Centrifugal Compressor – Page 2

This article is intended to serve as a guide in the development of equipment layout and piping layout for centrifugal compressors and their associated equipment, with the goal of producing safe, operable, economical and maintainable installations. Compressors are machines, which are used to increase the pressure of a gas by mechanically reducing its volume within the compressor casing. Compressor Types Positive Displacement CompressorsReciprocating compressorScrew CompressorsCentrifugal compressorsPipeline compressors Type of Compressor Drives Following are the various types of Compressor drives: Electric Motor DrivesAC Squirrel Cage Induction MotorSynchronous AC MotorGas TurbinesSteam TurbinesVariable Speed DrivesVariable Frequency DriveVariable speed (Hydraulic Coupling) Drives Auxiliary Equipment's Lube Oil Cooler (Supplied by Compressor Vendor)Lube Oil / Seal Oil Console (Supplied by Compressor Vendor)Surface CondenserCondensate PumpInlet Air Filters (Supplied by Compressor Vendor)Suction Scrubber (Upstream of Compressor)Air Cooler (Downstream of Compressor)Discharge Scrubber (Downstream of Air Cooler) Compressor Layout When locating compressors, consideration must be given to accessibility, maintenance, and loss prevention requirements.There must be Vehicular (Crane / Fork Lift Truck) Access-way on at least one side of the installation. Refer Fig. 1 Fig. 1: Figure showing the requirement of Crane Access A compressor is generally located inside Shed with the provision of Mono-Rail or EOT Crane for Maintenance. The capacity of the crane to be decided based on 150% of the highest weight of the component to be lifted. To be checked with the compressor vendor.A compressor can be installed in Series and Parallel arrangement.Minimum Distance between two Adjacent Compressors shall be 10m.Generally, Compressors are Grade Mounted (Fig. 2). But Process criteria/requirement will decide if it should be grade mounted or elevated Fig. 2: Grade mounted Centrifugal Compressor Compressor Piping Layout Suction & Discharge Piping (Fig. 3) Compressor Suction Piping Shall be as Short as Possible.Compressor Suction Piping should have Inlet Filter / Strainer. It can be Temporary or PermanentSuction Piping should be sloping/free draining towards Inlet ScrubberSuction lines require a minimum straight run of piping upstream of the suction nozzle which varies between 3 and 8 times the normal pipe size. (Vendor requirement)All operating valves must be readily accessible, preferably from grade.All line to Compressor shall be provided with break-up flanges for Maintenance.Compressor Suction Line Flowmeter: Suction routing shall be such that Upstream and Downstream straight length shall be sufficient for the performance of FlowmeterIsometrics – Both Suction and Discharge piping should have noted for “Pickling and Passivation” i.e. Chemical cleaning of Lines before commissioning. Fig. 3: Suction and Discharge Piping Anti-Surge Valve Is Designed and Supplied by Compressor Vendor.Input to Compressor Vendor for Designing / Sizing the Anti-Surge Valve is given by piping, by providing suction and discharge length.Anti-Surge Valve is located on Anti-Surge line which is basically a by-pass / recirculation line between Compressor Suction and Discharge Piping for Surge controlAnti-Surge Valve shall be located at Highest Point and shall be free draining on both side Lube Oil Cooler & Piping (Fig. 4) Lube Oil Cooler Shall be Accessible from Road.Lube Oil Cooler Shall be located as close to Compressor as Possible.Lube Oil Cooler Piping Should Not Interfere with Access and Maintenance space.Lube Oil Cooler line must be Free Gravity flow requirements.Lube Oil Cooler Piping Should have Break-up Flanges for Maintenance purpose.Lube Oil Cooler Isometric should also have noted for “Pickling and Passivation” i.e. Chemical cleaning of Lines before commissioning. Supporting of Compressor Piping First support from Compressor Suction and Discharge nozzle is either Spring support or Adjustable support for Alignment during Construction / Erection. Fig. 4: Lube Oil Cooler Compressor piping should never be supported by the Compressor foundation. Pipe supports must be provided with independent foundations to avoid transmission of vibration.Compressor Suction / Discharge Piping should be routed in such a way that it has enough flexibility to accommodate Thermal Expansion and to Reduce Nozzle Load.Compressor Suction / Discharge Piping should be adequately supported as per Stress Engineers Support requirements.Process Should be consulted for any possibility of two-phase flow/slug flow and the line should be supported accordinglyAs compressors are meant for Gaseous fluid, the Hydro-test load on supports may be very high for big bore line. Hence we can recommend Temporary supports to be erected during Hydro-testing with the help of a Stress Engineer. Utility Requirements Following are the utilities required for the Compressor: External Fuel gas for seal gas systemInstrument Air for the Instruments/Control system/Seal gas system Applications of Compressors RefineriesNatural Gas Compression & Transportation ServicesOil Exploration – Gas Reinjection, Gas lift, etc.Gas LiquefactionAir Compression serviceRefrigerant compression serviceRefueling applications Few more useful resources for you…Articles related to CompressorArticles Related to PumpsPiping Design and Layout BasicsPiping Stress Analysis BasicsPiping Materials BasicsArticles Related to Mechanical DesignArticles Related to Process DesignArticles Related to Heat Exchanger