Quick Answer
A 3 inch biogas line is DN80. For this size, a thermal mass flow meter is the right tool. The Silver Automation SRK-100 measures gas mass flow directly, with no separate pressure or temperature compensation. On DN80, the calibrated range runs up to roughly 1,800 Nm3/h depending on methane content, with accuracy around plus or minus 1 percent of reading.
Why DN80 Biogas Lines Need a Thermal Mass Flow Meter
Biogas is not a clean, fixed gas. Methane content swings between 50 and 70 percent on most digesters, with the rest made up of CO2, moisture, and trace H2S. Pressure on these lines is usually low, often close to atmospheric. Orifice plates and vortex meters need stable density and enough velocity to read correctly. On a low pressure biogas main, both struggle.
A thermal mass flow meter works differently. It heats a sensing element and measures how fast the gas carries that heat away. Because the reading comes from mass flow directly, there is no need for separate pressure or temperature compensation. We see this matter most on digester gas lines in Southeast Asia and Vietnam, where plant operators run low budget biogas to flares or boilers with no extra instrumentation to spare.
SRK-100 Specification Summary for DN80
| Parameter | Value |
| Pipe size | DN80 (3 inch) |
| Calibrated range | Up to about 516 Nm3/h on methane, exact figure depends on gas mix |
| Accuracy | Plus or minus 1% of reading, plus or minus 0.5% of full range |
| Turndown ratio | 100:1 |
| Sensor material | 316SST standard, hastelloy available or Teflon painted for H2S service |
| Output | 4-20 mA, RS485 Modbus, HART |
| Protection | IP65, Ex d II CT4 for hazardous areas, ATEX approved |
| Pressure rating | 0 to 1.0 MPa standard, up to 3.0 MPa with custom configuration |
Insertion or Flange Type for a 3 Inch Line
For DN80, we recommend the flange type. Insertion probes make more sense above DN100, where a flange body would be bulky and expensive. On a 3 inch line, the flange version installs cleanly between existing flanges and gives a shorter overall length, around 200 mm.
Last year a customer running a food waste digester in Thailand asked for a compact unit with local LED display and a 4-20 mA output to their PLC. We specified an integral SRK-100, 316SST sensor, Ex d rated housing, because the gas carried enough H2S to rule out a basic carbon steel probe stem.
Gas Flow Meters
Request a Quote
Send us your operating pressure (bar or MPa), gas temperature (degrees C), methane percentage, and expected flow range in Nm3/h. We will confirm the right SRK-100 configuration for your DN80 biogas line. Contact us at sales@silverinstruments.com.
