Transforming CO2 into revenue
Let’s think about CO2 as an asset or potential revenue rather than an atmospheric nuisance. Selling captured gas to oil companies or transforming it into salable materials and products could help offset the increased capture costs.
Many US CCS projects pump CO2 into drained oil reserves, using the method we referenced earlier, called enhanced oil recovery (EOR). The gas lowers the viscosity of the last dregs of oil, which can then be drawn out. But these projects are more demonstrations of storage than capture. The CO2 pumped underground comes from naturally occurring reservoirs or traditional industrial processes. At the right location, EOR projects can permanently store millions of metric tons of CO2 each year.
But many EOR projects do not completely store the CO2 because workers release small amounts of the gas trapped in the last glugs of oil pumped to the surface toward the end of the EOR project, according to Victor Der at the North America office of the Global CCS Institute. In Canada and the US, EOR projects might help spur full-scale CCS implementation because they develop some of the needed pipeline infrastructure and knowledge about safe underground storage. But some places in the world lack suitable oilfields for EOR, so geography and geology restricts this approach to carbon capture, utilization, and storage.
Another way to generate revenue from CO2 involves transforming it into a different salable product—specifically carbonates for cement production and bicarbonates in baking soda in a process called mineralization. Last June, BP and ConocoPhillips invested in Austin-based company Skyonic to help build a commercial-scale mineralization plant. When it opens in 2014, the plant will process about 15 percent of a nearby cement plant’s CO2 emissions.
The industrial process is based on reactions familiar to many high school chemistry students. First, carbon dioxide from flue gas dissolves in salty, alkaline water. The hydroxide base in the water transforms the CO2 into carbonate ions (CO3-2). Positive sodium ions in the water cling to the carbonates and form white powders. Stopping at this step, you have ingredients for cement. But push the reactions further and you can make baking soda (sodium bicarbonate, NaHCO3) purer than food-grade, like Skyonic does.
The market for baking soda is more lucrative than that for other carbonate products, says Skyonic founder and CEO Joe Jones. It can be used as an antacid for animal feed or eco-friendly sandblasting powder. Jones plans to sell hydrochloric acid produced during this process, too.
The plant will offset nearly 200,000 metric tons of CO2 otherwise used to mine and produce the same chemicals, in addition to the 75,000 metric tons of CO2 captured. By capturing carbon at a profit, Jones hopes to fund research and development so the technology becomes affordable for power plants.
His challenge is reducing the energy used to split water into the hydroxide base for mineralization. Currently, the overall energy penalty for mineralization is similar to carbon capture with amine solutions, Jones says.
Mineralization, however, has several advantages compared to amine scrubbing. Mineralization reactors remove flue gas contaminants, like mercury and sulfur- and nitrogen-containing gases, which often require separate scrubbers. The reactors can also utilize the less-concentrated flue gas directly from a cement or power plant.
Another company, Calera, is mineralizing CO2 to make cement-like building materials. And researchers at the University of Wyoming trigger mineralization using leftover ash from coal-fired power plants. They’ve tested their technology using samples of flue gas from a large power plant in Wyoming (Energy Procedia, DOI: 10.1016/j.egypro.2011.02.027).
Because mineralization is such a different technology than amine scrubbing, lessons learned from building these plants likely won’t transfer to other capture plants that create streams of CO2 to pump underground. Instead, it’s just another way to capture carbon.
Of the capture technologies that pull CO2 from flue gas once power plant fuel is burned, amine scrubbing is furthest along in development. The natural gas industry has proven the technology works. Now Rochelle and his research group are adapting it to work with the dirty flue gas from coal-fired power plants. They plan to test an amine scrubber at the US Department of Energy National Carbon Capture Center in Wilsonville, Alabama. The capture plant will receive flue gas from a nearby power plant on a scale equivalent to the emissions from a 0.5 MW power plant. That’s the capacity of the smallest power plant in the country in 2011, which supplies a correctional facility. Other researchers are already testing amine scrubbing on a similar scale at that site.
Pilot projects are planned across Europe to test amine scrubbers with emissions from the equivalent of 5 to 30 MW power plants. One in Houston, Texas, set to open in 2017 [PDF], should capture 90 percent of CO2 emissions from a 240 MW power plant. The captured carbon dioxide will be used to recover oil.
Regarding amine scrubbing for carbon capture, Rochelle says, "We’re five years away from having the technology ready to deploy, and we’ll be five years away until somebody tells us we have to."
Meanwhile, other large CCS projects under construction, like Gorgon on Barrow Island in Australia, are testing geologic storage and monitoring so there will be a safe place to store the CO2 once it’s captured.
The mechanics of carbon capture and storage are just one part of the battle over CCS. Technology, policy, and the market have to interplay in sync for CCS to work, Der says. They also influence financing and public acceptance, he adds.
To stem climate change, CO2 emissions must decrease. Renewable energy is only part of the solution, as we need to consider emissions from our current energy infrastructure too. Carbon capture and storage can be one way to reduce those emissions—once more of these systems are built, tested, and working on a large scale. And for now, a lack of a carbon policy and increased operating costs for a power plant equipped with CCS hinder that technology development in the United States.