Thermo-economic optimization of a novel hybrid structure for power generation and portable hydrogen and ammonia storage based on magnesium–chloride thermochemical process and liquefied natural gas cryogenic energy

Abstract

Storage and transfer of hydrogen (H2) from production sites/plants to large-scale demanding industries are one of the most challenging obstacles to hydrogen adoption. Hydrogen liquefaction and its chemical storage in the form of ammonia (NH3) can be used for safe and economic transportation. High energy consumption and carbon dioxide (CO2) emissions to supply the utility of these systems can limit the production of liquid H2 and liquid NH3. Therefore, efficient design and practical strategies to store hydrogen at a large scale with minimal energy consumption and CO2 emissions are necessary. In this research, an innovative hybrid system for portable hydrogen storage and power generation with zero CO2 emission through liquefied natural gas (LNG) regasification is developed. The proposed structure includes a cryogenic air separation unit, magnesium–chloride hydrogen production process, ammonia production system, hydrogen liquefaction cycle, and Rankine/oxy-fuel power plants. The heat loss of the proposed structure is utilized to supply the required heat load for the thermo-electrochemical unit. The LNG regasification operation is utilized for pre-cooling the hydrogen liquefaction system and the necessary refrigeration of the air separation process and the final products. The developed structure is fed by 1883 kmol/h LNG, which is converted to 120 kmol/h liquid NH3, 180 kmol/h liquid H2, 924.5 liquid CO2, and 16.09 MW power. The thermal and exergy efficiencies for the designed system are 20.33% and 22.76%, respectively. The results of the exergy investigation reveal that the largest contribution of exergy destruction occurs in heat exchangers (31.27%), combustion chamber (34.65%), and turbines (8.12%). The economic evaluation indicates that the net annual profit, added value, and payback period are 15.93 US$/yr, 0.0779 US$/kWh, and 5.646 yr, respectively, based on the energy potential of Newfoundland and Labrador in Canada. Three-objective optimization approach using the combination of genetic algorithm and neural network exhibits that the energy efficiency and net annual profit based on the Bellman-Zadeh approach increase up to 27.04% and 45.20 US$/MMBTU, respectively, and the irreversibility reduces to 99.4 MW.