Thesis

Development of robust modelling and experimental methods to advance mechanistic insights into the supercritical water gasification of biomass

Downloadable Content

Download PDF
Creator
Rights statement
Awarding institution
  • University of Strathclyde
Date of award
  • 2026
Thesis identifier
  • T17651
Person Identifier (Local)
  • 202161995
Qualification Level
Qualification Name
Department, School or Faculty
Abstract
  • Wet biomass is a classification of high-moisture organic materials that are challenging to handle, and the current conventional treatment of these materials contributes significantly to greenhouse gas emissions and local environmental damage. These materials arise from multiple sources; many of which are wastes such as sewage sludge and agricultural slurries, while others are purposely produced, such as microalgae. A commonality amongst them is their high water content which can be upwards of 90 wt.% water. Supercritical water gasification is a novel high temperature, high pressure treatment technique that uses conditions above the critical point of water (374◦C and 22.1MPa) to rapidly and effectively convert wet biomass into syngas fuel with water in-situ. The full-scale commercialisation of supercritical water gasification hinges upon overcoming present challenges which inhibit the efficiency and cost-effectiveness of gasifying biomass in supercritical water. This includes issues relating to poor gasification efficiencies, char formation, high energy demands, and salt deposition. A major problem is that there is currently a poor understanding of the mechanistic processes that underpin supercritical water gasification, and therefore it becomes ultimately harder to overcome the aforementioned challenges if it is not possible to make reference to an accurate, well-established portfolio of biomass reactions in supercritical water. The contents of this thesis aim to progress supercritical water gasification by presenting a series of novel methodologies that can be used to provide useful mechanistic insights into the fundamental processes which govern reactions of biomass molecules in supercritical water. A detailed kinetic model was updated and improved to explore the potential in enhancing syngas yields and carbon gasification efficiency, and mitigating char formation by changing sub-critical heating rates and heating profiles (e.g., linear, accelerating, decelerating). Slow sub-critical heating rates are found to be beneficial for increasing the yield of H2 from the SCWG of cellulose and hemicellulose compounds. The gasification of lignin could be enhanced by using faster heating rates, as it minimises the formation of char in the sub-critical region. This can guide potential tailored improvements to SCWG by controlling the sub-critical heating regime in accordance with the feedstock to optimise syngas yield and char formation. Secondly, a chemical kinetic sensitivity analysis of the biomass SCWG mechanism was conducted to present a methodology that can be used to discern the most influential reactions on the formation of target species. Here, the formation of H2 and acetic acid (a refractory intermediate) from cellulose were investigated as examples, and the rate-determining steps of their formation were determined. A thermodynamic model was developed using a novel perspective of elemental chemical potentials to produce a framework that could be used to evaluate and comparatively analyse any thermochemical or hydrothermal biomass conversion process. Here, ternary diagrams were used to illustrate how operating conditions (e.g., temperature and pressure) and additive agents (e.g., water and CO2) would influence chemical and phase equilibria. The ternary diagrams offer a unique visualisation of thermodynamic equilibrium and are robust, useful tools for revealing the optimum reaction conditions needed to convert any feedstock, without the need for further calculations or simulations. Finally, experimental methodologies were developed and demonstrated for a newly acquired batch reactor. This process included designing rigorous safety controls, calibrating analytical equipment, and testing the reactor with different feedstocks. The aim of this work was to establish a reliable experimental rig that could be used by the University of Strathclyde and external partners to conduct research into supercritical water gasification and other hydrothermal processes. Given the scarcity of experimental research in this field, the development of the rig is highly valuable, as the data obtained can both validate computational models and support groundbreaking research.
Advisor / supervisor
  • Lue, Leo
  • Li, Jun
Resource Type
DOI
Date Created
  • 2025

Relations

Items

Thumbnail Title Date Uploaded Visibility Actions
file details PDF of thesis T17651 2026-03-10 Public Download