Analysis of CO2 Emissions from Unconventional Fossil Fuel Resources
- Evaluate life-cycle greenhouse gas emissions from several oil sands and shale processes and compare these to conventional liquid-fuel production processes.
- Evaluate opportunities to reduce life-cycle CO2 emissions from these unconventional resources, such as the use of oxygen firing in upgrading and refining processes for CO2 capture.
- Develop a tool for predicting life-cycle CO2 emissions for these opportunities.
One important selection criterion for the nation’s energy supply in the future will likely include its life-cycle carbon footprint. The state of California has already adopted a carbon-based fuel standard, and similar standards are currently being discussed in several states. Consequently, the investigators are evaluating life-cycle greenhouse gas emissions (GHG) from several oil sands and shale processes and opportunities for reducing GHG emissions.
As a first step, the investigators are gathering and summarizing available data on life-cycle GHG emissions from a variety of oil sands and shale liquid-fuel production processes. It can be challenging to compare life-cycle estimates of GHG emissions from the production of transportation fuels because of differences in the functional unit (i.e., barrel of raw bitumen, barrel of synthetic crude, energy content), which processes are included in the assessment, (i.e., construction of the upgrading plant, transportation between the upgrading and refining facility, reclamation processes, etc.), and lack of detail on assumptions, conversion factors, and fuel quality. The figure below provides a comparison of life-cycle, well-to-pump GHG emissions from gasoline, oil sands, and oil shale processes. A summary of published ranges is listed above each column. For oil shale in general, estimates vary more widely (38 – 180 g CO2 eqiv/MJ) than for liquid fuels produced from petroleum or from oil sands because oil shale is not produced commercially in the U.S. and because of uncertainty over the amount of CO2 released from minerals in the oil shale during processing. Note that the high estimate for oils sands emissions (* 55 g CO2 eqiv/MJ) is the upper estimate for an integrated gasification process.
Because of concern over GHG emissions and the resulting carbon-based fuel standards and because unconventional fuel sources tend to have larger GHG life-cycle emissions than conventional petroleum-based sources, there is significant interest in reducing GHG emissions from unconventional fuel sources through efficiency improvements and carbon capture and sequestration (CCS). Estimates of CCS’s potential for reducing GHG emissions vary widely. For example, investigators suggest that approximately 50% of CO emissions from oil shale could be reduced through CCS, while a recent report from the World Wildlife Fund suggests that CCS will have limited ability to reduce GHG emissions from Canadian oil sands operations.
The refining industry, as the third largest stationary source of GHG emissions globally, is evaluating technologies, such as oxyfiring, for GHG reduction. Oxyfiring is a promising technology for reducing the CO2 footprint from this industrial sector, but it requires a significant amount of energy to generate oxygen in an air separation unit. We are currently evaluating the potential for reducing life-cycle GHG emissions from a refinery employing oxy-fuel combustion for CO2 capture in its boilers and process heaters. This evaluation includes the additional GHG emissions associated with the power required for air separation and CO2 handling; the fuel savings from oxyfiring compared to air firing; and the upstream GHG emissions associated with the additional fuel requirements.