Infrared Sensor Keeps Petrochemical Flares Smokeless

The new Model FM Flare Monitor for Smokeless Flares from Williamson Corporation (USA), as part of a petrochemical plant’s closed-loop control system, efficiently prevents smoke before it is produced, rather than reacting to smoke as most competing sensors do. It is also the only optical product of its type that is unaffected by the introduction of steam.

Unlike any other sensor, the Model FM Flare Monitor senses the conditions precursory to soot formation, not soot particulates. It monitors the ratio of carbon to oxygen within the flame, and its continuous output signal is proportional to that ratio and therefore proportional to the tendency of the flame to smoke. When the signal indicates that oxygen is becoming relatively scarce, a successful control scheme adds oxygen to the flame before the signal reaches the critical setpoint at which soot would form.

Thanks to its special narrow-band infrared filters, the Model FM’s output is reliable even through dirty optics, fog, rain, and snow, within limits. The output signal typically goes to a proportional-integral-derivative (PID) control system that activates a control valve to modulate the amount of added air or steam as needed, ensuring that there is always ample oxygen for the combustion to be complete, all without the need for operator intervention. For facilities that use steam, another benefit of such precision is that no steam is wasted.

The Model FM comes standard with through-the-lens sighting and an adjustable swivel bracket that facilitates installation and alignment. The sensor’s dual-wavelength technology ensures a large target area, further facilitating alignment. The unit, which is available with a standard (NEMA4/IP65) or rugged (NEMA7/ATEX/IECEx IIB+H2) housing, can be mounted at ground level, typically within approximately 1,500 feet (457 meters) from the base of the stack. The strength of the measured signal decreases with the square of the distance. Optical resolution is D/17 (60 feet at 1,000 feet).

The Model FM Flare Monitor is a complement to Williamson’s proven Model PM Pilot Monitor, which is used to confirm the presence of a stack’s pilot flame. Approximately a thousand units of this other model have been in use worldwide, over many years.