Muliti-Phase Flow: Gas Sweetening Hydrodynamic

Gas Sweetening System Hydrodynamic Analysis

Description

This project presents a computational fluid dynamics study of the hydrodynamic behavior inside a gas sweetening facility using ANSYS Fluent software. Gas sweetening is a critical industrial process used to remove hydrogen sulfide, carbon dioxide, mercaptans, and other contaminants from natural gas and synthetic gas streams, ensuring safe transportation and end use. Treating sour gas is essential because of the strongly corrosive effect of hydrogen sulfide and carbon dioxide on pipeline infrastructure, as well as their toxic effects on human health.

The computational domain involves two distinct materials: a specific sour gas composition and an amine solution stream. This study focuses exclusively on the hydrodynamic aspects of the process and does not model the actual gas removal mechanisms, which typically involve complex physical or chemical interactions. For this hydrodynamic analysis, water is used as a substitute for the amine. A Volume of Fluid (VOF) multiphase model is used to define the two-phase environment. The system features two separate inlets for the amine and gas streams, with the amine flow entering at a velocity of 0.3 m/s before meeting the gas stream inside the processing equipment.

The gas sweetening equipment is modeled in three dimensions using Design Modeler software, with realistic inlet configurations for the introduction of both the gas and amine streams into the vessel. The meshing is performed using ANSYS Meshing software, generating an unstructured mesh of 2,168,649 elements. This mesh density provides sufficient resolution to capture the complex multiphase flow interactions within the equipment.

Methodology

Several assumptions are applied in this simulation. A pressure-based solver is used for the incompressible flow analysis, and the simulation is run as a steady-state case. The effect of gravity is taken into account, with a gravitational acceleration of -9.81 m/s² applied along the vertical direction.

For the turbulence modeling, the RNG k-epsilon model with the standard wall function is used. The two-phase flow is captured using the VOF model with two Eulerian phases (gas and water) and a dispersed interface modeling approach.

Regarding the boundary conditions, the gas inlet is defined as a velocity inlet with a velocity of 0 m/s and a water volume fraction of 0, while the amine inlet is defined as a velocity inlet with a velocity of 0.3 m/s and a water volume fraction of 1.0. Both the gas outlet and the amine outlet are defined as pressure outlets with a gauge pressure of 0 Pa, and the equipment walls are treated as stationary walls with a no-slip condition.

In terms of the solution methods, the pressure–velocity coupling is handled with the SIMPLE algorithm. The PRESTO! scheme is used for pressure, second-order upwind for momentum, and first-order upwind for both the turbulence parameters and the volume fraction. The solution is initialized using the standard method, with zero gauge pressure, zero velocity components, and a zero water volume fraction throughout the computational domain.

Conclusion

After the solution, two- and three-dimensional contours of pressure, velocity, and the phase volume fractions for both the gas and water phases are obtained. The results show that the gas and amine streams collide after passing through the internal flow barriers within the processing equipment.

This collision demonstrates the ability of the amine stream to redirect part of the gas flow toward the equipment outlet. This behavior provides a basis for understanding the mixing and contact efficiency in real gas sweetening operations, where chemical absorption would take place between the amine solution and the acid gas components. The velocity and pressure contours offer valuable insight into the flow distribution patterns, mixing zones, and potential areas for equipment optimization, all of which are essential for designing efficient gas–liquid contact systems in industrial sweetening applications.