Westinghouse Sulfur Cycle

Carty R, Cox K, Punk J, Soliman M, Conger W (1977) Process sensitivity studies of the Westinghouse sulfur cycle... 

Brecher, L.E., S. Spewock, C.J. Warde (1977), The Westinghouse Sulfur Cycle for the Thermochemical Decomposition of Water , International Journal of Hydrogen Energy, Vol. 2, pp. 7-15, Pergamon Press. 

Brecher, L.E., Spewock, S., et al., Westinghouse Sulfur Cycle for the Thermochentucal Decomposition of Water, Proceedings of the V World Hydrogen Energy Conf, 1 9A, 1-16,1976. 

Westinghouse Electric Corporation (1980), A Study on the Electrolysis of Sulfur Dioxide and Water for the Sulfur Cycle Hydrogen Production Process, AESD-TME-3043, July. 

Farbman, G. H. NASA CR-134976 "The Conceptual Design of an Integrated Nuclear Hydrogen Production Plan Using the Sulfur Cycle Water Decomposition System" Westinghouse Electric Corporation April 1976. 

Farbman, G. H. Krasicki, B. R. Hardman, C. C. Lin, S. S. Parker, G. H. EPRI-EM-789 "Economic Comparison of Hydrogen Production Using Sulfuric Acid Electrolysis and Sulfur Cycle Water Decomposition" March 1978 prepared by Westinghouse AESD for Electric Power Research Institute Palo Alto, California 94304. 

Due to high T and 2 law efficiencies of sulfuric acid based cycles, to date, more than 20 sulfuric acid and/or metal sulfate decomposition based TCWSCs have been reported. Despite difficulties that challenge efficient electrolytic oxidation of sulfur dioxide (SO2), the Westinghouse hybrid cycle still remains as one of the most studied TCWSCs. The Westinghouse cycle is as follows [14] ... 

Fig. 2-10 Diagram of the Westinghouse sulfuric acid hybrid cycle, from [20]... 

In the Westinghouse sulfuric acid hybrid cycle shown in Fig. 2-10 (see also appendix A.3.2.), HTGR heat will be used for the H2SO4 decomposition step. Both high-temperature and electric steps have been experimentally investigated at the Research Center Julich. The above hybrid cycle has undergone a detailed balance and cost analysis already in a plant design based on nuclear power [8]. 

Electrochemical oxidation of aqueous SO2 on the electrode surface has also aroused interest in the large-scale hydrogen production processes via a hybrid sulfur cycle which was patented as Westinghouse Process. The electrochemical oxidation of aqueous sulfur dioxide with respect to the hybrid sulfur cycle has recently been reviewed and shown the importance of the mechanism of the oxidation of sulfur dioxide on the electrode surface. Platinum, gold, and carbon materials as electrocatalysts have been reviewed to compare the catalytic activity for SO2 oxidation [16]. The first step in the Westinghouse Process is the dissociation of H2SO4 into SO2 and O2 by thermal cracking at about 1,000 °C ... 

Of all these methods indirect oxidation of SO2 using redox mediators and electrochemically promoted oxidation seem to be the nearest alternatives to the commercial applications. The removal of SO2 by using redox mediators has already been tested in commercial scale in the processes named Peracidox and Ispra Mark HI. Westinghouse Process is another commercial application in terms of hydrogen production via hybrid sulfur cycle. 

The thermochemical and electrolytic hybrid hydrogen production process has been developed by Japan Nuclear Cycle Development Institute (JNC). The process is based on sulfuric acid (H2SO4) syntliesis and decomposition process developed earlier (Westinghouse process) and sulfur trioxide (SO,) decomposition process is facilitated by electrolysis with ionic oxygen conductive solid electrolyte at 500°C-550°C. Stable hydrogen and oxygen production for several hours by the process was already confirmed in the experiments performed by JNC. 

The Westinghouse cycle is a variant of sulfur—iodine and is a hybrid concept that requires both thermal and electrical energy. When the product of reaction (4.31) is cooled, sulfurous acid is formed and this is electrolyzed at around 80 °C to produce hydrogen and sulfuric acid for recycling, i.e.,... 

On the other hand, the test data available to date suggest that a number of matters remain to be resolved before this cycle can realistically be considered as a serious competitor to the sulfur—iodine and Westinghouse alternatives. Further experimental and engineering development work is required to address the following issues ... 

Thermochemical hybrid cycles offer the possibility of running low-temperature reactions on electricity. The expectations for realization of hybrid processes are similar to those for purely thermochemical processes. Various hybrid processes are energetically possible, but not always practicable. Important criteria are the minimum voltage for the electrolysis step, realizability, efficiency. The sulfuric acid hybrid or Westinghouse process is expected to reduce material streams as compared with the IS process. The electric energy demand here is a factor of 7 (in reality 3 - 4) lower than in the electrolytic water splitting process. Technological improvements are still possible. 

The sulfuric acid hybrid cycle (Westinghouse process) is given by the reaction equations... 

The hybrid sulfur process (also known as Westinghouse GA-22 and Ispra Mark 11) has a single electrochemical step that completes the cycle ... 

---