POWER September 2014 - 56

GAS POWER
Reciprocating Engines Expand
Roles
Once merely a staple of backup and distributed generation, reciprocating engines
are now challenging other resources for utility-scale generation-in
addition to carving out some new niches.
Thomas W. Overton, JD
G
rant County is a rural, sparsely populated
county in southwestern Kansas.
It doesn't have a lot of people-its
population in the 2010 U.S. Census was just
7,829-but what it does have a lot of is wind.
Like the rest of Kansas, Grant County is in
the middle of the nation's best wind resource
area, giving the state the second-highest wind
potential in the country, according to the
American Wind Energy Association. Kansas
gets about 20% of its electricity from around
3 GW of installed capacity, with more on the
way. One of those new wind farms, the Buffalo
Dunes Wind Project, a 250-MW farm
being developed by Lenexa, Kan.-based
Tradewind Energy, will be partly located in
Grant County.
The Mid-Kansas Electric Cooperative
is a coalition of five rural electric cooperatives
and one wholly owned subsidiary
serving customers in central and western
Kansas. Mid-Kansas owns 179 MW of
wind generation along with about 550 MW
of gas- and coal-fired capacity-the newest
of which came online in 1978. With the
Southwest Power Pool transitioning to an
integrated market this year, Mid-Kansas
needed quick-responding generation that
could meet its future needs while providing
badly needed voltage support for the
area.
It should come as no surprise that MidKansas
opted for gas-fired generation, but
not so long ago, it might have raised eyebrows
that it opted to use reciprocating engines
to power a 110-MW plant. These days
though, the combination of cheap natural
gas and advancing technology has taken reciprocating
engines out of their traditional
role as backup and distributed generation
into direct competition with gas turbines,
coal, and even nuclear.
Fast, Flexible, Efficient
" Reciprocating engines are becoming an
increasingly popular choice of prime mover
1. Ready to rock. This bank of 12 Caterpillar G20CM34 gas-fired generator sets will power
the new 110-MW Rubart Station plant in Kansas. Courtesy: Caterpillar
technology for utility-class generation assets, "
Dean Powell, general manager of
Power Plants & Key Accounts at Caterpillar
told POWER. In many ways, Mid-Kansas's
Rubart Station, under construction in Grant
County, with completion scheduled for this
month, exemplifies how gas-fired engine
plants are carving out a serious niche in
utility-scale generation worldwide. The project,
being built by Burns & McDonnell, will
comprise 12 Caterpillar G20CM34 generator
sets (Figure 1). The G20CM34 is a new offering
from Caterpillar, and Rubart Station
will be the first plant to employ it, as well as
the largest power plant Caterpillar has ever
built.
What Rubart will offer Mid-Kansas is a
plant that can reach full power in less than
8 minutes, ramp up and down continuously
with little effect on heat rate, while requiring
relatively little maintenance and support
compared to more complex gas turbine-
based plants. What engine-based plants give
up in efficiency compared to combined cycle
plants, they more than make up for in flexibility-and
those combined cycle efficiency
advantages start to ebb away in a rapid-cycling
environment.
The advantage comes in the modular nature
of the plant. Unlike gas-turbine plants
that may have only one or two units to ramp
up and down, multishaft engine plants can
scale their output by taking individual units
offline, while the remaining units can continue
running at peak efficiency. And when
waste heat recovery systems are added,
such as with Wärtsilä's Flexicycle design,
combined cycle gas engine plants can
match or beat combined cycle gas turbine
plants for efficiency in peaking and loadfollowing
modes. That matters for a plant
like Rubart, which will be backing up a lot
of wind generation.
Additionally, maintenance can be handled
with less overall downtime, since
each engine can be serviced individually
without affecting the others or requiring a
56
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POWER | September 2014
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POWER September 2014

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