A breakthrough in power plant waste heat conversion
May 23, 2014 | By
Barbara Vergetis Lundin
Through research funded, in part, by the U.S. Department of Energy (DOE), scientists at MIT and Stanford University have found a new alternative for low-temperature waste-heat conversion into electricity in cases where temperature differences are less than 100 degrees Celsius. Researchers have spent decades trying to harness the vast amounts of excess, wasted heat generated by industrial processes and electric power plants. Up to this point, most efforts have focused on thermoelectric devices, solid-state materials that can produce electricity from a temperature gradient, but the efficiency has been limited. The new approach, based on the thermogalvanic effect, combines the charging-discharging cycles of batteries with heating and cooling, so the discharge voltage is higher than charge voltage since the voltage of rechargeable batteries depends on temperature. The system can efficiently harness even relatively small temperature differences. The system aims at harvesting heat of less than 100 C, which accounts for a large proportion of potentially harvestable waste heat. In a demonstration with waste heat of 60 C the new system has an estimated efficiency of 5.7 percent. Although the basic concept for this approach was initially proposed in the 1950s, materials for the battery electrodes, as well as advances in engineering the system, have been developed that were not around then. The new system will require further research to assure reliability over the long term and improve the speed of battery charging and discharging. "Virtually all power plants and manufacturing processes, like steelmaking and refining, release tremendous amounts of low-grade heat to ambient temperatures," said Yi Cui, Stanford professor and project researcher. "Our new battery technology is designed to take advantage of this temperature gradient at the industrial scale." For more:
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