In Part IV of this series on gas flaring, we explore why flare gas flow measurement is needed and how thermal mass flow meters can satisfy the requirement while simultaneously offering significant savings versus the use of an ultrasonic flowmeter.

EPA 40 CFR part 98 Requirements to Measure Flare Flow

Flare Gas Flow Measurement
When flare gas flow measurement applications with known gas composition exist and water vapor isn’t condensing, thermal mass flow meters provide an attractive solution for flare gas metering.

There are many operations or applications where waste gas flares into the atmosphere. Flare stacks are typically seen at oil and gas wells, refineries, well-drilling rigs, natural gas plants, wastewater treatment plants, chemical plants, and landfills. Like the Mandatory Reporting of Greenhouse Gases Rule (40 CFR 98), strict regulations require operations to measure, record, and report the amount of flare gas emitted into the atmosphere. EPA 40 CFR part 98 requires reporting by 41 industrial categories. The categories are further divided into subparts. For more information on EPA 40 CFR 98 and its subparts, refer to the SAGE white paper “Greenhouse Gas Emissions Monitoring Using Thermal Mass Flow Meters.”

European Union Emissions Trading Scheme

The European Union’s Emissions Trading Scheme (EU ETS) is an approach to reducing air pollution through financial incentives, specifically by trading greenhouse gas (GHG) emissions allowances. The program began in 2005 and covered facilities in 30 countries. Each country is given a cap on total emissions allowed in this scheme. Each facility in the program must measure and report its emissions yearly and submit one allowance for every metric ton of CO2 or the equivalent amount of nitrous oxide (N2O) and perfluorocarbons (PFCs) they emit. If a facility emits less than its allowance, it can sell the designated credits; otherwise, it may purchase credits from other installations. We are currently in the third phase, which has a trading period from 2013 to 2020.

Flare Gas Flow Measurement through Sage

When flaring applications of known gas composition exist, and water vapor isn’t condensing, thermal mass flow meters provide an attractive solution for flare gas metering. The SAGE meter has wide turndown, or up to 1000:1 rangeability, which means it accommodates extreme flow conditions and large flow swings. Low velocities are associated with flare gas under normal venting situations, yet high velocities are typical in upset conditions. Additionally, their rapid response to flow changes, low-pressure loss, accuracy (1% of reading plus 0.5% of full scale over a 100 to1 turndown), and reproducibility make the meter a contender to ultrasonic flow meters in flare applications.

Companies are taking advantage of the installed cost savings associated with thermal flow meters. A thermal mass flow meter is $5,000 or less, while an ultrasonic application can cost  $50,000 (or more). Operators realize that by identifying the gas at the flare application. SAGE can adjust the meter to measure the known flare gas. This works for applications where compositional changes are known or are seasonal. While a bit more inconvenient than an ultrasonic meter, the savings justify the slight difficulty in many cases.

SAGE Insertion Style gas mass flow meters provide the wide turndown required to cover both the extremely low flows (low velocities) associated with normal venting and the extremely high flow (high velocities) associated with an upset condition. Their quick response to flow changes, low-pressure drop, and reproducibility are essential characteristics of a flare application.

In-Situ Calibration Verification

Also, SAGE products offer users a distinctive in-situ calibration check at a “no-flow” (0 SCFM) condition. This important procedure assures that the meter has retained the original NIST Traceable Calibration, verifies the meter’s accuracy, confirms that the sensors are clean and that the flow meter hasn’t drifted or shifted. This is a tremendous advantage since it eliminates the cost and hassle of annual calibrations on the flow meter and provides the information needed to comply with several environmental protocols.

In Part V of this series, we will continue the discussion on flare flow measurement in applications of biogas, landfill gas, and various stages of natural gas. If you’re interested in seeing the Sage Metering white paper in its entirety, see Flare Gas Measurement Using Sage Thermal Mass Flow Meters.