American Oil and Gas Reporter - March 2017 - 80

SpecialReport: Midstream & Infrastructure Update

Technology Limits Engine Emissions
By Colter Cookson
In the perilous world of Dungeons &
Dragons, a wise warrior often carries a
wide array of weapons. These include a
blade made of silver for slaying werewolves, a spear tipped with cold iron for
piercing demons' hides, an adamantine
mace for crushing skeletons, and a darkwood bow for felling any dragon foolhardy
enough to think flight means safety.
In the real world, the engine manufacturers, engine retrofitters, and compressor packagers that battle emissions
rely on an equally varied toolbox. They
say picking the right tool for the job is
the only way to reliably and efficiently
meet ever-stricter emission regulations.
Diesel engine manufacturers report
that one of the most important goals is
complying with the U.S. Environmental
Protection Agency's Tier 4 final standard,
which now is in effect. The standard caps
nitrogen oxide emissions from nonroad
diesel engines with more than 750 horsepower at 3.5 grams a kilowatt hour, and
particulate matter emissions at 0.04 grams
a kilowatt hour.
Patricio Escobar, the oil and gas segment lead for Cummins, predicts that selective catalytic reduction will play the

star role in meeting current and future
NOx limitations. "There are multiple
technologies that can reduce NOx, such
as exhaust gas recirculation and managing
valve timing," he notes. "We have had
success with most of these alternatives,
but for engines with a high displacement
volume, we believe selective catalyst reduction (SCR) is the future."
Escobar explains that necessity will
make the primary downside of SCR-the
need for diesel exhaust fluid-irrelevant
because producers will need to have it
available for other engines. "Most oil
and gas sites have engines that produce
power for high-pressure pumps or drilling
rigs. For power generation engines, Tier
4 limits NOx emissions to 0.67 grams,
which is low enough to need SCR," he
says.
"Other sites will have engines for small
pumps and tractors. For engines in nonroad
applications between 100 and 750 horsepower, the standard caps NOx emissions
at 0.40 grams a kilowatt hour, which is
even lower," Escobar continues. "SCR is
the best way to meet these limits, so upstream companies already will be bringing
diesel exhaust fluid to their sites."
Escobar emphasizes that SCR has several advantages over exhaust gas recir-

This Cummins QSK50 diesel engine meets the Environmental
Protection Agency's Tier 4 Final
emissions standard by using
high-pressure, common rail fuel
injection to reduce particulate
matter and a selective catalytic
reduction after-treatment system to remove nitrogen oxides
from the exhaust. The company
says both technologies are
proven, reliable, and economic.

80 THE AMERICAN OIL & GAS REPORTER

culation (EGR) methods in high-horsepower applications. "One of the biggest
is the ability to reach lower emissions,"
he says. "This can be critical in nonattainment areas, where local governments
may need to set limits far below those
required by EPA mandates."
SCR engines consume less fuel than
ones that use EGR, Escobar reports. "In
well servicing applications, we have seen
fluid consumption fall 3-5 percent, even
after factoring in the diesel exhaust fluid,"
he says.
These fuel savings occur because SCR
controls NOx by using chemical reactions
to convert it into nitrogen and water
vapor. In contrast, EGR prevents NOx
formation by introducing exhaust gas
into the combustion chamber to displace
oxygen, and therefore, reduce the combustion temperature, Escobar relates. He
says this works, but with the side effect
of less efficient combustion.
"To compensate for their low combustion efficiency, EGR engines need a
higher injection pressure and peak cylinder
pressure," he comments. "With SCR, we
can keep our injection pressures at 2,200
bar and manage our peak cylinder pressures at lower levels, improving engine
durability and reliability."
Because they have no need for exhaust
gas cooling equipment, SCR engines also
are lighter and more reliable; additionally,
their cooling packages do not require
significant capability increases for Tier
4, Escobar adds. He emphasizes that although these advantages make SCR the
right choice for high-horsepower engines,
EGR can deliver great results inside lower-displacement engines.
SCR only controls NOx, and not particulate matter. According to Escobar,
Cummins addresses PM inside the engine
using high-pressure common rail injection,
a technology it has employed since 2006.
Escobar says both SCR and common rail
injection have come a long way since introduction.
"Across market segments, we have
more than 1 million SCR units operating
and more than 30 million HP operating
in applications above 750 HP with highpressure common rail systems. These
technologies have proven they can offer
a low-risk way for engines to meet emission standards while maintaining or improving performance," he concludes.

American Oil and Gas Reporter - March 2017

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