Milton Mori

Simulation of an industrial wastewater treatment plant using artificial neural networks

Abstract This work presents a way to predict the environmental properties of the output stream from the wastewater treatment plant at Rhodiaco Ltda, one of the major chemical plants in Brazil. The industrial plant produces purified terephtalic acid and generates wastewater that should be treated in an activated sludge system. The influence of input variables is analyzed, and satisfactory predicted results are obtained for an optimized situation.

SIMULATION OF AN INDUSTRIAL WASTEWATER TREATMENT PLANT USING ARTIFICIAL NEURAL NETWORKS AND PRINCIPAL COMPONENTS ANALYSIS

This work presents a way to predict the biochemical oxygen demand (BOD) of the output stream of the biological wastewater treatment plant at RIPASA S/A Celulose e Papel, one of the major pulp and paper plants in Brazil. The best prediction performance is achieved when the data are preprocessed using principal components analysis (PCA) before they are fed to a backpropagated neural network. The influence of input variables is analyzed and satisfactory prediction results are obtained for an optimized situation.

Study of the interfacial forces and turbulence models in a bubble column

Abstract Three-dimensional Eulerian simulations of gas–liquid flows in a cylindrical bubble column were performed in order to evaluate the flow pattern in the heterogeneous flow regime. Simulations were conducted numerically by the finite element method using a commercial CFX code (v.12.0) and an analysis of interfacial forces such as drag, lift and turbulent dispersion, as well as a comparison of k – ɛ and Reynolds Stress (RSM) turbulence models were performed. Different bubble sizes and two boundary conditions for the column exit were also verified. Gas velocities and holdup profiles were compared with experimental data. Results have shown that at the sparger region and without any simplification on the boundary condition the RSM model better represents the flow. At the fully developed region k – ɛ also showed good results.

Three-dimensional modeling of fluid catalytic cracking industrial riser flow and reactions

Abstract A three-dimensional and two-phase flow model to predict the dynamic behavior of a fluid catalytic cracking (FCC) industrial reactor was developed in this work. The study took into account heat transfer and chemical reactions. A four-lump model was proposed to represent the catalytic cracking reactions in which the heavy oil (gas oil) is converted into gasoline and light hydrocarbon gases. Gas acceleration inside the reactor due to molar expansion and a model to describe undesirable catalyst deactivation by coke deposition on its surface were also considered. An Eulerian description of the phases was used to represent the two-phase flow. A commercial CFD code (Ansys CFX version 11.0) was used to obtain the numerical data. Appropriate functions were implemented inside the CFX code to model the heterogeneous kinetics and catalyst deactivation. Results show nonuniform tendencies inside the reactor, emphasizing the importance of using three-dimensional models in FCC process predictions.

Gas-solid flow in cyclones: The Eulerian-Eulerian approach

Abstract A computational fluid dynamic model was used to simulate the diluted gas-solid flow in a conventional cyclone. Most of the studies published in the literature present the Lagrangian model for solid phase. In this work, the model is based on the Eulerian approach for both phases considering the two fluid assumption in a 3-D symmetrical domain. The mathematical model was completed using of the k-ϵ turbulence model which was used to predict the eddy viscosity for axial and radial components of the Reynolds stress of the gas phase. Also, for the tangential velocity of the gas phase, the Prandtls mixture length theory was used to predict the tangential components of the Reynolds stress, and a wall function was used to predict the swirling near the wall. This turbulence model presents an anisotropic behaviour of the Reynolds stress on the gas phase. The solid phase flow was considered to be an inviscid flow, and only a drag force model was used for gas-solid interaction. Two physical situations were simulated to test the model proposed: one was clean air flow, and the other was air and spherical particles of glass in a diluted flow. The primary information obtained from the model was the influence of the solid phase on the gas phase. It was the possible to predict the reduction of the tangential velocity peak responsible for the pressure drop reduction due to the particle presence.

Comparison between staggered and collocated grids in the finite-volume method performance for single and multi-phase flows

Abstract This work presents the numerical results obtained when staggered and collocated grids were used in the finite-volume methods (FVMs) for four standard flows: developing laminar single-phase flow at the entrance of the tube; developing turbulent single-phase flow at the entrance of the tube; incompressible laminar flow through an orifice plate; and developing turbulent gas–solid flow in a vertical pipe. These test cases were chosen to embody a variety of pattern flows very common in computational fluid dynamics problems (CFD problems). The main aspects analyzed were: the convergence rate, the stability of the pressure–velocity coupling; the dependence of the solution on the grid concentration and on the variation of the under-relaxation parameters; and the capability of reproduction of the experimental data and/or analytical solutions. The paper also presents a discussion of the strategies to apply the collocated and staggered grids and some aspects of the pressure–velocity coupling for both procedures. The numerical results were compared with experimental data or with analytical solutions and they presented a good agreement. The results show that the staggered arrangement of the grid has an advantage when dealing with high pressure gradient and multi-phase flows.

CFD Study of Industrial FCC Risers: The Effect of Outlet Configurations on Hydrodynamics and Reactions

Fluid catalytic cracking (FCC) riser reactors have complex hydrodynamics, which depend not only on operating conditions, feedstock quality, and catalyst particles characteristics, but also on the geometric configurations of the reactor. This paper presents a numerical study of the influence of different riser outlet designs on the dynamic of the flow and reactor efficiency. A three-dimensional, three-phase flow model and a four-lump kinetic scheme were used to predict the performance of the reactor. The phenomenon of vaporization of the liquid oil droplets was also analyzed. Results showed that small changes in the outlet configuration had a significant effect on the flow patterns and consequently, on the reaction yields.

Modeling and simulation of a pseudo-three-phase slurry bubble column reactor applied to the process of petroleum hydrodesulfurization

Abstract This work presents a new CFD model for the hydrodesulfurization process in the petroleum industry. The new model considers the loss of effectiveness of the catalyst by coupling a model that considers the physical structure of the catalyst. The hydrodesulfurization process takes place in a pseudo-three-phase fluidized-bed slurry bubble column reactor with liquid and gas flowing upwards. This reactor presents a transient behavior for the catalytic effectiveness due to the obstruction of the catalyst pores, caused mainly by parallel reactions of hydrodemetalization acting on the catalyst. The emphasis of this work is the introduction of a kinetic model for the reactivity reduction of the catalyst inside slurry bubble column reactors. The hydrodynamic model is simple and adopts an Eulerian–Eulerian approach, where the momentum and mass conservation equations are used to describe the two-phase fluid dynamic fields. The k – ɛ model is used to account for turbulence. The kinetic model considers the reactions controlled by diffusion and occurring on the catalyst pores, which are obstructed along the process by the hydrodemetalization by-products. The model presented in this work allows for an assessment of the influence of the operational conditions of the reactor, such as liquid and gas feed velocities, as well as catalyst properties. The estimation of the yield of the process takes into account the transient activity of the catalyst.

Three-Dimensional Gas-Liquid CFD Simulations in Cylindrical Bubble Columns

Results from CFD simulations in a laboratory scale cylindrical bubble column with an internal diameter of 0.44 m under different operation conditions are presented. The effects of the continuous phase viscosity, bubble diameter and drag model were evaluated and the results were compared with experimental data found in the literature in three different gas inlet velocities. It was found that the approach used in this work provided physically consistent results, showing the transient effects in the column and good agreement with experimental data found in the literature for a homogeneous flow regime. Also, a case for a column with internals was simulated and a flow behavior qualitatively different from the column without internals was found.

Fluid dynamic modelling and simulation of circulating fluidized bed reactors : Analyses of particle phase stress models

Abstract The main objective of this work is to analyse the effect of the particle phase stress model on the accuracy of prediction of the fluid dynamic of Circulating Fluidized Bed (CFB) Reactors. The fluid dynamic prediction of CFB is fundamental in its development and optimisation. In this work a two-dimensional hydrodynamic model for gas-particle flow has been used to compute the porosity, the pressure, and the velocity fields of both phases in 2-D axisymmetrical cylindrical co-ordinates. The fluid dynamic model is based on the two fluid model approach in which both phases are considered to be continuous and fully interpenetrating. CFB processes are essentially turbulent. The k-ϵ turbulence model, modified to consider the presence of the particle phase, was used to calculate the effective viscosity of the gas phase. For the particle phase inviscid model, Newtonian fluid with experimentally obtained viscosity constant and viscosity which was calculated from emerging kinetic theory of granular flows (KTGF) have been used to simulate the fluid dynamic of the CFB reactors. The results are compared with experimental data available in the literature.