American Oil and Gas Reporter - May 2015 - 109

SpecialReport: Gas Compression Technology
operating in dual-fuel mode, zur Loye
says natural gas is introduced into the intake system. The air-to-natural gas mixture
from the intake is drawn into the cylinder,
just as it would be in a spark-ignited engine, but with a leaner air-to-fuel ratio.
Near the end of the compression stroke,
he continues, diesel fuel is injected, just
as it would be in a traditional diesel
engine. The diesel fuel ignites, and the
diesel combustion causes the natural gas
to burn.
"The dual fuel engine retains all the
performance ability of the base diesel
engine," points out zur Loye, "including
the same power density, torque curve,
and load acceptance capability."
Cannon claims Cummins' dual fuel
engines offer a gas-for-diesel substitution
rate of as much as 70 percent, which is
among the best in the industry, although
he admits "there is a complete operating
range" in hydraulic fracturing pumps. He
says the substitution rate depends on the
quality of natural gas available.
"Once the gas quality gets hot, the
substitution rate declines," he says. "There
is a wide range of savings, depending on
the cost of the fuel."
If operators can use line gas from dry
gas areas such as the Marcellus Shale in
Pennsylvania, that obviously means cheaper gas and more savings while creating
demand for natural gas. Cannon says the
dual fuel kit has the flexibility to use 800
to 1,200 Btu gas, but it can't have liquids
fall out.
"If operators have to bring in liquefied
or compressed natural gas, the costs deteriorate," he allows. "In the oil shale
plays such as the Bakken or the Permian
Basin, you have to process the gas. There
is an investment to gather and process
the associated gas, but we can run in any
play."
The dual fuel hydraulic fracturing
pump operates in the same manner as a
diesel pump, according to zur Loye,
except for one switch. "Everything else
is like every other job," he assures. "The
system is automated. It will tell the engine
to not use any gas, if necessary. You
want to optimize the substitution rate,
but you have to protect the engine."
Environmental Compliance
One challenge for engine manufacturers
is meeting the emissions standards set
by the Environmental Protection Agency
for nitrogen oxide, carbon monoxide and
particulate matter. Tier 4 final requirements

Since introducing its bifuel conversion kits late in 2012, Baker
Hughes reports it has converted
20 percent of its fleets. The company's Rhino bifuel pumps can
run on liquefied natural gas,
compressed natural gas or line
gas, and meet the Environmental
Protection Agency's final Tier 4
air quality standards for nitrogen
oxide, carbon monoxide and particulate matter emissions.

for some markets, including hydraulic
fracturing pumps, went into effect on
Jan.1, says zur Loye.
"Our system meets the Tier 2 requirements," Cannon adds. "Many customers
will be buying Tier 2 engines through
2017. Our dual-fuel Tier 4 final engines
are in development. We haven't yet announced a production date."
He points out that existing engines do
not have to be retrofitted to meet the new
standards, just like an older model car
doesn't have to meet new mileage standards. He says Cummins is trying to
meet both economic and environmental
demands with its dual fuel engines.

Bifuel Conversion
Meeting the EPA's Tier 4 requirements
is important to not only engine manufacturers, but also to frac fleet operators
such as Baker Hughes. Lutfi says his
company's Rhino bifuel pumps meet Tier
4 requirements.
"We started with Tier 2, and retrofitted
our pumps with the bifuel kits and the
added catalysts," he says. "We are not
changing the engines. Our kits simply
optimize the conversion rate."
Lutfi says not much has changed since
Baker Hughes introduced its bifuel conversion kits late in 2012. "We are trying
to improve the conversion rate and trying

to be more efficient," he maintains. "We
have converted 20 percent of our fleets
(to operate with bifuel capability). Our
fracturing pumps can run on LNG, CNG,
or line gas."
Lutfi comments that using bifuel hydraulic fracturing pumps depends on the
operator's goals, cost, availability of natural gas, and the need to meet emission
standards. For example, he says Baker
Hughes is trying to find additional solutions in California because of its stringent
regulations.
Eliminating flaring is one way to
reduce emissions, but Lutfi says there
generally aren't sufficient volumes of
flared gas to power pumps, which can
number from 10 to 32 during a hydraulic
fracturing operation. He says it is feasible,
however, to capture flare gas and store it
to be used with another natural gas source
to substitute for diesel.
"Our customers have different needs,"
he acknowledges. "Some are looking just
for cost savings; others are looking for
the latest technology to do what is right.
We have lost the former with the drop in
the fuel prices. Many companies have
other issues to deal with now. It is a circle."
Lutfi mentions that Baker Hughes can
scrub or dehydrate natural gas on site so
it can be used in its bifuel systems.
MAY 2015 109
American Oil and Gas Reporter - May 2015

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