Pусский
Typical high-temperature pumps in the petrochemical industry (hereinafter referred to as hot oil pumps) are the fractionation tower bottom pumps in each device. For example, atmospheric fractionation towers in atmospheric and vacuum distillation units, vacuum fractionation towers, fractionation towers in catalytic cracking and delayed coking units. The fractionation tower bottom pumps in these devices have the following characteristics: generally 360~380°C; low pressure: the inlet pressure of the pump is 0.1~0.3MPa, and the inlet pressure of the vacuum tower bottom pump is negative pressure (-0.03~ -0.02MPa). For double-supported pumps, the pressure at the sealing chamber at the outlet end is slightly higher, which is 0.6~0.9MPa; the viscosity of the medium is high: the viscosity at the working temperature is (0.06~2)×10¯4㎡/s (6~200 centistokes); The medium contains solid particles. Some are catalysts (such as catalytic slurry pumps); some are mechanical impurities, and some are generated coke. In addition, there is a certain degree of corrosion. These characteristics increase the difficulty of solving the shaft mechanical seal of the thermal oil pump.
The main form of failure of the mechanical seal of the hot oil pump is as follows: the sealing surface is worn out which means that When the rotary face is made of tungsten carbide & the stationary seat is made of graphite, and annular grooves emerge on the surface of the stationary seat; When the rotary face is hot-fitted on the stainless steel ring seat with a tungsten carbide ring, the tungsten carbide ring will become loose; Scale is formed between the rotary face and the shaft sleeve, and the rotary face cannot float; the sealing ring of the rotary face is worn or flanged (when made with 4F-V-shaped pads): the stationary seat is out of position, etc.The main reason is high temperature. High temperature vaporizes the medium in the sealing end faces of the mechanical seal; high temperature reduces the performance of the graphite ring; high temperature makes the cooling water scale; The high temperature makes the hot-packed tungsten carbide ring loose; due to the high temperature, the hot oil pump is easy to evacuate, causing the stationary seat of the mechanical seal to be out of position, and the rotary face of the sealing ring to have defects such as flanging. The presence of mechanical impurities will also aggravate the wear of the sealing surfaces of the mechanical seal.
The high temperature of the hot oil pump is the main reason for the failure of the mechanical seal, so it is very important to find a way to reduce the temperature of the seal. 1) The common method for domestic pumps and seals to reduce the temperature is to set a cooling water jacket around the seal cavity and pass cooling water for cooling. This method can reduce the temperature in the sealed chamber of the mechanical seal to 200~250°C. Due to the smaller radial size of the sealing cavity of the mechanical seal of domestic pumps, the method of installing a cooling coil in the sealing cavity is generally not used; the method of cooling the shaft sleeve is also not used, which will complicate the structure. The measure that Some factories adopt which is adopting water cooling around the stationary seat of the mechanical seal is advisable. 2) If it is a single-end seal, injection flushing can be used. It is an effective method to use clean, low-temperature candles (about 100°C) from the outside, which not only reduces the temperature, but also improves the working environment. 3) Quenching water is used outside the gland. In order to prevent water scaling, softened water at about 60°C can be used. In addition to lowering the temperature, it can also prevent the sewer pipe from being blocked.
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