A review of elemental sulfur deposition in high sulfur-content natural gas transmission pipeline

High sulfur-content natural gas includes hydrogen sulfide, mercaptans, sulfoethers, and other sulfurous substances, with the major component being hydrogen sulfide. The development of high sulfur-content natural gas fields worldwide ensures the supply of not only clean energy, but also raw materials for industrial sulfur products. However, supersaturated precipitation of gaseous sulfur yields solid sulfur particles by nucleation, coagulation, and agglomeration with changing operation pressure, temperature, and species and concentration of gas components in high sulfur-content natural gas transmission pipelines. The solid particles will flow with the natural gas, and when the dynamic conditions for particle deposition are fulfilled, they will be deposited in pipeline. The deposition of solid sulfur particles will cause blockages in the transmission pipeline; furthermore, the elemental sulfur contacting the metal surface of the pipeline will cause electrochemical and chemical corrosion reactions. Eventually, the consequences of sulfur deposition in high sulfur-content natural gas transmission pipelines will cause serious hazards for pipeline operation and production. This paper summarizes the advances in the calculation of the sulfur gas-solid phase equilibrium, understanding of the growth and ablation kinetics mechanism of solid sulfur particles, and development of a gas-solid two-phase flow mathematical model. To fulfill the need for theory and experimental methods for predicting and preventing sulfur deposition in high sulfur-content natural gas transmission pipelines, the following three topics should be emphasized in future studies: First, limited experimental data is available on elemental sulfur solubility in sour gas at the pressure and temperature conditions of transmission pipelines, so sulfur solubility measurements should be established in the pressure and temperature range ( P ≤15.0 MPa, T ≤333.15 K) of transmission pipelines, considering the very low sulfur solubility under these conditions. Second, mathematical models of solid sulfur particle growth kinetics should be established based on molecular dynamics (MD) simulations with statistical mechanics and thermodynamics, combined with crystallization kinetics theory to determine nucleation, growth, and ablation behavior under the conditions of natural gas transmission pipelines. Third, mathematical models of the gas-solid two-phase flow in the transmission pipelines should be built considering the gas-solid phase change of elemental sulfur, and the growth and ablation of sulfur particles these models should involve the coupling effects of multiple parameters such as pipeline pressure, temperature, gas composition, and flow rate. These models could provide a quantitative description of elemental sulfur precipitation, sulfur particle growth, and particle flow behavior in high sulfur-content natural gas. Accordingly, the exact quantity and position of elemental sulfur deposition in high sulfur-content natural gas transmission pipelines can be predicted. These achievements will contribute to sulfur deposition prevention and improvement of control technology, as well as provide technical support for the design and management of high-sulfur natural gas transmission pipelines.