In Northern California refineries, you’ll find many centrifugal compressors in operation that still use oil film seals. To function properly, a supply of oil must be delivered at a pressure to the seal to prevent process gas from leaking to the atmosphere. Although oil seals have been around for decades, in comparison to more modern dry gas seals, oil film seals have several inherent disadvantages. 

• Infrastructure (pump, pressure vessel, cooler, valves, and instrumentation) to supply oil at required flow and pressure entails higher operations and maintenance costs.
• Oil flowing into process gas can degrade the performance of downstream equipment or contaminate the air, thereby spoiling or contaminating the process later.
• Oil management: Process gas mixing with oil flowing through the inner seal ring must be drained to a trap system. This “sour” oil is either reclaimed or disposed of. If reclaimed it needs to be purged of process gas via heaters or degassing tanks. Any recovered process gas is routed to flair. 

Any experienced maintenance professional realizes the complexity in maintaining oil seals—oil supply, pump operations, and environmental requirements for disposal. In comparison, dry gas seals offer a far simpler solution with respect to infrastructure, operations, and maintenance. Need convincing? Let’s review the key dry gas seal advantages.

Dry Gas Seal Advantages

A dry gas seal serves the same purpose as an oil seal—prevent the flow of process gas across the seal and into the atmosphere—but takes a much simpler approach. No less than the Environmental Protection Agency (EPA) Natural Gas STAR Program has evaluated the dry gas seal technology and published some compelling reasons to make the change. The key dry gas seal advantages include:

• Lower leakage rates: When process gas mixed with oil is vented to atmosphere, leakage for dual oil seals can range from 40 to 200 scfm, depending on compressor size and operating pressure. In normal operations, dry seal leakage is 0.5 to 3 scfm across a seal, depending on seal size and operating pressure. 
• Eliminate oil leakage that contaminates process gas and can lead to degradation of the pipeline and other downstream equipment. 
• Lower power consumption: Oil seals use 50 to 100 kW per hour to run the pump and other components. Dry seals don’t need oil circulation pumps. Energy usage is about 5 kW per hour. 
• Design simplicity leads to improved reliability, reduced unplanned downtime, and lower maintenance costs. 
• Environmental: Eliminate costs and risks associated with oil supply, system maintenance, and disposal that could risk fines or sanctions from BAAQMD or Cal/OSHA. 

The relative simplicity of a dry gas seal and seal support system contributes to lower operational and maintenance costs. Multiplied by the number of compressors in a refinery, the long-term savings can be significant. 

Seal Support System Configuration Is Critical  

Although dry gas seals and their seal support systems are much simpler than oil seal arrangements, proper configuration—seal type and support system—is critical in fully realizing dry gas seal advantages. Because of the exacting tolerances of dry gas seals, a seal support system must be configured to deliver clean, dry gas. A properly-configured dry seal support system may include: 

Particulate filters for seal gas cleanliness. Gas seal manufacturers require the seal gas to be dry and free of particles 3 μm or larger. If the seal gas is an inert gas like nitrogen which is usually very clean, filtering is not required. Seal gas sourced from the pump discharge will require a filter to remove contaminants that can foul a dry gas seal. 

Condensation filters remove moisture. If the seal gas contains moisture that would undermine dry seal performance, a coalescing filter is needed. 

Seal gas pressure across the entire operating range. A reliable source of seal gas source must be available at a pressure higher than the required sealing pressure throughout all operational phases of the compressor—startup, running, idle, and shutdown. The actual pressure required will vary per process conditions. 

When configuring a dry gas seal support system like the two examples mentioned above, a comprehensive engineering analysis of the seal gas supply—source, quality, and composition—is required to determine to which components are incorporated into the design to deliver clean, dry gas at the proper pressure and flow.

Maximize Dry Gas Seal Advantages With Expert Guidance

When you’ve made the decision to replace oil seals with dry gas seals and consulted with your dry gas seal vendor regarding the appropriate dry gas seal designs, it’s best to then consult with a Bay Area dry gas seal support vendor like Swagelok. Here’s why.

Swagelok offers: 

• On-site evaluation of dry gas seal support system requirements, taking into account factors such as process gas, dry gas seal type, processing conditions, compressor infrastructure, gas seal supply source, and usage cycles that influence support system design
• Detailed technical documentation, including CAD drawings, regarding the proposed dry gas seal support system design for your review and approval 
• Easy access and efficient maintenance, locating commonly serviced items such as filters and regulators on the seal support system control panel
• ISO 9001 standards guide fabrication and testing of seal support systems prior to delivery to your site
• On-going technical support, by phone, email, or on-site to help ensure optimal performance of the compressor, gas seal, and seal support system

With decades of experience supporting the needs of the petrochemical industry in Northern California, there’s no better partner to help you in making the transition from oil seals to dry gas seals and support systems. 

To find out more about how Swagelok Northern California can help you benefit from the advantages of dry gas seal support systems by providing expert consulation and Assembly Services, contact our team today by calling 510-933-6200.

About Paul Lesnau | Sales Manager, Business Development Manager, and Field Engineer

Paul holds a B.S. in Mechanical Engineering from North Dakota State University. Before joining Swagelok Northern California, he was the West Coast Regional Sales Manager for an organization focused within the pneumatic and hydraulic industry where he supervised product distribution throughout the western United States, Canada, and Mexico. While in this role, he was able to help provide technical and application-specific expertise to customers and distribution to drive specifications.