Hydrogen Carriers from Industrial Biomass via Sub/supercritical water - A process modelling and technology evaluation study

Continued rise in global energy demand as well as concerns over the lasting impact of climate change call for revamping existing energy services and consumption models. Sub/supercritical water biorefineries are a technology platform that enable low carbon pathways for de-fossilizing existing infrastructure, in which electrification is limited. The complex physical nature of biomass feeds, especially industrial by-products, constitute the development of conversion technologies in which several valorization objectives are concurrently met. Sub/supercritical water reactor systems materialize various process intensification advantages for thermally efficient upgrading of biomass to hydrogen carriers. The presented research is a process modelling study. The first pathway investigated is subcritical liquefaction for renewable fuels production for the transportation sector. The second pathway is the gasification of biomass into enriched synthetic methane and green hydrogen carriers for chemical and power generation sectors. The main contribution of this dissertation is considered to entail model development for satisfactory predictions of organic valorization in highly non-ideal conditions. The developed liquefaction and gasification models provide fundamental understanding on the driving forces for specific elemental, phase and product component yields at high temperature and pressure reactive processes. The constrained equilibria models extend knowledge on organic conversion inefficiencies in supercritical water to account for the role of inorganics in determining product gas composition and yields. In addition, the developed biorefinery flowsheets, case studies and assessment provides additional insights on the techno-economic opportunity and limitations present for future commercialization of the envisaged sub/supercritical water biorefineries. It was found that a holistic and polygenerative nature of chemical and thermal products recovery is necessary for the examined biorefineries to offer improved technical and economic performance relative to other biomass based technologies. In considering the production of hydrogen carriers, power and heat, the thermal efficiency of liquefaction was found to be 41-87% and 67-84% for gasification. In terms of economics, they remain uncompetitive with fossil fuels, with non-catalytic liquefaction breaking even at a €150 price per oil barrel. The study did show that with a 30% reduction in reactor system capital costs and the availability of a solids biomaterial market, liquefaction is economically feasible under current carrier commercial prices. The integration with pulp mills showed that gasification would improve existing thermal performance, as well as act as a capture and utilization technology for excess biogenic carbon present. The study showed that with increased integration of the gasification technology, the processing benefits lead to reduced minimum selling price of the mill specialty pulp product.