The dry gas seal of the centrifugal compressor used in petrochemical industry is a non-contact seal. Its function is to create a fluid dynamic pressure effect during the seal operation by opening a shallow groove of a certain shape on the seal surface, forming a seal between the seal end faces. The layer is very thin in air film, so that the seal works in a non-contact state. Since the sealing surface does not contact, the friction heat generated by the sealing is small, the life of the sealing ring is long, and the sealing does not require a complicated oil sealing auxiliary system, and the cost and maintenance cost are low. In order to achieve localization of dry gas seals, we have been researching and developing dry gas seals since 1992.
Due to too many factors affecting the performance of dry gas sealing, we only optimize the following main geometric parameters during the development process. That is, the groove depth H of the spiral groove of the sealing surface; the helix angle A of the spiral groove of the sealing surface; the number of grooves n of the spiral groove of the sealing surface; the groove width and the width ratio a of the spiral groove of the sealing surface; the groove length and the dam of the spiral groove of the sealing surface Length ratio b; When optimizing, one of the parameters is changed, and the remaining parameters remain unchanged. The results of the above five parameters optimization (the results are dimensionless) are explained below.
The effect of fluid machinery on the dry gas seal performance from the depth of the spiral groove. The load capacity, leakage, stiffness, and just leak ratio have maximum values ​​(maximum values ​​appear between H = 2.54.5), indicating that the groove depth of the spiral groove has an optimum value.
Influence of the helix angle The choice of the helix angle of the spiral groove of the sealing surface has a great influence on the sealing performance. The helix angle is too large or too small, which will affect the stability of the sealing work. When the helix angle is between 10b18b, the sealed film stiffness and the near-leakage ratio of the seal are both larger, the bearing capacity is also larger, and the leakage of the seal is also larger.
The influence of the length of the spiral groove on the sealing performance was analyzed by the finite difference method. When b is less than 1.5, the seal film stiffness, the near leak ratio and the load carrying capacity change are large. When b is 23, the stiffness has a maximum value. Moreover, the stiffness changes little in this area. When b is 2.53.5, the just leak ratio and load carrying capacity have a maximum value. Therefore, when b is about 2.5, the seal has the best performance. The influence of the width of the spiral groove on the groove width of the spiral groove also has a certain influence on the sealing performance.
The influence of the number of spiral grooves is shown in Fig. 5. As the number of spiral grooves increases, the rigidity of the seal, the ratio of the leaks, and the bearing capacity increase, when the number of grooves reaches 40 or more. The four curves change very slowly. Since the number of slots is larger, the processing is more difficult, so the number of slots is preferably within 40.
The inclined bottom spiral groove adopts the following approximation method for the inclined bottom surface, that is, the step surface is used instead of the inclined surface, and when the number of the step surfaces is large, it approaches the inclined surface. When the ratio of the groove depth to the root groove depth is between 11.1, the load carrying capacity, leakage amount, stiffness, and just leak ratio vary greatly. When between 1.11.2, the four curves change less and reach a maximum. When it is between 1.21.4, the four curves change greatly, showing a rapid decline. It shows that the bevel groove design has an optimal parameter, and the sealing performance parameters are relatively stable.
The groove depth of the spiral groove root; H indicates the groove depth at the opening of the spiral groove. There is no spiral angle in the radial groove of the radial groove. Therefore, the optimization parameters of the radial groove are only the groove depth, the groove length, the groove width, and the number of slots. It can be seen from the calculation results that the influence of the above parameters on the sealing performance is similar to that of the spiral groove, but the bearing capacity and the film stiffness are smaller than the spiral groove.
The three dry gas seal groove structures are optimized. The results show that the oblique bottom spiral groove dry gas seal structure is the best. The dry gas seal of this structure has the maximum load capacity and the just leak ratio, but the leakage is correspondingly larger. . The performance of the radial groove seal is much worse than that of the spiral groove. The load carrying capacity is about 10% lower than that of the spiral groove seal, and the film stiffness is only 1/3 of the spiral groove seal. This is due to the radial groove seal. There is only a step effect in operation, and there is almost no compression effect. The spiral groove seal has both a step effect and a compression effect, and the parameter directly affecting the compression effect of the spiral groove is the helix angle. There is therefore an optimum helix angle that produces the greatest compression effect.
The performance of the flat-bottom spiral groove seal is not much different from that of the oblique bottom spiral groove seal, and the processing of the inclined bottom spiral groove is quite difficult. Therefore, the flat-bottom spiral groove type is selected. After the experiment, the sealing performance reached the design requirements. It was supplied to Zhenhai Refining & Chemical Co., Ltd. at the end of April 2001, and was officially put into operation in early May of the same year. It has been operating safely ever since.
The stability and reliability of the spiral groove dry gas seal designed according to the optimized result are very good, and the seal realizes the film lubrication. The test and industrial operation prove that the dry gas seal has no wear during operation, but only after the parking is repeated for many times, there is a very small friction trace. The spiral groove dry gas seal has good sealing performance and the gas leakage is small (always stable/h) Indicates that the dry gas seal product designed and manufactured is successful. Comparing these four combinations, it is found that the main factor affecting the jet flow field is the distance between the main stream and the wall. The distance between the wall and the main stream will affect the mainstream range and the formation of the return flow, which will affect the combustion of the burner fuel and the self-circulation of the flue gas. The flow field of the nozzle-attached jet can be conveniently obtained by PIV velocity measurement technology. In the first time, the experimental study on the nozzle wall jet was carried out. The jet velocity field of the four bevel and nozzle combinations was considered, which provided a certain data basis for the design of the flat flame burner for the double-sided radiation coking furnace.
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