Thursday, 3 May 2012

Carbon Capture and Storage: What's the Big Deal?

The U.S. Department of Energy has released the North American Carbon Storage Atlas (NACAS).  The atlas is a compendium of geologic sites across Canada, the United States and Mexico where it is theoretically possible to store CO2 produced from stationary sources like power plants, cement factories and the like.

The idea is that this atlas would be used to find and evaluate carbon storage sites close to big greenhouse gas emitters across the continent.  This, in turn, would help to improve the economics of carbon capture and storage (CCS) by reducing the logistics costs associated with transporting millions or billions of tonnes of liquified CO2 long distances.

Carbon capture and storage is one of a number of potential tools we can wield in the fight against climate change.  The technology has many variants, but the basic approach is to use chemical or mechanical systems to capture CO2 from exhaust gase. Another approach is to chemically remove and capture the CO2 from the fuel before it is burned. In either case, the CO2 is then liquified under pressure, transported to a geologic storage site, and injected into underground basins, where it intended to remain for hundreds of years.  After all, CO2 from burning fossil fuels only contributes to global warming if the gas is released to the atmosphere.

NACAS researchers estimate a potential storage capacity of 136 billion tonnes of CO2 in oil and gas fields (where CO2 injection can also release the last remaining oil, which ironically will release more CO2 when burned); 65 billion tonnes in coal fields; and 1.7trillion tonnes in saline reservoirs.

How does that compare to current emissions?  In 2010 U.S. greenhouse gas emissions were approximately 6 billion tonnes CO2 equivalent, with 2.25 billion tonnes from electric power plants. So there is enough potential storage in oil, gas and coal fields to storage 88 years of CO2 from power plants, at today's rates of emissions.  If coal consumption increased as a result of population growth, economic activity or the lack of viable alternatives, this storage potential would not go as far.  And while saline reservoirs have the potential to hold several centuries' worth of CO2, appreciable injection rates can only be achieved at present with hydraulic fracturing (or "fracking"), a process that has caused tremendous concern when used to extract shale gas.

The North American Carbon Storage Atlas therefore serves a useful role in highlighting the theoretical potential of CCS in the fight against climate change.  However, it is still not clear whether CCS can play a practical role.  One rule of thumb is that commercial-scale CCS would consume approximately 20% of a power plant's output, which means that each unit of electricity sold to end users would be that much more expensive.  That figure does not include the cost to transport the liquid CO2 to the injection site and pump it into a storage reservoir 3 kilometers deep.  These cost considerations raise doubts about the potential of CCS at a time when wind and other clean energy technologies are falling rapidly in cost, and with governments unable or unwilling to invest billions in pilot schemes to perfect the technology.

The debate over CCS has now shifted to the U.N. Clean Development Mechanism, where proponents are exploring the use of carbon credits sales to help overcome the financial and technical barriers to implementation. Work continues on this front, with the CDM in its CMP 7 report in Durban agreeing to explore ways to develop acceptable rules governing long-term liability, site safety, permanence of the emission reductions, and a host of other issues.

I generally advocate a team approach to carbon reduction, where we pursue multiple emission reduction measures at the same time.  However, CCS is potentially so big that, despite its challenges it bears watching closely.  Stay tuned.