Argonne LCA study finds many alternative fuels consume more water than petroleum and natural gas fuels
Researchers at Argonne National Laboratory have analyzed the water consumption for transportation fuels in the United States using an extended lifecycle system boundary that includes the water embedded in intermediate processing steps.
In a paper published in the RSC journal Energy & Environmental Science, they compared the water consumed per unit energy and per km traveled in light-duty vehicles. They found that many alternative fuels consume larger quantities of water on a per km basis than traditional petroleum and natural gas pathways. The authors concluded that it will be important to consider the implications of transportation and energy policy changes on water resources in the future.
Energy production processes consume water resources and accelerate fluxes of water from land surfaces to the atmosphere. Increases in population, energy and food demand now strain previously abundant sources of water. For these reasons, it is important to characterize the relationships between consumption of water resources and the production of energy.
… Transportation fuels are produced using interconnected pathways composed of numerous individual production processes. Many of these production processes generate intermediates that are later consumed for the ultimate purpose of generating transportation. Each process in a pathway may consume water resources, so it is necessary to analyze the water consumed throughout the pathway to understand the net impact that a fuel will have on water resources. For example, biodiesel and ethanol production consume water in both the agricultural operations used to produce biomass and in the conversion of the biomass to fuel; thermoelectric power generation consumes water in fuel cycle operations and cooling in thermoelectric power plants; hydroelectric power plants require water-consuming reservoirs to generate electricity; hydrogen fuel cells consume water as a feedstock for the fuel and for cooling excess energy generated by the process; petroleum and natural gas require water for recovery and subsequently for processing.
… LCAs [life cycle analysis] of water consumption are challenging to perform due to differences in definitions and terminology associated with water data. … The goals of this study were to develop a comprehensive baseline LCA of water resource consumption associated with transportation fuel production, highlight the uncertainties and implications in the results, and identify important outstanding gaps in the data. There have been other LCAs performed on water consumption associated with transportation; however, these analyses ignored the water embedded in many intermediate resources such as transportation fuel and intermediate chemicals or utilized economic input–output modeling to fill process data gaps.—Lampert et al.
The Argonne team developed an extensive inventory of process-level water consumption factors for the major transportation fuel pathways in the US consistent with the structure in the lifecycle analysis tool GREET. They used the inventory with the GREET framework to estimate the anthropogenic-induced water consumption associated with the various transportation fuels.
|Well-to-wheels pathways for transportation fuels and passenger vehicles analyzed by Lampert et al.. Click to enlarge.
System boundaries for the life cycle water consumed in the production of the transportation fuels in the study included mining and recovery operations; agricultural production of biomass; agricultural chemicals manufacturing; biofuel conversion; crude oil and natural gas refining and processing, and transportation and distribution. Life cycle water consumption was computed for each fuel pathway using the 2014 version of GREET.net.
Their findings included:
Fossil fuel pathways generally have the least impact on water resources. Petroleum-based gasoline and diesel consume slightly more water than CNG because of the water consumption associated with enhanced recovery technologies.
Corn and soy biofuel production show the largest water consumption impact among all the fuels with the exception of electricity from hydropower. Water consumption associated with irrigation for a particular crop may be much less than or much greater than the US average, they noted.
electricity generation pathways have both the smallest (wind) and largest (hydropower) impact on water resources. Thermoelectric power generation pathways consume more than twice the water of fossil fuel pathways primarily for waste heat dissipation.
Using dry cooling technologies would bring electricity water consumption estimates into a similar range as the baseline fossil fuels, although these technologies carry both a capital and energy penalty.
More than 70% of this water is associated with evaporation from hydropower reservoirs. Because electricity is a fundamental input for essentially all the other pathways, a detailed analysis of the water consumption associated with hydropower is in need of further characterization, the researchers said.
Pathways for centralized production of hydrogen fuel showed similar water consumption footprints to the thermoelectric pathways on an energy basis. A large portion of the total is associated with water embedded in electric compression than can be traced to hydropower generation. Processing and cooling constitute the other major contributors to the H2 pathways.
In terms of water liters/100 km, compressed natural gas vehicles show the lowest burden on water consumption—the majority of the water is associated with electric compression of the fuel and not with the recovery process. Reforming natural gas to H2 for use in a FCEV more than doubles the water consumption intensity of transportation.
Coal or biomass-based gasification in central facilities is expected to consume a similar amount of water as the SMR-based H2 pathway.
BEVs were estimated to consume almost twice the water as the E10 baseline on average in the US. However, electricity-based transportation exhibits high variability depending on the regional electricity mix.
|Life cycle water consumption (L per 100 km) associated with transportation in light-duty vehicles from select pathways. Lampert et al. Click to enlarge.
Moves towards alternative fuels appear to have a greater impact on water resources than fossil fuels. Energy and environmental policy should consider the implications of alternative vehicles on water resources when planning changes to the transportation and energy infrastructure. The values outlined in this study should not be interpreted as absolute inputs for specific projects since many processes (e.g., agriculture, mining) exhibit high degrees of spatial and temporal variability. Actual projects must therefore be evaluated on their specifics and not on national or regional averages.—Lampert et al.
The research was supported by the Bioenergy Technologies Office, Fuel Cell Technologies Office, and the Vehicle Technologies Office of the Department of Energy’s Office of Energy Efficiency and Renewable Energy.
David J. Lampert, Hao Cai and Amgad Elgowainy (2016) “Wells to wheels: water consumption for transportation fuels in the United States” Energy & Environmental Science doi: 10.1039/c5ee03254g