Abstract: This paper addresses the problem of frequent leakage of mechanical seals in the CDU tower bottom pumps of a new refinery during the startup phase. By conducting failure mechanism analysis, seal structure analysis and DCS operational data comparison, the root causes of the seal leakage were determined to be seal face misalignment due to thermal deformation of the seal chamber, insufficient PLAN53B pressure settings and cooling deficiency caused by PLAN32 filter failure. A series of optimization measures have been taken to address the causes of the leakage including enhancing pump case insulation to mitigate environment thermal transients; raising PLAN53B pressure at nondrive end to prevent media backflow; installing PLAN32 orifice plates for precise flushing pressure control; implementing PLAN61 backcooling system to inhibit coke formation and substituting the original white oil with high flashpoint barrier fluid. After the implementation of these measures, the tower bottom pump runs smoothly, and the mechanical seal leakage has been permanently eliminated. This mechanical seal leakage solution can provide some reference for addressing mechanical seal failures of the same type of hightemperature oil pumps under complex operating conditions.

Key words: rotating equipment, CDU tower bottom pump, mechanical seal, fault handling