In the background of the carbon peaking and carbon neutrality goals, China is accelerating the construction of a new power system in which the proportion of new energy sources is gradually increasing, and coal-fired power plants are currently the most economical regulating power sources for the large-scale grid connection of renewable energy. Due to their inherent advantages, circulating fluidized bed boiler units are crucial for the deep and flexible peaking of coal-fired power plants. However, because of their peculiar design and mode of operation, these units have a low load change rate, making it necessary to increase their capacity to absorb large amounts of new energy for the grid. The influencing factors that governed the load change rate of circulating fluidized bed boilers were analyzed including the inertia of gas-solid two-phase flow, combustion of solid particles, heat transfer between the water side and the furnace side, hydrodynamic safety, dynamic matching problem of the turbine and boiler, and the physical mechanism of inertia generation was also explained. The key technologies to improve the rapid load change capability of the circulating fluidized bed unit were summarized. By accelerating the flow parameters, improving the heat transfer coefficient, reducing the heat capacity of the furnace side, enhancing the heat transfer between the furnace and the water side, strengthening the combustion reaction, optimizing the control strategy, and considering the feasibility of industrial size boilers, a comprehensive optimization technology solution was proposed, namely the concept of an "intelligent take in/out" system, which was validated in a 135 MW circulating fluidized bed boiler. The results indicate that it is possible to enhance the boiler′s average load change rate by 16% and sustain a short-term maximum load variation rate of up to 4%/min. According to this, using a data-driven dynamic model of the thermal system, a multi-temporal matching operation technology of the thermal system incorporating innovative technologies, an advanced collaborative control system with "three self-integrated", and a reference to the established energy storage and utilization technology of pulverized coal-fired power plants, the design idea of a circulating fluidized bed unit with flexible operation at a wide range of load was provided, which offered theoretical guidance for future practical industrial applications in China.