Pumps & Systems, April 2008
Called the "fastest-growing alternative fuel" in the United States by the Department of Energy, biodiesel continues to play an increasingly significant role in the nation's future motor-fuel supply. In fact, the Congressional Budget Office and the U.S. Department of Agriculture confirmed in 2006 that biodiesel is the lowest-cost alternative fuel option for meeting the Energy Policy Act of 2005's alternative fuel use requirements. Late last year President Bush signed the Energy Independence and Security Act of 2007, which further expands the renewable fuels standard and mandates one billion gallons of biodiesel use by 2012.
Because of its use of renewable feedstocks, energy efficiency, compatibility with the existing fuel-distribution infrastructure and ability to reduce greenhouse gas emissions, biodiesel is the one alternative fuel capable of making a difference in the nation's diesel-fuel use patterns-today.
Biodiesel, or B100, is manufactured through a process called transesterification, which converts any number of available feedstocks-most often various animal fats, vegetable oils and recycled greases-into chemicals called long chain mono alkyl esters, or biodiesel. These chemicals can also be referred to as fatty acid methyl esters (FAME). In the manufacturing process, the oils or fats are reacted with a short chain alcohol-usually methanol, but sometimes ethanol or other alcohols-in the presence of a catalyst such as sodium hydroxide or potassium hydroxide to form biodiesel.
B100, sometimes called "neat" biodiesel, is most often blended with regular diesel fuel at an 80 percent diesel, 20 percent biodiesel ratio to form B20. If formulated to conform to ASTM D975, the B20 blend can generally be used interchangeably with diesel fuel for normal usage as long as it meets the requirements of ASTM D6751, and the cold-flow properties of the blend are adequate for the geography and time of year the fuel will be used.
Most current technologies that handle petroleum diesel can handle B20. In fact, in its B20 configuration, biodiesel has been shown to have very little, if any, adverse effects on compression-ignition engines, fuel-oil and heating-oil boilers, turbines, or pumps, hoses, seals, gaskets, swivels, loading arms, valves, fittings and other equipment used in its handling, transportation and storage. (Users should be aware that B20 may degrade faster than petrodiesel if oxidizing metals such as copper, bronze, brass or zinc are present.)
Areas of Concern
While federal mandates appear to guarantee a boost in alternative fuel use now and into the future, the companies that manufacture the equipment used for the processing, handling, transporting and storing of these fuels must first be confident in that equipment's ability to handle any new formulations to ensure their safe implementation into the motor-fuel pool. Among the critical areas of concern for any manufacturer when designing and engineering new equipment are material compatibility, operational reliability, maintenance requirements and energy savings.
As with any new fuel or chemical formulation, care must be taken to ensure material compatibility. Studies have shown that although B20 is well suited for use with existing diesel technology, B100 and other higher biodiesel blends require special handling with equipment engineered to be compatible with the fuel.
B100 will degrade, soften or seep through some hoses, gaskets, seals, elastomers, glues and plastics with prolonged use; compounds especially susceptible to degradation include nitrile rubber, polypropylene and polyvinyl materials. Nonmetallic materials that have been shown to be compatible with B100 include PTFE, some FKM formulations, various fluorinated plastics and nylon. Compatible metals with B100 include ductile iron, stainless steel, carbon steel and aluminum; brass, bronze, copper, lead, tin and zinc are incompatible.
One pump capable of handling biodiesel through its production, transportation and storage phases is a positive displacement pump featuring sliding vane technology. Sliding vane technology is featured in positive displacement pumps that can handle thin liquids.
Sliding Vane Technology for Biodiesel Production
Sliding vane technology offers high efficiency and low maintenance advantages, which are important factors in today's era of rising energy costs, lean personnel staffs and high demand for increased profitability.
For even greater flexibility, efficiency and productivity, advanced vane pump designs include motor speed technology and "designed in" features such as a hydrodynamic journal bearing and one mechanical seal. These features serve to further improve the fundamental pumping process in biodiesel manufacturing. In fact, sliding vane pumps have become a pump technology of choice in biodiesel production plants throughout North America for these same reasons.
The secret behind a sliding vane pump's operational characteristics is the vanes that slide in and out of slots in the pump rotor. The pump's rotation draws liquid in behind each vane, through the inlet port and into the pumping chamber. As the rotor turns, the liquid is transferred between the vanes to the outlet where it is discharged. Each vane provides a positive mechanical and hydraulic displacement of the liquid. Vanes are actuated by three forces: (1) centrifugal force from the rotor's rotation, (2) push rods moving between opposing pairs of vanes and (3) liquid pressure entering through grooves and acting on the rear of the vanes.
Each revolution of a sliding vane pump displaces a constant volume of fluid; variances in pressure have a negligible effect. Energy-wasting turbulence and slippage in the pump are minimized and high volumetric efficiency is maintained. The sliding vane technology also results in superior priming and suction capabilities, making the pumps a good choice for line-stripping, the evacuation of heels and pumping from underground or top unloaded storage tanks. Sliding vane pumps for biodiesel applications are available with capacities from 1-gpm to 2,300-gpm.
Sliding vane pumps with hydrodynamic journal bearings eliminate shaft-to-bearing contact, meaning that there is virtually no contact or wear, resulting in longer bearing life and pump efficiency. Advanced sliding vane pumps can also include cavitation/noise-suppression liners that control the wear effects of cavitation and reduce noise levels up to 15-dbA. Compactly designed, motor-speed sliding vane pumps have been created for reliable continuous-duty operation.
If need be, sliding vane pumps can be serviced with the piping attached; if the vanes become damaged, replacement is accomplished by removing the outboard head assembly, sliding out the old vanes, inserting new ones and reinstalling the head.
Taking note of the cautions that are required for the handling of B100, upgraded elastomer seals in many lines of sliding vane pumps allow for compatibility with all biodiesel blends. FKM formulations have been upgraded to high-grade compounds that allow for much broader compatibility with a wider range of fuels. These elastomers are UL-listed and approved for all ethanol and biodiesel blends, including B100.
Conclusion
In the past, because of its ready acceptance of diesel fuel and its corresponding technology, Europe represented nearly 90 percent of global biodiesel consumption. Recently there has been a ramping up of biodiesel production in the United States. In fact, according to the National Biodiesel Board, U.S. production of the fuel reached approximately 450 million gallons in 2007, up from a scant 2 million gallons as recently as 2000. The NBB also reports that as of late 2007, there were 165 U.S. biodiesel manufacturing plants online with the capacity to produce 1.85 billion gallons of the fuel per year. In addition, another 80 plants were under construction and expected to be completed by mid-2009.
Therefore, with biodiesel production and use continuing to grow in the United States, there is a profound need for materials and equipment capable of handling its production, transportation and storage. With a history of handling thin liquids, sliding vane technology is one choice for the pumping requirements of a biodiesel plant, tank truck and railcar fleet or storage facility.
