Measurement apparatus and method for measuring an energy quantity flow transported by means of a liquefied natural gas flow

Abstract

The invention relates to a measurement apparatus for measuring an energy quantity flow transported by means of a liquefied natural gas flow, comprising an ultrasonic measurement device that is configured to measure the flow velocity of the liquefied natural gas flow and the sound velocity in the liquefied natural gas flow based on determined transit times of ultrasonic signals transmitted and received with and against the flow of the liquefied natural gas flow on a measurement path; a temperature sensor that is configured to measure the temperature of the liquefied natural gas flow; and an evaluation unit that is connected to the ultrasonic measurement device and the temperature sensor to receive respective measurement values for the flow velocity, the sound velocity and the temperature, wherein the evaluation unit is configured to determine the volume flow of the liquefied natural gas flow at least based on the flow velocity and the cross-sectional area of the liquefied natural gas flow, to determine the volume-related calorific value of the liquefied natural gas flow at least based on the sound velocity and the temperature by means of a model function, and to determine the transported energy quantity flow based on the determined volume flow and the determined volume-related calorific value, wherein the model function is determined based on a data set that specifies the volume-related calorific value of a respective composition for a plurality of different compositions of liquefied natural gas. The invention further relates to a measurement apparatus for measuring an energy quantity flow transported by means of a liquefied natural gas flow using a mass flow meter and to corresponding methods.

Claims

1. A measurement apparatus for measuring an energy quantity flow transported by means of a liquefied natural gas flow, comprising an ultrasonic measurement device that is configured to measure the flow velocity of the liquefied natural gas flow and the sound velocity in the liquefied natural gas flow based on determined transit times of ultrasonic signals transmitted and received with and against the flow of the liquefied natural gas flow on a measurement path; a temperature sensor that is configured to measure the temperature of the liquefied natural gas flow; and an evaluation unit that is connected to the ultrasonic measurement device and the temperature sensor to receive respective measurement values for the flow velocity, the sound velocity and the temperature, wherein the evaluation unit is configured to determine the volume flow of the liquefied natural gas flow at least based on the flow velocity and the cross-sectional area of the liquefied natural gas flow, to determine the volume-related calorific value of the liquefied natural gas flow at least based on the sound velocity and the temperature by means of a model function, and to determine the transported energy quantity flow based on the determined volume flow and the determined volume-related calorific value, wherein the model function is determined based on a data set that specifies the volume-related calorific value of a respective composition for a plurality of different compositions of liquefied natural gas.

2. The measurement apparatus according to claim 1, wherein the model function is an interpolation polynomial that is determined by interpolation of a plurality of support points included in the data set, with the support points specifying a volume-related calorific value determined by calculation and/or experimentally at least for a respective sound velocity and a respective temperature.

3. The measurement apparatus according to claim 2, wherein the interpolation polynomial is determined by the equation $H_V=a_{00}+a_{10}.Math.c+a_{01}.Math.T+a_{20}.Math.c^2+a_{11}.Math.c.Math.T+a_{02}.Math.T^2,$ where H.sub.V is the volume-related calorific value of the liquefied natural gas flow, c is the sound velocity of the liquefied natural gas flow, T is the temperature of the liquefied natural gas flow, and a.sub.ij are coefficients.

4. A measurement apparatus for measuring an energy quantify flow transported by means of a liquefied natural gas flow, comprising a mass flow meter that is configured to measure the mass flow and the density of the liquefied natural gas flow based on the Coriolis principle; a temperature sensor that is configured to measure the temperature of the liquefied natural gas flow; and an evaluation unit that is connected to the mass flow meter and the temperature sensor to receive respective measurement values for the mass flow, the density and the temperature, wherein the evaluation unit is configured to determine the mass-related calorific value of the liquefied natural gas flow at least based on the density and the temperature by means of a model function, and to determine the transported energy quantity flow based on the determined mass flow and the determined mass-related calorific value, wherein the model function is determined based on a data set that specifies the mass-related calorific value of a respective composition for a plurality of different compositions of liquefied natural gas.

5. The measurement apparatus according to claim 4, wherein the model function is an interpolation polynomial that is determined by interpolation of a plurality of support points included in the data set, with the support points specifying a mass-related calorific value determined by calculation and/or experimentally for a respective density and a respective temperature.

6. The measurement apparatus according to claim 5, wherein the interpolation polynomial is determined by the equation $H_M=b_{00}+b_{10}.Math.?+b_{01}.Math.T+b_{20}.Math.{?}^2+b_{11}.Math.?.Math.T+b_{02}.Math.T^2,$ where H.sub.M is the mass-related calorific value of the liquefied natural gas flow, p is the density of the liquefied natural gas flow, Tis the temperature of the liquefied natural gas flow, and b.sub.ij are coefficients.

7. The measurement apparatus according to claim 2, wherein the data set comprises a respective group of a plurality of support points for a plurality of different predetermined compositions of liquefied natural gas.

8. The measurement apparatus according to claim 5, wherein the data set comprises a respective group of a plurality of support points for a plurality of different predetermined compositions of liquefied natural gas.

9. The measurement apparatus according to claim 2, wherein a calculation of the support points takes place using the GERG-2008 algorithm, the standard ISO-6578 and/or the standard ISO-6976.

10. The measurement apparatus according to claim 5, wherein a calculation of the support points takes place using the GERG-2008 algorithm, the standard ISO-6578 and/or the standard ISO-6976.

11. The measurement apparatus according to claim 1, wherein the measurement apparatus further comprises a pressure sensor that is connected to the evaluation unit and that is configured to measure the pressure of the liquefied natural gas flow, with the evaluation unit being configured to receive measurement values for the pressure from the pressure sensor and to additionally determine the calorific value of the liquefied natural gas flow based on the pressure.

12. The measurement apparatus according to claim 4, wherein the measurement apparatus further comprises a pressure sensor that is connected to the evaluation unit and that is configured to measure the pressure of the liquefied natural gas flow, with the evaluation unit being configured to receive measurement values for the pressure from the pressure sensor and to additionally determine the calorific value of the liquefied natural gas flow based on the pressure.

13. A method for measuring an energy quantify flow transported by means of a liquefied natural gas flow, comprising the steps: measuring the flow velocity and the sound velocity of the liquefied natural gas flow based on determined transit times of ultrasonic signals transmitted and received with and against the flow of the liquefied natural gas flow on a measurement path; measuring the temperature of the liquefied natural gas flow; determining the volume flow of the liquefied natural gas flow based on the flow velocity and the cross-sectional area of the liquefied natural gas flow; determining the volume-related calorific value of the liquefied natural gas flow at least based on the sound velocity and the temperature by means of a model function, wherein the model function is determined based on a data set that specifies the volume-related calorific value of a respective composition for a plurality of different compositions of liquefied natural gas; and determining the transported energy quantity flow based on the determined volume flow and the determined volume-related calorific value.

14. A method for measuring an energy quantity flow transported by means of a liquefied natural gas flow, comprising the steps: measuring the mass flow and the density of the liquefied natural gas flow based on the Coriolis principle; measuring the temperature of the liquefied natural gas flow; determining the mass-related calorific value of the liquefied natural gas flow at least based on the density and the temperature by means of a model function, wherein the model function is determined based on a data set that specifies the mass-related calorific value of a respective composition for a plurality of different compositions of liquefied natural gas; and determining the transported energy quantity flow based on the determined mass flow and the determined mass-related calorific value.

Description

[0034] FIG. 1 a block diagram of a measurement apparatus according to a first embodiment;

[0035] FIG. 2 a block diagram of a measurement apparatus according to a second embodiment; and

[0036] FIG. 3 a three-dimensional diagram of a model function for the measurement apparatus according to FIG. 1.

[0037] In the following, the same or similar elements are designated by the same reference numerals.

[0038] In FIGS. 1 and 2, exemplary measurement apparatus 10, 20 are schematically shown that are arranged at or in a respective pipeline 2 that is flowed through by a liquefied natural gas 4.

[0039] The measurement apparatus 10 according to FIG. 1 comprises an ultrasonic measurement device 12 that is arranged at the pipeline 2 and that is configured to measure the flow velocity of the liquefied natural gas flow 4 and the sound velocity in the liquefied natural gas flow 4 based on determined transit times of ultrasonic signals transmitted and received with and against the flow of the liquefied natural gas flow 4 on a measurement path. The measurement apparatus 10 furthermore comprises a temperature sensor 6 that is arranged at the pipeline 2 and that is configured to measure the temperature of the liquefied natural gas flow 4. Furthermore, the measurement apparatus 10 comprises an evaluation unit 14 that is connected to the ultrasonic measurement device 12 and the temperature sensor 6 to receive respective measurement values for the flow velocity, the sound velocity and the temperature.

[0040] The evaluation unit 14 is configured to determine the volume flow of the liquefied natural gas flow 4 based on the flow velocity and the cross-sectional area F of the liquefied natural gas flow 4, said cross-sectional area F, in the embodiment, being determined by the cross-sectional area of the pipeline 2.

[0041] The measurement apparatus 20 according to FIG. 2 comprises a mass flow meter 22 that is arranged at the pipeline 2 and that is configured to measure the mass flow and the density of the liquefied natural gas flow 4 based on the Coriolis principle. The measurement apparatus 20 likewise comprises a temperature sensor 6 that is configured to measure the temperature of the liquefied natural gas flow 4. Finally, the measurement apparatus 20 comprises an evaluation unit 24 that is connected to the mass flow meter 22 and the temperature sensor 6 to receive respective measurement values for the mass flow, the density and the temperature.

[0042] The mode of operation of the measurement apparatus 10 will now be explained in more detail with reference to FIGS. 1 and 3.

[0043] First, some basic principles for determining the energy in a quantity of liquefied natural gas or for determining the energy quantity flow that is transported by means of a liquefied natural gas flow will be explained. The following observations each relate to an energy quantity or energy E, a volume V, and a mass M. It is understood that the relationships can also be analogously applied to the derived quantities of an energy quantity flow, a volume flow and a mass flow since an energy quantity flow is defined as energy or an energy quantity per unit of time, a volume flow is defined as a volume per unit of time, and a mass flow is defined as a mass per unit of time. Accordingly, with the measurement apparatus according to the invention, by integrating a measured transported energy quantity flow over time, energy or an energy quantity transported in this time can in turn be determined. In this regard, the measurement apparatus or methods can also include the function of energy meters.

[0044] In general, the energy E released during the combustion of a gas quantity corresponding to a volume V.sub.LNG of liquefied natural gas can be described by the equation

[00003]$\begin{array}{cc}E=V_{\mathrm{LNG}}.Math.{?}_{\mathrm{LNG}}\left(T,p,x\right).Math.H_{M,\mathrm{LNG}}\left(x\right).& \left(1\right)\end{array}$

[0045] The energy E is here specified in relation to the combustion under standard conditions, i.e. the combustion of gas at a temperature of 20? C. and a pressure of 0 bar. The volume V.sub.LNG of the liquefied natural gas, like its density ?.sub.LNG, refers to the prevailing transport conditions that are determined by the pressure p and the temperature T of the liquefied natural gas. Furthermore, the density ?.sub.LNG, just like the mass-related calorific value H.sub.M, LNG, depends on the composition of the examined liquefied natural gas, wherein this dependence on the chemical composition of the liquefied natural gas is illustrated by the argument x. The mass-related calorific value H.sub.M, LNG refers to the energy released during the combustion of a certain mass under the above-defined standard conditions (20? C., 0 bar).

[0046] In equation (1), possibly occurring energy losses that result during the transmission or due to vaporization of liquefied natural gas are not considered since their detection by measurement technology is associated with considerable difficulties. Any transmission losses can be neglected or, if necessary, considered on a summary or estimation basis.

[0047] The energy E released during the combustion of regasified liquefied natural gas results from the equation

[00004]$\begin{array}{cc}\frac{E\left(T_1,p_1,x\right)}{\left[\mathrm{MJ}\right]}=\frac{V\left(T_1,p_1\right)}{\left[m^3\right]}.Math.\frac{?\left(T_1,p_1,x\right)}{\left[\mathrm{kg}/m^3\right]}.Math.\frac{H_M\left(T_1,p_1,x\right)}{\left[\mathrm{MJ}/\mathrm{kg}\right]},& \left(2\right)\end{array}$

where T.sub.1 and ?.sub.1 denote the temperature and the pressure at combustion conditions of the (gaseous) natural gas, e.g. the above-mentioned standard conditions, and T.sub.2 and ?.sub.2 denote the temperature and the pressure at transport conditions of the (cryogenic) liquefied natural gas.

[0048] According to the law of conservation of mass, the following equation results:

[00005]$\begin{array}{cc}\frac{V\left(T_1,p_1\right)}{\left[m^3\right]}.Math.\frac{?\left(T_1,p_1,x\right)}{\left[\mathrm{kg}/m^3\right]}=\frac{V\left(T_2,p_2\right)}{\left[m^3\right]}.Math.\frac{?\left(T_2,p_2,x\right)}{\left[\mathrm{kg}/m^3\right]}& \left(3\right)\end{array}$

[0049] Equation (2) can thus be reformulated as:

[00006]$\begin{array}{cc}\frac{E\left(T_1,p_1,x\right)}{\left[\mathrm{MJ}\right]}=\frac{V\left(T_2,p_2\right)}{\left[m^3\right]}.Math.\frac{?\left(T_2,p_2,x\right)}{\left[\mathrm{kg}/m^3\right]}.Math.\frac{H_M\left(T_1,p_1,x\right)}{\left[\mathrm{MJ}/\mathrm{kg}\right]}& \left(4\right)\end{array}$

[0050] The value for V(T.sub.2, ?.sub.2) is determined in the evaluation unit 14 based on the flow velocity determined by the ultrasonic measurement device 12 under the aforementioned transport conditions and on the cross-sectional area F of the liquefied natural gas flow 4. Thus, to determine the energy E, only the product of the density ? of the liquefied natural gas at transport conditions (i.e. at T.sub.2, ?.sub.2) and the mass-related calorific value H.sub.M in relation to a combustion under standard conditions has to be determined. This product represents the volume-related calorific value H.sub.V of the liquefied natural gas:

[00007]$\begin{array}{cc}\frac{H_V\left(T_2,p_2,x\right)}{\left[\mathrm{MJ}/m^3\right]}=\frac{?\left(T_2,p_2,x\right)}{\left[\mathrm{kg}/m^3\right]}.Math.\frac{H_M\left(T_1,p_1,x\right)}{\left[\mathrm{MJ}/\mathrm{kg}\right]}& \left(5\right)\end{array}$

[0051] The volume-related calorific value H.sub.V(T.sub.2, p.sub.2) thus refers to the volume and the density of the liquefied natural gas under transport conditions, i.e. to the cryogenic liquid phase. Thus, the volume-related calorific value H.sub.V(T.sub.2, p.sub.2) reflects the energy per volume of the liquid phase, whereas a volume-related calorific value is usually specified in relation to a combustion in the gaseous phase under standard conditions, i.e. for one energy per volume of the gas phase.

[0052] If the composition of the liquefied natural gas flow to be measured were known, the volume-related calorific value could, for example, be taken from a database and included in the calculations of the energy quantity flow. However, this is not possible for unknown or partially unknown liquefied natural gas compositions.

[0053] The invention is based on the surprising finding that there is a well-defined relationship between the sound velocity c and the temperature T of the liquefied natural gas, on the one hand, and the volume-related calorific value H.sub.V of the liquefied natural gas, on the other hand.

[0054] This relationship is shown in FIG. 3. The support points represented by filled circles define associated values for the volume-related calorific value H.sub.V of the liquefied natural gas for different values of the temperature T and the sound velocity c. The diagonally extending rows of support points recognizable there each represent a defined chemical composition of the liquefied natural gas.

[0055] The support points forming a data set are advantageously determined by calculation from various reference liquefied natural gas compositions by means of established algorithms. For example, the publication GIIGNL Annual Report 2018, published by the International Group of Liquefied Natural Gas Importers, accessed on Dec. 14, 2022 at: https://giignl.org/document/giignl-2018-annual-report/, includes a data collection for 22 liquefied natural gas compositions originating from different production sites. These data can also be found in the standard ISO-cross-section23306 (ISO 23306:2020, published October 2020). The density, the molar mass and the sound velocity can be determined for various reference compositions by means of the so-called GERG-2008 algorithm, which is described in detail, for example, in the document Kunz, O. and W. Wagner, The GERG-2008 Wide-Range Equation of State for Natural Gases and Other Mixtures: An Expansion of GERG-2004, J. Chem. Eng. Data, 57 (11), 2012, pp. 3032-3091, and/or the standard ISO-6578 (ISO 6578:2017, published October 2017). The calculation of the mass-related calorific value H.sub.M preferably takes place according to the method described in the standard ISO-6976 (ISO 6976:2016, published August 2016).

[0056] To determine the support points for a respective composition, a temperature range can, for example, be predefined for which the respective values are calculated. For example, a temperature interval of 10? C., starting from the boiling point of the respective composition, can be selected as the upper limit of the temperature interval that is divided into suitable temperature steps, for example steps of 1? C.

[0057] It has been shown that the support points determined by calculation or experimentally can be adapted very well using an interpolation polynomial as a model function:

[00008]$\begin{array}{cc}{H}_V=a_{00}+a_{10}.Math.c+a_{01}.Math.T+a_{20}.Math.c^2+a_{11}.Math.c.Math.T+a_{02}.Math.T^2,& \left(6\right)\end{array}$

where a.sub.ij are fitting coefficients of this model function.

[0058] By using this model function in the evaluation unit 14, the volume-related calorific value H.sub.V of the liquefied natural gas flow can be determined at least based on the measured sound velocity c and the measured temperature T of the liquefied natural gas flow. The transported energy volume flow can then be determined based on the determined volume flow and the determined volume-related calorific value H.sub.V.

[0059] In FIG. 3, the model function according to the interpolation polynomial described in equation (6) is shown as a shaded area.

[0060] The measurement method described with reference to the measurement apparatus 10 of FIG. 1 and FIG. 3 can be analogously applied in the measurement apparatus 20 according to FIG. 2 in which a mass flow of the liquefied natural gas is determined by means of the mass flow meter 22. It has been shown that there is also a well-defined relationship between the density p and the temperature T of the liquefied natural gas, on the one hand, and the mass-related calorific value H.sub.M of the liquefied natural gas, on the other hand.

[0061] With the aid of the measurement apparatus 20, the energy E can be determined analogously to equation (2) based on the mass M of the liquefied natural gas according to the following equation:

[00009]$\begin{array}{cc}\frac{E\left(T_1,p_1,x\right)}{\left[\mathrm{MJ}\right]}=\frac{M\left(T_1,p_1,x\right)}{\left[\mathrm{kg}\right]}.Math.\frac{H_M\left(x\right)}{\left[\mathrm{MJ}/\mathrm{kg}\right]}& \left(7\right)\end{array}$

[0062] Equation (7) can also be written taking into account the law of conservation of mass:

[00010]$\begin{array}{cc}\frac{E\left(T_1,p_1,x\right)}{\left[\mathrm{MJ}\right]}=\frac{M\left(T_2,p_2,x\right)}{\left[\mathrm{kg}\right]}.Math.\frac{H_M\left(x\right)}{\left[\mathrm{MJ}/\mathrm{kg}\right]}& \left(8\right)\end{array}$

[0063] The variables ?.sub.1, ?.sub.2, T.sub.1, T.sub.2, x have already been explained above with reference to the measurement apparatus 10 according to FIG. 1.

[0064] To calculate the energy or the energy quantity flow based on equation (8), the mass-related calorific value H.sub.M is again determined by means of a model function. The density ? of the liquefied natural gas flow measured by the mass flow meter 22 and its temperature T measured by the temperature sensor 6 are used as input variables for the model function. The following interpolation polynomial is used as a model function for the mass-related calorific value H.sub.M:

[00011]$\begin{array}{cc}{H}_M=b_{00}+b_{10}.Math.?+b_{01}.Math.T+b_{20}.Math.{?}^2+b_{11}.Math.?.Math.T+b_{02}.Math.T^2& \left(9\right)\end{array}$

[0065] The fitting coefficients b.sub.ij can be determined by adapting the interpolation polynomial to a data set that includes support points for various different chemical compositions of liquefied natural gas. The support points of the data set can be calculated using the algorithms already explained in relation to the embodiment of FIG. 1, wherein the GERG-2008 algorithm and/or the standard ISO-6578 can be used for calculating the density and the molar mass and the standard ISO-6976 can be used for calculating the calorific value.

[0066] In both variants of the measurement apparatus 10, 20 described or of the corresponding measurement methods, it is not mandatory to generate the data sets for the adaptation of the respective interpolation polynomial on the basis of real chemical liquefied natural gas compositions. Rather, support points for various randomly generated liquefied natural gas compositions can also be generated. Advantageously, these artificially generated compositions are within the limits for minimum and maximum mole fractions that were determined with reference to the 22 real compositions described in the GIIGNL Annual Report 2018 or in the standard ISO-23306. The mole fractions of the various components of these compositions are within the following limits: [0067] Methane: 87.3 to 99.7 mol % [0068] Ethane: 0.09 to 10.3 mol % [0069] Propane: 0.07 to 3.3 mol % [0070] Butane and higher alkanes: 0.01 to 1.5 mol % [0071] Nitrogen (N.sub.2): 0 to 0.7 mol %

[0072] The density of these compositions (in the liquid phase) at ?160? C. varies between 421 and 467 kg/m.sup.3.

[0073] The errors occurring when determining the calorific values H.sub.V, H.sub.M according to the methodology explained above are well below 1%. Error influences in particular result when determining the sound velocity or the density of the reference compositions by calculation based on the GERG-2008 model, when measuring the sound velocity, the density and the temperature, and due to a deviation of the actual pressure under transport conditions from an assumed reference pressure.

[0074] The estimation errors for the calorific values H.sub.V, H.sub.M can be further reduced if the actual pressure of the liquefied natural gas flow 4 is additionally considered, which can, for example, be realized by means of an extended model function or by applying a pressure-dependent correction factor. To measure the pressure of the liquefied natural gas flow 4, a corresponding pressure sensor (not shown) connected to the evaluation unit 14 can be provided in the pipeline 2 in both embodiments.

REFERENCE NUMERAL LIST

[0075] 10, 20 measurement apparatus [0076] 2 pipeline [0077] 4 liquefied natural gas [0078] 6 temperature sensor [0079] 12 ultrasonic measurement device [0080] 14, 24 evaluation unit [0081] 22 mass flow meter [0082] F cross-sectional area