ABSTRACT

Natural gas transmission networks tend to be dynamic in nature and the majority in Europe do not normally operate on a simple steady-state basis. Loads ramp up and down in response to changing demands, driven to some extent by the new emerging European market. The packing and drafting generated by end-users, can make it difficult to understand the dynamics of a network, particularly when using steady-state analysis, as it offers only a limited view of the system. This paper discusses how and why, a transient model of Dublin City was developed, and how the model was subsequently and successfully used to identify additional capacity within the system. There is also some theoretical information outlined within the paper which provides an outline of the engineering principle underlining this case study. An outline is provided as to how a request for additional firm capacity in the Dublin area was technically analysed. Steadystate analysis produced insufficient evidence to support the accommodation of the request for extra capacity. In light of this, a transient model was developed which facilitated determination of a suitable network arrangement. In summary, the paper is an example of how using transient analysis facilitates asset optimization in a gas transmission network.

INTRODUCTION

In late 2003, Ireland's largest electrical generation company, state owned ESB, enquired about the feasibility of securing additional capacity for one of its plants in central Dublin, Poolbeg, shown above. Bord Gáis Éireann (BGE) have in recent years, made significant reinforcements to the Dublin area transmission system. In light of these infrastructural developments, it was felt that the network should be able to accommodate additional flows of gas to the relevant power stations. However preliminary steady-state modelling indicated that the request could not be accommodated because certain system capacities were exceeded. However by building a transient model a better understanding of the network was established and additional capacity was successfully identified.

TRANSIENT THEORY OVERVIEW

The majority of problems analysed by engineers involve some form of transient phenomena. Transient solutions to problems, whilst often attempted, are not always fully utilised or understood. The reasons for this may include:

  • Steady-state analysis provides an adequate approximation

  • Transient analysis is complicated

  • Transient analysis is time consuming Whilst the point that steady-state analysis provides an adequate approximation may be argued, with modern software and personal computing power available the points regarding the complexity of transient analysis and the time consuming nature of transient analysis may be disregarded. The question may then be asked : "Why use a transient simulation?" Transient simulations of a pipeline support a more detailed understanding and appreciation how a pipeline will behave under operational conditions.

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