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

Abstract

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.