ABSTRACT

APO reduces the amount of fuel used in compressor stations of transmission pipeline systems, thereby significantly reducing cost. APO phase 2 emulates transient optimization by incorporating "Black Box" logic, Transition and Administrative Tools. Of significance in the Administrative Tools package is "Measurement," where accurate cost savings are identified and validated through "Calibration" an automated method ensuring the coefficients of the modeling programs are properly "tuned." The APO process combines known engineering technologies into an on-line operational tool that minimizes fuel used in compressor stations by 10 to 15 percent.

Chapter 1: Where we've been Background of System

Initial APO has been operational since late 1999. Its purpose is to minimize fuel usage at compressor stations while operating the pipeline within required engineering and contractual constraints. APO is a process, which combines the software technologies of SCADA (Supervisory Control and Data Acquisition), steadystate fuel optimization and a model based supervisory controller working in conjunction with field compressor logic (Figure 1).

Benefits of initial system

The optimization software (Figure 3):

  • Provides realistic fuel-efficient compressor configurations. It's an excellent product which determines the optimal stations to run and what type of compressor unit, by size, to operate.

  • Provides realistic fuel-efficient discharge pressure targets. It's interesting to note that these solution targets are not necessarily intuitive.

  • Provides the above stated optimal targets within programmed engineering and contractual constraints.

  • Provides a fuel usage target to be used for measurement purposes.

The advanced controller software:

  • Handles "common" upsets (transients) and dynamics of supplies and deliveries. It's also an excellent product that "smoothes" the operation of the compressors' discharge pressures (optimal targets) by controlling the downstream stations suction pressure.

  • Controls the compressor set points relatively close to the optimal steady-state targets.

  • Automatically takes corrective action if a compressor stops.

  • Provides the above stated supervisory controls within programmed engineering and contractual constraints.

The initial system:

  • Achieves increased fuel-efficient operations but was not well documented.

Deficiencies of the initial system
  • Larger upset conditions of supplies and deliveries usually led to high discharge pressures at the stations. Gas Control Operators would have to manually balance a "tight system."

  • "Transition" (the process of shifting the pipeline 1 See "Figures" for enlargements of all exhibits system to a new optimal solution, usually involving a change in the configuration of units running) was deactivated due to inappropriate methodology of the algorithms.

  • Deactivation of Transition led to inefficient fuel consumption during the change process and/or timing problems to accept increased supplies. The pipeline system, on occasion, had too high a pressure to accept an increase in supplies on a timely basis.

  • Measurements of results were not captured. We didn't know conclusively what initial APO saved the company in fuel efficiency.

  • No tools existed to aid the engineer in calibration of the models.

  • Not user-friendly to expand the product throughout the DTI system.

  • The system required weekly re-booting.

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