Fuel Gas Compressor Piping Transient Analysis

Evaluate Transient Flow at Gas Turbine Inlet

Reciprocating compressors are often used for fuel gas booster applications, feeding one or more gas turbines. Gas turbine manufacturers (OEMs) have strict requirements for flow and pressure variations in the fuel gas supply.

This analysis will assess these transient conditions and provide recommendations to modify the piping system if required. The evaluation includes the piping system between the discharge of the fuel gas compressor to the inlet of the gas turbines. 

Field testing the pulsation and transients in a fuel gas system (Asia). Testing verified the accuracy of Wood’s transient analysis results (fuel gas reciprocating compressor feeding gas turbine).

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1 Scope

The scope of the analysis can include these activities:

• Evaluate the steady state pressure pulsations in the system to ensure design specifications are met.
• Evaluate the transient conditions, and determine if a gas accumulator (buffer tank) is required between the booster compressor and gas turbine to reduce pressure variations.
• Provide sizing of buffer tank if required.
• Evaluate criteria such as mean pressure fluctuation, speed of mean pressure variation, and amplitude of pressure variation.
• Evaluate the transient flow and pressure variation through the piping system during start-up or upset conditions. For example:
  • A system has 2 fuel gas booster compressors and 2 gas turbines operating at maximum capacity. Evaluate transient pressure changes if one turbine trips causing subsequent shutdown of one compressor. Assess pressure changes in the piping system based on timing for shutdowns, valve operations, etc., and include the “water hammer” due to the sudden stop of the flow. 
  • Assess the start-up of new turbines added to an existing gas supply system (feeding other gas turbines).

The computer simulation software used for this analysis is Wood’s MAPAK transient solver. This proprietary non-linear, time domain software is used for simulation and analysis of compressor performance, acoustics, pulsations, and transients.
MAPAK software

Various scenarios are evaluated based on operating assumptions provided by the operator. Variables include in the transient model include:

• Time delay between shutdown of compressor and start-up, and loading of the standby compressor
• Fuel gas compositions, flow rates, and bypass valve operating characteristics
• Compressor performance characteristics and volume in the piping system
• Operating pressures and maximum rate of change in pressures allowed at the gas turbine
• Time delays due to control system
• Pressure drop in the piping system

Our clients for these transient studies include:

• Equipment packagers
• Machinery and equipment OEMs
• Engineering, Procurement, and Construction (EPC)
• Owners and operators for gas turbine facilities

2 Related Services

• Reciprocating Compressor: Pulsation and Mechanical Analysis
• Vibration Inspection Program
• Bottle Sizing Service
• Review and Design Support
• Small-Bore Connection (SBC) Assessment 

3 Example Projects

Acoustic Models of Reciprocating Compressor Discharge to Turbine Inlet

Transient analysis determines pressure at the turbine inlet for different operating scenarios to ensure gas system meets OEM requirements.

4 Keywords

• Transient flow at gas turbine
• Fuel gas transient flow