TFL SEP
8
in diesel fuel
CLEAN
FUEL
CORNER
By Deena Kasavelu
Raw, ultralow, sulphur diesel
fuels coming out of today’s
modern refineries require
various additives to bring them
into specification. Although the
details of each fuel spec vary
in different parts of the world,
the function of an additive is
generally the same: to give
the fuel a characteristic that
it otherwise wouldn’t have
straight out of the refinery.
SPECIFIC ADDITIVE FUNCTIONS
in fuel vary, from corrosion inhibitors to lubricity, cold
flow, and cetane improvers, to name a few. There are also a lot of choices in the marketplace
for additives that are dosed into diesel at the end-user level.
Just like everything else, there are right ways and wrong ways to dose additives. Best practices
typically include blending at similar temperatures, using the right type of dosing system (viz
injection of the additive while the fuel is flowing through a pipe to promote good blending).
But what does this have to do with fuel filtration? As the filtration industry works to design
fuel filters to meet the cleanliness specifications of the new injection system, filtration
efficiencies are getting tighter and tighter. To guarantee the cleanliness in the harsh operating
environments in which onboard fuel filters live, manufacturers are designing to beta ratios
previously never required, nor achieved. Unfortunately, this highly efficient filtration has some
adverse effects and has caught many in the industry by surprise.
While aiming to achieve ‘clean enough’ fuel in bulk and onboard filtration, filters sometimes
start plugging with soft organic material, not hard particulate.While filters are designed in the
laboratory to capture hard particulate, they aren’t particularly good at the soft stuff. Capacities
are decreased significantly, in some instances filters plug more than 1000 times faster.
So what now that these soft organics are showing up on filter media? Numerous papers have
been published since sulphur was removed from fuel about six years ago, highlighting injector
deposit problems. It’s quite possible (but not proven) that these deposits are caused by exactly
the same substance that is now plugging the filter. Why didn’t it plug before? Quite simply,
fuel filters may not have been efficient enough to catch the problem. Injection systems could
tolerate six micron and smaller particles, so filters weren’t designed to catch particulate much
smaller. Now, with the sensitivity of HPCR around two to three microns, the potential to filter
out more ‘stuff’ is there.
Of course this leaves us with many more questions than answers, which may be a bit
frustrating. There are too many stakeholders in this discussion for one point of view to come
in and solve it. Are the additives unstable? Under what conditions are they unstable? Have
they always been that way, or is this a new phenomenon caused by something else? Does
the high efficiency of the filter media act as a catalyst for this to happen? What about the
filter medium itself? Do the properties of the fuel change downstream of the filter once these
organics are captured? If they are all captured, will injector deposits disappear?
At this point we can only say that if you have issues with plugged bulk or onboard filters, work
closely with your fuel, additive, and filter suppliers and identify and solve the problem. As an
industry, we’re publishing as much information as possible about these incidents and learning
more about their cause and what might prevent them. Most importantly, remember that in all
cases, a plugged filter did its job by preventing unwanted material from passing downstream.
ADDITIVES
FREIGHT AND LOGISTICS
FUEL
