Thermochemical Conversion

Pyrolysis and gasification are thermochemical conversion processes, where the biomass feedstock is heated up in an oxygen-depleted atmosphere, to a temperature between 400 and 1100°C depending on the process. In these conditions, biomass decomposes into gases, vapours and solid products.

Pyrolysis is carried out in complete absence of oxygen, in the temperature range 400-800°C and the products include pyrolysis gas, bio-oils (liquids) and biochar (solids). Pyrolysis gas and bio-oils can either be used on-site for energy production via direct combustion or upgraded: pyrolysis gas can be used as raw material for catalytic methanol synthesis, or for methane production via biological fermentation (bio-methanation), while bio-oils can be upgraded to become liquid fuels. Biochar is a promising amendment for agricultural and environmental applications. Approximately half of the carbon in the feedstock ends up in the biochar, where, thanks to the high temperature thermal treatment, it acquires a more ordered and stable form compared with the original biomass. This makes it very difficult to degrade for microorganisms, therefore if biochar is applied to soils, it can persist for hundreds or even thousands of years, providing a carbon sequestration effect, called biochar carbon removal (BCR). In addition, biochar can provide positive effects on soil health and productivity.

In contrast with pyrolysis, gasification is operated in the temperature range 700-1100°C and with a small addition of oxygen and reforming agent (CO₂ or H₂O) to favor gasification reactions: this makes the gas yield much higher than in pyrolysis. The product gas from thermal gasification, or producer gas, is rich in CO and H₂, therefore can be used on site for electricity production via engines or can be upgraded to produce high quality energy carriers such as hydrogen or methanol.

Research goal and purpose

Research activities in this field within the CHEC group aim at supporting the upscaling of pyrolysis and gasification technologies and pave the way to the extensive use of pyrolysis and gasification products in society. The research work is therefore carried out in close collaborations with industrial partners, and focused on characterization, optimization and testing of products such as biochar and bio-oils.

Special focus is dedicated to the evaluation of potential environmental risks of large-scale pyrolysis systems, where biochar is produced for use on agricultural land and environmental management, while the other pyrolysis products are used as energy carriers.

The CHEC group has a long history of research and development of thermal conversion systems, dating back to the early ´90s. Today, such established knowledge is the basis to take pyrolysis and gasification of biomass into the future through laboratory, pilot and industrial-scale research activities.

The work within this area focuses on:

• Feedstock characterization and pre-treatment (e.g. pelletization)
• Laboratory scale pyrolysis and gasification for preliminary testing of biomass feedstock and products
• Characterization of biochar
• Biochar modification and testing for agricultural soil and alternative applications (filtering material, feed additive, others)
• Investigation of the fate of harmful substances (e.g. PAHs, PFASs, heavy metals, dioxins) within industrial-scale pyrolysis systems
• Characterization of pyrolysis bio-oils
• Mixing and catalytic upgrading of pyrolysis bio-oils to improve quality and applicability.
• Use of pyrolysis and gasification gas for synthesis of liquid fuels and chemicals