KGRA: Harvesting Megawatts From the Air

When you’ve got 800-degree exhaust gas at a refinery, you’ve got the opportunity to make power.
In the relatively near future, a fracking company may harvest electricity from the Marcellus Shale formation, too.

The power won't come from converting shale gas into electricity. Instead, it will be created by harvesting the 840-degree waste heat exuded by compressors onsite needed to squeeze the methane extracted from the rock into pipelines. The five compressors at the operation give off enough heat to generate nearly 2 megawatts of electricity, according to Jason Gold, CEO of waste heat developer KGRA Energy. The letter of intent has been signed and the formal deal should be announced soon, he added.

KGRA also hopes to finalize a project to produce 4 to 5 megawatts of electricity from the hot (887 degrees Fahrenheit) exhaust emanating from a cement factory. Another project will create electricity from the heat absorbed from liquid hydrocarbons in distillation towers at refineries.

This week, KGRA signed a deal to build an 800-kilowatt waste heat recovery system at Weyerhauser's Greenville, North Carolina plant.

"The amount of energy being wasted is staggering," said Gold.

The company embodies two trends in renewables. First, there's a growing interest in harvesting waste heat. The U.S. consumes 100 quads, or quadrillion BTUs, of energy a year, and 55 to 60 quads get dissipated as waste heat, according to research conducted at UC Berkeley. The heat emanating from car engines, notebook bricks and industrial ovens is really just energy purchased, but not used efficiently, by someone.

As an added bonus, power generated from waste heat tends to mimic baseline power, unlike the intermittent nature of wind or solar power. As long as the factory hums along, power is generated.

"This is utility-grade power," Gold said. "24 hours a day, seven days a week, 365 days a year."

The power figures above, Gold added, are for net power produced. KGRA deducts the power required for its own equipment from the total.

Second, it's the developer business model. KGRA, he emphasized, is a developer and not a manufacturer. The company essentially finds opportunities, tries to estimate the costs and output of a potential projects, and then signs the appropriate offtake agreements, pretty much like your typical solar developer. The company is both brand- and technology-agnostic, meaning that it will install heat recovery systems from General Electric, Ormat, Pratt & Whitney or whomever might work best in the given circumstances.

Structuring the deal so the end-user buys kilowatts instead of capital equipment, in general, helps eliminate the obstacles to acceptance. (Traditionally, industrialists bought the equipment and the vendor and contractor were often associated with the terms of the deal.) Most of the time, the end-user consumes all of the energy. If excess exists, it can be delivered to third parties via the grid. In some states, renewable credits bolster the price.

There's also an efficiency play here. Capturing waste heat and converting it to electricity reduces overall power consumption. Air conditioners can be turned down and onsite power generation reduces demand for power on the grid. At the oil refinery mentioned above, large electrical fans are employed to get rid of the heat. Because of the power conservation potential, some states and utilities will provide credits and rebates to waste heat projects, similar to how some utilities are subsidizing building retrofits and ice air conditioners under the guise of reducing peak power.

While KGRA will work with different technologies, the company primarily concentrates on organic Rankine cycle (ORC) machinery. In ORC waste heat recovery, captured heat is used to turn an organic liquid into vapor. The vapor then cranks a turbine. The key is that the vapor boils at a far lower temperature than water. ORC plants can operate with exhaust heat at 500 to 800 degrees Fahrenheit. Waste heat systems that rely on steam need heat in the 800-degrees-Fahrenheit-and-above range.

A total of 150 large-scale ORC plants have been erected in Europe and 25 have been launched in the U.S. "It is beyond a shadow of a doubt that it [ORC] works," Gold emphasized.

Whether a plant is appropriate for waste heat depends on a variety of factors and circumstances. How much exhaust does a plant produce and what is the temperature? Does power cost quite a bit or very little? How much will the end-user consume? Overall, though, ORC equipment in positive circumstances can generate power for a capital cost of $3.50 a watt.

Some companies, such as Phononic Devices and Alphabet Energy, are developing semiconductors that can convert heat directly into electricity, no turbine needed. The simplicity will lower the capital costs to $1 a watt, says Alphabet. But these chips, often relying on relatively new materials like silicon nanowires, tend to be in the experimental phase.

Waste heat doesn't enjoy the same level of support of subsidies as wind or solar, but that could change. For one thing, it's a competitive, rapidly growing field. Last year, the VC firm Westly Group experienced three IPOs: one was waste heat specialist China Recycling Energy Corp. Leaders in Washington also probably like the concept. Arun Majumdar, the director of ARPA-E, was the one who gave me those BTU figures noted above. He also conducted the research behind Alphabet Energy. Majumdar, of course, worked with Energy Secretary Steve Chu at Lawrence Berkeley Labs, which has been the epicenter of efficiency research for years.

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