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Cosa Instrument has announced the Focus Probe optical flow meter (OFM) for flare gas monitoring.

This flow meter has been specifically developed for gas applications with highly variable flow rates and a wide range of pipe diameters in very tough and dirty applications.

The OFM uses laser beams to measure the gas flow by sensing the velocity of microscopic particulates naturally occurring in the gas.

Small particles that accompany natural and industrial gases pass through two laser beams focused in a pipe by illuminating optics.

Laser light is scattered when a particle crosses the first beam.

The detecting optics collects scattered light on a photodetector, which then generates a pulse signal.

When the same particle crosses the second beam, the detecting optics collect scattered light on a second photodetector, which converts the incoming light into a second electrical pulse.

By measuring the time interval between these pulses, ‘t’, the gas velocity is calculated as ‘V=S/t’ where S is the distance between the laser beams.

The OFM accuracy is immune to: gas composition/changes; pipe vibration; acoustic noise; low flow rates; ‘fogging’ or moisture buildup; and CO2.

Contamination of optical components is a concern when considering a flow measurement system using optics in a flare gas environment.

This is especially so with flare gas, which generally has a variable composition and liquid content.

This issue had been addressed at the beginning of the Focus Probe development by implementing a shroud design.

This solution improved the resistance of the device to concurrent liquid hydrocarbons, which are known to cause problems for other types of flare meters.

Another improvement aimed at liquids dropping out of the gas was the application of heated windows.

In early commercial installations it was discovered that many flare and biogas facilities deal with wet gas.

Keeping the windows warmer than the ambient gas prevents laser light from scattering due to foggy or wet window surfaces.

Currently this is a standard feature for all L2F OFMs.

The OFM is compliant with ASME Code Section VIII, Division 1 and has been designed, manufactured, inspected and tested according to its recommendations.

These units can be used in Class 1 Div 1 or Zone 1 applications using the appropriate flow processors.

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