June
2016
33
HYDROCARBON
ENGINEERING
O
ver the years, the US Environmental Protection
Agency (EPA) has been actively involved in various
flare enforcement initiatives, as flares can be a
significant source of emissions. EPA actions include
enforcing a number of consent decrees, establishing standards
for proper destruction removal efficiencies (DRE), and
supporting environmental group civil suits against end users. On
30 June 2014, the EPA proposed revisions to the National
Emissions Standards for Hazardous Air Pollutants (NESHAP) for
petroleum refineries to include flare monitoring and
operational requirements, and to mandate that flares serving as
control devices at petroleum refineries achieve a minimum
destruction efficiency of no less than 98%. The EPA then
consolidated those efforts into a final rule known as
40 CFR Parts 60 and 63. The new refinery regulation was
published in the Federal Register on 1 December 2015, making
the effective date of the regulation 1 February 2016, and the
compliance deadline 31 January 2019.
Unlike other emission sources, combustion in an industrial
flare occurs in open air, so it does not allow for a practical
method to directly monitor post-combustion flare gases. Current
combustion efficiency (CE) flare monitoring methods include the
extractive method (directly sampling post-combustion flare
gases), open path Fourier Transform Infrared spectroscopy (FTIR),
and the use of surrogate parameters (e.g., heating value, exit
velocity) to indirectly predict CE. Monitoring flare performance
using open path FTIR and extractive methods is not practical for
continuous monitoring, as confirmed by the EPA in the recent
refinery rule documentation, while the monitoring of indirect
parameters is inadequate, complex and costly.
Flare manufacturers take a number of process parameters
into account when designing flares so they combust at least 98%
of the hydrocarbons being supplied to the flare tip, optimising
CE. Flare manufacturers provide plant operators controls to
optimise flare operation by adjusting the steam to vent gas ratio,
adding supplemental fuel, or changing the fuel to air ratio.
However, actual flare emissions and CE are typically estimated
after the fact based on input streams, combustion equations and
indirect measurements, such as the speciation of the waste
stream, are sent to the flare. There is a need for a real time post
combustion measurement of CE, which could be used by plant
operators to maintain optimal flare performance.
Scot Smith and Christopher Filoon, Zeeco, USA,
explain how the employment
of direct flame monitoring technology can help operators comply with
increasingly stringent flaring regulations.
SCORCHING
SOLUTIONS
