High-temperature carbonate/MgO composite materials as thermal storage media for double-walled solar reformer tubes

Abstract

The composite materials of molten alkali-carbonate/MgO-ceramics are examined as thermal storage media in a tubular reformer using a double-walled reactor tube of a laboratory scale. The concept of a double-walled reformer tube is proposed as a solar tubular reformer and involves packing a molten salt/ceramic composite material in the annular region between the internal catalyst tube and the exterior solar absorber wall. The composite materials of Na 2CO 3, K 2CO 3, and Li 2CO 3 with magnesia are tested as thermal storage media. The reforming performances of the composite materials are tested in the cooling mode of the double-walled reactor tube. The experimental result obtained under feed gas mixture of CH 4/CO 2 = 1:3 at 1 atm shows that the use of 80 wt%Na 2CO 3/20 wt%MgO composite material successfully delayed the cooling time of the catalyst bed by 5–19 min in comparison to the case without a composite material. In addition, the Li 2CO 3/MgO and Na 2CO 3/MgO composite materials relatively revealed good performances: they prolonged the cooling time by over 10 min in the gas hourly space velocity (GHSV) range of 5000–12,500 h −1. The application of the reactor tubes to solar tubular reformers is expected to realize stable operation of the solar reforming process under fluctuating insolation during cloud passage.