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˚F and an input temperature of 40˚F, for example, 92% regeneration would save almost $16,000 annually. Savings almost double to $31,165 at 94% regeneration. It’s even possible to achieve a 96% rate that would yield $46,000 in savings, according to Don Bohner, manager-heat exchangers at the Vernon Hills, IL, supplier.

“High regeneration and heat recovery has been a focus of our technology development since the early 1980s, when the first energy crisis occurred,” says Bohner.

“People who were realizing two effects (with steam evaporators) before now want three or four effects,” adds H. “Sam” Kumar, global R&D director of heat transfer at Invensys APV’s Goldsboro, NC, plant. A falling film evaporator with plates measuring 3 meters in length and almost 45 sq. ft. of surface that the firm developed five years ago achieves up to five effects: for every pound of steam inputted, up to five pounds of water are removed. “It’s a niche product,” Kumar admits, but it underscores his point: “As energy costs rise, people become more interested in efficiency.”

The evaporator was installed at a large Iowa ice cream plant, with the vapors removed from milk to boil off more water in the next heat exchanger. The condensate eventually is sent to a boiler or used for washdown, resulting in additional energy savings.

Efficiency usually takes a backseat to production requirements and maintenance considerations. Those needs are being addressed in collaborations between chemists, mechanical engineers and product development specialists in specifying and sizing heat exchangers. The days of 316 stainless steel-only fabrication and glue-in gaskets are long gone, points out A&B’s Zirbel. Today’s specification process begins with a detailed discussion with food scientists to learn what types of reactions will occur at a given operating temperature and consultation with heat exchanger suppliers’ technical staffs to determine the best solution. “We really need to know what is in today’s products before specifying a solution,” he says. “If we don’t, the system can’t be properly sized, and if the wrong materials are used, plate pitting will occur and ultimately lead to complete failure.”

Firms such as Alfa Laval, Tetra Pak and APV have extensive databases of operating results with plate, tube and scraped surface heat exchangers involving a wide variety of foods. The information is being augmented with predictive software to calculate flow rates and fouling potential. “Modeling work is nascent, but we’re beginning to be able to calculate performance, even with new foods,” says APV’s Komur.

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.

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˚F), triggering an evaporation-condensation cycle that is lethal to microbes on the almond’s surface. The 99.999% kill rate is achieved in less than 40 seconds, according to Weng. Surface temperatures were validated by including thermocouple-equipped aluminum “almonds” with test batches.

“It’s quite a sizable unit,” he adds. The first installation, at a firm called Going Nuts in Madera, measures 36-ft. long and 11-ft. wide. More than 20,000 lbs. of almonds an hour can be processed. Weng estimates energy costs at 0.003 cents per pound of product. He sees potential applications for beef jerky, dry corn susceptible to mold and other dry meats and produce.

Another California food processor on the leading edge of heat transfer technology is Clement Pappas & Co., a copacker of fruit juices, cranberry sauce and other products. The company’s Ontario, CA, facility is a field site for Super Boiler, a compact unit that provides high efficiency and low emissions. The US Department of Energy, the Gas Technology Institute (GTI), Cleaver-Brooks Inc. and several other organizations developed the gas-fired boiler. Depending on the maintenance/durability testing at Clement Pappas and another field demonstration at a rubber-products manufacturer, Super Boiler could be available commercially within a year.

The fire-tube boiler incorporates finned tubes that give the unit half the footprint and weight of a conventional boiler, according to Rick Knight, GTI’s R&D manager. Low emissions and high fuel-to-steam efficiency are the main advantages: while most gas-fired boilers perform in the 75% to 83% efficiency range, Super Boiler topped 94% in lab tests. Emissions of nitrogen oxide and carbon monoxide are under 5 ppm each at full load and 30 ppm at partial load, eliminating the need for scrubbers and other remedial processes. The strictest emissions standards are 50 ppm, Knight says.

A water-tube version of the boiler is under development, he adds.

Whether heat-transfer concepts are borrowed from other applications, as with the almond pasteurizer, are new-to-the-world approaches, as with reciprocal-motion retorts, or reflect continuing improvement, in the case of heat exchangers, thermal technology for the food industry continues to advance.

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

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.”