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Pinch and exergy evaluation of a liquid nitrogen cryogenic energy storage structure using air separation unit, liquefaction hybrid process,and Kalina power cycle
Type Article
Cryogenic energy storage system Air separation cycle Nitrogen liquefaction process Kalina power cycle Peak load shaving Pinch and exergy analyses
Starting up thermal power plants for peak shaving is very time-consuming and expensive. Therefore, when the consumption demand is less than the baseload, the surplus energy that can be produced can be stored in a cryogenic energy manner, and in the hours of increasing demand, the stored energy can be injected into the consumption network as electrical energy. The main problems of liquid air energy storage systems are the high cost of development and low energy efficiency. In the present study, an integrated power generation system with liquid nitrogen recovery as a cryogenic energy storage system is developed. For this purpose, by producing pure nitrogen through air separation unit and liquefaction it during off-peak time and recovery it at the on-peak time, the required power of the grid is supplied. By using the excess heat of the integrated system in the Kalina power cycle and producing more power during the on-peak time, an attempt has been made to increase the system round-trip efficiency. Important parameters of the proposed system are the liquid yield (59.17%), multifunctional round-trip efficiency (40.67%), and baseline round-trip efficiency (54.69%). Pinch analysis is applied to the multi- stream exchangers of the system and the corresponding heat exchanger networks being extracted. The results of exergy analysis show that the exergy efficiencies of the nitrogen liquefaction unit and power generation unit are calculated as 79.75% and 85.11%, respectively. The exergy efficiency of the whole integrated system is 43.85%. The most exergy destruction belongs to the heat exchangers, which accounts for 48.56% of the total destruction. One of the important results of the parametric study is the increase of baseline round-trip efficiency to 57.24% by increasing the Kalina cycle pressure up to 1100 kPa.
Researchers Armin Ebrahimi (First researcher) , Bahram Ghorbani (Second researcher) , Masoud Taghavi (Third researcher)