Page 101 - Compression Machinery for Oil and Gas

90 SECTION II Types of Equipment

The API 617 and 686 standards are quite detailed and specific in regards to
support structures and alignment provisions and should be followed. Base
plates, or individual sole plates for compressor and driver, should be aligned
before grouting on a concrete subbase or anchoring to structural steel supporting
members in order to provide a proper basis for alignment and leveling of com-
pressor and driver shafts. Mounting surfaces must be flat, have good surface
finish, and be parallel to each other. Jack screws are provided to allow shifting
the compressor horizontally and axially. Vertical jack screws are provided to
raise the compressor for shimming.

Auxiliary Systems/Supporting System
Seal Systems

The primary purpose of a seal system is safety. Emissions reduction, while an
objective, is of secondary importance.

Dry Gas
Most centrifugal compressors are equipped with DGSs as shaft end seals, as
they are currently the best way to meet the requirements for safety, reliability,
and economy. In principle, four different types of DGS arrangement are used,
see Fig. 3.58. All arrangements have in common that treated process gas is
injected at between the process seal and the primary seal. The process seal is
shown as a labyrinth. The majority of the seal gas flows across the process seal
and a minor amount flows across the primary seal faces. The amount of seal gas
is designed to maintain a minimum velocity in the gap of the labyrinth. This
prevents migration of untreated process gas into the area of the DGS. Typical

FIG. 3.58 DGS system.