Compression Plant Design Services

The PCRC Design Facility* at Southwest Research Institute (SwRI) is dedicated to improving and optimizing compressor, pump, and piping systems for the natural gas, petrochemical, and process industries. To prevent many operational problems before a facility is built, a planned compressor/piping system should undergo integrated design analysis, to study its:

• Acoustic response
• Mechanical dynamics
• Thermal flexibility

Excessive vibration, stress, cylinder loads, thermal distortion, and pressure loss can lead to early component failure, reduced capacity, and unsatisfactory equipment efficiency. SwRI's integrated approach ensures the safe, reliable, and efficient performance of new plants and provides a powerful troubleshooting and problem-solving capability for existing plants. Institute engineers have completed in excess of 7,000 plant design and problem-solving projects over the more than 40 years the design facility has been in operation.

Design facility simulations use analog and/or time and frequency domain numerical techniques.

Originally designed for reciprocating compressors, the facility's capabilities have been expanded to include reciprocating and centrifugal pumps, centrifugal compressors, and foundation design and analysis. An industry-driven research and development effort continually upgrades the facility's technologies and capabilities. The SwRI goal is to provide clients with the most comprehensive, cost-effective, and timely design and analysis services.

SwRI begins the design process with client discussions and interaction to identify the problem, define the system, and establish cost-effective design options. This definition process is necessary to ensure that client needs are fully understood before a project is initiated. To achieve project continuity and desired results, face-to-face meetings or teleconferences are often conducted at project startup to review drawing and available data.

The Institute recommends a concurrent engineering approach, addressing all three analytical and design aspects of the system. Though generally interactive, the design modules can be performed singly or in any combination.

The concurrent engineering approach provides many benefits, including:

• Improved compressor, piping, and metering performance
• Elimination of harmful pulsation effects
• Reduced operating and maintenance costs
• Improved system operability and reliability
• Validated pipe support and clamp design and placement
• Optimized pulsation bottle sizing
• Minimal static and dynamic system pressure losses

Acoustical Design

Engineers use acoustical modeling to predict and eliminate operationally undesirable or structurally damaging pulsations resulting from interactions between fluids and machinery. Using analog or time and frequency domain numerical techniques, SwRI engineers model gas dynamics in complex systems to instantaneously define pressure and flow variation at any point in the system. Designs are developed to comply with applicable criteria, such as API 618, or with client specifications.

For acoustical design analysis, SwRI typically provides spectral analysis of pulsation waveforms for the piping system as well as a compressor cylinder pressure-volume diagram.

To avoid poor performance or excessive dynamic loads on the compressor and piping system, acoustical design recommendations typically detail:

• Piping sizes and lengths
• Compressor cylinder bottle size and length
• Compressor cylinder bottle internal dimensions
• Acoustic filter details

Acoustical analysis provides data on:

• Pulsation (pressure, flow) variations
• Acoustical shaking forces
• Compressor cylinder performance
• Pressure drop
• Compressor rod load

Mechanical Design

SwRI uses mechanical modeling techniques to eliminate excessive vibration and dynamic stress caused by mechanical and pulsation-induced shaking forces. Natural frequencies and mode shapes are calculated to predict vibration amplitudes and dynamic stresses on compressor cylinders and pipes exposed to shaking forces. Using the model, engineers design the piping system and its restraints to ensure system safety and reliability.

The Institute applies piping support and restraint technology to correct mechanical problems in piping systems.

Typical mechanical design recommendations detail:

• Piping configurations
• Piping support types and locations
• Compressor cylinder bottle and piping supports and locations
• Compressor cylinder supports
• Vessel and gas cooler structural supports
• Piping branch connections

Thermal Design

Institute engineers model piping systems and major system components -- such as cross-head guides, support structures, filter bottles, coolers, and separators -- to determine static stress from thermal expansion, pressure, and weight. Piping configurations, diameters, restraints, and branch connections are modified to reduce stress to within specifications. Engineers also determine the forces and movements on major system components such as compressors, coolers, and vessels to meet client or code criteria. Recommended system modifications are input into the acoustical and mechanical models to ensure that new system parameters meet performance criteria in these areas.

This diagram shows piping configurations and restraint locations used in a system modeling thermal flexibility.

A thermal design typically includes:

• Piping stress calculations per applicable code
• Recommended modifications to the piping and restraint systems
• Restraint loads
• Loads on equipment

Additional information can be collected on piping such as displacements, forces, and moments.

Prediction Capabilities and System Optimization

Analog and digital acoustical simulations predict pulsation frequencies and amplitudes. To predict how pulsation affects cylinder performance, engineers analyze pressure-volume diagram cards, compressor valves, flow, horsepower, and efficiency. Steady-state and dynamic pressure losses through the system components are also predicted.

SwRI optimized systems by adjusting:

• Piping diameter, length, sizes, and layouts
• Pulsation bottle size, design, and placement
• Compressor valve parameters
• Piping support type and location

SwRI routinely offers short courses on the control of pulsation in compressors, pumps, and piping systems.

Design services include validating designs before construction and correcting problems in existing plants. By minimizing static and dynamic pressure losses, fuel costs are reduced and throughput is increased. The Institute demonstrates compliance with applicable codes for piping stresses, deflections, pulsation, and pressure losses.

Additional Services

In addition to compression plant design services, SwRI offers a variety of related services, such as:

• Field engineering for reciprocating and rotating machinery
  • Signature analysis
  • Performance evaluation
  • Fluid pulsation analysis
  • Piping vibration
  • Foundations and structures
  • Plant noise 
• Compressor diagnostics
• Transient flow analysis
• Critical speed analysis
• Electronic monitoring and control of machinery
• Engine design and monitoring
• Emissions measurement and control

Services have numerous applications, including:

• Carbon dioxide systems
• Chemical plants
• Fossil power plants
• Gas compressor stations
• Gas metering facilities
• LDPE plants
• Liquid pump stations
• Manufacturing facilities
• Mining operations
• Nuclear power plants
• Offshore installations
• Oil and gas fields
• Petrochemical plants
• Pipeline facilities
• Processing plants
• Pulp and paper mills
• Refineries
• Ships and tankers
• Slurry systems
• Steel mills

*The Pipeline and Compressor Research Council (PCRC) of the Southern Gas Association is a nonprofit organization with more than 60 members, representing natural gas transmission and production, petrochemical, and equipment companies. SwRI and PCRC have collaborated since 1953 to meet the needs of the gas pipeline, refining, and process industries.

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