Processors Look to Refrigeration When Analyzing Energy Costs

June 4, 2014
Opportunities abound to reduce a food plant’s energy load, but refrigeration is a logical place to start processors of frozen goods and other products.

A technician prepares a condensing economizer for installation. A variation of conventional economizers, these units harvest much more of the waste heat for re-use. Photo: Woodard & Curran

Interest in energy efficiency waxes and wanes, and food professionals can be excused for any eye-rolling when the topic comes up. Throughput pays the bills, and shaving a few zeroes off the annual utility bills may barely rate an “attaboy” from bonus plans that put finished goods first and foremost.

Mainstream indifference aside, the pendulum may be swinging in efficiency’s direction, though it has less to do with rising electrical and gas rates than pressure from food companies’ customers. A recent survey by GE Capital’s corporate finance division of middle-tier food and beverage firms — defined as companies with revenues from $10 million to $1 billion — found that three in 10 of these organizations have implemented sustainability programs. The interest coincides with the desires of retailers and chain restaurants.

The majority of foodservice and retail sales are controlled by mere handfuls of channel masters, points out Chris Nay, senior managing director-food and beverage in GE Capital’s Chicago office. Food processors intent on winning and retaining business relationships with those channel masters are undertaking energy efficiency and resource conservation programs.

Good-faith efforts by their suppliers create a halo effect for Walmart and others, Nay notes. More than a few processors who publicize their programs have experienced a retail sales bump, he adds.

Improvement projects begin with low-hanging fruit. In the case of frozen foods, refrigeration systems are the most inviting target for energy conservation. Optimizing an industrial refrigeration system is the best opportunity for cuts and often yields the quickest payback, according to Calvin Wohlert, principal of Solution Dynamics, an Olathe, Kan., engineering firm. If processors tackle refrigeration in conjunction with new lighting, boiler heat recovery and compressed air projects, they “could cut their energy bill by 20 percent, some as high as 40 percent,” he says.

An upgrade in controls hardware on ammonia compressors is a can’t-miss improvement with quick payback, says Brian Strother, senior energy engineer at E4E Solutions LLC, Atlanta, particularly when slide-valve controls are replaced with variable speed drives. Even simple housekeeping improvements can yield savings at minimal cost.

Strother cites a recent project at a refrigerated foods plant with twin freezer lines. “One was in a state of disrepair, with dirty evaporator coils, poor air flow and warm air leaking in,” he recalls. “Simply performing the necessary maintenance probably saved the firm as much money as our controls project.”

In its recently released corporate responsibility report, Hormel Foods Corp. highlights the most dramatic cost-reduction projects involving energy consumption over the last year. Topping the list is an overhaul of the ammonia refrigeration system at its headquarters plant in Austin, Minn.

Upsized condensers at Hormel Foods’ Austin, Minn., facility opened the way to changes that allowed engineers to lower the discharge pressure on the ammonia refrigeration system, lowering annual electrical consumption by 2.9 million kWh.

Two of the system’s condensers had reached the end of their service life. Typically, the units would be swapped out for comparable condensers, but this time a team of engineers and refrigeration experts met to explore other options. By “right-sizing” to bigger units and making downstream changes in valves and piping, they determined discharge pressure could be lowered sufficiently to reduce the energy used to power compressor motors, reducing annual consumption by 2.9 million kWh.

The new condensers added capital costs to the replacement project. “But when we optimized the system at a cost of $6,000, we generated a ROI of $250,000,” according to Thomas Raymond, Hormel’s director-environmental sustainability. “That’s pretty easy to cost-justify.”

Sustainability programs are driven by executive management, but often there is a disconnect between lofty goals and factory execution. “Even when there’s interest in energy savings at the corporate level, improvements can be put on the back burner at the plant level,” says E4E’s Strother. “We’ve pointed out things that can be done by plant personnel, not us, but they don’t get done because their focus is on meeting production targets and keeping safe.”

Mining waste heat

Low U.S. energy costs frustrate champions of efficiency improvement, making it more difficult to cost-justify them. An example is a thermal recovery system engineered by Atlas Copco Compressors LLC in Rock Hill, S.C., five years ago. The first installation was at Hormel’s Dubuque, Iowa, plant, a LEED gold-certified facility that came on line in early 2010. Water is channeled through three modified oil-free compressors, cooling the machines and then being routed to a 200,000-gallon tank for use in sanitary clean up, boiler feed and other applications.

Marketed as CarbonZero, the water-cooled compressor system boosted the efficiency of these energy-intensive machines to the 90-95 percent range. A dozen systems similar to Hormel’s are now in operation at other U.S. facilities, though much more interest has come from Europe, where high energy prices make the upfront investment easier to cost-justify. “It hasn’t taken off as much as we hoped in the U.S.,” allows Rick Schadt, a product manager in Atlas Copco’s West Springfield, Mass., office.

System design and additional cost are dictated by the manufacturer’s application. The modified compressor itself adds a 10-15 percent premium, Schadt calculates, with piping and hot water storage additional. Hormel determined a temperature range of 125°-140°F was adequate, though some systems have been designed to deliver 195° water. Typically the water exits the compressor at 150°-190°, according to Schadt, with the demand for hot water dictating the set point: the higher the temperature desired, the slower the flow of water through the compressor.

Economizers are a less exotic option for thermal recovery. They are associated with boilers that vent gases in the 700°F range. But boiler economizers only capture about a tenth of the gas’ energy, suggests Bert Wesley, senior project manager in the Duluth, Ga., office of the engineering firm Woodard & Curran. That’s because preheating of boiler feed-water is the only use made of the recovered energy, he says. “On a closed-loop system, that’s peanuts.”

A condensing economizer, on the other hand, harvests more latent heat because it applies it to additional uses. “If you have a heat sink, you’re in business,” says Wesley. Limiting factors are where the recovered energy can be used — if the re-use is 700 ft. away, the plumbing or ductwork costs may be financially prohibitive — and the need to bypass the system when demand drops.

Wesley’s design includes a T connection with a damper on the roof of the building. When the damper is open, a fan draws vent gas through a heat exchanger, where energy is transferred to oil or other fluids. When the process isn’t running, the damper closes, protecting the heat exchanger from damage.

Flu gas was used in a recent installation to heat incoming lake water for a Chicago beverage bottler, replacing other heating systems except in the coldest winter months. Although the project cost exceeded $1 million, savings from energy-use and maintenance reductions produced a payback in six months, according to Wesley.

“Every plant is unique,” he concedes, and favorable economics in one facility don’t mean the technology will work in a similar plant making the same products. Another barrier is lack of trust: Engineers understand the technology and can crunch the numbers, but plant engineers are a vanishing breed, and financial officers are ill-equipped to validate the ROI numbers. Wesley recalls the CFO who rejected a project involving VFD installations that would have produced an eight-month payback, rationalizing he needed a three-month return.

Uncertainty about future pricing for natural gas is keeping many food companies on the sidelines when it comes to energy efficiency projects. For those resigned to higher costs as a long-range trend and with the cash resources to pursue them, the options for lowering energy costs are plentiful.

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