Measuring instrument for determining the gross or net calorific value of a hydrocarbon-containing fuel gas
The gross or net calorific value of a hydrocarbon-containing fuel gas is determined by using a Raman photometer. A Raman radiation obtained following interaction of laser light with the fuel gas is limited by a bandpass filter to a wavenumber range of the C—H stretching vibrations of the hydrocarbons contained in the fuel gas around 2900 cm −1 and is supplied to a photomultiplier and integratively detected by the photomultiplier. The gross or net calorific value is determined from the output signal of the photomultiplier.
1 . A method, comprising:
limiting a Raman radiation obtained as a result of an interaction of laser light with a hydrocarbon-containing fuel gas to a wavenumber range of C—H stretching vibrations of hydrocarbons around 2900 cm −1 ;
supplying the limited Raman radiation to a first photomultiplier;
integratively detecting the limited Raman radiation by the first photomultiplier;
generating an output signal by the first photomultiplier in response to the integrative detection of the limited Raman radiation;
determining a gross or net calorific value of the hydrocarbon-containing fuel gas from the output signal of the first photomultiplier;
further limiting the Raman radiation;
supplying the further limited Raman radiation to a second photomultiplier;
integratively detecting the further limited Raman radiation by the second photomultiplier;
generating an output signal by the second photomultiplier in response to the integrative detection of the further limited Raman radiation; and
correcting the gross or net calorific value of the hydrocarbon-containing fuel gas determined from the output signal determined by the first photomultiplier with the output signal of the second photomultiplier.
2 . The method of claim 1 , wherein the hydrocarbons comprise C1 to C5 alkanes and their isomers.
3 . The method of claim 1 , wherein the gross or net calorific value of the hydrocarbon-containing fuel gas is determined at an increased pressure of the fuel gas of 1 bar absolute up to 10 bar absolute.
4 . The method of claim 1 , wherein the gross or net calorific value of the hydrocarbon-containing fuel gas is determined at a pressure of at least 5 bar.
5 . The method of claim 1 , wherein the gross or net calorific value of the hydrocarbon-containing fuel gas is determined at a wavelength of the laser light of 405 nm±10 nm or 450 nm±10 nm.
6 . The method of claim 1 , wherein the Raman radiation is limited by a bandpass filter having a central wavelength of 459 nm±13 nm or 518 nm±13 nm and a full width at half maximum of 5 to 10 nm.
7 . The method of claim 1 , wherein the further limited Raman radiation is in a wavenumber range of the C—C vibrations of the hydrocarbons contained in the fuel gas and having two or more carbon atoms around 990 cm −1 .
8 . The method of claim 7 , wherein the Raman radiation is further limited by a bandpass filter.
9 . The method of claim 1 , wherein the hydrocarbon-containing fuel gas contains hydrogen, and the further limited Raman radiation is in a wavenumber range around 4155 cm −1 .
10 . The method of claim 9 , wherein the Raman radiation is further limited by a bandpass filter.
11 . A measuring instrument, comprising:
a Raman photometer including a first bandpass filter configured to limit a Raman radiation obtained as a result of an interaction of laser light with a hydrocarbon-containing fuel gas to a wavenumber range of C—H stretching vibrations of hydrocarbons in the fuel gas around 2900 cm −1 , and a first photomultiplier receiving the limited Raman radiation and generating an output signal commensurate with the limited Raman radiation;
a second bandpass filter to further limit the Raman radiation;
a second photomultiplier receiving the further limited Raman radiation and generating an output signal commensurate with the further limited Raman radiation; and
an evaluation device configured to determine a gross or net calorific value of the hydrocarbon-containing fuel gas from the output signal of the first photomultiplier and to correct the gross or net calorific value of the hydrocarbon-containing fuel gas determined from the output signal of the first photomultiplier with the output signal of the second photomultiplier.
12 . The measuring instrument of claim 11 , configured to execute a method as set forth in claim 1 .
13 . The measuring instrument of claim 11 , wherein the Raman photometer includes a measuring cell in which the fuel gas is held at an increased pressure of the fuel gas of 1 bar absolute up to 10 bar absolute.
14 . The measuring instrument of claim 13 , wherein the fuel gas is in the measuring cell has a pressure of at least 5 bar.
15 . The measuring instrument of claim 11 , wherein the first bandpass filter has a central wavelength of 459 nm±13 nm or 518 nm±13 nm and a full width at half maximum of 5 to 10 nm.
16 . The measuring instrument of claim 11 , wherein
the further limited Raman radiation is in a wavenumber range of the C—C vibrations of the hydrocarbons contained in the fuel gas and having two or more carbon atoms around 990 cm −1 .
17 . The measuring instrument of claim 11 , wherein
the further limited Raman radiation is in a wavenumber range around 4155 cm −1 , when the hydrocarbon-containing fuel gas contains hydrogen.