Hybrid process using cryogenic and pressure swing adsorption process for CO2 capture and extra H2 production from a tail gas in a steam methane reforming plant

Abstract

Efficient technologies for fuel cell-grade H₂ recovery and CO₂ capture are required to meet the need for the carbon mitigation. In this study, a novel hybrid process consisting of cryogenic distillation and a two-stage pressure swing adsorption (PSA) process was developed to capture CO₂ and produce additional H₂ from the tail gas (2359 kmol/h and H₂:CO:CH₄:CO₂ = 27.2:6.7:17.7:48.4 mol%) of a vacuum pressure swing adsorption process in a commercial steam methane reforming plant. After validating mathematical models, a sensitivity analysis was conducted. Because the extract from the CO₂ removal PSA was recycled to cryogenic distillation, and the raffinate was provided to the H₂ purification PSA, it affected the performance and cost of the hybrid process. Since the high interconnectivity and complexity of the hybrid process led to a very long computational time, this study developed multiple deep neural network (DNN) models using 789 case results. DNN-based optimization for a minimum separation cost was conducted with constraints: CO₂ capture rate of > 90 % and fuel cell-grade H₂ purity of ≥ 99.999 % (≤ 0.2 ppm CO). According to techno-economic analysis, the hybrid process could achieve a separation cost of 4.11 USD/kgH₂ and a CO₂ capture cost of 72.68 USD/tonCO₂. Considering extra blue H₂ production, the CO₂ capture cost was significantly reduced in the range of 50.57 to 36.02 USD/tonCO₂, depending on the H₂ production cost provided from the DOE report (1.43 to 2.27 USD/kgH₂). Because this novel hybrid process can be installed downstream without revamping an existing steam methane reforming plant, it can be regarded as a competitive option for CO₂ capture and additional H₂ recovery.