Silicon Carbide (SiC) Foam for Molten Salt Containment in CSP-GEN3 Systems
- Touchstone Research Laboratory
Touchstone Research Laboratory, LTD, is reporting on the results of its DOE SBIR Phase I project for determining the feasibility in synthesizing silicon carbide foam from coal precursor. In the present study, a silicon carbide foam was produced using coal (carbon source) and a preceramic polymer resin (silicon source). A review of the silicon carbide (SiC) compound species, alpha (α-SiC) and beta (β-SiC), and the processing route for the newly developed product via a direct-synthesis manufacturing approach is presented. Silicon carbide synthesis from coal makes available affordable, large form factor, monolithic shapes previously not available. The manufacturing approach is leveraged off Touchstones experience in producing carbon foam (CFOAM®) from coal, where coal selection and blending by Rank permits carbon foam density and subsequent structure to be tailored, or optimized, for application and use. Now the final product may be a silicon carbide that fills technology gaps in many state-of-the-art carbon areas, in high temperature oxidizing atmosphere for example. Thus using coal precursor and out-of-autoclave (OOA) processing developed in this Phase I allows foaming, cross-linking and pyrolysis to occur in a single furnace process run, without pressure, which makes substantial impact in reducing cost for silicon carbide products not previously available. Porous silicon carbide foam, i.e. for containing molten salt phase change material (PCM), was analyzed using a storage system modeled after a modular design developed by Argonne National Laboratory. For the simulations, a plant capacity of 100 MWe was considered with a storage of 12 h. The key result shows that the use of silicon carbide foam, having thermal conductivity of 25 W/m-K, enhances the thermal performance of the storage system and achieves the potential of meeting the round trip and exergetic efficiencies as required by the Department of Energy’s Solar Energy Technology Office. Model and simulation results provided by Argonne National Laboratory (ANL) indicate that the silicon carbide foam/PCM composite can potentially achieve round-trip exergy efficiency 90-95%. Based on the investigations on the full-scale system, the silicon carbide foam could significantly improve the heat transfer performance of the molten salt thermal energy storage (TES) systems. It is revealed that the silicon carbide foam can accelerate the melting and solidification processes for thermal energy storage and release, respectively. Hence, use of silicon carbide foam can reduce the number of required heat transfer fluid (HTF) tubes as compared to a PCM-only system and lead to cost reduction in the concentrated solar power (CSP) plant. Furthermore, the silicon carbide foam/PCM composite could achieve the round-trip exergy efficiency to meet the storage target for the TES system thermal performance, which cannot be accomplished by using pure PCM. Touchstone successfully manufactured β-SiC from coal that has density 0.6 gm/cm³ and porosity 80%. Further, a microstructure characterization approach was developed that will enable future product development efforts in Phase II. The characterization method involves converting 3D Computational Tomography (CT-scan) of foam structure into a solid model geometry for Finite Element (FE) analysis. Touchstone’s ANSYS Workbench and Fluent Software Platform can now be used to facilitate foam structure optimization through computational fluid dynamics (CFD), steady-state & dynamic heat transfer, and structural analyses. In conclusion, results in the Phase I effort show feasibility in manufacturing silicon carbide foam with low cost materials (coal) and processes (OOA). The models developed in Phase I provide an analytical approach to materials development and manufacturing in Phase II and will facilitate acceleration of product(s) to market. As part of the Phase II activity, it will be proposed to focus on optimizing the product’s microstructure, crystallinity and purity to maximize properties as deemed necessary for intended use and application. In the case of molten salt TES applications, for example, coal and resin blending techniques will be researched to increase swell during foaming, hence lower density to reach ~90% porosity for optimal PCM loading.
- Research Organization:
- Touchstone Research Laboratory
- Sponsoring Organization:
- USDOE
- Contributing Organization:
- Argonne National Laboratory
- DOE Contract Number:
- SC0018678
- OSTI ID:
- 1507005
- Type / Phase:
- SBIR (Phase I)
- Report Number(s):
- DE-SC0018678-Final; 3045475800
- Country of Publication:
- United States
- Language:
- English
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