In partnership with the compressor manufacturer, National Grid settled on a solution that EagleBurgmann specifically developed to adress such problems. “One out of five dry gas seal failures is caused by a contamination with bearing oil”, explains Alastair Dodd, key account and project development manager at EagleBurgmann. “To eliminate this problem, we developed the CobaSeal.” The CobaSeal is a coaxial separation seal that is designed similar to a dry gas seal and replaces the existing carbon ring separation seal. It consists of a rotating ring made of stainless steel and a stationary face from silicon carbide. To achieve additional robustness, both sliding faces are coated with special EagleBurgmann high performance iDLC (in situ diamond-like carbon).
Nitrogen is guided between the faces through axial bores in the stationary face. It acts as a separation gas and flows off towards the inner as well as outer edge of the sealing rings, thereby creating a stiff gas film that prevents the sliding faces from touching. This coaxial design addresses many of the problems commonly associated with traditional carbon ring seals, allowing for wearfree operation with extremely low leakage. The gas film protects the sliding faces in all operating modes that occur during operation of a compressor connected to a major gas delivery network, such as “slow roll”, “turning gear” and “coast down”. Furthermore, vibrations at the compressor shaft that led to malfunctions at the previous separation seal are now compensated reliably.
Extensive testing to simulate all operating scenarios
In Nether Kellet, the CobaSeal saw its very first practical application. “You can understand that the customer was a little cautious”, explains Alastair Dodd. “But our comprehensive research and development efforts as well as testing of the seal convinced National Grid that they weren’t handed a prototype, but in fact a fully qualified and proven product.” Another factor in favor of EagleBurgmann was the relationship to the customer that had grown over several decade since EagleBurgmann first delivered products to National Grid. “Due to the constantly high standard of our products and services, the client perceives us as a technology leader in the field of turbomachinery sealing solutions”, summarizes Dodd.