Flow instability of 600 MW supercritical boiler water-cooled wall under low-load in deep peak-shaving process

During deep peak shaving process, the flow instability may occur within the water-cooled-wall of supercritical boiler, posing a serious challenge to the thermal system's security. In this study, a general model based on the time-domain method with customized heat transfer and multi-tube parallel model is developed to analyze the flow instability in water-cooled-wall system. The model was verified by a comparison between the computational results and experimental data. Building on this model, the flow instability characteristics of the water-cooled-walls in a 600 MW supercritical once-through boiler were analyzed under Boiler Maximum Continuous Rating (BMCR), 75 % Turbine Heat Acceptance (THA), and 30 % THA. The results indicate that during deep peak shaving, the stability is relatively poor at low-load conditions. As the load decreases, the duration of oscillations increases from 81 s to 115 s (increased by 41.98 %). For multi-tube parallel under low-load, the influence of various thermal parameters on flow instability was also investigated. When the number of parallel tubes increases to 20 and 40, the critical heat load shows an increase to 0.51 % and 1.02 %, reaching 39.5 kW m⁻² and 39.7 kW m⁻², respectively. Furthermore, it increases almost linearly with inlet pressure, significantly with inlet mass flow rate, and decreases with increasing inlet temperature. The inlet mass flow rate and temperature significantly influence the threshold heat flux.