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Ceramic–metal composites for heat exchangers in concentrated solar power plants


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 (sCO2) recompression cycles, instead of using conventional (such as subcritical steam Rankine) cycles with inlet temperatures below 823 kelvin1,2,3, 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 storage4,5,6) would be an important step towards direct competition with fossil-fuel-based plants and a large reduction in greenhouse gas emissions7. However, the inlet temperatures of closed-cycle high-pressure sCO2 turbine systems are limited8 by the thermomechanical performance of the compact, metal-alloy-based, printed-circuit-type heat exchangers used to transfer heat to sCO2. 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 kelvin9. 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 sCO2 at 1,023 kelvin and 20 megapascals was achieved10 by bonding a copper layer to the composite surface and adding 50 parts per million carbon monoxide to sCO2. Techno-economic analyses indicate that ZrC/W-based heat exchangers can strongly outperform nickel-superalloy-based printed-circuit heat exchangers at lower cost.

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Fig. 1: Fabrication of dense, channelled ZrC/W plates.
Fig. 2: Corrosion resistance of a Cu-bearing ZrC/W composite to a buffered supercritical CO/CO2-bearing fluid at 1,023 K.
Fig. 3: Calculated power density of a printed-circuit-type heat exchanger versus allowed stress at 1,073 K.

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Data availability

Data generated or analysed during this study are available from the corresponding author on reasonable request. Data reported are available within the paper. The Ricardo Excel model of ZrC/W-based heat exchanger processing costs is available from the corresponding author on reasonable request.


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This work was supported by the US Department of Energy, Office of Energy Efficiency and Renewable Energy (award number DE-EE0007117). We thank S. H. Hwang for assistance with electron microscopy and I. Itskou for assistance with the preparation of Cu-encased ZrC/W specimens.

Reviewer information

Nature thanks L. F. Cabeza, O. Graeve, C. Turchi and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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Authors and Affiliations



M.T.-K., A.R.S. and S. Singnisai conducted the WC preform processing and analyses, with assistance from N.R.K. and with K.H.S. providing guidance. M.C. conducted the melt infiltration processing, and analysed the microstructure and chemistry of the resulting ZrC/W composites, with A.R.S., M.T.-K. and A.S.C. providing assistance and with K.H.S. providing guidance. Mechanical tests of ZrC/W composites were conducted and analyzed by S. Sahoo, G.I. and A.M.-R., with E.L.-C. providing guidance. Cu-encased ZrC/W corrosion test specimens were prepared by M.T.-K. Corrosion tests of the Cu-encased ZrC/W specimens were conducted by A.M.S., with M.H.A. providing guidance. Specimen cross-sectional analyses after the corrosion tests were conducted by A.S.C., with assistance from N.R.K. and with K.H.S. providing guidance. Thermodynamic and kinetic calculations associated with corrosion were conducted by K.H.S. Performance calculations of ZrC/W heat exchangers were conducted by S.P., T.K. and D.J., with assistance from K.H.S. and A.H., and with D.R. providing guidance. Economic analyses were conducted by A.D.R., S.P., and A.H., with A.R.S., M.C., G.I. and K.H.S. providing assistance. M.C., G.I., A.H. and K.H.S. drafted the majority of the manuscript. All authors contributed to the writing and review of the manuscript. K.H.S. supervised the overall effort.

Corresponding author

Correspondence to K. H. Sandhage.

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Competing interests

A.H. and K.S. are inventors on patent applications related to this work that have been filed by (and are owned by) Purdue University and the Georgia Institute of Technology (see refs 10,11). Patent application number PCT/US17/28091 includes the fabrication and use of ZrC/W composites for heat exchangers. Patent application PCT/US17/56015 includes enhancement of the high-temperature oxidation resistance of ZrC/W composites through the use of carbon monoxide-bearing supercritical carbon dioxide and a copper surface layer. The other authors declare no competing interests.

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Extended data figures and tables

Extended Data Fig. 1 Schematic illustration of a concentrated solar power plant.

The thermal energy storage medium is KCl-MgCl2 molten salt (67% mol%–33 mol%36,37) and the plant uses a sCO2 Brayton cycle for power generation.

Extended Data Fig. 2 More channels in the heat exchanger reduce the values of pressure drop.

Variations of the channel length, and the values of the pressure drop for the molten salt and sCO2 streams, are plotted as a function of the number of channels for each fluid.

Extended Data Fig. 3 Higher allowed stresses reduce the required plate thickness and channel spacing.

Values of the minimum plate thickness and minimum channel spacing associated with a given allowed stress are plotted for a compact, printed-circuit-type heat exchanger.

Extended Data Table 1 Characteristics of the reaction for fabrication of the heat exchanger plates
Extended Data Table 2 Material characteristics for ZrC/W, Inconel 740H and Inconel 617
Extended Data Table 3 Operating conditions representative of an intermediate heat exchanger for a 10-MWe concentrated solar power plant

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Caccia, M., Tabandeh-Khorshid, M., Itskos, G. et al. Ceramic–metal composites for heat exchangers in concentrated solar power plants. Nature 562, 406–409 (2018).

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