Co-pyrolysis and HTC refined biomass-biosolid-mixes: combustion performance and residues

Corn stover (CS) and biosolids (BS), two easily accessible biomass (BM) resources, were combined in Co-pyrolysis (Co-Pyr) and Co-hydrothermal carbonization (Co-HTC) processes. The beneficial or catalytic effects of BS on CS in this process were identified by characterizing the following measured parameters of the produced char: ultimate and proximate analysis, higher heating value (HHV), van-Krevelen-diagram, activation energy ( A E ), and combustibility index S . The influence of the BS on CS was indicated by comparing the stated values of the CS/BS-mixed samples with the results of the pure BS- and CS-samples and the values of the unprocessed original BS and CS. The following developments were recognized: HHV of pure CS increased to 21–23 MJ/kg, that of pure BS was reduced to 7–9 MJ/kg, and for the mixed samples, one CS:BS-ratio showed beneficial interactions and resulted in 20–21 MJ/kg. The carbonization rate was advanced for the Pyr samples, ranging in the areas of coal and lignite, and most HTC samples in the area of peat and the original BM. The A E decreased from 65 and 41 kJ/g for the starting materials to an average of 30–40 kJ/g for most samples, and several samples reached 20–25 kJ/g. Hydrochars made from combined BM presented advanced combustibility index S values, passed 1 × 10 –6 , compared to Co-Pyr, and its biochar did not reach this combustibility index. CS and BS in pure and mixed forms, treated with Pyr or HTC, led to advanced solid fuels for different aspects of the analysis focus and depending on the composition of the sample.