Production of hydrogen by direct thermal decomposition of water: Preliminary investigations

Abstract

The present paper describes preliminary results obtained in a theoretical and experimental study of direct thermal decomposition of water for the production of hydrogen. Steam dissociates when contacting a zirconia surface heated up to high temperature with the help of an image furnace or in other high temperature furnaces simulating the future use of concentrated solar energy. Two different experimental devices were tested. In the first, the gaseous mixture resulting from steam decomposition and evolving from the high temperature zone is quenched by rapid turbulent cold jets. The amount of evolved hydrogen increases with the stirring flow rate and with quenching efficiency. The molar fraction of hydrogen decreases as the input water flow rate increases, but by a compensation effect the net production of hydrogen increases to reach almost 11. STP per hour. In the second device, in order to avoid any recombination of the dissociation products in the medium temperature part of the apparatus, one of the gaseous components issued from the steam decomposition, i.e. oxygen, was separated by means of an oxygen semi-permeable membrane. The flow rate of evolved hydrogen appears to depend primarily on the electrical characteristics of the membrane and mainly on the electronic conductivity of stabilized zirconia. Experimental data concerning the hydrogen flow rate collected at the reactor gas outlet are in good agreement with the theoretical values calculated by a reactor simulation.