A hydrogen-based burner concept for pilot-scale spray-flame synthesis of nanoparticles: Investigation of flames and iron oxide product materials

Nanoparticle synthesis in spray flames is a flexible method to produce materials with a wide range of compositions, morphologies, and properties. On the road to industrial application, the transfer from laboratory to pilot scale is an important intermediate step. In the present paper, nanoparticle synthesis based on spray combustion combined with a novel burner concept based on a fuel/air pilot flame ignited by an electrical heat ring is presented. When operating with H2, the burner concept allows nanoparticle production with a sustainable fuel. The temperature profile in the flame is one of the key factors determining the kinetics of precursor decomposition, particle formation, and growth. In this work, we have studied the gas-phase temperature in the reactive zone using non-intrusive multi-line NO-LIF temperature imaging. A solution of iron nitrate nonahydrate dissolved in ethanol was used as nanoparticle precursor mixture, atomized by a commercial two-fluid nozzle, and ignited by the premixed flame to synthesize iron-oxide nanoparticles. The burner can be operated at different conditions to direct the properties of the nanoparticles produced. To this goal, process conditions were varied in a targeted manner. In addition to variations in fuel gas and flow rates, the use of compressed air instead of pure O2 as a dispersion gas has also been investigated. The effects of these variations on temperature distribution and materials properties have been investigated. It has been determined that the dispersion gas mass flow has relatively small influence on the materials properties, while higher flame temperatures are advantageous to suppress the often-undesired liquid-to-particle synthesis pathway.