Handbook of Energy Storage for Transmission or ... - W2agz.com

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Unresolved issues
Several advances in the CAES technology have yet to be demonstrated or tested in the field
environment. The following concepts offer significant theoretical advantages but require
practical validation:
• Demonstrate air storage in porous rock and in hard rock storage formations
• Demonstrate surface piping for air storage CAES application
• Demonstrate the storage of thermal energy -- recover the thermal energy from the heat of
compression to reheat the air withdrawn from storage many hours later
• Demonstrate a “hybrid” CAES plant
Summary of Innovative Development Efforts
The conventional single-shaft configuration for a CAES plant was used for the McIntosh and
Huntorf projects. The compressors, motor/generator, and expanders are all on the same shaft,
separated by clutches. This low initial capital cost concept requires only a single motor /
generator that supports both the compression and power generation cycles. The expanders can
be used to start the compressor train. The advanced recuperator used in the McIntosh plant is a
necessary component to reduce the heat rate, and the plant is operating much of the time.
Dresser-Rand is a promoter of the conventional configuration as well as other plant
configurations.
OEMs and developers are also promoting several innovative CAES plant concepts; the
innovation lies in the use of present day turbo-expanders, compressors, new thermal cycles,
different turbomachinery configurations, and different component selection. The innovative
development efforts are summarized in Table 6 and described in the text below.
• Innovative Concept 1 -- This multi-shaft concept includes a reheat expander train (with a
recuperator) driving the electric generator for peak power generation and a number of
parallel independently operating motor-driven intercooled compressors trains for charging
the underground storage. This concept has higher capital costs but provides significant
operating flexibility. This concept is currently under consideration for a number of projects.
Both Dresser Rand and Alstom commercially offer this configuration.
• Innovative Concept 2 – In this concept, a high-pressure recuperator is used instead of the
high-pressure combustor in the expansion train. The only combustor is a conventional lowpressure
combustor installed upstream of the low-pressure turbine. This concept eliminates
the high-pressure combustor, which is a relatively new and technically challenging
component and is a significant source of NO x emissions. Alstom is promoting this concept
for 300-400-MW e CAES plants.
Compressed Air Energy Storage (CAES) Page 21