Published: Jan 2010
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FOR PURPOSES OF THIS CHAPTER, THE TERM “biodiesel” is a fuel comprised of mono-alkyl esters of long chain fatty acids derived from vegetable oils or animal fats meeting ASTM D6751 specifications and is designated as B100. Biodiesel is an ultra-low sulfur, renewable fuel that can be used as a neat (pure) fuel but is most often blended into petroleum diesel (petrodiesel). To distinguish the amount in the blend, the convention prescribed in D6751 is to state the amount of biodiesel in the blend by the volume percentage preceded by the uppercase letter “B.” Therefore, a 5 % blend of biodiesel in petrodiesel is B5 and a 20 % blend of biodiesel in petrodiesel is B20. Biodiesel blends can be used in many applications where petroleum middle distillate (i.e., diesel fuel) products are used, such as on-road and off-road diesel, home heating oil and boiler fuel, marine diesel fuel, and nonaviation gas turbine fuel. There may be some limitations on the blend percentages used in unmodified diesel engines, and the original equipment manufacturer (OEM) should be consulted, especially if using higher blend ratios. Most biodiesel made today is not suitable for use in kerosene lamps due to its higher viscosity and surface tension, resulting in less than optimum wicking properties, although it can be used in heating applications where wicking is not important. The biodiesel industry focus in the United States over the past 10 years has been the on-road and off-road diesel market and the home heating oil market. Biodiesel is most commonly used as a blend of B5 with conventional petrodiesel in the existing equipment that more traditionally has operated solely on petrodiesel. Blends in the range of B6 to B20 are also in regular usage with heavier duty diesel trucks and buses. Other sections of this manual cover in more detail both general and special engine and burner equipment considerations when using petrodiesel. These same considerations are also valid for the use of biodiesel blends and will not be covered further in this chapter. Biodiesel's long straight chain hydrocarbon structure with a limited number of double bonds (directly related to the structure of the natural oils and fats from which it is produced) coupled with an ester linkage with a short chain alcohol (usually methanol or ethanol) provides for naturally high cetane, good lubricity, biodegradability, and lower emissions . Combustion of biodiesel in a diesel engine results in lower emissions of unburned hydrocarbons, carbon monoxide, and particulate matter (i.e., black smoke) when used in unregulated engines and compared to conventional petrodiesel . For some applications biodiesel also provides reductions in nitric oxide (NOx) due to its oxygen content (i.e., 20 % NOx reduction with B20 for home heating oil), while in other applications the use of biodiesel can be NOx neutral or have a slightly higher NOx (i.e., 10 % NOx increase for B100 in on-road diesel engines) depending on the amount of biodiesel, the duty cycle and the engine technology . Beginning in 2010, new diesel engines will be fitted with catalytic technology to reduce NOx from both biodiesel and diesel fueled engines by over 90 %, so any detriment of biodiesel on NOx will not be an issue with post-2010 diesel engines. The 2008 volatility in the cost of a barrel of crude oil, with a high of over $140/bbl, and increased concern over global warming has caused the interest in biomass-based fuels, and biodiesel in particular, to skyrocket. Federal legislation in the United States provides for a $1.00 per gallon tax incentive for B100, and there are some state incentives and some state usage requirements. The state of Minnesota requires 5 % biodiesel in most of the diesel fuel used in the state, and the states of Washington and Oregon also require biodiesel to be blended into diesel. Additionally, the U.S. Congress, as part of the Energy Independence and Security Act of 2007, passed the second version of a national Renewable Fuel Standard (RFS2), which requires over 1 billion gallons of biomass-based diesel be used in the U.S. diesel fuel pool by 2012. These state and anticipated federal mandate volumes, specific to biodiesel, have caused a dramatic increase in the building of production capacity and overall product volumes for biodiesel (see Figs. 1 and 2).
MARC-IV Consulting, Inc., Kearney, MO