While sulfur continues to be an important industrial chemical, increased processing of sour fossil fuels is causing a sulfur glut in the world market. In places like Kazakhstan and western Canada, yellow sulfur has begun to pile up near gas and oil sand processing units, and no working solution exists to deal with all of it. With the processing of sour natural gas and oil sands on the rise, sulfur has become a major industrial waste stream. Sulfur piles present environmental and safety hazards that need to be resolved. Limited storage capacity may also impact refinery operation when sulfur stocks overflow, effectively threatening refinery shutdown.

We propose safe and permanent disposal technologies based on stabilizing sulfur in the form of gypsum and other stable sulfur minerals as alternatives to the long-standing practice of converting hydrogen sulfide to elemental sulfur and of injecting acid gas into underground reservoirs. We focus, in particular, on technologies that take advantage of the energy released during the process of generating gypsum as a chemically stable waste product.

Figure 1. Heat releases of stabilizing reactions (∆H in kJ/mol).

With a chemical potential on the same order as coal's, sulfur removed from hydrocarbons as H₂S is energy-rich enough to suggest that harnessing this energy is worthwhile. Every annual megaton of sulfur (Mt/yr) could provide the fuel for a 300 MW steam turbine power plant operated at 40% efficiency. This reflects the amount of energy released as heat, when hydrogen sulfide is converted to gypsum. Harnessing the heat of combustion of hydrogen sulfide can significantly reduce a hydrocarbon processor's own energy demand on site, running equipment and/or generating steam for, say, oil sands extraction.

For the refining and processing of sour fossil fuels, solving the sulfur problem has several desirable outcomes. (1) The stabilization of mobilized sulfur is an important step toward making fossil fuels more environmentally acceptable. (2) The development of a scalable and cost efficient process eliminates a considerable hurdle in the pursuit of sour hydrocarbon reserves. (3) By utilizing the energy from sulfur, net carbon emissions can be reduced. (4) Solving the sulfur problem is analogous, though small by comparison, to solving the CO₂ problem via carbon capture and storage, thus providing the oil and gas industry a chance to increase knowledge about practical issues in large scale acid disposal.

Researchers

Tim Rappold, Ph.D. Candidate, Earth and Environmental Engineering, tar2102@columbia.edu
Klaus Lackner, Ewing-Worzel Professor of Geophysics, klaus.lackner@columbia.edu