| Title | Assisted Ignition of Hydrothermal Flames in a Pilot Hydrothermal Spallation Drilling Plant |
|---|---|
| Authors | Panagiotis STATHOPOULOS,Tobias ROTHENFLUH, Martin SCHULER, Dragana BRKIC, Philipp RUDOLF VON ROHR |
| Year | 2012 |
| Conference | Stanford Geothermal Workshop |
| Keywords | hydrothermal spallation drilling, hydrothermal flames, assisted ignition, pilot plant |
| Abstract | Spallation drilling is a promising drilling technique that could prove to be economically advantageous over rotary techniques for deep wells needed e.g. for geothermal energy production. It takes advantage of the properties of certain rock types, to spall rock to small disk-like fragments due to thermal stresses. In water-filled boreholes 2-3 kilometers deep, water exceeds its critical pressure (220.64 bar) and hydrothermal flames can provide the required heat to spall the rock. One potential spallation drilling head consists of a combustion chamber fed by water, fuel and oxidant. The reactants are preheated and react to a supercritical (≥ 220.64 bar, ≥ 374°C), hydrothermal flame in the aqueous environment of the burning chamber. The water in the combustion chamber reaches high temperatures and exits through a nozzle together with the combustion products. The resulting supercritical water jet is directed to the rock surface causing fragmentation. Building on the investigations on hydrothermal flames carried out in our lab for almost two decades, the work presented in this paper focuses on the assisted ignition of these flames. For the investigation of spallation drilling, a novel hydrothermal spallation drilling pilot plant was built, able to reach power up to 120kW. The self-ignition methodology used in all the previously published research is not an option anymore, especially when such power values are used. Additionally, the assisted ignition of a hydrothermal flame is the only option for the field application of spallation drilling, where the flame has to be ignited in a 2.5 kilometers deep borehole. The implemented ignition set-up, an ignition model and the corresponding experimental results of the assisted flame ignition are presented. The experimental results comprise of ignition surface temperatures and igniter power values combined with the corresponding heat transfer coefficient measurements for the annular flow of supercritical water. |