The BOG (boil off gas) reliquefaction system (DH-reli) is a system that reliquefies the BOG generated in a tank storing ultralow temperature fluids. The system is an optimum system to collect the BOG generated in large cargo tanks of LNG carriers or other types of cargo ships. Based on the system design technology, we use a compact heat exchanger (PFHE, PCHE), and combine optimum compressors through our affiliated company Donghwa Pneutec, and guarantee the best performance. We also supply control & monitoring systems and safety systems for optimum operation in addition to machine equipment.