An experimental study of deposition of suspended magnetite in high temperature-high pressure boiler type environments

• Published in: Colloids and surfaces. A, Physicochemical and engineering aspects Physicochemical and engineering aspects, 2016-11, Vol.508, p.48-56
• Main Authors: Raman, Balaji, Hall, Derek M., Shulder, Stephen J., Caravaggio, Michael F., Lvov, Serguei N.
• Format: Article
• Language: English
• Subjects: Deposit characterization; DLVO theory; Fouling in boilers; High temperature deposition cell; In situ electrochemical impedance spectroscopy
• ISSN: 0927-7757; 1873-4359
• DOI: 10.1016/j.colsurfa.2016.08.018

[Display omitted] •High temperature cell to simulate Fe3O4 deposition in boiler type environments.•DLVO type behavior of suspended Fe3O4 in boiler water at 300°C was verified.•EIS was used to identify deposition at the metal solution interface.•Results corroborated using ex situ analysis. Fouling in boilers has been a problem for decades. In addition to iron oxide deposits on tube walls impeding heat transfer, some forced circulation boilers experience magnetite deposition in lower orifices. These deposits impede flow, cause inefficiencies and lead to boiler tube failures from overheating and corrosion. Particle deposition in some boiler/reactor type environments has been attributed to particle transport and the probability of particle attachment. The attachment is governed by both the inter-particle and particle-substrate interactions, which depend on the aqueous environment. In this study, a novel experimental system is presented, which focusses on the particle attachment aspect of the deposition issues observed in boiler type environments. To identify the effect of boiler water chemistry on the deposition of suspended magnetite on stainless steel, a high temperature high pressure electrophoretic deposition cell with provisions to test metal substrates and different chemistries was developed. Tests were conducted at pH25°C of 9.3 in simulated boiler conditions in terms of temperature, pressure and water chemistry. In addition to visual observations, the deposition was investigated using in-situ Electrochemical Impedance Spectroscopy (EIS) and post-test surface analyses including Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). As predicted by Derjaguin-Landau-Verwey- Overbeek (DLVO) theory, deposition was confirmed possible in the above-mentioned aqueous environment at 300°C. The experimental system presented here was successful in simulating boiler type environments with accelerated deposition. The capability to understand particulate fouling and also to study interfacial phenomena in high temperature, high pressure aqueous environments has been demonstrated.