Solar thermochemical hydrogen: The heat source-process interface

A discussion of issues and considerations related to the interface between a solar heat source and a thermochemical hydrogen process and some details of a tubular heat exchanger operating as such an interface in a cavity-type receiver are presented. The issues include the temperature and heat input requirements for the endothermic reaction, type of receiver, heat storage, transient operations, and control. A thermal performance analysis of a tubular reactor/heat exchanger operating in a cavity-type solar receiver is applied to SO₃ decomposition. The analysis produces axial distributions of temperature tube wall and process fluid, reaction rate, conversion, velocity, density, pressure and residence time. Process fluid conditions at the inlet, tube characteristics, reaction kinetics and cavity operating temperature are inputs. The cavity temperature affects average heat flux and, therefore, heat-exchanger cost and receiver efficiency and, therefore, mirror field cost. A design which minimizes the combined cost may be found and examples are shown.