ABSTRACT

In a gas pipeline network, a compressor station is responsible for forcing the gas through the pipes. It is a thermodynamic device, imparting energy to the gas. Detailed compressor models exist that calculate the thermodynamic properties and other characteristics of a compressor. Many properties are calculated using curve fits of manufacturer's data. This type of compressor station modelling could be added to a mathematical network model to produce accurate results with proper consideration of the control systems. In this paper, the opposite view of compressor station modelling is explored. A compressor station is a network object with a certain network role to play. The individual details of the compressor station model are left abstract, with detail, or lack of detail, left to the individual requirements of each system. 'I'he main requirements of a compressor station model in a network are explored in detail. Concepts of idealized control are reviewed. NOVA owns and operates a gas pipeline network in the province of Alberta, Canada through its Alberta Gas Transmission Division (AGTD). The pipeline has over 11,000 miles of pipe carrying over 75% of all marketed Canadian natural gas each year. In 1992, 3.44 trillion cubic feet of natural gas were transported by the pipeline. The system contains 44 compressor stations representing total compression power of over one million horsepower. A transient gas pipeline simulator built within AGTD has been designed as a tool to train gas controllers. One of the more challenging pieces was development of a compressor station model adequate for the complex AGTD network. This paper presents an overview of the design process for a compressor station model that is part of a network model.

INTRODUCTION

A compressor station plays an important role in a gas pipeline network. It adds m 1993 energy to the gas, increasing the pressure, to help force it through the pipeline. In a mathematical model of gas flow in a pipeline network, a compressor station model demands thorough treatment. Detailed compressor station models exist and have been discussed in previous papersl$. Compressor station models impact network models as boundary conditions or added constraints to the hydraulic pipe equations. Understanding this role helps in developing a compressor station model that meets the needs of the application. This paper develops a compressor station model from the viewpoint of the network model that contains it. It discusses a black box approach to the model. The method of construction is from a simple high level model that can be expanded and developed into a more complicated representation according to needs. The idealized control approach is also discussed, as well as the choice of internalizing or externalizing calculations.

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