Compressors high-speed

Positive-Displacement Compressors Reciprocating compressors are built in different sizes (up to about one megawatt refrigeration capacity per unit). Modern compressors are high-speed, mostly direct-coupled, single-ac ting, from one to mostly eight, and occasion-aUy up to sixteen c inders. 

Synchronous speeds are calculated by Eq. (29-10). Speeds above the limits given are obtained through step-up gears large high-speed centrifugal compressors are examples. Two-pole (3600 r/min at 60 Hz) synchronous motors can be built but are uneconomical in comparison with geared drives. 

Kenneth, E. A. and Robert, X. P, Influenee of Gas Seals on Rotor Stability of a High Speed Hydrogen Reeyele Compressor, 17th Turbomaehinery Symposium, Texas A M University, 1982. 

Monitoring should include the usual parameters worthy of surveillance in high-speed turbo machinery the temperature of journal bearings, vibration and axial position of the pinions, inlet and discharge temperatures combined with discharge pressure from the individual compressor stages, and various lube oil system devices. Competent manufacturers make sure all measurement locations are completely prewired on the machine and made available at predefined interfaces or in terminal boxes for connection at the plant site. 

Digital control methodologies similar to the Elliott Digital System program evolved from successful and proven reliable high-speed air compressor management and control approaches. 

The main power source is a 2,200 kW rated motor, which drives two high-speed pinions through integral gears. The first stage of the compressor operates at 17,900 rpm, while the second and third stages operate at 21,800 rpm. The unit is controlled by a local control system, but operators can also monitor the operating parameters from the plant control room. 

Boyce, M.P., Morgan, E., and White, G., Simulation of Rotor Dynamics of High-Speed Rotating Machinery, Proceedings of the First International Conference in Centrifugal Compressor Technology, Madras, India, 1978, pp. 6-32. 

For most of the rotary compressors in process service, the driver is an electric motor. Compressors in portable service, however, particularly the helical-lobe compressor, use internal combustion engines. Many of the rotary compressors require the high speed that can be obtained from a direct-connected motor. The dry type helical-lobe compressor is probably the main exception as the smaller units operate above motor speed and require a speed increasing gear which may be either internal or external (see Figure 4-1). The helical-lobe compressor is the most likely candidate for a driver other than the electric motor. Aside from the portables already mentioned, engines are used extensively as drivers for rotaries located in the field in gas-gathering service. Steam turbines, while not common, probably comprise most of process service alternate drive applications. 

Axial compressors are high speed, large volume compressors but are smaller and somewhat more efficient than comparable centrifugal com-... 

Synchronous and induction motors cannot always be compared on an equal speed basis. In geared applications such as high-speed centrifugal compressor drives (above 3,600 rpm), the most economical induction moior speed is usually 1,800 rpm. The most economical synchronous motor speed for the same application might be 900 or 1,200 rpm, depend-... 

Reciprocating compressors are classified as either high speed or slow speed. Typically, high-speed compressors run at a speed of 900 to 1200 rpm and slow-speed units at speeds of 200 to 600 rpm. 

Figure 10-2 shows a high-speed compressor frame and cylinders. The upper compressor is called a two throw machine because it has two cylinders attached to the frame and running off the crank shaft. The lower compressor is a four-throw machine because it has four cylinders attached to the frame. The number of throws refers to the number of pistons. 

Figure 10-2. High-speed reciprocating compressor frames and cylinders. [Courtesy of Dresser-Rana Company.)...

High-speed units are normally separable. That is, the compressor frame and driver are separated by a coupling or gear box. This is opposed to an integral unit where power cylinders are mounted on the same frame as the compressor cylinders, and the power pistons are attached to the same drive shaft as the compressor cylinders. 

High-speed units are typically engine or electric motor driven, although turbine drivers have also been used. Engines or turbines can be either natural gas or diesel fueled. By far the most common driver for a high-speed compressor is a natural gas driven engine. 

The major characteristics of high-speed reciprocating compressors are... 

Plate valves are typically used for high speed separable compressors. Plate valves are similar to ring valves with the rings connected by ribs. Instead of individual elements opening and closing, all valve ports o[)en and close at the same time. 

For smaller, high-speed compressors the piping sizing rules of thumb discussed above, in conjunction with pulsation bottles sized from Figure 11 -24, should be sufficient for individual field compressors. These niles of thumb can also be used for preliminary sizing of piping and bottles in preparation for an analog study. 

As previously discussed in this chapter and in Chapter 10, reciprocating compressors are generally classified as either low-speed (integral) compressors or high-speed (separable) compressors, API has provided a standard and specification for each type of compressor to help the user and the facility engineer provide reliable compressor installations. 

API Specification IIP Specification for Packaged Reciprocating Compressors for Oil and Gas Production Services covers packaged high-speed separable compressors with speeds from 600 to 1,200 rpm. The majority of reciprocating compressors sold in today s market fall into this category. 

Figure 12-59. Performance ranges for special high-speed/high-pressure, single-stage Sundstrand Compressors (except model HMC 5000) centrifugal compressors. Special impellers are available for performance outside the envelopes shown. Performance varies with the gas involved. (Used by permission Sundstrand Compressors Bui. 450, April, 1995. Sundstrand Fluid Handling Corporation.)...

Screw compressors operate at rather high speeds. Thus, they are rather high volumetric flowrate compressors with relatively small exterior dimensions. 

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