Flue Gas Flow Meter

The TMF series covers medium temperatures from -45 °C to +150 °C; that defines the flue-gas-wetted bore this model works inside. In-scope: post-cooler boiler stack lines after a tubular or quench cooler has dropped flue temperature below 150 °C; RTO (regenerative thermal oxidizer) outlet metering after the heat-recovery section; industrial drying-oven and process-oven exhaust at ambient or near-ambient temperature; sample-conditioning loops on CEMS-adjacent skids where the hot stack is sampled, dried, cooled, and metered downstream. Out of scope on the standard inline TMF: raw boiler-stack service at 200–400 °C, utility-stack DN800+ service, and corrosive H2SO4 acid-dewpoint condensing service. For high-temperature raw-stack or large-stack insertion service, the engineering team will quote a separate sample-conditioning skid or hot-tap probe.

The TMF-FG ships at ±1.0 % of rate as the standard grade A configuration, with ±1.5 % of rate available as the grade B economy option for monitoring service. Repeatability is ±0.5 %. Velocity turndown is 1:1200 across the product line (0.1 to 120 Nm/s) and 1:600 practical on a single configured low-flow build. Response time is 1 second. Every unit ships with an ISO 9001 calibration certificate with each meter and a factory K-factor pre-loaded for the configured medium at the operating pressure and temperature on the order.

The thermal-dispersion principle measures mass flow directly from the heater power required to maintain a fixed temperature difference between the heated and reference RTDs. Heat transfer through the gas depends on gas mass flow rate; pressure and temperature factors drop out of the measurement equation because they affect both sides of the heat-balance simultaneously. Compare this to a vortex or DP-orifice meter, which reads volumetric flow at line conditions and needs a separate temperature transmitter, pressure transmitter, and flow computer running a compressibility table to convert to standard-condition Nm³/h. The TMF-FG outputs Nm³/h directly on the 4-20 mA loop without any of that; one instrument, one cable, one calibration certificate.

The standard 316L wetted parts handle clean post-cooler boiler exhaust, RTO outlet, and dry industrial drying-oven exhaust where the gas is below the moisture dew point and free of acid condensate. For streams that may carry trace acid condensate, residual SO2, or chloride content (cooled biomass-boiler exhaust, sample-conditioning lines on coal-utility CEMS sample loops), Hastelloy C wetted parts are the corrosion-resistant option. The TMF principle works on common stable gases; flue gas after standard conditioning is within the working range. Raw acid-dewpoint condensing service falls outside the range and requires a different model.

CNEX Ex d IIC T6 Gb (flameproof, Zone 1, gas group IIC, surface-temperature class T6) ships as standard for hazardous-area orders; confirm the zone on the quote. Even on conditioned flue gas where the gas itself is not flammable, the meter is often installed in a plant zone where adjacent fuel-handling, gas-train, or biogas-skid equipment puts the area into a Class I / Zone 1 / Zone 2 classification. The flameproof housing is the safe default that passes the area-classification review without a separate IS-barrier loop. IP65 / IP66 / IP67 ingress protection is available. EMC compliance to the EU Electromagnetic Compatibility Directive 2014/30/EU (Annex II) ships as standard, covering EN IEC 61000-6-1, -6-2, -6-3, -6-4, EN IEC 61000-3-2, and EN 61000-3-3.

Standard practice is 10× DN of straight pipe upstream and 5× DN downstream from the last fitting (valve, elbow, or reducer). With a flow-straightener sleeve the requirement drops to 5D / 3D. On a typical post-cooler flue line, install the meter at least 10× DN downstream of the cooler outlet and 5× DN upstream of the next ID-fan or duct-tee, with the flow-direction arrow aligned to flow. Mount horizontal, vertical, or any tilt angle as long as the arrow follows the gas direction. Wiring runs only the 4-20 mA loop or the digital output back to the DCS, since temperature and pressure are read on-board.

Three questions narrow the choice fast. First, is the gas conditioned (cooled, quenched, or sample-line) or raw stack? If the gas is below 150 °C and reasonably clean, the standard TMF-FG is the lowest-installed-cost match. For raw stack at 200–400 °C, the standard TMF is outside the rated range; the engineering team will quote a sample-conditioning skid or a separate insertion-probe model. Second, what is the working flow range? A single TMF-FG covers 1:1200 turndown so a header swinging from idle to peak demand sizes on one meter; a vortex meter would need two parallel meters to span the same range. Third, what does the DCS need on the wire? If the answer is Nm³/h or kg/h directly, thermal mass is the cleanest path.

5–7 business days from the factory for every configuration in this model; DN10 through DN300, integral or remote transmitter, with or without the sensor heating cable option. Engineering review on the configurator submission turns around within 4 business hours and locks the TMF model code before production starts.