Optimization and economic evaluation of carbon dioxide BOG Re-liquefaction process considering storage pressure and nitrogen impurity

The increasing demand for carbon capture and storage (CCS) has heightened the need for liquefied carbon dioxide (LCO 2 ) carriers, which require re-liquefaction systems to manage boil-off gas (BOG) generated during transportation. This study proposed new two-stage separation re-liquefaction processes with mixed refrigerants for CO 2 BOG containing nitrogen impurity. The proposed processes were evaluated and compared with conventional processes based on annual CO 2 emissions under different storage pressure conditions of 6.5 bar and 15 bar. The results demonstrated that the proposed processes reduced annual CO 2 emissions by up to 71.6 % and 35.6 % at the storage pressure of 6.5 bar and 15 bar, respectively. Furthermore, the economic feasibility was assessed by considering annual CO 2 emissions and annual transported CO 2 amount under both pressure conditions. The results indicated that the cases of storage pressure at 6.5 bar resulted in lower costs due to reduced tank costs and the higher density of LCO 2 . • New two-stage process with mixed refrigerant is proposed to re-liquefy CO 2 &N 2 BOG. • Proposed process reduces CO 2 emissions by up to 71.6 % and 35.6 % at 6.5 and 15 bar. • New economic index is proposed considering net CO 2 emissions and transported CO 2 . • It is the most economical at 6.5 bar due to lower tank costs and higher CO 2 density.