Exergoeconomic optimization of a novel multigeneration system driven by geothermal heat source and liquefied natural gas cold energy recovery

Abstract

Multigeneration systems driven by renewable sources are proved as cutting-edge technologies for multiple productions purposes to curb greenhouse gas emissions. With this regard, a novel geothermal-based multigeneration system is proposed to produce multiple commodities of cooling, heating, power, and hydrogen, simultaneously, using liquefied natural gas as cold energy recovery. To demonstrate the feasibility of the proposed multigeneration system, energy, exergy, and exergoeconomic analysis are employed as the most effective tools for performance assessment of the proposed system. Also, to enhance the performance of the system, single- and multi-objective optimizations are carried out, using genetic algorithm. It is found that the proposed multigeneration system can be run with the optimum basic ammonia concentration of 0.42, geothermal inlet temperature of 160.5°C, evaporator temperature of 7.76°C, vapor generator pressure of 33 bar, mass extraction ratio of 0.2, condenser temperature of 29.01°C, separator 2 pressure of 4.99 bar, vapor generator terminal temperature difference of 7°C, and turbine 2 inlet pressure of 22.11 bar. In this case, the optimum thermal efficiency, exergy efficiency, and total SUCP (sum unit cost of the product) of the system are calculated 62.74%, 33.82%, and 125.4 $/GJ, respectively. Moreover, a comprehensive parametric study is carried out and it is shown that a higher thermal efficiency can be obtained by increasing the vapor generator pressure and evaporator temperature, or decreasing the mass extraction ratio, separator 2 pressure, turbine 2 inlet pressure, geothermal inlet temperature, vapor generator terminal temperature difference, and basic ammonia concentration.