Biogas Swirl Flow Meter

Three reasons that line up with biogas’s unusual physics. (1) Wet, low-pressure tolerance: digester output is typically 2–10 kPa gauge and water-saturated. Vortex shedding gets noisy below ~5 m/s and the wet condensate impacts the bluff body; a swirl meter’s piezoceramic pair sits outside the main flow stream, immune to liquid impingement, and the swirl generator forces a clean precession period down to 2 m/s. Orifice plates lose their square-root authority below 50 mbar differential and are not practical at biogas line pressures. Thermal-mass meters are velocity-based and need a separate density input that is unstable for variable CH₄ content. (2) Sour-gas service: Hastelloy C-276 wetted parts ship as standard for biogas, so H₂S to 10 000 ppm is in scope without a metallurgy upgrade. (3) Composition-aware Nm³/h: the on-board flow computer accepts a live CH₄% input (manual, RS485 inline-GC, or HART) and re-computes density and energy on every cycle; orifice and thermal meters need an external flow computer for this.

Hastelloy C-276 wetted parts ship as the LUXB-BG standard configuration; both the swirl-generator vanes and the body’s flow-contact surfaces. Hastelloy C-276 is standard for sour-gas service to 10 000 ppm H₂S in wet conditions, well above the 100–500 ppm typical of post-desulphurisation biogas and the 1 000–3 000 ppm seen in raw landfill or agricultural digester gas. The piezoceramic sensor pair is encapsulated and isolated from the gas stream; only the protective hat sees gas, and that hat is also Hastelloy C-276 standard. Pressure diaphragms are 316L isolated; for severe sour applications above 5 000 ppm continuous, specify the full Hastelloy diaphragm option. a Hastelloy C-276 mill traceability note is included on every sour-service order at no additional cost.

Yes; the optional heat-value output module computes calorific energy on every measurement cycle and exposes it as a separate 4-20 mA channel (configurable as kJ/Nm³ or kWh/h) plus a Modbus register. The calculation follows the factory-loaded biogas heating-value table. Inputs are the live CH₄ fraction (from local entry, inline-GC over RS485, or HART burst from a separate analyser) and the factory composition table. Most CHP installations use the kWh/h output as the billing meter feed and the Nm³/h output as the volumetric audit trail. For sites without a real-time GC, a fixed CH₄% pre-load with a daily manual check is acceptable for allocation-grade sub-measurement; high-precision sub-measurement benefits from the live composition input.

The meter is calibrated for CH₄ 45–98 % with the balance as CO₂ plus typical biogas trace components (N₂, O₂, H₂S to 10 000 ppm, NH₃ to 100 ppm, water vapor saturated). Three composition-input options. (a) Local manual entry; operator types CH₄% and trace breakdown into the local display; appropriate for stable-composition sites with weekly lab analysis. (b) RS485 Modbus RTU input from an inline gas chromatograph (Servomex, ABB EL3060, Siemens MAXUM); the meter polls CH₄% on a configurable interval (default 5 minutes) and re-runs the on-board compressibility calculation every cycle. (c) HART burst input from any HART-compatible composition analyser. The compressibility re-computation is automatic; no SCADA scripting needed. For high-accuracy billing applications, the inline-GC input is the standard pattern.

One LUXB-BG model covers both. For raw biogas service the Hastelloy C-276 wetted parts handle H₂S and humidity carryover. For upgraded biomethane downstream of the H₂S-removal scrubber, specify the standard 316L wetted-parts version for lower cost. The on-board CH4% input handles the composition variance across the working range. Lead time stays 5–7 business days from the factory.