Industry Market Trends

Recycling Heat Into Electricity is Getting More Feasible

Feb 22, 2013

Slowly but surely, waste heat recovery is becoming more cost effective for more manufacturers. Credit: Durr. Slowly but surely, waste heat recovery is becoming more cost effective for more manufacturers. Credit: Durr.

In all the discussion of clean energy production in the U.S., one thing that doesn't get talked about too much is waste-to-heat. Thermoelectric generation produces electricity from heat that otherwise would simply dissipate in the air.

In the past manufacturers haven't bothered with it, because it's an expensive and not too terribly efficient way of recycling heat into usable electricity. But recent advances have made it more attractive to manufacturers using heat-intensive power.

It's a promising option. According to a recent report on advances -- "breakthroughs," according to IEEE Spectrum -- in the field at Northwestern University, "when utilities burn fossil fuels to produce electricity, roughly two-thirds of the energy in the feedstock is lost as waste heat." Obviously if there's a way to capture that and recycle it to usable energy that's both efficient and not expensive, that would be wonderful news not just for utilities, but for any manufacturer using boilers and other equipment currently generating waste heat.

Progress Made Last September

Evidently we're getting pretty close to that, as reports from Northwestern University last winter indicate.

The key to getting worthwhile results from thermoelectric material is inhibiting its thermal conductivity. Without going into numbing scientific detail, suffice it to say that many approaches were tried, and in 2004, Mercouri G. Kanatzidis's group at Northwestern University was able to practically double the amount of electricity generated for a given amount of thermal energy applied.

In September 2012 Kanatzidis's group figured out how to develop a thermoelectric device that will convert roughly 20 percent of waste heat into electricity. As he explains it, the process is like a chocolate chip cookie: "The field got to 1 ZT by refining the formulation of the chocolate chips. That is the atomic scale. More recently, we improved things by determining where on the cookie the chips should be placed. That is the nanoscale that improved the state-of-the-art to about 1.8 ZT. And here, now we have adjusted the size of the cookie and how it is stacked in the package."

Given Kanatzidis's results, published in the journal Nature, others now think it's reasonable to assume even greater efficiencies are possible.

Using a cookie and chocolate chips as a metaphor, a Northwest University researcher demonstrates how he has nearly doubled waste heat recovery efficiency. Credit: Robyn Lee. Using a cookie and chocolate chips as a metaphor, a Northwest University researcher demonstrates how he has nearly doubled waste heat recovery efficiency. Credit: Robyn Lee.

It's for reasons like this that NARUC, the National Association of Regulatory Utility Commissioners recently issued a resolution calling for "accelerating investment in industrial energy efficiency" which NARUC officials maintain could benefit manufacturers, utilities and consumers.

Waste To Heat for Manufacturers: 15 Percent Savings

Recycled Energy Development (RED), a company working in the field, calls the waste-heat and CHP potential "substantial."  It's website states, "Wallboard manufacturers, glass makers, cement kilns, steel smelters, and most manufacturers can obtain vast savings by reducing their energy waste and generating heat and power together."

RED officials say that in fact, manufacturers can reduce energy costs "typically by at least 15 percent" by doing it right.

It's not exactly a brand-new idea. Some sources say waste to heat technology was around back during America's space program. TEGpower, a manufacturer of thermoelectric generators, says they've "been in use for many years by NASA to power spacecraft and the oil and gas industry to power remote monitoring stations around the globe," and that it's only recent that they've been available to the public for use.

Recognized In 14 States

Waste-heat-to-power is already recognized by 14 states "as part of their renewable and clean energy portfolio standards or energy efficiency resource standards," NARUC officials say. the resolution commends Baltimore Gas and Electric Co. as an example, for "pushing combined heat and power as part of its effort to meet Maryland's energy efficiency targets" by offering "incentives of up to $2 million toward the installation of combined heat and power units," among other innovations.

As our esteemed ThomasNet colleague Tracey Schelmetic explained it a while ago, thermoelectric generators -- TEGs or simply "thermogenerators" -- "convert heat into electricity, using two materials at different temperatures, directly into electrical energy. The greater the differential (delta temperature, or DT) between the 'hot' side and the 'cold' side, the more power can be produced."

A TEG, Schelmetic said, creates electricity from waste heat thrown off by energy generation or industrial processes, and can provide this juice "to a load directly when a constant heat source is available, or they can be used in combination with batteries if the heat source is not constant." Another advantage is that TEGs, which are highly durable, don't need their own power source, since they can get power from any device that releases enough heat -- they're even possible on cars, incinerators and spacecraft, given their durability.

Some Drawbacks, Yes: Efficiency, Cost...

The University of the Pacific has produced some good research on thermoelectric generators, saying they can be installed to work with "ovens, burners and furnaces, as well as machines that produce heat as a by-product of creating power for other functions, such as propulsion."

But one reason we haven't seen them around much in daily life is how expensive they are and how inefficient. According to the University of the Pacific, "a single thermoelectric module capable of producing 14 watts of electrical power costs approximately $100." Not a great deal in the short run, when you can usually buy 1,000 watts -- burning a 100 watt light for 10 hours -- for about fifteen cents. No, if you decide to adopt thermoelectric generation it's because you're in this for the long haul, because you want to put a TEG on a heat source and have it generate recycled electricity for you for years to come.

And the University of the Pacific's research found that in recent years, thermoelectric generators have had "an average efficiency of 4 percent, which means the generators cannot pass on 96 percent of the energy they obtain from heat sources." Recent breakthroughs have improved that, but there's still a considerable amount of work to be done to render them a feasible part of a manufacturer's daily energy plan.

The EPA's Boiler MACT Rule

IEEE Spectrum reports that Cheryl Roberts, commissioner emerita of Ohio's Public Utilities Commission, says it's possible for boiler operators to "economically use combined heat and power when they begin to be affected by the U.S. EPA's boiler MACT rule," by retrofitting boilers to include control equipment.

According to an industry journal, Power Engineering, some manufacturers will be affected by the recent U.S. Environmental Protection Agency's changes to Clean Air Act standards for boilers and certain incinerators, the Boiler Maximum Achievable Control Technology (boiler MACT) rule, setting "numerical emission limits for high emitting boilers and incinerators, which accounts for less than 1 percent of boilers in the sector.  For these boilers and incinerators, typically operating at refineries, chemical plants and other industrial facilities, EPA is establishing more targeted emissions limits."

But there's a lot of heat out there just waiting to be recycled into usable electricity. Jonathan Hesener, GE's company sales manager, said GE considers waste heat and power "an integral component of increasing energy efficiency and reducing CO2 emissions. Hesener estimated that there is currently "more than 130 GW of opportunity in the U.S. for combined heat and power and waste heat recovery," but added that many of those don't have much commercial potential.