Ready to Burst

A two-grade system would force the industry to respond. Luckily, cavitation technology is here.
By Luke Geiver | February 09, 2011

Tom McGurk wasn’t always in the business of bubbles. The current CEO and president of Advanced Biofuel Solutions, McGurk currently heads a team responsible for creating a controlled cavitation reactor that harnesses the power of bubbles, the same reactor that just might solve a complex issue related to biodiesel production: monoglycerides. “We had a chemical company for years,” McGurk says, “and then we got into biodiesel.” Compared to making industrial chemicals, “producing biodiesel was very difficult because the feedstock varied from load to load.” A former chemical engineer, McGurk now spends his time in Rome, Ga., the home of the ShockWave Power Biodiesel Reactor, which he explains could transform the industry through its ability to deal with monoglycerides.

But to fully understand why Georgia, of all places, and why McGurk’s technology based on cavitation (and other similar reactors) may be important to the industry now more than ever, consider ASTM’s main committee ballot that proposed a two-grade system for biodiesel. The ballot, which has since been voted down, originally presented a two-grade system that would include a grade of biodiesel suitable for cold climates, a grade that would ultimately be determined by monoglyceride levels present in the fuel.

“There are probably many reasons why it failed,” Robert McCormick, principal engineer of fuels performance at the National Renewable Energy Laboratory in Golden, Colo., tells Biodiesel Magazine. Proposed in June, the ballot met its end in a main committee-level vote in December. “I think after people had six more months to think about it and really understand where they are going with it, the proposal wasn’t really ready," he says. It's not over yet for a system that would mimic the petro diesel system that features several grades of fuel though. “I think there is a consensus, however, that we need to move to these two-grades of biodiesel,” he says.

The proposal’s sticking points, McCormick says, included different levels of total monoglycerides for biodiesel in different ranges of cloud point. “As you went to biodiesel that had a higher cloud point, it required a lower level of total monoglycerides,” he says. When you look at the precision of the cloud point measurement, and then the precision of the total amount of monoglycerides, it was hard to make a case that these requirements (a lower monoglycerides spec) really meant anything. Along with the confusion over what exactly the cloud point measurements showed, McCormick says the ballot also faltered due to a lack of an official ASTM test for monoglyceride levels, and because “everybody agreed that what we needed to limit was the concentration of saturated monoglycerides, not total monoglycerides.”

As McCormick suggested, any confusion created from the first attempt to create a two-grade system will someday find clarity. When that time comes, and monoglyceride levels act as the line between grade one and two, what can the industry do to meet the new standards? Distillation, for one thing. It is the “sledgehammer,” as McCormick says. “It’s going to work” but, he adds, it’s also expensive to build and use. “Distilled biodiesel, if properly stabilized is at an extremely high quality,” he says. “But, for many producers, I’m not sure that is going to make economic sense.”

Controlled Cavitation

McGurk says cavitation is a physical phenomenon that creates low-pressure bubbles within the fluid that cannot self-sustain and eventually implode. When they burst, a shock wave sends cavitation bubbles out  into the fluid. If those shock waves are left unchecked, the heat and mixing power of the bursting bubbles can create a lot of equipment damage. “Conventionally, engineers are taught to avoid cavitation,” he says. McGurk found a pathway that allows him to harness that energy, to control it, a technology that drives a reaction in a matter of seconds versus the minutes or hours typically seen in a continuous stir tank reactor.
As an example of just how damaging some methods of cavitation can be, McGurk sites a retrofit project his team worked on in a chemical plant considering switching to biodiesel production. The plant was using a stir tank reactor set-up with cavitation. The system required the sparging of air into the tanks and when combined with the cavitation, the bubbles were so powerful they “ate through the walls at several points” and caused the two-story reactor tanks to lift off the floor.

The ShockWave Power Biodiesel Reactor employs the “controlled” approach and uses a spinning rotor with depressions in it. As the device spins, cavitation bubbles are formed in the depressions, and as the fluid flows over the depressions the bubbles burst, sending out a massive wave of energy and heat that drives futher reaction of the materials. The amount of energy created by the bubbles breaks down the material into smaller pieces, creating more surface area for the reactants to take place, a situation McGurk says also helps to reduce side or reverse reactions.

Already used in eight different biodiesel plants, including one of the largest production facilities in the country, the ShockWave Power Biodiesel Reactor is an option for producers who, McGurk says, don’t want—or can’t afford—distillation. Some producers have sent McGurk samples of biodiesel that showed only a .19 monoglyceride content with a total glycerin content of .055, he says. “You are looking at a fifth of the total glycerin and that is with waste cooking oil, and many plants aren’t able to handle that in their transesterification process.”

The idea of cavitation as a means to solve high mono levels in biodiesel produced from beef tallow or waste vegetable oil isn’t a new one though. Companies like Ultrasonic Power Corp. out of Freeport, Ill., employ a sound wave, or ultrasonic-based cavitation approach to biodiesel production. While cavitation approaches vary, the ultrasonic unit at Freeport, like the mechanical version, can reduce the one- to four-hour process to less than 30 seconds, while effectively dispersing nanoparticles and deconglomerating coalesced materials in the fluid.

Mike Kass from Oak Ridge National Laboratory even recently investigated using ultrasonic acoustic energy (similar to that of Ultrasonic Power Corp.’s version) to remove precipitate formation in biodiesel. The rationale, Kass says, was that the application of ultrasound would concentrate heating at the precipitate-liquid interfacial region. “The advantage of this approach is that you can focus the heating on the precipitate itself rather than heating the bulk solution.”

To test the theory that ultrasonic cavitation does, in fact, reduce precipitates, Kass and his team, which includes Sam Lewis and Maggie Connatser, performed a modified version of the ASTM D7501 Cold Soak Filtration Test. The team used a sample of SoyGold 1000 biodiesel that was first tested and filtered, then spiked with precipitate precursors and remeasured for filtration time. The team then chilled the biodiesel overnight and let the sample return to room temperature. “We ran the filtration test on the spiked sample and the filtration time increased as you would expect with the formation of precipitates,” Kass says. The team sonicated the spiked sample and the filtration time decreased to the original time of the spiked sample. The team also evaluated a sample that was heated conventionally, and the bulk heating was not found to reduce precipitates.

So how does this technology solve the issues of producers for whom the two-grade system could eventually be a reality? Kass says while it is not necessary to induce cavitation to reduce or eliminate precipitates, “you do need an ultrasonic field.” The bottom line, he says, is that many of the issues dogging the biodiesel industry “may be mitigated with the use of ultrasonication.” As McGurk’s sentiments show, that is a real benefit to the industry. “If you can replace or augment your reactors with a system that can provide many of the same quality characteristics of distilled products at a fraction of the cost in a much simpler installation,” he says, “then it will allow companies that may decide to stop producing or reduce their production targets to rethink their goals.”

A Serious Need

With the working group still reformulating the definition of that highly-contested winter grade of biodiesel, McCormick provides his idea on what to expect. What he suspects is the working group will come forward with a more modest proposal, something that for the winter grade is more restrictive than what is in place for all grades. More than likely, he says, the new ballot will “directionally” correct the problem, but there will still be several people who don’t feel it goes far enough. But he notes, as time goes by, “We will be able to collect more data” and “improve the test methods for monoglyceride levels.” That might not necessarily eliminate all biodiesel that is going to have these unexpected low-temperature operability problems, McCormick says, but it would limit a lot of them.

There is a possibility, he also says, that if a new ballot goes out in April, and earns approval in June, before winter there could be a two-grade system in place. While that is still unlikely, “that is the fastest a change could be made.” McGurk says they’ve already seen customers who were waiting for the tax credit to come back before pulling the trigger on retrofit purchases.

The dollar being back for this year doesn’t mean the biodiesel industry is free of all impediments. A two-grade system may still be on the way and, with it, new quality issues that several producers will have to face. And, although it might already be well understood, as McGurk says, “The ability to use lower quality feedstocks and still achieve an extremely high level of quality could make the difference in success or failure in many biodiesel plants.”

Author: Luke Geiver
Associate Editor, Biodiesel Magazine
(701) 738-4944

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