Effective Time Method for the Determination of Interface Diffusion of H2S Slugs in Natural Gas Pipeline Systems

The primary objective of the work described in this paper is to examine the fate of H₂S contaminated natural gas slugs as they travel through a gas pipeline network. The important phenomenon that affects the spread of the H₂S slug as it travels downstream of a pipe is the diffusion with the sweet gas at the front and back interface of the slug. It was determined that the diffusivity constant (D) used in the calculation of the interface spread varies along the pipeline, which prohibits the use of a closed form solution of the Fick’s law equation. An effective time parameter has been introduced to account for the variation in the diffusivity in a “marching in time” scheme of solution. The model has been utilized to demonstrate the effects of pipe diameter, mean flow velocity and pipe internal roughness on the contamination spread. A test loop has also been constructed to validate the diffusion coefficient in gaseous flows. Excellent agreement was obtained between the measured vs. predicted results. The mean error in predicting the interface spread was approximately 6.2%.