The upper half of the case is bolted and doweled to the lower half. The case is manufactured in one of two basic types:Ĭonstruction can be cast (iron or steel), forged, or fabricated by welding.Ī horizontally split case is split parallel to the axis of the rotor. The flange connections must be properly sized to limit the gas velocity as necessary. The case also contains nozzles with inlet and discharge flange connections to introduce flow into and extract flow from the compressor. Bearings are attached to the case to provide both radial and axial support of the rotor. The case houses the stationary internal components and the compressor rotor. The case (casing or housing) is the pressure-containing component of the compressor. 5-Dual-flow centrifugal compressor cross section (courtesy of Dresser-Rand). This section describes the major elements of centrifugal compressors.įig. The major components of various centrifugal compressor flowpath configurations are illustrated in Fig. In the overhung configuration, the impeller is located at the nondrive end of the shaft (outboard of the nondrive end radial bearing). Single-stage centrifugal compressors may be configured as a beam design or with an overhung impeller arrangement. All of these configurations described are beam-type designs in which the impellers are located between the radial bearings. In a double-flow arrangement, half of the flow enters the compressor through an inlet connection at each end of the casing and exits the casing through a common discharge connection in the center. For high-flow/low-head applications, a double-flow configuration is sometimes employed. For applications that require intercooling, the resulting two-section compressor may be configured in either an inline (compound) or back-to-back arrangement. When intercooling is not needed, the arrangement is usually a straight-through (inline) configuration. Multistage centrifugal compressors can be arranged in a variety of flowpath configurations employing from one to ten impellers, depending on the head required for the process duty. Multi and single stage centrifugal compressors Multi-stage centrifugal compressors 1-Two-case centrifugal compressor package (courtesy of Dresser-Rand). The compressor shown is mounted on a single baseplate and is driven by an electric motor.įig. A typical centrifugal compressor package is shown in Fig. The API has produced an industry standard, API Standard 617, which is frequently used to govern the design and manufacture of centrifugal compressors. For further discussion of this subject, see the section below on compressor selection. For this reason reciprocating compressors often are more appropriate for low-volume flow applications. Depending on the particular application, centrifugal compressor powers can range from as low as 500 hp (400 kW) to more than 50,000 hp (40 MW).Īt low volume flow rates, the width of the gas passages in a centrifugal compressor becomes narrow, and the effects of friction become significant, resulting in reduced efficiency. Power requirement is related to mass flow, head, and efficiency. Conversely, low-volume flow compressors may operate at speeds up to 30,000 rpm. Very large (i.e., high-volume) flow compressors may operate at speeds as low as 3,000 rpm. The rotating speed of a centrifugal compressor is an inverse function of diameter to maintain a desired peripheral speed at the outer diameters of the impellers regardless of the physical size of the compressor.

The compression ratio (or head) determines the number of stages (length). The physical size (diameter) of a centrifugal compressor is determined by the volumetric flow rate at the inlet. 3.1.1 Horizontally (axially) split case.

2.2 Single-stage centrifugal compressors.

2.1 Multi-stage centrifugal compressors.

2 Multi and single stage centrifugal compressors.

Compressor 4