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Unscheduled shutdowns caused by loss of control of the seal oil system and/or seal oil pumps/driven failures. Dry seals offer an alternative for dusty or extremely viscous applications that guarantees complete sealing, minimum maintenance, protection of the other system components such as the wear of the shaft and less energy consumption due to motor friction.
To eliminate many of the problems noted above, there are some dry gas seal upgrades that can improve the reliability of turbocompressors. To create the right environment for the seal, contamination must be prevented from entering the seal. From the process side, a process seal is required to prevent process gas from contaminating the dry gas seal environment. On the atmospheric side, where lubrication oil is present, the oil must be stopped from entering the dry gas seal environment. The rotating seat is fixed to the compressor rotor, and the stationary face is connected to the compressor case. The stationary face must adjust axially to maintain the gap as the rotating face/compressor rotor moves and as the compressor case expands and contracts from changes in heat and pressure. To manage axial movement, the stationary face must move freely when required, and as a result, the dynamic secondary sealing design is key to attaining a response to axial changes without resistance or delay. Therefore, a reliable dry gas seal will have a parallel gap of 150 to 200 micro-inches between the rotating seat and the stationary face even when axial movement occurs.In case of dirt and contaminations in a seal assembly, all parts and components should carefully be investigated to find a clue about where dirt or contamination comes from. A source of dirt is the seal gas itself, for example, because of insufficient or inefficient seal gas filtration. If the seal gas supply line does not appear dirty, but the seal assembly is dirty, this could indicate that the dirt or contamination entered the seal chamber directly from the compressor casing. The reason could be an insufficient seal gas pressure during transient situations, such as the startup. If painting DRY SEAL do so within a month of application. If painting at a later date, lightly sand to create a key
Figure 1 shows an example of a modern centrifugal compressor. The dry gas seals are shown at both ends of the rotor. The seals are located between the process section and the bearing. This effect should not be confused with the "beading" effect often associated with water repellents. Seal gas booster: A commonly reported root-cause for seal failures has been low pressure of seal gas at startup, which resulted in dirty gas moving to the dry gas seal from the compressor casing. It is recommended to install seal gas boosters to ensure supply of seal gas during standstill and transient conditions, if a reliable source of seal gas with suitable conditions is not available for these transient times (particularly the startup). Flowmeter on secondary vent: A good recommendation is to consider a flowmeter on the secondary vent. This can give good information regarding the secondary seal health and the overall seal system conditions. Double opposed seal - Used when the processed gas is abrasive (like hydrogen) and lower pressure designs.Adjoining Surfaces: Due to the thixotropic nature of this product, where it is applied by brush or roller, accidental contamination of non-target surfaces can usually be avoided by taking reasonable care. Material selection is critical for sealing elements. The compatibility of sealing element materials with process gas compositions in all operating cases (normal and abnormal) is important. These sealing elements require robust and sound designs to ensure long-term, trouble-free seal operation. Each of these sealing elements (U-ring, O-ring and V-ring) could easily be damaged in a careless installation or overhaul exercise. The deterioration of seal elements (such as different rings) could be due to abrasive wear from dirt or contamination from dirty process gas. Since clearances between seal faces are usually less than 4–10 microns, the seal gas passing between faces should be clean and dry. While the seal filtration requirement is 1–3 microns, 1-micron filtration systems are typical for dry gas seals. Their specifications and functionalities make them ideal for food, chemical, pulp and paper or recycling sectors.
Dry Seals can be offered in different versions with an included bearing, a split system and/or a food certification.
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The seal gas filter system: Standard filters are typically small in capacity and large in the mesh size. For dry gas seals, filters should be 2-5 times larger (in terms of capacity), and 3-4 times smaller in mesh size than typical standard models. As noted earlier, it is not uncommon for dry gas seal systems to employ filtration of 1 micron or less. Dry Seals adapt to all kind of equipments thanks to a floating design of the flange, helping to easily assemble to a bearing to simplify the system.
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