GPA '18: Adsorption-based separation technology for gas treating

AUSTIN—On Day 1 of GPA Midstream's 2018 Annual Meeting, Chien-Chiang Chen of ExxonMobil Upstream Research Co. talked about the concept of process intensification using an adsorption-based separation technology. Adsorption-based separation processes are widely used in the gas treating industry for dehydration, CO2 removal and helium recovery.

The conventional approach requires multiple-hour cycles. "The consequences of this approach are that the overall system can become very large, very quickly," Chen said. However, by applying process intensification using rapid cycles of less than 5 min, equipment size, weight and footprint can be reduced, and a higher level of modularization can be achieved.

Technology description. The technology is similar to conventional adsorption in that it is a continuous process flow achieved by contacting multiple beds sequentially. Beds are regenerated using pressure and/or temperature swing. It differs from conventional adsorption in that high gas velocities are used for a high mass transfer rate. It uses structured adsorbent beds versus packed beds for low-pressure drop and high mass transfer area. ExxonMobil's current focus is deep dehydration and low-level CO2 removal for cryogenic applications.

The reduced cycle time is enabled by two key mechanical systems: fast-acting (rapid-cycle) valves and structured adsorbent beds. The rapid-cycle valves must be actuated and operated over a short duration of time and be able to withstand millions of cycles.

ExxonMobil has entered a joint development agreement with Johnson Matthey to design and fabricate the structured adsorbent beds, which comprise a selection of coated parallel channels oriented lengthwise. The linear flow path minimizes pressure drop. The mechanical structure allows for rapid cycling with counter-current flow, and multiple modules are stacked vertically.

Technology application. Several experiments were performed at a variety of scales to understand the desorption rates with short contact times. Slower velocities indicated longer water breakthrough profiles. To test the technology at a larger scale, ExxonMobil is building a multi-bed field unit in Fort Worth, Texas. Startup is tentatively scheduled for late 2018, and the unit is planned to run for 1–2 yr. ExxonMobil also plans to test startup, shutdown, and a wide range of upset scenarios at the field unit.

In summary, Chen said, the process intensification technology offers significant benefits by adapting rapid pressure and/or temperature swing cycles. Key enabling mechanisms for the technology have been developed, including rapid-cycle valves and structured adsorbent beds. Pilot studies have confirmed the technical feasibility for deep dehydration.

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