Abstract
The present work deals with the corrosion of mild steel (1.0037) used as the outer construction material of the preheater of a modern industrial cement production facility. The facility uses secondary fuels, which introduce considerable amounts of corrosive species. The situation at the examination sites in the preheater zone is tracked over a period of two years including operation and shut-down periods. The investigation is focused on (i) the acquisition of the underlying physicochemical conditions, such as moisture, temperature, and contamination data at the examination site of the preheater, (ii) the multianalytical identification of the formed corrosion products using scanning electron microscopy combined with energy-dispersive X-ray analysis, infrared spectrometry, Raman spectrometry, X-ray diffractometry, and Möβbauer spectrometry, and (iii) voltammetric and EIS laboratory investigations using model solutions. It was evidenced that corrosion takes place at a temperature level of about 100°C in the presence of moisture and oxygen as well as chloride ion as a consequence of the usage of secondary fuels. Typical hot-gas corrosion could be excluded under the current conditions. Appearance, structure, and nature of the corrosion products were found to be not mainly dependent on the varied length of exposure, but on the conditions of the hosting preheater intake. In addition to different FeOOH phases and hematite, magnetite was found, dependent on the oxygen concentration in the process gas. The decisive role of oxygen as key factor for the corrosion rate was electrochemically confirmed.
Highlights
The cement production is inevitably connected with two critical phenomena, which shall be addressed at first: energy and fuel consumption and the release of carbon dioxide as one of the green-house gases
Unlike earlier investigations that were directed to the events in the rotary kiln region, this study focused on the corrosion and the underlying conditions in the zone of the preheater of a running cement clinker production facility, more precisely at the inner surface of the mild steel preheater cladding
The following conclusions are drawn from the exposure experiments performed over a long-term period of 24 months as well as from the lab investigations: (i) It was possible to record humidity and temperature on-line during the production process by inserting special sensors directly at the specific preheater sites that were relevant for the corrosion investigation
Summary
The cement production is inevitably connected with two critical phenomena, which shall be addressed at first: energy and fuel consumption and the release of carbon dioxide as one of the green-house gases. A detailed report of the German Umweltbundesamt sums up a substituted energy equivalent of 40 PJ alone for the German cement industry in the year 2004 [4]. This corresponds to a fraction of more than 42% of the total thermal energy consumption in the cement production sector. 16 different types of industrial, agricultural, and urban refuse-derived SFs are discerned by ref. [4], representing different consistency and degree of preprocessing
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