By Cindy Green
Don’t blame it all on biodiesel .
In the fall 2005, soon after a Minnesota mandate kicked in requiring a 2-percent biodiesel blend, truckers and bus drivers started complaining that the soy-based diesel was clogging fuel filters. Just before Christmas, the state lifted the mandate for 21 days, then extended the waiver another 30 days until the fuel-plugging problems could be solved.
“Quality issues were taken seriously and addressed by Minnesota biodiesel producers,” says Rose Patzer, AURI associate scientist. Clogged-filter complaints subsided after producers made sure all biodiesel going on the market met quality standards, and the 2- percent mandate went back into effect.
But was biodiesel the problem? “In some cases, yes, but many other things contributed,” Patzer says. “We haven’t seen many issues with Minnesota’s biodiesel this season. And most of those were relating to higher blends or biodiesel that was produced from other states.”
AURI just released findings of its two-year study of blended-fuel filter plugging. While results are not conclusive, it’s likely that storage issues, water contamination, microbes and other secondary causes are as much to blame as fuel quality.
Perfect storm
Filter clogging in late 2005 was caused by several converging circumstances. “It was a perfect storm — a coming together of bad events” Patzer says. The temperatures dropped to around zero degrees, which can cause gelling in high-percentage biodiesel blends. “Last year people were regularly using blends above the recommended levels. They are taking destiny into their own hands when they go higher than B20.”
Hurricane Katrina exacerbated the problems. “Terminals ran out of fuel. When a tank is emptied, sediment settles at the bottom,” for microbes to feed on.
But most of the contamination was water in fuel storage tanks. “Diesel will always be on top of the water, but if there are bugs, the interface between the fuel and water is where they’ll survive,” Patzer says. She explains that in both biodiesel and petrodiesel, if a thin grey line is present in the fuel tank, that indicates live microbes are present. “If the line is black, generally they’re dead.”
“We want to isolate and identify the microbes, then take those cultures and put them in biodiesel and see what damage they do.”
Too clean
“From my perspective, I don’t think we’ll ever resolve (the plugging issue) because we don’t have all the pieces – but through characterizing, we can come to some conclusions.”
Acting like a cleaning agent, biodiesel may remove sludge and varnish-like deposits in tanks and components, which can plug fuel filters. Chemicals will kill the bacteria but water needs to be pumped out first, and emptying and cleaning tanks can be expensive.
A 2004 U.S. Department of Energy biodiesel handling report says that using blends with 20-percent biodiesel or less minimizes problems with tank sediments, although filter plugging may be an issue in the initial weeks of B20 use. The DOE recommends always storing blends above 20 percent in clean, dry tanks as is recommended for conventional diesel.
High glycerin concentrations in biodiesel can also cause a wax coating on fuel filters. But if fuel is stored below ground where it’s better insulated and warmer than above-ground storage, there may be fewer problems with glycerin.
Soy sterol glucosides are another contaminate and usually eliminated during soybean oil or biodiesel production, but it can remain in up to 3 percent of the fuel. “We need to figure out how to make sure it’s eliminated,” Patzer says.
Inconclusive tests
When Minnesota truckers started having problems with clogged filters in October 2005, some were advised to send their filters to AURI’s oils lab in Marshall for testing.
“One of the problems was, we were never able to obtain an actual diesel sample,” Patzer says, so the oils lab didn’t know if the trucker had used B2, B5, B20, 100-percent biodiesel or regular diesel when the gelling occurred. “We only had part of the picture.”
Biodiesel may not even have been a factor. Lower-sulfur petrodiesels now on the market could be prone to contamination, as sulfur has an anti-microbial effect “When there is a (fuel) quality issue, then we have an obvious answer – through chemical analysis. When it isn’t a quality issue … it could be water in the bottom of a tank where there could be microbial activity.”
“There is no one answer — and no one cure-all,” Patzer says. “There are many problems, many different issues.”¦
>Rose Patzer, AURI associate scientist (left) and Ranae Jorgenson, chemist, inspect one of the fuel filters that truckers sent to AURI in late 2005 after complaints arose that state-mandated biodiesel blends were causing filter plugging. An AURI study revealed that storage and handling problems contributed to fuel gellin
