Heat Transfer: advances, borrowed and new

December 1, 2006
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As throughput demands at food plants ratchet up, suppliers are responding with larger plates and bigger ports on heat exchangers. This Tetra Pak unit has a 6-in. port and can handle up to 350,000 lbs. of cheese milk an hour. Source: Tetra Pak Inc.


Heat transfer is core technology in food and beverage processing, yet the days when in-house engineering expertise on thermal transfer existed are fading fast. “As people drift away from engineering as a discipline, there are very few plant experts left who really understand the thermal dynamics of combustion control,” laments Marc Hunter, principal global product marketing manager for Invensys’ Foxboro A2 controls package.

While Hunter was speaking about boilers, efficient heat transfer is a common processing objective. Tradeoffs between efficiency, throughput rates, maintenance requirements and other factors usually are required with heat exchangers. Values change with the composition of the food being processed, adding a level of complexity that goes beyond thermodynamic expertise. Increasingly, food companies are collaborating with food scientists, system fabricators and equipment suppliers’ engineers to specify the most appropriate heat-transfer system for their application.

Heat exchangers are models of efficiency, and rising energy costs are helping manufacturers rationalize the cost of making them even more efficient. “If you can give people a reasonable ROI on a higher efficiency regeneration section, 90 percent will make the investment,” suggests John Zirbel, project manager with A&B Process Systems, Stratford, WI. Boosting regeneration and heat recovery rates a few percentage points can result in substantial operational savings.

Assuming electric rates of 8 cents per kWh and steam generation at $10 per 1,000 lbs., Tetra Pak Inc. created a regeneration calculator that lets manufacturers estimate total savings by moving from a 90% regeneration base to 92% and 94%. Assuming 50,000 lbs. an hour of fluid milk throughput at a pasteurization temperature of 176

A lab version of a reciprocal-motion retort featuring Allpax’s innovative spring system is in production. The company’s engineers believe they will be able to scale up to a full-size production unit in the near future.

Heat transfer containers

In rotary and static retort systems, heat penetrates from the outside of the container to the product’s center point, a process that requires significant thermal input and often results in overcooking of the food bordering the container’s walls. Process Engineer Richard Walden reasoned that reciprocal motion could agitate product and effectively turn the container into a heat exchanger to accelerate come-up and sterilization time. Walden, founder of Oxfordshire, UK-based Zinetec Ltd., dubbed his technology the Shaka process and licensed it to three retort fabricators, two in Europe and Covington, LA-based Allpax Products Inc.

While European manufacturers are fabricating small-scale commercial retorts employing the technology, Allpax engineers have focused on lab units that also operate in spray, steam and rotary modes. Half a dozen of the R&D retorts are in the field or being built, and the company hopes to build a commercial unit capable of processing up to 1,000 containers at a time in 2007.

Rapid back-and-forth motion of a loaded basket weighing close to a ton creates considerable stress. Instead of a sinusoidal drive to control the load, Allpax’s engineers incorporated springs into their patented design, an approach that absorbs load inertia and returns energy on the backstroke. They also devised a system offering both vertical and horizontal motion, an option that can make the unit more compatible with existing material handling systems, depending on the product and container being retorted.

“One of my engineers had the idea of putting in only a small amount of energy at a time, causing the product to oscillate and shake at its natural frequency,” explains Trae Miller, engineering director. “The springs are storing the energy.” Besides eliminating stress on connecting rods, cams and other mechanical parts, the pilot unit has achieved up to 8.3 strokes a second. Miller estimates the force approaches 5 Gs.

The Shaka process assumes 2 Gs of force, though early testing suggests the appropriate level is product dependent. An experiment with a carrot in a jar demonstrated that ratcheting up the force only slightly was the difference between a stationary carrot and “an orange blur,” he says. “While the process is terrific, you can’t simply throw any product into it and think the benefits are going to be wonderful. There is a very fine line where the process works or doesn’t.”

Jet-impingement heat transfer has been used successfully for both cooking and cooling foods for a number of years. Now it will be applied to dry foods as a pasteurization step to destroy pathogens.


Heat exchangers are being sized to handle higher throughput demands, with 6-in. inlet ports rapidly replacing 4-in. ports as the industry standard. Source: Invensys APV.

Three outbreaks involving Salmonella Enteritidis PT30 on raw almonds in recent years have threatened the premium segment of a crop worth close to $3 billion. “Up to now, PT30 has been the most thermally resistant salmonella found,” according to Jun Weng, research fellow at FMC FoodTech, Madera, CA. Roasting the nuts would destroy germination and lower their value, but Weng reasoned impingement ovens produced by the company’s Sandusky, OH, division could be modified to kill bacteria in crevices in a short-time process. The result is the JSP-1 pasteurizer, which has been validated to deliver a 5 log reduction in PT30 salmonella. Weng, who developed FMC’s NumeriCal and other model predictive controls, has dubbed the system’s modeling software AlmondCal.

Raw nuts are lightly wetted in a chamber before being conveyed to a second chamber, where superheated steam meets saturated air (dew point is 201

For more information:

John E. Zirbel, A&B Process Systems, 715-687-3089, jzirbel@abprocess.com

Trae Miller, Allpax Products Inc., 985-893-9277, traem@allpax.com

Jun Weng, FMC FoodTech, 559-661-3200, jun.weng@fmcpi.com

H. “Sam” Kumar, Invensys APV, 919-731-5321, sam.kumar@invensys.com

Don Bohner, Tetra Pak Inc., 847-955-6332, don.bohner@tetrapak.com


Thermocouples in aluminum almonds linked to a data logger were used to validate 5 log kill rates for a heat-resistant strain of salmonella that has created a demand for pasteurization of raw almonds. Source: FMC FoodTech.

Sidebar: Going nuts for pasteurization

While the resources of major equipment suppliers often are required to develop new technology, implementation of those innovations often depend on small, entrepreneurial food companies. FMC FoodTech’s new almond pasteurizer is a case in point.

Salmonella incidents in 2001 and 2004 have undermined the raw almond business, forcing growers to either blanch or roast much of their crop. FMC FoodTech’s JSP-1 surface pasteurizer has the potential to revive the raw almond market, and the company found a willing partner in Going Nuts, a family business located across town in Madera, CA. The company handles 300,000 lbs. of its own nuts but is targeting 5 million lbs. of throughput for the pasteurizer.

“We’re doing this for profit, but it’s also something I really believe needs to be done,” says Bill Alquist, Going Nuts’ owner. “With this process, the salmonella problem is eliminated, and the product looks like it’s cleaned and polished.”

Alquist and his son-in-law, Zeb Brown, are overseeing installation that includes the construction of a clean room, a horizontal f/f/s packaging line and a compact water-tube boiler that relies on a helical coiled heat exchanger to generate steam without a large pressure vessel. December start-up for the process was targeted.

While he estimates the capitalization and operating cost will be about a nickel per pound of finished goods, “it’s going to be the way to go,” Alquist predicts. “It’s a heck of a piece of technology.”

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