Natural Gas Thermal Mass Flow Meter

Each of the four candidate technologies has a sweet spot; and TMF-NG owns a very specific one. Orifice plate + DP transmitter is the legacy reference for custody-transfer fiscal measurement at high pressure (AGA 3 / ISO 5167) but its square-root authority collapses below 20 % of rated flow; a modulating industrial boiler running 10:1 turndown is invisible to an orifice below low-fire. Turbine meters (AGA 7) hit ±0.5 % accuracy and 10:1 turndown with wet-calibration but have rotating bearings that wear, suffer jet-contamination stalls on dirty landfill-adjacent gas, and cannot sit on a line that occasionally runs in reverse. Ultrasonic (AGA 9) is the modern custody-transfer standard for transmission-pipeline scale (DN300+ at 6.3 MPa+) but carries the capital cost to match. TMF-NG fits the five cases those alternatives struggle: (1) industrial boiler fuel line that needs 100:1 turndown from low-fire hold to high-fire peak, (2) no budget for a flow computer to run AGA-style on a 1.0 MPa supply where the correction is inside the accuracy range anyway, (3) the line has solenoid shut-off trip cycles that would stall a turbine’s bearings, (4) the measurement point has < 10D upstream straight pipe, (5) the site needs one instrument for each branch meter with full Ex d (CNEX flameproof) factory-standard, not as an optional upgrade. Specify natural-gas vortex when the clean dense-gas retrofit needs the lower capital cost per DN. Specify natural-gas precession swirl when space is tight and 3D+2D straight-pipe is the decisive constraint.

It depends on the line pressure. Below 2.5 MPa; which covers the vast majority of industrial boiler-fuel and process-heating installations; the compressibility factor Z for typical pipeline-quality natural gas is 0.99 to 1.00, so AGA-style correction is below the meter’s ±1.0 % of rate accuracy range and you can safely skip it. Above 2.5 MPa; city-gate branch lines, high-pressure industrial mains, gas-turbine feed; Z drops into the 0.96 to 0.94 range and the correction becomes measurable. For those cases the TMF-NG offers an optional on-board AGA-style / GB/T 11062 compressibility block: enter gas-chromatograph composition and the meter applies the Z-factor correction internally using the raw sensor-bus pressure and temperature readings. This avoids the external flow computer but still delivers AGA-style-traceable Nm³/h. The TMF is not, by itself, a custody-transfer meter; if the application is fiscal measurement at a city-gate, pair it with an ultrasonic (AGA 9) primary and use the TMF-NG for check-measurement, not as the fiscal reference. For boiler fuel, CHP input, and factory branch flow measurement (the 80 % of applications), the native reading is accurate enough without AGA-style correction at all.

Ex d (CNEX flameproof) flameproof is the standard build on the TMF-NG; not optional; because any line carrying pipeline-quality natural gas is classified Zone 1 or Zone 2 by default under IEC 60079 / GB 3836. Zone 1 covers the immediate area around flanges, valves, and the meter body where a gas release is expected during normal operation (typically 1 meter radius). Zone 2 covers the wider boiler room, metering station enclosure, or utility tunnel. IIB is the gas group for methane-based fuel gases (IIB1 for pure methane, IIB for typical pipeline NG with some ethane and propane). T4 is the temperature class; surface temperature limit 135 °C, which leaves adequate margin over the meter’s internal electronics. The TMF-NG ships with CNEX and CNEX certificates covering flameproof construction, flameproof cable-gland entries, and the integral display window. For Zone 0 applications (very rare in NG service; typically only inside a vent stack) the insertion TMFW with remote transmitter and a Zone 0-rated sensor head is the correct product. If the line routes through a general-purpose metering cabinet where the atmospheric concentration is positively below 10 % LEL under all failure modes, the meter can be derated to IP66 general-purpose; but that is an engineering exercise you do not want to run on anything new. Default is Ex d (CNEX flameproof).

Not as the primary fiscal reference. Custody transfer at the city-gate is governed by AGA 3 / AGA 7 / AGA 9 in the US, and GB/T 21391 (turbine) or GB/T 18603 (ultrasonic) in China; these require type-approval testing and ±0.5 % uncertainty budgets. Thermal mass falls under GB/T 32201 as a measurement-grade technology, not a fiscal reference. Where the TMF-NG earns its place: (a) check-measurement against a primary AGA 9 ultrasonic to detect drift and composition shifts, and (b) industrial sub-measurement where the operator bills at the city-gate master and the site splits the invoice by actual Nm³ — more accurate than burner-capacity allocation. If the facility is itself the fiscal seller (e.g. CHP steam to a tenant), specify AGA 9 ultrasonic or AGA 7 turbine as primary and use TMF-NG for operational instrumentation.