Two challenges facing the biofuels industry involve compliance with blend quality standards and wastewater regulations. According to a study done by the National Renewable Energy Laboratory, 1 the chief problem found with biodiesel blends was inaccurate blend ratios. Retail customers and fleet managers do not typically worry about whether the blend ratio is correct until a problem occurs. For fleet managers, this can mean a total shutdown of operations. Since bad news often spreads faster than good news, fleet-stopping events do not help to promote public acceptance of biofuels.
Environmental upsets also hurt the public image of the biofuels industry. Last year, several biodiesel plants in the U.S. were fined for illegally discharging vegetable-based oil and grease and polluting nearby streams. The U.S. EPA has established limitation guidelines for discharges of “oily wastes” from facilities utilizing any type of oil and grease in their manufacturing process. While biofuels plants are new to the industrial community, they need to be good neighbors and properly dispose of and comply with regulations regarding oily wastes. Current limits on oil and grease concentration levels require producers to monitor their waste byproducts more closely prior to discharging, which means measuring the oil and grease to ensure compliance.
While illegal discharges of oily waste can have far-reaching environmental effects, the blend ratio can affect cold weather performance, tax incentives, engine performance, and warranty issues. Portable infrared analyzers offer a quick analytical method capable of determining the biodiesel and ethanol blend ratio or the amount of oil in wastewater.
There are basically two ways to blend biodiesel: splash blending (either in a tank or in the delivery truck) and in-line blending. The fact that biodiesel is typically denser than petroleum diesel and has different cold flow properties is an additional challenge to getting an adequate mix during blending. Probably the biggest concern with the biodiesel blends is what happens in cold weather. The cold filter plug point (CFPP) is the temperature at which the crystals begin to form in the biodiesel. These crystals can then plug the fuel filter. The amount of biodiesel in a blend is often reduced in the winter to avoid filter plugging. Blending in more biodiesel than specified can stop an engine.
The most common and least accurate method of blending used for biodiesel is splash blending. Diesel fuel and biodiesel are pumped by the distributor directly into the delivery truck when it is loaded. The hope is that the blend will be adequately mixed by the time the truck gets to the delivery site.
During a demonstration with a portable fixed-filter infrared analyzer (see Figure 1) at a splash blending distribution facility, a sample was taken from a delivery truck destined to deliver B20 (20% biodiesel in diesel) and the reading was determined to be 8.7% biodiesel. The analyzer accuracy was checked with a B20 standard, and the reading was 20%. After much questioning, the truth came out: The facility had run out of biodiesel and the truck had been topped off with diesel. In another demonstration test, 5 min after splash-filling the truck for a B20 blend, a sample taken from the top was 11.9% and from the bottom was 24.1%. The first delivery was less than four miles away, offering little chance for a thorough mix. Efforts to convince a driver to draw a sample at each delivery to check the blend have not yet been successful.
Due to the difference in densities between diesel and biodiesel, blending fuels in cold weather with nonheated biodiesel reduces the chance of an adequate blend prior to delivery. If biodiesel is loaded first into an empty delivery truck on a very cold day, there will be little or no mixing. Residual diesel or biodiesel left in the truck from prior deliveries can also skew the blend.
Splash blending has inherent difficulties that lead to inaccurate mixing. Infrared analysis, described in detail below, offers a quick on-site test method for verifying the blend ratio and avoiding offending problems.
In-line (injection) blending
In-line blending is not new to pipeline terminals and racks, especially for blending ethanol in gasoline. On the other hand, relatively few fuel biodiesel distributors are using in-line blending. With in-line blending, the biofuel is metered into the petroleum fuel as it travels through a pipe. Although this method offers better blend consistency for biodiesel than splash blending, density and viscosity changes in the biodiesel require adjustments to the meters for an accurate blend.
As more mandates for a minimum of ethanol in gasoline come into effect, a large number of major oil companies are blending higher percentages of ethanol at their terminals. Although manufacturers of in-line blending systems claim indisputable accuracy, a quick check for the correct blend gives real data to a claimed assumption.