Desenvolvimento de prato perfurado sem downcomer com geometria fractal: avaliação fluidodinâmica e ambiental

Abstract

Distillation columns are classified as tray column, packing or mixed (hybrid) depending of tower internal type placed inside. Tray internals are classified in with or without downcomer and the simplest models of trays without downcomer are called dual-flow. Dual-flow trays have advantages such as low cost, constructive simplicity and self-cleaning capacity. However, have disadvantages as restricted operating ranges for project and lower efficiency caused by flow instability due formation of exclusive regions of liquid and vapor passage through the tray openings causing phases segregation. Once distillation columns are important equipment to obtain raw materials and products with high purity, improvement of such equipment becomes necessary. This study evaluated the influence of hole diameter (d) and the free area ratio (φ) of dual-flow tray on dry tray pressure drop (ΔPd) fluid dynamic parameter through comparison of experimental, computational and predicted results by correlations of literature. In sequence, was carried a study that proposed a new dualflow tray geometry based on fractal concept and evaluated through multiphase flow experiments. Fluid dynamic parameters evaluated were ΔPd, wet tray pressure drop (ΔPw), foam height (H), clear liquid height (hCL), froth porosity (ε) and regime formation on the tray. The last study evaluated the manufacture of tray and hybrid distillation columns with dual-flow internals using the Life Cycle Assessment (LCA) methodology in order to identify the column with the lowest impact about the environment. Results showed that φ has a more pronounced effect than d on ΔPd and a φ of 20% was indicated. Subsequent analysis showed that dual-flow tray with φ of 20% and with 5 and 7 mm alternating diameters distributed in fractal shape improved the tray operability, stabilizing the ΔPw and maintaining similar values of H, hCL, ε and, regime formation on the tray to those obtained for the better conventional dual-flow tray. The last evaluation performed showed that the hybrid distillation column manufacturing reduced the environmental impacts by 15% compared to the tray column manufacturing. This reduction is equivalent to the emission reduction of 180.7 kg CO2eq due to the replacement of stainless steel tray by Raschig packing of polypropylene, in column rectification section.