Keeping The Flow

Cold winters aren't stopping states like Minnesota and Illinois from placing biodiesel mandates on the books, even when low temperature performance is a concern. To cultivate additional winter-market growth, the biodiesel industry has the summit of cold flow's learning curve locked in its sights.
By Ron Kotrba | October 01, 2005
It won't be long before the early chill of winter descends upon the northern reaches of the United States and Canada. The season's first flakes of snow-the ones that reach the tips of children's outstretched tongues and melt on sidewalks-represent the annual onset of winter.
Seen initially as a wondrous spectacle, the cold and snow that inevitably follows can become dreaded nuisances in every sense.

Temperatures in Minnesota-where the country's first B2 mandate just went into effect-on occasion plunge to minus 40 degrees Fahrenheit. Combine those temperatures with steady straight-line winds of appreciable magnitude, and it becomes hard to even venture outside to start the car. If that vehicle has a compression ignition engine burning blended biodiesel, take solace in the fact that the industry has made great strides in addressing the renewable fuel's cold flow issues.

Climatically speaking, North America is about as diverse as any continent on Earth. Latitudinal changes and variations in elevation, along with proximity to the warmer coastal environments, all contribute to differences in climate. For biodiesel producers, blenders and users in the northern, higher and, for the most part, inland regions of the continent, these geographic concerns drive various actions taken in the winter months to combat fuel operability problems.

Like clockwork, when temperatures during those fall nights start consistently dipping well below the freezing mark, blenders and retailers roll out their winter-blend diesel. In colder climates, the winter blend often consists of No. 2 diesel mixed with No. 1 fuel oil (kerosene) in such blends as 40/60 or 50/50 respectively, said Rod Lawrence, Magellan Midstream Partners LP's manager of quality control. Magellan has been providing testing, assets and fuels through seven terminals to get Minnesota's B2 mandate off the ground. "You're blending No. 1 and No. 2 for climatic reasons," Lawrence said. Were it not for the fear of the freeze, it wouldn't be prudent to blend No. 1 with No. 2 because of kerosene's lower Btu content. Lawrence told Biodiesel Magazine that No. 1 diesel's cloud point temperature-or the temperature at which crystallization of the paraffin molecules in diesel fuel can be observed-is approximately minus 40 degrees, whereas the cloud point of No. 2 diesel is between 4 degrees and 6 degrees with extremes reaching 14 degrees.

Along with blending No. 1 and No. 2 diesel fuels in the colder months, other strategies are commonplace in preventing cold-related usability issues with diesel fuel. Additives might be used to suppress the pour point and cold filter plugging point of petroleum diesel. The fuel lines of some diesel vehicles travel to the engine and return to the fuel tank before reaching the fuel pump and filter. This circulates warm fuel and prevents it from crystallizing.. Many diesel owners and operators park their diesels inside or near a building in cold months to keep from having operability problems, according to the National Biodiesel Board (NBB).

Petro-diesel storage, on the other hand, isn't quite as critical as the storage of neat biodiesel. "Diesel fuel is not ordinarily stored in a heated tank," said Robert Dunn, a food and industrial oils chemical engineer with the USDA's Agricultural Research Service National Center for Agricultural Utilization Research (NCAUR) in Peoria, Ill. Of course, that's not the case for B100, which can start crystallizing at approximately 35 degrees.

Cold weather measures taken to prevent biodiesel flowability troubles essentially boil down to two issues: the treatment, transportation, storage and handling of neat biodiesel prior to and during blending, and the transportation, storage and use of biodiesel blends (B2, B5, B20).

The NBB's Cold Flow Impacts paper states what many other biodiesel connoisseurs already surmised-in cold weather, biodiesel blends up to 20 percent really need no additional treatment over and above what is already taken with petroleum diesel fuel. The consideration then must ultimately and very importantly rest on the transportation and storage of neat biodiesel prior to and during blending.

Moiety math-addition and subtraction
It's well known that adding certain materials to biodiesel or any other fuel can enhance its performance, including cold flow. Interestingly enough, the opposite is also true. Particular portions of biodiesel fuel also can be removed to improve its cold weather characteristics.

Although the word "additive" reverberates with the zing of a magic bullet, there really is no such thing. Whether it is emissions or cold flow, various additives aren't cure-alls for biodiesel's few weaknesses. They can help in some circumstances, however. "[Additives] don't affect cloud point," Dunn said. "They will affect pour point, under some circumstances CFPP (cold filter plugging point), but they really don't affect LTFT (low temperature flow test) that much, at least in our experience. Most of our experience is with blends of biodiesel, conventional diesel and biodiesel by itself." Dunn said while the cloud point is a conservative gauge of flowability, the pour point is too extreme to measure.

Cold flow-improving additives are blended in doses far less than 1 percent by mass, mainly due to cost. Most cold flow-enhancing additives on the market were developed for conventional diesel fuel, but they work just as well for biodiesel, Dunn said.

The chemical bases for these additives are paraffin-like structures. "That would be like an acetate or copolymer group," Dunn told Biodiesel Magazine. The additives don't prevent the formation of crystals though. "What it does do is prevent the growth of that individual crystal," he said.

Contrary to blending in additives, the cold characteristics of biodiesel can also be improved by removing solids from a chilled volume of the fuel. This process is called dry fractionation-a common variation of this is winterization. "[Dry fractionation] changes the fatty acid profile to make it more amenable to lower temperatures," said Gary Knothe, a research chemist with the NCAUR. On the downside, when this procedure is done, it makes the combustion properties worse by lowering the cetane number, which has a negative effect on emissions-specifically on NOx.

"Essentially, what you do-I'm talking about winterization now-is you cool it down, filter it, filter out the stuff that gets solid and keep the stuff that remains liquid," Knothe said. The solids are the saturated esters. The remaining liquid is mainly unsaturated esters. While Knothe expressed concern about the detrimental effect on emissions after removing saturates, Dunn said his concern in leaving just the unsaturated esters was a reduction in the fuel's oxidative stability. In spite of its faults, Knothe said he gathers the industry has some interest in using winterization.

The chemical composition of the fatty acid esters is a determining factor in how that fuel will react to the cold. Therefore, choices in feedstock and conversion process alcohols have consequential effects on the resulting biodiesel's cold flowability.

If cold weather concerns are an issue, careful consideration should be given to using the right feedstock. "What really defines the cloud point, or the cold flow, of biodiesel is its level of unsaturated or polyunsaturated esters that are present in it," Dunn said. Soybean oil typically has 15 percent to 20 percent saturated esters by mass. Numbers like that are typical for most varieties of first-use vegetable oils, whether it's canola, soy or mustard. "The vegetable oils are better than, say, tallow or waste vegetable oil (WVO)," Knothe said.
WVO has a higher cloud point than virgin vegetable oils, but not as high as tallow (see chart). Although WVOs are typically vegetable oils,

Dunn said once they are used for cooking applications, hydrogenation and chemical transitions that occur during the extreme frying temperatures cause the resulting WVO to contain higher melting points and, thus, higher cloud points. First-use animal fats, or tallow, have much more saturated content by mass than vegetable oils or WVOs. "Tallow might have 40 percent to 45 percent [saturated esters], palmitic or steric-very high melting point-type esters," Dunn said. All things considered, feedstock is the main variable when looking at cold flow properties of biodiesel.

A producer's choice of alcohol for the reaction process during production can also affect the resulting esters' cold flow characteristics, according to Knothe, who has done considerable research on this. Structures of the fatty compounds that make up biodiesel can be altered during the production process by using alcohols other than methanol to branch the fatty acid esters. Replacing methanol with isopropyl or ethanol will give way to isopropyl esters or ethyl esters, respectively. "Take isopropyl for example," Knothe said. "It lowers the melting point of individual components by about 12 degrees to 13 degrees Celsius lower than other methyl esters. Ethanol [as a reactant] would be beneficial in terms of cold flow. Ethyl esters have lower melting points than methyl esters. That's one reason I'd like to say that, actually, methanol is the worst alcohol to make biodiesel with. The only justification is that it's the cheapest alcohol. Ethanol and isopropyl give better biodiesel."

The logic of logistics
From the time B100 gets stored on-site by the producer to the time the blended product heads for the retailer, the biodiesel's transportation, storage and blending are of the utmost importance to ensure successful low temperature pouring. One of the Cold Flow

Blending Consortium's lead conclusions in the group's collaborative look at cold blending, titled Biodiesel Cold Weather Blending Study, was that biodiesel, in general, must be kept at 10 degrees above its cloud point upon blending with diesel fuel for a successful merger of the fuels.

In Minnesota, Magellan already has the tools in place to put this supposition into practice. Magellan has spent a considerable amount of time studying this in the lab, Lawrence said. It started its first biodiesel blending project in 1995, and the company has honed its practices down to a science.

For starters, the trucks offloading neat biodiesel at Magellan's terminals are either heated or insulated, according to Lawrence. "Some may have to travel hundreds of miles," he said. Insulation alone may do the trick-Lawrence said he has visited plants where the biodiesel is stored on-site at temperatures up to 100 degrees, so if the fuel gets loaded into an insulated tanker truck at those temperatures, staying 10 degrees above the biodiesel's cloud point shouldn't be a problem. Most biodiesel plants, however, recommend on-site storage temperatures of 80 degrees, Lawrence noted. At Magellan terminals, the B100 tanks are kept at a comfortable 60 degrees, well above the cloud point for methyl soyates. Of course, with tallow's high melting and cloud points, this temperature would not be able to reach the "plus 10 degrees" spec with respect to tallow's cloud point prior to blending. "It is unlikely that [WVO- and tallow-based biodiesel] will meet our cold flow specs in the colder months," Lawrence told Biodiesel Magazine.

Magellan terminals also house top-of-the-line heated tanks and fuel lines for proper proportional blending. Proportional, or injection, blending is the only recommended blending practice in freezing temperatures. The sequential, or splash, blending of warm biodiesel with colder diesel fuel can cause thermal shock, or severe and instant crystallization of the biodiesel, disallowing it to blend successfully. "There's a smaller amount of change in the crystals with proportional blending," Lawrence said.

The technology offered by Magellan's refined blending systems is helping the industry reach that frosty peak atop the cold flow learning curve. The fuel is tested as it comes into the terminal, Lawrence said. Afterwards, tanker truck drivers simply punch in their code, and the system is programmed and automated to dispense whatever blend is needed via the blenders' requests. Additives are also blended at the terminals, as individual blenders require. Although it's an option, nitrogen agitation really isn't required to agitate the fuel to prevent the formation of large crystals. "When you're looking down that hatch as the fuel is being pumped in at 600 gallons per minute, you'll find that is ample agitation," Lawrence said.

Magellan's assets and blending terminals are more large scale than other facilities in the distribution chain. One up-and-coming storage tank manufacturer, Calgary, Alberta-based TankSafe Inc., has already made a name for itself in western Canada's oil and gas industries and in the U.S. chemical storage market. Biodiesel storage is naturally its next progression. The company manufactures and markets "environmentally responsible" dual-containment, aboveground, heated storage tanks. According to Reinhard Schuetz, professional engineer and president of TankSafe, the company's uniquely designed tanks offer several advantages over others: superior insulating value, added mechanical protection, minimum 110% secondary containment capacity to safely accommodate overflow, while avoiding product and ground contamination, and substantial energy savings. TankSafe's heated tanks can reduce energy consumption from approximately 200,000 Btus per hour, which some conventional fire-tube heated tanks use, down to approximately 8,000 Btus per hour, or less using its patented design, Schuetz said. TankSafe can also provide a split tank for storage of biodiesel on one side with petroleum diesel on the other. The company could install the necessary manifolds, pumps and flow valves to properly blend the mix within an attached and warmed utility shed to help prevent thermal shock. "We have a very effective and economical means for biodiesel storage," Schuetz said.

Overall, many approaches are available for successful biodiesel storage, blending and use during the frigid winter months. As the industry's growth plows through concerns over biodiesel's low temperature performance, inventive researchers, technology and good old-fashioned gusto will surely assist in keeping the flow.

Ron Kotrba is a Biodiesel Magazine staff writer. Reach him by e-mail at [email protected] or by phone at (701) 746-8385.
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