Moving Brick Receiver-Reactor (MBR2): A Solar Thermochemical Reactor and Process Design with a Solid-Solid Heat Exchanger and On-demand Production of Hydrogen and/or Carbon Monoxide

Kurzfassung

Two crucial aspects still to be overcome to achieve commercial competitiveness of the solar thermochemical splitting of water and carbon dioxide are recovering the heat and achieving continuous or on-demand production beyond the hours of sunshine. To tackle both aspects we propose a moving brick receiver-reactor (MBR2) design with a solid-solid heat exchanger. In short, the MBR2 consists of (i) bricks that are reversibly mounted on a high temperature transport mechanism, (ii) a receiver-reactor where the bricks are reduced by passing through the concentrated solar radiation, (iii) a solid-solid heat exchanger under partial vacuum in which the reduced bricks transfer heat to the oxidized bricks, (iv) a first storage for the reduced bricks, (v) an oxidation reactor, and (vi) a second storage for the oxidized bricks. Because of the high temperature of up to 1800 K in the receiver-reactor, the transport mechanism has to be made out of ceramic material, for example a ceramic chain. On such a ceramic chain grippers can be fixed in order to hold the bricks during transport. The velocity of the transport mechanism can be adjusted as desired depending on the actual incoming solar radiation and the reaction kinetics. The key benefits of the MBR2 include the possibility to efficiently recover the sensible heat in the reduced bricks, the precise residence time control of the bricks in the receiver-reactor, the steady-state operation of the receiver-reactor after startup, the adjustability of inclination of the receiver-reactor, the possibility to optimize the bricks for radiation absorption and reaction characteristics, the possibility to store the reduced bricks and feed the oxidation reactor continuously or on-demand, the reduction of dust production due to highly reduced abrasion, and the good scalability. To quantify the effects of these benefits on the overall efficiency we performed first theoretical calculations of the heat exchanger and receiver-reactor subsystems. We show that the heat exchanger may recover a large share of the sensible heat which typically is more than half of the total heat loss. On the basis of these calculations, we expect the MBR2 to increase the overall efficiency of solar syngas production substantially.