A numerical comparison of heavy-purge and dual-reflux strategies in pressure swing adsorption for methane enrichment

Dual reflux pressure swing adsorption (DR-PSA) has been regarded as a state-of-the-art adsorption-based process which can simultaneously obtain two streams of pure product gases with a narrow pressure window. However, the DR-PSA has not yet been reported in industrial applications. Herein, a DR-PSA and a heavy-purge pressure vacuum swing adsorption (HP-PVSA) were numerically investigated for the enrichment of 1%, 8% and 15% CH₄ from N₂ gas mixtures in pilot-scale. Key separation indicators such as purity, recovery and energy cost of the two cycles were compared to analyze the limitations of the DR-PSA process while scaling-up. This study reveals the impact of heavy to feed (H/F) ratios on purity and recovery for both cycles and analyses the energy consumption of each process. For feed gas with 15% CH₄, while DR-PSA can achieve a slightly better purity and recovery (88.3% and 88.3%, respectively) compared to HP-PVSA (87.5% and 80.3%, respectively), it also involves an order of magnitude higher energy consumption (181.6 versus 24.6 kJ/mol CH₄ captured). DR-PSA shows significantly superior performance than HP-PVSA when the CH₄ content in the raw feed gas is low. Under the investigated operating conditions, HP-PVSA can only enrich 1% CH₄ to 10% with 78.7% recovery while DR-PSA can obtain 75.3% purity and 77.3% recovery. Results indicate that DR-PSA exhibits superiority in enrichment of dilute gas, however, its high energy consumption, high capital expenditures and limitations in processing high throughput are the chief reasons hindering its industrial application.