This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Carbon Capture and Sequestration (CCS) could be a key technology option in reducing carbon dioxide emissions from the world’s fossil fuel power plants. But, the technology has become better known for its setbacks than successes in recent years. This week revealed a glimmer of hope for CCS supporters as the U.S. Department of Energy (DOE) announced that construction has begun on the world’s largest post-combustion CCS facility.
The Petra Nova project is located near Houston, Texas and is a joint venture between the U.S. DOE, NRG Energy and JX Nippon. With a current price tag topping $470 million, the project is expected to capture up to 90% of emissions from 240 MW of electricity generation capacity.
The idea behind CCS technology is that carbon dioxide (CO2) emissions that would normally be released in the combustion process are instead captured and stored. These emissions can be captured before or after the combustion process, depending on the technology and approach used. As a result, CCS can “clean up” fossil fuel powered plants, including the coal plants that account for 37% of the U.S. electricity supply.
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CCS technology is frequently criticized for two reasons: cost and effectiveness. The former is a big question mark, with infrastructure cost overruns being sited for many project cancellations. Furthermore, CCS technology uses energy to both capture and store carbon, creating a parasitic load on the system that results in higher production costs for the power plant.
The effectiveness question comes into play with the concept of “permanently” storing CO2 underground. The emissions that are captured by the CCS system can be either:
1) stored immediately after capture and/or
2) used in enhanced oil recovery (EOR) before being stored.
In both cases, concerns exist as to whether or not the greenhouse gas can be stored permanently, without significant leakage over time. In the case of EOR operations, additional concerns exist regarding potential leakage from these wells and the overall CO2 balance of EOR operations (i.e. using CO2 to produce products that will later lead to more CO2 emissions…).
The Petra Nova project might overcome some of the existing cost concerns through its use of technology that has already been tested in another DOE-sponsored project. That 3-year pilot-scale test project in Alabama successfully captured more than 150,000 metric tons of CO2 per year from a coal power plant using an advanced amine-based CO2 capture system to gather the carbon emissions that are released in the power plant after combustion.
In terms of effectiveness, the DOE reports that the amine-based solvent used in this system will effectively strip these carbon emissions from the plant’s flue gas stream (i.e. post-combustion) before it is released into the atmosphere using less energy (a.k.a. with a smaller parasitic load) than previous designs. The captured emissions will then separated from the solvent, compressed, and then transported via pipeline to the West Ranch oil field in nearby Vanderbilt, Texas for enhanced oil recovery (EOR). The project will include a monitoring program to determine if the CO2 actually remains in the well.
Graphics courtesy of NRG and the US Department of Energy