How a Seal Support System Aids Recovery of Hydrocarbons

Refinery processes involving light hydrocarbons and high vapor pressure fluids present challenges in ensuring that that they remain safely contained within the systems, piping, and pumps involved in the process. Centrifugal pumps that drive these processes present critical points of potential leakage. Dual mechanical seals and seal support systems that deliver buffer or barrier fluid to the seal are the methods of choice for maintaining pump integrity and avoiding any leakage to the atmosphere. 

API Plan 72 is often chosen to supply a clean, dry buffer gas (typically nitrogen) between the dual seals at a pressure lower than the process pressure. A pressure regulator sets the nitrogen pressure, which is usually no higher than 10 psi (0.68 bar) as it enters the seal chamber. This allows minor amounts of process fluid to leak across the inboard seal into the buffer gas. The nitrogen dilutes process leakage from the inboard seal and sweeps it to a vapor recovery collection system. 

If the leakage is significant, or any loss of process fluid equates to lost revenue or environmental pollution, the refinery may choose to return the leakage captured in the vapor recovery system to the process rather than vent it to flare. API Plan 76 is often recommended as the seal support system for the recovery of non-condensing leakage.  

API Plan 76: Seal Support System for Recovery

API Plan 76 is a non-condensing leakage collection system. It collects leakage from the inboard seal in centrifugal pumps where process fluid leakage does not condense between the seals at ambient temperatures. This vaporous leakage from the inboard seal exits through the containment seal vent port located at the top of the outboard seal gland. The orifice is sized to create the necessary back-pressure for a pressure transmitter to send an alarm in the event of a seal failure. Vapor is then transported to a recovery system. This seal support system for recovery of leakage ensures virtually no process emissions from the outboard containment seal in a dual seal arrangement.

Designing a Seal Support System for Recovery Optimization 

Although the functional designs of API Plan 72 and API Plan 76 are standardized, not specified, there’s good reason to work with an experienced fluid systems engineer when implementing a new system or updating an existing seal system. They’ll evaluate the specific process conditions and consider factors that influence system design. 

• Design decisions for API Plan 72 may include the type of buffer gas and source, buffer gas pressure, a coalescing filter to remove moisture or particulates, a flowmeter, and possibly a pressure gauge or transmitter to monitor buffer gas. 
• Design decisions for API Plan 76 will likely include tubing diameter to transport vapor to the vapor recovery system, a flow control orifice size to generate required back pressure, and a pressure gauge and/or a pressure transmitter with an alarm to alert when the pressure in the vapor collection system increases—indicating unacceptable leakage across the inboard seal.

These design decisions are critical to the proper functioning of the mechanical seal support system and its ability to effectively recover hydrocarbon leakage into the seal chamber.

Seal Support Systems for Recovery: A Combined Solution

Because API Plans 72 and 76 are frequently deployed together, the systems can be combined into a single panel to simplify installation, management, and maintenance. The combined panel controls the delivery of buffer gas to the dual mechanical seal, as well as collects process fluid leakage into a recovery system.

Panel with combined API Plans 72 and 76

API Plans 72 and 76 connected to pump

Swagelok Expertise Aids Hydrocarbon Recovery

If any of your currently installed mechanical seal support systems are underperforming in their ability to capture and recover hydrocarbons because of changes to process conditions, aging components, maintenance difficulties, or poor design and implementation, Swagelok will work with you to understand the issues and recommend solutions that eliminate those problems. Our local Field Engineers will conduct an onsite analysis of the pumping process, identify factors that undermine performance, and recommend components, design changes, upgrades, or even replace seal support systems, if necessary.

For more than 50 years, Swagelok has been serving the needs of the chemical and petroleum industries in Northern California. Swagelok maintains an extensive inventory of top-quality fluid system components in our Bay Area facilities. Our local technicians can quickly build and test any assemblies or complete seal support systems prior to delivery. When you work with Swagelok, you benefit from our refinery experience, the convenience of local support, and the backing of worldwide Swagelok industry expertise.

To find out more about how Swagelok Northern California is helping refineries design and deploy seal support systems to aid hydrocarbon recovery, by providing expert consultation and Assembly Services, contact our team today by calling 510-933-6200.

Morgan Zealear | Product Engineer – Assembly Services

Morgan holds a B.S. in Mechanical Engineering from the University of California at Santa Barbara. He is certified in Section IX, Grab Sample Panel Configuration, and Mechanical Efficiency Program Specification (API 682). He is also well-versed in B31.3 Process Piping Code. Before joining Swagelok Northern California, he was a Manufacturing Engineer at Sierra Instruments, primarily focused on capillary thermal meters for the semiconductor industry (ASML).