POWER October 2013 - 72

Gas Power
Reciprocating Engines Continue to
Be Flexible Workhorses
With applications that range from firming intermittent resources to providing combined
heat and power solutions, reciprocating engine manufacturers have
made strides to improve their machines' efficiency and environmental profile.
David Wagman
R
eciprocating gas engines find work in
multiple power generation applications,
from providing fast-start backup generating
capacity for intermittent renewable resources
to offering scalable and increasingly efficient
solutions for commercial and industrial
combined heat and power (CHP) systems.
Major global manufacturers such as GEJenbacher,
Cummins, and Wärtsilä have focused
engineering efforts in recent years on
improving their machines' efficiency and
meeting environmental regulations, particularly
nitrogen oxide (NOx
) emission rules.
Another factor driving interest in reciprocating
engines for industrial CHP applications
in the U.S. is the long-term prospect for
plentiful natural gas supplies and relatively
stable prices. Commercial and industrial
customers are finding in some instances that
they can generate their own electricity for
less money than if they were to buy power
from the grid, said Scott Nolen, product line
management leader, GE Gas Engines for
Power Generation. Creative uses of reciprocating
engine technology that include not
only power generation but also thermal energy
and even captured emissions are gaining
traction in some parts of the country.
For example, in August 2012, GE and Houweling's
Tomatoes, a leading California-based
greenhouse, completed work on a CHP project
that also captures carbon dioxide (CO2
)
from the engine exhaust for plant fertilization.
Using two GE 4.36-MW Jenbacher J624 twostaged
turbocharged natural gas engines and
a GE-designed CO2
plant provides heat, power, and CO2
fertilization system, the
to Houweling's
125-acre tomato greenhouse in Camarillo,
Calif. The system provides 8.7 MW
of electrical power and 10.6 MW of thermal
energy (hot water) for heating the greenhouses.
The system offers a total thermal efficiency
of nearly 90%. When considering the avoided
energy that would be required to externally
source the CO2
the exhaust, GE said the overall system efficiency
(effectiveness) exceeds 100%.
This past July, the largest power plant
72
running exclusively on gas engines on the
African continent-and among the first of
its kind in the Republic of South Africa-
entered service. The Sasol Gas Engine Power
Plant, located south of Johannesburg, is powered
by 18 Wärtsilä 34SG gas-fired generating
sets with a combined operating capacity
of 140 MW (see the Top Plant story on this
plant in the September issue). Electricity produced
by the plant is used by Sasol's nearby
chemical factory, with about half of the electricity
production fed to the national grid.
One of Wärtsilä's largest U.S. installations
is the 202-MW Pearsall Power Plant owned by
South Texas Electric Cooperative. The plant includes
24 reciprocating engines and is used to
firm intermittent wind generation resources.
And on Long Island, N.Y., about 60 miles
east of New York City, the William Floyd
School District, with a student population
of approximately 11,000, faced steadily rising
on-peak electric rates that were straining
operational budgets. The district decided to
install a CHP system from Cummins Power
Generation, which supplies on-peak electricity
as well as heating and cooling to three school
buildings. In the first three years of operation,
the CHP system saved the school district more
than $1.2 million. The CHP system consists of
two PowerCommand 1.25-MW reciprocating
engine generators with a combined capacity of
2.5 MW. The generator sets feature a QSV91G
lean-burn natural gas engine, which is a 91liter
engine with a high exhaust temperature in
relation to the amount of electricity produced,
making it a good fit for CHP applications with
large heating or cooling loads.
" It is the best performing plant I've been
and the recovery of water from
involved with, " said Peter Schroeck, manager
ESB North America/Caribbean Business Development
for Cummins Engines. He said the
growth potential for CHP applications has benefited
from prospects for stable and more predictable
natural gas prices. Gas price volatility
in the past made it difficult to build a financial
model that would hold up with any certainty.
A barrier to growth for reciprocating engines
that still must be addressed is the lower
www.powermag.com
heat rate common with many technologies.
System efficiencies typically range from
36% to 45%, Schroeck said, with a 1 percentage
point gain in efficiency considered " tremendous. "
Much of the current effort aimed
at improving efficiency focuses on reducing
friction in the engine and working to reduce
exhaust temperatures, both of which can help
produce more high-value product, he said.
Mature Technology
A 2011 report by the North American Electric
Reliability Corp. (NERC) said that reciprocating
engine-based generators are among
the most mature distributed generation (DG)
technologies available, accounting for about
90% of current DG installations in North
America. The generators themselves are typically
synchronous machines that can provide
dynamic reactive power and voltage control.
Applications include utility power generation,
peak shaving, and remote customer and
backup power. Reciprocating engines can run
on a range of fuels including diesel, natural
gas, gasoline, propane, and methane. (This article
focuses on natural gas-fueled machines.)
Reciprocating engines also are typically fast
starting, fast ramping, and have good part-load
performance. The NERC report said these
characteristics make reciprocating engines
a good reliability resource when they are responsive
to system operator commands.
CHP, also sometimes known as cogeneration,
is one form of DG that generates both
electric power and thermal energy. According
to the Department of Energy, at the end
of 2011 nearly 70 GW of CHP generating
capacity was installed across the U.S. and accounted
for almost 7% of total U.S. installed
capacity. Of that 70 GW, 25 GW was in the
industrial sector, 2 GW in the commercial
sector, and 43 GW in the electric power sector.
The average capacity factor for generators
at industrial CHP plants was around 57%.
Not all of that DG capacity represented reciprocating
engines, by any means. Combustion
turbines and even coal-fired boilers are in
use. Even so, natural gas is the most common
POWER | October 2013
http://www.powermag.com
POWER October 2013

Table of Contents for the Digital Edition of POWER October 2013
