ID 216

Development of Internal Mixing Twin Fluid Atomizer with Multi Exit Port for Heavy Oil Fired Boilers

 

Abstract:

Recently, new-type internal-mixing twin fluid atomizers are being used for advanced low-grade oil fired boilers provided by Mitsubishi Heavy Industries group. The present research focuses on the spray characteristics of two atomizer types (LSF and LCF) with different liquid-gas mixing methods. In the LSF type atomizer the liquid is fed straight along the atomizer centerline and intersects with the gas fed from the surroundings, whereas the LCF type feeds the gas in the center and the liquid from the surroundings. The dynamic two phase flow inside the atomizer effects on the liquid breakup, spray formation processes and fluctuations of the spray. First, two-phase VOF simulations were applied to elucidate the liquid behaviors at the primary mixing zone inside the internal mixing chamber and at the exit port. At the exit port, the LCF type produces a thin liquid film around the inner wall with a nearly symmetric velocity profile, whereas the LSF type produces a thicker liquid film with a less symmetric velocity profile. Second, the differences in the spray characteristics were experimentally investigated. The LCF type produces a more uniform and thinner liquid film, resulting in finer droplets compared to the LSF type. Finally, experiments were performed to observe the rapid fluctuations of sprays immediately downstream of the exit ports using a high-speed video camera. The prominent frequencies of the fluctuations with the order of a few kHz are observed in the experiments, which agree with the simulation results.