Characteristics of ultra-low load and flexible peak shaving – a study on circulating fluidized bed preheating combustion

The global transition towards renewable energy necessitates enhanced operational flexibility in conventional coal-fired power plants to ensure grid stability. Circulating fluidized bed (CFB) combustion, while fuel-flexible, faces inherent limitations in peak-shaving applications due to its large thermal inertia, slow load-following rate, and challenges in maintaining stable combustion at ultra-low loads. This study addresses these critical issues by investigating a novel pulverized coal preheating technology within a CFB system, focusing on its rapid peak-shaving capability and low-load combustion stability. Experimental results demonstrate that this technology enables stable fluidized bed combustion at a ultra-low load of 18 %. Furthermore, when utilizing the pre-CFB for load regulation, a maximum peak shaving rate of 3.75 %/min was achieved at medium–high loads representing a 3.78-fold increase during the 55 % to 75 % load transition. A detailed analysis of the properties of preheating coal char and gas under varying loads revealed the underlying mechanism for the rapid and flexible load-changing characteristics. This work provides fundamental insights into the process mechanism of deep and flexible load changing process using fuel preheating, offering a viable pathway for upgrading existing CFB units worldwide to better support power systems with high shares of intermittent renewables.