NHA Annual Hydrogen Conference 2008
Sacramento Convention Center, CA
March 30 – April 4, 2008
Extended Abstract
The copper-chloride cycle is a thermochemical cycle that can be used to produce hydrogen using nuclear or solar heat.  Several types of nuclear reactors can be used as a heat source.  Examples are the super critical water reactor being developed in Canada, CANDU Mark 2, the lead cooled reactor, or the high temperature gas reactor. All these provide heat near or above 550C, the maximum temperature required for the cycle.  Solar heat sources such as the tower, the dish, or the advanced tower could also be used.  However, the tower is the most likely solar heat source since it is commercially proven technology and can provide heat at 550C.  

The cycle consists of three major reactions.  All of the reactions have been demonstrated in proof-of-concept experiments.  Temperatures for the two thermal reactions, the hydrolysis of cupric chloride, (CuCl₂) and the decomposition of copper oxychloride (Cu₂OCl₂), have been proven.  The maximum temperature of 550C is required for the copper oxychloride decomposition.  In the bench scale experiments, all of the oxygen was recovered at 530C.   The electrolytic reaction in which CuCl₂ is produced at the anode and H₂ at the cathode was demonstrated at the Atomic Energy of Canada, Ltd. (AECL) at Chalk River recently.   The electrolysis reaction is the least studied reaction in the cycle and comparatively little is known about it. 

We have completed a conceptual process design for the cycle that consists of two sections: (1) the electrolyzer and crystallizer and (2) the hydrolyzer and oxychloride decomposition reactors.  In the first section, the crystallizer precipitates excess CuCl₂ from the anode effluent containing dissolved CuCl, CuCl₂ and HCl.  In the second section, solids move from the hydrolyzer to oxychloride decomposition reactor via gravity flow through an L valve.  An Aspen Plus flowsheet was developed using this process design.  The energy and mass were balanced, the heat exchanger duties and shaft work were calculated, and heat recovery was optimized with pinch analysis.   Because there is no performance data for the electrolyzer in the Cu-Cl cycle, we used the performance targets used for the hybrid sulfur cycle.  The efficiency was calculated as 44.4% (LHV).

The hydrogen production cost was estimated using the H2A methodology.  Capital costs and operating costs for the thermal processes were estimated using Capcost software.  An equipment list was prepared and vessel sizes were estimated.  Costs for the electrolyzer were assumed to be the same as those for the hybrid sulfur electrolyzer.    The costs for heat and electricity were included parametrically as $60/MWh(t) and $20/MWh(e).   The resulting cost for producing hydrogen was $2.77/kg

The results of the efficiency calculation and the cost analysis are promising and are comparable to those of the more advanced sulfur-iodine (S-I) and hybrid sulfur (HyS) cycles as well as to high temperature steam electrolysis (HTE), all of which require process heat around 825-850C.  Hydrogen cost from these processes is estimated as $2.90 to 3.50/kg.      

Further development of the cycle requires meeting the technical challenges in the chemistry of the cycle.  Progress made in meeting these challenges will be briefly described.