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Natural Gas with Carbon Capture (CCUS)

Natural gas with carbon capture  uses post-combustion capture technology on natural gas power plants.  For the US to meet mid-century near zero carbon emissions, CCS will need to be installed not just on coal, but natural gas too.  

The world's hunger for natural gas has dramatically increased of late with the recent "shale gas revolution" in the US. This unconventional gas resource has brought about extremely low gas prices in the US, changed the dynamics of the global energy market and spawned the desire of other nations to mimic the US's push for unconventional gas and new dry gas discoveries. As countries move away from coal, or shutter their nuclear power plants, the global demand for gas has skyrocketed.

Were it not for climate change, this transition might be all well and good. Unfortunately, however, burning natural gas creates carbon dioxide. In addition, unburned methane is a vastly more potent greenhouse gas than carbon dioxide itself, and so gas discharged upstream of its end use adds significantly to the overall climate change impact of the fuel.

Post-combustion capture (PCC) technology is commercially available for natural gas combined cycle plants. The technology faces fewer technical hurdles than coal-PCC in part because the emissions from gas contain fewer contaminants. At the same time, new capture technologies are being developed (for example, at the Technology Center Mongstad, Sargas and Next Power) that could drive current natural gas CCS costs down.

If the US were to close all of our existing coal power plants and replace them with modern NGCC, for example, we would reduce our national CO₂e emissions by only about 16 percent. The benefit of natural gas is offset significantly by direct emissions of unburned methane released upstream of the point of end use (e.g., gas wells, pipelines, etc.). As a result, simply substituting natural gas for other fossil fuels appears unlikely to significantly reduce climate forcing.

Switching fuels does not solve the carbon dioxide emission challenge. To meet mid-century climate change targets, carbon dioxide emissions from natural gas combustion must be captured and sequestered in deep geological formations (essentially returning the carbon to the Earth's crust, from whence it came). Using carbon capture and sequestration technology, a natural gas power plant would emit only about 5 percent of the carbon dioxide of a new conventional coal power plant without CCS. This represents a significant emissions reduction potential.

Gas will increasingly displace some coal.  But even if all coal plants were replaced with natural gas, the reduction in CO₂ would be about 50%. . Natural gas will not be a bridge to a low-carbon future unless critical measures are in place to minimize its problems, and maximize its advantages. Therefore CCS on gas is important.

Natural gas can be an advantageous fuel for power generation with CCS for several reasons:

• Natural gas combined cycle combustion turbines capital costs roughly one third those of conventional coal power plants.

• NGCC produce roughly 60% less CO₂ than conventional coal for an equivalent amount of electricity generated, CCS results in considerably less CO2 to capture, compress, and sequester with gas. 

• Natural gas appears to be quite a promising fuel for advanced technologies like solid oxide fuel cells (“SOFC”), which may be able to both operate at extremely high efficiency and inherently separate CO₂ from other exhaust gases.   Utilizing coal in a fuel cell is a much more daunting technological prospect (though there are companies making the attempt).