Design of Hydrogen Separation from Depleted Gas Field Mixtures Under Variable Operating Conditions

Large-scale and long-term hydrogen storage is one of the main obstacles to the wider use of hydrogen as a possible substitute for natural gas. A solution could be depleted natural gas fields, which have proven capacity and are already geologically prospected. However, part of this field remains occupied by residual natural gas, meaning that hydrogen is mixed with natural gas during storage and purification after extraction is therefore necessary. The aim of this study was to design and evaluate a hydrogen purification process for separating hydrogen from natural gas after extraction from a depleted natural gas field while maintaining the required hydrogen purity and recovery. Input data provided by Nafta a.s. were used for the mathematical simulation of hydrogen separation throughout a 150-day extraction period. A mathematical model of membrane separation and pressure swing adsorption (PSA) was developed. A single membrane stage was only able to operate effectively during the first 50 days of withdrawal while maintaining at least 80% hydrogen recovery. A two-stage membrane configuration achieved hydrogen purity above 98% with final recoveries above 80–85%, while the hybrid membrane–PSA system enabled hydrogen purity of 99.8% and total recovery of 82.5% on the last day of extraction.