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Measuring Methane, an FID Option...
Flame ionization devices (FID’s) are most commonly used in accordance with USEPA Method 21(M-21) and Method 25 (M-25), however its most common environmental use is conducting ambient surveys of open and closed landfill sites which falls under Method-21.
Measurement ranges frequently encountered under M-21 are routinely measured as a percentage of the lower explosive limit (LEL). In ambient monitoring processes the detectable levels often fall into the low 10’s & 100’s parts per million (ppm).
M-25 Section 1.2.4 states the use of FID’s as screening tools, however Section 6.1 states heated traps maintained at >129c. M-25 quantifies a more rigorous specification for the FID and gas handling system. Knowing that this is not possible or available in a portable handheld, it renders the method logistically, stationary.
M-21 has calibration specifications to be followed.
Section 7 States 7.0 Reagents and Standards.
7.1 Two gas mixtures are required for instrument calibration and performance evaluation:
7.1.1 Zero Gas. Air, less than 10 parts per million by volume (ppmv) VOC.
7.1.2 Calibration Gas (Span gas). For each organic species that is to be measured during individual source surveys, obtain or prepare a known standard in air at a concentration approximately equal to the applicable leak definition specified in the regulation.
What Value Calibration(Span) Gas should you use?
USEPA M-21 States;
”3.1 Calibration gas means the VOC compound used to adjust the instrument meter reading to a known value. The calibration gas is usually the reference compound at a known concentration approximately equal to the leak definition concentration”
“3.5 Reference compound means the VOC species selected as the instrument calibration basis for specification of the leak definition concentration. (For example, if a leak definition concentration is 10,000 ppm as methane, then any source emission that results in a local concentration that yields a meter reading of 10,000 on an instrument meter calibrated with methane would be classified as a leak. In this example, the leak definition concentration is 10,000 ppm and the reference compound is methane.)”
FID’s Over the years we have used two main models of the FID; TVA-1000 which is branded Foxboro, Thermo, Landtec, or Century and the MicroFID. Both these models have been designed for users to measure methane with a traditional flame ionization method.
Compound of Interest and Instrument Response
USEPA define an FID as;
“Flame Ionization Detector (FID) A FID is an instrument often used in conjunction with gas chromatography to measure the change of signal as analytes are ionized by a hydrogen-air flame. It also is used to detect phenols, phthalates, PAHs, VOCs, and petroleum hydrocarbons.”
FID’s do respond to more than just methane (CH4) as listed in manufacturers specifications.
MicroFID specifies its Detectible Compounds as; Saturated Hydrocarbons - Methane, Ethane, Propane, n-Hexane Aromatics - Benzene, Toluene, Naphthalene Unsaturated Hydrocarbons - Acetylene, Ethylene, 1,3-Butadiene Chlorinated Hydrocarbons - Vinyl Chloride, Chloroform, Trichloroethylene, Methylene Chloride Ketones - Acetone, Methyl Ethyl Ketone, Methyl Isobutyl Ketone Alcohols - Methanol, Ethanol, Isopropanol, n-Butanol
Thermo has two models of the TVA-1000, A & B. In this instance an A B or both are added to the compound showing response to the instrument. Acetic Acid (AB), Acetone (AB), Acetonitrile (B), Acrylic Acid (B), Allyl Alcohol (AB), Amyl Alcohol (AB), Benzene (AB), Benzyl Chloride (AB), 1,3-Butadiene (AB), n-Butane (AB), 1-Butanol (AB), 2-Butanone (MEK) (AB), 1-Butene (AB), Butyl Acetate (AB), Butyl Acrylate (AB), CFC 12 (AB), CFC 113 (AB), Chlorobenzene (AB), Chloroform (AB), 2-Chlorotoluene (AB), m-Cresol (B), Cyclohexane (AB), n-Decane (AB), Dimethylformamide (AB), Ethane (AB), Ethanol (AB), 2-Ethoxyethanol (AB), Ethylbenzene (AB), Ethyl Acetate (AB), Ethyl Acrylate (AB), Ethyl Lactate (B), Ethylene (AB), Ethylene Oxide (AB), Formaldehyde (AB), n-Heptane (AB), n-Hexane (AB), Iodomethane (B), Isobutanol (AB), Isobutylene (B), Isopropyl Alcohol (AB), Isopropyl Ether (B), Methanol (AB), MethylChloride (AB), Methylcyclohexane (AB), Methylene Chloride (AB), MIBK (AB), MTBE (AB),n-Nonane (AB), n-Octane (AB), n-Pentane (AB), PGME (B), PGMEA (B), Propane (AB), Propylene (AB), Styrene (AB), Tetrachloroethylene (AB), 1,1,1,2-Tetrafluoroethane (B), Tetrahydrofuran (AB), Toluene (AB), Trichloroethylene (AB), Triethylamine (AB), Vinyl Acetate (AB), Vinyl Chloride (AB), Vinylidene Fluoride (B), Xylenes (AB)
You should understand that the instruments will respond to these gases but that it is not calibrated (focused) for this gas. This means these gases interfere with your measurement if in the testing environment. You can account for them as background but there is still limitation with the detection technology since inception. You can not take it for granted you’re measuring methane!
Does cost make a better instrument?
FID’s are historically expensive considering what your get. Think about it, a PID measures so much more and cost about half the price. It calibrates easily and works efficiently at what it does. Have FID’s evolved like the PID’s? I think not. Both the models mentioned in this article haven’t evolved much in 5 years. I do hear that Gas Dynamics will release a new FID model with GPS. I’ll wait to be provided a demo unit!
With any of these instrumental methods we find cost associated with equipment, training, calibration and, most importantly with the FID based instruments, fuel. Fuel for an FID can be a nightmare; 3000psi of 99.9998% pure hydrogen. Safety and transport of these containers make it prohibitive to ship hydrogen charged units, meaning onsite filling. Potential of contamination, filling and transport mishaps could make even the most seasoned safety officer sweat.
In field we have shown the landfill survey method comes with imperfections simply in measuring methane. We really believe that an FID needs trained operators and a person responsible for its upkeep. These have shown over the years to be problematic in consulting firms with many users. Methodology is usually referred to the manual and as we all know it’s like programming time on a DVD player. It doesn’t happen, or there are AM/PM mistakes. You cannot account for everything.
M-21 offers compliance teams options in measurement technology in Section 6
USEPA M-21 States; “6.1 The VOC instrument detector shall respond to the compounds being processed. Detector types that may meet this requirement include, but are not limited to, catalytic oxidation, flame ionization, infrared absorption, and photoionization.”
Answers? - RKI Eagle with Catalytic Sensor for Methane
Costing a fraction of the price of an FID, we find very few reasons not to replace your FID with these units. The RKI Eagle is not the prettiest instrument but it is cost effective and user friendly. RKI support the Eagle and other gas detectors with YouTube training and service videos.
The RKI Eagle with Catalytic Sensor beat FID's in functionality and cost.
The Eagle’s Catalytic Sensor needs no fuel which proves an asset in any transport option as well easing the safety and technological gap. It is no more difficult than a PID.
The Eagle’s Catalytic gases of detection; Methane, Ethane, Propane, Butane, Pentane, Hexane. Other alkenes, alcohols, and amines monitored Butadiene, Isopropylamine, Propylene, Ethylene Oxide, Propylene Oxide, Ethanol, Methanol
Other gases that can be added or used to customize your Eagle Standard Gases: Hydrocarbons (CH4, std), Oxygen (O2), Carbon Monoxide (CO), Hydrogen Sulfide (H2S)
Toxics Gases: Ammonia (NH3), Arsine (AsH3), Carbon Dioxide (CO2) (I R Sensor), Chlorine (Cl2), Chlorine Dioxide (ClO2), Fluorine (F2), Hydrogen Fluoride (HF), Hydrogen Chloride (HCl), Hydrogen Cyanide (HCN), Hydrogen Sulfide (H2S), Isobutane (C4H10) (IR Sensor), Methane (CH4) (IR Sensor), Nitrogen Dioxide (NO2), Nitric Oxide (NO), Ozone (O3), Phosphine (PH3), Silane (SiH4), Sulfur Dioxide (SO2)
Eagles can be upgraded to handle six gases making it a competitor to the GA series Landfill Gas Meters.
Pricing of the Eagle single gas for Methane (CH4) (ppm) start $1,700 USD, $2,260.00 AUD and $2,695.00 NZ at today’s exchange rate. The Eagles prices are a fraction of the cost for a similar FID.
Small Print - Price variable on exchange rate and subject to change. Prices exclusive taxes and duties but include shipping in Australia (AUD), and New Zealand (NZD)