||Research of design, simulation and demonstration of solar reactor with ceria coated ceramic foam device for two-step thermochemical water-splitting cycle
Cho, Hyun Seok曺, 賢石
162 , 2015-03-23 , 新潟大学
学位の種類: 博士（工学）. 報告番号: 甲第4042号. 学位記番号: 新大院博（工）甲第424号. 学位授与年月日: 平成27年3月23日
A two-step thermochemical water splitting cycle using a none-stoichiometric ceria is one of the promising processes for converting concentrated solar high-temperature heat into clean hydrogen in sun-belt regions. The two-step cycle, however, requires heat above 1400˚C minimum. This provides challenges to solar “windowed” reactor concepts. Direct irradiation of the redox working material enables the reactor to respond very quickly to the intermittent heat supplied by concentrated solar radiation. Niigata University has been developing a novel solar reactor concept using a ceria-coated ceramic foam device. In this paper, this reactor concept is up-scaled for solar demonstration using a 45 kW_<th> solar furnace at Korea under the collaboration research between Niigata University and Korea Institute of Energy Research (KIER). The first-type of the up-scaled solar reactor with the flat disk foam device coated with ceria was designed .and fabricated. For the solar demonstration the solar reactor was set on to KIER solar furnace and additional operating system of the solar reactor was designed and constructed at KIER solar furnace together with KIER members. Three ceramic foam devices coated with different ceria loadings were tested in the solar reactor on hydrogen production performance at the solar furnace. 30 cycles of the two-step water splitting were demonstrated in total, and solar operation method of this foam device reactor was improved. Hydrogen could be successfully produced in the repeated cycles by input of 10-18 kW_<th> of concentrated solar irradiation. On the basis of the experimental data of the solar demonstration, a new design of the solar reactor with a conical or cylindrical foam device was proposed in order to improve hydrogen production performance. Comparing the previous flat foam device, the conical or cylindrical foam device can create a more uniform heat flux distribution on the foam device surface, which expands the solar-heated high-temperature region of the foam device. In addition, the conical or cylindrical foam device can improve the heat transfer between gases and surface. Four different-shaped foam devices of conical or cylindrical types were designed, and numerical simulation was done for them by optical modeling. Then the second-type of the solar reactor with a conical shape foam device without ceria coating was fabricated. And the new solar reactor was tested on temperature distribution of conical foam device at the KIER solar furnace. 23 ～ 24 kW_<th> of solar concentrated radiation was irradiated to the conical foam device. More uniform temperature distribution was created on the surface of the conical device comparing with that of the flat device. The high temperature region (T > 1400 ℃) could be expanded as expected. Additionally, the numerical simulation in terms of pressure drop, temperature distribution, and path lines of the two tested solar reactors was studied for analysis of heat transfer characteristics.