It is important for the sustainable development of economy to exploit new energy. The utilization of lowgrade
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%.