August 09, 2011

Store CO2 Underground and Extract Electricity

This looks like a maze, but it's actually a schematic of a way to combine CO2 storage and geothermal energy production. Starting with CO2 on the left, follow the arrows to learn how the proposed pilot test will work.

A team led by Lawrence Berkeley National Laboratory (Berkeley Lab) scientists hopes to become the first in the world to produce electricity from the Earth’s heat using CO2. They also want to permanently store some of the CO2 underground, where it can’t contribute to climate change.

About a year from now, two nondescript shipping containers will be installed in a field in Cranfield, Mississippi. They’ll house turbines designed to generate electricity in a way that’s never been done before. If initial tests go well, the technology could lead to a new source of clean, domestic energy and a new way to fight climate change

The idea is to inject CO2 three kilometers underground into a sedimentary layer that’s 125 degrees Celsius. CO2 enters a supercritical state under these conditions, meaning it has both liquid and gas properties.

The CO2 will then be pulled to the surface and fed into a turbine that converts heat into electricity. Next, it will loop back underground and through the cycle again. Over time, some of it will be permanently trapped in the sediment. More CO2 will be continuously added to the system to keep the turbines spinning.

The technology could help offset the cost of geologic carbon storage, a promising climate change mitigation strategy that involves capturing CO2 from large stationary sources and pumping it deep underground. This enables the burning of fossil fuels without releasing the greenhouse gas into the atmosphere. But it’s expensive.

“Carbon storage takes a lot of power – large pumps and compressors are needed. We may be able to bring down its costs by generating electricity on the side,” says Freifeld.

It also offers a new way to tap geothermal energy, which is a tough sell in arid regions where every drop of water is spoken for. For more than a decade, scientists at Berkeley Lab and elsewhere have theorized that supercritical CO2 can be used instead of water. Their work has shown that supercritical CO2 is better than water at mining heat from the subsurface. But no one has tried to do it until now.

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