I have finally managed to get an article about Adiabatic Compressed Air Energy Storage (A-CAES) published in Applied Energy, after starting to think about A-CAES in 2010. Granted, that makes for a disappointing ratio of years-to-articles but whatever, it’s progress!
The link to the article “Adiabatic Compressed Air Energy Storage with packed bed thermal energy storage“, is here.
Anyway, the article deals with an A-CAES systems that uses packed bed regenerators to store the heat of compression and return it again, rather than indirect-contact exchangers and a thermal fluid. As far as I know it is the first article out there to rigorously analyse a system with packed beds, so hopefully it will be a useful contribution. Other articles have considered packed beds for use in Pumped Thermal Energy Storage. I think that an A-CAES system based around packed beds is a better preliminary design than a system which uses indirect-contact heat exchangers (i.e. shell and tube, plate-fin etc) and stores the compression heat in some kind of thermal fluid.
The packed beds allow the stratification of heat at different temperatures to be preserved during the storage process. And we all know that allowing heat at different temperatures to mix involves exergy destruction, so by keeping the heat stratified, a higher efficiency may be achieved. In the system I analyse, most of the exergy is destroyed by the compressors and expanders, with roughly 7% lost as heat escape from the packed beds. The article also explains that due to leftover heat in the beds, during continuous cycling the temperatures of the beds is significantly increased and results in a slightly lower efficiency – reduced from 71.1% to 70.8% in a system with 3 stages. The article develops and validates a numerical model which is available to download. I also made an animation of the simulation which shows how the temperature profile in the packed beds evolves as the system is charged, left in storage, and discharged again (shown below).
The appendix also derives a set of analytical equations for the work available from tank of compressed air in which the pressure in the tank depends on the volume of air contained.
Once more, here’s the link.