An Investigation of a Dryer Can Failure in a Paper Mill
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TECHNICAL ARTICLE—PEER-REVIEWED
An Investigation of a Dryer Can Failure in a Paper Mill M. Ananda Rao • M. V. Pavan Kumar
Submitted: 17 April 2014 / in revised form: 19 December 2014 Ó ASM International 2015
Abstract The failure of a rotary dryer in a paper manufacturing facility is reported and analyzed. The primary cause of failure is identified as a weakened structure and as a consequence, inlet pressure of the steam into the dryer reaching a critical limit. Post failure, the shell, and the two heads of the dryer were analyzed using characterization techniques such as stereomicroscopy and scanning electron microscopy with energy dispersive analysis. The threads of the shell were found completely chipped off. In the microchemical analysis, silicon in the form of quartz was found inside the shell at the threads. Silica in the form of quartz is theorized as having entered through the steam and becoming entrapped in the gaps of the threaded connections. Although wear between brittle shell and the connecting bolts can potentially develop torsion and lead to the chipping off of the crest regions of the threads over the time, the deposition of silica might have instigated and aggravated the same. Keywords Corrosion weakening Catastrophic failure Failure analysis Wear Metallurgical investigation
Introduction Even in the current digital era, almost all human activities are associated with the use of paper and its allied M. Ananda Rao (&) CSIR-National Metallurgical Laboratory Madras Center, Taramani, Chennai, India e-mail: [email protected] M. V. Pavan Kumar Department of Chemical Engineering, National Institute of Technology Calicut, Kozhikode, India
products. Equally, the paper making industry has remained as one of the most prominent process industries today. Apart from the procurement of the raw materials, the paper making process can be chiefly understood as a systematic de-watering of the pulp for different varieties of paper, classified based on the end use. In general, the de-watering step is carried out as a series of unit operations, namely gravity separation, vacuum filtering, and drying to bring the water content of the end product to nearly 5% down from the initial water content of about 99.5%. In the de-watering step, drying is critical to the properties of the paper produced. In the paper making industry, web of paper is dried by passing it on a continuous fett belt over a series of steam-heated cylinders. The cylinders’ exterior is in continuous contact with the fett belt and, hence, the paper web. Steam is supplied into the cylinders as heating medium for the drying of paper web and the steam condensate is drained out continuously. The existing theories and practice of paper drying and the industrial perspective of the process are described in detail by Ghosh [1]. In paper mills, the drying operation is monitored very closely due to its enormous impact on the quality of the final product. Cast iron which exhibits high thermal conductivity is used for the rolling cylinder cans and this ensur
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