Flare Gas Measurement Innovation: Retain Flow Metering Accuracy Even if Gas Composition Changes

It’s a fact oil wells almost always produce natural gas along with the petroleum. Nine times out of ten, the excess gas (typically hydrocarbons) is flared off or simply vented as-is during upset conditions in the process. The environmental impacts of “flaring” this excess gas into our atmosphere has resulted in government regulations like 40 CFR Part 60 Subpart OOOO (also known as Quad O) as well as new RSR MACT rule for refineries requiring oil & gas companies to report the flare gas emitted.

Traditionally, in upstream oil and gas applications, orifice plates and turbine meters have been used to measure the flare gas to comply with these government regulations.  Thermal mass flow meters are also gaining ground as a reliable and accurate direct mass flow measurement of flare and combustor gas.

The Problem:

Most thermal mass flow meters, however, have an inherent disadvantage in the challenging flare gas measuring application because each well head has its unique and constantly changing characteristics including varying gas composition. Over the lifetime of the well, flare gas composition and density varies, so a typical total flare gas flow measurement error could be as high as 20%. Most thermal flow meters cannot manage these gas composition changes, as they are factory calibrated for a specific gas, and need to be sent back to the factory for recalibration for the new gas composition. This is not only time consuming for the oil & gas operators and engineers, but the flare must be shut down, the thermal meter taken out of the inlet flow, and sent to the factory for recalibration.

Recent Innovation, New Solution:

Today, a new generation of four-sensor “Quad” thermal mass flow meters retains accuracy even if gas composition changes.  Sierra’s QuadraTherm 640i/780i thermal mass flow meter, is becoming a popular choice for flare and combustor (VOC/VRU) measurement due to its unique onboard qMix gas mixing software which allows operators to manage the changes in flare gas composition in the field-no factory recalibration necessary. Operators can use the onboard qMix gas mixing software to select the new gas composition and upload this new gas into the QuadraTherm meter in the field in minutes. The accuracy of the flare gas measurement for this new gas composition is retained improving downtime and  EPA regulation compliance.

Benefits of QuadraTherm thermal mass flow meters in upstream oil & gas applications:

• High Turndowns 100:1 and measures very low flows


• Extreme accuracy +/- 0.75% of reading (+/- 0.5% for 780i inline with built in flow plates)


• High flows up to 60,000 sfpm (0 to 305 smps)


• Eliminate drift with patented DrySense™ sensor-Lifetime sensor


• qMix Gas Mixing App manages changes in gas composition in the field—no recalibration needed


• In-situ ValidCal™ Diagnostics, Dial-A-Gas & Dial-A-Pipe


• Low and high-pressure hot tap


• 40 CFR Part 60 (Quad 0), Boiler MACT Greenhouse Gas (GHG) certified

New Flare Gas Measurement Application Tech Note!

Download our new Flare Gas Mass Flow Measuring Tech Note  for more information on how qMix gas mixing software makes QuadraTherm thermal mass flow meters the most flexible and economic solution for flare and combustor gas measurement.