Researchers at Hunan University of Technology in China have found that changing the way air is injected into underground compressed air energy storage (CAES) caverns can improve storage performance.
The team developed a numerical model to study how airflow patterns wellbore size and surrounding rock properties affect temperature, pressure and heat loss inside storage caverns. The model was also validated using operating data from Germany’s Huntorf CAES facility.
Researchers compared four injection strategies while storing the same amount of air over eight hours. The approach that gradually increased the airflow from 10 kg/s to 150 kg/s delivered an energy storage rate of 87.5%, compared with 85.5% for a constant 80 kg/s flow.
The increasing flow method also raised the average cavern temperature by about 1 kelvin and pressure by 0.13 MPa. However, it increased the work done on the compressed air by around 12.7% and heat loss to surrounding rock by about 11%.
The study also found that wellbore diameter plays an important role in controlling heat losses. Increasing the diameter from 0.5 metres to 2 metres reduced heat loss through the wellbore wall from 8.5 × 10⁸ joules to 2.5 × 10⁸ joules.
The researchers said the findings could help improve the design and operation of large scale underground CAES facilities by optimising both air injection strategies and system components. The study was published in Case Studies in Thermal Engineering.