Flare Design: Steam-assisted flares

Image courtesy of Zeeco, Inc.® – all rights reserved.

Summary

Steam-assisted flare design utilizes steam for efficient air/waste gas mixing and turbulence which provides smokeless flaring while maintaining the desired combustion efficiency.

How it works

• Steam is injected into the flare gas stream via nozzles on an external ring around the top of the flare tip (upper steam) and/or by steam tube(s) (center or lower) located concentrically within the tip. Center steam is introduced into the stack of a flare to reduce burn back. Lower steam is piped to an exterior annular ring near the lower part of a flare tip, which then flows through tubes to the flare tip, and ultimately exits the tubes at the flare tip.
• Steam assisted tip design vary by manufacturers and can be a single or multiple steam addition locations.

An industrial flare performance was done on steam-assisted flares organized by the Texas Commission on Environmental Quality, working through the University of Texas.

The steam-assisted flare operated with a 36” diameter flare tip. This flare tip has an upper ring for injecting steam around the perimeter of the tip as showed in Figure 2.

A series of tests was performed on the above steam-assisted flare to explore the destruction and removal efficiency (DRE) for different Combustion ZoneThe area of the flare flame where the gas and vapours found just after a flare tip combine for combustion. Elevated Flare definitions and calculation methods from 40 CFR 63… Gas Net Heating Values (CZG NHVs) and flaring rates.

Figure 3 shows observed DRE as a function of CZG NHVs. DRE was high (typically > 95%) for CZG NHVs above 250 BTU/scf. Below this value, DRE and combustion efficiency fell off rapidly. The scatter in the DRE values reported in Figure 3 is due to variety of factors such as inherent variability in the flare operation, uncertainty in measurements, and differences in ambient conditions.