Technical and Economic Assessment on Different Separation Technologies for Nitrogen Removal in Post Treatment of CO2 from Natural Gas

This paper presents the techno-economic analysis of separation technologies to remove high nitrogen concentration with a high concentration of CO₂ (~70%) in the natural gas stream. This is a very challenging process since the contaminants gasses are higher than the hydrocarbon gas stream. This study focuses on nitrogen removal after the bulk removal of the CO₂. The CO₂ stream's removal down to 20% leads to the high nitrogen content of ~10 mole % in the sales gas product. Hence, this study evaluated technologies that can remove nitrogen down to 1 mole% with minimal hydrocarbon loss to meet the LNG product specification. Furthermore, the hydrocarbon gas's high nitrogen concentration might lead to a lower heating value and corrosion issues in the downstream process equipment.

The technical and economic analysis was conducted to provide a semi-quantitative assessment to identify the potential gaps and find opportunities derived from the selected technology to meet the LNG product's nitrogen specification. The technologies were assessed based on four main criteria: technical, economic, operational, and strategic (technology advantage and risk) performance, including operating conditions, capital and operating costs, and technology readiness level. From the study, Cryogenic technology scored 76.3% of the overall rating for the nitrogen removal down to less than one mole% with the lowest cost other types of NRU technologies evaluated for nitrogen removal in the presence of high CO₂ (20 mol%). It is due to the higher pre-treatment cost of non-cryogenic technologies prior liquefaction process. Finally, the assessment leads to potential development, and process intensification of conventional cryogenic technology was identified for the nitrogen removal process and its' application.