| Title | Heat or Power?: Proposing Geothermal Development on the Basis of Fossil Fuel Displacement |
|---|---|
| Authors | Casey LAVIGNE, Maria GUDJONSDOTTIR, Jonathan BANKS |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | Canada, geothermal, power, heat, Monte Carlo, binary power plant, resource assessment, fossil fuel |
| Abstract | This study applies a fossil fuel 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 was estimated and two exclusive development scenarios – power generation and space heating – were analyzed. Monte Carlo simulations were used to estimate the thermal power available in the sample reservoir, resulting in a potential wellhead thermal output of 226 MWth at 95% cumulative probability for a project lifetime of 50 years. The thermal power was converted to a brine flow rate estimate of 540 kg/s at the average reservoir temperature of 118°C. Using the estimated geothermal flow rate as an input, a binary power plant was modelled and optimized in Engineering Equation Solver (EES). The resulting n-butane power plant model produced 12.1 MWe net power at a thermal efficiency of 9.2%. Colder air temperatures in the winter resulted in an output of 16.1 MWe, while a minimum of 9.5 MWe is produced by the model in summer conditions. A residential district heating system, the second development scenario, was modelled in EES using an 80/40/-20 design criteria. The design resulted in a system capable of heating over 18,000 houses year-round, with excess energy at ambient temperatures above -20°C available to a larger heating system and/or industry partners. The heating system operates at 92.4% energy efficiency under design conditions. The power plant scenario provides 108 GWh annually, which translates to 649 TJ of fossil fuel energy savings per year. The district heating option provides a total 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. As the district heating network operates at lower than maximum capacity for much of the year, its project lifetime can be prolonged to 630 years if used exclusively for Hinton residential heating. The prospective heating network would then save 213 PJ (5.76B m3 NG) of non-renewable energy, more than six times the 32.4 PJ (0.87B m3 NG) saved by the power generation scenario. Correspondingly, the greenhouse gas emissions avoided in the heating scenario amounts to 10.8 Mt CO2, compared to just 1.6 Mt in the power generation scenario. The seminal finding from the study is the conclusion that the fossil fuel energy payback of direct-use heating utilization was 6.6 times that of indirect power generation. Developing available geothermal resources to replace space heating most readily fulfills the objective of displacing the maximum amount of non-renewable energy. The results of this case study analysis are applicable to any similar community with an energy economy dominated by fossil fuels. |