Design, commissioning and start-up of a new hydrothermal liquefaction continuous pilot unit

Hydrothermal liquefaction (HTL) has been demonstrated to be an effective emerging technology for the conversion of various biomass slurries into valuable biofuels and bioproducts precursors. Many studies have been carried out in batch laboratory-scale apparatus, an effective technique to understand the conversion process applied on several wet materials, from algae to organic wastes and lignocellulosic streams. On the other hand, some examples of continuous system have been implemented and tested worldwide as first step for the industrial scale-up of the technology. This work focuses on the development from the design to the start-up and commissioning of a new continuous HTL unit, established in RE-CORD laboratories. The plant is capable of converting 1-2 kg/h of slurry at about 10 wt.% of biomass to water ratio. The hydrothermal conversion unit comprises a high-pressure slurry feeder, an indirectly heated plug flow reactor, a cooling system, a pressure let-down system and liquid-gas separator. The reactor can reach and keep the converting material at 350 °C at a pressure of 220 bar for a residence time of 5 to 24 min. The solid content can be filtered in-line or separated at the end of the process depending on the physical characteristics of the suspended solid residues. Two different depressurizing system have been designed and implemented in parallel for the continuous discharge of the liquid products, widening the operability of the system to a larger selection of feedstock. The plant commissioning allowed to assess the process analysis in term of heating, pressurizing and reaction control. Flow rate, temperature and pressure profiles along the reaction and cooling zones have been acquired by a National Instrument data acquisition system. The software for data acquisition and for the control of the heaters and the depressurizing system was internally developed with NI LabView.