Sustainability analysis and optimization of innovative geothermal-driven energy storage system for green production of H2, NH3, and pure O2

Abstract

Significant increase of greenhouse gas emissions and the emergence of global warming have drawn more attention to the use of renewable energies. In the pursuit of this objective, a novel geothermal-driven system consisting of steam and organic Rankine cycles, high-temperature solid oxide electrolysis cell (SOEC), and thermoelectric generator (TEG), NH3 synthesis unit is proposed for power, NH3/H2/O2 productions. The produced hydrogen is completely consumed. Fraction of hydrogen produced by SOEC is injected into the boiler for power generation through the SRC, and the remaining is fed into an ammonia synthesis unit to produce NH3. Moreover, the TEG is used as the condenser to increase system efficiency through waste heat recovery. The proposed system is comprehensively analyzed from energy, exergy, economic, and sustainability perspectives. Also, parametric analysis is conducted to evaluate the effect of important design parameters such as geothermal mass fraction ratio, H2 mass fraction ratio, N2 feeding rate, ammonia reactor pressure, and temperature on the performance and economic indicators of the power plant. Furthermore, comparative multi-objective optimization via the evolutionary genetic algorithm (NSGA-II) is developed in MATLAB to optimize the energy system. Moreover, two different scenarios for the optimization process were considered to compare the optimum solution points with each other. The results show that considering sustainability index and total cost rate as the target functions, by assigning the (m2˙m˙10) = 250, ΔTpp = 11.83, j = 2400 A/m2 and (m˙24m˙23) = 0.76, the highest achievable sustainability index and minimum cost rate are 1.875 and 328.94 $/h, respectively. In the second scenario, by choosing the (m2˙m˙10) = 80, ΔTpp = 19.37, j = 2400 A/m2 and (m˙24m˙23) = 0.3, the rate of ammonia production and total cost rate are reported to be 522.66 kg/h and 300.59 $/h, respectively, when the rate of ammonia production and total cost rate are considered conflicting objectives.