Efficiency of Power Generation by LNG Cold Energy

In this paper, a comparative study for the practical power generation from LNG cold energy with the Organic Rankine Cycle (ORC) + Direct Expansion (DE) combined cycle, the ordinary ORC and the irreversible Carnot cycle has been performed. The optimized LNG cold energy utilization temperature for obtaining the highest efficiency of power generation were revealed and the characteristics of the enthalpy and entropy as well as the availability for the LNG cold sinks with different pressures were studied. The results show that the optimized LNG utilization temperature exists and increases with the LNG vaporizing pressure, while the power output by unit LNG and the availability efficiency are reduced accordingly. For applying the higher LNG vaporizing pressure, the efficiency of the combined cycle is considerably superior to the ordinary Rankine cycle, due to the recovery of power from the direct expansion.