Basis for Emission Calculation from Flare Systems

In 1983, the Chemical Manufacturer's Association (CMA) sponsored a study in an attempt to define emission factors for flare systems. The study encompassed several variables including the lower heating value of the gas, relief gas flow rate, air assist rate, and steam assist rate. Emissions were continuously monitored by a sample probe located above the flare flame to analyze the concentrations of carbon dioxide, carbon monoxide, total hydrocarbons, sulfur dioxide, nitrogen oxides, and oxygen. The US Environmental Protection Agency (EPA) published the AP-42 guideline for flare system emissions, citing values that are essentially averages considering all of the CMA testing data. Unfortunately, companies using the AP-42 data as their guideline for permitting elevated flares could be citing values that are far from accurate, considering the wide range of conditions tested in the CMA study. This paper will examine the original CMA test data, discuss possible variations between the testing from 1983 and modern flare system designs and operation, and identify the applicable conditions for employing the various published factors for flare emissions