Transient Wall Temperature Characteristics and Effects on Load Cycling Rates of Water Walls With Various Materials

The continuous expansion of renewable energy installed capacity has propelled an increasingly urgent demand for deep peaking operations of coal-fired power units within the power system. However, the frequent and rapid load cycling operations of these units induce drastic alterations in the flow and heat transfer characteristics of the working fluid within water wall tubes. As a direct consequence, the risk of water wall overheating and bursting has escalated significantly. To tackle this critical issue, this study develops a one-dimensional dynamic model of the water wall. The research delves into the mechanism through which uneven water wall flow distribution affects the metal wall temperature during rapid load cycling processes. Additionally, maximum load cycling rates of the units under various metal material conditions are determined. Results clearly demonstrate that the wall temperature in the dry-out zone is remarkably higher compared to other sections of the water wall. For boilers equipped with a water wall made of 15CrMoG material, at 50% and 30% THA (turbine heat acceptance) operating conditions, the peak wall temperatures in the dry-out zone reach 419.5 and 389.5°C, respectively. When water wall temperature is factored in as a limiting parameter during load cycling operations, the maximum power ramp rate of the unit registers 1.0% P_e/min during the 30%–50% THA loading up process. When the water wall material is switched to 12Cr1MoVG, the unit's maximum load cycling rate surges by 0.5% P_e/min, hitting 1.5% P_e/min. Further substitution with P91 material leads to an even more substantial increase of 1.5% P_e/min, with the maximum load cycling rate peaking at 2.5% P_e/min. By quantitatively assessing the risk of water wall overheating and bursting, this study lays a theoretical foundation for the peaking operation retrofit of coal fired power units.