The increasing accumulation of biomass and plastic waste presents significant environmental
challenges, necessitating the development of effective recycling technologies. Hydrothermal
liquefaction (HTL) emerges as a promising solution, converting these wastes into valuable
hydrocarbons, platform chemicals and materials under mild temperature and pressure in the
presence of water. Compared to conventional methods such as pyrolysis and incineration,
HTL offers several advantages, including higher efficiency, reduced emissions, and the ability
to process wet feedstocks without prior drying. Despite its potential, the current state of HTL
technology predominantly involves batch-scale studies, with limited continuous pilot-scale and commercial-scale implementations. Research at TU Delft has significantly contributed to this field, conducting numerous batch experiments with various feedstocks and catalysts. To bridge the gap between laboratory research and industrial application, scaling up to a continuous pilot scale plant is essential. This thesis presents the design of a pilot-scale continuous HTL system for biomass and plastic. This design addresses the major challenges associated with scale-up, providing a blueprint for future advancements in sustainable waste management and resource recovery.
The design process began with identifying three major challenges in continuous HTL: high-pressure solid-liquid slurry pumping, lower heating rates leading to ash formation and reduced yield, and the need for a robust separation system for gas, liquid, and solid phases. The first step involved establishing the basis of design, including selecting the primary feedstock, thermophysical properties, and required solid particle size. A block flow diagram was then developed to define the battery limits. The continuous pilot-scale HTL system was divided into three main sections: feed introduction, reactor, and product separation. All potential options and equipment were evaluated, and the most suitable ones were chosen. Various equipment manufacturers were consulted to understand the suitability and cost implications. Based on the selected equipment, a process flow sheet was generated, followed by detailed sizing of all equipment and finalizing the process and instrumentation diagram. Finally, a cost analysis was conducted to determine the capital expenditure and operational expenditure of the designed plant.
During the design process, it was observed that only one commercially available pump could achieve the required pressure. However, the cost of this pump was extremely high. To address this, a dual piston pump system was developed, effectively pressurizing slurries to the required process pressure (200 bar). This system uses two asynchronously operated hydraulic power pistons and measures the slurry flow rate based on the position of the piston, eliminating the need for flow indicators or control valves. Additionally, a heating system consisting of a tubular preheater and an induction heater was proposed, capable of heating the slurry at a rate of 4°C/s. The separation system was designed with a solid filter, flash tank, and gravity settler to extract bio-crude oil or plastic oil as the final product. Economic analysis showed that operational costs are around 18-21.5% of the capital cost per year, with feed introduction and reactor costs accounting for 85% of the total capital cost. Overall, two design alternatives were developed during the thesis, addressing all identified major challenges. These alternatives provide cost-effective solutions for parametric studies of the HTL process.