Theoretical analysis on response characteristics of mass flow in supercritical pressure circulating fluidized bed boiler

• Response characteristic can be quantized by flow sensitivity coefficient.
• Response characteristic of mass flow is affected by multiple factors.
• There is a critical mass flow to distinguish PRC and NRC.
• PRC of vertical tube depends on the total pressure drop variation within tube.
• Water wall of SCFBB studied has PRC at low load operations.

Under the working conditions of 600 MW supercritical pressure circulating fluidized bed boiler, this paper conducted a theoretical analysis on the response characteristics of mass flow with respect to a heat disturbance within furnace. The main objective has focused on the effects of multiple factors on the variations of flow sensitivity coefficient and the corresponding mechanism was discussed in detail. It was found that the flow sensitivity coefficient decreases with increasing steam quality and increases with increasing heat flux, suggesting a stronger flow sensitivity within low quality range accompanied by a high heat flux. The flow sensitivity is more pronounced for the working condition with low mass velocity. There is a critical mass velocity that can be used as a demarcation line to distinguish the Positive Response Characteristic (PRC) and Negative Response Characteristic (NRC) of mass flow within vertical tube. The effects of pressure are mainly reflected in two aspects as the pressure varies, which are the variations of flow sensitivity coefficient and the critical mass velocity. The mass flow deviations at 40%, 50% and 75%THA are all greater than zero when the heat flux of vertical tube is increased by 30%. The steam deviations of SCFBB are much smaller than those of supercritical pressure coal-pulverized boiler under similar boiler loads, indicating that the SCFBB studied in this paper has distinct advantages in assuring good hydrodynamic performance of water wall.