Aspen Plus Modeling of the Three-Reaction Version of the Copper-Chloride Thermochemical Cycle for Hydrogen Production from Water
The Copper-Chloride thermochemical cycle for producing hydrogen from water has the attractive feature of low temperature requirements. A further desirable property is that possibly the cycle can be implemented such that minimal solids transfers are required. Previous modeling efforts for this cycle involved a four-reaction scheme as follows:
4CuCl → 2CuCl2(a) + 2Cu (electrochemical) 25°C
2Cu + 2HCl(g) → 2 CuCl(l) + H2(g) 450°C
2CuCl2 + H2O(g) ↔ Cu2OCl2 + 2HCl(g) 375°C
Cu2OCl2 → 2CuCl + O2(g) 550°C
The most serious drawback of the four-reaction cycle is the presence of elemental copper. Therefore, a three-reaction scheme has been proposed as follows:
2CuCl + 2HCl → 2CuCl2 + H2 (electrochemical) 100°C
2CuCl2 + H2O ↔ Cu2OCl2 + 2HCl (vacuum) 375°C
Cu2OCl2 → 2CuCl + 0.5O2 550°C
To our knowledge, no prior work has been done on mechanistic modeling of the electrolyzer for the hydrogen production step of the three-reaction scheme. Prior simulations of the four-reaction step used a simple stoichiometric reactor model for the electrolyzer. In the current work, we present an Aspen Plus model for the three-reaction system that includes a realistic model (written as a user-supplied Fortran model) of the electrolyzer.
We developed the Aspen Plus model in three steps. First, a flowsheet was developed in which all reactors are stoichiometric with reactions going to completion. The second phase included the CuCl2 hydrolysis step as an equilibrium reactor. The final step involves the inclusion of the Fortran code to describe the operation of the electrolyzer.
The currently proposed Aspen flowsheet with the actual process implementations described in this paper has two significant advantages:
• No Compressors (Only Pumps & Throttling Valves)
• No Solids Transfer Steps (With Fluidized Bed for O2/HCl Production Section)
Other topics that are addressed in the paper include the following: