In the 1970s and 1980s, multistage centrifugal compressors in the 3,000 acfm (about 5,000m3/hr) and lower flow ranges were largely confined to instrument and plant air duties. Three stages with intercooling were common. Only a Colorado-based centrifugal compressor manufacturer concentrated on developing vertical single-stage machines.1 Forward-looking users applied these new single-stage machines in steam recompression and select process gas services, as shown in Fig. 1.1
| Fig. 1. Inlet volumetric flow vs. pressure ratio |
for single- and four-stage integrally gear-
driven compressors. Source: Sundyne LLC,
New compressor for gas applications
In the early 2000s, the compressor manufacturers began to capitalize on four decades of know-how regarding single-stage, high-speed, low-flow centrifugals.1 Using API-617 and API-614 standard baseline-compliance guidelines, newly designed multistage compressors (Fig. 1) were developed for virtually all process gases.2 The inlet flows and achievable pressure ratios for four stages quite obviously bracket ranges that were previously reserved for positive displacement machines. Benefits with the multistage compressor in gas applications include high efficiencies (80%+) and low maintenance requirements. Accordingly, these attributes make integrally geared compressors ever more attractive.
Fig. 2 is the general layout of a typical multistage centrifugal compressor. It is a modular design with drivers from 40 kW to 3,000 kW. Technological advances become evident as reliability professionals consider the design details such as deflection pad bearings, impeller attachment and tandem dry-gas seals with separation labyrinths, as summarized in Table 1. This compressor manufacturer plays a lead role in its commitment to delegating the design and manufacture of seal support systems to the companys in-house talent.
| Fig. 2. General layout of a four-stage process |
gas compressor. Source: Sundyne LLC,
Together with reciprocating and twin-screw compressors, well-designed integrally geared centrifugals machines open new possibilities for modern users. One particular manufacturer has built 12,000 of these machines. Because these designs are mature and provide up new possibilities for many users, they will be the subject of a follow-up article planned by Hydrocarbon Processing.
During a recent factory visit, HPs reliability editor was impressed by the packaging: spotlessly executed welds, intelligently placed overhead air-cooled heat exchangers, piping and conduit flawlessly configured. The manufacturers approach to closed-loop testing differs from the standard of convenience occasionally practiced in the compressor manufacturing industry. We observed that rather expensive refrigeration gas mixtures were being used. Test loop gas parameters simulated and closely matched the purchasers ultimate process gas operating conditions. Our opinion for the products and process: Well done.
1 Colorado-based Sundyne LLC concentrated on developing vertical single-stage (BMC) machines.
2 Sundyne LLC developed the multistage LF2000 compressor.
Heinz P. Bloch resides in Westminster, Colorado. His professional career commenced in 1962 and included long-term assignments as Exxon Chemicals regional machinery specialist for the US. He has authored over 540 publications, among them 18 comprehensive books on practical machinery management, failure analysis, failure avoidance, compressors, steam turbines, pumps, oil-mist lubrication and practical lubrication for industry. Mr. Bloch holds BS and MS degrees in mechanical engineering. He is an ASME Life Fellow and maintains registration as a Professional Engineer in New Jersey and Texas.