Transport Processes in Reacting Hydrothermal Flames with Applications to Military Waste Destruction in Supercritical Water and Geotechnical Rock Excavation

Abstract

Abstract : A hydrothermal flame is a flame that exists in a supercritical aqueous medium and is characterized by steep temperature and density gradients. The overall objective of our project was to increase understanding of heat, mass, and momentum transport processes within hydrothermal flames. Specifically, we planned to study hydrothermal flame characteristics such as flame temperature and stability, and to develop a method for modeling heat and mass transport processes in the hydrothermal flame and supercritical water environments based on experimental observations. With this knowledge, hydrothermal flames can be tailored to the task of destroying aqueous wastes such as chemical and biological warfare agents or municipal sludges, or used to perform thermal spallation and/or fusion of rock surfaces in a deep-borehole environment for rock drilling and excavation. An autoclave reaction system was designed and constructed to create flame jets in water using both methanol and hydrogen as fuel at a pressure of 250 bar. The temperatures of these flames were measured, and attempts were made to use the flames to spall small rock samples. The experimental system was modified to study the centerline temperature decay of supercritical water jets injected at temperatures up to 525 degrees C into ambient temperature water. A device for measuring the heat flux from these jets was designed, constructed, and used to determine the heat transfer coefficients of the jets impinging against a flat surface. Together, these studies indicate that the necessary temperatures and heat fluxes required to induce thermal spallation in rocks can be achieved in a deep borehole. A detailed account of the experiments and results summarized below is available in Thesis Dissertation Hydrothermal Spallation Drilling and Advanced Energy Conversion for Engineered Geothermal Systems by Chad Augustine.