TY - JOUR
T1 - Conceptual design of a two-step solar hydrogen thermochemical cycle with thermal storage in a reaction intermediate
AU - Xu, Rong
AU - Wiesner, Theodore F.
N1 - Funding Information:
Acknowledgment is made to the donors of The American Chemical Society Petroleum Research Fund ( ACS PRF 49638-ND10 ) for support of this research. The sponsor had no role in the collection, analysis, and interpretation of results, in the writing of the report, and in the decision to submit the paper for publication.
PY - 2014/8/13
Y1 - 2014/8/13
N2 - This paper presents the conceptual design for a two-step thermochemical cycle producing hydrogen continuously, even off-sun, with the concentrated solar energy as the heat source. For a case study, the two-step iron oxide cycle (Fe3O4/FeO) is selected to illustrate the design concept. Two reactors, one storage tank and the solar collector comprise the system. Molten wustite (FeO) is accumulated in the storage tank on-sun. The FeO is not only involved in the reactions but also acts as the heat transfer medium, obtaining the energy from the solar insolation and delivering energy to support the thermal decomposition of magnetite (Fe3O4). In this way, the temperature limitation (<800 K) of molten salt is solved, and the intermittency problem of variable insolation is circumvented. A simple feedback scheme is used to control the flow rate between the storage tank and the reactors in order to minimize the temperature fluctuations. For the wustite hydrolysis reaction, the volumetric flow rate of water is regulated to control the temperature in the reactor. We derived the kinetics of the two-step iron oxide cycle from previous experimental reports. We simulated the dynamics of the system over 50 days with mass and energy balances. The simulation results show that the storage tank temperature will be stationary at 2250 K. After five days, the decomposition temperature at 2100 K, and the hydrogen production stabilized at 7 kg/min. Admitting the difficulty of high temperature operation, this design is still promising due to the high efficiency of two-step cycle itself, the process intensification of the FeO acting as the reactant/product/heat transfer medium (no need of heat exchangers), and the continuous operation/production of hydrogen.
AB - This paper presents the conceptual design for a two-step thermochemical cycle producing hydrogen continuously, even off-sun, with the concentrated solar energy as the heat source. For a case study, the two-step iron oxide cycle (Fe3O4/FeO) is selected to illustrate the design concept. Two reactors, one storage tank and the solar collector comprise the system. Molten wustite (FeO) is accumulated in the storage tank on-sun. The FeO is not only involved in the reactions but also acts as the heat transfer medium, obtaining the energy from the solar insolation and delivering energy to support the thermal decomposition of magnetite (Fe3O4). In this way, the temperature limitation (<800 K) of molten salt is solved, and the intermittency problem of variable insolation is circumvented. A simple feedback scheme is used to control the flow rate between the storage tank and the reactors in order to minimize the temperature fluctuations. For the wustite hydrolysis reaction, the volumetric flow rate of water is regulated to control the temperature in the reactor. We derived the kinetics of the two-step iron oxide cycle from previous experimental reports. We simulated the dynamics of the system over 50 days with mass and energy balances. The simulation results show that the storage tank temperature will be stationary at 2250 K. After five days, the decomposition temperature at 2100 K, and the hydrogen production stabilized at 7 kg/min. Admitting the difficulty of high temperature operation, this design is still promising due to the high efficiency of two-step cycle itself, the process intensification of the FeO acting as the reactant/product/heat transfer medium (no need of heat exchangers), and the continuous operation/production of hydrogen.
KW - Continuous hydrogen production
KW - Dynamic simulation
KW - Iron oxide cycle kinetics
KW - Two-step thermochemical cycle
UR - http://www.scopus.com/inward/record.url?scp=84905252950&partnerID=8YFLogxK
U2 - 10.1016/j.ijhydene.2014.06.064
DO - 10.1016/j.ijhydene.2014.06.064
M3 - Article
AN - SCOPUS:84905252950
VL - 39
SP - 12457
EP - 12471
JO - International Journal of Hydrogen Energy
JF - International Journal of Hydrogen Energy
SN - 0360-3199
IS - 24
ER -