Characterization of the deposition and transport of magnetite particles in supercritical water

Several online and offline techniques for characterizing the deposition and transport of magnetite particles in supercritical water were investigated using a once-through flow apparatus. Ferrous chloride and ferrous sulfate precursor solutions were injected into a 1.8m heated test section at temperatures ranging from 200 °C to 400 °C. Silver membrane filters of 0.2 μm pore size were used to collect particles under supercritical conditions. Thermal resistance monitoring on the test section showed asymptotic, linear fouling and deposition-removal cycles. A novel method for qualitatively determining the strength of the oxide to the tube surface using a combination of ultrasonic and acid wash procedures demonstrated that at supercritical conditions, a stronger bond is formed which is speculated to be caused by the precipitation of dissolved ferrous species. A comparison between different conditions of pH, heat flux, and precursor were examined using the experimental techniques which are presented in this study. It was found that multiple techniques are needed to characterize the fouling process if the underlying rate-limiting steps are not known a priori.

Figure optionsDownload as PowerPoint slideHighlights
► Magnetite particles of 200–2000 nm were formed in sub- and supercritical water.
► Particles were in turbulent flows with different values of pH and temperature.
► Microscopy and tube cleaning techniques were used to analyze deposits.
► Deposits formed at supercritical temperature were strong.
► Deposits formed at subcritical temperature were relatively weak.