New technology to exploit waste heat efficiently

(A large amount of excess heat arises from industrial processes and power generation projects, researchers around the world have spent decades searching for ways to exploit waste heat. Most efforts focus on thermoelectric devices, solid materials that can produce electricity from a temperature difference (thermal gradient), but the effectiveness of devices Such is limited by the available materials.

Now researchers at Stanford University have found an alternative to turning low-temperature waste heat into electricity, where the temperature difference is less than 100 degrees Celsius.

This new approach is based on a phenomenon called the thermogalvanic effect (roughly translated as 'electrothermal') , which was described in an article presented in Nature Communications by postdoctoral researcher Dr. Yuan Yang. and Professor Gang Chen at MIT, senior researcher after Dr. Seok Woo Lee and Professor Yi Cui at Stanford and three other researchers.

Since the voltage of rechargeable batteries depends on temperature, a new system combines the charge-discharge cycles of these batteries with heating and cooling, so the discharge voltage is higher than with charging voltage. The system can effectively exploit even small temperature differences, such as a temperature difference of 50 degrees Celsius.

To start, uncharged batteries are heated with waste heat. Then, while at a higher temperature, the battery is charged, once fully charged, it is cooled. Because the charging voltage is lower at higher temperatures than at low temperatures, so once the battery has cooled it can produce more electricity than the electricity used to charge it. This extra amount of energy, of course, is not by itself: It comes from the heat that was added to this system.

The said system is designed to exploit heat sources less than 100 degrees Celsius, accounting for a large proportion of potential sources of waste heat. In an experiment with a waste heat of 60 degrees Celsius, this new system was effective at an estimated 5.7%.

The basic concepts of this approach were initially proposed in the 1950s, but Chen said, 'an important step of this study is the use of materials not available at the time. ' for battery electrodes, as well as advances in this system design technique.

Previous research was based on temperatures of 500 degrees Celsius or higher, Yang added; Most heat recovery systems now work best with higher temperature differences.

While this new system has an important step forward in energy efficiency, it now has a much lower energy density - total energy can be released for a given weight - lower than with thermoelectricity. Further research is also needed to ensure long-term reliability, and to improve battery charging and discharging speed, Chen said.'There will be a lot of work to get the next step forward,' he said.

Chen, professor of energy engineering Carl Richard Soderberg and principal of MIT's School of Mechanical Engineering, said there is no good technology that can effectively use low temperature differences. This system can be exploited.'This system has the effect that we think is quite attractive , ' he said. 'There is a tremendous amount of waste heat at such low temperatures, if this technology can be created and deployed to use those waste heat sources.'

Cui said: 'Almost all power plants and manufacturing processes, such as steel production and refining, produce large amounts of waste heat with low temperatures into the surrounding environment. Our new battery technology is designed to take advantage of this temperature gradient at an industrial scale. '

Lee added: ' This technology has the added advantage of using rich and low-cost materials that have been widely used in the battery manufacturing industry,' Peidong Yang, a professor of chemistry at the University of California at Berkeley, who did not participate in this study, said: " By effectively exploiting the thermogalvanic, [by MIT and Stanford research] was able to convert low temperatures into It is a very promising technology . This is a smart idea, and we see that low-temperature waste heat is everywhere.

MIT's Yang stressed this point: "One-third of all US energy consumption ends as a low-temperature waste heat source. " MIT's work is funded in part by the US Department of Energy, a Part through the Solid-State Solar-Thermal Energy Conversion Center, and the US Air Force, Stanford research is funded in part by the DOE, the SLAC National Accelerator Laboratory, and the National Research Foundation (National Research). Foundation) of Korea.