By 2050 at least 100 GW of electricity could be generated by geothermal power
plants in the U.S. for a maximum investment of 1 billion US Dollars in research
and development[1]. These numbers show clearly the enormous potential of
geothermal power. However, temperatures high enough in terms of electricity
production are commonly only found in holes reaching down to 4-10 km below
the earth’s surface. The MIT report[1] shows that drilling costs increase
exponentially with depth. New drilling technologies are therefore needed to
reduce costs for geothermal wells. Apart from conventional mechanical drilling
by means of a rotary drilling bit, there is a technology called “Spallation Drilling”.
Therein, a flame jet or laser is directed to the rock to cause fragmentation. In
simple terms, spalling is a form of crackling caused by an unequal expansion of
rock crystals. While this technology, also known as “thermal rock
fragmentation”, is already used in Russia and the Ukraine to drill large diameter
holes in surface mining, in our laboratory we aim to investigate the possibility of
using this technology to drill deep holes for geothermal power plants. Beyond
3000 meters supercritical conditions for water are found. Our theoretical and
experimental experience with hydrothermal flames is used and shall allow
spallation in this supercritical environment. Fundamental experimental and
theoretical research will been done on heat transfer, transport of spalled
material and burner nozzle design. Ignition and stability of the flame are further
investigated, as these are main conditions for the operation downhole. These
data then allow the design of a pilot facility for geothermal application.
[1] The Future of Geothermal Energy, MIT press, Cambridge (2006),
http://geothermal.inel.gov/publications/future_of_geothermal_energy.pdf
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