Resource Assessment of Geothermal Reservoir in Western Alberta and Evaluation of Utilisation Options Using Non-Renewable Energy Displacement
Author: Casey Lavigne
Year: 2018
Supervisors: María Sigríður Guðjónsdóttir
Abstract
Geothermal resources can be employed in service of either direct-use heating applications or indirect-use power generation. This study applies a non-renewable energy savings approach to the evaluation of a prospective geothermal reservoir near the town of Hinton in Western Alberta, Canada. The energy content of the resource is estimated and two exclusive development options – power generation and space heating – were modelled and analysed.
Monte Carlo simulations were used to determine an estimated wellhead thermal output of 226 MWth at 95% cumulative probability for a project lifetime of 50 years. The thermal power energy was converted to a brine flow rate of 540 kg/s at the reservoir average temperature of 118°C. A binary power plant was modelled and optimized in EES using the estimated geothermal flow. The resulting n-butane power plant model produced 12.1 MWe net power with a seasonal range of 9.5-16.1 MWe. The model operated at a thermal efficiency of 9.2% and functional and overall second law efficiencies of 36.4% and 20.0% respectively. A residential district heating system was modelled in EES using a 80/40/-20 design criteria. The design resulted in a system capable of heating over 18,000 houses year-round, with excess energy available to potential industry partners. The heating system operates at 92.4% of the time under design conditions.
The power plant scenario provides 108 GWh annually, translating to a fossil fuel energy content savings of 649 TJ per year. The district heating option provides a potential of 3840 TJ of thermal energy annually, resulting in a fossil fuel savings of approximately 4267 TJ – an increase of 557% from the power generation scenario.
In total, the prospective heating network would then save 213 PJ (5.76B m3 natural gas) of non-renewable energy, more than six times the 32.4 PJ (0.87B m3 natural gas) saved by the power generation scenario. Alternatively, if designed to serve only the residential energy needs of the nearby town of Hinton, the power plant could provide 100 TJ/year for almost 200 years and the heating system 301 TJ/year for over 630 years.
The results of this case study analysis are applicable to any similar community located within an energy economy dominated by fossil fuels. The seminal finding from the study is the conclusion that the non-renewable energy payback of direct-use application was 6.6 times that of the indirect application. Using available geothermal resources to replace space heating most readily fulfils the objective of displacing the maximum amount of non-renewable energy.