Session: 09-01 Compressed Air Energy Storage

Paper Number: 127710

127710 - A Perspective on the Process and Turbomachinery Design of Compressed Air Energy Storage Systems 

Solving the energy trilemma (energy security, energy sustainability, and energy affordability) requires new integrated strategies to balance the mismatch between intermittent energy production from renewables and predictable, cyclical consumption. As renewable penetrations on a grid rise, storage is required to enable their continued adoption. The storage of energy can be achieved using various technologies, with different maturities, ideal use cases and energy densities. A key enabler in exploiting renewable energy sources is the ability to store significant amounts of energy and then discharge it over a long duration. 
Advanced compressed air energy storage (A-CAES) is a promising solution for long duration energy storage because of its low capital costs, technological maturity, and high round-trip efficiency.
The present paper will describe the Baker Hughes experience in the development of the turbomachinery equipment for Hydrostor’s A-CAES system.
Hydrostor’s A-CAES system contains two main features which combine to allow for its attractive efficiency and fuel-free nature, and differentiate it from other CAES technology. Both of these elements affect turbomachinery definition. They are: hydrostatic compensation of the air cavern, and capture and re-use of the heat of compression. 
Hydrostatic compensation means that the compressors charge the system against a nearly constant backpressure and the turbines operate with a nearly constant inlet pressure. This allows both to operate at peak efficiency. 
The reuse of the heat of compression allows for a fuel-free system. To do this efficiently, the charge/discharge processes are split into multiple segments with heat take-offs/re-injections between each. Each segment features a pressure ratio which produces/consumes heat of a magnitude which can reasonably be stored in water and which does not challenge the limits of normal compressor materials of construction. This does however run contrary to most standard compressor designs, which feature heavy intercooling.  
To achieve a reliable and effective solution, the expander is obtained from the architecture of Baker Hughes steam turbines, which was adapted to match the specific process needs. The criticalities that were addressed and solved to derive the expanders from the original steam turbine are presented.
Specifically, the paper describes the activities performed to optimize the inlet and exhaust sections of each segment, the development of the blades for high atmospheric volume flow, and the implications that thermal transients have on the machine reliability.
The inlet and exhaust sections were arranged according to the layout constraints, which were set to mitigate the effects of the thermal stresses and to reduce the weight to facilitate the machine transportation, while maintaining high aero-performance. As for the expander, a single-body configuration was selected to optimize capital expenditures and reduce leakage to atmosphere.
A new set of blades derived from Baker Hughes’s Steam Turbine stages were developed. This new stage is characterized by rotating blades with high radius ratio; therefore an optimization strategy was adopted to include the mechanical constraints from the beginning of the design cycle and obtain a final geometry that can be used with different flow path and operating conditions. Finally, the 3D full Navier Stokes Computational fluid dynamics analysis was used to assess the performance of the new stages in nominal and off-design conditions. 
A detailed analysis of the thermal transient of the expander parts with FEA methods was performed to assess the life expectations of the equipment. The FEA results are discussed in the paper to show the capability of the machine to sustain an extremely fast start up sequence. 
Compressor train is characterized by a multiple body configuration. A detailed optimization was performed to improve the efficiency and the availability of the selected solution. In particular the low-pressure axial compressor discharge section has been optimized to reduce losses and a detailed study of rotor has been performed to evaluate the capability to withstand a high number of start and stop cycles.

Presenting Author: Gianfranco Maffulli Baker Hughes

Presenting Author Biography: -

Authors:

Gianfranco Maffulli Baker Hughes
Angelo Grimaldi Baker Hughes
Andrew Mcgillis Hydrostor
Lorenzo Succi Baker Hughes
Przemyslaw Przybytko Baker Hughes
Nicola Maceli Baker Hughes
David Brown Hydrostor
Graham Brook iO Consulting
Scott Earle Hydrostor