When resource availability becomes an issue in rolling brownouts and drought-driven water shortages, production can grind to a halt or be curtailed. The technology to reduce consumption exists, and plants are deploying it when the rate of return meets hurdle rates.
Variable frequency drives are a case in point. A rarity in food plants a decade ago, VFD installations have increased as their costs have declined. Ammonia compressors for refrigeration were among the earliest applications, and many companies were pleasantly surprised by the extent of the savings found in post-project audits.
The use of VFDs in newer facilities has spread well beyond the engine room. When Commonwealth Dairy built its yogurt plant in Brattleboro, Vt., VFDs were installed in every motor larger than 1 hp, according to maintenance manager Daniel Frommel. An ultraviolet light pasteurization system for process water replaced conventional thermal-treatment tanks, a decision Frommel termed a "no brainer."
Waste heat recovery and reuse is an opportunity well suited to food production, given the amount of product heating and cooling that goes on. Adena Beef, a grass-fed beef operation in Fort McCoy, Fla., actually flirted with a tri-gen system for its 63,113-sq.-ft. packing house. Gas-fired turbines would have generated the plant's electricity, with waste heat harvested for hot water and space heating, as well as for absorption chillers tied to a cascade refrigeration system, an environmentally friendly technology receiving renewed interest in North America. The tri-gen concept would take the plant off the grid and possibly defuse local opposition to the related cattle operation, although the nine-year payback was a problem.
Nonetheless, energy recapture is an intriguing opportunity for food facilities, and many engineering minds are focused on making it economically feasible. Emerson Climate Technologies is touting a system that concentrates the energy in ammonia refrigerant, which usually is too low-grade to justify recovery, and harvests it with a heat pump. The enabling technology is a single-screw compressor manufactured by Milwaukee-based Vilter Manufacturing LLC, which Emerson acquired in 2009.
Refrigerant heat harvesting
Vilter's single-screw compressor can handle pressure that is multiples higher than the 185 psi of returned ammonia refrigerants. Instead of venting the heat in the ammonia, the Emerson technology elevates it above 500 psi and harvests the energy for boiler feed or direct heating of municipal water.
"It sounds like a lot of pressure, but there is a strong track record of safe operating at those pressures," assures Sam Gladis, business director-heat pumps for Emerson, Sidney, Ohio. The resulting energy is sufficient to raise the temperature of cold water to 145° F, high enough for sanitary washdown.
The first application was in 2010 at a Nestle chocolate plant in the U.K. Sixteen have followed, including at Kraft Food Group's Davenport, Iowa, facility. Part of Kraft's Oscar Mayer network, Davenport bills itself as the world's largest bologna plant, producing more than 3 million lbs. a week of the deli staple.
Kraft's investment is producing annual savings of almost $300,000 and 14 million gal. of water, with coefficient of performance (COP) of 6.51 in summer, significantly above the typical COP of 4 for ammonia systems (COP declines in winter, when demand for refrigerant declines). Kraft declined to provide an ROI timeframe, but Gladis indicates corporate engineers were "extremely pleased" with the economics. "We're seeing paybacks in the 2.5-3.5-year time frame for many of the projects," he adds.
As with Kraft, many of the installations have been retrofits, which can mean additional piping if the engine and boiler rooms are isolated from each other. But the savings in energy costs are substantial: Chile's dominant poultry processor, Super Pollo, slashed heat energy costs 72 percent at its San Vicente plant.
The engine rooms of these plants don't look very different than those with conventional systems (although presumably they're cooler). The same holds true in many plant improvements, like the one executed by Siemens Inc. last year at Minn-Dak Farmers Cooperative in Wahpeton, N.D. The sugar beet processing facility uses the same heavy-duty centrifuges to separate the sugar from the molasses as it did before the project. But installation of advanced drives and state-of-the-art controls have helped the plant shatter a dozen throughput records in the past year, while lowering energy consumption by almost half.
State model displays with lights denoting the machine's current state used to guide the plant's operators, leaving them without the ability to shorten a batch cycle if the process was completed early, explains Adam Shively, a drives & motion specialist with Atlanta-based Siemens. The drives were equally antiquated and prone to unscheduled maintenance.