Theoretical performance analysis of hydrate-based heat engine system suitable for low-temperature driven power generation

We analyzed a heat engine using clathrate hydrate as its working media and evaluate the performance of this system operated with high and low temperature reservoirs of 295 K and 280 K "OTEC (Ocean Thermal Energy Conversion)" may be a prospective example of the technologies utilizing the small-temperature difference for power generation. This heat engine generates mechanical power through the cycle of following processes: hydrate formation at low temperature, pumping of hydrate, isobaric heating of hydrate, hydrate dissociation and adiabatic expansions of dissociated gas and water. The thermal efficiency for Kr, Xe, CH₃F, CH₂F₂ and CH₄ hydrates were evaluated. The analysis showed the dominant properties were the enthalpy difference of the working media in the adiabatic expansions, the pressure range in the whole process and the dissociation heat. The thermal efficiency is 2.20% for Kr hydrate and 2.89% for Xe hydrate. While these are slightly inferior to those of Rankine cycle: 3.30% for C₂H₃F₃ and 3.34% for C₃H₈, Kr and Xe hydrates are greatly favorable in terms of environmental friendliness. These results indicate the prospects of the hydrate heat engine for the power generation utilizing a small temperature difference as an environment-friendly technology.