Modeling and cost analysis of helium recovery using combined-membrane process configurations

This study used process simulations to evaluate the potential of three configurations of cascade membrane process flowsheets to recovery helium from a stream containing 1% helium in 98.3% nitrogen and 0.7% methane, which represents a typical vent stream from nitrogen rejection units in some liquefied natural gas (LNG) plants. We considered three-stage cascade membrane process flowsheets and investigated the placement within these stages of three types of commercial membranes - Hyflon (R) AD60X, polyimide (PI), and polysulfone (PS). Flowsheet simulations conducted in Aspen HYSYS with a custom membrane unit and the simulation data used in techno-economic analyses to evaluate recovery of helium to upgraded helium with at least 90 mol. % He and grade-A with 99 mol % He purity. To produce the 90 mol % He stream at a 95% He recovery, we found that a configuration with the high permeability-moderate selectivity AD60X membrane in the first and second membrane stages and the moderate selectivity-moderate permeability PI membrane in the third membrane stage lead to the lowest helium breakeven production cost of US.$ 149.89/MSCF. To produce the 99 mol % He stream, the best configuration also had AD60X in the first two stages but required the most selective membrane, PS, in the final stage to produce the minimum helium breakeven production cost of US.$ 187.81/MSCF for grade-A helium at an 82% He recovery. We included a sensitivity analysis to understand how the He recovery rate, cost of electricity, and membrane price may effect the breakeven production cost