In their search for reliable, flexible, low-cost sources of power, inves- tor-owned utilities, municipal utilities and rural cooperatives have varying
pressures and selection factors but many
of them choose the same technology
solution: reciprocating engines.
Overall power trends affecting their
choices in the U.S. are readily visible:
Decommissioning of small and medium
coal-fired units, natural gas-fired power generation for peaking and base-load
capacity, rapid growth of renewables;
growth of distributed generation and
mixing of power generation technologies
within a utility.
The versatile reciprocating engine
is increasingly being selected as the
solution to these challenges, from one
small engine to a bank of larger engines. While the engines can operate
on fuel oil or other liquid fuels, they
primarily burn natural gas.
NEEDS VARY: A TALE OF A
The city of Alexandria, Louisiana’s
contract with the local utility had ended.
How could the city upgrade its aging fleet,
be self-sufficient and stabilize rates for 20
to 30 years while joining the Midconti-nent Independent System Operator? City
officials also wanted a diverse, sustainable fuel source.
The city’s prior fuel mix for generation was 80 percent coal, 17 percent
gas and 3 percent hydroelectric. As part
of the EPC team selected for the project, Stanley Consultants acted as engi-neer-of-record for the balance of plant
for the installation of the seven, 9 MW
Solving the Power
Puzzle for Municipal and
BY ANDY UNGERMAN, PE, SENIOR MECHANICAL ENGINEER, STANLEY CONSULTANTS
Wartsila reciprocating engines that satisfied Alexandria’s requirements.
The engines can be started up in about
five minutes, which means that sudden
demands from the grid could be accommodated. All or one of the engines can be
used at any time, providing more reliability and flexibility. The engines even fit in
a tight space adjacent to the city’s existing
plant in the middle of town and meet the
city’s stringent noise requirements. After
installation, the fuel mix is 47 percent
coal, 50 percent gas and 3 percent hydro.
BUILD THIS PLANT FAST
Tallahassee needed to add power generation quickly, and reciprocating engines
fit the bill.
Power production manager Triveni
Singh said the multiple small units fits
the city’s load profile and will complement the planned 20 MW solar facility.
Efficiency, low maintenance and high reliability in addition to the quick-start capability were also keys, Singh said, as well
as lower C02 emissions and the ability to
be located at distributed sites.
Matanuska Electric Association is Alas-
ka’s oldest existing and second-largest
electric cooperative. MEA’s service area
includes more than 4,300 miles of pow-
er lines in Southcentral Alaska. MEA had
purchased power from another Alaska co-
operative but wanted to be more self-suf-
ficient and generate their own. Stanley
Consultants served as owner’s engineer
for the project.
The needs? Reliable, affordable energy
and the ability to operate in temperatures
as low as 40 degrees below zero Fahrenheit. In addition, in case the supply of natural gas was interrupted, the plant could
switch to fuel oil stored onsite. The cooperative would also be asked to produce as
much as 145 MW during the winter and
as little as 50 MW during the summer. The
installation of 10 new Wartsila 17. 1 MW
engines met MEA’s needs because of their
ability to add grid reliability and fast response time in case of load following. The
plant is 30 percent more efficient than its
former power supply. MEA is producing
electricity for its members at a lower cost
and generating additional revenue from
selling excess capacity to other utilities.
THE BENEFITS OF THE
Reciprocating engines provide a
proven, reliable technology, but recent
upgrades in efficiency and reliability
are making them the go-to choice for
the addition of small to medium-sized
For larger applications, reciprocating
engines may not be a fit. The overall plant
footprint is smaller for a combustion
turbine, and the heat rate, or efficiency
looks better, especially in combined cycle
mode. In larger plants, capital costs can be
lower with combustion turbines as well.
According to the U.S. Department of
Energy, “Gas-fired reciprocating engines
are the fastest-selling, least expensive
distributed generation technology in the
world today.” The technology does not fit
every situation, but has found its way into
the power generation ecosystem.