The ethylene plant residue pump is a tower bottom delivery pump for cracked fuel oil and gas towers, which delivers the residue liquid mixed with the diesel components to the finished product tank area. 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. First, the basic situation: The pump is a single-suction cantilever horizontal centrifugal pump, the damage is as follows: 1, moving ring and ring seat, the gap between the shaft sleeve is blocked 2, ring and static ring ring wear marks 3, seal Cavity with viscous polymer, coke-like particles and other impurities 4, the spring rust serious by impurities and polymer jams, lack of flexibility The main technical parameters are as follows: Dielectric medium temperature medium viscosity flow head suction / discharge pressure shaft power Motor revolutions Residual oil 170 ℃ 7.15mm2 / s 8.9m3 / h 76m 0.091MPa / 0.785MPa 15KW 2950r / m Second, the failure analysis: The main reason for the seal failure caused by the failure of the end liquid film, the material is incompatible with the media, As well as manufacturing and installation issues. End face specific pressure is an important mechanical seal performance parameters, the end face to pressure within the scope of the design (internal mechanical seal is generally 0.4 MPa ~ 0.7 MPa), in order to ensure the mechanical seal face with a good fit, so that the sealing surface between the formation of effective solution membrane. The formula for calculating the end face specific pressure is: Pb = Pt + Pp-Pm Pb = Pt + (K-λ) P Where: d2 = 72mm d1 = 37mm d2 = 34mm Spring specific pressure Pt = Ft / [π / 4 (D22-d12) = 1.056 Membrane pressure coefficient λ = 0.742 Medium pressure in sealed chamber P = (inlet pressure + outlet pressure) / 2 = 0.438MPa It can be calculated that the specific pressure Pb of the original 8B1-P type mechanical seal end face is 0.586 MPa, which is in accordance with the design specifications and can meet the production requirements under normal working conditions. This is in line with the actual situation, in the early use of mechanical seals do not leak, then the cause of its failure is what? This must be from the mechanical seal of the working environment for a comprehensive analysis. E-GA103 pump rinse solution from the pump outlet, after the filter into the E-GA103 pump. In the actual production process, due to the relatively large viscosity of residual oil, poor fluidity, and the residue medium containing granular and powdery coke, there is inevitably around the friction pair coke, which is a considerable harm to the friction pair . Through a thorough examination of the flushing system, found that flushing fluid tube serious coking blockage. As the pump is at the bottom of the stripper, corrosion of piping and equipment, and contaminants and heavy polymer are all deposited on the bottom of the tower. Residue in the pump body contains significant amounts of impurities and polymers and, due to insufficient flushing, Impurities and polymers inevitably deposited in the sealed chamber, resulting in the moving ring and the ring seat, the gap between the sleeve is blocked, resulting in the ring moving in the axial direction is not flexible or even stuck, the spring was jam, can not Provide the original design pressure of 0.586MPa end face, resulting in the sealing surface can not be properly affixed and the liquid film balance is destroyed, then the seal will be slightly leakage, as the polymer and foreign particles into the friction surface, the sealing surface gradually being Wear, coupled with the axial compensation of the moving ring is not working, resulting in increased leakage seal, eventually leading to complete failure of the seal. Third, the improvement measures According to the sealing failure reasons, we targeted from the following aspects of the technical transformation: 1, change the sealing structure according to the specific conditions of the pump conditions, we use the Ai-318 type card End mechanical seal (cartridge), the main features are as follows: Precise centering by automatic locking ring. Adjustable gland can be used directly with the commonly used bolts, container-mounted structure easy to install. Spring is located outside the auxiliary seal, completely separated from the media to avoid the jamming of the spring. Ring is used in the overall floating non-mosaic, static ring is a computer analysis, the design of the Z-shaped, its advantages are good heat dissipation, heat should not accumulate. 2, the use of diesel components for flushing fluid Residual oil components due to overweight and contain more impurities and polymers, the flushing line blocked and cause mechanical seal damage, it must choose the right flushing fluid. In accordance with the ethylene process, the diesel component of the E-DA103 column will be mixed with the residual oil to produce the final product. We believe it to be more suitable to use mixed diesel as a rinse solution for the following reasons: 2.1 The blended diesel component is clean, Good compatibility. 2.2 mixed diesel components of the pressure and temperature are suitable for residue pump conditions. Mixing diesel oil fraction above 300 ℃, while the residue of the working temperature of 170 ℃, mixed with diesel fuel for flushing will not be vaporized, effectively avoiding the pump cavitation. E-DA103 bottom circulating pump E-GA105 pump outlet pressure of 0.54MPa, the outlet temperature of 80 ℃. The pressure in the sealed chamber of the E-GA103 pump can be estimated by the following formula: P = (inlet pressure + outlet pressure) /2=0.438MPa The rinse liquid pressure is about 0.1 MPa greater than the pressure in the sealed chamber and is well suited to direct E-GA105 pump outlet can be introduced into the sealed chamber. 2.3 Mixing diesel components as the rinse solution is the most economical, almost useless to increase any input, because this part of the diesel fuel components and ultimately to be mixed with the residue. E-GA103 two pumps from January 2001 began using the mechanical seal card, from the scene point of view the sealing effect is very good, there is still no signs of leakage until now, the service life of up to 2 years. The original 8B1-P machine seal each set price of 960 yuan, 2500 yuan each card-type mechanical seal, mechanical seal spare parts costs within two years alone save more than 1 million yuan, by removing the seal flushing to improve the effective pump flow and economic benefits It is obvious. Fourth, the conclusion Through the transformation of the mechanical seal of the residue pump, and the rational use of flushing fluid to improve the performance of the mechanical seal to solve the frequent leakage of mechanical seal problems and reduce equipment maintenance and repair costs to ensure the continuous and stable device produce.
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