Analysis of power cycle based on cold energy of liquefied natural gas and low-grade heat source

It is important for the sustainable development of economy to exploit new energy. The utilization of low-grade heat source is confined for its lower utilizing efficiency. Liquefied natural gas (LNG) at 110 K has plenty of physical cold exergy besides its high quality chemical energy. A power cycle with natural gas directly expanding based on the cold energy of LNG and a low-grade heat source has been established in this paper. Some parameters of the cycle have been investigated. The results indicate that the temperature of low-grade heat source, the condensing temperature of second medium, and the inlet pressure of the turbine are the key factors affecting the thermal and exergy efficiencies of the power cycle. The thermal and exergy efficiencies will be improved with the increasing of the temperature of the low-grade heat source, the decreasing of the condensing temperature and the increasing of the inlet pressure of the turbine. The thermal efficiency and exergy efficiency of the power cycle will be above 30% and 40%, respectively, after optimizing the key parameters. In order to further improve the utilizing efficiency of low-grade heat source, a regenerative power cycle has been put forward and analyzed. The results show that under the same conditions the thermal and exergy efficiency of the power cycle increase 3–5%.