The total heat produced by Earth is immense, yet exploitation has to date been limited to shallow areas near the surface where the heat is carried up via groundwater transfers. Deeper in the Earth’s crust, the temperature increases on average 25 °C per km. The EU-funded CHPM2030 project has developed the technology to both harness this deep geothermal energy and extract valuable metals from the geothermal fluid, something that has never been done before.
A hot idea moves full steam ahead
Enhanced geothermal system (EGS) technology relies on injecting cold water through a drill hole down to 4-5 km at high pressure, ‘enhancing’ natural fractures. The water is heated as it passes through the fractures in the hot rock and comes to the surface through another drill hole where the hot vapour is used to produce heat and energy. The key barriers to EGS adoption are the efficiency of the underground heat exchanger and the costs of investment and operation. Project coordinator Éva Hartai explains: “Combined heat, power and metal (CHPM) extraction from the geothermal fluid will make EGS more economically attractive. To accomplish it, we identified deep metal enrichments throughout Europe that are relevant for the CHPM technology, proved the applicability of the concept and delivered a roadmap for implementation.” In the CHPM2030 concept, an efficient underground heat exchanger relies on the slow dissolution of metal-bearing minerals to further open natural fractures. According to Hartai: “No high-pressure stimulation is needed as it is accomplished via the leaching process itself. It also gradually increases the flow rate and thermal output of the wells over time. In addition, reverse power electrodialysis using the high-salinity geothermal brine generates additional power so the total energy output of a CHPM plant will be even higher than in a traditional EGS plant.” Amongst the most exciting results were experiments investigating metal recovery using patented gas-diffusion electroprecipitation and electrocrystallisation (GDEx). As Hartai explains, “GDEx is a novel way to recover metals from dilute solutions. It enabled nearly complete recovery of the relevant metals present. The GDEx experiments are upscalable and preliminary economic feasibility calculations show positive results.”
Impact far and wide as well as deep
“A mathematical model of engineering subsystems enables stakeholders to simulate different scenarios and optimise systems,” says Hartai. A decision support tool that assesses economic feasibility from both the energy and metal extraction revenue streams will remain available on the website of MinPol (Agency for International Minerals Policy), a private company that participated in the project. As the project name suggests, CHPM2030 identified four pilot sites after screening Europe’s mineral belts for their EGS potential, and created a 2030 CHPM roadmap for exploiting them. Actions, targets and milestones were also established for 2050. An ambitious outreach campaign spread the word through numerous multimedia materials, social media and the dissemination channels of project partner the European Federation of Geologists. The innovative technology combined with extensive outreach and clear roadmaps should ensure widespread uptake. This will increase energy independence and enhance economic competitiveness with local extraction of strategic raw materials of industrial relevance.
CHPM2030, heat, geothermal, energy, power, metals, extraction, GDEx, EGS, enhanced geothermal system, heat exchanger, minerals, electroprecipitation, electrocrystallisation