Shear madness

November 5, 2004
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Mixing technology is emerging as one of the most dynamic equipment categories, and high-shear units are redefining the science.

A technician adds ingredients to a pre-engineered in-line dispersion and batch blending system. Source: Admix Inc.
For Walter Farr, a 20-year quest to bring physical refining to the vegetable-oil extraction process reached a turning point when he found a mixer that took high-shear to a new level.

A chemist by training and chemical engineer in practice, Farr served as an expert in fats and oils with Kraft Foods until four years ago, when he joined De Smet Process & Technology Inc., Marietta, GA. Earlier, he began experimenting with alternatives to chemical processing of soybean oil, conducting bench-top experiments that applied high-shear instead of acids and caustics as part of the extraction process.



APV’s Flex-Mix Instant incorporates a rotor stator adjacent to a pre-mixing chamber in a recirculation system that links with the unit’s discharge pump. Source: Invensys APV.
Commercial applications began in Europe and South America a quarter-century ago, but the results were less than satisfactory. Those plants had to revert to hybrid systems relying on costly processing aids that compromised oil quality.

"The only bench-top high-shear mixer available at the time was a heavy-duty Waring blender," Farr says of his early experiments. "I used it for years and was getting very good results, provided the crude oil going in was very good quality." Unfortunately, poor crops are as inevitable as good ones, and Farr tried a number of high-shear units before applying what he describes as an ultra-shear mixer: a machine capable of applying 100,000 reciprocal seconds of shear force.

"When I began using a three-stage rotor-stator assembly from IKA Works, I started to get dramatically better results, but this was bench-top, not commercial scale," he recalls. He worked with Michael Janssen and engineers at IKA's Wilmington, NC, shop to devise a process using a pre-stage mixer as an alternative to acids to hydrate phosphatides in the bean, then a second mixer instead of caustic to remove free fatty acids before the oil enters the deodorizer, where vacuum steam distillation is applied to remove volatile compounds. If bean quality is low, some caustic may be necessary upstream of the deodorizer, resulting in "semi-physical refining," Farr explains. Still, chemical use is significantly reduced, and the process results in "dramatically improved yields," he says. "It's difficult to define, but in a large refinery, even a one percent yield improvement can be worth millions of dollars a year."



Though he retired from De Smet and established his own consultancy in Olive Branch, MS, a year ago, Farr continues working closely with the firm and IKA to implement his process. An Illinois-based edible oils facility deployed the process four years ago, and Mexico's first greenfield plants in 30 years are "operating very well" with the system, he says. A processing facility being built in Alexandria, Egypt, also will utilize physical extraction, and he anticipates retrofitting existing plants.

Optimizing the system is how Farr and other specialists make their livings, but essentially the trade-off is high-shear for chemicals. "It's impossible to get too much shear," says Farr.



A controls technician performs integration work on an automated food mixer. Plummeting prices for variable frequency drives and other components are bringing mixer control technology within the reach of most food processors. Source: Ross Systems and Controls.

Less is more

The more shear, the merrier is true with oils and most food-mixing applications, but a point can be reached where increased shear is counterproductive. Rob Lanham, general manager of Ross Systems and Controls in Savannah, GA, recently worked with a processor who crossed a threshold where a gravy began thickening as more shear was applied. "The more shear they put in, the more heat was generated," says Lanham, theorizing the dynamics broached a point where the mixture entered a transition phase.

Tip speed and particle-size reduction are only two of many variables of interest to controls experts such as Lanham. How much vacuum to pull and when to de-aerate, where to set product temperature and when to accelerate or decelerate mixing speed become more important as the complexity of the mixture increases. Recipe-driven PLC controls are critical if multiple variables are to be managed consistently from batch to batch, and the affordability of those controls is within reach of most food processors, Lanham points out.

"Ten years ago a variable frequency, 150 HP drive cost $100,000," he says. "Today, it's in the $7,000 to $15,000 range."

From a mixer-maker perspective, however, the mantra is higher shear. If it can be delivered in-line, so much the better, notes Doug Cohen, technical director in the mixer division of Charles Ross & Son Co., Hauppauge, NY. That has been the evolution for Ross's SLIM (Solid/Liquid Injection Manifold) powder induction technology. The mixer uses high vacuum to convert powders to a mist-like stream that immediately disperses when injected into a high-velocity liquid stream. A batch version debuted in the late 1990s, and Ross now is optimizing an in-line version with more vacuum and shear.

SLIM is applicable for processes in which agglomeration is an issue, such as the introduction of gums and other thickening agents to a product. For broader applications, the company offers MegaShear, a rotor-stator design capable of achieving sub-micron emulsions. Tip speeds of up to 12,000 feet per minute are achieved, triple the speed of the previous generation of mixers, Cohen says. In some food applications, high-shear rotor stator assemblies have replaced pressurized homogenizers. "Anytime you can move an application from homogenization to rotor stator, you have done the customer a service," he maintains.

"Going to extreme shear levels is the trend in mixing," agrees Lou Beaudette, president of Manchester, NH-based Admix Inc. "We're approaching the capabilities of the pressurized homogenizer. Eventually, processors will be able to mill whole pieces of fruit or vegetable to maximize the yield. Finding the right design that can handle the skins as easily as the pulp still remains to be done, but we are on the verge of extreme milling machines."

Admix offers a range of units for different processing jobs, with the Boston Shear Mill topping the roster for extreme shear force. Particle reductions down to one micron for softer materials are possible. The in-line mixer also is appropriate for creating emulsions, according to Beaudette. Particle sizes that only were possible with a high-pressure homogenizer five years ago can now be handled by the shear mill but with less energy and maintenance requirements and more throughput, he says.

For some products, plant operators will combine a high-shear mixer with a homogenizer, relying on the rotor stator assembly to reduce particles to a size that the homogenizer can handle while also reducing maintenance requirements. Beaudette says his Boston Shear Mill can process viscosities of up to 50,000 centi-Poise (c-P), the thickness of ketchup at room temperature. At 25

High-shear mixers are adept at tasks other than size reduction. Rapid, finite dispersion of ingredients also is accomplished, as this progression demonstrates. Dispersion was accomplished in 60 seconds. Source: Motech Manufacturing Company Inc.

Better batching

The Breddo Likwifier is a seminal example of high-shear mixing in the food industry. A workhorse in batch mixing and blending, the Likwifier is undergoing retooling to keep it in step with the changing nature of food engineering.

Over the years, some users have retrofitted their units to blend, cook and chill ingredients. Relying on in-house engineers, manufacturers jacketed the bowls and added the plumbing necessary to create de facto heat exchangers. By introducing hot water or steam, the Likwifier cooks a batch while blending is done. Flushing the unit and then introducing chilled water returns product to ambient temperature or lower.



Phase two of progression
If all the water isn't evacuated before steam is introduced, a phenomenon known as "steam hammering" occurs, points out Bill Wade of American Ingredients Co., the Kansas City-based fabricator of the Likwifier. The consequences are serious damage to the mixing unit, underscoring the importance of proper installation and controls. With fewer in-house engineers available to properly retrofit high-shear mixers, Breddo has engineered a Likwifier with all the necessary valves, plumbing and controls, including PLCs for recipe management. The units have been well received by makers of icings, strawberry purees and pectins, and reduce mixing times by as much as 80 percent, according to Wade.



Phase three of progression
A new kid on the food mixing block is Mixing Technologies, a division of Motech Manufacturing Company Inc., Medley, FL. The firm designed a high-speed batch unit with an unusual tulip-shaped mixing bowl, wider at the base than the top. The high-intensity mixers feature an impeller with three blades at a 120 arc to each other in the middle of the bowl and a second "chopper" blade on the periphery of the bowl. The impeller rotates at up to 300 RPMs, causing product to surge toward the top. The counter-rotating chopper "breaks the product free from the surface of the bowl while also folding it back into the mix," according to Sales Engineer William Butch. The synergy of the dual-blade configuration produces mixing activity equivalent to 3,000 RPMs, says Butch.



Phase four of progression
The PLC-controlled, all-316 stainless steel mixer with mirror-finish was first sold to pharmaceutical manufacturers, who demand finite dispersion of almost trace amounts of active ingredients. Motech guarantees dispersion to at least 10 parts per million in a mixture, Butch says, and it accomplishes those levels in significantly less time than a ribbon mixer. A vacuum recovery filter captures any lost particulate and puts it back into the batch, a very important feature when mixing expensive ingredients.

"When you're asking for products to be finitely mixed, you have to use this kind of technology," he adds. "Stratification is eliminated and product uniformity is improved."



Phase five of progression
The turbo mixer is 3-A approved and suited for drink powders, granulations, dispersions and shortening mixing without agglomeration. Because the pharmaceutical industry demands a higher sanitary standard than food, a new P-3A standard may be established for those applications. Butch expects the turbo mixer to meet or exceed that standard.



Phase six of progression
The meaning of high shear varies with the perspective of the speaker. For some, it connotes size reduction; for others, its essence is total dispersion. The common denominator is higher speed and faster processing time, benefits with appeal to most food and beverage manufacturers.

For more information:

Lou Beaudette, Admix Inc.,
800-466-2369

Bill Wade, American Ingredients Co.,
816-561-9050,
sales@aic-breddo.com

Walter Farr, Walter E. Farr & Associates,
770-366-3723,
wef@desmetusa.com

Michael Janssen, IKA Works Inc.,
800-733-3037, ext. 210,
mjanssen@ika.net

Stig Christensen, Invensys APV,
011-458922-8922,
Stig.H.Christensen@invensys.com

William Butch, Motech Manufacturing Company Inc.,
786-229-7607,
butch@mixingtechnologies.com

Doug Cohen, Charles Ross & Son Co.,
800-243-7677

Rob Lanham, Ross Systems and Controls,
912-238-5800
rlanham@mixers.com

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