Production and characterization of a new quality pyrolysis oil, char and syngas from digestate - Introducing the thermo-catalytic reforming process

A 2 kg/h laboratory scale thermo-catalytic reforming (TCR®) unit was designed and commissioned at Fraunhofer UMSICHT to convert digestate into enhanced pyrolysis products. The TCR® reactor is an intermediate pyrolysis screw reactor connected to a reformer. In the experimental series reported, digestate pellets were used as feedstock. The aim herein was to test and characterize the TCR® reactor for the feedstock digestate and its products for syngas applications and decentralized power production. Prior to the pyrolysis experiments thermal gravimetric analysis was used to analyze the weight loss over temperature. The digestate was pyrolyzed at a constant temperature of 400 °C, whereas the reformer temperature was varied between 500 and 750 °C. Following the cooling and condensation of pyrolysis vapors, these separated into bio-oil, an aqueous phase and permanent gases. Hydrogen concentration increased together with increased reforming temperatures and reached a maximum of 35 vol% at 750 °C. The bio-oil generated at 750 °C had a higher heating value of 33.9 MJ/kg, 1.7 wt% water content and a total acid number of 4.9 mg KOH/g. It was possible to convert over 91% of the energy content of the biomass into usable products. These results are analyzed together with the extensive feedstock and product characterization and the experimental parameters and discussed.