A vital safety mechanism in industrial plants , flares stacks are used to burn off flammable gases released by pressure relief valves , avoiding unplanned pressure build-ups and disposing of excess gases . They are also used for the planned combustion of gases over short periods during plant start-ups or shut-downs .
A flare stack is an elevated vertical stack or chimney , and steam-assisted flaring of the associated gas occurs at the top of this structure to control the Combustion Efficiency ( CE ), a percentage that represents the number of molecules of the compound destroyed by incineration relative to the amount that entered the system . In an efficient flare system , the CE should be 98 % or higher .
Combustion of the vent gas is much more environmentally responsible than simply releasing the gas into the air . For example , if methane is burnt , the products are CO 2 and water , which are much less harmful than releasing methane itself .
Flares are active all the time , with a continuous release of gas being burned off at the flare stack . When this mix of stream and hydrocarbons is correct , the flame is clean and no harmful emissions escape into the atmosphere .
In steam-assisted flares , the ratio of steam to vent gas is critical . Understeaming leads to an inefficient process , while over-steaming can be a cause of incomplete combustion , and visible smoke is a clear sign of pollutants being released into the atmosphere .
Recently , the United States has been a leader in the field of studying flare stack emissions , with the most recent performance tests of steam-assisted flares by Marathon Petroleum in Detroit .
While there are obvious commercial benefits in keeping the process as efficient as possible , these studies are also driven by a desire to stay ahead of impending changes to US Environmental Protection Agency ( EPA ) regulations .
Based on the latest industry-scale flare tests , the EPA has proposed revisions to the flare exit velocity limit and introduced new metrics for flare operation under refinery Most Achievable Control Technology ( MACT ) regulations . MACT standards were developed by the EPA to reduce the effects of hazardous air pollutants generated by industry .
The major implication of the proposed rules is the requirement for flare monitoring , which the EPA estimates will cost the industry $ 147 million in capital investment for flare monitoring infrastructure .
The SpectraScan 2400 / H2Scan system is so reliable it can be used as a benchmark to determine the performance of GC / calorimeter analyzers .
FLARE SYSTEM
Servomex ’ s system , comprising the SERVOTOUGH SpectraScan 2400 and the SERVOTOUGH H2Scan working in combination , gives a continuous reading with a good compositional measurement .
It measures 14 components , with an overall BTU value and individual component values .
Flare Tip
Pilots
Steam or Air-Assist
Molecular Seal
SERVOTOUGH SpectraScan 2400 H2Scan
Flare Stack
Waste gas from process
Purge
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Knockout Drum |
Flare Header |
Liquid Seal |
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P09 |