School of Materials Engineering, Purdue University, West Lafayette, IN, USA.
George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA.
Nature. 2018 Oct;562(7727):406-409. doi: 10.1038/s41586-018-0593-1. Epub 2018 Oct 17.
The efficiency of generating electricity from heat using concentrated solar power plants (which use mirrors or lenses to concentrate sunlight in order to drive heat engines, usually involving turbines) may be appreciably increased by operating with higher turbine inlet temperatures, but this would require improved heat exchanger materials. By operating turbines with inlet temperatures above 1,023 kelvin using closed-cycle high-pressure supercritical carbon dioxide (sCO) recompression cycles, instead of using conventional (such as subcritical steam Rankine) cycles with inlet temperatures below 823 kelvin, the relative heat-to-electricity conversion efficiency may be increased by more than 20 per cent. The resulting reduction in the cost of dispatchable electricity from concentrated solar power plants (coupled with thermal energy storage) would be an important step towards direct competition with fossil-fuel-based plants and a large reduction in greenhouse gas emissions. However, the inlet temperatures of closed-cycle high-pressure sCO turbine systems are limited by the thermomechanical performance of the compact, metal-alloy-based, printed-circuit-type heat exchangers used to transfer heat to sCO. Here we present a robust composite of ceramic (zirconium carbide, ZrC) and the refractory metal tungsten (W) for use in printed-circuit-type heat exchangers at temperatures above 1,023 kelvin. This composite has attractive high-temperature thermal, mechanical and chemical properties and can be processed in a cost-effective manner. We fabricated ZrC/W-based heat exchanger plates with tunable channel patterns by the shape-and-size-preserving chemical conversion of porous tungsten carbide plates. The dense ZrC/W-based composites exhibited failure strengths of over 350 megapascals at 1,073 kelvin, and thermal conductivity values two to three times greater than those of iron- or nickel-based alloys at this temperature. Corrosion resistance to sCO at 1,023 kelvin and 20 megapascals was achieved by bonding a copper layer to the composite surface and adding 50 parts per million carbon monoxide to sCO. Techno-economic analyses indicate that ZrC/W-based heat exchangers can strongly outperform nickel-superalloy-based printed-circuit heat exchangers at lower cost.
利用集中式太阳能发电厂（使用镜子或透镜将阳光集中以驱动热机，通常涉及涡轮机）从热能中发电的效率可以通过提高涡轮机入口温度来显著提高，但这需要改进换热器材料。通过使用闭式高压超临界二氧化碳（sCO）再压缩循环在入口温度高于 1023 开尔文的条件下运行涡轮机，而不是使用入口温度低于 823 开尔文的常规（如亚临界蒸汽朗肯）循环，可以将相对的热-电转换效率提高 20%以上。这将导致集中式太阳能发电厂的调度电力成本降低（加上热能储存），这将是与基于化石燃料的工厂直接竞争并大幅减少温室气体排放的重要一步。然而，闭式高压 sCO 涡轮机系统的入口温度受到用于将热量传递给 sCO 的紧凑、基于金属合金的印刷电路板式热交换器的热机械性能的限制。在这里，我们提出了一种在 1023 开尔文以上温度下用于印刷电路板式热交换器的陶瓷（碳化硅，ZrC）和难熔金属钨（W）的坚固复合材料。这种复合材料具有吸引人的高温热、机械和化学性能，并且可以以具有成本效益的方式进行处理。我们通过多孔碳化钨板的形状和尺寸保持的化学转化，制造了具有可调通道图案的 ZrC/W 基热交换器板。致密的 ZrC/W 基复合材料在 1073 开尔文下表现出超过 350 兆帕的失效强度，并且在该温度下的热导率比铁基或镍基合金高两到三倍。通过在复合材料表面键合铜层并向 sCO 中添加 50ppm 一氧化碳，实现了在 1023 开尔文和 20 兆帕下对 sCO 的耐腐蚀性。技术经济分析表明，ZrC/W 基热交换器可以以更低的成本大大优于镍基高温合金印刷电路板热交换器。
