Optimum Gas Transportation: Validation and Guidelines
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The gas transport system on the Norwegian continental shelf (NCS) consists of 7 800 km of pipelines and is the largest offshore network of its kind in the world. Natural gas is processed at treatment plants in Norway, and dry gas exported through pipelines to customers in the UK and continental Europe. These customers have the opportunity to make varying gas delivery nominations, and meeting such sales gas commitments is important. A major challenge is to operate the network at minimum cost, with minimum environmental emissions, fulfilling variations in contractual nominations and maintaining a sufficient pipeline inventory to provide operational flexibility. A model of optimum operation of a gas export system, including customer nominations, system integration, and operation of pipelines and compressor stations has been established in earlier studies by PhD student, Vibeke S. Nørstebø. This model is based on analyses of actual operating data from the gas export system on the NCS. The scope of the work presented in this master thesis has been to validate this model so that it can be implemented in planning and operation of the gas export system. The purpose of the validation process is first to confirm that the model results are correct in such a way that they represent actual system performance. Second, it aims to confirm that the model provides a more energy efficient operation of the system than current system operation. The established optimisation model is documented and validated in accordance with the actual performance of the system and system components. Comparison with historical data shows that operating in accordance with the established model implies lower pressure in intermediate pipelines, different flow distributions and number of compressors in operation. The model is also used to perform sensitivity analyses dealing with different conditions for the export compressors and varying prices on energy and emissions. Effect of starting up a new compressor and consequences on delivery security are also analysed. On the basis of the model results, operational guidelines and visual displays have been established for use in actual daily system operation. Implementing this optimization model and guidelines based on it in planning and system operation will increase energy-efficiency by lowering compressor power consumption and environmental emissions, and accordingly provide savings in system operating costs.