Mass Flow Meter Measures Biogas and All Methane Composition Gases
Fluid Components International (FCI) has released its Model ST51 Mass Flow Meter for owners, operators and manufacturers of biogas production and methane capture and recovery systems. The Model ST51 is easy-to-install, safe and requires virtually no maintenance.
In anaerobic digester produced biogas, gas flow measurement is challenged by the wet, dirty nature of biogas. The biogas produced is a potentially dangerous mixed composition of primarily methane (CH4) and carbon dioxide (CO2), with smaller percentages of hydrogen sulfide (H2S) and other gases. The wetness, H2S and other particulates in the gas create a corrosive condensate that deposits itself on the pipe wall and the instruments in the pipe. The gas flow varies widely too — based on fluctuating plant process demands and seasonal variations in temperature and humidity.
FCI’s ST51 Flow Meter is designed to measure biogas and all methane composition gases including natural gas. The ST51 features a thermal mass, insertion-style flow element with flow accuracy up to ±1% of reading over a broad flow range from 0.3 to 400 SFPS (0.08 to 122 MPS) and a repeatability of ±0.5% of reading. The flow element is available for use in line sizes from two to 24 inches (51 to 610 millimeters) in diameter. It operates over a wide turndown range of 100:1, which is essential due to the variable gas flows in wastewater treatment. It operates at temperatures from 0 to 250°F (-18 to 121°C) and withstands
pressures of up to 500 psig [34 bar (g)].
The ST51’s robust thermal mass flow sensing element has no moving parts and no orifices to clog or foul to attain virtually maintenance-free service in wet, dirty biogas applications. It also includes built-in temperature compensation circuitry for accurate, repeatable measurement year-round as temperatures rise and fall seasonally. The flow element is constructed with a 316L stainless steel body and Hastelloy C-22 thermowell sensors to resist corrosion. It is approved for use in hazardous environments with approvals that include: FM, CSA/CRN, Class 1, Div 1, Groups B, C, D; Class 1, Div II, Groups A-D, ATEX Zone 1, II 2 G Ex d IIC T6 T3, II 2 D Ex tD A21 IP67 T90°C T300°C. The ST51 flow meter also offers outputs for user interfaces and information. Dual 4-20mA analog outputs are user assignable to flow rate and/or temperature, and there is a 0-1kHz pulse output for totalized flow. The transmitter’s digital communications include an RS-232C port, and, with units that have the digital display option, there is a wireless IR link for PDA use.
The ST51’s optional integral digital display features a two-line, 16-character LCD screen that is easy to read and can be rotated in 90-degree increments for optimum viewing and installation flexibility. The LCD screen’s top line is assigned to flow rate, and the bottom line is user assignable for temperature readings or totalized flow. For applications with difficult access or display readability, the ST51’s flow transmitter is also available in a remote mount configuration that can be mounted up to 50 feet (15 meters) away from the flow element. Both the remote mount and the integral transmitters are housed in an aluminum enclosure that is NEMA 4X approved and meets IP67 requirements for water and dust ingress protection. Input power for the ST51 can be selected as either 18 to 36 Vdc or 85 to 265 Vac.