Biodiesel and its blends with petroleum diesel
will cloud and gel at higher temperatures than normal winterized petroleum
diesel fuel. As temperatures drop, wax-like crystals form in the fuel. These
crystals will potentially clog fuel filters or fuel-line inlet screens, causing
stalls or failure to start. Plugged fuel filters may strain injection pumps,
possibly reducing the longevity of these expensive components. Users are
advised to prepare for cold temperatures in advance in order to avoid vehicle
and equipment problems associated with cloudy or solidified fuel. The petroleum
diesel used in cold climates should be winterized diesel fuel.
A fuel’s cloud point (CP) is the temperature at
which it first begins to appear cloudy, as crystals start to form. The pour
point (PP) is the minimum temperature at which the fuel can be considered a
liquid—below this temperature the fuel will be fully gelled. The cold filter
plugging point (CFPP) is usually closely related to the cloud point, thus
testing for cloud point may be the most practical way to predict a fuel’s
winter performance. Commercial fuel producers are required to notify customers
of a given fuel’s pour characteristics, and small-scale producers are advised
to be aware of pour points in the biodiesel they produce. The introduction of
ultra-low sulfur fuel (ULSF) makes this more important, since early indications
are the high ULSF can also contribute to the low temperature problem.
Cloud point and pour point of biodiesel will
vary according to feedstock. Of the vegetable oils, canola oil is the best for
producing winter biodiesel fuel, with a cloud point in the 20- to 30-degree
range (F). Soy biodiesel typically clouds around 32 degrees Fahrenheit (0
degrees Celsius). Biodiesel made from animal fats, tallow, or hydrogenated
(creamy) vegetable oils will cloud and gel at temperatures above freezing, and
thus these fuels perform best in southern regions or summertime.
Freezer Test
Small producers who use oils from multiple
sources are advised to test each batch of biodiesel fuel for cold weather
performance. A simple test using jars, a freezer, and a thermometer is
effective to determine proper winter blending rates. Blends of biodiesel and
winterized petroleum diesel fuel of varying proportions (e.g, B10, B20, B50)
are made up in small jars and then placed in the freezer. By frequently
checking the temperature of each jar, a producer can roughly determine the
temperature at which clouding and gelling will occur for each blend. Knowing
the expected low temperature, users can then predict which blend will be
trouble free. Extreme care must be taken not to spill diesel or biodiesel
blends in a freezer that is used for food storage. Use a plastic tub for
secondary containment, and place in a secure, level spot. Do not leave fuel in
freezer where others may disturb it accidentally.
A rough version of this test can be performed
by leaving marked blended jars of fuel in an outdoor, unheated location during
the winter. It is best to start blending biodiesel with petroleum diesel
conservatively well before winter to prevent filter plugging in unexpected cold
snaps.
Additives
Several fuel additives are available for
winterizing petroleum diesel fuel, and a handful are specifically designed to
winterize biodiesel blends. Several commercial biodiesel additives are
effective at reducing the pour (gel) point of blends, but they have little
effect on the pour point of B100. Furthermore, the additives do not
significantly reduce the cloud point (key to prevent filter plugging) of
biodiesel blends, even at several times the recommended usage rates. Some
individuals do report successful reduction of cloud points with various
unconventional additives, but users are advised to test blends before using in
their equipment and to err on the side of caution.
Preparing for Winter Trouble
It is advisable to be familiar with the fuel
system in vehicles and machinery using biodiesel in case any winter troubles
arise. It is always helpful to carry a spare fuel filter and the tools to
change it, especially in winter. If equipment stalls due to fuel starvation,
exchanging the waxed filter for a fresh one filled with petroleum diesel may
get it back in service. A spare five-gallon tank of fresh winterized petroleum
diesel (or kerosene for off-road equipment) can be quite handy. If temperatures
drop unexpectedly below the cloud point of biodiesel in the equipment’s fuel
tank, adding fresh diesel to top off the tank may help prevent clouding and
filter plugging. This is especially effective if the diesel fuel is stored in a
heated space. Block heaters are effective at keeping the engine warm enough to
start, but if a gel layer forms in the fuel tank, problems will persist. When
all else fails, the vehicle can be towed to a heated garage to thaw out.
Blending for the Cold Season
It is
best to blend biodiesel with winterized petroleum diesel fuel (cut with
kerosene by the fuel distributor). Small producers will typically “splash
blend” by simply pouring the two fuels into a tank at the desired proportions.
Biodiesel will mix readily with diesel fuel simply through the agitation
generated by driving a vehicle. For stationary tanks, it is best to add
biodiesel on top of petroleum diesel, as biodiesel is denser and will settle to
the bottom, blending on its way down. When blending, both biodiesel and
petroleum diesel should be at temperatures above the biodiesel cloud point, as
experience has shown that fuels blended at cold temperatures may not stay
mixed. For this reason, small producers working in unheated shops may want to
blend up a large batch of winter fuel before outdoor temperatures drop in the
late fall. If biodiesel should cloud or gel, it will need to be warmed to well
above its cloud point to fully dissolve waxy crystals that formed at low
temperatures. Note: When blending fuels, tanks should be grounded to avoid
static charge buildup.
Δεν υπάρχουν σχόλια:
Δημοσίευση σχολίου