By analyzing the reasons of the frequent failure of the mechanical seal of the lye circulation pump in the ethylene plant, the sealing structure and the friction pair material are improved, and the good sealing effect and economic benefits are achieved.  Ethylene plant compression system concentrated lye circulation pump is the bottom tower circulating pump caustic tower, it will be cracked gas caustic lye transported to the top of the tower, so that lye recycling. The pump in the actual operation, frequent leaks, mechanical seals in the installation and operation of a week or so began to leak, 1 to 2 months the amount of leakage increased, can not continue to use. Seriously affected the device's environmental standards and long-term stable operation.    1 Basic situation: The pump is a single suction cantilever horizontal centrifugal pump, the main technical parameters as follows:    Medium ingredients    Containing gel, particle impurities 20% NaOH liquid    Medium temperature