Hydrogen production energy conversion efficiency

Heat from all the hot exhaust gas streams is used for steam generation to drive the steam turbine. Thus, the final products from the GE fuel-flexible process are pure hydrogen from the first reactor, C02 from the second reactor, and heat for electricity production from the third reactor. A portion of the solids in the chemical loops needs to be purged to avoid ash accumulation and maintain solid reactivity (Rizeq et al., 2002). The overall energy conversion efficiency for the GE fuel-flexible process is estimated to be 60% (Rizeq et al., 2003). 

Miyake J, Miyake M, Asada Y (1999) Biotechnological hydrogen production research for efficient light energy conversion. J Biotechnol 70 89-101... 

Improved Solar Energy Conversion Efficiencies for the Photocatalytic Production of Hydrogen via TiCte Semiconductor Electrodes Heat treatment of Ti metal found to influence performance. 234... 

Figure 2.37. Attenuation of solar radiation as a function of penetration into a biohydrogen reactor containing partly modified cultures of Rho-dobacter spheroides. Reprinted from J. Miyake, M. Miyake, Y. Asada (1999). Biotechnological hydrogen production research for efficient light energy conversion. Journal of Biotechnology 70, 89-101, with permission from Elsevier.

There are several ways to produce energy by fermentation, such as methane fermentation, ethanol fermentation and hydrogen fermentation. Of these, methane fermentation is rather organic waste treatment than energy production, while ethanol fermentation is of practical importance under certain conditions as demonstration in Brazil. Hydrogen fermentation is still not in practical use because the energy conversion efficiency from substrates is fairly low (Table 1), and also is not estimated from a suitable point of view for utilization. 

If similar processes could be developed at energy conversion efficiency levels that are comparable to the present day SMR-based NH3 synthesis plants, then it would be possible to realize a major reduction in the production costs of ammonia-borane complex. We note that a concept similar to that discussed above has already been developed for nitric acid synthesis process based on boron nitride analogous to the Haber-Bosch route for nitric acid production from NH3. Finally, recent results have shown that unusual parallel behavior exists between hydrocarbons and their corresponding B-N analogues. Thus, hydrogenation of benzene to cyclohexane may also provide a model for the reformation of borazine to other amine-boranes. 

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