A cost-effective approach on CO2 emission factor estimation for flare ultrasonic metering systems
In flare gas systems, flow measurement is important both for reports of gas emissions and for process control. Due to the nature of such systems, the flow rates in a flare line varies from very low at normal operations to full flare with very high flow rate in the case of flaring events. This means that a flow metering system for flares typically has to be able to measure flow velocities from 0.1 m/s or less, to more than 100 m/s in order to cover all cases.
The measurement of the amount of flare gas is usually carried out by an ultrasonic flare gas meter. Such meters have been in operation
for several decades. They are primarily volumetric flow meters measuring the actual (line) volume flow rate of the flare gas. By
calculations using the measured pressure and temperature, the volume at a selected reference condition (in Norway typically standard condition of 1.01325 bar and 15 °C) is found. Then accumulation of standard volume is carried out.
The ultrasonic flare gas meters also measure the velocity of sound in the flare gas. From the velocity of sound, pressure and temperature, the density of the flare gas can be estimated by vendor-specific algorithms. Thus, the ultrasoni c flare gas meters can also provide the mass flow rate and the accumulated mass of flare gas flowing through the meter.