Featured Research

from universities, journals, and other organizations

Tapping Geothermal Energy: New Drilling Method With Fire And Flame In The Depths

Date:
September 15, 2009
Source:
ETH Zurich
Summary:
With increasing depth, geothermal energy offers an almost inexhaustible potential for renewable energy. The drilling costs however, rise exponentially with depth in the case of conventional rotary drilling. A thermal drilling method, which will allow for reaching greater drilling depths in a more efficient and more cost-effective way, is currently under development.

Model of the experimental reactor.

With increasing depth, geothermal energy offers an almost inexhaustible potential for renewable energy. The drilling costs however, rise exponentially with depth in the case of conventional rotary drilling. A thermal drilling method, which will allow for reaching greater drilling depths in a more efficient and more cost-effective way, is currently being developed at the ETH Zurich.

Tobias Rothenfluh, a doctoral student at the Institute for Process Engineering, climbs up a small ladder into the three-story pilot plant. Pipelines lead through metering and safety valves into the reactor, which is affectionately known as “Betsy”. Inch-thick plates, made of heat-resistant steel, prevent the reactor from bursting, even at a pressure of 300 bars. “In our experimental reactor we are able to ignite a flame underwater at a pressure of around 250 bars and 450 degrees Celsius” says Rothenfluh. “Thus we are able to experimentally simulate the temperature and pressure conditions prevailing in a borehole, about three kilometers below the earth’s surface.” He has constructed a first burner prototype over the last few months together with his colleagues Martin Schuler and Panagiotis Stathopoulos.

Laboratory experiments at high pressure

Heated oxygen, ethanol and water are pumped into the reactor burner through various pipelines and valves and mix under temperature and pressure conditions, which correspond to the supercritical state of water (see box). The auto-ignition of the mixture is being observed through small sapphire-glass windows by means of a camera. A newly developed sensor plate measures the heat flux from the flame to the plate and records the temperature distribution on the surface for different distances between the burner outlet and the plate.

Based on these experimental results, conclusions are drawn concerning the heat transfer from the flame to the rock. “The heat flux is the crucial parameter for the characterization of this alternative drilling method”, explains Philipp Rudolf von Rohr, professor at the Institute of Process Engineering of the ETH Zurich and supervisor of the three PhD students.

Erosion in fast motion

During the experiment, the flame reaches a maximal temperature of about 2000C. Rapid heating of the upper rock layer induces a steep temperature gradient in it. “The heat from the flame causes the rock to crack due to the induced temperature difference and the resulting linear thermal expansion”, explains Tobias Rothenfluh. The expansion of the upper rock layer causes natural flaws, already existing in the rock, act as origin points for cracks. Disc - like rock fragments in the millimeter scale are formed in the spallation zone. These particles are transported upwards with the ascending fluid stream of the surrounding medium. “One of the main challenges of the spallation process is to prevent the rock from melting, whilst it’s being rapidly heated”, says Tobias Rothenfluh. “The lager the temperature gradient in the rock, the faster you can drill.”

The method is particularly suitable for hard, dry rock, normally encountered at depths greater than three kilometers. In such depths conventional drilling bits wear out much faster, and their frequent replacement, renders the conventional drilling techniques uneconomic: a 10 km borehole costs around 60 million US dollars. In the case of the so-called “hydrothermal spallation drilling” method, however, the burner - drill bit wear is considerably less, because there is no mechanical contact with the rock. “It is expected that the drilling costs will rise linearly with depth in the case of spallation drilling, instead of exponentially, which is the case of the conventional methods”, says Philipp Rudolf von Rohr.

Simulation and demonstration

In order to test the flame’s behavior under different conditions, the doctoral student Martin Schuler is developing a tool for the numerical simulation of the reaction and transport processes in cooperation with the master’s student Karl Goossens. “The simulation enables us to change and optimize parameters like fuel mass flow rates, temperature and pressure, as well as the geometry of the burner”, says Martin Schuler.

The experimental results from the current test set-up are being used to design a pilot plant, on which Panagiotis Stathopoulos is working. The 1.2 million-Swiss-franc plant should demonstrate that it is actually possible to drill through rock by means of hydrothermal flames. The project is funded by the Swiss Federal Office of Energy, the industrial organization swisselectric research, ETH Zurich and the Swiss National Science Foundation.

Research in breadth and depth

The interest of federation and industry confirms the high potential of “hydrothermal spallation drilling”. Some time will pass until the method is industrially applicable, but the feasibility is undoubted so far. “It is for sure possible to speed up the project towards the industrial application”, Philipp Rudolf von Rohr realizes, “but we still want to focus on basic research at a university like the ETH Zurich”.

After all, the Institute of Process Engineering is currently worldwide the only group investigating the heat transfer characteristics of a flame in supercritical water. “We literally want to research in both depth and breadth”, says Tobias Rothenfluh. In the future, the knowledge acquired might be useful not only for geothermal energy, but also for other applications.

Supercritical water

Above a temperature of 374.12C and a pressure of 221.2 bars, water vapor and liquid water can no longer be distinguished from each other in terms of their density. In this supercritical state, water is less polar, has no phase boundaries any more and is a good solvent for non-polar gases like oxygen. Under these conditions fuel and oxygen can be mixed without any bubble formation and in the case of ethanol as fuel, auto-ignition occurs at approximately 450C.


Story Source:

The above story is based on materials provided by ETH Zurich. Note: Materials may be edited for content and length.


Cite This Page:

ETH Zurich. "Tapping Geothermal Energy: New Drilling Method With Fire And Flame In The Depths." ScienceDaily. ScienceDaily, 15 September 2009. <www.sciencedaily.com/releases/2009/09/090912144809.htm>.
ETH Zurich. (2009, September 15). Tapping Geothermal Energy: New Drilling Method With Fire And Flame In The Depths. ScienceDaily. Retrieved July 23, 2014 from www.sciencedaily.com/releases/2009/09/090912144809.htm
ETH Zurich. "Tapping Geothermal Energy: New Drilling Method With Fire And Flame In The Depths." ScienceDaily. www.sciencedaily.com/releases/2009/09/090912144809.htm (accessed July 23, 2014).

Share This




More Matter & Energy News

Wednesday, July 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Robot Parking Valet Creates Stress-Free Travel

Robot Parking Valet Creates Stress-Free Travel

AP (July 23, 2014) 'Ray' the robotic parking valet at Dusseldorf Airport in Germany lets travelers to avoid the hassle of finding a parking spot before heading to the check-in desk. (July 23) Video provided by AP
Powered by NewsLook.com
Boeing Ups Outlook on 52% Profit Jump

Boeing Ups Outlook on 52% Profit Jump

Reuters - Business Video Online (July 23, 2014) Commercial aircraft deliveries rose seven percent at Boeing, prompting the aerospace company to boost full-year profit guidance- though quarterly revenues missed analyst estimates. Bobbi Rebell reports. Video provided by Reuters
Powered by NewsLook.com
Europe's Car Market on the Rebound?

Europe's Car Market on the Rebound?

Reuters - Business Video Online (July 23, 2014) Daimler kicks off a round of second-quarter earnings results from Europe's top carmakers with a healthy set of numbers - prompting hopes that stronger sales in Europe will counter weakness in emerging markets. Hayley Platt reports. Video provided by Reuters
Powered by NewsLook.com
9/11 Commission Members Warn of Terror "fatigue" Among American Public

9/11 Commission Members Warn of Terror "fatigue" Among American Public

Reuters - US Online Video (July 22, 2014) Ten years after releasing its initial report, members of the 9/11 Commission warn of the "waning sense of urgency" in combating terrorists attacks. Mana Rabiee reports. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins