Control Strategies

Conventional endothermic reactions are controlled by variation of heat input. In solar-driven operation however, control has to be developed around mass flow variation. Solar irradiation input patterns are stochastic in nature and, at times of fast cloud transients, can be very extreme with time constants well below one second.

Control of the reaction extent of ammonia dissociation via mass flow variation has been trialed using a prototype solar reactor. The assessment of solar transient experiments has shown that the dynamics of the reaction extent is very much congruent with the peak operating temperature of the reactants. Control disturbances arising from solar irradiation, system pressure and peak reactant temperature were found to be insignificant due to the large thermal inertia of the thick-walled pressure vessel design necessary to undertake high-pressure solar ammonia dissociation. If part of a closed-loop system, the solar ammonia dissociation reaction can therefore be operated via conventional temperature control (PI or PID), which negates the need for gas analysis.