Hierarchical Structures for Isothermal Compression / Expansion for Energy Storage

In industry, compressed air is so widely used that it is often regarded as the fourth utility after electricity, natural gas, and water.  Compressed air energy storage (CAES) typically uses power from renewable energy (i.e., wind, solar) to compress air, and to generate electricity through a turbine when needed, as a way of (i) mitigating the intermittency of renewable energy sources, and of (ii) matching power supply and demand, which are time dependent.

Further, when storage demand is more than five hours, CAES is viewed as an alternative to Li-ion batteries, which face raw material scarcity, supply chain security, and environmental concerns.

Compressed air is more expensive than electricity, natural gas, and water power when evaluated on a per unit energy delivered basis.  Despite this strong demand for compressed air, there is a lack of efficient systems requiring low energy consumption and this lack drives costs higher all the while the demand increases.  While economies of scale may benefit the CAES if employed long term and on a wide scale, the classical configuration of a CAES plant is exceptionally inefficient and only a few plants have been built worldwide.

Isothermal CAES (I-CAES) plants are preferred because there is no temperature change during the compression and expansion stages, which leads to much higher thermodynamic efficiency and therefore lower operating costs.

The investigators have found cost-effective isothermal compression and expansion of gaseous streams is achievable through vasculatures with lung-like gas flow paths embedded in phase change material (PCM) or thermochemical materials. Their design is highly scalable; a patent has been applied for.

In previous attempts to obtain isothermal compression / expansion, temperature increase and decrease was managed primarily by spraying liquids into the cylinder of a common piston machine during compression, or by compressing a pre-mixed foam. However, these designs are not scalable and increase the overall system cost.

The inventors project the cost of using their system will be substantially lower than current diabatic plants, because the multiple compressors and coolers of current diabatic plants will be replaced by a single isothermal compressor.  The Lorente-Bejan invention features a scalable design, for all sizes of CAES plants, particularly for the basic compressor to a large power plant.

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