MEA and other materials used in the capture process, they found that life-cycle CO2e emissions doubled.
Key factors affecting natural gas CO2 emissions from natural gas facilities include plant efficiency and natural gas losses from production and distribution. Emissions for natural gas combined cycle (NGCC) plants had a small range of 469 to 518 g CO2e/kWh. A higher value of 608 g CO2e/kWh was reported for the only gas-fired plant evaluated (Hondo, 2005). CCS is not expected to have as large an impact on natural gas carbon emissions as it does for coal because upstream emissions are more significant in the natural gas fuel cycle. Two studies evaluated the future deployment of CCS with MEA for NGCC plants. Odeh and Cockerill (2008) found CCS reduced emissions from 488 to 200 g CO2e/kWh and Spath and Mann (2004) found emissions dropped from 499 to 245 g CO2e/kWh. The Spath and Mann (2004) result does not include CO2 emissions associated with production, regeneration, or disposal of MEA.
For nuclear technologies, the studies reviewed report values from 3 to 106 g CO2e/kWh, with all values except the low and high values clustered from 15 to 25 g CO2e/kWh. The low value of 3 g CO2e/kWh is from Vattenfall (2004) and the high value of 108 g CO2e/kWh is from Storm van Leeuwen and Smith (2008). The Vattenfall study used PA methods to analyze two Swedish reactors where 80 percent of the fuel enrichment was performed by centrifuge. The reactors were assumed to operate at 85 percent capacity with a life expectancy of 40 years. The Storm van Leeuwen and Smith (2008) study used EIO methods to analyze a nuclear facility located outside of Sweden with fuel enrichment via gas diffusion and an 82 percent operational capacity over a life expectancy of 30 years. The nuclear subgroup of the America’s Energy Future (AEF) Committee uses a narrower range of 24 to 55 g CO2e/kWh. The narrower range was developed by the nuclear subgroup of the AEF Committee to represent the CO2 emissions from the current fuel enrichment situation in the United States.
Fthenakis and Kim (2007) attribute most of the difference between low and high estimates on nuclear power to three factors: the energy mix of the country developing the plant, whether enrichment is via centrifugation or diffusion (diffusion tends to use 40 percent more electricity), and the type of LCA method used.