GasTerra is aware that in the long term, green gas can be a sustainable alternative for natural gas. But until then, existing techniques to produce green gas – by fermentation or gasification – still have to be developed further. Sometimes, this research involves taking small steps, such as unlocking new sources of biomass, such as ditch cuttings. But we also want to look at more 'disruptive' techniques: Concepts that are highly innovative and have the potential to make a huge contribution to a more sustainable society. One example of such a technique is high-pressure fermentation.
The concept of high-pressure fermentation, or 'Autogenerative High Pressure Digestion' (AHPD), was developed by Kirsten Zagt of Bareau. It involves the fermentation of sludge at a pressure rising to 20 bar, a process which normally takes place at atmospheric pressure. The result is an efficiency that can increase to up to 90 percent, instead of the usual 65 percent. To examine how the efficiency of the process can be increased even further, GasTerra and its partners Gasunie and Bareau, with support from the municipality of Groningen, are realizing a test facility at EnTranCe. EnTranCe is the Energy Transition Center of the Energy Academy Europe, the innovation centre for energy systems where research institutions and industry are working together on the future of the Dutch energy supply.
The research at the test facility will focus on the possibility of increasing the efficiency of the process even further by injecting hydrogen, which is then called the AH2PD process. In theory, this allows up to 98 percent of the available material to be converted, which would reduce CO2 emissions from the fermentation process to almost zero. This reduction is possible because the high pressure of the process dissolves the added hydrogen in the reaction mixture and mixes it so well that bacteria can convert this and the dissolved CO2 into methane in the reactor. The idea, of course, is that in time the hydrogen will be obtained from surplus sustainable electricity, so that the process not only helps to optimize biomass, but also increases the use of renewable electricity.
Illustration: Set-up of the 'Autogenerative High Pressure Digestion' facility at EnTranCe