Imaginative heat-management schemes cut processing costs of snacks, fruits and spices. Could your process benefit from such an approach?



Legend has it that the renowned Greek mathematician and inventor Archimedes (287-212 BCE) -- originator of the compound pulley and the hydraulic screw -- used the sun's heat as a weapon of war in defending the Sicilian city of Syracuse from a Roman invasion fleet. Employing the principle of the parabolic reflector, as seen in a modern solar furnace, Archimedes is said to have arranged an array of mirrors on a hillside to focus the sun's rays on the invaders' ships, thus igniting them. Fact or fancy, the story indicates that making heat work harder is a preoccupation of long standing.

Today, spurred by accelerating costs, processors are turning to equally imaginative methods to boost energy efficiency. Two common methods are the recovery and recycling of heat generated during processing; and the use of equipment to keep energy consumption to a minimum without sacrificing results.

Steam generators can be an essential part of a heat-recovery system. They capture gases that would be exhausted and employ that heat for a boiler system.

Toasting Corn Chips, Dehydrating Blueberries

Among the numerous facilities operated by one of the world's best-known snack-food manufacturers is a 350,000 ft2complex in southern Georgia, where vast quantities of corn chips and snack specialties are produced. There, gas-fired ovens on three parallel processing lines use heat to toast corn chips. Until recently, however, once its mission was accomplished, the heat was simply stack-vented from the plant's roof.

Realizing that the heat could be recovered, converted to steam, and reintroduced into the plant's main steam supply stream, management thoroughly quantified the energy cost reductions that this would realize, and researched available heat-recovery technology.

Diagonally at the opposite end of the country, another company has gained recognition for the heat transfer technology it had introduced. MCD Technologies of Tacoma, Wash., manufactures dryers and evaporators that employ the company's Refractance Window design to dry food products and nutraceuticals quickly and gently, resulting in good retention of color, flavor, aroma, nutrients and actives.

In addition to selling equipment, MCD provides custom contract services in its Tacoma plant, including processing, test-drying and scaleup drying. This segment of its business also serves to demonstrate the benefits of the dryer design and operation. To succeed at this, however, MCD needed a source of steam that is dependable, efficient and compact to meet space constraints.

At a major corn chip and specialty snack plant, heat-recovery boilers capture heat from toasting ovens and convert it to steam that is re-introduced into the main steam line. The system paid for itself in less than a year.

Back in Georgia, the snack-food company addressed its heat-recovery challenge by contacting Clayton Industries, City of Industry, Calif., a designer and manufacturer of steam generators and heat recovery systems. Engineers at Clayton recommended that the snack-food maker install three roof-mounted heat-recovery boilers (because roof mounting is less expensive than ground installation), each serving its own toasting oven.

The toaster ovens are situated in long conveyor systems that deliver corn chips formed and cut from a batter. Toasting adds the “crunch” that appeals to snack-lovers, and heat is subsequently directed to a vertical channel much like an exhaust hood outlet, then introduced into a heat recovery boiler. The heat creates steam in the boiler core. The steam is routed to a remotely located separator, which in turn sends it to the processing supply stream. Processing heat is captured and returns as processing heat.

In this drying system, fresh blueberries are washed and pureed before being placed on a moving sheet of clear plastic. Water beneath the sheet, heated by a steam generator, is the source of infrared energy that is transferred into the moist product at the speed of light. Drying is completed in four minutes.

Using Infrared Energy

Back in the Tacoma drying lab, MCD's dryers and evaporators are used to demonstrate how quality-conscious processors can use the systems and operate at low temperatures without a vacuum. The company's Refractance Window technique uses steam to heat the water beneath a continuous sheet of clear plastic. The process allows infrared energy to pass through the plastic with the speed of light and into the moist product atop the belt, which dries rapidly at atmospheric pressure.

According to the company, the result is a modest operational cost and high retention of desirable properties. Among the products that can benefit from the drying method are spices and herbs, dairy products, flavorings, fruits and vegetables, meat, poultry, fish, starch and cereals.

Essential partners in both the toasting and drying processes are the heat-recovery boilers from Clayton Industries. The boilers were installed at the snack-food company in the fall of 2007. The economies enjoyed as a consequence have confirmed the accuracy of its executives' predictions, and the company's capital investment has already been recouped.

MCD says a small footprint was essential for its in-plant steam generator because a designated boiler room would not accommodate a conventional steam boiler of sufficient capacity. The Clayton unit they acquired leaves space for storage in the boiler room, executives say. Equally important, they add, the Clayton steam generator comes up to pressure rapidly, maintains pressure despite demand fluctuations, and is easy to operate and maintain.


Clayton Industries, City of Industry, Calif., manufactures direct-fired steam generators and waste heat steam generators. For more information from Clayton Industries, call (800) 423-4585 or visit www.claytonindustries.com. For more information from MCD Technologies Inc., call (253) 476-0968 or visit www.mcdtechnologiesinc.com.

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