Flare Gas Monitoring at Lower Cost

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Flare gas monitoring is a mandated requirement for some processes in petrochemical, wastewater treatment, landfill, and biogas applications. Environmental agencies specify continuous monitoring that must meet stringent conditions for accuracy and repeatability.

Most existing flare gas monitoring systems rely on complex time-of-flight ultrasonic systems that require four probes for a pressure transmitter, a temperature sensor, and two ultrasonic flow sensors. Other flow sensing technologies, such as orifice plates and Venturi tubes, do not meet today's emission reporting regulations, are difficult to install, and may require a lot of maintenance.

The new GF03 flowmeter from FCI meets all mandated requirements with a single instrument and a single process penetration. The GF03 is simple to install, inexpensive to maintain, and highly reliable, according to Eric Wible, FCI's director of engineering.

The flowmeter features what the company claims is an industry-first flow sensing element that combines state-of-the-art thermal mass flow and gas composition sensors. Wible says this breakthrough delivers a superior and low total cost solution in flare and other variable mixed-gas composition measurement applications.

The GF03 flowmeter's temperature-compensated thermal mass flow and gas composition sensor assembly continuously measures mixed gas and applies a special flow correction technique to report flow rate and total flow.

Flare gas streams vary depending on industry application and can contain mixtures of volatile hydrocarbon gases including methane, butane, ethane, pentane, and others. Gases such as oxygen, nitrogen, carbon dioxide, hydrogen sulfide, hydrogen, and propylene also can be present. Gas stream flow rates are extremely variable, and temperatures range 0-140° F in the flare process piping prior to reaching the combustion source.

There are several types of flare systems including gas combustion and gas recycling for plant reuse. Proper flare gas combustion requires optimization of the air supply and the flare fuel mixture. The process may include adding fuel, air, or steam to achieve 98% or better destruction of volatile organic compounds, as stipulated by EPA 40 CFR Section 60.18.

In continuous flaring applications where there is a constant supply of gas, recycling the gas for applications such as driving a cogeneration plant are becoming widely used as a method to derive value from troublesome waste gas streams.

The GF03 flowmeter is suitable for installation in these harsh flare gas applications and meets or exceeds the most stringent regulatory agency specifications. These specifications typically require +/- 5% accuracy with repeatability of 0.5% of reading over a wide flow range of 0.50-275 standard feet per second.

"The GF03 flowmeter's performance and programmable outputs mean it is equally effective for reading and reporting both low flows, such as those occurring during a leak, as well as the high flow rates that occur with a major flaring event," according to Wible.

The flowmeter consists of a flow sensor inserted into the gas stream and a separate enclosure that houses all associated electronics and components. The enclosure can be mounted up to 1,000 ft. away from the probe.

The flow sensor is housed in an all-welded 316L stainless steel enclosure so there are no holes to leak, clog, or foul. Its single-insertion probe simplifies installation with only one device placed in the flow stream and reduces tap points to the fewest possible in order to minimize pressure drop and leakage potential.

The standard GF03 is a complete flare gas flow monitoring solution with a large LCD digital readout, a rugged keyboard, fully user-scaleable and programmable 4-20 mA outputs, an RS-232C digital I/O communications port, and two user-programmable 10A relay outputs.

The standard enclosure is rated NEMA Type 4X (IP-66) for weatherproof outdoor installation. Optional explosionproof enclosures suitable for Class 1, Div. 1 environments are available. Other options include varying cable lengths from the flow sensor probe to the enclosure, custom calibration to match specific application requirements, and an in-situ cleaning nozzle.

The GF03 can be provided with digital communication capability in the form of Modbus, Profibus-DP, HART, or Ethernet 100BaseT. Digital communications allow remote monitoring of instrument parameters such as flow rate, total flow, temperature, service diagnostic information, and all instrument set-up parameters.

The flowmeter gives users a simple, low-cost, and reliable method for measuring flare gas flow streams. "The GF03 achieves the accuracy, range, and resolution required to meet the most stringent air pollution regulations, while significantly reducing process complexity and cost," concludes Wible.

For more information call 800/863-8704 or visit www.fluidcomponents.com.

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