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Components for Gen3 CSP Thermal Transport Systems


h.      Components for Gen3 CSP Thermal Transport Systems

In support of DOE’s Energy Storage Grand Challenge [1], this subtopic seeks proposals for the design of components for the next generation of Concentrating Solar-Thermal Power (CSP) generation technologies.


CSP technologies can be used to generate electricity by converting energy from sunlight to power a turbine. SETO is developing next generation CSP technologies (Gen3 CSP) which aim to deliver heat to a supercritical carbon dioxide (sCO2)-based turbine at or above 700 °C. The Gen3 CSP program [2] identified several heat transfer media (HTM) that showed promise in meeting SETO’s electricity cost goals of $0.05/kWh. The program was then organized by the phase of matter for leading HTM— gas, liquid, or solid. Released in 2017, the Gen3 Roadmap study describes the best understanding of potential Gen3 technologies [3]. Since 2017, additional relevant research and analysis has entered the public domain [4-8].


At a high level, the candidate Gen3 CSP thermal transport systems are based on:

·         Chloride salt blends. A mixture of magnesium chloride, sodium chloride, and potassium chloride (MgCl2-NaCl-KCl) is a leading salt-based HTM candidate for Gen3. Major impediments to Gen3 paradigms using this HTM in the receiver include catastrophic corrosion in the presence of oxygen or moisture, low thermal conductivity limiting the maximum thermal flux on the leading nickel alloy receivers, and freeze risk. The Gen3 liquid-phase team has determined that a liquid sodium receiver is ultimately less risky than a chloride salt receiver with technologies presently available, however, this salt remains the leading choice of the Gen3 team to transport energy up and down a tower and to act as the thermal energy storage (TES) medium.

·         Supercritical fluids. Supercritical carbon dioxide (sCO2) has been considered as a HTM for the Gen3 gas phase system. Major impediments to Gen3 paradigms using this HTM in the receiver include: high-pressure and low thermal conductivity limiting the maximum allowable flux on nickel alloy receivers; high parasitic losses in circulation greatly impacted by pressure drop in the receiver; creep and fatigue failure of the receiver; and, a higher receiver outlet temperature needed for additional temperature drops in indirect thermal energy storage systems (such as particle beds).

·         Particles. Sand-like particles may avoid many of the issues associated with fluid high temperature systems due to the ability to operate at ambient pressure and with limited corrosion or thermal stability risk. Challenges include: operability limitations; risk of particle degradation with time at temperature; scaling limitations; efficiency of heat exchange in the receiver and primary heater; and general challenges in particle transport and mass flow control.


To further develop Gen3 CSP systems and ensure their feasibility in the market, there is a need to design, build and test Gen3 system components that will be economically viable in future Gen3 plants. Applicants are expected to include the design, feasibility, and cost validation of new or improved components and subsystems during their Phase I application; lab scale testing, and prototype manufacturing of such components is of interest in Phase II applications. 


The following are specific components that are of interest for development and desired performance parameters that would be supported under this subtopic: 



·         Receivers:

o   Thermal efficiency > 90%.

o   Cost < 75 $/kWth (receiver only; excludes tower and piping).

o   Total receiver system cost including tower, piping, and cold salt pump < 150 $/kWth.

o   Lifetime > 10,000 cycles.

o   Applicable to gas, particle, or molten salt operation at >750°C.

·         Hot and cold salt pumps:

o   Designed for 720°C operation.

o   Operating power less than 5% of plant annual output. Developers can focus on subcomponents of the pumps and manufacturing processes for these subcomponents such as bearings, impellers, shafts.

·         Particle elevators:

o   Designed for 750°C operation.

o   Operating power <5% of plant annual output.

·         Thermal energy storage system:

o   Containment design for solid and liquid thermal energy storage at 720°C.

o   Cost target of 15 $/kWth.

o   Energetic efficiency >99%; exergetic efficiency >95%.

·         Balance of plant systems:

o   Low cost piping.

o   Low cost pipe and containment insulation for 720°C operation.

o   Design and manufacture of valves and fittings for 720°C operation, including check valves, control valves, gate valves and slide gates for solids.

·         Heat exchanger

o   Particle, salt, and gas to sco2 heat exchanger designs sought.

o   Cost target of 150 $/kWth power block energy input.

o   720°C sCO2 outlet temperature.

o   90-95% effectiveness depending on primary media.


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