Biogas Analysis for AD Plants
Real-time gas composition monitoring for process control, optimisation and safe, efficient plant operation
Over 45 Years in Operation
1000's of UK Installations
Supporting 100's of UK Sites
The Challenge: Understanding Biogas Composition
In anaerobic digestion (AD) plants, knowing how much gas you produce is only part of the picture. Understanding what’s in the gas is just as critical.
Biogas composition directly affects:
- CHP engine performance and efficiency
- Gas upgrading and grid injection quality
- H₂S control and desulphurisation processes
- Overall plant stability and output
However, biogas is constantly changing:
- Methane (CH₄) levels fluctuate with feedstock and digestion conditions
- H₂S levels can vary rapidly and unpredictably
- Oxygen (O₂) must be tightly controlled in biological processes
- Moisture and contaminants affect measurement reliability
Without accurate, continuous analysis, operators are effectively running blind.
The Solution: Continuous Biogas Analysis
Online biogas analysers provide real-time measurement of key gas components, enabling operators to monitor, control and optimise their process.
Typical gases measured include:
- Methane (CH₄) – energy content and plant performance
- Carbon dioxide (CO₂) – process efficiency and gas quality
- Hydrogen sulphide (H₂S) – corrosion and process control
- Oxygen (O₂) – critical for biological desulphurisation
- Hydrogen (H₂) and carbon monoxide (CO) (where required)
This allows operators to make informed decisions and maintain stable, efficient operation.
How It Works
Biogas analysers continuously sample gas from the process and measure composition using a combination of sensor technologies.
Systems typically:
- Extract gas samples from one or multiple locations
- Condition the gas (cooling, filtering, moisture handling)
- Measure gas concentrations with high accuracy
- Log and transmit data to control systems
Advanced systems can:
- Sample sequentially across multiple digesters
- Provide historical data and trend analysis
- Integrate with plant control systems (PLC / SCADA)
Result: complete visibility of biogas composition across the process
Where Biogas Analysis Is Used
Biogas analysers are typically installed across key points in the process:
- Digester outlet (process monitoring)
- CHP feed (performance optimisation)
- Gas upgrading systems (grid compliance)
- Desulphurisation systems (control of H₂S removal)
- Flare lines (safety and reporting)
Multi-point measurement provides a complete picture of plant performance.
Recommended Products & Technologies
Biogas Analysers (Core Technology)
- Multi-channel gas analysis (CH₄, CO₂, H₂S, O₂, H₂, CO)
- Sequential sampling from multiple locations
- Integrated data logging and communications (4–20mA, Profibus, Ethernet)
- Capable of automated process control (e.g. desulphurisation)
- Proven across hundreds of AD installations
✔ Ideal for complex or multi-digester sites
✔ Supports advanced process optimisation
- Single-channel, cost-effective analyser
- Reliable monitoring of key gas components
- Suitable for smaller plants or single measurement points
✔ Simple, robust and low maintenance
- Handheld analyser for spot checks and diagnostics
- Measures up to 6 gases
- ATEX-rated for hazardous environments
✔ Ideal for commissioning, troubleshooting and validation
Technical Insight: Why Biogas Analysis Is Critical
Biogas analysis is not just about measurement, it is a fundamental biogas process solution to process control and optimisation.
Process Stability
Changes in methane or CO₂ levels can indicate digestion issues, feedstock variation or instability.
H₂S Management
Real-time H₂S measurement allows:
- Early detection of spikes
- Control of desulphurisation systems
- Protection of downstream equipment
Oxygen Control
Precise O₂ monitoring is essential for:
- Biological desulphurisation
- Preventing over-aeration
- Maintaining safe operating conditions
Performance Optimisation
Operators can:
- Improve CHP efficiency
- Optimise gas upgrading
- Maximise energy output
Without continuous analysis, these optimisations are not possible.
Our Experience in Biogas Analysis
Allison Engineering has extensive experience supporting biogas analysis across the UK:
- Hundreds of analyser installations on AD plants
- Integrated systems for monitoring and control
- Support for commissioning, calibration and servicing
We work closely with operators to:
- Identify optimal measurement points
- Configure systems for their process
- Provide ongoing support and optimisation
This ensures systems deliver not just data, but actionable insight.
Key Benefits
- Real-time visibility of gas composition
- Improved process control and stability
- Reduced risk of equipment damage
- Optimised desulphurisation performance
- Improved energy efficiency and output
- Supports compliance and reporting
Need information or advice?
Speak with our friendly, expert team to discuss your requirements and find out how we can help you.
Biogas Analysis FAQs
Common questions about biogas analysis in AD plants, including measurement technology, system design and process optimisation.
Why is biogas analysis important in AD plants?
Biogas analysis is essential because it provides operators with real-time insight into the composition of the gas being produced. This directly impacts plant performance, energy output and equipment protection. For example, methane concentration determines energy value, while H₂S levels affect corrosion risk and maintenance requirements.
In practice, operators rely on continuous analysis to identify process instability, respond to changes in feedstock and ensure systems such as CHP engines and gas upgrading plants operate efficiently and safely.
What gases should be measured in biogas systems?
The key gases typically measured are methane (CH₄), carbon dioxide (CO₂), hydrogen sulphide (H₂S) and oxygen (O₂). Depending on the application, hydrogen (H₂) and carbon monoxide (CO) may also be measured.
From a practical standpoint, CH₄ and CO₂ indicate process efficiency, H₂S is critical for corrosion and desulphurisation control, and O₂ is particularly important where biological desulphurisation or oxygen dosing is used. Measuring the correct combination of gases ensures operators have a complete understanding of process conditions.
How does a biogas analyser work?
A biogas analyser works by extracting a gas sample from the process and passing it through sensors that measure the concentration of different gases. The system typically includes gas conditioning components such as filters and coolers to remove moisture and contaminants before measurement.
In real-world applications, analysers are often configured to sample multiple points sequentially, allowing operators to monitor different parts of the plant with a single system. Data is logged and transmitted to control systems, enabling both monitoring and automated process control.
Can biogas analysers be used for process control?
Yes, modern biogas analysers are not just monitoring devices — they are often used as part of closed-loop control systems. A good example is biological desulphurisation, where analyser readings are used to automatically adjust oxygen or air dosing.
This allows the system to maintain optimal H₂S levels without manual intervention. In practice, this improves consistency, reduces operator workload and ensures the process remains stable even as conditions change.
How many measurement points are needed on an AD plant?
The number of measurement points depends on the complexity of the plant, but typical locations include the digester outlet, CHP feed, flare line and gas upgrading system.
On larger or more complex sites, multi-channel analysers are used to sample several locations sequentially. This approach provides a more complete view of plant performance while keeping system costs manageable.
What are the main challenges in biogas analysis?
The main challenges include dealing with wet, contaminated gas, maintaining accuracy at low pressures, and handling fluctuating gas composition. H₂S is particularly aggressive and can damage poorly specified equipment.
From experience, the key to reliable analysis is selecting the right analyser with appropriate gas conditioning and ensuring it is correctly installed and maintained. Systems designed specifically for biogas applications are far more reliable in the long term.
How do I choose the right biogas analyser?
Choosing the right analyser depends on several factors, including the number of measurement points, required gases, site conditions and whether the system will be used for monitoring or control.
For example, a single-channel analyser may be sufficient for a simple CHP application, while a multi-channel system is better suited to larger AD plants or those requiring automated control of desulphurisation. The best approach is to review the application in detail and match the analyser to the specific process requirements.
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Need Help Optimising Your Biogas Process with Accurate Gas Analysis?
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