Techno-economic assessment of cryogenic Rotating Packed Beds for nitrogen removal from natural gas

The global energy demand is projected to rise by 190 Trillion Cubic Feet (TCF) by 2040, compelling industries to monetize ‘low-quality’ gas fields with high nitrogen (N₂) content. However, conventional N2 removal methods result in substantial hydrocarbon losses, necessitating the adoption of Nitrogen Rejection Units (NRU) to enhance N₂ removal efficiency and maximize hydrocarbon recovery. This study presents a techno-economic evaluation of three NRU configurations, comparing single-stage (case 1), dual-stage N₂ expanders (case 2) and dual-stage CH4-N2 expander (case 3) integrated with a Cryogenic Rotating Packed Bed (CryoRPB) NRU against a base case employing a conventional flash vessel. The analysis considers capital expenditure (CAPEX), total annual cost (TAC), unit technical cost (UTC), and net present value (NPV) over a 25-year operational period, incorporating sensitivity analysis to assess the impact of discount rate, LNG price, and natural gas cost on overall economic viability. The results demonstrate that the dual-stage N₂ expander with CryoRPB NRU achieves the lowest UTC ($3.72/MMBtu) while delivering a substantial improvement in specific energy consumption (SEC) by ∼60 % compared to the base case. Furthermore, the CryoRPB NRU significantly reduces hydrocarbon loss by ∼30 %, enabling the production of 0.02 MTPA LNG with greater feedstock utilization efficiency. The dual-stage N₂ expander also significantly reduces power consumption by ∼3 MW compared to the single-stage configuration. In contrast, the methane CH4-N₂ refrigerant mixture in Case 3 offers only marginal efficiency gains over Case 2. The tornado plot analysis revealed that LNG price had the highest impact on NPV, causing fluctuations of ±36 %, followed by feed gas capacity, which improved NPV from -32 % to +22 % as capacity increased. While the discount rate and NG cost positively influenced NPV, N2 content had a negative impact (-20 %), and operating hours had the least effect. This study provides a comprehensive framework for CryoRPB NRU with single and dual refrigeration configurations for LNG production. Future research should focus on developing scalable solutions for commercial deployment and integrating renewable energy sources. These advancements will significantly enhance LNG production's sustainability and economic viability utilizing RPB.