(122b) Application of Controlled Freeze Zone™ Technology for Commercialization of Sour Natural Gas Resources

The demand for natural gas, considered the cleanest burning hydrocarbon fuel available, is expected to rise significantly over the next few years. However, natural gas coming from many major reservoirs can contain significant amounts of sour gas components such as carbon dioxide (CO₂), hydrogen sulfide (H₂S), and other contaminants, and must be treated before it can be used as an environmentally acceptable fuel. Economically separating these components from highly sour natural gas (e.g. gas containing CO₂ and H₂S in excess of 20%) can be particularly challenging. Additionally, there is the challenge of management and disposal of these contaminants in an environmentally benign way. H₂S is a highly toxic gas, which can be converted to elemental sulfur, a safer chemical. However, limited demand for elemental sulfur has made this practice less desirable. Also, venting of CO₂ is significantly limited due to the Kyoto protocol requirements for reduction in CO₂ emissions. ExxonMobil’s Controlled Freeze Zone™ (CFZ™) technology addresses both of these challenges. CFZ™ is an efficient, single-step cryogenic distillation process for removal of CO₂, H₂S, and other impurities from natural gas. CO₂ present in natural gas freezes at cryogenic temperatures, and therefore, most separation processes have tried to avoid this. Rather than circumventing this phenomenon, CFZ™ allows for solidification of CO₂, albeit in a controlled fashion. The resulting purified natural gas is sent to the pipeline or used as feed for LNG liquefaction, while the impurities are removed as a high pressure liquid stream that is ready for underground injection for enhanced oil recovery applications or acid gas injection (AGI) disposal.

A 14 Mscfd CFZ™ Commercial Demonstration Plant (CDP) has been undergoing testing and demonstration operations in Wyoming, co-located with a large gas plant which processes one of the lowest hydrocarbon content sour gases in the world. Operation of the CDP was evaluated for various blends of methane, CO₂, and H₂S, representative of major global sour gas resources. Feed streams containing 10-70% CO₂ and 0-35% H₂S were successfully processed at pressures up to 625 PSIG. Additionally, integration of the sour gas components with an AGI facility was demonstrated.

Highlights of the operational experience at the CFZ™ CDP are discussed in this presentation. The influence of operational parameters such as feed compositions, flow rates, operating pressures, and temperatures on the overall process will be discussed. Operational characteristics, stability and robustness of the process, and other lessons from over a year of testing will be presented.