System efficiency for two-step metal oxide solar thermochemical hydrogen production – Part 3: Various methods for achieving low oxygen partial pressures in the reduction reaction

Ehrhart, Brian David; Muhich, Christopher L.; Al‐Shankiti, Ibraheam; Weimer, Alan W.

doi:10.1016/j.ijhydene.2016.07.106

Cited by 51 publications

(35 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The pump work term (QPUMP) is only used for a system operating under vacuum for the reduction reaction. This is not considered here, but explored in a subsequent analysis [38]. In this analysis, QPUMP is set to zero.…”

Section: Auxiliary Heating Requirements and Benefitsmentioning

confidence: 99%

“…pAR is obtained by calculating the equilibrium oxygen partial pressure above the reactive solids that are at the reduction temperature (TRED) and the oxidized stoichiometric state (δOX). It should be noted that the validity of this method of calculating inert gas flow (as well as other inert gas assumptions) will be discussed in subsequent analyses [38,40]. An example of the range of nio values for an example calculation is given in Section S.4 of the Supplemental Information.…”

Section: Recycled Inert Gas Termsmentioning

confidence: 99%

“…The mole fractions are calculated using the oxygen partial pressures that were used to calculate nio (Equation (26)). Realistic practical values for many of these parameters are unknown, and so a more thorough examination of the sensitivity of these values has been carried out in Ref [38]. An oxygen product purity after separation of 100% was assumed for this closed system, and the oxygen partial pressure for reduction (pRED) was used to determine the final effluent oxygen concentration.…”

Section: Recycled Inert Gas Termsmentioning

confidence: 99%

“…The same temperatures are considered for ceria in order to make more direct comparisons between the two materials. A reduction partial pressure for oxygen of 0.1 Pa was used, though alternate partial pressures are considered elsewhere [38]. Only a single value of FR = 1 (100% active material) is considered, as the addition of inert solid material will decrease efficiency in a predictable way.…”

Section: Calculation and Analysismentioning

confidence: 99%

See 3 more Smart Citations

System efficiency for two-step metal oxide solar thermochemical hydrogen production – Part 1: Thermodynamic model and impact of oxidation kinetics

Ehrhart

Muhich

Al‐Shankiti

et al. 2016

International Journal of Hydrogen Energy

Self Cite

View full text Add to dashboard Cite

A comprehensive solar-to-hydrogen (STH) efficiency model, which includes the effect of oxidation kinetics, is developed for two-step solar thermochemical redox water splitting processing. Active materials flow through separate reduction and oxidation reactors. Two active redox materials are considered and compared in order to assess the impact of the rate of redox and the hydrogen productivity per cycle on STH efficiency. Reported oxidation rates for reduced cerium oxide (fast kinetics/lower H2 productivity/cycle) and a ferrite/zirconia composite (slow kinetics/higher H2 productivity/cycle) are used in the model in order to make a realistic comparison. Generally, the efficiency at thermodynamic equilibrium is higher for the ferrite/zirconia composite than ceria. Interactions between material specific parameters are compared, such as the combination of heat capacity and flow rate on sensible heating loads.Additionally, the sensitivity of oxidation kinetics on the overall cycle efficiency is illustrated.Model results show that kinetics can have a drastic effect on STH efficiency. Near-isothermal redox processing is more optimal for materials with slower kinetics, and especially with moderate to high gas heat recuperation. The kinetic effects are negligible for those active materials having fast oxidation rates, i.e. ceria, which benefit from a larger temperature difference (thermodynamic driving force) between the reduction and oxidation steps. This leads to different optimal operating conditions when oxidation kinetics are included in the analysis as compared to prior models when only thermodynamic equilibrium is considered.

show abstract

Section: Auxiliary Heating Requirements and Benefitsmentioning

confidence: 99%

Section: Recycled Inert Gas Termsmentioning

confidence: 99%

Section: Recycled Inert Gas Termsmentioning

confidence: 99%

Section: Calculation and Analysismentioning

confidence: 99%

See 2 more Smart Citations

System efficiency for two-step metal oxide solar thermochemical hydrogen production – Part 1: Thermodynamic model and impact of oxidation kinetics

Ehrhart

Muhich

Al‐Shankiti

et al. 2016

International Journal of Hydrogen Energy

Self Cite

View full text Add to dashboard Cite

show abstract

“…These errors are prevalent in the field of thermochemical fuel production via either membrane reactors or redox cycles. [7][8][9][10][11][12] Thermochemical fuel production systems are proposed as a means of converting heat to chemical energy, by driving chemical reactions that produce a fuel such as syngas. Many authors take the approach of setting the concentration [A] at the exit of each flow to be equal to the concentration at the inlet of the opposite incoming stream.…”

Section: Introductionmentioning

confidence: 99%