Competence at work for service and innovation

Centrifugal compressors

Design, Testing and Service

CST: Range of Activities

  • Aero-dynamic design (CFD) & performance assessment
  • Optimized geometries to maximize efficiency and flow rangeability
  • Mechanical design & impeller modal analysis Rotor-dynamic and bearings analysis
  • Support to Production and Testing of new Machines

CST: FIELD OF EXPERTISE

  • All main compression services (Upstream, Midstream, Downstream)
  • Blower, Integrally Geared, Horizontally split & Barrel type
  • Power range from few KW to 100+ MW (LNG service)
  • Rotating speed up to 50.000 rpm
  • Pressure up to 800 bar for Natural Gas Reinjection
  • Labyrinth, Carbon Ring, Dry Gas Seals (as a function of the service)
  • Revamping & Uprating of existing compressors (trouble-shooting, flow/efficiency increase, control upgrade)

Know-how, Experience and the most modern design tools are the ingredients of the CST design of centrifugal compressors

Leveraging the state of the art know-how and technological edge of its engineering staff, CST has developed a structured approach for designing compressors (aero-dynamic, mechanical and rotor-dynamic) based on complete compressor stage simulation and performance assessment. This approach results in an outstanding quality in compressor design and analysis (Root cause analysis & troubleshooting, Modifications and upgrades, Reverse engineering and modernization, Rehabilitation).
Design usually involves a preliminary definition of the compressor configuration and stage/s selection, followed by special analysis aimed to verify aero-dynamic performances and structural integrity of the selected compressor. These analysis, such as 3D Computational Fluid Dynamics (CFD), Finite Element Analysis (FEA) and rotor-dynamics (lateral and torsional analysis), are used also for in Field Support activities in order to investigate specific issues customers may face.

Stage selection

CST optimizes the compressor thermodynamic design, starting from standardized compression stages (integrally geared or between bearings compressor layout, 2D or 3D open or close impellers, vaneless or vaned diffusers, bladed return channels or volutes), to be adapted to customer requirements. Through this approach, we select the best stage configuration, matching the specific application and compressor performance curves, from choke to surge as a function of speed or IGV position.
Real gas equations of state are used to guarantee accurate performance curves.

Typical Table of standard compressor stages
Typical Table of standard compressor stages
Typical centrifugal compressor performance curves
Typical centrifugal compressor performance curves

Once the machine configuration is selected, the aerodynamic design of rotating and stationary components is defined. All geometries (impellers, diffusers, volutes or return channels) are optimized to maximize efficiency and flow capability across the operating range.

Aero-Dynamic Impeller Blade Design
Aero-Dynamic Impeller Blade Design
3D Model of impellers and shaft
3D Model of impellers and shaft

3D model CFD simulation

3D CFD simulations are widely used by CST for:

  • Detailed design and optimization of standardized stages (impeller, diffuser and volutes or return channels). CFD allows to obtain an accurate characterization of velocity fields, pressure distribution and minimize sources of losses.
  • Performance assessment on design and off-design conditions, determining compression efficiency and power consumption to verify the preliminary stage selection.
  • Specific investigation for In-Field Support activities (e.g. justify performance decay, investigate modifications/actions aimed to refurbish old compressor).

impeller blade static pressure distribution
impeller blade static pressure distribution
diffuser and volute flowfield visualization
diffuser and volute flowfield visualization

FE structural & modal analyses

The Finite element analysis (FEA) is typically performed by CST, here are some applications:

  • Characterize the structural behavior of every critical component, to assure compressor integrity and rubbing avoidance (e.g. impeller tip/casing shroud clearances).
  • Impeller dynamic behavior assessment (natural frequencies and mode shape); Singh's Advanced Frequency Evaluation (SAFE) diagram approach is used to avoid resonance conditions.
Compressor casing deformation in operating conditions
Compressor casing deformation in operating conditions
Two-diameter mode shape of an open impeller
Two-diameter mode shape of an open impeller

Rotor-Dynamics

CST gives special attention to all the aspects of the dynamic behavior of rotating parts
In addition to impeller modal analysis a rotodynamic study of rotating parts (pinion shaft of IGC, compressor shaft of between bearings ) is carried out by Lumped Parameter Models. This is according to API617 and API684 Standards, focusing on:

Lateral analysis for calculation of:

    • natural frequencies & mode shapes,
    • response to unbalance,
    • stability.
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Torsional analysis for calculation of:

      • natural frequencies & mode shapes,
      • torsional forced response.
  • Lateral analysis for calculation of:
    • natural frequencies & mode shapes,
    • responce to umbalance,
    • stability
  • Torsional analysis for calculation of:
    • natural frequencies & model shapes
    • torsional forced response

Lumped parameter shaft model
Lumped parameter shaft model
Lateral analysis of an IGC high speed shaft
Lateral analysis of an IGC high speed shaft

Inlet guide vane

Variable Inlet Guided Vanes (known as IGVs) are commonly used to control the inlet mass flow of integrally geared compressors. IGV can lead to important energy savings with respect to a conventional inlet butterfly valve. This component strongly affects overall compressor performance and represents a critical component to design. CST has invested a significant effort to design IGVs for both levers and gear actuating system.

 

Variable inlet guide vade
Variable inlet guide vade

 

Fully comprehensive compression unit engineering design

Process centrifugal compressors are designed by CST based on customer’s needs and requirements, in accordance with API617 Standards or API672 in case of packaged IGC for air.

Control and anti-surge

CST engineering services also include the philosophy of the control system, and the study and optimization of the best solution to prevent surging.

Dry gas seal system selection and specification

CST collaborates with the most reputed suppliers of dry gas seals with the aim to select the best solution for this very important component and its relevant system.

Lubrication systems for rotor bearings, gearbox and motor

CST can design customized systems based on specific requirement for the machine and customer needs.

CST: From conceptual design to Testing and Service

  • All main compression services (Upstream, Midstream, Downstream)​

  • Blower, Integrally Geared, Horizontally split & Barrel type

  • Power range from few KW to 100+ MW (LNG service)​

  • Rotating speed up to 50.000 rpm 

  • Pressure up to 800 bar for Natural Gas Reinjection​

  • Labyrinth, Carbon Ring, Dry Gas Seals (as a function of the service)

  • Revamping & Uprating of existing compressors (trouble-shooting, flow/efficiency increase, control upgrade)

CST: Field of expertise

  • Aero-dynamic design (CFD) & performance assessment

  • Optimized geometries to maximize efficiency and flow rangeability​

  • Mechanical design & impeller modal analysis

  • Rotor-dynamic and bearings analysis​

  • Support to Production and Testing  of new Machines

SOME EXAMPLES OF THE CST DESIGN ACTIVITY
FOR CENTRIFUGAL COMPRESSORS

CFD Analysis

Pressure distribution along the flow path of the compressor stage

CFD Analysis

Impeller flow-field visualization

FEM Analysis

Compressor casing deformations during operation

FEM Analysis

Impeller overspeed test simulation

Rotor-dynamic Analysis

Pinion mode shape in operating condition

Rotor-dynamic Analysis

Response to unbalance of a centrifugal compressor pinion

Casing Manufacturing

From CAD to plant: stage with cast casing

Casing Manufacturing

From CAD to plant: stage with forged casing and IGV

Centrifugal compressor auxiliaries

Example of compressor console

Centrifugal compressor upgrade

From riveted to machined impeller

Corroded compressor rehabilitation

Performance improved after detailed CFD investigation

Old Compressor upgrade

Rerating of very old centrifugal Compressor (manufactured in 1961)

Compressor manufacturing, assembling, and testing

CST together with its qualified partners have the capability to manufacture all components and assemble and test compressors.

Reconditioning of existing compressors

CST service is not limited to the design of new units but can assist its customer for repairs instructions, parts reverse engineering, and provision, modification, and optimization of existing compressors to meet new plant requirements, different gas condition and improve compressor performance, including re-bundling and sealing system upgrade (i.e., changing from oil to dry gas type). Learn More.