Coupling Thermochemical Water Splitting with a Desalination Plant for Hydrogen Production from Nuclear Energy

Nuclear energy has the ability to provide a significant share of energy supply in the future without the negative environmental impacts associated with current energy resources.  While nuclear energy has mainly been used for electric power generation, it can also be used in thermochemical water decomposition to produce hydrogen.  Orhan et al. (2010) explored configurations for coupling the Cu-Cl cycle with a desalination plant using nuclear or renewable energy and assessed the viability of these systems.  It was found that capital cost of the Cu-Cl cycle per unit of hydrogen output is less for a larger capacity plant while production cost remains constant.  Additionally, the total cost of hydrogen production is inversely proportional to the relationship with plant capacity.  The overall unit capital cost of the coupled system was found to vary with production capacity, but not with the type of desalination method.  In regards to energy use, the effect of the Cu-Cl cycle is dominant on the overall efficiency of the system because the desalination plant uses much less energy.  The highest efficiency coupled system is the configuration that utilizes nuclear energy to power the desalination plant. — Carolyn Campbell
Orhan, M.F., Dincer, I., Naterer, G.F., Rosen, M.A., 2010. Coupling of copper-chloride hybrid thermochemical water splitting cycle with a desalination plant for hydrogen production from nuclear energy. International Journal of Hydrogen Energy 35, 1560–1574.

          Orhan et al. analyzed the different configurations for coupling a Cu-Cl cycle with a desalination plant using nuclear energy to produce hydrogen.  The Cu-Cl cycle consists of a set of reactions to achieve the splitting of water into hydrogen and oxygen.  The production of hydrogen through this cycle provides a pathway for the utilization of nuclear thermal energy.  Orhan et al. studied the options for coupling the Cu-Cl cycle with a desalination plant.  Case I couples the Cu-Cl cycle with a desalination plant powered by nuclear energy.  The desalination process is carried out using the waste energy from the nuclear reactor and the resulting fresh water is decomposed into hydrogen and oxygen through the Cu-Cl cycle driven by nuclear energy.  Case II uses recovered energy from the Cu-Cl cycle to drive the desalination process, with the desalination plant as a sub-system of the Cu-Cl cycle.  Additionally, process/waste energy from the nuclear reactor is used to power the Cu-Cl cycle.  One drawback of this system is the efficiency decrease in the Cu-Cl cycle due to the fact that the recovered energy is used for desalination rather than within the cycle itself.  Case III uses nuclear energy directly in the desalination process.  The Cu-Cl cycle is powered by process energy from the nuclear reactor and energy recovered from the cycle.  Case IV uses solar energy to drive desalination while process and waste energy from the nuclear plant is used for the Cu-Cl cycle.  One drawback of this configuration is that solar energy is intermittent and therefore much attention must be paid to site selection.  Finally, Case V uses off-peak electricity to power both desalination and the Cu-Cl cycle.
          The authors performed a comparison of the cost and energy use of the different configurations.  The capital cost of the Cu-Cl cycle was found to vary from 1.8 to 0.3 $/kg H2 depending on the capacity of the cycle.  The capital cost of the cycle per unit of hydrogen output is inversely proportional to the size of the system because the reaction energy of any chemical or physical reaction in the Cu-Cl cycle does not change based on plant capacity.  The overall unit capital costs of the coupled system were found to be the same for all configurations since the cost contribution of the desalination plant is small compared to that of the Cu-Cl cycle.  Case III had the highest capital and production cost of the desalination plant, using a MSF system, while Caste I, using a humidification-dehumidification system, had the lowest cost.  The unit energy consumed was also greatest for Case III, but lowest for Case V.  Finally, the energy efficiencies of the entire configuration were assessed.  The effect of the Cu-Cl cycle on the overall system is dominant, thus the overall efficiency of the systems are very similar for each case.  However, it was found that Case I had the highest efficiency since waste energy from the nuclear reactor was used.  In contrast, Case II operated at lower efficiencies using recovered energy from the Cu-Cl cycle.  

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