A Holistic Approach to Sustainability for Power Plants

A Holistic
Approach to Sustainability for Power Plants

There has been a great deal of focus on methods to
capture and manage CO₂ emissions from coal-fired power plants. Much
of this work has focused on the techno-economics of the process as well as the
feasibility of using capture processes to retrofit existing power plants. There
also has been extensive discussions regarding ?fuel switching?, i.e.
transitioning a plant from using coal as a fuel to the use of natural gas.

It is important to note that the power plant is simply
one component within the coal supply chain. It is also important to consider
going beyond the management of air emissions (i.e. CO₂, primary
pollutants) and consider solid and liquid waste generation. For example, coal
fines and tailings can be a significant solid and liquid waste issue when
considering the ?upstream? portion of the coal supply chain. If carbon capture
and sequestration is performed, ?downstream? management of saline water
displaced from aquifers as a part of the sequestration process can be a major
concern. It is also well documented that plants outfitted with carbon capture
will consume more water than non-capture plants.

A number of studies and activities have begun to
address factors that influence the overall sustainability of the coal supply
chain (e.g. Pacific Northwest National Laboratory, Bettercoal.org, Deutsche
Bank Group, US EPA).  The tools used by these groups include Life Cycle
Assessment (LCA), self and third party assessment toolkits, as well as
analytical models and databases. Work has also been performed by groups, such
as EPRI, to include sustainability metrics as part of the performance metrics
for power plants. These sustainability metrics also include mitigating the
impact of the plant on the natural and cultural history of the surrounding
community.

The Illinois Sustainable Technology Center (ISTC) and
Illinois State Geological Survey (ISGS), as part of the Prairie Research
Institute within the University of Illinois, has undertaken efforts throughout
the coal supply chain in order to improve the sustainability of Illinois based
coal-fired power plants. Both the ISTC and ISGS work in conjunction with their
sister surveys, the Illinois State Water Survey (ISWS), Illinois State
Archeological Survey (ISAS), and Illinois Natural History Survey (INHS), to advance
the sustainability of coal-fired power plants.

Some of the ?upstream?
sustainable activities undertaken have been to manage ultra-fine coal and coal
tailings at the coal preparation plant. A non-conventional approach to
dewatering ultra-fine coal and coal tailings utilizing an osmotic gradient has
been demonstrated to be a simple, robust, and low cost alternative. The further
development of this dewatering technology could play an important role in
reducing the volume of coal tailings currently disposed to holding ponds.
Additionally, it could enable recovery of a significant proportion of the
ultra-fine (< 105 µm) coal particles (constituting about 10% of total coal
production) through dewatering of fine coal froth concentrate that is currently
wasted in Illinois on an annual basis. The recovered water could be recycled
back to the coal preparation plant thereby reducing usage of valuable fresh
water.

?Downstream? sustainable
activities include producing fired-clay bricks with 40% to 50% substitution of
fly ash and bottom ash and autoclaved aerated concrete (AAC) blocks containing
around 70% fly ash. Other downstream sustainable activities include the use of
ash pond effluent for reuse within the process, evaluating Forward Osmosis ?to
reduce cooling load while simultaneously desalinating ash pond water and FGD
scrubber blow down.

Planning activities
surrounding carbon capture and sequestration for Illinois based coal-fired
plants have been part of the planning process. The potential to retrofit plants
with a novel capture process has been assessed. The subsequent sequestration of
the captured carbon in aquifers would then
result in the formation of brines with TDS greater than 180,000 mg/L. These brines can be repurposed for use as cooling tower
make-up by using advanced water integration within power plants.

The overall
impact of implementing these changes throughout the supply chain can be
evaluated.  This approach provides for a means to examine the supply chain from
a systems level, as compared to optimizing a portion of the supply chain.