Proactive biodiesel blending practices help improve performance

By Paul Nazzaro, Advanced Fuel Solutions Inc. | June 05, 2017

As biodiesel continues to emerge as a sought-after blending component for generic distillates in the Northeast and beyond, a recent study commissioned by the Connecticut Energy Marketers Association highlighted why it’s imperative that those handling the fuel educate themselves on the proper storage, blending, and distribution practices required to maintain biodiesel’s national quality standards.

Throughout 2016, to gain a better understanding of how much biodiesel is being blended into Connecticut’s heating oil pool, CEMA analyzed the biodiesel content of nearly 100 fuel samples from bulk storage tanks containing a range of blend levels. What they found, in some cases, was concerning—although not entirely surprising considering how commonplace below-the-rack blending has become.

A number of the samples CEMA pulled contained more than 20 percent biodiesel, with some north of 40 percent, when the fuel was labeled—and being sold—as B15 or lower blends. The wholesalers and distributors involved were left scratching their heads. What could possibly be causing such a significant discrepancy? After some investigation, it was determined that the storage facilities in question had one thing in common: blending into bulk storage systems ill-equipped to achieve homogeneity.

When a truck offloads neat biodiesel into a large bulk storage tank already containing distillate fuel at speeds of up to 300 gallons per minute, the odds of achieving a homogenous blend throughout the tank are not very likely. As most professional fuel handlers know, biodiesel is slightly heavier than distillate fuel, meaning, if not properly mixed, it won’t create consistent blend levels throughout the tank. This becomes increasingly probable in colder temperatures, when fuels are transported at or near their respective cloud points. If the heavier biodiesel is concentrated at the lower part of the tank, where it is then suctioned up and out to the rack, the blend ratio of the outbound fuel may far exceed what the fuel dealer was expecting.

To prevent this from happening, a strategy often relied upon is circulating the fuel throughout the tank using an air compressor and hose. This is not recommended for successful biodiesel blending. The introduction of oxygen into the fuel will degrade, destabilize and potentially drive the fuel out of specification—specifically in its oxidative stability value. This is why, although this type of blending has proven to be the most economical and convenient method by which to blend biodiesel into distillate, it can also be the most problematic.

Those who value fuel quality and work diligently to ensure the satisfaction of their customers should consider a wild stream blending scheme that incorporates regular fuel monitoring to ensure that the biodiesel remains on spec. For those hesitant to make the investment in a costly tank mixer, a static line mixer or a simple y-connector to offload dual trucks (replicating a wild stream blending environment) are more cost-effective options.

Whether in storage or transit, any stable liquid fuel can be thrown off spec by improper handling, contamination, fuel aging or oxidation. If you intend to continue to base line splash blend and circulate air through the tank, be sure that you at least know what you are buying to begin with. Ask your supplier for their most recent certificate of analysis on the fuel being brought to your facility. Be sure that the biodiesel meets EN 15751, which measures the oxidative stability of the fuel and should be a minimum of three hours. If it does not meet ASTM specifications as defined within the D6751 standards, it’s possible that an aftermarket fuel stabilizer can bring the fuel back into specification. Over the past few months, I have reviewed fuel samples leaving deep water terminals that did, in fact, meet specification, yet the fuel was no longer in accordance with the proper limits when that fuel was retrieved from the homes of several of the fuel dealers’ customers. This is why constant vigilance is required.

The CEMA study further validates the importance of closely monitoring your fuel. Using a Bacon bomb fuel thief, storage facilities should be routinely retrieving top, middle and bottom tank samples to ensure that API gravity levels (a measure of density) and FAME concentrations (biodiesel content) are consistent throughout the tank and in line with ASTM specifications. If the samples show variations inconsistent with an on-spec fuel, contact your suppliers or fuel quality partner for recommendations on how to immediately address the situation. 

In the meantime, everything you need to know about the proper storage, blending and transporting of biodiesel can be found in the U.S. DOE’s Biodiesel Handling and Use Guideline (Fifth Edition).

Author: Paul Nazzaro

Founder and President, Advanced Fuel Solutions Inc.


[email protected]


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