CO2 Capture and Enhanced Hydrogen Production Enabled by Low-Temperature Separation of PSA Tail Gas: A Detailed Exergy Analysis

Abstract

Hydrogen from natural gas reforming can be produced efficiently with a high CO2 capture rate. This can be achieved through oxygen-blown autothermal reforming as the core technology, combined with pressure-swing adsorption for hydrogen purification and refrigeration-based tail gas separation for CO2 capture and recirculation of residual hydrogen, carbon monoxide, and methane. The low-temperature tail gas separation section is presented in detail. The main objective of the paper is to study and quantify the exergy efficiency of this separation process in detail. To achieve this, a detailed exergy analysis is conducted. The irreversibilities in 42 different process components are quantified. In order to provide transparent verification of the consistency of exergy calculations, the total irreversibility rate is calculated by two independent approaches: Through the bottom-up approach, all individual irreversibilities are added to obtain the total irreversibility rate. Through the top-down approach, the total irreversibility rate is calculated solely by the exergy flows crossing the control volume boundaries. The consistency is verified as the comparison of results obtained by the two methods shows a relative deviation of 4·10−7. The exergy efficiency of the CO2 capture process is calculated, based on two different definitions. Both methods give a baseline exergy efficiency of 58.38%, which indicates a high degree of exergy utilisation in the process.