January 21, 2020 | 4 minute read
Centrifugal compressors equipped with wet oil seal technology used in the oil and gas, and petrochemical industries, are generally acknowledged as being the leading source of methane emissions offshore and the fourth most significant onshore. Facility operators, charged with mitigating methane emissions across oil and gas production, transmission and storage sectors, are challenged with evaluating multiple technological approaches to determine the ideal system solution for their rotary machinery applications, along with optimized cost efficiency and maximized methane recovery.
Sealing systems are vital to maintaining pump efficiency, reliability, energy consumption, water usage and control of emissions to the environment. These factors can materially facilitate a process plant in achieving total lifecycle cost reduction and sustainability objectives. In support of achieving these objectives, sealing performance can be considerably improved in most centrifugal pump applications by upgrading from oil seals to dry gas seal technology.
The benefits of dry gas seals include the following factors:
Dry gas seals are non-contacting, dry-running mechanical face seals that consist of a mating (rotating) ring and a primary (stationary) ring. When operating, lifting geometry in the rotating ring generates a fluid-dynamic lifting force causing the stationary ring to separate and create a gap between the two rings.
Machined-in lift profiles on one side of the seal face direct gas inward toward an extremely flat portion of the face. The gas that is flowing across the face generates a pressure that maintains a minute gap between the faces, optimizing fluid film stiffness and providing the highest possible degree of protection against face contact. The seal's film stiffness compensates for varying operations by adjusting gap and pressure to maintain stability.
In contrast to the oil seal technology, gas seal technology eliminates the need for oil lubrication and the resulting need to address methane that becomes entrapped in the oil, thereby significantly reducing emissions by design.
Elimination of Fluid Consumption and Leakage
Oil seals used in abrasive pumping applications require significant volumes of liquid to be injected into the seal chamber. Dry gas seals require no flush liquid to be injected into the seal chamber, consequently, there is no leakage to the atmosphere.
Reduced Power Consumption
The amount of power required to drive a dry gas seal is up to 80 percent less when compared to oil seals, primarily because the seal faces have less frictional energy losses due to the extremely precise mating between the stationary and rotating elements. Additional energy reduction requirements take the form of the eliminated need for flush liquid to be pumped into the seal, which is required with oil seals.
Dry gas seal technology is one of a very few technology solutions that has the potential to simultaneously meet the needs of industry, governments and other stakeholders.