Tamar Hallerman
GHG Monitor
09/28/12
A “promising” CO2 utilization technology that could also produce zero-carbon electricity has been able to make only limited progress in recent years due to the lack of a price on carbon, researchers said this week. In recent years, scientists have touted the potential for using captured CO2 as a working fluid for enhanced geothermal systems (EGS), or deep geothermal energy production. However, like most other carbon capture, utilization and storage applications, would-be developers have few economic options so far to purchase the large supplies of CO2 needed for operations due to the lack of incentive to capture emissions from power generation and industrial plants. “The technology is largely there, and we can see that it has a very large potential,” the University of Queensland’s Hal Gurgenci, an early leader in CO2-EGS research, said in an interview. “However, it’s not commercial because in order to do so you need to have carbon capture on coal-fired power plants because you need millions of tons of CO2. If you don’t have that, this concept will not work.”
EGS for power generation is a newer technology in itself. Now in its pilot testing phase with water or brine in projects in Europe, Australia and the U.S., the operations circulate the working fluids in a loop throughout the ultra-deep geothermal reservoirs, which are located more than a mile and a half underground, to help extract heat and raise it to the surface, where it can be run through a turbine to help generate zero-carbon electricity before being cooled and recirculated into the reservoir. However, while water is cheap working fluid, it is also sensitive to reservoir permeability, Gurgenci said, making the production process more difficult. Because of that, many researchers have welcomed the prospect of using supercritical CO2 as a working fluid because of its increased reservoir permeability, efficiency and other thermodynamic advantages. According to the Global CCS Institute, EGS with CO2 has the potential of storing 24 tons of CO2 per day per MWe of EGS.
Lack of Carbon Legislation Has Slowed Some Work
However, despite the technology’s potential, EGS with CO2 has largely been stunted in recent years, according to Gurgenci, due to the fact that most governments have not yet mandated capturing carbon emissions. EGS operations require millions of tons of CO2 during startup and throughout production. Given the sheer volume required, CO2 would have to be essentially free in order to become economic for EGS operations, according to Gurgenci, meaning that the price on CO2 would have to dramatically decrease via some sort of legislative driver. Gurgenci added that a CO2 source would need to be located near the EGS site so that CO2 could be constantly piped into the reservoir. To date, some smaller CO2-EGS research projects have been developed, but little has been proven so far in the field. In the In the U.S., a few companies have pitched pilot projects, but none have moved forward very far to date, according to the Global CCS Institute. Gurgenci said the Australian government has expressed interest in a 50 MW pilot project for 2022, but funding must be lined up in order to move forward.
Despite the uncertainties, Gergenci said CO2-EGS could be a boon to coal-reliant nations like the U.S. and Australia even in a carbon-restrained economy. “It is something that gives you a sort of ‘get out of jail free’ card for the usage of your coal,” he said. “You can continue to burn coal without emitting CO2 while also producing more electricity from geothermal at an acceptable cost. It’s a win-win situation.”
Mark Summers, a senior manager for renewable energy at Alberta Innovates, said CO2-EGS is a technology that could have great potential in western Canada. “It’s an area of increased interest in Alberta because of the push for climate change mitigation and greenhouse gas emissions reductions,” he said in an interview. “While we haven’t had any formal projects yet, it’s an area of interest for us and we’re continuing to engage technology developers, as well as potential up-takers of the technology, to try and push things forward in the province.” Alberta Innovates is a corporation owned by the government there that invests public money in new energy technologies on behalf of the province. Summers said the group is “in the position to potentially invest” in a CO2-EGS demonstration. “I think in the coming three years, we hope to find a good opportunity to invest in,” he said.
