Trending science: Researchers harvest low-grade waste heat
Low-grade waste heat is an artefact of many energy-generating methods. In cars, waste heat generated in winter is diverted to run the vehicle heating system, but in the summer, that same waste heat is released into the environment. Coal, nuclear and other power plants require high heat to produce electricity, but after producing electricity the excess waste heat is routed to cooling towers to dissipate. Researchers from Penn State University in the US want to take this waste heat and capture it to produce more power. The team is using a thermally regenerated ammonia-based battery that consists of copper electrodes with ammonia added only to the anolyte – the electrolyte surrounding the anode. Fang Zhang, postdoctoral fellow in environmental engineering at Penn State explains the procedure: ‘The battery will run until the reaction uses up the ammonia needed for complex formation in the electrolyte near the anode or depletes the copper ions in the electrolyte near the cathode. Then the reaction stops.’ Using low-grade waste heat from an outside source, the researchers distill ammonia from the effluent left in the battery anolyte and then recharge it into the original cathode chamber of the battery. The ammonia liquid stream can convert the thermal energy to electrical energy in the battery. Science Daily quotes Bruce E. Logan, Kappe Professor of Environmental Engineering at Penn State: ‘The use of waste heat for power production would allow additional electricity generation without any added consumption of fossil fuels. Thermally regenerative batteries are a carbon-neutral way to store and convert waste heat into electricity with potentially lower cost than solid-state devices.’ The researchers report published in the current issue of Energy and Environmental Science notes, ‘Here we present a highly efficient, inexpensive and scalable ammonia-based thermally regenerative battery where electrical current is produced from the formation of copper ammonia complex … When needed, the battery can be discharged so that the stored chemical energy is effectively converted to electrical power.’ Engineering.com recalls the problems with previous methods of harvesting low-grade waste heat: ‘The amount of energy produced in, for example, a system using salty and less salty water to generate electricity, was too small relative to the amount of water used. The thermally regenerative ammonia battery system can convert about 29 percent of the chemical energy in the battery to electricity and can be greatly improved with future optimization.’ According to Penn State News, the researchers produced a power density of about 60 watts per square metre over multiple cycles, which is six to 10 times higher than the power density produced by other liquid-based thermal-electric energy conversion systems. The researchers advise that the current thermally regenerative ammonia battery is not optimised, so that tinkering with the battery could both produce more power and reduce the cost of operating the batteries. Penn State News concludes, ‘The researchers were able to increase power density by increasing the number of batteries, so that this method is scalable to something that might be commercially attractive.’ For more information, please visit: http://pubs.rsc.org/en/content/articlelanding/2015/ee/c4ee02824d#!divAbstract
Countries
United States