The most advanced Calcium Looping configuration relies on the use of a twin circulating fluidized bed system. An important characteristic of this configuration is the link between the solid circulation and the gas velocity through the reactors. FlexiCaL aims to analyze the dynamic response and performance of the dual fluidized bed system against flue gas loads. Moreover, in order to improve the flexibility of Calcium Looping system, a new CaL reactor configuration for decoupling the gas flows through the carbonator from the solid circulation flows between reactors will be analyzed. This new carbonator can be operated under bubbling bed conditions at low flue gas load up to edge of circulating FB conditions at full load.
A second aim of FlexiCaL project is to improve the flexibility by the integration of an energy storage system into the boundaries of the Calcium looping. This system will include at least two silos connected to the carbonator and calciner reactors. During low thermal load periods in the power plant, the CO2 load to the carbonator is reduced and the excess of thermal input in the calciner can be used to heat up and calcine carbonated solids fed from the low temperature silo. Likewise, during high thermal load periods in the power plant, the increase of CO2 load into the carbonator can be fulfilled by feeding a stream of hot CaO from the high temperature silo. This also allows producing extra power from the stored solids during high demand periods by avoiding the penalties associated with CaCO3 regeneration (storing carbonated solids).
By adjusting the flow of solids between silos and reactors, the calciner can be operated at base load during the high and low demand periods, including the air separation (ASU) and CO2 purification and compression (CPU) units. Another important advantage is that the capacity of the CaL system, including the ASU and CPU, can be under-sized respect to the power plant allowing for a substantial reduction of capital costs of the CO2 capture system, while allowing keeping high CO2 capture rates at any load.