Flow Meters for Biogas Measurement

Accurate biogas flow measurement plays a critical role in energy management, process control, and commercial settlement for biogas plants, landfill gas systems, and waste-to-energy projects.
However, biogas is a challenging medium due to high moisture content, composition fluctuations, and impurities such as H₂S and dust.

This article provides a structured overview of commonly used flow meter technologies for biogas, analyzing their performance, limitations, and suitable application scenarios to support reliable instrument selection.

Key Characteristics of Biogas That Affect Flow Measurement

Before selecting a flow meter, it is essential to understand the operating conditions:

• High water vapor content and possible condensation

• Variable methane concentration

• Presence of corrosive gases such as H₂S

• Flow rate fluctuations caused by production and consumption changes

These factors directly impact measurement accuracy, sensor durability, and long-term stability.

Ultrasonic Flow Meters for Biogas Applications

Why Ultrasonic Technology Is Widely Used

Ultrasonic gas flow meters are commonly applied in biogas systems due to their strong adaptability to wet and unstable gas conditions.

Main advantages:

• High tolerance to water vapor and light condensation

• No moving parts and no pressure loss

• Typical accuracy of ±0.5% to ±1.0%

• Wide turndown ratio, suitable for fluctuating flow rates

• Capable of bidirectional flow measurement

Typical applications:

• Biogas main pipelines

• Generator inlet gas measurement

• Gas holder inlet and outlet

• Post-desulfurization wet gas measurement

Selection recommendation:
Choose ultrasonic models designed for wet gas service. Instruments with self-diagnostic functions can help detect signal degradation caused by contamination.

Vortex Flow Meters for Stable Biogas Conditions

Practical and Economical Choice

Vortex flow meters are often used where operating conditions are relatively stable and installation requirements can be met.

Main advantages:

• Robust mechanical structure

• Good resistance to moisture

• Typical accuracy of ±1.0% to ±1.5%

• Moderate cost and low maintenance requirements

Key limitations:

• Sensitive to pipeline vibration

• Requires a minimum gas velocity, usually above 5 m/s

• Sticky or heavy impurities may affect the vortex shedding body

Suitable applications:

• Medium to large biogas pipelines

• Systems with stable flow and limited vibration

Differential Pressure Flow Meters for Harsh Environments

Traditional and Durable Measurement Method

Differential pressure flow meters, such as orifice plates and V-cone meters, are widely used in demanding environments.

Main advantages:

• High tolerance to moisture and contaminants

• Simple structure and strong environmental adaptability

• Suitable for large pipe diameters and high-pressure systems

Main disadvantages:

• Permanent pressure loss increases operating costs

• Requires temperature and pressure compensation

• Lower overall system accuracy compared to ultrasonic technology

Typical applications:

• Landfill gas collection systems

• Large-scale projects with stable operating conditions and limited energy efficiency requirements

Thermal Mass Flow Meters in Biogas Measurement

Important Usage Limitations

Thermal mass flow meters are sometimes considered for biogas measurement due to their ability to measure mass flow directly. However, their application in wet biogas systems requires caution.

Main risks:

• Condensation removes heat from the sensor, causing significant measurement errors

• Liquid droplets may lead to unstable readings or sensor damage

• Long-term exposure results in sensor fouling and zero drift

Acceptable conditions:
Only suitable for fully dried, filtered, and purified biogas, with operating temperatures consistently above the dew point.

General recommendation:
Thermal mass flow meters should not be selected for untreated or moisture-rich biogas.

Key Selection and Installation Guidelines

Define Gas Conditions Clearly

• Raw biogas or purified biogas

• Moisture content and dew point

• H₂S concentration and particulate level

Gas Pretreatment Is Critical

• Gas-liquid separators

• Filters and condensate traps

• Dehydration equipment

Proper pretreatment protects the flow meter and improves long-term measurement reliability.

Installation Considerations

• Vertical installation with upward flow is preferred when liquid carryover is possible

• For horizontal pipelines, install sensors on the side of the pipe rather than at the bottom

• Maintain sufficient straight pipe lengths, typically 10D upstream and 5D downstream

Safety and Signal Output

• Select instruments with appropriate explosion-proof certifications, such as Ex d IIB T4

• Ensure compatibility with 4–20 mA, pulse output, or Modbus communication protocols

Comparison of Flow Meter Technologies for Biogas

Conclusion

Selecting a suitable flow meter for biogas requires careful consideration of moisture content, flow variability, accuracy requirements, and long-term operating costs.

For most biogas applications involving wet gas and fluctuating conditions, ultrasonic flow meters offer a well-balanced solution in terms of accuracy, reliability, and operational efficiency. Vortex and differential pressure flow meters remain practical options under specific conditions, while thermal mass flow meters should only be used after complete gas drying and purification.

Providing detailed process parameters—such as gas composition, pressure, temperature, humidity, and pipe size—before instrument selection is essential for achieving stable and accurate measurement results.

If you need professional advice or product recommendations, feel free to contact us anytime.