Biogas and RNG Processing: Oxygen and pH Measurement Solutions
Introduction
Biogas, a renewable energy source, is produced from the anaerobic digestion of organic materials like manure, dairy, swine and waste. This application note explores the crucial role of pH and oxygen measurements in biogas production, purification, and upgrading to renewable natural gas (RNG)/biomethane, with specific solutions designed to improve efficiency and safety.
Biogas Composition
Biogas contains a mixture of gases, primarily:
- 50-60% Methane (CH4)
- 30-40% Carbon Dioxide (CO₂)
- 3-6% Water (H2O)
- Trace amounts of Nitrogen (N2), Hydrogen Sulfide (H2S), Oxygen (O2), Hydrogen (H2), and other gases
The exact composition varies based on the organic material used in the process.
The Biogas Production Process
Biogas, as it leaves the digester, contains moisture and contaminants like H2S and CO2, which can cause acid gases. To prepare biogas for use, it must undergo several purification stages:
- Moisture Removal
- H2S & CO2 Removal
Once cleaned, the methane concentration increases to over 95%, making it suitable for energy production or transmission as Renewable Natural Gas (RNG).
Critical Measurement Challenges: Oxygen
Methanogenic bacteria used in biogas production cannot survive in oxygen-rich environments. Hence, measuring oxygen levels is critical. Oxygen must be kept between 0.8 to 1.2% to avoid system inefficiencies and ensure safety by preventing the risk of explosive limits.
Upgraded RNG or biomethane must be oxygen free, and measured for trace oxygen, < 10 ppm O2 before being introduced onto transmission line at the custody transfer point.
Measurement Solutions
OXYvisor Optical Oxygen Analyzer: This innovative device uses fluorescence quenching technology, allowing accurate oxygen measurements even in moist and contaminated environments without risk of sensor poisoning from H2S or CO2. Its design simplifies maintenance and improves response times. The SafeTap sensor can be installed Insitu to eliminate issues associated with sample wet biogas for oxygen measurement. The analyzer technology is the best choice for both % level O2 in wet biogas and trace ppm O2 level for the upgraded RNG (biomethane).
pH Measurement in Biogas Purification
Maintaining pH levels is essential for both the bacterial digestion process and downstream purification, particularly in caustic scrubbers. Barben Analytical offers:
- High-Performance pH Sensors: Designed with long-lasting materials like high-temperature glass electrodes and Teflon junctions, these sensors are resistant to harsh chemicals, ensuring reliability and reducing maintenance.
Conclusion
For biogas and RNG production facilities, the Barben Analytical range of oxygen and pH measurement solutions ensures efficient, safe, and environmentally responsible operations. By optimizing measurement accuracy, operators can reduce maintenance costs and improve overall process performance.
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