Thermochemical cycles, hydrogen production from

The sulfur-iodine thermochemical water-splitting cycle (S-1 cycle) developed for hydrogen production from water is fundamentally based on the following three chemical reactions (Wang, 2007) ... 

Bamberger, C.E. (1978), Hydrogen Production from Water by Thermochemical Cycles A 1977 Update , Cryogenics, 170-183. 

A recent screening of several hundred possible reactions (Besenbruch et al 2001) has identified two candidate thermochemical cycles for hydrogen production from water (i.e., cycles that enable chemical reactions to take place at high temperatures) with high potential for efficiency and practical applicability to nuclear heat sources. These are the sulfur-iodine (S-I) and calcium-bromine-iron (Ca-Br) cycles. Also, Argonne National Laboratory (ANL) has identified the copper-chlorine (Cu-Cl) thermochemical cycle for this purpose (Doctor et al 2002). A hybrid sulfur-based process that does not require iodine but has a single electrochemical... 

A new thermochemical and electrolytic hybrid hydrogen production system in lower temperature range has been developed by the Japan Nuclear Cycle Development Institute (JNC) to achieve the hydrogen production from water by using the heat from a sodium cooled fast reactor (SFR) [7]. 

Orhan, M. F. Dincer, I. Naterer, G. F. Rosen, M. A. 2010, Coupling of copper-chloride hybrid thermochemical water spUtting cycle with a desalination plant for hydrogen production from nuclear energy. Hydrogen Energy 35, 1560 1574. 

Abanades, S. and Flamant, G. (2006) Thermochemical hydrogen production from a two-step solar-driven cycle based on cerium oxides. Solar Energy, 80, 1611-1623. 

Water is decomposed into hydrogen and oxygen as the net result of the Cu-CI thermochemical cycle. The cycle involves five steps, as listed in Table 1 1) HCl(g) production using equipment such as a fluidised bed 2) oxygen production 3) copper (Cu) production 4) drying 5) hydrogen production. Recent studies by Chukwu, et al. (2008) and Orhan, et al. (2008) have analysed the overall thermal efficiency of the five-step Cu-CI cycle. The efficiency of the cycle versus temperature was analysed for three cases x = 0.2, 0.3 and 0.4, where x refers to the fraction of heat loss to heat input to the cycle. The calculated efficiencies varied from 42 to 55% at 550°C. 

Naterer, G.F., et al. (2008), Thermochemical Hydrogen Production with a Copper-chlorine Cycle, I Oxygen Release from Copper Oxychloride Decomposition , International Journal of Hydrogen Energy, 33, 5439-5450. 

A modelling and experimental effort has identified a new uranium thermochemical cycle (UTC) for the production of hydrogen from water. The peak temperature within the cycle is below 700°C - a temperature achievable with existing high temperature nuclear reactors and some solar systems using commercially auailable materials. This paper describes the new process and some of the experimental work. It is an early report of chemical feasibility. Much work will be required to determine engineering and economic viability. 

Hydrogen is used in many industrial processes, such as the production of ammonia for fertilizer. Hydrogen also has been considered to have a potential as an energy source because its combustion yields a clean product and it is easily stored as metal hydrides. Thermochemical cycles (a series of reactions resulting in a recycle of some of the reactants) can be used in the production of hydrogen from an abundant natural compound— water. One process involving a series of five steps is outlined below. State assumptions about the states of the compounds. 

Apart from the ANL s current effort on Hybrid Cu-Cl Cycle, there have been only a limited number of other processes proposed for moderate temperature thermochemical hydrogen production. Dokiya and Kotera [3] proposed a cycle with a significant variant of the Hybrid Cu-Cl Cycle involving a direct electrochemical hydrogen generation reaction. More recently, Simpson et al. [4] have proposed a hybrid thermochemical electrolytic process for hydrogen production based on modified Reverse Deacon Reaction (generation of HCl gas) and gas phase electrolysis of HCl. 

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