Additively Manufactured Ceramic Combustor for Power-Plant Scale Electricity Generation

Existing power plants have many downsides, as they have low efficiency, emit CO2, and include high-temperature rotating machinery requiring frequency maintenance. However, they are dispatchable, which provides a direct benefit over variable renewable energy resources such as solar. The ideal technology would be both dispatchable and solid-state. A recent alternative is fuel cells, which can directly extract the chemical energy in fuels into electricity with electrochemistry, but they require expensive catalysts and have low power density.<br/><br/>Combustion-powered thermophotovoltaics is a promising alternative for power generation. In this system, a combustor is designed that preheats air above the auto-ignition point of a fuel, such that the mixture combusts upon contact. The heat from combustion is used to heat up an emitter to ultra-hot temperatures, and the emitter radiates heat to the TPV cell. The TPV cell converts the emitted light to electricity. If hydrogen is used as the fuel source, the electricity produced is clean, creating a solid-state, catalyst-free method of generating electricity.<br/>When combined with high-efficiency, high-power density TPV cells, this combustion-TPV system has the potential to be high-performing. However, there are many challenges in the system design, for example that high temperatures (2000C) are required, hefty insulation is needed to prevent heat loss, and cost may be high.<br/><br/>Thus, this study addresses three key challenges in the combustor design: materials identification, scalable design, and fabrication with additive manufacturing.<br/><br/>For materials identification, the objective of the material is to limit thermal stresses when a thermal gradient is applied, meaning the product of Young’s modulus and coefficient of thermal expansion must be low. The material’s yield strength must also be high, so that it does not fracture when a thermal stress is present. Due to the extreme environments present, the material should also be oxidation resistant and have high service temperature. Thus, oxides are the best option, and yttria-stabilized zirconia (YSZ) is identified as the candidate material due to its reduction resistance in the presence of high-temperature hydrogen.<br/><br/>Next, we design a high-efficiency combustor with 93% combustion efficiency using YSZ, enabled by milli-scale channels and a large surface area to volume ratio. The combustor also features a near-isothermal emitter wall at approximately 2000C. It is also modular, enabling vertical and horizontal stacking to reach the large length scales required for cheap insulation and grid-scale power generation.<br/><br/>However, the intricate internal geometries enabling the effective heat transfer within the device necessitate additive manufacturing. Because this technique can be expensive, two techniques are used to ensure cost-competitiveness. One is maximizing the power output per volume of the device, which is enabled by a large emitter surface area surrounded by high-power density TPV cells. Another is design for manufacturing, in which the device is 3D printed in 3 sections which are joined together in post-processing. This enables parallel processing and easier access to the internal channels, which would otherwise be difficult to clear. One challenge of this stacking method is how to properly join the slices, and a leak-proof joining methodology is developed to solve this.<br/><br/>Based on these improvements, we achieve a predicted cost per power of $0.30/W, which is significantly less than the cost of a natural gas turbine at $1/W, and leaves room for balance-of-plant costs such as pollution control, TPV cooling, and electronics.<br/><br/>Overall, in this work we push the boundaries of ceramic additive manufacturing to develop a next-generation power plant based on hydrogen combustion coupled with thermophotovoltaics.