Supercritical carbon dioxide geothermal energy system analysis

Taylor, Patrick (2014) Supercritical carbon dioxide geothermal energy system analysis. [USQ Project]

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Abstract

There has been considerable interest in the possibility of using supercritical carbon dioxide (SCCO2) as a geothermal heat mining fluid instead of water. Some favourable fluid transport properties may prove to give an advantage in some circumstances. The low viscosity to density ratio suggests higher mass flow rates and better suitability to low permeability reservoirs may be possible. Higher frictional losses in the wellbores may degrade that advantage.

It has been shown that SCCO2 has the potential to utilise buoyancy effects such that a thermosiphon circulates the geothermal fluid without the need for a pump. In addition, it has been proposed that SCCO2 could be used to drive a turbine directly rather than a conventional binary heat exchange system. This could dramatically reduce surface plant complexity and cost.

This study details the creation of a Matlab model of the subsurface circuit of geothermal fluid. After establishing a reference case to study general fluid and system behaviour, the model is used to test and compare the effects of wellbore diameter variation, reservoir depth, permeability and temperature on the net exergy and thermal efficiency using each of water and SCCO2.

For the specific test cases, SCCO2 was shown to perform significantly better than water with increased well bore diameter, low permeability and low temperature reservoirs. The performance was found to degrade with shallower reservoirs; although this leads to observations that the SCCO2 system operates on a narrow band of efficiency which could make the system less robust than comparable water based system.


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Item Type: USQ Project
Item Status: Live Archive
Additional Information: Bachelor of Engineering (Mechanical) project.
Faculty / Department / School: Current - Faculty of Health, Engineering and Sciences - School of Mechanical and Electrical Engineering
Supervisors: Mossad, Ruth
Date Deposited: 09 Sep 2015 05:16
Last Modified: 09 Mar 2016 05:30
Uncontrolled Keywords: geothermal heat; geothermal fluid; supercritical carbon dioxide; SCCO2; mining; wellbores
Fields of Research : 09 Engineering > 0913 Mechanical Engineering > 091305 Energy Generation, Conversion and Storage Engineering
URI: http://eprints.usq.edu.au/id/eprint/27247

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