KOTZEBUE, Alaska–This part of Alaska is one large frozen tundra much of the year; so, you might think the last thing an Alaskan needs in this fishing village 30 miles south of the Arctic Circle is an icemaker. But an icemaker can mean the difference between profit and loss during the 70[degrees]F, six-week-long summer fishing season on Kotzebue Sound.
Villagers use ice from rotary drum flake icemakers to keep their commercial Chum salmon catches fresh in their air trip south to the lower 49.
While the village’s four 6-ton-per-day icemakers, driven by conventional electric compressors, did an admirable job, their age and inefficiency increased energy consumption that cut deeply into profits.
Because the village is not connected to an electricity grid, it pays a hefty 21[cents]/kWh for dieselgenerated electricity, which calculates to about $7 per daily ton of ice.
An Annapolis, Md., research and development firm, Energy Concepts Co. (ECC), proved to the village that an ammonia absorption icemaker powered by recovered waste heat saves 70% of the previous energy outlays.
Now villagers have more disposable income to spend on other items, thus raising the local economy and living standard a notch higher.
More important, “We’ve been able to increase the value of our fish,” since they leave colder and fresher, says Brad Reeve, general manager of the Kotzebue Electric Association.
With financial support from two state agencies, Energy Concepts president Donald Erickson used an absorption cycle that first appeared in ASHRAE papers back in 1930, but was forgotten after electric vapor compression technology began dominating the refrigeration industry.
The cycle takes waste heat from a 180[degrees] jacket cooling water of the village’s 1,500-kW diesel generators to produce heat-activated compression in the ammonia system, thus eliminating the need for electric compressors.
ECC faced some design hurdles. The 180[degrees] jacket water temperature and 70[degrees] ambient temperature were insufficient to produce an optimal operating range of -10[degrees], needed by conventional icemakers.
Another source of waste heat was the diesel generators’ 842[degrees] exhaust, but attempts at recovering heat from typically dirty diesel exhaust had histories of unreliability and costly cleaning procedures.
Instead, Erickson employs what he calls an ammonia absorption vapor-exchange cycle with a double lift.
“Normally, in conventional ammonia absorption refrigeration systems, the aqua ammonia leaving the low-pressure absorber is pumped all the way up to the high pressure, i.e., the condenser pressure,” he says.
“In a conventional single-effect absorption cycle, you’d have only the low-pressure absorber and high-pressure generator operating at 230[degrees]. But in the double-lift cycle, two intermediate-pressure devices — the intermediate-pressure absorber and intermediate-pressure generator — give a needed extra lift, using a source temperature (180[degrees] jacket water) that’s not hot enough to drive the single-effect cycle.”
Modification of the diesel engines was minimal, with a simple tap into the water jacket supply and return headers.
ECC used many off-the-shelf components in constructing the unit. North Star Ice Equipment supplied the icemaker; Grundfos Pumps supplied centrifugal pumps; the Basco Division of American Precision Industries supplied two shell-and-tube heat exchangers; and Henry Valve supplied the valves and fittings.
The system was installed immediately outside the Kotzebue Electric Association power plant. KEA also supplied people to operate the icemaker.
It cost $18,000 to transport the 12.5-ton unit. ECC shipped the unit in component pieces by rail to Seattle, by boat to Anchorage, and finally by air to Kotzebue, because its bay was frozen during shipping season.
Because the unit is ideal for remote villages, shipping cost is a major concern that Erickson is tackling with the use of lighter components in future projects.
Such an icemaker, producing 15 tons of flake ice daily, carries a hefty up-front cost of $70,000, about $15,000 more than conventional icemakers. However, the daily savings of $106 per day in electric costs translates into a price difference carrying a payback of 141 days of operation, says Erickson.
“This $70,000 is about $1,000 per daily ton higher than the cost of comparable electric compression systems,” he says. “However, the power demand per daily ton decreases from 2 kW to 0.6 kW. The capital cost of 1.4 kW of electrical generation easily exceeds $1,000.”
The Alaska Energy Aughority became interested to help lessen the electric load on its equipment from icemakers in other fishing villages.
“Many isolated villages relying on diesel-generated electricity have a capacity problem, in addition to the problem of high electric cost,” says Erickson.
“More ice capacity or refrigerated store room capacity is not possible unless more electric generation capacity is first installed. Indeed, many of the large-scale fish processors are forced to install their own diesel generators.”
Although ECC installed the first unit, future waste heat-powered absorption installations will be handled through mechanical contractors who will operate as subcontractors or licensees.
“We’re not in the installation business,” says Erickson. “We intend to hand this technology over to other firms, so we can concentrate on our specialty: r&d.”
Other applications could include industrial sites, food manufacturing, and petrochemical plants. ECC is currently courting a race track that needs to ice down horses after training and racing.
Furthermore, the company has applied similar technology and produced a solar-powered icemaker in a Mexican fishing village.
Reeve estimates there are about 120 Alaskan villages unconnected to electricity grids that could use this type of system. Kotzebue hopes to add another ammonia absorption design to lessen the electric load on a cold storage facility linked to fish smoking.