If the models are correct that global carbon emissions will keep rising until at least 2040 then carbon capture and storage (CCS) is essential. And most of the vast amounts of CO2 we must capture won’t be “utilised” as it’s more than we can possibly use. So storage is an essential part of the equation, explains Jim Conca. He scopes out the problem before looking at two innovations that can bring costs down and bring the technology one step closer to commercialisation and therefore take off. For capture directly from fossil power plants, a solvent called EEMPA can absorb carbon far better than the usual water-based ones that must be heated and cooled, using up energy and money. Costs can be cut by 20%. The casing and components are plastic, not steel – saving more money – and can be swapped into existing CCS systems. For storage, injecting the CO2 (released from the EEMPA) into underground volcanic rock turns it into minerals over a two year period, where they will stay. Far better than storing it underground as a gas.
Let’s face it – we are not decarbonising at all. Global carbon emissions are still increasing and all serious modelling shows that will continue at least until 2040. Not surprising since we are still building coal plants like crazy in Africa and Asia, and gas plants in the developed world.
In all fairness, those coal plants are being built to raise half a billion people up out of poverty, so it’s not like we can say no.
But even if we can’t decarbonise in time to stop the worst of global warming, we have to do something. And that is capturing the carbon, either directly from the atmosphere or from where it’s produced before it gets away into the atmosphere.
Then we have either use it for something or put it someplace where it won’t get back out quickly.
This set of strategies are referred to as carbon capture and sequestration. It is better to capture the carbon before it gets into the atmosphere, but there are things we can do if we fail in that as well.
EEMPA solvent for carbon capture
Enter PNNL. Researchers from the U.S. Department of Energy’s Pacific Northwest National Laboratory – along with partners from Fluor Corp and the Electric Power Research Institute – are using the unique properties of a solvent, known as EEMPA (N-(2-ethoxyethyl)-3-morpholinopropan-1-amine), that allow it to sidestep the energetically expensive demands incurred by traditional solvents (see figure below).
Traditional methods use aqueous amine compounds to absorb CO2 from flue gases which are later stripped of the gas, then compressed and stored. But because they’re water-rich, they must be boiled at high temperatures to remove CO2 and then cooled before they can be reused, driving energy requirements and costs up.
However, water-lean solvents like EEMPA can significantly reduce both energy and capital costs by about 20%, especially when the solvent is chemically changed to be less viscous (less sticky like water versus honey), in fact, a hundred times less viscous (see figure below).
Plastic components, not steel
The researchers also switched from steel components to plastic. Plastic is lighter, doesn’t corrode anywhere near as much as steel, doesn’t sorb the solvent itself like steel and can have much greater surface area for the chemical reactions to occur, making it much cheaper and easier to use.
Next year, the PNNL team will produce 4,000 gallons of EEMPA to test in the facilities at the National Carbon Capture Center in Shelby County, Alabama, in a project led by the Electric Power Research Institute in partnership with Research Triangle Institute International.
They will continue testing at increasingly larger scales and further refining the solvent’s chemistry, with the aim to reach DoE’s goal of deploying commercially available technology that can capture CO2 at a cost of $30 per metric ton of CO2 captured by 2035, down significantly from the present $58.30 per metric ton.
Most carbon will have to be stored
When we do capture the carbon, we can use some of it to produce products like methanol (see figure below) that can be used to make various things like fuels, synthetic fabrics, plastics, paint, plywood, pharmaceuticals and agrichemicals.
But the huge amounts of CO2 we have to capture to make any difference to the climate is more than we can possibly use. So we need to sequester it, most likely deep in the ground in a way that is stable for geologic time.
Turning CO2 into rocks
It turns out that PNNL has also addressed this issue. Dr. Pete McGrail, leading a group of scientists, has found the ideal rock, and has figured out how inject carbon dioxide into the rock so that it turns into carbonate rock.
Just inject thousands of tons of CO2 dissolved in water a half-mile down into a particular vesicular volcanic rock, a basalt, so that the CO2 precipitates as new limestone-like rock. CO2 precipitates naturally as limestone and other carbonate rocks. But the PNNL project demonstrated how to reduce the time to do this from a thousand years to just two.
It’s critical that it forms a mineral, not just stays as gas. Injecting lots of gas and liquids into the shallow crust sometimes causes earthquakes. But if the injected CO2 turns into a solid mineral at depth in the rock, then the volume of the CO2 would be reduced to a small fraction of what it is as a gas. It would be stable for geologic time and would not cause earthquakes.
McGrail and his team found such a rock formation and performed a field test site in it that worked great (see figure below). It took place at Wallula, in southeastern Washington, where thousands of feet of basalt erupted over millions of years. The geochemistry of these rocks is ideal for this process.
The basalt is pockmarked with holes like a sponge, and the CO2 moves through the holes, reacting with water and some elements in the basalt, like calcium, iron, magnesium and manganese, to form a new mineral.
The project injected almost 1,000 tons of CO2 dissolved in water a half-mile down into these basalt lava flows. After 24 months, the CO2 had formed into a carbonate mineral called ankerite, Ca(Fe,Mg,Mn)(CO3)2, a calcium, iron, magnesium, manganese carbonate mineral similar to the calcite and dolomite minerals that make up limestones, carbonate reefs and other carbonate rocks on Earth.
Fortunately, the United States has a lot of basalts, enough to take care of this problem for eons, as do India and China, two countries with huge and rising CO2 emissions.
James Conca is an earth and environmental scientist and a regular contributor to Forbes magazine