Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Karamanev, Dimitre

Abstract

This research introduces compressed air energy transmission (CAET) via pipelines as a novel alternative to traditional electrical transmission. Unlike electrical systems that require separate energy storage solutions, CAET inherently stores energy within the compressed air pipeline, offering an efficient and cost-effective alternative. The study identifies key variables influencing system efficiency and costs, filling a gap in existing literature. Two compression/expansion processes, diabatic and isothermal, are analyzed, with the latter achieving 93% efficiency using an innovative approach. Power losses are calculated across three transmission system sections: compression, pipeline, and expansion. The analysis begins with a short pipeline to determine losses and extends to long-distance pipelines with optimized compressor station placement. Three decision variables, pipe diameter, number of pipes, and distance between compressor stations, are optimized to minimize total annual costs.

Comparing CAET with electrical transmission reveals that while CAET infrastructure may have slightly higher initial costs, its integrated energy storage capability offers significant advantages. A 100 km pipeline can store compressed air sufficient to deliver nominal power for over two hours. Integration with underground caverns for additional storage eliminates conversion losses inherent in electrical storage, improving overall system efficiency and reducing the levelized cost of storage.

Summary for Lay Audience

With the growing use of renewable energy sources like wind and solar, the need for effective energy storage in electrical grids has become increasingly important. Electricity, though a highly efficient energy carrier, cannot be stored directly, posing a significant challenge. Various solutions have been proposed, but many face issues with energy loss during the conversion processes needed for storage, making them less cost-effective. Compressed air offers a promising alternative, as it can transport energy over long distances via pipelines while also serving as a natural energy storage system. Unlike traditional electrical grids, compressed air energy transmission (CAET) eliminates the need for separate energy storage facilities, as the energy is stored directly within the pipeline. This study evaluates CAET in terms of cost and efficiency, comparing it with electrical transmission systems. The results indicate that CAET is approximately 40% cheaper in capital costs than current electrical transmission systems. Over long distances of 1,000 km with 10-hour energy storage, CAET experiences about one-third less power loss compared to electrical grids. For shorter distances of 100 km, CAET achieves around 30% lower annual costs. Moreover, for a 2-hour energy storage capability, CAET incurs only one-eighth the power loss of electrical grids, making it eight times more efficient. These findings emphasize the significant potential of CAET as a cost-effective and energy-efficient solution for both short- and long-distance energy transmission, particularly as the world increasingly adopts renewable energy sources.

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