IEEE Power & Energy Magazine - November/December 2014 - 88

Part of our target 4 research and analysis addresses the
ability of various turbine technologies to provide fuel switching "on the fly." in theory, new dual-fuel gas turbines can
switch from gas to liquid fuel and back again while maintaining operations. in many cases, however, the units must be
throttled back from 100% output to facilitate the switchover.
We have therefore assessed the response of gas-only combustion turbines when gas supply pressures fall below design levels. in some cases, derating or tripping may not be a direct
consequence of pressure sensing. Many gas turbines can operate stably at part load even if there is insufficient pressure for
full load. in a situation examined for target 3, for example, a
trip may occur following a rapid pressure loss even if the final
pressure is sufficient to sustain steady-state operation-not as
a result of a control action initiated by a pressure measurement
but rather due to flame dynamics in the combustors. Prominent
manufacturers have supported eiPc's research objectives by
providing information on the responsiveness of gas turbines to
pressure variations and the ability of aeroderivative and frame
gas turbine units to switch to liquid back-up fuel automatically
in the event of a low-gas pressure signal. Most gas turbines
can be supplied with an autotransfer capability triggered by a
low-gas pressure signal that would switch the unit from gas
to liquid backup fuel. this transfer should occur with no need
for operator interaction, as long as the backup fuel system is
operational and not disabled for maintenance or other reasons.
as part of the target 4 deliverable, Lai prepared a technical
summary of the fuel-switching capabilities of various turbine
units and an estimate of the reaction time required for each
turbine type to switch from natural gas to oil.
an analysis of the liquid fuel market was performed, including the ability to provide backup fuel for dual-fuel power plants
on a routine basis and limitations on that ability. Lai investigated the key infrastructure planning and operational issues
surrounding liquid backup fuel storage and delivery capacities,
delivery system flexibility for meeting short- and long-term
demands of interruptible service customers, and costs and barriers associated with expanding oil infrastructure. We subdivided
liquid fuel types by resupply option, from tanker trucks and
barges to fixed pipelines from tank farms to the power plants,
and provided perspective on how power plant oil refill efforts
affect the petroleum delivery system when seasonal constraints
tax the ability of truck haulers and barges to meet the coincident
requirements of high-priority rci customers while replenishing
oil inventories at power plants in metropolitan areas.
Barriers to the use of alternative fuels were examined-
for example, air permit restrictions on liquid fuel operation
and siting restrictions on liquid fuel storage tanks. drawing on Lai's experience on behalf of the PPas, generation
companies, electric distribution companies, and state regulatory bodies, we defined the operational issues associated
with liquid fuel inventory management. the cost of incorporating dual-fuel capability was defined on a locational
basis and included 1) the incremental capital cost for tanks,
fuel inventory, burners, controls, and so on, 2) the loss of
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output, efficiency, or dispatchability, and 3) secondary cost
considerations of property taxes, insurance, and so on, as
well as other financial components.
another integral task that was part of our target 4 analysis pertained to the relative economics of dual-fuel capability versus incremental firm transportation to satisfy the PPas'
fuel assurance objectives. drawing from the frequency and
duration analysis conducted for target 2 for the array of case
sensitivities related to different energy futures and natural gas
prices, Lai compared the annuitized cost of liquid fuel capability versus incremental firm transportation, where locational
constraints are likely to preclude reliable plant operation on
natural gas under nonfirm transportation arrangements.

Conclusions
the research and analysis that made up the four-part target
study funded by the doe have provided the six PPas with
valuable technical insights into risk factors affecting the delivery of natural gas to power plants across the study region.
experience shows that the risk factors are not fixed constructs:
they are constantly changing in response to economic, regulatory, technological, and market dynamics. these dynamics
can exacerbate gas infrastructure constraints, thus heightening
concerns over electric reliability. the ebb and flow of gas-electric interdependencies are motivating the PPas to maintain a
variety of planning tools with which to safeguard reliability
through rigorous study, the results of which inform stakeholders what's at risk, the magnitude of the risks, where the risks
are, and what to do about them.

Acknowledgments
the authors wish to thank John P. Buechler, president of the
eiPc steering committee, and david a. Whiteley, eiPc
project manager, for their support and leadership regarding the formulation of this approach. We also acknowledge
the technical contributions of Lai's Matthew J. decourcey,
senior consultant, and alex Mattfolk, consultant, in the preparation of this article.

For Further Reading
eastern interconnection Planning collaborative. (2014).
gas-electric. [online]. available: http://eipconline.com/gaselectric.html
Ferc, "Winter 2013-2014 operations and market performance in rto and isos," Ferc staff presentation to the
commission, tech. rep. ad14-8-000, apr. 1, 2014.

Biographies
Richard Levitan is with Levitan & associates, inc., Boston,
Massachusetts.
Sara Wilmer is with Levitan & associates, inc., Boston,
Massachusetts.
Richard Carlson is with Levitan & associates, inc., Boston, Massachusetts.
p&e

november/december 2014

http://www.eipconline.com/gas

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