![]() Once surge occurs, the output pressure of the compressor is drastically reduced, resulting in flow reversal within the compressor.” API 617 (1) defines surge as “… a characteristic behavior of an axial or centrifugal compressor that can occur when inlet flow is reduced such that the head developed by the compressor is insufficient to overcome the pressure at the discharge of the compressor. Entire graduate-level courses could be taught on surge, surge detection, mediation, and antisurge controls. No discussion about centrifugal compressors can take place without mentioning surge. Each of these process stages may have multiple compressor stages. For example, a C3 refrigeration compressor with two sideloads has three process stages - inlet to sideload 1, sideload 1 to sideload 2, and sideload 2 to discharge ( Figure 3). You can distinguish between a process stage and a compressor stage by remembering that a flange-to-flange process is a process stage. Although this simplified compressor has three process stages, it has four compressor stages. These parts allow the process components to do the required work safely and reliably. The mechanical components are the pressure-containing and support systems of the compressor - the casing, nozzles, end walls, journal and thrust bearings, and seals. These parts do the work required by the process. The process components are those that are in direct contact with the gas - the rotor (with its impellers), the diaphragms (which contain diffusers), return bends, and volutes. ![]() From single-stage air blowers to 100-MW multibody cracked-gas compressors, the principle of operation is the same.Ĭentrifugal compressors are employed in ethylene plants because they can handle very large volumes and are very robust, allowing for continuous operation in critical services.įor the purpose of this discussion, the centrifugal compressor can be broken down into two sets of components: process and mechanical. The gas is redirected to the next impeller in the return channel, or collected in a volute and discharged through the discharge nozzle. ![]() It then decelerates in the diffuser, and that energy is converted into pressure. The gas exits with a radial velocity equal to the tip velocity of the impeller. The impeller imparts work to the gas by accelerating the gas from the eye of the impeller out toward the tip. The gas enters the impeller with little or no radial velocity. Image courtesy of Elliot Group.Ĭentrifugal gas compressors are dynamic machines that impart kinetic energy to process gas by accelerating the gas through impellers ( Figure 1). They recover that energy as pressure within the diffusers. Centrifugal gas compressors are dynamic machines that impart kinetic energy into a gas by accelerating the gas through impellers.
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