Abstract
Subsea natural gas processing attracts increased interest due to the smaller environmental footprint. Natural gas (NG) dehydration and sweetening are the main processing steps to avoid pipeline plugging and corrosion caused by the presence of water and CO2. Triethylene glycol (TEG) and amine absorption are the commercial technologies for these applications. However, membrane technology is considered as promising solutions for alternative subsea gas processing technologies, which provides unmanned operations without the requirements for rapidly periodical maintenance. In this work, a hybrid membrane process was designed for integrated dehydration and sweetening of a saturated natural gas containing 10 mol% CO2, and the process operating parameters such as inter-stage feed and permeate pressures are investigated. The simulation results indicated that the optimal permeate pressure in the 2nd -stage unit is 4 bar, and the optimal 3rd-stage feed and permeate pressures are15bar and 2 bar, respectively. The minimum specific cost of <2.71 × 10−3 $/m3 sweet natural gas was estimated to achieve the separation requirement of <2.5 mol% CO2 in purified NG together with captured high purity CO2 (>95 mol%) for enhanced gas recovery. However, due to the relatively low water selectivity of the dehydration membranes at high pressure of 60 bar used in the simulation, the hydrocarbon loss is still quite higher. Thus, advanced membranes with high H2O/CH4 selectivity at high pressure should be pursued to promote the application of the designed membrane system for subsea natural gas dehydration and sweetening.
Highlights
Natural gas (NG) is considered as one of the less carbon-intensive energies, and the demand of has been increased in the recent decade [1]
Membrane gas or vapor separation systems are often compact with a small footprint, and without moving parts and the need of on-site attention when operated in remote/subsea locations [2,5,6], which enables a higher potential application in subsea natural gas processing comparing to absorption technology
Different types of membranes tested for H2O/CH4 separation in natural gas dehydration were reviewed in the literature [2,6], and very high H2O/CH4 selectivity for some membranes such as polyimide (Kapton) cellulose acetate, and Nafion® 117 were reported
Summary
Natural gas (NG) is considered as one of the less carbon-intensive energies, and the demand of has been increased in the recent decade [1]. Implementation of unmanned operations is crucial in subsea natural gas processing without the requirements for rapidly periodical maintenance. Membrane contactor has advantages of high interface between gas and liquid phases and no flooding or foaming, which was reported to be feasible for natural gas dehydration [2,4]. Membrane gas or vapor separation systems are often compact with a small footprint, and without moving parts and the need of on-site attention when operated in remote/subsea locations [2,5,6], which enables a higher potential application in subsea natural gas processing comparing to absorption technology. It should be noted that the reported performances
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