TYPES AND STATISTICAL DATA ANALYSIS OF SCRAPE CRYSTALLIZERS FAILURES IN OIL DEWAXER UNITS

Abstract

The efficiency and performance of the oil dewaxing unit depends not only on the physicochemical properties of the raw materials, but also on the equipment’s performance. Maintaining equipment in working condition and preventing premature failures are basic principles in operating equip- ment. Since complex equipment is used for crystallization processes, increasing reliability is important for the oil refining industry. Considered scraper crystallizer is a pipe in pipe heat exchanger with internal scraper devices. The advantages of this equipment are the developed heat exchange surface, continuous operation mode, ease of regulation of the operating mode, the possibility of the process with minor supercooling of the separating mixture. Crystallizers are horizontal pipe-in-pipe heat exchangers. The inner tube is equipped with a rotating shaft with metal scrapers to remove the paraffin layer from the pipe walls. The solution of the dewaxed raw material is pumped through the internal tubes, and the refrigerant (ammonia, propane, ethane or cold filtrate) is countercurrent through the annular space. Practice shows that the repair of a scraper crystallizer of the «pipe in pipe» type is a complex process that requires substantial expenses, both for capital and for physical strength of workers. Repair schedule complicates equipment failures due to premature wear of components. The failure of one crystallizer reduces the installation load by 10-15 %, which in turn affects the final production of oils. This article describes the principle of operation and the types of failures to the components of the scraper crystallizer; analysis of the replacement of worn parts, failures of crystallizers, and examples of worn parts. As a result of analyzing the data of parts replacement during of scraper crystal- lizers repairs collected over many years of operation, it was concluded that the most susceptible to wear of the crystallizers’ parts are scrapers and tee bearings, the premature wear of which is in most cases are root causes of the equipment failure.