Advancements in thermal spallation drilling technology

Thermal spallation of hard rocks has been used commercially for many years to cut granite in quarries and to produce blasting holes in taconite mines. It is potentially an economic process for creating cavities in hard rocks that are difficult to drill or mine by conventional methods. These cavities might have application for storage of liquids and gases and of energy in several forms. They may also be used as high-pressure, naturally heated retorts for certain chemical processes. This report describes the spallation process, including the fluid dynamics and heat transfer from flame jets to the rock and subsequent rock failure. Our model of the spallation process predicts with good accuracy the surface temperatures and heat-transfer rates required to maintain desired drilling rates. Field tests, including site selection, equipment, field operations, and accomplishments, are also described in detail. 31 refs., 13 figs., 1 tab.