In an integrally geared centrifugal compressor (IGCC), several pinion shafts are arranged around a large central bull gear. An impeller (usually a 3D semi-open one) can be mounted on each end of a pinion shaft. Currently, machines with up to 10 impellers (5 pinions) are available. The compressor shafts can run at high rotational speeds — up to 75,000 rpm. The bull gear generally is driven by an electric motor, which can be a conventional 1,500–1,800-rpm unit or a high-speed 3,000–3,600-rpm one.
In contrast to conventional centrifugal compressors in which all impellers run at the same speed, in IGCCs each pinion can run at a different speed. Thus, every impeller pair can operate at its optimum aerodynamics speed. This is an important advantage — particularly for gases with medium or high molecular weights — that results in higher efficiencies than those of conventional compressor designs.
Protecting electrical controls and equipment within food and beverage plants presents unique challenges due to the sanitation requirements of the hygienic environment.
