Method and ultrasound flow measurement unit for the determination of the CO2 emission factor in flare gas plants

The invention relates to an improved and simpler method and to an apparatus for the determination of the CO2 emission factor in flare gas plants comprising the steps: a) measuring the speed of sound in the flare gas; b) detecting known proportions of N2, CO2 and H2O; c1) calculating a maximum speed of sound of the flare gas under the assumption that the hydrocarbon proportion of the flare gas only consists of alkanes having a chain length i; c2) calculating a minimal speed of sound of the flare gas under the assumption that the hydrocarbon proportion of the flare gas only consists of alkanes having a chain length i+1; c3) varying the chain length i for so long until the measured speed of sound lies between the calculated minimal speed of sound and the calculated maximum speed of sound; d) varying the proportions of the alkanes having the chain length i and the chain length i+1 determined in step c) for so long until the speed of sound calculated with these proportions lies within a predefined difference from the measured speed of sound; e) calculating the equivalent chain length; and f) calculating the emission factor.