Computer modelling dispersion plume of Tebar - Petrobrás submarine outfall

Abstract

Fluent can model the mixing and transport of chemical species by solving conservation equations describing convection, diffusion, and reaction sources for each component species. The transport of species simulation is applied in this present paper for the TEBAR Submarine Outfalls. The São Sebastião Channel (25km long, 40m depth and with a narrowest section of 2km) contains one of the largest oil terminals in Brazil (Tebar of Petrobrás - Petróleo Brasileiro S.A.). The submarine outfalls are formed by two outfall lines build of HDPE - High Density Poliethylene. Both of them have three risers each with 0.15m of diameter and 1.5m of height. They are located between 19.15m to 25.45m of depth. The highest current intensity is 0.90m/s and medium intensities between 0.40m/s and 0.60m/s are to northward. The effluent was sampled from April 2000 to March 2002 by Petrobrás. In this period, it was founded high concentrations of ammonia (125.5mg/L in April 2001), trespassing the limited value for emission of CONAMA 20 Resolution - Art.21 (5mg/L). The salinity of effluent is of order 52,8% at a temperature of 27.3ºC for the same period. This range of values results in a density of 1036.7 kg/m3. Computer modeling uses for the waste water dispersion process description in water bodies is a modern tool as a decision support for the environmental agencies and for the industries. A CFD - Computer Fluid Dynamics uses finite volume technique, and FLUENT is one of the applied software. The process of dilution of the plume in the near and far field is a powerful tool for the simulation of industrial waste dispersion process with variable batimetries and considering discharges from multi-port diffusers with complex geometries (ORTIZ&BESSA, 2004). The geometry creation and mesh generation of São Sebastião Channel was based using the software Gambit. The hexahedral structured mesh was built for the whole channel, including the contours around ports. The 3D mesh has a total of 655.452 volumes. © 31st IAHR Congress 2005: Water Engineering for the Future, Choices and Challenges. All Rights Reserved.