Hydrocarbon Processing - April 2021 - 44
Clean Fuels
by higher-cost) ultra-low-sulfur distillates
that are only more readily available during
2020-2021 due to decreased demand for
transportation fuels because of the global
pandemic. However, the asphaltenes present in residual streams are often not compatible with paraffinic distillates, which
may cause serious problems.
Commercial experience, and several
prior and recent industry surveys, show
that blending to produce a low-sulfur
fuel oil can result in a fuel that is incompatible with ship engines.10 In addition,
blends " loaded on top " of residual fuels,
distillate fuels or other blends in storage
tanks or on ships can cause precipitation
of asphaltenes due to incompatibility of
these blends with other fuels. With these
unstable blends, precipitated asphaltenes
form sludge in tanks that can plug filters,
purifiers, fuel injection equipment and
even fuel lines. Precipitated asphaltenes
cannot be brought back into solution,
meaning that this sludge formed by a
blended VLSFO will also need to be
cleaned from tanks and fuel systems before being safely disposed of on land.
FIG. 2. Fuels for compatibility testing.
The author's company has carried
out compatibility and miscibility tests
to demonstrate that the proprietary fuel
does not create or experience these issues. The proprietary VLSFO was tested
with RMG, RMK and distillate grades of
marine fuels, and has proven to be miscible with residual fuels, as well as MGO
and ultra-low-sulfur diesel (ULSD) in
mixtures of 50/50, 30/70, 20/80, 10/90
and 5/95. Compatibility test samples
and results are shown in FIGS. 2 and 3.
Shelf life. Shelf life refers to the length
of time that fuel oil remains stable and in
solution in storage. The reserve stability
number (RSN)-as measured by ASTM
D7061-is an industry-accepted measurement of the stability of marine fuels. Fuels with an RSN of less than 5 are
considered to pass and have a high stability reserve. Asphaltenes are not likely
to flocculate, and the fuel is stable with a
commercially reasonable shelf life. Fuels
with an RSN of 5-10 have a much lower
stability reserve, with limited shelf life
and may flocculate. Fuels with an RSN
greater than 15 are considered unstable. Testing has shown that, after more
than a year in storage, the proprietary
VLSFO had an RSN of 1.2-thereby
demonstrating that the proprietary fuel
is stable and has no issues around shelf
life. Blends and other VLSFO/ULSFO
products on the market are reported
to have shelf-life problems and may be
stable for just a matter of days or weeks
in storage. This can create major issues
with sludge formation over time in storage tanks on land and onboard ships.
Costly and time-consuming cleaning of
tanks and maintenance of ship fuel systems are required when unstable fuels
have been bunkered.
Ignition and combustion properties.
Ignition delay is the time that elapses
from the start of fuel injection to the point
of combustion. A long ignition delay results in an accumulation of unburned
fuel in the combustion chamber, which
can cause knocking, poor engine performance and, eventually, engine damage.
The proprietary fuel demonstrated superior ignition properties when tested using
the combustion pressure trace test.
FIG. 4 illustrates the proprietary fuel's
combustion and ignition properties vs.
" normal " fuel (ECN=29) and a " problem " fuel (ECN=8), as taken from the
International Council on Combustion
Engines' (CIMAC's) 2011 " Fuel Quality
Guide-Ignition and Combustion. "
Poor combustion performance is
normally characterized by an extended
combustion period, along with low rates
of pressure increase and low maximum
pressure, resulting in incomplete fuel
combustion. In contrast, good combustion exhibits a minimal ignition delay, a
rapid combustion period, and high rates
of pressure increase and high maximum
pressure. The proprietary fuel possesses
superior combustion performance, as
demonstrated by the rate of heat release
(ROHR) curve in FIG. 4.
FIG. 3. Fuels for miscibility testing: (A) 20% RMG 380/80% distillate, (B) 20% proprietary fuel/80% distillate, and (C) 30% proprietary fuel/
70% distillate.
44
APRIL 2021 | HydrocarbonProcessing.com
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Hydrocarbon Processing - April 2021
Table of Contents for the Digital Edition of Hydrocarbon Processing - April 2021
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Hydrocarbon Processing - April 2021 - Cover1
Hydrocarbon Processing - April 2021 - Cover2
Hydrocarbon Processing - April 2021 - Contents
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Hydrocarbon Processing - April 2021 - Cover3
Hydrocarbon Processing - April 2021 - Cover4
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Hydrocarbon Processing - April 2021 - GP-44
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https://www.nxtbook.com/nxtbooks/gulfpub/hp_202007
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https://www.nxtbook.com/nxtbooks/gulfpub/petrochemical_2018_v2
https://www.nxtbook.com/nxtbooks/gulfpub/petrochemical_2018
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201812
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