Sustainable fertilizer production from sun, air and water
In Düsol, solar research of DLR uses its expertise from solar fuel generation and applies it to another sustainable chemical process. The final product is aimed to be a nitrogen based fertilizer. This is a class of fertilizers which contains the element nitrogen (N).
More than 90 percent of the fertilizers produced today are contain nitrogen. As all of those fertilizers require ammonia for (NH3) their synthesis, it is important to generate ammonia in a sustainable way. However, today the production is based on vast amounts of natural gas. The energy content of the natural gas used for fertilizers worldwide is equivalent to the primary energy need of Germany. Thus, fertilizer production still holds great potential to cut down emissions.
State of the art in ammonia production is the well-known Haber-Bosch process. In this process, natural gas (mainly CH4) is used to provide the required hydrogen via reforming and to extract nitrogen from air. Subsequently, hydrogen and nitrogen are converted to nitrogen under high pressure in the Haber-Bosch reactor.
In the Düsol concept, a large part of the Haber-Bosch process remains unchanged. Only the natural gas input is replaced by solar processes. As the natural gas is also used as a chemical, other – cleaner – recourses are to be used. A scheme of the Düsol concept is shown in Figure 1.
To provide hydrogen, a thermochemical cycle for water splitting is employed. That process is already under investigation in other projects for solar fuel generation. To provide nitrogen, another thermochemical cycle shall be used. This cycle can separate oxygen from air. Altough the remaining components Argon, CO2 and other trace gases remain in the nitrogen, it can be used in the subsequent Haber-Bosch reactor.
Especially the solar thermochemical nitrogen production is a very young field of research. Therefore, special emphasis will be put on this process step. The first major challenge is to find redox materials (MO’’ in figure 1) which are suitable to abstract oxygen from air in an efficient way. After the redox material of choice has been identified, an appropriate reactor will be constructed to run the reduction step in a solar simulator facility of DLR. As the reduction step is more critical, focus will be directed on the thermal reduction.
Further parts of the Düsol project include a fundamental process design of the complete plant. Eventually, this design will be assessed economically.
GTT Gesellschaft für Technische Thermochemie und –physik mbH
European Regional Develoopment Fund within the framework of the "Leitmarktwettbewerb ErneuerbareEnergien.NRW"