In a high-temperature reactor, technologies for chemical reactions at high temperatures are demonstrated. The high temperatures, usually above 500 °C, are reached by integration of concentrated solar radiation. The most common reaction technologies are thermochemical cycle processes based on redox systems for production of fuels such as hydrogen or synthesis gas, or for the production of fertilizers and thermochemical energy storing. Other reactors are be used for reformation, metal recycling and high-temperature electrolysis.
Point focusing systems enable the required process temperatures to be reached. The concentrated solar radiation is absorbed by a receiver and makes heat available for the chemical process. Detailed knowledge concerning the physical and chemical procedures inside the reactor is essential for an optimized and scalable design of the complete system. In particular, the kinetics of the involved reactions, the mass transport within the gas phase and solid as well as the mechanism to efficiently transfer heat are under investigation and further developed. Basic studies for these procedures are done by numerical simulations and by experiments in laboratories, among others in the competence center CeraStorE®. Here, the implementation of new ceramic materials for the use in energy technology is investigated by the department of Solar Chemical Engineering together with the DLR Institutes for Engineering Thermodynamics and Materials Research.
Several processes under investigation in the Department of Solar Research are composed of two reactions that are performed under different temperatures as well as different gas atmospheres. Two chamber solar reactors are very feasible to demonstrate such processes. In Figure 1, a reactor for the splitting sulfuric acid firstly in water and sulfur trioxide and subsequently into sulfur dioxide is depicted. The two chambers allow the conduction at different temperatures and dwell times corresponding to the individual reaction.
Another innovative concept to realize thermochemical processes is the rotary kiln (Figure 2). The smart transport mechanism of this reactor enables the continuous feed-through, an effective mixing of the particles, an intense contact between solid and gaseous phase and solarthermal heating of particles. Some typical application fields of the rotary kiln reactor are the solarthermal reduction of redox material, recycling of solids and production of cement. Since this concept involves moving parts, in particular the sealing of the reactor against the ambient gas atmosphere is complicated and subject of today’s research.
A successful small-scale validation in the lab or solar furnace is usually followed by a field test in a demonstration plant in the scale of a few hundred kW up to 1 MW in a solar power tower, for instance in Jülich or Almería.