Process Development Unit (PDU) for Hydrothermal Carbonization (HTC) of Lignocellulosic Biomass

Abstract

Hydrothermal carbonization (HTC) is an effective means of upgrading raw lignocellulosic biomass to a more uniform solid hydrochar, having increased energy density. The HTC process is conducted in hot (200–300 °C) pressurized liquid water. Most experimental investigations of HTC have been conducted at small scale, using bench-top batch reactor vessels. In this work, we report the design, fabrication, and demonstration of a larger-scale process development unit (PDU) that enables semi-continuous HTC treatment of approximately 3 kg of biomass. This auger-equipped tubular reactor system conveys raw biomass through a zone of hot pressurized water, and deposits the solid hydrochar product in an accumulator vessel that is maintained at a lower temperature. Gaseous and liquid samples can be collected both while the PDU is at operating temperature, and after it has cooled. Characterization of gaseous, aqueous, and solid samples from a set of PDU experiments indicated good agreement with results from previous HTC experiments conducted in a much smaller (2-L) batch reactor. This suggests that the PDU provides a reliable scale-up of the HTC process.