Powder cloud reactors.An attractive concept to run solar high-temperature reactions

Abstract

The direct absorption of concentrated solar radiation in a powder cloud is a promising reactor concept to thermally decompose metal oxides to lower valence metal oxides or metals. This decomposition accomplishes direct conversion of solar to chemical energy. To investigate these decomposition reactions two different groups of reactors were developed. The first group consists of small windowless prototype reactors that has the potential be scaled up to industrial scale. Based on the results four main criteria were proposed for their development. In a recent work we were able to build a reactor that fulfilled three of the four criteria. As a result maximum particle temperatures of 1900 K as well as stable temperature differences particle/wall of more than 500 K were achieved. In conjunction with a water-spray quenching unit, MnO 2 could be successfully reduced to a mixture of MnO/Mn 3 O 4 . The reactors of the second group were aimed as tools to investigate chemical reactions at high temperatures in a solar furnace. Thus, control of the gas atmosphere and temperatures as high as possible were prioritized. With a win dowed solar reactor equipped with a secondary concentrator, reduction of spinel type mixed iron oxides, (Fe 0.9 M 0.1 ) 3 O 4 (M=Mn, Mg), was achieved in less than 50 milliseconds.