Biogas and RNG Flow Meters

Organic industrial waste from food processing and slaughterhouses, food waste from restaurants and homes, manure collected from livestock, as well as energy crops can be digested in anerobic conditions in reactor tanks, also called fermentation towers. The output from this biomass digestion process is biogas, a mixture of methane (CH4), carbon dioxide (CO2), water and trace hydrogen sulfide (H2S). The entire process involves gas creation, cleansing, storage (tank or bag-type accumulator), and ultimately the use of biogas, also known as renewable natural gas or RNG, as a fuel source for heating or generating electricity. A ground flare is an integral part of the safety system for the process. Installation of biogas flow meters and RNG flow meters at several points in the system provides operators with critical information for optimal gas production, control, safety and reporting.

Biogas flow meter applications present several challenges for successful selection:
  • Low flow sensitivity during start-up and for seasonal changes which produce lower flow rates
  • Temperature compensation for correct readings in varying temperatures
  • Calibration for mixed gas composition of CH4 + CO2 + trace gases
  • Wet, dirty gas with corrosive H2S content
  • Potentially flammable or explosive gas installation environment
  • Easy, low cost installation and low maintenance

Biomass Fermentation

Key Criteria For Flow Meter Selection

  • Mass flow measuring of both rate and totalized flow
  • No moving parts or small holes to clog or foul in dirty or wet gas environments
  • Biogas-specific calibration
  • Low flow sensitivity, at least 0.6 FPS [0,2 m/s] and wide turn-down of 100:1
  • Pressure drop over flow element should be limited to 0.01Psi [1 mBar]
  • All wetted parts resistant to H2S corrosion; minimum of 316L stainless steel
  • Easy and safe removal under line pressure with simple ball valve
  • System agency approvals for safe installation in Division 2 [Zone 2] or Division 1 [Zone 1]

FCI ST Series thermal dispersion flow meters, in both insertion and in-line styles, are optimal for biogas flow measurement. In addition to meeting all of the key selection criteria above, FCI uses a constant power measuring technique that, because of a slight heating effect, actually dries condensate moisture off the sensor. This feature provides better performance and repeatability in moist biogas measuring applications. Where ever the installation along the biogas system, FCI has successfully applied ST Series gas flow meters.

For line sizes larger than 2.5" [63 mm]
For line sizes 2.0" [51 mm] and smaller
* FCI Model FLT93 switches provide level detection for Knock-Out Pot (KOP) and condensate pot applications.