Pipeline Compressors Dry Gas Seal Retrofits

Methane emissions are classed as one of the most important contributors to climate change. This greenhouse gas has a global warming potential 21 times that of Carbon Dioxide. In the Oil and Gas industry, pipeline compressor emissions have been identified as an important source of methane released into the atmosphere. Wet seals (oil seals) technology will not meet new targets being set for methane emissions. John Crane has therefore developed a new dry gas seal design with a significantly narrower cross section to allow historically high value compressor assets to continue to function without the need for extensive redesign or replacement. This dry gas seal has been specifically engineered to replace wet seals within older centrifugal pipeline compressors. The main reasons associated with conversion from wet seals to dry gas seals include: moving to non-contacting technology which reduces seal wear issues, reduced operating costs from removal of oil seal supporting systems including degassing equipment, lower energy consumption due to the shear losses associated with oil seals, reduced maintenance costs by having a simpler supporting system and less frequent routine maintenance, and reduced emissions. Wet seals are typically compact in nature and are therefore very flexible in how they can be installed into a compressor. Traditional dry gas seals occupy a larger cross-sectional footprint and therefore it was necessary to develop a brand new gas seal that can retrofit into the same cavity without the need for expensive and prohibitive machining of the compressor shaft or housing. The resulting gas seal design is significantly compact when compared to a standard gas seal, yet provides sealing at maximum pipeline compressor duties of up to 120barg and 100m/s. In order to create a compact seal, John Crane has significantly reduced the cross section of the rotating (mating) and stationary (primary) sealing faces. This change brings about an increased level of complexity associated with dry gas seal design. In-house FEA and CFD simulations have been used to optimize the seal design and groove patterns. Results documenting the extensive design and simulation activities will be presented to demonstrate effective separation of the sealing faces throughout the entire seal performance envelope. A number of tests were specifically designed to thoroughly validate the seal design by simulating compressor field conditions. The product has undergone a series of testing through its entire performance envelope for pressure, speed and temperature. Specific accelerated tests were also designed to replicate the seal lifetime. The paper will describe the test setup and present the validation results.