Customized single cartridge mechanical seal AS-C454 is single seal made as per drawing.

Customized single cartridge mechanical seal AS-C454 is single seal made as per drawing.

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Cause analysis and improvement measures of mechanical seal leakage of constant top reflux pump

1 Overview of normal top reflux pump operation The normal top reflux pump is an important piece of equipment in the normal and pressure reducing device. The model is CD8 8xl R14M-h. The serial number in the device is P110. During normal production, one is used and the other is spared. The pump is driven by a 6000V three-phase motor with a rated current of 26.3A. The operating parameters of the pump are as follows: the medium is naphtha, the medium density is 700kg •m-3, and the medium temperature is 120 degrees Celsius. The pump inlet pressure is 0.2MPa and the pump outlet pressure is 1.0MPa. The working speed is 2980r • min-1, and the normal flow rate is 629m3 • h-1.

The normal top oil and gas are extracted from the top of the normal pressure tower C101, and enter the normal top reflux tank D105 after heat exchange in the normal top oil and gas-crude oil heat exchanger E102. The constant top naphtha is extracted from the bottom of the tank and enters the inlet of the constant top reflux pump P110. After being pressurized by the pump, it is divided into 3 paths: 1) Passes the control valve FV1038. It merges with the gas phase coming out of the constant top reflux tank and then enters the constant top air cooling A101; 2) Return to the inlet of the normal top reflux tank through the control valve FC1037 as the minimum reflux line of the pump; 3) Return to the top of the normal pressure tower through the control valve FV1039 as the heat reflux of the normal pressure tower. The simple flow chart of the constant top system is shown in the figure below.

2 Analysis of causes of mechanical seal leakage
2.1 Introduction to mechanical seals
The pump seal uses double mechanical seal. The seal flushing solution is PLAN 11+PLAN52. The materials of the mechanical seal's inner sleeve, set screws, inner gland anti-rotation pin, pin and spring box are all OCr18Ni9 austenitic stainless steel, the rotary face is made of resin-impregnated graphite, and the stationary seat is made of silicon carbide, the O-ring is made of fluorine rubber, the sealing gasket is made of polytetrafluoroethylene, and the transmission ring, pumping ring, outer gland and limit plate are all made of 2Cr13.During normal production operation, the mechanical seal of the constant top reflux pump leaked in less than one month after being put into use. When the leak occurred, the liquid level and pressure of the secondary pump sealing tank rose slowly, and at the same time, a sharp whistle sounded from the mechanical seal.

2.2 Analysis of causes of mechanical seal leakage
Laboratory analysis of Changding naphtha showed that its chloride ion content was as high as 156.4 mg*kg-1. An analysis of the chloride ion content of the acidic water discharged from the top of the house showed that it was as high as 164mg*L-1, far exceeding the indicator of 30mg*L-1. The reflux of naphtha at the top is a cyclic reflux extracted from the reflux tank and the top of the normal pressure tower. Chloride ions have a certain degree of aggregation. After running for a certain period of time, the chloride ion content in the naphtha at the top will increase, which will cause damage to the machinery. The parts inside the mechanical seal made of austenitic stainless steel will undergo extremely strong corrosion, causing seal failure. In the PLAN 11 flushing scheme, the flushing oil is not cooled down. The temperature of the process medium led from the pump outlet to the seal chamber flushing is as high as 120 degrees Celsius. It cannot effectively take away the heat generated by the friction pair of the mechanical seal, causing the flushing oil entering the seal chamber to vaporize , causing the friction pair of the mechanical seal to dry grind, resulting in a sharp whistle sound.

3 improvement measures
In order to solve the problem of repeated leakage of the constant top reflux pump and improve the reliability of equipment operation, the following improvement measures have been determined.
3.1 Improve flushing plan
Change the level one PLAN 11 flushing plan to the PLAN 32 plan. Lead a DN20 pipeline from the outlet of the normal top product pump next to it and connect it to the primary flushing line of the normal top return pump. The outlet pressure of the constant top reflux pump is 1.1Mpa, and the pressure entering the sealing chamber of the mechanical seal is controlled at 0.45Mpa, which is about 0.25Mpa higher than the sealing chamber pressure (the sealing chamber pressure is 0.20Mpa). The flushing medium is naphtha with a density of 700kg*m-3, which is the same as the operating medium of the constant top reflux pump, ensuring the purity of the medium. The flushing oil temperature is 40 degrees Celsius, which can effectively take away the heat generated by the friction of the friction pair of the mechanical seal, thereby ensuring the stability of the oil film and preventing dry wear of the friction pair of the mechanical seal.