Session: 10-08-01: Multiphase Flows and Applications

Paper Number: 141635

141635 - Experimental Investigation on the Transcritical Dynamic Characteristics of Water Wall for a Supercritical Cfb Boiler 

As China’s “dual carbon” policy advances, the share of renewable energy sources such as wind and photovoltaic power in the national power grid has been steadily increasing. Consequently, traditional thermal power plants are now required to take more responsibility of deep peak shaving. During deep peak shaving, supercritical circulating fluidized bed (CFB) operate under variable pressure conditions, transitioning from supercritical to near-critical pressures while maintaining relatively stable heat flux in furnace. This transcritical process presents unique flow and heat transfer phenomena within the water wall, which are critical for the boiler's safe and stable performance. To investigate these phenomena, an experimental study was conducted on the dynamic flow and heat transfer characteristics within a vertical upward smooth tube of a supercritical CFB boiler during transcritical pressure process. The experiments were performed with pressures ranging from 23 to 21 MPa, mass flows between 400-740 kg/(m²·s), and heat fluxes from 225-300 kW/m². Test material of the tube is 1Gr18Ni9Ti. The diameter and wall thickness are 30 mm and 5.5mm. The length of the test section is 2 m. The experimental results indicated that as system pressure decreased from 23 MPa to 21 MPa, the mass flow within the tube increased sharply, and the outlet fluid temperature decreased. Concurrently, a rapid rise in wall temperature was observed, attributed to heat transfer deterioration in the near-critical pressure region. As the inlet mass flow increased, the wall temperature eventually returned to the normal value. The dynamic heat transfer coefficients were calculated throughout the transcritical process, revealing stages of heat transfer deterioration, subcooled boiling, and single-phase water heat transfer. The study identified a specific enthalpy range within which a rapid rise in wall temperature occurs during the transcritical process. Outside this range, such temperature rise was not observed. The effects of mass flow and heat flux on dynamic characteristics were found to be opposite. Increased mass flow raised the enthalpy threshold for the rapid rise in wall temperature and reduced the amplitude of temperature fluctuations. In contrast, higher heat flux lowered the enthalpy threshold and increased temperature fluctuations. The enthalpy ranges associated with heat transfer deterioration under various operational conditions were delineated. This research provides valuable insights into the dynamic flow and heat transfer behavior of water wall in supercritical CFB boilers during deep peak shaving. The findings offer guidance for optimizing operational parameters to ensure the safe and efficient performance of these boilers under variable pressure conditions.

Presenting Author: Dong Yang Xi'an Jiaotong university

Presenting Author Biography: Dong Yang, professor, doctoral supervisor, Xi'an Jiaotong University. Mainly engaged in research on supercritical fluid flow heat transfer, supercritical boiler hydrodynamics and flow instability.

Authors:

Dong Yang Xi'an Jiaotong university
Xiaocheng Du Xi'an Jiaotong University
Zerui Guo Xi'an Jiaotong University
Ning An Xi'an Jiaotong University
Lei Han Xi'an Jiaotong University
Ziyu Wei Xi'an Jiaotong University