Flow and residence time distribution characteristics in continuous hydrothermal reactor under different heating schemes

Residence time distribution (RTD) is of significance for reflecting materials or intermediate products dispersion and actual reaction time inside continuous hydrothermal reactors of supercritical water gasification technology. Generally, RTD is strictly related to flow field, which can be affected by wall heating schemes. In order to propose methods to regulating RTD, effects of different heating schemes on flow and RTD characteristics are investigated and compared by numerical simulation. The results indicate that increasing heat flux, interrupting boundary flow by interlace heating, and setting cooling walls can significantly regulate RTD. By analyzing the correspondence of flow and RTD, the mechanisms of increasing materials and intermediate products dispersion can be attribute to the increase of flow instability and the generation of additional vortices. For example, in the cases of present work, the narrow-strip double-vortex generated by mixing between thermal boundary flow and branch flow may significantly increase average residence time and materials distribution range from 10.93 s and 1.00 to 22.83 s and 1.51. In the region above branch inlet without time-averaged vortex structure, the increasing of flow instability caused by wall heating is observed to widen materials distribution range from 0.75 to 0.99. Heating scheme customized according to these mechanisms can regulating RTD as expected, proving the feasibility and significance of regulating RTD by heating schemes.