Page 128 - Compression Machinery for Oil and Gas

Centrifugal Compressors Chapter 3 115

(12,000psig) [25a]. The Petrobras Tupi III project also deserves mention due to
achieving 8120psi (560bar) during compressor test with an extremely high-
density gas [25b]. The Tupi III compressor is said to have the highest discharge
gas density ever achieved in a centrifugal compressor at 556.1kg/m 3
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(34.72lb m /ft ). Interestingly, all three of these projects were by different
original equipment manufacturers (OEMs).
Most projects do not set new records for pressure or gas density. Fig. 3.75
shows a modern gas reinjection centrifugal compressor. A cross section of this
compressor is shown in Fig. 3.76. This compressor was used for gas reinjection
at 560bar (8100psia). It was tested out to a pressure of 648bar (9400psia) with
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associated discharge density of 426kg/m .
There are several items worth noting for this compressor. The compressor
shown in Fig. 3.74 has the following features:
l Thickened barrel design for high pressure, rated at 700bar (10,100psi).
l Thrust brakes at stages 2–5 for thrust management and rotordynamic stabil-
ity improvement (Fig. 3.77).
l Hole-pattern balance piston seal with swirl brakes in front to improve rotor-
dynamic stability (Fig. 3.78).
End users manage their risk by requiring class 1 testing for certain applications.
For one end user, applications above roughly 30MPa get special attention in
terms of requiring a class 1 test [26]. Still, other end users may manage their
risk differently by requiring rotordynamic stability testing in lieu of a class 1
test [27], rotordynamic stability test in addition to a class 1 test [27a],or

FIG. 3.75 Gas reinjection compressor. (Figure 8 from Y. Bidaut, U. Baumann, S. M. H. Al-Harthy,
Rotordynamic stability of a 9500 psi reinjection centrifugal compressor equipped with a hole pat-
tern seal—measurement versus prediction taking into account the operational boundary conditions,
in: Proceedings of the Thirty-Eighth Turbomachinery Symposium, Turbomachinery Laboratory,
Texas A&M University, College Station, TX, 2009, pp. 251–259.)