INTRODUCTION

The Florida Gas Transmission (FGT) modeling project started in 1995 when the pipeline network was being expanded to a capacity to enable deliveries of about 1.5 BCF a day. This model was built by and for FGT's Gas Control group and was completed in 1996. Early in the project it became clear that a model that did not include most of the functionality in the compressor stations would not be useful; thus, a model was built that has the majority of the actual functionality of each of the compressor stations. This paper will emphasize the following four aspects of our complex compressor station modeling:

  1. The model has the ability to simulate almost all possible operational scenarios within each compressor station. At some stations this results in 50+ different possible operational modes.

  2. All of the reciprocating and centrifugal compressors within the stations are individually modeled. This includes the horsepower curves, fuel curves, and loading/unloading sequences.

  3. The modeled compressor station control includes: the ability to set individual unit swing priority; the ability to try and meet multiple set points; and, the ability for units to automatically come on-line and off-line.

  4. The model uses automatic line pack tuning instead of automatic pipeline roughness tuning.

OVERVIEW OF FGT'S SYSTEM

With approximately 5,000 miles of pipe and 300,000 horsepower on the system, the delivery capacity is approximately l. SBCF a day. FGT's system is characterized by the pipeline's dynamic swings in line pack caused by delivering the majority of the gas to electric generation power plants. Unlike most other North American pipelines, the system's peak deliveries are during the summer when trying to meet cooling loads. INITIAL REASON FOR BUILDING THE MODEL FGT's Gas Control department is asked several times a week how much an upcoming pipeline segment or compressor unit outage will decrease the ability to deliver gas; thus, the Gas Control department decided to build a model with the emphasis placed on being able to run predictive (or What If?) scenarios.

MODELING STATIONS WITH MANY DIFFERENT OPERATIONAL MODES

To minimize the amount of manual input required to keep the model in a realistic and usable condition, 99% of the time the model changes operational modes within the modeled stations by using data received from SCADA concerning pressures, regulator set points, and valve positions. The last 1% of the operational mode changes are handled by manual input. The following figures are examples of some of FGT's modeled compressor stations. As shown in Figure 2, compressor station i6 is modeled to reflect the ability to feed the two laterals, that originate from the station, either from the suction side or the discharge side of the station. This station can also have one or two units dedicated to moving gas exclusively down one of the laterals. This station switches its laterals from suction or discharge daily; thus, these signals are received from SCADA and fed into the model.

This content is only available via PDF.
You can access this article if you purchase or spend a download.