Krohne announces ultrasonic flowmeter for biogas

German flowmeter specialist Krohne has announced a new flowmeter specially designed for use with biogas. The OPTISONIC 7300 Biogas ultrasonic flowmeter is able to measure both wet and dry biogas compositions, and continues a growing trend of fluid handling equipment being designed with biogas application in mind.

Flowmeters operating on the ultrasonic principle require particulates or bubbles in the flow in order function. They employ the frequency shift (Doppler effect) of an ultrasonic signal when it is reflected by suspended particles or gas bubbles. Ultrasonic sound waves are transmitted into a pipe with a flowing liquid or gas. As the waves encounter the bubbles or particulates they are reflected back with a different frequency that varies depending on the rate of flow of the fluid, in turn allowing the flowrate to be measured.

Until now, it has been difficult to use ultrasonic flowmeters in biogas applications because the carbon dioxide and high water content in biogas dampen the acoustic signals. Krohne claims that the OPTISONIC 7300’s signal transducers transmit a stronger signal, which combined with specialised signal processing enables better detection of the small, heavily dampened signals in biogas.

The OPTISONIC 7300 Biogas flowmeter has a measuring tube made of stainless steel to overcome the corrosive properties of the hydrogen sulphide common in biogas, as well as transducers that are made of NACE approved grade 29 titanium for maximum corrosion resistance. The device’s measurement accuracy is specified at 1% of actual measured flow rate, when calibrated with air, starting from 3.28 feet per second flow velocity. When 2% accuracy is sufficient, users can select a dry calibration alternative at a lower price.

Krohne’s new biogas flowmeter 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 2, 3, 4, 6, and 8 inches.