Methane emissions can be minimized by operating a flare in a manner that ensures adequate combustion efficiency and destruction efficiency. One method for ensuring adequate combustion efficiency and destruction efficiency is to calculate the net heating value of the flare’s combustion zone and to operate the flare to ensure the calculated net heating value of the combustion zone is maintained above a certain threshold. The premise behind this approach is that gases routed to a flare, including methane, will properly combust if the net heating value at the flare tip is sufficiently high, taking into account all material routed to the flare tip including vent gas, assist steam, and/or assist air.
This approach relies on determining the flowrates and net heating values of various streams routed to the flare tip, and using the calculated net heating value as a surrogate for combustion efficiency and destruction efficiency. The net heating value of the combustion zone is not directly measured. Combustion efficiency and destruction efficiency are not determined or estimated.
There are several metrics, several methods to calculate the metrics, and potentially variation in the recommended thresholds. The approach presented here is based on the approach first implemented in the United States by [40 CFR 63.670].
The primary metric is Combustion Zone Net Heating Value (NHVcz), which can be applied to all flares. The secondary metric is Combustion Zone Het Heating Value Dilution Parameter (NHVdil), which should be applied to all air assisted flares and to steam assisted flares with an effective flare tip diameter less than 9 inches (0.2286 m). Refer to for definitions of effective flare tip diameter and perimeter assist air.
