Flow Measurement & Control


Ultrasonic flowmeter for biogas

June 2018 Flow Measurement & Control

Krohne now offers the Optisonic 7300 Biogas ultrasonic flowmeter, which has been specially designed to measure dry and wet biogas with variable composition. The flowmeter provides additional functions like calculation of standard volume, methane content measurement, and diagnostics features. It features no moving parts and no pressure loss.

The Optisonic 7300 Biogas overcomes the limitations of the ultrasonic principle in biogas applications due to high damping of the acoustic signals by carbon dioxide and high water content in the biogas. Its signal transducers provide a stronger ultrasonic signal into the gas, and specialised signal processing enables better detection of small, strongly dampened acoustic signals. These features, along with the mechanical design of transducers and transducer pockets, make the measurement insensitive to liquid water and biological scaling.

Optisonic 7300 Biogas features a maintenance-free full bore flow sensor without any moving parts. Because the hydrogen sulphide in biogas is corrosive when dissolved in water, the measuring tube is made of stainless steel 1.4404/316L and the transducers are made of NACE-approved grade 29 titanium for maximum corrosion resistance.

It is equipped with lap joint flanges to lower its overall weight. The measurement accuracy is specified at 1% of actual measured flow rate, when calibrated with air, starting from 1 m/s flow velocity. When 2% accuracy is sufficient, users can select a dry calibration alternative at a significantly lower price.

The Optisonic features a built-in temperature sensor that facilitates direct measurement of methane content using calculation of the molar mass, in combination with the measured velocity of sound. This enables end-users to determine the exact methane content of the biogas, necessary when the biogas is used as fuel for gas engines in a combined heat and power (CHP) unit. It can also provide calculation of gas flow volume to standard conditions by using an additional pressure sensor. The electronics also include diagnostics to validate the flowmeter functions and the process. For output of the measured values, 4…20 mA and pulse outputs are available. HART and Modbus (optional) are included for field communication.

The Optisonic is certified for use in explosive areas (zone 1). Since no pressure drop is generally allowed in biogas pipelines, the device is available in common line sizes of 5, 7,5, 10, 15 and 20 cm.

For more information contact Clayton Duckworth, Krohne SA, +27 (0)11 314 1391, c.duckworth@krohne.com, www.za.krohne.com



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