Hydrocarbon Processing - January 2022 - 39

Biofuels and Alternative/Renewable Fuels
Part 1 of this article will examine LNG,
hydrogen and ammonia. Part 2, to be published
in the February issue, will examine
methanol and biofuels.
RESULTS AND FINDINGS
The following are the results and findings
for LNG, hydrogen and ammonia.
LNG. As a preliminary requirement, an
alternative marine fuel should contain
less carbon than the existing hydrocarbons
used in the industry. LNG is considered
an interim potential solution, since
it contains less carbon per unit of energy.5
When burned during combustion, LNG
will release less CO2
vs. conventional fuels.
For years, LNG has been used as a
secondary fuel through combusting boiloff
gas from LNG cargoes.6
Due to the
IMO's sulfur standard regulations, LNG
could act as a fuel replacement. Many
companies in the marine industry considered
switching to LNG-fueled engines,
since they emit less than 0.1% of the fuelequivalent
threshold.7
LNG is produced via the hydraulic fracturing
extraction of natural gas, which is
then liquefied and stored under cryogenic
conditions (-160°C). The main source of
natural gas is primarily underground reserves,
but some companies utilize biogas.
Natural gas in its liquid state is about 600
times smaller in volume than in its gaseous
state.8
Therefore, natural gas is liquefied to
enable easy global transportation.
In terms of energy requirement, the
production process extraction and liquification
is energy intensive. It requires a relatively
high initial capital investment, which
involves exploration, drilling, piping to a
coastal liquification plant and the liquification
process. In addition, shipowners
can expect to pay approximately $5 MM
more for an LNG-fueled vessel than one
that is run off conventional marine fuels.9
LNG engines require a larger investment
than installing scrubbers on ship, which is
another alternative solution to adhere to
the IMO requirement. However, an offset
of the capital investment is expected, due
to fuel cost advantages-LNG is the most
cost-efficient fossil fuel, once its production
infrastructure is secure.10
However, LNG has a lower energy
density than diesel. The Alternative Fuels
Data Center reports that LNG has a specific
energy density of 21,240 Btu/lb and
a mass density of 3.49 lb/gal, while lowsulfur
diesel has a specific energy density
of 18,122 Btu/lb and a mass density of
7.09 lb/gal.11
While the specific energy
density is slightly comparable, the large
difference in mass densities means that
diesel has nearly twice the amount of energy/gal
when compared to LNG. Ships
fueled by LNG also require more space for
fuel tanks, which may limit cargo capacity.
All major shipping companies are either
developing, or have already launched,
a variety of engines that run on LNG.
These technologies include a two-stroke
engine and a dual-fuel, slow-speed engine
that operates on LNG as the primary fuel
and on diesel as a secondary fuel.12
A variety
of engines can use LNG or natural
gas. These include steam engines, leanburn
spark-ignition engines, low-pressure
injection dual-fuel (LPDF) engines, highpressure
injection dual-fuel (HPDF) engines
and gas turbines.
Although LNG emits 20%-30% less
carbon during combustion, LNG has a
large carbon footprint. Pavlenko et al.
analyzed LNG's lifecycle when used in
different engines.13
methane, each engine releases unburned
methane due to incomplete combustion.
Fugitive methane is a more potent
GHG than CO2
Since LNG is mostly
, and its emissions are
more detrimental to the environment.
To perform a complete lifecycle analysis,
the upstream and downstream emissions
had to be evaluated. Pavlenko et al. evaluated
the upstream emissions of LNG using
GHS, regulated emissions and energy use
in transportation (GREET) modeled by
the Argonne National Laboratory. Downstream
emissions were sourced from available
company data sets. As shown in FIG. 3,
LNG has higher upstream emissions than
conventional fuels such as MGO, very-lowsulfur
fuel oil (VLSFO) and HFO. These
high emissions are a result of high methane
emissions due to leakage that occurs during
extraction, processing and transport.
In addition, the liquification process contributes
to upstream emissions. Although
LNG has lower downstream emissions
than conventional fuels, LNG has a higher
total GHG emissions rate when the upstream
emissions and methane slips are
accounted for, irrespective of engine types.
Hydrogen. According to the International
Energy Agency (IEA), hydrogen
is a potential carbon-zero fuel alternative.
With byproducts like water and steam, hydrogen
can eliminate pollutants from the
transportation industry. Hydrogen is also
abundant in the environment and can be
produced from diverse sources. Its use in
the transportation sector is still in the primary
phase. Hydrogen became popular
with the use of fuel-cell-powered vehicles.
Using hydrogen fuel cells integrated with
an electric motor is about three times
more efficient than gasoline-powered
ICEs.14
Hydrogen is used in light-duty,
fuel-cell vehicles; however, can it be used
to propel ships across the ocean?
One challenge with using hydrogen as
a fuel is its production process. Readily
available substances, such as organic matter,
water and hydrocarbons, can be used
FIG. 3. Lifecycle GHG emissions by engine and fuel type.5
Hydrocarbon Processing | JANUARY 2022 39
Hydrocarbon Processing - January 2022

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