The Controlled Freeze Zone Technology for the Development of Sour Gas Resources

Abstract

Controlled Freeze Zone™ is an efficient single-step cryogenic distillation process for the removal of carbon dioxide, hydrogen sulfide and other impurities from natural gas. Rather than avoiding the freezing of CO2 at cryogenic temperatures, the solidification is allowed to take place, albeit in a very controlled fashion. The technology has shown the potential to more efficiently and cost-effectively separate carbon dioxide and other impurities from natural gas, and to discharge these contaminants as a high-pressure liquid stream ready for underground injection, either for enhanced oil recovery applications or for acid gas injection disposal. Introduction Natural gas is the cleanest burning hydrocarbon fuel available and its growing demand is only projected to rise throughout this century. ExxonMobil anticipates total global energy demand to grow 35% by 2040 relative to 20101. Greater demand for electricity accounts for more than half of this increase. The clean burning characteristics of natural gas and its increasingly competitive economics for power generation are driving its expanded use in electrical power generation. Natural gas emits up to 60 percent less CO2 than coal when generating electricity, which becomes quite significant as costs arising from greenhouse gas policies mount. ExxonMobil forecasts natural gas to emerge as the leading source of electricity generation by 2040, and to become the second largest global fuel by 2040 behind oil, displacing coal from the second spot.

Insights on Cryogenic Distillation Technology for Simultaneous CO2 and H2S Removal for Sour Gas Fields

“…The combination of CFZ™ and AGI technology facilitates the geo-sequestration of CO 2 for enhanced oil recovery by exploiting the high-pressure liquid stream discharged at the bottom of the column. On the other hand, the CFZ™ process also imposed a less stringent dehydration requirement rendered by the high water-holding capacity of the liquid CO 2 [131]. Valencia et al [131,132] reported that compared to Ryan Holmes and combined bulk fractionation-Selexol processes, CFZ™ demonstrated lower capital expenditure by 5% and 10%, respectively.…”

Conceptual Process Design of CO2 Recovery Plants for Enhanced Oil Recovery Applications

“…When high purity methane is separated from CO 2 -rich gas, the top of the distillation column can reach very low temperatures (−90 °C ≈ −70 °C), causing CO 2 solidification. One way to prevent CO 2 solidification is with the addition of extra additive and another way is to use a distillation column modified to overcome the CO 2 freezing problem . Also, azeotrope issues can occur when CO 2 is separated from NGL components, in particular ethane.…”

“…For EOR applications, CO 2 recovery processes should deal with high inlet CO 2 compositions, and in these cases distillation columns are mainly used for CO 2 separation. ,− The separation of CO 2 through distillation has two problems: solidification of CO 2 and the azeotrope between ethane and CO 2 . Solidification of CO 2 due to freezing can be prevented by the injection of additives or using a specially modified column with a CO 2 freezing zone . For example, to overcome the azeotrope between ethane and CO 2 , additives can be introduced to change the composition in the distillation column .…”

“…Solidification of CO 2 due to freezing can be prevented by the injection of additives 5 or using a specially modified column with a CO 2 freezing zone. 6 For example, to overcome the azeotrope between ethane and CO 2 , additives can be introduced to change the composition in the distillation column. 7 The Ryan/Holmes process is a typical CO 2 recovery process based on distillation, 3,8 which autonomously overcomes both problems using produced C4+ components as an additive.…”

“…One way to prevent CO 2 solidification is with the addition of extra additive 5 and another way is to use a distillation column modified to overcome the CO 2 freezing problem. 6 Also, azeotrope issues can occur when CO 2 is separated from NGL components, in particular ethane. In this case, additional solvent is required to break the azeotropic conditions.…”