Scalable, Transportable Thermochemical Energy Storage for Industrial Process Heat and Steam on Demand

Energy storage based on reversible chemical reactions, termed thermochemical energy storage (TCES), has been proposed since the 1970s. TCES based on calcium oxide and hydroxide, where dehydration of Ca(OH)2 to CaO stores energy and the hydration of CaO to Ca(OH)2 releases the energy, is especially promising. The material is cheap at $100/ton, has high energy density at ~500 (W·h)/kg, the reaction is highly reversible, and the reaction temperatures of >550 C can serve ~75% U.S industrial process heat demand. Additionally, the temperatures are high enough to drive efficient heat-to-power conversion cycles for electricity generation. However, the commercialization of TCES has been hindered due to: 1) a large heat exchange surface requirement that accounts for ~80% of heat storage system cost, making it expensive and non-scalable and 2) storage material challenges of agglomeration, and low heat and mass transfer. Cache’s innovative system solves both problems by using high-strength CaO pellets flowing through a continuous fluidized-bed reactor (FBR). Since the storage material is fluidized and flows through, instead of being packed inside the reactor, the system can be scaled to 100s of hours of continuous energy storage/supply without scaling up the reactor. The FBR has ~10x higher heat and mass transfer compared to conventional reactors, reducing the heat exchanger surface required and hence the system cost significantly down to $ 5-10 /kWh. The CaO pellets have high strength and prevent fine particle generation and thus agglomeration. Once charged with waste heat or renewable electricity, the pellets store energy at ambient temperature and can be easily transported to other sites where energy is needed. The proposed highly scalable energy storage system can dispatch energy continuously for >100 hours while storing energy at ambient conditions, insulation free for up-to > 6 months with near zero loss. The technology enables energy transportability while providing high temperature process heat/high quality steam for ~75% U.S industrial demand