An operation diagram for the qualitative comparison of diagnosis variables is proposed.
Diagnosis of unacceptable changes through the dynamic system response is successful.
Volatile fatty acids to total alkalinity ratio (VFA/TA) is best in a wide range.
Hydrogen in headspace is not a good indicator for process failure.
With today’s growing focus on on-demand energy production, the dynamic operation of biogas plants is becoming more and more important. Detecting unacceptable load changes and so preventing process failures is vital. In the present contribution, we propose an operating scheme that includes the detection of disturbances and intervention. This is then evaluated systematically with the help of a mathematical model for step changes in the organic loading rate. We summarize the qualitative results for each diagnosis variable in an operation diagram, enabling an intuitive, comprehensive comparison. Of the diagnosis variables analyzed, we find that the most promising for identifying incipient process failures in biogas plants are the volatile fatty acids to total alkalinity ratio (VFA/TA), followed by the ratio of methane to carbon dioxide γ in the biogas. In addition, the combination of the online measured variables pH value and gas composition can reveal disturbances early on in a wide range of different conditions.
- Biogas plants;
- Dynamic operation;
- Anaerobic digestion
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