Pinch and exergy evaluation of Kalina/Rankine/gas/steam combined power cycles for tri-generation of power, cooling and hot water using liquefied natural gas regasification

Abstract

Today, due to the increasing trend of energy demand in the world, the use of energy types with the approach of maximizing the efficiency of energy systems is inevitable. In this paper, an integrated power generation system consisting of low-temperature organic Rankine cycle, gas and steam combined power plant and Kalina power generation unit is developed and analyzed. Liquefied natural gas regasification is employed to supply the cooling for the hybrid system. This integrated system generates 158.5 MW power, 9.498 MW cooling, and 46.02 kg/s hot water. The total electrical, thermal, and exergy efficiencies of the integrated system are 48.62%, 55.18% and 67.74%, respectively. System exergy analysis shows that reactors and heat exchangers accounted for the largest share of total exergy destruction, each accounting for 59.91% and 15.76% of total energy destruction, respectively, indicating that these two parts have more than 75% of the destruction occurred. The pinch method was used to extract the heat exchanger network related to the multi-stream heat exchanger of the integrated system. In the parametric analysis, the effect of air/fuel molar ratio (input to the combustion chamber) on system performance has been investigated. One of the most important results is the increase in the total thermal efficiency of the system to 56.15% if the inlet air into the combustion chamber is reduced to 250.0 kg/s. The parametric analysis results also show that in addition to increasing the efficiency of the system due to the decrease in the amount of incoming air, the ratio of power production as the main product to byproducts (hot water and cooling) increases.