Double-walled reformer tubes using high-temperature thermal storage of molten-salt/MgO composite for solar cavity-type reformer

Composite materials with alkali carbonate and magnesia have been examined for high-temperature thermal storage in solar tubular reformers. The concept of a double-walled reactor tube involves packing a molten-salt/ceramic composite material into the annular region between internal catalyst tube and exterior solar-absorber wall. In this paper, the shape and interior structure of the reactor tube are newly designed for use in solar cavity-type reformers using straight reactor tubes. Na2CO3, K2CO3, and Li2CO3 composite materials with magnesia were tested as thermal storage media for CO2 reforming of methane during cooling mode of the reactor tube at a laboratory scale. The efficiency of Na2CO3/MgO composite with various MgO contents was also estimated. Composite materials of Na2CO3 80–90 wt% and MgO 20–10 wt% were successfully delayed the cooling of the catalyst bed and sustained methane conversion at >90%. A solar cavity-type reformer consisting of multiple straight reactor tubes is expected to enable stable operation of the solar reforming process under fluctuating solar insolation during cloud passage.