Aside from emitting less carbon dioxide (CO2), switching much of
the Texas power generation portfolio from coal-to-natural gas could
also conserve a lot of water.
That’s the crux of a newly-released report from researchers at
the University of Texas at Austin.
“Replacing Texas’ coal-fired power plants with natural gas combined
cycle plants (NGCCs) would reduce annual freshwater consumption in
the state by an estimated 53 billion gallons per year, or 60% of
Texas coal power’s water footprint, largely due to the higher
efficiency of NGCCs,” according to the report.
That’s enough water conserved to supply a million people, assuming
140 gallons of daily consumption per person, according to the
report.
The study, “Can switching fuels save water? A life cycle
quantification of freshwater consumption for Texas coal-and natural
gas-fired electricity,” was released Oct. 8. Report authors are
Emily Grubert, Fred Beach and Michael Webber.
Study looks at plant cooling water use and fuel extraction issues
The study looks at the water intensity of fuel extraction for Texas
lignite coal, conventional natural gas and 11 unconventional natural
gas basins in Texas. The study also touched upon “second-order
impacts associated with multi-stage hydraulic fracturing” or
fracking.
“Despite the rise of this water-intensive natural gas extraction
method, natural gas extraction, appears to consume less freshwater
than coal per unit of energy extracted in Texas because of the high
water intensity of Texas lignite extraction,” according to the
report.
Natural gas has been grabbing a larger ratio of new power generation
capacity largely because of its falling price and smaller emissions
footprint compared to coal, the report notes.
The relative water intensity of coal and natural gas fuel cycles has
received less attention, the report authors say. Texas produces all
of its natural gas and about a third of its coal energy, primarily
lignite, according to the report. As a result, Texas is a net
importer of coal.
Water use for energy is an increasingly big deal in Texas. Virtually
all of Texas experienced drought at some point in 2011 and dry
conditions left over 11 GW (about 1%) of power generation capacity
at risk of curtailment due to water limitations. Securing water
rights has become a major challenge for new power plants, according
to the plant.
This limited life cycle analysis assesses freshwater consumption
associated with fuel extraction, power plant cooling and pollution
controls, which together typically account for over 95% of
electricity-related freshwater consumption, according to the study.
Included in the evaluation of water needs for pollution controls are
carbon capture and storage (CCS) systems, which are not yet
operating in Texas but could be installed in response to future CO2
control policies.
The study says about 60% of Texas’ coal-fired generation uses once
through cooling, with the remaining 40% using wet recirculation.
Texas’ NGCC generation is overwhelmingly cooled with wet
recirculating systems (over 90%), with the remainder using once
through (about 5%) or air cooling.
Texas coal-fired power generation accounted for an estimated 90
billion gallons of freshwater consumption in 2007 from its full fuel
cycle, including about 10 billion gallons from mine dewatering.
Generating the same amount of power from Texas fleet-average NGCC
units would consume 37 billion gallons of Texas freshwater,
according to the report.
The study found that Texas coal extraction consumes over seven times
as much freshwater per KWH as Texas natural gas extraction. This
finding is somewhat unexpected given the amount of water used for
hydraulic fracturing, the report authors said.
When consumption from dewatering coal mines is excluded, Texas coal
and Texas natural gas extraction consume roughly the same amount of
freshwater per kWh. One major reason for the similarity is that
existing NGCCs are about 30% more efficient than pulverized coal
units and thus require less fuel to produce electricity.
This research was funded by the George and Cynthia Mitchell
Foundation, the U.S. Department of Energy and the U.S. National
Science Foundation’s EFRI-RESIN (Emerging Frontiers in Research and
Innovation for Resilient Infrastructures) program.
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