Centrifugal Compressor Equipment Interaction

download Centrifugal Compressor Equipment Interaction

If you can't read please download the document

  • date post

    27-Nov-2014
  • Category

    Documents

  • view

    311
  • download

    26

Embed Size (px)

Transcript of Centrifugal Compressor Equipment Interaction

centrifugal compressorUnderstanding centrifugal compressor equipment interaction

Equipment Interaction

SSB

Equipment InteractionThe compressor is taking suction from a source, point A at pressure P1, and discharging at pressure P2 at point B into a process system consisting of pipelines, valves and equipment. The gas is transported through this system to be delivered to point C at pressure P3. The line pressure drop, (P2-P3), is usually denoted as p (delta P) of the systemSSB

System curvePlot of pressure drop versus flow gives the system curve. The total pressure drop has two components, the superincumbent pressure or static pressure difference between Points B and C, and the dynamic pressure drop, i.e., the drop due to friction, velocity change.SSB

System curveClick to edit Master text styles Second level Third level Fourth level Fifth level

SSB

Compressor CurveThe flow Q, HEAD, P, and speed N relationship of a centrifugal compressor . It can be seen that pressure increase as the flow drop till reaches the surge line. Similarly if the flow increase it reaches the stone wall limit for the particular speed.

SSB

Compressor Curve

SSB

Relationship between Compressor and System Curves.When a compressor is connected to a system, the operating point can be obtained by superimposing the system curve on the compressor curve, it can be noted that although a system is quite independent of its upstream source equipment, in this case of compressor; operation is very much dependent on its downstream connected system.

SSB

Relationship between Compressor and System Curves.

SSB

Single-speed CompressorSimple arrangement of a centrifugal Single-speed compressor drive with suction/discharge pressure control

SSB

Incoming Flow to Compressor DecreasesSuction pressure reduces Discharge control valve closes System curve moves to left with new operating point.

SSB

Incoming Flow Drops Below Surge Control PointDischarge control valve closes Anti surge valve opens New system curve and operating point is located

SSB

Gas Demand Increase at the Consumer EndFlow increases

System curve shift to left

Pressure drop increase

SSB

SummaryIn summary, for all single-speed compressors, variation in flow is achieved only by varying the system curve position backward and forward. The operating point shifts along the compressor curve,

SSB

Variable-speed Compressor Drive with Speed ControllerThe speed is changed by a variable-speed driver to achieve varying flow-pressure requirements. The driver is often a gas or steam turbine, although variable-speed electric motors are also used in certain cases.SSB

Variable-speed Compressor Drive With Speed Controller

SSB

Incoming Flow to Compressor DecreasesSuction pressure reduces Speed reduces New operating point is reached where the discharge flow equals the reduced incoming flow .

SSB

Incoming Flow Drops Below Surge Control PointSpeed reduces to minimum Anti surge valve open to control the flow

SSB

Gas Demand Decrease at the Consumer EndFlow decreases System curve shift to left Speed reduces till it met the compressor curve at reduce flow rate

SSB

Compressor Delivers at a Fixed Pressure to Consumer, Set Pressure Changedw

w

w

w

Static pressure moves down Flow increases Suction pressure drops Speed reducedSSB

Summarywhen a compressor is driven by a variable-speed drive (gas turbine, steam turbine, etc.), the operating point may shift either along the compressor curves, the system curve, the fixed pressure line, or a combination of them depending on the nature of change as discussed. This is quite different from a compressor driven by a single-speed drive (electric motor) described earlier:SSB

Gas Molecular Weight ChangesMolecular weight decrease pressure decrease Increase speed If on margin new curve will be formed and flow reduces. Increases suction pressure Molecular weight increase, pressure increase Flow increases new curve will be formed If gas is not available Speed reduces

SSB

ConclusionCompressor-like a centrifugal pump can be operated anywhere on its curve between surge point (or surge control line, SCL) and stonewall by shifting the system curve, provided the driver is adequately sized. However, if the increase is due to a change in MW where the compressor curve itself shifts, this should be limited to the specified MW variation range.SSB

Number of Impellers at Different Compression Ratios

SSB

Characteristics ShapeImpeller and diffuser geometry influence compressor performance

SSB

Blade AngleIf blade angle is zero resulting basic slope normally shows 2 or 3 percent head rise when going from design flow to minimum flow . If angle is 45 impeller will typically produce a head rise of 20 percent or more, when moving from design flow to minimum flow. industry standard for conventional closed impellers is represented by the middle line, which is 25 to 35" of backward lean.SSB

Blade Angle

SSB