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RESEARCH PAPERS

# Evaluation of Electricity Generation From Underground Coal Fires and Waste Banks

[+] Author and Article Information
A. D. Chiasson

Geo-Heat Center,  Oregon Institute of Technology, 3201 Campus Drive, Klamath Falls, OR 97601

C. Yavuzturk

Department of Civil & Architectural Engineering,  University of Wyoming, 1000 E. University Avenue, Dept. 3295, Laramie, WY 82071cyturk@uwyo.edu

D. E. Walrath

Department of Mechanical Engineering,  University of Wyoming, Laramie, WY 82701

J. Energy Resour. Technol 129(2), 81-88 (Jul 18, 2006) (8 pages) doi:10.1115/1.2718576 History: Received September 09, 2004; Revised July 18, 2006

## Abstract

A temperature response factors model of vertical thermal energy extraction boreholes is presented to evaluate electricity generation from underground coal fires and waste banks. Sensitivity and life-cycle cost analyses are conducted to assess the impact of system parameters on the production of 1 MW of electrical power using a theoretical binary-cycle power plant. Sensitivity analyses indicate that the average underground temperature has the greatest impact on the exiting fluid temperatures from the ground followed by fluid flow rate and ground thermal conductivity. System simulations show that a binary-cycle power plant may be economically feasible at ground temperatures as low as 190$°$C.

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Copyright © 2007 by American Society of Mechanical Engineers
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## Figures

Figure 1

Schematic diagram of (a) a direct-flash steam power plant and (b) a binary-cycle plant

Figure 2

Conceptual diagram of the underground energy extraction system

Figure 3

Conceptual diagram of concentric-type underground Earth heat exchanger

Figure 4

Underground heat extraction model component configuration for TRNSYS

Figure 5

Exiting fluid temperatures from the ground and heat extraction rates for a 61m deep single borehole

Figure 6

Number of 61m deep boreholes required to produce 1MW of electrical power at 20% thermal conversion efficiency at various average underground temperatures

Figure 7

Normalized results of sensitivity analyses

Figure 8

Heat extraction rate of a 10×10 borehole field as a function of borehole spacing

Figure 9

Net present value of an underground coal fire thermal energy extraction system with binary-cycle power plant at various drilling costs, various thermal conversion efficiencies (n), and various power selling rates to the grid

Figure 10

Effect of average underground temperature on net present value of an underground coal fire thermal energy extraction system with binary-cycle power plant at various drilling costs, various thermal conversion efficiencies (n), and various power selling rates to the grid

Figure 11

Effect of average underground thermal conductivity on net present value of an underground coal fire thermal energy extraction system with binary-cycle power plant at various drilling costs, various thermal conversion efficiencies (n), and various power selling rates to the grid. Solid lines=$0.03∕kWh selling rate to the grid. Short dashes=$0.04∕kWh selling rate to the grid. Long dashes=\$0.05∕kWh selling rate to the grid.

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