Fisher Scientific, Waltham, Massachusetts
purging and combustion of waste gases via flaring is common practice in the
petrochemicals and organic chemicals sectors but has come under increased
scrutiny during the last decade. Governing bodies around the world, such as the
U.S. Environmental Protection Agency (EPA), are now routinely introducing
stricter regulations to limit hazardous emissions, with a particular focus on
flares. To adhere to these guidelines, it is essential for processing plants to
analyze the composition of these waste gases to identify and mitigate the risk
of pollutants being vented into the environment. This article takes a deep dive
into the state-of-the-art technologies that can be employed to ensure
compliance with these increasingly stringent regulations.
Laying down the law—what are the rules?
Industrial plants, chemical companies, refineries, the coal
industry and landfills practice gas flaring as a safety measure to relieve
pressure or dispose of excess gases. Flaring can also
occur during startup, shutdown or unplanned operational interruptions, such as
The process involves combining the unwanted gases or liquids with steam, and
then burning them off in a flare system. This produces water vapor and greenhouse
gases—including carbon dioxide—which cannot be recovered or recycled.
Regulatory bodies around
the world now require numerous categories of industrial processing companies to
monitor the emissions generated by their flare stacks, and to mitigate the
pollution entering the atmosphere. For example, the Clean Air Act in
the U.S. requires the country’s EPA to regulate hazardous air pollutants from industrial
facilities, including the petrochemicals and organic chemicals sectors. In March
2020, the U.S. EPA signed numerous Risk and Technology Review rules, and in May
of that year, finalized amendments to the 2003 National Emission Standards for
Hazardous Air Pollutants. It was estimated that these changes would decrease toxic
emissions from flares by approximately 260 tpy in the U.S. alone. The updated
requirements defined five flare operating limits:
In particular, the legislation specified an NHVCZ minimum
operating limit of 270 Btu/sft3, based on a 15-min block period.1 This is
calculated by measuring the net heating value of the vent gas (NHVVG),
making flare gas analysis a crucial step in achieving compliance with the new rules.
Achieving compliance with process mass spectrometry. Despite its importance in
monitoring aerial industrial emissions, flare gas analysis presents a series of
challenges. First, the composition of gases generated is typically complex,
comprising both inorganic and organic species. It also changes dramatically
over time as process conditions change.
speed is crucial, as the heating value of the flare can quickly change—a wait
of just a few minutes for results can increase the risk of a plant failing to
meet its prescribed emissions standards. Together with other
limitations, these factors make reliable and accurate flare gas analysis difficult,
time-consuming and expensive, hindering a plant’s abilities to monitor and control
Magnetic sector-based process mass spectrometers (FIG. 1) are an ideal solution to this
problem, as they perform accurate multicomponent analysis of the composition of
multiple flare gas streams simultaneously, all within just 30 sec. This technology provides fast,
lab-quality online gas analysis and process analytics, enabling predictive
control systems to be updated in real time. These versatile instruments also feature automated
calibration methods, allowing quick and easy optimization of an unlimited number of analytical
techniques on a per-stream basis. These features make it possible for
hydrocarbon processing plants to rapidly modify a diverse range of production stages,
as well as to measure their stack emissions, helping to guide mitigation steps
towards reaching compliance.
Scanning magnetic sector technology offers
the best performance for industrial online gas analysis due to its accuracy and
precision, long intervals between calibrations and resistance to contamination.
For example, platforms based on this technology are between two and ten times more
precise than a quadrupole analyzer, depending on the gases analyzed and the complexity
of the mixture. The performance advantage of magnetic sector mass spectrometers is even greater at low mass
numbers. FIG. 2
shows how scanning magnetic sector mass spectrometers detect the sulfur
concentration of flare gas streams.
analysis of flare gas streams. Improperly operated flares may emit sulfur
dioxide and other sulfur compounds, which form acid rain in the presence of
This harms trees and other plants by damaging foliage and decreasing growth.
In addition, these substances react with other compounds in the atmosphere to form small
particles, contributing to particulate matter pollution. These particles can
penetrate deeply into the lungs and, in sufficient quantities, can contribute
to numerous severe long-term health issues.
U.S. EPA’s air quality standards are designed to protect against exposure to
sulfur oxides, so refinery regulators are interested in values for total reduced
sulfur (TRS) and hydrogen sulfide (H2S). However, there is a decided
lack of uniformity on what constitutes TRS, as it can be defined as H2S
together with carbonyl sulfide and carbon disulfide, or as a mixture of
compounds that contain a sulfur component in its reduced form.
To circumvent this absence of clarity, online
sulfur analyzers are now being used extensively in many oil- and gas-related
industries to quantify the total sulfur content of hydrocarbon samples,
regardless of their chemical or molecular form. These analyzers use pulsed
ultra-violet fluorescence (PUVF) technology—illustrated in FIG. 3—to provide a
continuous measurement of total sulfur, allowing plant operators to adjust their
processes for desulfurization. For example, operators may adapt the stack exit
temperature on the waste-heat recovery unit or the boiler feedwater temperature
to reduce the emissions of sulfur pollutants.
New state-of-the-art online total sulfur analyzers have
been developed (FIG. 4)
that have a dynamic measuring range from 10 parts per million (ppm) to 100%, with
excellent linearity and precision specifications. These high-spec platforms are
also configured specifically for high dewpoint vapor samples and can constantly
monitor flare feed sulfur content via a 30-sec injection period. This capability
enables the analyzers to provide highly accurate measurements, with a fast
response time to changes in concentrations.
Investing in a greener future. Using technologies such as mass spectrometers and PUVF
to analyze the chemical composition of flare gases helps operators to pinpoint
the source of an emission, right down to a specific part of the plant. This enables
the timely optimization of equipment and workflows to ensure that flare waste
gases are burned to complete combustion before they are released from the stack.
Continually adjusting process parameters contributes greatly to minimizing the
venting of pollutants into the atmosphere, helping to ensure regulatory compliance
and significantly enhancing the sustainability of the petrochemicals and
organic chemicals industries in the long term. HP
a Thermo Scientific™ Prima PRO Process Mass
Thermo Scientific™ SOLA iQ Online Sulfur Analyzer