Hydrothermal carbonization of agricultural residues

•HTC converts organic residues into a solid fuel comparable to brown coal.•Most of the tested agricultural residues are suitable for the HTC process.•Blending of different agricultural residues ensures a successful carbonization.•Dewatering and drying properties of most HTC-Biochars are very good.•HTC-process water can be used in biogas plants increasing process energy efficiency. The work presented in this article addresses the application of hydrothermal carbonization (HTC) to produce a solid fuel named HTC-Biochar, whose characteristics are comparable to brown coal. Several batch HTC experiments were performed using agricultural residues (AR) as substrates, commonly treated in farm-based biogas plants in Germany. Different AR were used in different combinations with other biomass residues. The biogas potential from the resulting process water was also determined. The combination of different AR lead to the production of different qualities of HTC-Biochars as well as different mass and energy yields. Using more lignocellulosic residues lead to higher mass and energy yields for the HTC-Biochar produced. Whilst residues rich in carbohydrates of lower molecular weight such as corn silage and dough residues lead to the production of a HTC-Biochar of better quality and more similar to brown coal. Process water achieved a maximum of 16.3L CH4/kg FM (fresh matter).