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Biogas Flow Meter: Thermal Mass Systems for Corrosive Methane Lines
Quick Answer: Thermal mass flow meters give you direct mass flow measurement of biogas without needing temperature or pressure compensation. They handle wet, dirty, and corrosive methane lines common in landfills, digesters, and wastewater plants. Silver Instruments supplies inline and insertion thermal mass meters with Hastelloy wetted parts and PTFE lining for aggressive gas streams.
Biogas is not clean natural gas. It carries moisture, hydrogen sulphide, siloxanes, and often a shifting mix of CH4 and CO2. A standard gas flow meter fails fast in these conditions. Engineers at biogas plants in Thailand and Australia keep asking us the same question. They want a meter that survives the gas and gives a reliable reading for flaring, CHP engine feed, or boiler control. Our answer is a thermal mass flow meter built for corrosive service.
Why Thermal Mass Works Where Others Struggle
Differential pressure devices clog. Turbine meters corrode and stick. Ultrasonic meters lose signal when condensate coats the transducers. Thermal mass meters have no moving parts. They measure flow by the cooling effect of gas passing over a heated sensor. This principle gives you a reading directly in kg/h or Nm3/h. No separate temperature sensor needed. No pressure transmitter needed. The meter does the compensation inside.
Here is the thing. In a biogas line, the gas composition varies. Methane can be 50% one day and 65% the next. A thermal mass meter calibrated for the actual gas mix still returns useful mass flow data. We help customers in Indonesia and Mexico set up their meters with a mixed-gas calibration that matches the average site composition. The repeatability is solid, usually plus or minus 1% of reading.
Materials for Wet, Sour Biogas
Standard 316L stainless steel sensor probes degrade in H2S environments. We have seen probes from other brands develop pits after six months in a landfill site in Malaysia. For corrosive methane lines, we specify Hastelloy C276 sensor elements and a PTFE-lined flow body or insertion probe. The electronics housing stays sealed. We rate most of our biogas thermal mass meters IP67 or better.
You can get the Silver Instruments TM series in sizes from DN15 to DN300 inline, or as an insertion meter for pipes up to DN2000. The insertion version uses a hot-tap assembly. You do not need to shut down the gas line to install it. Just weld a 1.5 inch ball valve, drill, and retract. Our Colombian distributor has done dozens of these hot-tap installs on HDPE and steel pipes without interrupting the digester.
Typical Biogas Applications
Anaerobic digester gas to CHP. Measure wet, low-pressure gas before the engine. The meter helps balance the air-fuel ratio. Pipe sizes often start at DN80. Our inline TM80 with PTFE liner and Hastelloy sensors works here.
Landfill gas extraction. Wells pull gas at negative pressure. An insertion thermal mass meter with low-flow sensitivity catches leaks and falling well performance. We have clients in Australia running 50 wellheads monitored with insertion probes on a data logger.
Wastewater treatment plant digester gas. Gas pressure is usually below 200 mbar. The low pressure drop of a thermal mass meter matte
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Biogas upgrading to biomethane. After H2S scrubbers and CO2 separation, the gas gets injected into a natural gas grid. The requirements are stricter. Here we can supply meters with ATEX Zone 1 certification and SIL 2 functional safety. The output signals are 4-20 mA HART and Modbus RTU for your SCADA.
Outputs and Integration
All our thermal mass meters come with a standard 4-20 mA output for flow, a pulse output for totalization, and RS485 Modbus. You can poll the meter directly into a PLC. The local display shows Nm3/h, kg/h, totalized volume, and gas temperature. A PT100 sensor sits next to the heated sensor and acts as the reference. The meter continuously adjusts for ambient temperature drift, which matters on sites where the meter sits outside in the sun or cold.
How to Specify Your Meter
We need a few numbers from you to size the right meter. Pipe inner diameter, minimum and maximum flow (in kg/h or Nm3/h), gas composition (CH4, CO2, H2S ppm), operating pressure in bar, and gas temperature in degrees C. Also tell us if the pipe is horizontal or vertical and the available straight run. We usually want 15D upstream and 5D downstream straight pipe. If you are tight on space, we can supply a flow conditioner.
Send these details to our engineers. We reply with a datasheet, dimensional drawing, and a quote within one working day. WhatsApp us at 86-135-12131526 or call +86-135-1213-1526. You can also reach us on WeChat at +86 13512131526. Tell us your application and we will recommend the exact model and wetted materials for your corrosive methane line.
FAQ
Can the thermal mass meter handle condensed water droplets in the biogas? Yes. Small droplets pass through the flow path and do not damage the sensor. The meter dampens the signal fluctuation caused by intermittent droplets. We do recommend installing a drip leg and drain upstream for heavy condensate loads.
How often do we need to recalibrate a biogas thermal mass meter? For landfill and digester gas with moderate H2S, we recommend checking calibration every 12 months. If the gas is very aggressive (more than 2000 ppm H2S), inspect the sensor every 6 months. We can supply a validation kit so you can check it on-site without removal.
Does the meter need explosion-proof certification for biogas? Many biogas zones require ATEX Zone 1 or 2, IECEx, or NEC Class I Division 2. Silver Instruments provides certified meters for these zones. Specify your hazardous area requirement when you request the quote.
What is the turndown ratio of your thermal mass meters? We offer a standard turndown of 100:1. In practice, you can read flow from 0.5 Nm3/h up to 500 Nm3/h on the same DN50 inline meter. Accuracy stays within plus or minus 1.5% of reading across most of that range.
Can I use a thermal mass meter on the biogas outlet of a covered lagoon digester? Yes. These lines often run at very low pressure, maybe 20 mbar. The thermal mass meter needs almost no pressure to operate. We have installed insertion meters on large lagoon gas collection headers in Brazil. Just keep the sensor clean of slime and inspect it every quarter.