July 21, 2020 | 5 minute read
API Standard 692: Dry Gas Sealing Systems for Axial, Centrifugal and Rotary Screw Compressors was first published in June 2018. It covers the minimum dry gas sealing system requirements for use in the petroleum, chemical and gas industry services as described in API 614, and is increasingly being used to specify dry gas seals on new and upgrade projects.
It is a very comprehensive document, and the result of a great effort from expert users, specifiers and vendors, with the intent of increasing the reliability of dry gas seal systems. It is undoubtedly a significant document that will have an impact on our industry for years to come.
The document is divided into four parts:
- Part 1: General requirements
- Part 2: Dry gas seals
- Part 3: Dry gas seal support systems
- Part 4: Installation and commissioning
John Crane has published a guide to describe the main changes between the API 614 and the new API 692 design standard for seal gas systems. Read it here.
Purpose of a Seal Gas Booster
API 692 requires the use of a booster to consolidate the function of the seal gas support system, unless the system design eliminates the conditions when a booster is needed. The seal gas booster is used to guarantee supply of conditioned gas flow and pressure differential to the dry gas seals at compressor standstill.
As the title of API 692 suggests, its purpose is to stipulate the minimum requirements for dry gas sealing systems, or the conditions you need to run your centrifugal compressors reliably.
Reliable dry gas seal performance and centrifugal compressor operation is dependent upon a constant supply of seal gas at a pressure above that of the process. In normal dynamic operation, the seal gas flows across the primary seal toward the primary vent, and across the process labyrinth, back into the process. This creates a pressure differential that prevents dirty, unfiltered process gas from entering the dry gas seal (seal gas is cleaned and conditioned process gas from discharge, so as to be completely dry and free of particulate contamination).
However, compressor duty cycles often require equipment to be on standby mode and when the machine is stationary there is no flow through the system, and no pressure differential between the gas seal and the process gas, which can then leak back into the seal. Deposits arising from a lack of gas flow can lead to poor seal performance and a lower mean time between repair.
Solutions for Conditioned Gas Flow
There are various solutions available to provide alternate sources of conditioned gas flow and pressure differential, but options can be limited when used in midstream and upstream applications where sites are more remote and extra services are scarce. In such scenarios, a booster is often the simplest and most cost-effective way to sustain reliable operation. Seal gas boosters are specified when there are no alternative solutions available for supplying the gas at the appropriate pressure to the compressor gas seals during settle-out conditions. Even on less remote sites, alternate seal gas supply is not always part of the system design as system design is dependent on customer specifications.
Watch the video below to learn more about the GCU Seal Gas Booster and how it works with API 692 standards to boost operational performance of dry gas seals and systems.
API 692 also specifies required seal gas booster functionality and performance. The booster is used to establish the minimum pressure differential between the supply line and process gas. This differential allows the dry gas seal to run on a clean gas across the seal faces.
- The booster will operate when process compressor is idle or pressurized, when there is insufficient differential pressure provided by the main process compressor.
- The booster shall be sized to provide the seal gas normal flow. The vendor shall supply the basis for these requirements for the range of all specified utility conditions.
- API692 requires additional monitoring of reciprocating boosters. John Crane Seal Gas Booster is a centrifugal booster cycle count is not required for centrifugal boosters. Required flow rates, and additional monitoring of reciprocating boosters, suggest that centrifugal boosters are preferred for API692 compliance.
Introducing John Crane’s GCU Seal Gas Booster
John Crane recently launched its new GCU Seal Gas Booster to support its extensive range of dry gas seals and seal gas filtration and seal gas support systems.
The GCU seal gas booster has been designed with a focus on operational efficiency and reliability; centrifugal operation, magnetic bearings, electrical motor power and zero preventive maintenance enable the booster to run trouble-free between compressor shutdowns. It will provide a reliable, automatically triggered source of clean, dry process gas, with the result that your dry gas seals remain in optimum operational condition and equipment is always ready, allowing for trouble-free start-up the first time, and every time.