Hydrothermal carbonisation (HTC) is a thermal conversion process for producing sustainable carbon from biomass and waste materials. These sustainable carbons known as hydrochars can be used for a wide range of applications, including combustion fuels, catalysis, absorbents in environmental remediation and soil additives. The process works by submerging biomass in water and heating to temperatures in the range of 180-250ºC, while maintaining sufficient pressure to keep the water liquid. Under these conditions the physio-chemical properties of water change and water becomes both the catalyst, reagent and reaction media to a series of transformative reactions. These reactions convert the biomass into a coal like material using the same process chemistry that formed our geological coal deposits. Due to the coal like properties of the hydrochar the material is now often called a bio-coal when used in energetic applications.

The ability to convert low value biomass, (e.g. agricultural wastes, Miscanthus, AD digestate and even seaweeds) into direct substitute power station grade coals has seen HTC undergo substantial development over the past 10 years. For Miscanthus it is possible to harvest and processed green, enhancing yields per hectare by over 40 %[1], while producing a bio-coal equivalent to a high grade, high-volatile sub-bituminous coal with a HHV of 30 MJ/kg and a carbon conversion in excess of 90% within three hours, start to finish. HTC research at AU looks at both the fundamental chemistry of the process, particularly fate and influence of inorganics, chlorine and oxygen in a range of feedstock, and the influence of reaction parameters on the humic chemistry. AU is also heavily involved in process scale-up to larger scale continuous plant. A 30 l/h continuous facility is currently under construction at the Centre for Biorefining Technologies, AU Foulum. The increased throughput facility will provide hydrochars/bio-coals for a range of experiments and allow for a scale up in materials testing by both AU and in collaborative partners. The system has been designed to be highly flexible in terms of reaction parameters with both multistage heating and inline sampling, enabling feedstock and application specific optimisation and process insights required for further scale-up.