Tech Note: Upstream Oil & Gas Applications

Flare Gas Mass Flow Measuring

Thermal Flow Meters Offer Most Flexible & Economic Solution

Application Challenges

Oil wells almost always produce natural gas (“associated gas”) along with the petroleum. In many cases, it is uneconomical to process due to heavy contamination. As a consequence, this gas is combusted, “flared off” or simply vented as-is during upset conditions in the process. Newly updated EPA regulations like 40 CFR Part 60 Subpart OOOO (also known as Quad O) as well as the new RSR MACT rule for refineries, requires oil & gas companies to report the fl are gas emitted to our atmosphere. Monitoring the fuel at the inlet of the flare is part of meeting these EPA requirements (See Figure 1). Flare and combustor gas measurement is a challenging application because each well has its unique and constantly changing characteristics that include depth, temperature, pressure, flow rate, soot content, and varying gas composition.

Sierra’s advanced QuadraTherm 640i Thermal mass Flow meters accurately measures the flow rate with the changing gas compositions, very low flows, and high velocity at upset conditions and offer a more reliable solution than turbine meters and orifice plates.

High Turndowns of 100:1 & Measures Very Low Flows

Handle very low flows and high flows at upset conditions; flow range 0 to 60,000 sfpm (0 to 305 smps).

Most Accurate Thermal Flow Meter-Easily Meets EPA Regulations

With four-sensor thermal sensor technology and the on board Raptor II operating system, accuracy specifications are +/- 0.75% of reading, comparable to four-path ultrasonic meters at a much more economical price. Eliminate drift with patented DrySense™ sensor with lifetime warranty.

Very Low Pressure with Variable Temperatures

The multivariable 640i VT measures very low pressure gas with no pressure loss.

Uniform Flow Profile

Flare stacks generally have asymmetric and swirling flow. The 640i has a Reynolds’ number correction built in to smooth the Flow Profile.

Easy-to-Install-Dial-A-Pipe to Cover Various Pipe sizes

Roaring flames, difficult access and regulatory requirements make flares difficult to service. Insertion thermal flow meters come with hot tap option for no process shutdown, and Dial-A-Pipe to use one flow meter for varying pipe sizes—without factory recalibration.

qMix App Adjusts for Changing Gas Composition—No Recalibration Needed.

Flare gas composition and density varies over the lifetime of the fl are. With changing gas compositions, a typical total flow measurement error could be as high as 20% in applications with widely varying compositions. QuadraTherm thermal fl ow meters can manage the changes in fl are gas composition through the qMix gas mixing app which computes the mass flow rate of any gas composition and retains accuracy without factory recalibration.

Through the on board qMix gas mixing app:

• Operators can select gas, choose composition and create new gas mixture
• Upload new gas to QuadraTherm 640i meter in available gas slots (up to 3 in the field)
• Retain accuracy without sending the meter back to the factory for recalibration
• Your “My Gases” Library can store unlimited new qMix gas compositions
• Operators have access to all AGA compliant gas properties needed to make the algorithmic gas mass flow rate calculations