Energy yield from biogas can be improved
Even more biogas can be extracted from the biogas process than is currently being achieved. Scientists at the Faculty of Agricultural Sciences at Aarhus University and their partners are endeavouring to realise the full potential of this climate-friendly gas. This is done at the experimental biogas plant at Research Centre Foulum.
The plan is to monitor different parameters online in the course of the production and adjust the processes accordingly.
- As it is at the moment, the production managers at the biogas plant are always in fear of the process turning acidic. This means that the pH of the liquid falls to a level that inhibits the methane-generating bacteria. This can lead to process shutdown which requires the tank to be emptied, followed by a slow start-up, explains head of research unit Anders Peter Adamsen from the Department of Biosystems Engineering at the Faculty of Agricultural Sciences.
To avoid this situation – which can lead to several weeks’ loss of production – the production managers at the biogas plant take a careful and conservative approach to the running of the plant. This means that they never make use of its full potential. The new monitoring project should overcome this.
Optimised measurements
In large biogas plants the pH value and concentration of volatile fatty acids are regularly measured, but there is a considerable need for new and improved methods to monitor, control and regulate biogas plants.
The development and demonstration project "Real-time control of biogas reactors" investigates three promising technologies for optimising the biogas process:
- Near-infrared spectroscopy (NIR) measures the concentration of volatile fatty acids in the liquid
- Gas chromatography (GC) measures methane, nitrogen and hydrogen concentrations in the gas
- Membrane-inlet mass spectrometry (MIMS) can measure carbon dioxide, methane, hydrogen sulphide and volatile fatty acids in the biogas itself
In addition, the volatile fatty acids in the liquid are measured using a gas chromatograph with a view to further development of the NIR method. The three technologies supplement each other by each having the capacity to measure several interesting compounds, both in the liquid and in the gas phase.
Experience and data collection
The project is now one year old. The instruments have been installed on one of Xergi’s pilot reactors at the biogas plant at Research Centre Foulum. Unique experience in terms of instruments, data collection and process understanding is already being harvested.
In the coming months the project participants will process the collected data to find the best methods for process prediction and in 2010 the experience gathered will be used to actually control the process.
- In 2008 biogas accounted for 0.5 per cent of the total Danish energy production. That number can be increased by 10 per cent if the monitoring of the biogas process is improved and used to control the process, says Anders Peter Adamsen. This will be on the basis of a more stable process, better utilisation of the biomass and the possibility for a more optimal feeding of the reactor.
The project is a collaboration between the Faculty of Agricultural Sciences, The Danish Technological Institute and Xergi A/S, and is financially supported by the ForskEL programme under energinet.dk .
