Hydrogen production thermochemical methods

Multistep Thermochemical Water Splitting. Multistep thermochemical hydrogen production methods are designed to avoid the problems of one-step water spHtting, ie, the high temperatures needed to achieve appreciable AG reduction, and the low efficiencies of water electrolysis. Although water electrolysis itself is quite efficient, the production of electricity is inefficient (30—40%). This results in an overall efficiency of 24—35% for water electrolysis. 

As well as the previously described methods of hydrogen production, there are other commercial processes whose application is restricted to specialised production conditions. These include the partial oxidation of heavy hydrocarbons, autothermal reforming and the Kvcerner process. In addition, there are numerous production processes that are still at the basic research stage, but show promising potential. These primarily include thermochemical hydrogen production, photochemical and biological processes. The main characteristics of these methods are outlined below. For a more detailed discussion, please refer to the relevant specialist literature. 

Research on methods of hydrogen production by thermochemical decomposition of water has been carried out in several laboratories with increasing interest during the last decade. 

The cost of nuclear hydrogen supply for transportation usage, by thermochemical and electrical decomposition methods, was evaluated in order to compete with gasoline. The total cost for a centralized hydrogen production consists of production cost, delivery cost, and station cost [16]. 

Y. Chikazawa et al., Conceptual Design of Hydrogen Production Plant with Thermochemical and Electrolytic Hybrid Method Using a Sodium Cooled Reactor , ICAPP 05-5084, 2005 International Congress on Advances in Nuclear Power Plants, Seoul (May 2005). 

Alternative methods of hydrogen production are thermochemical water decomposition, photoconversions, photobiological processes, production from biomass, and various industrial processes where it is a by-product. 

As shown in Table 4.2, large break LOCA events involve the most physical phenomena and, therefore, require the most extensive analysis methods and tools. Typically, 3D reactor space-time kinetics physics calculation of the power transient is coupled with a system thermal hydraulics code to predict the response of the heat transport circuit, individual channel thermal-hydraulic behavior, and the transient power distribution in the fuel. Detailed analysis of fuel channel behavior is required to characterize fuel heat-up, thermochemical heat generation and hydrogen production, and possible pressure tube deformation by thermal creep strain mechanisms. Pressure tubes can deform into contact with the calandria tubes, in which case the heat transfer from the outside of the calandria tube is of interest. This analysis requires a calculation of moderator circulation and local temperatures, which are obtained from computational fluid dynamics (CFD) codes. A further level of analysis detail provides estimates of fuel sheath temperatures, fuel failures, and fission product releases. These are inputs to containment, thermal-hydraulic, and related fission product transport calculations to determine how much activity leaks outside containment. Finally, the dispersion and dilution of this material before it reaches the public is evaluated by an atmospheric dispersion/public dose calculation. The public dose is the end point of the calculation. 

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