Dry Gas Seals For High-Pressure Gas Injection Compressors

By Peter Droescher, Michael Sattler, Andreas Schruefer and Armin Laxander, EagleBurgmann Industries, Germany | June 2011 Vol. 238 No. 6

Figure 1: Tandem dry gas seal with intermediate labyrinth.

The escalating worldwide demand for oil and the continuously rising prices are driving oil companies to explore new oil field resources. However, exploration also incurs increasing expense in terms of technology. Many of these projects have a common need in that natural gas, which is associated with crude oil, has to be re-injected into the reservoirs.

The required injection pressure can reach values up to 800 bar (11,600 psi). Sophisticated ultra-high-pressure centrifugal compressors cover this application. The seal solution for the main shaft seal of the machines is based on the well-proven Dry Gas Seal (DGS) technology.

This article describes Dry Gas Seal solutions in centrifugal compressors used in extreme high-pressure service for gas injection. It provides a summary of the R&D and qualification programs for the seals and explains design features and operating limits.

Leading oil companies are continuously increasing their investments to satisfy global hunger for energy. A typical example is the exploration of the Tengiz and Kashagan oil fields in the Caspian region. The Kashagan field, one of the largest reservoirs discovered in the past 30 years, has an estimated recovery of 13 billion barrels of oil. One major technological challenge is compressing the associated, highly corrosive sour gas to ultra-high-pressure for re-injection. A compressor train, consisting of three centrifugal compressors driven by a 30-MW gas turbine, undertakes the high-pressure service.

Based on the expectation of a growing demand for ultra-high-pressure shaft seals, EagleBurgmann, in 1996, started an R&D project to develop dry gas seal technology for extreme pressures. In 2000, the European Union sponsored a joint project, the Method Project. Among the project partners were the University of Florence, GE Oil & Gas and EagleBurgmann. The Method Project’s objective was to evaluate the feasibility of a DGS operated at a pressure of 560 bar (8,120 psi). From this project were derived valuable insights into the special requirements for a DGS operated under extreme conditions.

In 2005, EagleBurgmann was invited by GE Oil & Gas to join a qualification program for a DGS to be operated at 425 bar (6,160 psi).

Operating Conditions
Gas-injection service at extreme high pressure is undertaken by a compressor train, consisting of three centrifugal compressors (LP, MP, HP), driven by a gas turbine. Table 1 shows the typical design conditions for the Dry Gas Seals.

Table 1.jpg
Table 1: Typical design conditions for high-pressure dry gas seals.