Renewable hydrogen is no longer considered a utopia in the future energy supply but a realistic element. The main track is to produce hydrogen with water and electricity through electrolysis. Today, hydrogen is usually made from fossil natural gas. Researchers from Lund University are now working on a new approach: to utilise the plant residues left over from the forestry and agricultural industries, which are currently often used for district heating.
More energy efficient than electrolysis
By heating these twigs and other undergrowth in a closed, oxygen-deficient environment, the biomass is converted into an energy-rich black oil, known as pyrolysis oil, and pyrolysis gas. There are no emissions from this step.
In the next step, the pyrolysis gas is burned and the pyrolysis oil is allowed to react with the carbon dioxide produced. The result is mainly hydrogen - which can be used, for example, as an energy carrier or as a raw material for the chemical industry.
`We hope that the technology can become an alternative to hydrogen production with less energy losses than electrolysis,’ says Christian Brackmann, senior lecturer in combustion physics at the Department of Physics and coordinator of the project.
`An additional advantage is that the process also does not require catalysts, which often consist of rare and expensive materials.´
The biochar bonus
Overall, the hope is to reduce the input of carbon dioxide into the atmosphere with this approach. The process also creates biochar, which can be used as a nutrient supplement in arable soil. In this way, nitrogen is also managed in a cycle, as nitrogen can be added to the biochar. The technology will first be developed for lab scale in 2028, after which the next step could be studies in a pilot plant.
How unique is this approach?
‘The steps have previously existed separately, but what is new is combining them into a coherent process and also making it flexible so that it can be adapted to the conditions on site. But the technology for burning the pyrolysis gas that provides energy for the reaction with pyrolysis oil and carbon dioxide is new,’ says Christian Brackmann.
What are the challenges of the method?
`It is about identifying the appropriate scale of the method, carbon capture and the appropriate balance of biochar production and syngas, which is a mixture of the gases carbon monoxide and hydrogen. Should you maximise the recovery of syngas or the potential for carbon and nitrogen uptake?
How the technology works
As a first step, pyrolysis oil and biogas are produced by heating plant residues from forestry and agriculture in an oxygen-free closed environment.
In the next step, researchers react the pyrolysis oil with carbon dioxide. This produces synthesis gas, which is a mixture of carbon monoxide and hydrogen. The synthesis gas, also known as syngas, can be upgraded and used in energy production and synthesis in the chemical industry. In addition to pyrolysis oil, biochar is produced, which can absorb carbon dioxide and nitrogen and be used as a nutrient supplement in cultivated soil. The process can be adapted and customised for different applications.
This technology should not be confused with carbon capture and storage (CCS), which involves capturing carbon dioxide from the stack of a coal-fired power plant or from the chimney of a combined heat and power plant.
About the project
Lund University is coordinating the project, called MINICOR, which includes three other European research groups. The total project budget for all partners is SEK 37 million.
The project is part of a portfolio, together with seven other projects funded in the same European Innovation Council call, focusing on sustainable management of carbon and nitrogen through value-adding processes that utilise these resources.