Biogas Flow Measurement for AD Plants
Accurate, reliable gas flow measurement for monitoring production, improving efficiency and supporting compliance
Over 45 Years in Operation
1000's of UK Installations
Supporting 100's of UK Sites
The Challenge: Measuring Biogas Accurately
Biogas flow measurement is critical in anaerobic digestion (AD) plants, but it is also one of the most technically challenging applications.
Operators need accurate data to:
- Monitor gas production and plant performance
- Control CHP engines and gas utilisation
- Measure flow to flares and safety systems
- Report emissions and energy output
However, biogas presents difficult measurement conditions:
- Low pressure and low flow rates
- Wet, dirty and corrosive gas
- Fluctuating flow due to biological processes
Many traditional flow technologies struggle to provide reliable, stable measurement under these conditions.
The Solution: Thermal Mass Flow Measurement
Thermal mass flow meters are widely used for biogas applications because they measure mass flow directly, rather than relying on inferred volumetric calculations.
- No need for temperature or pressure compensation
- High sensitivity at low flow rates
- No moving parts → low maintenance
- Reliable performance in wet and contaminated gas
This makes them particularly well suited to raw biogas from digesters, landfill gas and gas-to-grid systems.
How It Works
Thermal mass flow meters use a heated sensor and a reference sensor:
- Gas flow removes heat from the heated element
- The rate of heat loss is proportional to mass flow
- The instrument calculates flow rate and totalised flow
Because measurement is based on heat transfer, the system can:
- Maintain accuracy across varying gas compositions
- Provide stable, repeatable readings
- Operate effectively in low pressure systems
See also:
Biological Desulphurisation for AD Plants
Where Biogas Flow Measurement Is Used
Biogas flow measurement is typically installed at multiple points across an AD plant:
- Digester gas outlet (production monitoring)
- CHP feed lines (energy generation)
- Flare lines (safety and compliance)
- Gas upgrading systems (gas-to-grid)
- Distribution and storage systems
Measuring at multiple points provides full process visibility and optimisation opportunities.
Recommended Products & Technologies
Thermal Mass Flow Meters (Primary Solution)
ST51 / ST75 / ST100 Series
- Direct mass flow measurement (Nm³/hr or kg/hr)
- Suitable for wet, dirty and low-pressure biogas
- Wide turndown ratio for fluctuating flow
- ATEX certified for hazardous areas
- “Live” insertion and removal capability
✔ Proven across landfill, wastewater and AD plants
✔ Hundreds of UK installations
Supporting Technologies
Biogas Analysers (AwiFlex / AwiEco)
- Gas composition monitoring (CH₄, CO₂, H₂S, O₂)
- Supports performance optimisation and control
- Flow/no-flow detection
- Protection of downstream systems
Technical Insight: Why Biogas Is Difficult to Measure
Low Pressure & Low Flow
Biogas systems often operate at very low pressures, meaning conventional differential pressure technology is useless.
Dirty & Contaminated Gas
Biogas will quickly clog and foul any flow meter with moving parts.
Moisture, condensate and H₂S can damage or foul traditional turbine flow meters
High H2S
H2S can quickly go into solution in saturated biogas and corrode plastic O rings and bearings used on many flow meter technologies. Thermal mass flow technology overcomes these challenges by providing stable, direct measurement with minimal maintenance requirements.
Our Experience in Biogas Flow Measurement
Allison Engineering has extensive experience supporting biogas applications across the UK:
- Hundreds of installed flow meters in AD and wastewater sites
- Proven solutions for CHP, flare and gas-to-grid applications
- Experience with wet, dirty and low-pressure gas systems
We support customers through:
- Application review and system design
- Product selection and specification
- Installation, commissioning and ongoing service
Key Benefits
- No moving parts
- All 316 st/st wetted parts
- “Hot tap” installation
- N.I.S.T traceable calibration for OFGEM reporting
- ATEX certified
Need information or advice?
Speak with our friendly, expert team to discuss your requirements and find out how we can help you.
Biogas Flow Measurement FAQs
Common questions about measuring biogas flow in AD plants, including technology selection, installation and application considerations.
Why is biogas flow measurement important?
Accurate flow measurement is essential for monitoring gas production, optimising energy recovery, controlling CHP systems and meeting emissions reporting requirements.
What makes biogas difficult to measure?
Biogas is typically low pressure, saturated with moisture and contains corrosive gases such as H₂S. It also varies in composition and flow rate, making consistent measurement challenging.
Why are thermal mass flow meters used for biogas?
Thermal mass flow meters are chosen for biogas and AD plants as they measure mass flow directly, require no pressure or temperature compensation, and perform reliably in low-flow, wet and contaminated gas conditions.
Where should flow meters be installed on an AD plant?
Typical locations include digester outlets, CHP feed lines, flare systems and gas upgrading processes to provide full visibility of gas production and usage.
Can flow meters be installed without shutting down the plant?
Yes. Many insertion-type thermal mass flow meters can be installed or removed under live conditions using a full-bore ball valve arrangement.
How do I choose the right biogas flow meter?
Selection depends on gas composition, moisture content, pressure, flow range, pipe size, hazardous area classification and installation requirements.
Relevant Links
Why Trust Allison Engineering
We are committed to delivering the highest standards across the specialist areas we support, combining proven products with practical engineering knowledge and dependable service.
Need Help Measuring Biogas Flow Accurately?
Speak to our team to identify the right flow measurement solution for your AD plant, from digester monitoring to CHP, flare and gas-to-grid applications.