Robust Flow Regulation Using Orifice and J-Valve Combination in Circulating Fluidized Bed Thermal Energy Storage

With the expansion of renewable energy deployment, characterized by its variability, stabilizing power and heat supply has become a critical issue. To address this challenge, large-scale and low-cost energy storage technologies are essential, and thermal energy storage (TES) is considered one of the promising solutions. Among large-scale TES systems, Circulating Fluidized Bed TES (CFB TES) is a technology that stores energy as sensible heat in high-temperature sand and utilizes it for power generation using high-temperature steam or steam turbines when needed, offering high compatibility with existing infrastructure. While the underlying circulating fluidized bed system is a well-established technology, precise control of circulating particle flow rates remains a technical challenge due to differences from conventional circulating fluidized beds. In this study, we propose a mechanically simple and thermally durable flow control system that combines an orifice for stepwise flow adjustment and a J-valve (loop seal) for on/off particle transport. In this study, the flow characteristics of the orifice, the minimum fluidization velocity (umf≈ 0.076 m/s), the transient stabilization behavior, and the effects of downstream pressure (back pressure) were evaluated in lab-scale experiments. The results showed that particle flow rate follows a power-law relationship with the orifice diameter, stabilizes when fluidization velocity exceeds umf, and decreases linearly with increasing back pressure. Based on these findings, we established design guidelines incorporating orifice sizing, fluidization control, and back pressure compensation.