Energy, exergy, exergoeconomic, and economic analysis of a novel power generation cycle integrated with seawater desalination system using the cold energy of liquified natural gas

Utilizing the cold energy of liquefied natural gas can reduce the demand of burning fossil fuels for work production and employing refrigeration cycles for seawater desalination. A novel low-temperature cascade power generation cycle combined with a seawater freeze desalination system is proposed to retrieve the cold energy from liquified natural gas. Binary working fluids are utilized to decrease the irreversibilities of the power cycle and enhance the energy recovery efficiency. The effects of the important temperatures of the cycle, pinch temperature of the heat exchangers, number of turbines and their efficiency on the cycle performance are investigated. Optimization of the work production showed that the cycle could achieve 105 kW per unit mass of liquified natural gas while increasing its temperature to -47.48 degrees C. An exergoeconomic model is developed to assess the exergy costs of the system operation and minimize the sum of the unit of production cost. A multiobjective optimization is conducted to maximize the work production and minimize the production costs. Results show that the cycle has the best performance while working at its exergoeconomic optimal point. Using the same amount of cold energy that was used for producing a particular work in the literature, the current system can produce 0.537 to 0.441 kg of ice along with generating the same work. Using the remaining cold energy of liquified natural gas for work production in another stage in series with the cycle instead of exploiting it in a freeze desalination system would increase the work production between 5.7% and 9% compared to the literature. Although this leads to an addition of 6.7% to the work production of the cycle, the payback period increases by 25%. Hence, from economical point of view, dedicating a specific portion of the cold energy of liquified natural gas for freeze desalination is more effective than using the entire cold energy for work production. Thus, a limit for the maximum temperature of liquified natural gas should be considered at the exit of the cycle for more efficiency.

Automated summary

By utilizing the cold energy of liquefied natural gas for power generation and seawater desalination, a novel low-temperature cascade cycle has been developed to enhance energy recovery efficiency. Optimization of the cycle performance and work production showed significant improvements in efficiency.