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Monitoring & metering


Reducing VOc emissiOns in the usA


In the United States, the Clean Air Act is a federal law regulating air emissions from stationary and mobile sources. The Act authorises the United States Environmental Protection Agency (US EPA) to establish National Ambient Air Quality Standards (NAAQS) to protect public health and to regulate the emissions of hazardous air pollutants. The EPA has therefore published a list of hazardous air pollutants, many of which are VOCs. VOCs can contribute to non-attainment with


the NAAQS or may adversely affect the attainment status of an area. The EPA has addressed serious violations through enforcement actions, achieving measurable pollutant reductions and improving air quality. Through partnerships with state and tribal authorities, the US EPA has conducted multiple joint inspections and joint enforcement actions, and this has resulted in a significant reduction of VOC emissions, particularly from the oil and gas sector. In the US, Method 25 is applicable for the determination of VOCs (measured as total gaseous non-methane organics (TGNMO) and reported as carbon) in stationary source emissions. The Method says: “Direct measurement of an effluent with a flame ionization detector (FID) analyser may be appropriate with prior characterisation of the gas stream and knowledge that the detector responds predictably to the organic compounds in the stream. If present, methane (CH4) will, of course, also be measured. “The FID can be used under any of the following limited conditions:


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Where only one compound is known to exist.


When the organic compounds consist of only hydrogen and carbon.


Where the relative percentages of the compounds are known or can be determined, and the FID responses to the compounds are known.


4 5


Where a consistent mixture of the compounds exists before and after emission control and only the relative concentrations are to be assessed.


Where the FID can be calibrated against mass standards of the compounds emitted (solvent emissions, for example).


“Another example of the use of a direct FID is as a screening method. If there is enough information available to provide a rough estimate of the analyser accuracy, the FID analyser can be used to determine the VOC content of an uncharacterised gas stream. With a sufficient buffer to account for possible inaccuracies, the direct FID can be a useful tool to obtain the desired results without costly exact determination.”


Instrumentation Monthly April 2021 Alternatively, Method 25A applies to the


determination of total gaseous organic concentration of vapours consisting primarily of alkanes, alkenes, and/or aromatic hydrocarbons. The concentration is expressed in terms of propane (or other appropriate organic calibration gas) or in terms of carbon. Again, the Method stipulates the collection of a heated gas sample which is passed to a flame ionization analyser.


VOc mOnitORing


As outlined above, the level of monitoring required by regulators is dictated by the scale of an operator’s VOC emissions, with continuous monitoring required for the larger emitters and discontinuous monitoring for processes with lower emissions. Signal Group has therefore developed VOC analysers to meet both requirements – a portable heated FID (Signal MiniFID 3010) for periodic measurements and a continuous heated FID (SOLAR) for permanent installations. The continuous heated FID SOLAR


analyser can be easily fitted into a 19” rack cabinet for indoor or outdoor installation. The analyser has an embedded microprocessor which automatically starts the analyser upon receipt of a command from a detachable tablet, or from a remote installation with Signal’s S4i software. This command sets in place a sequence of analyser actions which prepare the analyser to take samples and report calibrated readings to the instrument’s internal datalogger. Using an optional detachable tablet, users


are able to manage the analyser wirelessly up to 50 metres away from the analyser. In addition, using the remote S4i software over an Ethernet connection, the analyser can be operated from anywhere at any time. This remote accessibility also means that the Signal after-sales team can monitor alarms, conduct remote calibration and even troubleshoot if necessary. The portable heated FID MiniFID 3010 is suitable for a variety of applications:


Compliance monitoring where the permit requires discontinuous measurements Calibration of CEMS Temporary back-up for CEMS Checking abatement performance Fugitive emissions investigations Process optimisation


In contrast with most of the other


‘portable’ FIDs on the market, the MiniFID 3010 was designed as a rugged, portable field- use instrument. With an optional internal datalogger (and memory stick), sample pump, inlet filter, heated line controller and a detachable gas bottle holder, the MiniFID 3010 is ideal for use on ducts and stacks


with difficult access. The analyser’s detachable bottle holder accommodates both the burner gas and the calibration gas, with zero air provided with a background hydrocarbons purifier. The frame is made from lightweight


aluminium and the instrument is supplied with lifting eyes and a comfortable shoulder strap. Portable FIDs often need to operate with extended power cables, so the MiniFID is able to operate without a power-hungry microprocessor, (110VAC or 220VAC is specified when purchasing). The heated line (optional 5m or 10m) is powered from a socket on the side of the analyser, which helps to reduce the amount of cabling required. The heated line is supplied with a stainless steel sintered filter probe for insertion into the stack or duct. The instrument is simple to operate:


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Switch on, wait for the temperature interlock to reach set temperature.


Turn gases on, press “Ignite” switch.


Wait for the reading to settle, select “Zero” gas and adjust dial to read zero on the analyser display.


Select “Span” and adjust span dial to read the value of the calibration gas.


Select “Sample” and the analyser will start drawing sample gas through the heated line.


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Wait a few minutes for the sample gas to arrive at the analyser and the instrument will start to display readings, which may be logged to the memory stick for later


examination and reporting. Many MiniFID 3010 users are process


operators, but a larger number are environmental consultants or test houses that provide monitoring services. This is because stack testers require instruments that are rugged, reliable and designed for field operation.


summARy


FID analysers are ideal for a variety of solvent emissions monitoring applications – the list given in Method 25 provides a useful guide. It is important to remember that while Flame Ionisation is the reference method for the monitoring of VOCs, the response of the analyser will vary according to the VOC or VOCs present in the sample. With many decades of experience in the


development of FIDs, Signal Group is able to provide help and advice on which instruments and accessories are necessary, and on how to deliver high quality, reliable, defensible monitoring data.


Signal Group www.signal-group.com 25


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