Gas Sweetening Hydrodynamic

Gas Sweetening Hydrodynamic, ANSYS Fluent CFD Simulation Tutorial

Description

This project simulates the hydrodynamic behavior inside a gas sweetening unit using ANSYS Fluent. Gas sweetening is a critical process in the natural gas industry, removing hydrogen sulfide, carbon dioxide, mercaptans, and other contaminants from sour gas streams before transportation and end use. Treating sour gas is essential for two reasons: hydrogen sulfide and carbon dioxide are severely corrosive to pipeline infrastructure, and hydrogen sulfide is highly toxic to human health.

The study concentrates exclusively on the hydrodynamics of the process — the flow interaction and contact between the gas stream and the amine solution — rather than the chemical absorption mechanisms themselves. Water serves as a substitute for the amine material in this hydrodynamic analysis. Understanding how the two streams meet, mix, and distribute inside the vessel forms the foundation of contact efficiency in real sweetening operations, where chemical absorption occurs at the gas–liquid interface.

Methodology

The three-dimensional geometry of the sweetening equipment, including the inlet configurations for both the gas and amine streams, is constructed in Design Modeler. An unstructured mesh of 2,168,649 elements is generated in ANSYS Meshing, providing adequate resolution for the multiphase flow interactions inside the vessel.

The case is solved as a steady-state, pressure-based simulation with gravity applied at −9.81 m/s² in the vertical direction. The two-phase environment is defined with the VOF multiphase model using two Eulerian phases (gas and water) with dispersed interface modeling, and turbulence is handled with the RNG k-epsilon model with standard wall functions.

The amine stream enters through a velocity inlet at 0.3 m/s with a water volume fraction of 1, while the gas stream enters through its own inlet with a water volume fraction of 0. Both the gas and amine outlets are defined as pressure outlets at 0 Pa gauge, and the equipment walls carry the no-slip condition. The numerical setup uses SIMPLE pressure–velocity coupling, the PRESTO! scheme for pressure, second-order upwind for momentum, and first-order upwind for the turbulence and volume fraction equations, starting from standard initialization.

Analysis

At the end of the solution process, two-dimensional and three-dimensional contours of pressure, velocity, and phase volume fraction are extracted for both the gas and water phases. The results show that the gas and amine streams collide after navigating through the internal flow barriers of the equipment — the key hydrodynamic event of the process.

This collision demonstrates the amine current's ability to redirect portions of the gas flow toward the equipment outlet, revealing the mixing zones and contact patterns that would govern absorption efficiency in an actual sweetening operation. The velocity and pressure contours identify the flow distribution and potential areas for equipment optimization — insights essential to designing efficient gas–liquid contact systems. By completing this project, you will learn to set up a VOF simulation with dual inlet streams, model gas–liquid contact hydrodynamics, and interpret phase distribution results in the context of industrial gas treatment equipment.