kal ) are detected and that the correction function for determining the under Operating conditions measured density is used depends on the operating temperature of the gas and the calibration temperature of the calibration gas. 8. The method according to claim 7, characterized in that the density of the gas is determined using the following correction function:
ρ _corr = ρ _BDA . [1 + K _{ρ n} .Δρ _n + K _{H n} .ΔH _n ] + K _T .ΔT,
where K _{ρ n} and K _{H n are} constants or functions of ρ _BDA and / or temperature, K _{T is} a constant or function of ρ _BDA , and
Δρ _n = ρ _{n, mess} - ρ _{n, cal} ,
ΔH _n = H _{n, meas} - H _{n, cal} and
ΔT = T _mess - T _kal . 9. The method according to claim 7, characterized in that the density of the gas is determined using the following correction function:
ρ _corr = ρ _BDA . [1 + K _{c n} .Δc _n + K _{H n} .ΔH _n ] + K _T .ΔT,
where K _{c n} and K _{H n are} constants or functions of ρ _BDA and / or temperature, K _{T is} a constant or function of ρ _BDA , and
Δc _n = c _{n, meas} - c _{n, cal} ,
ΔH _n = H _{n, meas} - H _{n, cal} and
ΔT = T _mess - T _kal . 10. The method according to any one of claims 1, 4 or 7, characterized in that the carbon dioxide part of the gas and the calibration gas (x _{CO2, measuring} , x _{CO2, cal} ) is also detected and that the correction function for determining the under Operating conditions measured density is used, depending on the carbon dioxide content of the gas and the calibration gas. 11. The method according to claim 10, characterized in that the density of the gas is determined using the following correction function:
ρ _corr = ρ _BDA . [1 + K _{ρ n} .Δρ _n + K _{H n} .ΔH _n + K _CO2 .Δx _CO2 ] + K _T .ΔT,
where K _{ρ n} , K _{H n} and K _{CO2 are} constants or functions of ρ _BDA and / or temperature, K _{T is} a constant or function of ρ _BDA , and
Δρ _n = ρ _{n, mess} - ρ _{n, cal} ,
ΔH _n = H _{n, mess} - H _{n, cal} ,
ΔT = T _mess - T _kal and
Δx _CO2 = x _{CO2, mess} - x _{CO2, cal} . 12. The method according to claim 10, characterized in that the density of the gas is determined using the following correction function:
ρ _corr = ρ _BDA . [1 + K _{c n} .Δc _n + K _{H n} .ΔH _n + K _CO2 .Δx _CO2 ] + K _T .ΔT,
where K _{c n} , K _{H n} and K _{CO2 are} constants or functions of ρ _BDA and / or temperature, K _{T is} a constant or function of ρ _BDA , and
Δc _n = c _{n, meas} - c _{n, cal} ,
ΔH _n = H _{n, mess} - H _{n, cal} ,
ΔT = T _mess - T _kal and
Δx _CO2 = x _{CO2, mess} - x _{CO2, cal} . 13. The method according to any one of claims 8 to 12, characterized in that K _{T is determined} using the following function: K _T = K _{T 0} + ρ _BDA .K _{T 1} , where K _{T 0} and K _{T 1 are} constants . 14. A method for determining the density of a gas, in particular natural gas, under operating conditions, wherein
an operating density sensor containing a vibrating body is calibrated with the aid of a calibration gas,
and a measured density value of the gas under operating conditions (ρ _BDA ) is measured with the aid of the operating density _sensor , characterized in that
the speed of sound and the viscosity of both the gas and the calibration gas are determined under operating conditions (c _mess , c _kal , η _mess , η _kal ) and
the density of the gas under operating conditions is determined from the density measured value with the aid of a correction function which is dependent on the speed of sound and the viscosity of the gas and the calibration gas. 15. The method according to claim 14, characterized in that the density of the gas is determined using the following correction function:
where τ: period of the vibrating body,
T: temperature and
K _C , K _η , K _T0 , K _{T1 are} constants. 16. The method according to claim 14, characterized in that the density of the gas is determined using the following correction function:
where τ: period of the vibrating body,
T: temperature and
K _C , K _η , K _T0 , K _{T1 are} constants. 17. The method according to any one of claims 1 to 16, characterized characterized in that methane is used as the calibration gas.   18. The method according to claim 17, characterized in that K _c ² and K _η by calibration with a second Kali briergas in addition to methane, for. As argon, ethene or nitrogen, can be determined and treated as type-specific constants. 19. The method according to any one of claims 14 to 18, there characterized in that the speed of sound of the Ga ses and / or the calibration gas as a function of density and operating conditions and density under standard conditions and / or the temperature and / or the calorific value and / or of the carbon dioxide content is determined. 20. The method according to claim 19, characterized in that when determining the density of natural gas methane is used as the calibration gas,
that the speed of sound of methane (c _{CH 4} ) is calculated according to the following equation:
c _{CH 4} = A ₀ + (A ₁ + A ₂ .T _mess ) .T _mess + (A ₃ + A ₄ .ρ _BDA + A ₅ .ρ ² _BDA ) .ρ _BDA + (A ₆ + A ₇ .T _mess ) .T _mess .ρ _BDA
and the speed of sound of the natural gas (c _mess ) is determined according to the following equation:
C _mess = C _{CH 4} + [(B ₁ + B ₂ .Δρ _n + B ₃ .T _mess ) + (B ₄ + B ₅ .T _mess + B ₆ .ρ _BDA + B ₇ .ρ _BDA .Δρ _n ) .ρ _BDA ] .Δρ _n
+ [(C ₁ + C ₂ .T _mess ) + (C ₃ + C ₄ .ρ _BDA + C ₅ .T _mess ) .ρ _BDA ] .ΔH _n + [D ₁ .ρ _BDA ] .X _{CO 2} ,
where A ₀ -A ₇ , B ₁ -B ₇ , C ₁ -C ₅ and D _{1 are} constants,
X _{CO 2} indicates the carbon dioxide content in natural gas,
Δρ _n = ρ _{n, mess} - ρ _{n, CH 4} and
ΔH _n = H _n , meas - H _{n, CH 4} . 21. The method according to any one of claims 14 to 20, there characterized in that the viscosity of the gas and / or of the calibration gas as a function of density under operating conditions conditions and density under standard conditions and / or Temperature and / or the calorific value is determined. 22. The method according to claim 21, characterized in that methane is used as calibration gas when determining the density of natural gas,
that the viscosity of methane (η _{CH 4} ) is calculated according to the following equation:
η _{CH 4} = A ₀ + A ₁ .T + (A ₂ + A ₃ .ρ _BDA ) .ρ _BDA
and the viscosity of the natural gas (η _mess ) is determined according to the following equation:
η _mess = η _{CH 4} + B ₁ (1 - ρ _BDA ) .Δρ _n + B ₂ .ΔH _n
where A ₀ -A ₃ , B ₁ and B _{2 are} constants,
Δρ _n = ρ _{n, mess} - ρ _{n, CH 4} and
ΔH _n = H _{n, meas} - H _{n, CH 4} . 23. The method according to any one of claims 1 to 22, characterized characterized that to find the parameters and Kon suitable functions, especially correction functions, performed several measuring cycles with reference gases whose compositions are known.