At Gasunie the capacity planning of transfer stations is done in two steps. The first step is to find a set of capacity operation patterns of the station. Such a pattern is made by calculating the capacity of the station for different inlet-pressures. Because of reliability-issues, the planning is done with a fixed set of scenario's, which describes total failures of streets and overloading of equipment. Each scenario will give a capacity operation pattern. The second step is to match the forecasted demand with these behaviours. The calculation of a capacity can be looked at as an non-linear optimalization problem. Using a linearization process this problem is solved iteratively, in which Piecewise Linear Programming is used in each iteration. The model used, is dealing with thermo-dynamics and is considered as an isenthalpic process.
For planning purposes it is necessary that the whole Dutch gas transport, from transmission to station networks, is simulated. In former PSIG sessions simulation models for the transmission network has been explained. In this paper the planning of the station-networks, in particular the custody transfer stations, will be explained. In the first section the transmission system will be shown. In the next section the custody transfer station will be considered. Because of historical and practical issues the capacity planning is done in two steps, in which reliability-issues play an important role. In section 4 this will be described. The planning of the transmission network is done with an optimalization model. This model has shown its great benefits over the years for the planning department. Its success lays in the way the gas transport problem is formulated. The transport problem is treated as a constrained problem. This idea is also used in the new built model to calculate the capacity of a transfer station. A new aspect in modelling was the thermodynamics. In section 5 this will be shown.
The Gas transport system consists of supplies, pipelines, compressor stations, reducer stations, blending stations, and offtakes. At a supply point gas comes in at a certain pressure. The gas is transported via pipelines. To transport gas over a larger distance there are compressor stations, that raise the pressure of the incoming gas. At the supply side there are various gas qualities, while at the offtake side there are contractual requirements on the quality to meet. Therefore blending stations are installed where gases are mixed together in a controlled matter. Holland is a small country of about 200 km x 300 km. Gasunie's gas transmission system consists of a high pressure and a regional network. The high pressure network is about 6000 km with an average diameter of 1 metre and pressures ranging from 40 to 67 bar. The regional network is about 6000 km with an average diameter of 25 cm and pressures ranging from 8 to 40 bar. The high pressure network transfers gas via 75 ‘measuring and regulating’ (M&R) stations to the regional network. The offtakes of the regional network are custody transfer stations to local distribution networks and industries, in which the pressure is reduced to approximately 8 bar. Currently there about 1100 custody transfer stations.