Gas companies have long felt the need for flow modelling in natural gas transmission and distribution systems. With the emergence of digital processing of the information related to an in-depth physical study of gas phenomena it became possible to develop network calculation. And, the evolution of DP hardware combined with their ever decreasing cost expanded their use.
Two main categories of applications make use of these calculations : pipeline sizing studies and pipeline management network monitoring and control
The first category corresponds to static applications where the totality of the network's component parts have to be considered in order to find a technical economic optimum of the capital investments both as concerns network reinforcements and network extensions.
The second category entails the analysis of dynamic physical quantities such as flow rates and instantaneous pressures acquired and processed in real-time. In this case, the aim is to give the monitoring station operator a snapshot of his network and prediction of its behavior under various operating configurations.
The present paper analyzes the DP hardware and software suitable for these two kinds of application and pays special attention to the interactive and ergonomic aspects.
The Gaz de France Distribution Division operates three categories of networks within different pressure ranges. Within an urban center, the primary network, called feeder network with a pressure between 14 × 10 and 20 × 10 Pa carries the gas coming from the high pressure delivery stations on the transmission grid to the various districts or neighborhoods. Then, the secondary networks often meshed and with a pressure between 4 × 10 and 12 × 10 Pa or at 21 × 10 Pa, takes over to service, running along the streets, the industrial and residential customers. Finally, a fair number of dead-end extensions or spur lines, making up the tertiary network, and operated-at the same pressure as the secondary network, have been built to feed customers in new neighborhoods situated on the outskirts of the city.
Whether concerned by gas transmission or distribution network, the gas companies have been obliged to study and build models of the flows in these networks in order to ensure their customers quality and security of service.
Numerous empirical pressure drop formulae for gaseous flows in the various domains of Reynolds have been found. Thus, Gaz de France uses Renouard's formula, based on an explicit calculation of the pressure drop coefficient for distribution networks and Colebrook's formula for entirely turbulent flows for transmission.
The Renouard and Colebrook formulae furnish, each in its own domain, the pressure drop on a pipeline of a given diameter and a given length ; there then remains to extend these results to the totality of the pipelines making up the gas distribution or transmission network.