The paper formulates the problem of reinforcing existing meshed regional gas transmission networks which mainly made of an important number of pipelines (between 50 to 500) but with very few compressor stations(at most 2). The presented techniques determine (1) the selection of pipelines to loop (adding parallel branches), (2) the diameters to lay out along the selected pipelines among a commercial list, and (3) the building timetable in order to minimize the discounted costs. Optimization algorithms to solve these problems are detailed as well as results on French regional networks.
Downstream of the main European and national high pressure gas transmission networks, less capacited structures feed the French territory: the regional transportation networks. The networks are mainly made of valves and pipes, the diameters of which do not exceed 24 inches 9 approximately 600mm). They are located between the main Network and the Distribution Networks. The networks embedded in the French transportation network supply a large number of delivery points (4300 delivery points for the entire network). Hence they are complex structures, made up of several sections of different diameters. Each section must be adapted to the various conditions of flow and pressure. Although the most of them are gunbarrel-like or tree-like systems, the largest networks have several supply nodes and contain lots of loops. To cope with the forecasted demand in natural gas as well as to meet the regulated and contractual delivery requirements, the gas networks have to be regularly reinforced. On these networks the financial income is guaranteed thanks to the consumptions. To charge shippers with the least tariff under a regulated regime, GRTgaz ha to minimize on the long run the total amount of its investments. Hence, the reinforcement of the network is a major issue for a gas transportation operator. The aims of this planification are to:
Identify the optimal set of pipelines to reinforce,
Choose the right diameter on the identified pipelines among a range of commercially available sizes,
Set up the building timetable in order to minimize the discounted costs. With the discount rate(tied to the Weighted Average Cost of Capital) applied each year, the more the project of laying down new pipelines is postpones, the cheaper it is. The problem as stated in this generality is a very difficult one. Enumeration of all combinations is too complex to be practically carried out within reasonable time. To tackle this problems, we propose in this paper a decomposition approach with, first, the choice of pipes and associated diameters and, second, the determination of the best schedule. This decomposition allows to provide a solution in reasonable computation times. Parts 2 and 3 focus on the methods to select of pipes and diameters with a given scenario of demand on one period. Taking into account that the selection of diameter has been made on a target year of demand, the determination of expansion times for each facility is then described and solved in parts 4,5 and 6.