(391b) Aspen Plus Modeling of the Three-Reaction Version of the Copper-Chloride Thermochemical Cycle for Hydrogen Production from Water

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)

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No Solids Transfer Steps (With
Fluidized Bed for O₂/HCl Production Section)

Other topics that are addressed in the paper include the
following:

• Continued Overall Process Flowsheet Development
• Sensitivity of Electrolyzer Parameters to Process Conditions
• Water/HCl Purification
• Materials of Construction