Comparison of Multi-step Indirect Solar Thermal Hydrogen Processes

2 Comparison of Multi-step Indirect Solar Thermal Hydrogen Processes 

Early studies performed on H2O splitting thermochemical cycles were mostly cha racterized by the use of process heat at temperatures below about 1200 K, available from nuclear and other thermal sources. These cycles required multiple steps (more than two) and had inherent inefficiencies associated with heat transfer and product separation at each step. An overview of indirect thermochemical processes for hy drogen generation using more than two steps has been presented by Funk,4 and sev eral of these cycles are summarized in Table 3. An example includes cycle No. 2 in Table 3, which utilizes the following reaction steps  

Status reviews on multiple step cycles have been presented,46,47 and include the leading candidates GA s 3-step cycle based on the thermal decomposition of H2SO4 at 1130 K,48 and the UT3 s 4 step cycle based on the hydrolysis of CaBn and FeBn at 1020 and 870 K 49 This process involving two Ca and two Fe compounds has received some attention.4 The process is operated in a cyclic manner in which the solids remain in their reaction vessels and the flow of gases is switched when the desired reaction extent is reached  

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