Solubility of Sulfur in Hydrogen Sulfide and Sour Gases

Abstract

Abstract In recent years the search for natural gas has yielded many reserves that contain high concentrations of hydrogen sulfide.1 Production of sour gas initially was on a limited scale but since has increased considerably as a result of price increases for fossil fuels. Substantial quantities of sulfur now are produced from the hydrogen sulfide in these natural gas sources. In several of these natural gas fields – e.g., in Canada and north Germany – gas production is hampered severely due to the presence of elemental sulfur dissolved in the gas. The gas-bearing deposits are interspersed with elemental sulfur, which is dissolved to a greater or lesser extent in the sour gas, the solubility being strongly dependent on the pressure, temperature, and composition of the gas. It is well-known that the solubility of sulfur increases with increasing pressure, temperature, and hydrogen sulfide content. As a result of the geothermal temperature profile, the gas stream cools as it rises up the production tubing and there is a drop in pressure due to frictional effects. Consequently, the solubility drops and sulfur is deposited when the solubility limit is exceeded. The gases dissolved in the liquid sulfur – principally hydrogen sulfide and carbon dioxide – lead to a lowering of the freezing point. At temperatures between 393.15 and 373.15 K, the sulfur begins to solidify in the line, blocking the tubing and bringing gas production to a standstill. To prevent such blockages, suitable solvents are pumped into the well via an annular space surrounding the production tubing to dissolve the sulfur, which then is carried to the surface with the gas stream. A discussion of the technological problems involved in this process is beyond the scope of this paper.