Study on the condensation behavior of KCl vapor on wall surfaces under pressurized condition

As a pivotal renewable energy source, biomass energy suffers from ash deposition induced by KCl condensation during thermal conversion, which impairs its efficient utilization; yet pressure's impact on KCl condensation remains unclear. Here, the effects of pressure on KCl vaporization and condensation were investigated via a pressurized experimental system, thermodynamic calculations, and characterization techniques including scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and X-ray diffraction (XRD). Results showed that pressure significantly affected solid KCl's vaporization temperature: at 0.1 MPa, KCl began to vaporize at 725 °C and fully vaporized at 1300 °C, while at 1.4 MPa, these temperatures increased to 900 °C and 1700 °C, respectively. Similarly, gaseous KCl's condensation temperature rose with pressure, with solid KCl precipitating at approximately 1200 °C under 0.1 MPa and 1700 °C under 1.4 MPa. At 1000 °C, increasing pressure reduced KCl's vaporization rate from 52.0 % (0.1 MPa) to 35.2 % (1.4 MPa) and made condensation products smaller, more uniform-the average size fell from 5.89 ± 1.74 μm (0.1 MPa) to 1.20 ± 0.49 μm (1.4 MPa). XRD analysis indicated that pressure minimally influenced KCl's crystal structure but significantly altered the intensity and width of diffraction peaks. This study proposes a KCl condensation mechanism under different pressures and temperatures, providing a basis for addressing ash deposition and slagging in biomass thermal conversion. • Investigated KCl gasification/condensation behavior under varying pressures. • Found rising pressure increases gasification/condensation temperatures. • Higher pressure decreases KCl gasification rate and particle size. • Clarified pressure-dependent KCl condensation mechanisms.