Modeling of Elemental Sulfur Deposition in Sour Gas Petroleum Pipelines

Sulphur deposition has been a prominent issue in sour gas pipeline integrity matter.  In this paper, a theoretical model was proposed to predict the behaviours of elemental sulphur (S₈) deposition in sour-gas petroleum pipelines.  During the modeling, pressure and temperature profiles were first calculated.  Following this, S₈ solubility alteration along the pipelines was acquired.  When the initial sulphur-vapor concentration in the gas stream hit the solubility value, the saturation distance was obtained.  Further decreases in pressure or temperature instigated a thermodynamic instability.  Once a threshold of free energy change was overcome, elemental sulphur started to be precipitated.  The nucleation rate was determined from classic nucleation theory.  Particle coagulation and agglomeration were approximated using the Smoluchowski’s analytic model.  The precipitated amount in each subregion was achieved in terms of solubility change.  As a result, transient particle size was assessed.  Particle trajectories were tracked by solving the motion equation in which an empirical formula was assigned for turbulent single-phase gas flow.  As particles touched the metal surface, the Tabakoff’s model was applied for the interaction between particles and the pipeline metal surface.  Consequently, the maximum travelling distance of the particles could be quantified.  Furthermore, the effects of initial production rate, S₈ vapour concentration, pressure, and temperature on the S₈ deposition behaviour were characterized.