Forecasting of Gas Quality

Brzeczkowski, Stanislaw (National Gas Dispatching, Gas Transmission System Operator GAZ-SYSTEM S.A.) | Szeniawski, Maciej (National Gas Dispatching, Gas Transmission System Operator GAZ-SYSTEM S.A.)



Knowledge of natural gas quality in the short-term future (24 h) is expected by many of end users. Also, European Union Law requires to provide such information by Transmission System Operators. In case of multiloop network which is supplied with many sources and different gas compositions, the dynamic network simulation combined with forecasting of behavior all sources and offtakes, is necessary.

The article describes model of full chain of calculation. At entries, there are: productions, storages and interconnectors with more less stable gas compositions and LNG Terminals where gas composition smoothly change in function of time or significantly due to filing in from next vessel. At exits forecasting of demand relates to nomination processes (industrial end users) or forecasting systems (city gates to household areas). Between them the multiloop transmission network is dynamically simulated with full quality tracking model.

The paper contains also our practice experience based on Polish transmission system which has many entries from production, interconnectors, storages, more than 900 exits and new LNG Terminal. The multiloop network has also several compression stations and reduction points. There is a possibility of determining the degree of gas mixing i.e. providing clients with such information with simulation software. Such analyses are executed on a regular basis. Calculations are performed in three minute cycles (reconstruction network state) and future calculation are performed with the 15-minute step. For future calculations city gate exit points demand is obtained from the forecasting system (short-term forecasts - 10 days) or nominations used in supply points or industrial exits. Such values are compared up – to – date with the values obtained from chromatographs located in the transmission system network – reference chromatographs.

Finally, the article presents the case study of stream mixing degree depending on gas composition from different gas sources, exit point demand and settings of the non-linear network elements. The analyses were performed for both static and dynamic scenarios where one of the parameters is a dynamic change of the quantity and quality supply from LNG Terminal to the network.