- September 25, 2025
- FCI - Fluid Components International
SAN MARCOS, Calif., Sept. 25, 2025 – Plant engineers measuring toxic and combustible waste gases from municipal or industrial processes, including wastewater treatment and landfills, will find that the ST80 Series Thermal Flow Meter from Fluid Components International (FCI) delivers precise, repeatable gas flow measurement in an instrument with global HazEx approvals and much more.
The composition of wastewater digester gas, for example, is primarily methane (CH4) and carbon dioxide (CO2) with a small percentage of trace gases. This gas composition varies with the plant, process and temperature (e.g., seasonally), but a typical average is in the range of 65% (±5%) CH4 and 35% (±5%) CO2. Digester gas is also a wet and dirty gas, typically containing entrained hydrogen sulfides, which condense and deposit on pipe walls and anything else in the pipe.
The accurate measurement of gas production is proportional to the efficiency of the digester process itself. If the gas harvested is also reused as fuel in a CHP or cogeneration system, the amount of gas sent to the engine(s) is a key control variable. Furthermore, if any gas is released or flared, because CH4 and CO2 are known polluting greenhouse gases (GHG), local environmental regulations typically mandate reporting of the quantity of gases emitted or flared.
The most important criteria for choosing a digester gas flow meter are accuracy, safety, installation, service access and lifecycle costs. As CH4 is a combustible, potentially explosive gas, instrumentation should carry agency approval certification for Div1/Zone 1 HazEx installations. If the flow meter’s installed location occurs before gas drying/cleaning or without that step altogether, then engineers must also consider measuring success (as in moist gases, plugging or fouling of orifices or moving parts due to H2S deposits), and the labor cost and ease of technician access for periodic cleaning to remove H2S residue.
With its no-moving parts, simple insertion-style design and global HazEx approvals, FCI’s ST80 Thermal Mass Flow Meter is the ideal solution for wastewater digesters or other waste gas flow measurement challenges. The ST80 meter is a high-performance, rugged thermal dispersion technology air/gas flow meter that combines ultra-reliable, feature-rich electronics and FCI innovations such as Adaptive Sensing Technology (AST).
With the industry's most extensive selection of application-matched flow sensors, including FCI's wet gas flow element, the ST80 Flow Meter provides a truly superior solution for moisture-rich digester or other waste gas applications. In addition, it combines these features with a robust, rugged transmitter enclosure and the industry’s broadest selection of process connections to provide the longest service life and ease-of-installation in the user installation’s pipe or duct.
Featuring an insertion-style configuration for wastewater digester gas, the ST80 Flow Meter is a single-point meter for pipe diameters greater than 2 inches (51 mm). It operates over a wide flow range: 0.25 to 1000 SFPS (0,07 to 305 NMPS). Flow accuracy is ±1.0% of reading, 0.5% full scale and repeatability is ±0.5% of reading. It operates over a broad turndown ratio that is normally factory set and is field adjustable from 2:1 to 100:1 within the calibrated flow range.
This flow meter’s transmitter outputs are a match to user DCS, PLC, SCADA, recorder or alarm systems. Whether the application’s output needs are traditional 4-20 mA analog or advanced digital bus communications such as HART, Foundation Fieldbus, PROFIBUS PA, PROFIBUS DP or Modbus, the ST80 meter has it covered. Then, for a local display, the ST80’s graphical, backlit LCD is unmatched in showing what’s happening in the pipe.
Flow rate, totalized flow and temperature are continuously displayed in both a digital and bar graph presentation, while alarms and/or diagnostic messages will display as needed to alert operators.
The ST80 Flow Meter’s transmitter enclosure is NEMA4X/IP67 rated and available in painted aluminum or stainless steel. FCI’s ST80 digester gas flow meter’s HazEx agency approvals are on the entire instrument, not just the enclosure and its full pedigree of approvals includes: ATEX, CE, CPA, CRN, FMc, FM, Foundation Fieldbus, HART, EAC/TR CU, EMSA EQM-EX, IECEx, NEPSI, PROFIBUS, SIL (IEC 61508), UKCA, UKEX.
A DwyerOmega brand, FCI delivers precise flow and level instrument measurement solutions using advanced thermal dispersion technologies. With more than 60 years of experience and the world’s largest installed base of thermal flow meters, flow switches and level switches, FCI is the trusted expert in flow and level instrumentation.
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