To eliminate many of the problems noted above, there are some dry gas seal upgrades that can improve the reliability of turbocompressors.

The following points shall be thoroughly analyzed prior to the replacement of Liquid seals with DGS. This effect should not be confused with the "beading" effect often associated with water repellents. Large numbers of dry gas seal assemblies have problems because of an issue with an O-ring or a V-ring. There are many sealing elements (O-rings, V-rings, U-rings, etc.) in a seal assembly, which can cause seal operational problems. If an O-ring or a V-ring allows gas to bypass, the gas stream would pass up the primary vent. In many cases, the deterioration of a ring or a sealing element may explain the rise in the primary vent flow, which could be confused with seal face deterioration.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. The oil carryover from the upstream can generally be a problem. Compressors in the upstream — whether oil-flooded screw compressors, oil-lubricated reciprocating compressors, or old-fashioned, oil-sealed turbocompressors — can introduce oil into the gas flow, which usually creates some problems for compressors with dry gas seals in the downstream. Other installations, such as reactors and processing equipment, can contaminate the gas with dirt, dust or liquid in normal or abnormal situations.

John Crane Inc. issued a patent for dry gas seals in 1968 with field applications beginning in 1975, though the technology is now widely available among seal manufacturers. When the technology is aimed at correcting the problems with dry gas film environments by eliminating friction. Soon, the technology became a common replacement for other lubricated seals. The patented spiral-groove (constant depth / variable diameter) technology of the dry gas seal allows for easy lifting and separation of seal faces during operation. Also the dry gas seal lift geometry can be unidirectional or bidirectional, depending on the specific design of the lifting geometry. 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. Differential pressure on any seal stage: Another good recommendation is the installation of differential pressure for each seal stage including the primary seal, the secondary seal, and the barrier seal (acting as the tertiary seal). In this way, the differential pressure (and the condition of each seal) can be assessed, verified and compared to results obtained by other instrumentation and monitoring systems.

Choosing a Seal Configuration

Over the years, features in dry gas seals have changed, improving the technology. Many small adaptations have taken place to correct the flaws or deficiencies of past dry gas seal systems. These changes range from adjusting the hardness/durometer of an o-ring for handling high-pressure dry gas seals to using polymer gaskets, which have no depressurization limits and will not take a set such as elastomers do. The question is, “Although these are small improvements, how do they affect the reliability of dry gas seals?” An important section of a dry gas seal is the vent system. Special attention is required for the primary vent system (vent system of primary seal). In the primary vent system, a vent rupture disc is typically installed in parallel with the vent line to rupture at a set pressure and prevent excessive pressure to instruments on a primary seal failure. A pressure-relief valve (PRV) may be installed instead of rupture disc, particularly for large machines. 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.

In a case study for a turbocompressor, the original seal filter meshing was 4 microns. The upgraded seal filter was a filter system with the 1 micron mesh size and the dimensions 2.5 times larger than the original filter. As the population increases more and more buildings are going to be built to accommodate a already over populated world and if the problems of today’s technologies are not changed when we have solutions to change them, then our planet will just spiral out of control! Figure 2. An example of a 3D model of a modern dry gas seal. The dry gas seal details are shown in this 3D model. The range of Dry Seals is specified for powdered or scarcely lubricated products, applications that are not possible to work with secondary cooling or lubricating fluids due to the peculiarities of the materials of sealing, such as all those related to food. Available utilities can affect which seal configuration is used. Other aspects to consider include: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. The quality of the seal supply gas must also be assessed to ensure that no liquids are formed during changes in gas pressure and temperature. The seal gas will drop in pressure from the supply pressure all the way to the atmospheric side as it leaks through the dry gas seal. Factors that can influence seal gas temperature are process gas temperature or environmental conditions, which can drop the temperature of pipes or the compressor to the point that liquid will form in the seal gas supply. All these conditions must be identified to ensure that no liquids form that will affect the operation of the dry gas seal during dynamic as well as static conditions. 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.