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Research Papers

# Molten-Salt Tubular Absorber/Reformer (MoSTAR) Project: The Thermal Storage Media of $Na2CO3–MgO$ Composite Materials

[+] Author and Article Information
Tatsuya Kodama1

Department of Chemistry and Chemical Engineering, Faculty of Engineering, and Graduate School of Science and Technology, Niigata University, 8050 Ikarashi 2-nocho, Niigata 950-2181, Japantkodama@eng.niigagta-u.ac.jp

Nobuyuki Gokon, Shin-ichi Inuta, Shingo Yamashita

Department of Chemistry and Chemical Engineering, Faculty of Engineering, and Graduate School of Science and Technology, Niigata University, 8050 Ikarashi 2-nocho, Niigata 950-2181, Japan

Taebeom Seo

Department of Mechanical Engineering, Inha University, No. 253 Yanghyundong, Namgu, Incheon 402-751, Korea

1

Corresponding author.

J. Sol. Energy Eng 131(4), 041013 (Sep 30, 2009) (8 pages) doi:10.1115/1.3197840 History: Received February 02, 2009; Revised July 12, 2009; Published September 30, 2009

## Abstract

The molten-salt tubular absorber/reformer (MoSTAR) project aims to develop a novel type of “double-walled” tubular absorber/reformer with molten-salt thermal storage at high temperature for use in solar natural-gas reforming and solar air receiver, and to demonstrate its performances on the sun with a $5 kWt$ dish-type solar concentrator. The new concept of double-walled reactor tubes is proposed for use in a solar reformer by Niigata University, Japan, and involves packing a molten/ceramic composite material in the annular region between the internal catalyst tube and the exterior solar absorber wall. This solar tubular absorber concept may be also applied to solar air receiver for solar thermal power generation. The MoSTAR project includes the development of molten-salt thermal storage media, the new design and the fabrication of absorber/reformer with the double-walled absorber tubes, and finally the solar demonstration on the $5 kWt$ dish concentrator of Inha University in Korea. In this paper, thermal storage media of the series of $Na2CO3–MgO$ composite materials were tested in a double-walled reformer tube with a thermal storage capacity of about 0.3 kWh. The chemical reaction performances for dry reforming of methane during cooling or heat-discharge mode of the reactor tube were investigated using an electric furnace. The experimental results obtained under feed gas mixture of $CH4/CO2=1:3$ at a residence time of 0.3 s and at 1 atm showed that the single reactor tube with $90 wt % Na2CO3/10 wt % MgO$ composite material successfully maintained a high methane conversion above 90% with about 0.9 kW reforming scale based on high heating value during 45 min of the heat-discharge mode. The chemical reaction performances of the reactor tube were investigated also for the solar-simulating operation mode. The application of the new reactor tubes to solar tubular reformers is expected to help realize stable operation of the solar reforming process under fluctuating insolation during a cloud passage.

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## Figures

Figure 1

Examples of solar-directly-irradiated tubular reformer: upper left (8), lower left (17), upper right (16), and lower right (7)

Figure 2

Chemical equilibrium composition of the system CH4+3CO2 at 1 atm

Figure 3

Design of a double-walled reactor tube for solar reforming of methane

Figure 4

Experimental setup of double-walled reactor tube for CO2 reforming of methane: (a) overall and (b) cross section of the reactor tube

Figure 5

Temperature dependence of heat capacity Cp for carbonate salts and MgO

Figure 6

Thermal storage capacities of the Na2CO3/MgO composite materials and Na2CO3 only packed in the annular region of the reactor. The thermal storage is calculated from Refs. 21-22.

Figure 7

Typical time variations of the methane conversion and catalyst-bed temperature during the cooling or heat-discharge mode of the reactor with (a) the 80 wt % Na2CO3/20 wt % MgO composite material, (b) the 90 wt % Na2CO3/10 wt % MgO composite material, and (c) the noncomposite of 100 wt % Na2CO3

Figure 8

Reforming period of time with high methane conversion above 90% during the cooling (the τTSM and τblank) at various residence times

Figure 9

HHV of the reformed output gas at various residence times

Figure 10

Methane conversions after 60 min of cooling time at various residence times

Figure 11

Efficiency of the storage materials for the reforming reaction during cooling from 920°C to 640°C.

Figure 12

Time variations of methane conversions and outer tube, molten salt, and catalyst temperatures

Figure 13

Photographs of a 5 kWt, Inha University’s dish concentrator in Korea. Left photograph: front side of dish concentrator, upper right: receiver, and lower right: back side of dish concentrator.

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