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Evaluation of a North Sea oil platform using exergy analysis
Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, Department of Energy and Process Engineering.
2013 (English)MasteroppgaveStudent thesis
Abstract [en]

The motivation is to explore the applicability of exergy analysis as an evaluation and monitoring tool for an offshore platform. The focus should be turned from energy efficiency to exergy efficiency, because to use an efficiency that does not account for the quality of the energy may be misleading for the improvement potential. The exergy efficiency contains the improvement potential, while current commonly used performance parameters only focus on power consumption. An exergy analysis is a good method to detect, locate and quantify the theoretical potential for savings and it is more useful the more complex and advanced the system to be analyzed is. Exergy efficiency can be used together with industries? own standard measures, such as specific CO2-emissions. An exergy analysis is seldom systematically used in the industry yet, but the more details we have on the use of exergy, the more opportunities we have to foster environmental friendly technologies. This thesis contains an exergy analysis of the oil and gas processing plant and the power generation system and distribution systems at a particular North Sea offshore platform. In the oil and gas processing a mix of reservoir petroleum and water is separated into oil, gas and water. The oil is exported through a 212 km long pipeline to an onshore terminal, gas and water are reinjected into the reservoir and some of the gas is used for gaslift. Gas can also be imported through a 50 km long pipeline from a nearby gas center to cover the need for gas injection. A fraction of the gas is combusted in power turbines and in pilot flames in the flare system. The oil and gas processing can be divided into six sub-processes; the production manifolds, the separation train, the recompression train, the reinjection train, the export system and the fuel gas system. The power generation system consists of three gas turbines, one mechanical drive and two generator drive. They cover the power demand at the platform. A seawater distribution system and a hot water distribution system supplies consumers with cold and hot water, respectively. A process flowsheet of the oil and gas processing plant, power generation system and distribution systems is simulated in the chemical process simulator HYSYS. The exergy loss in the whole oil and gas processing process, the power generation system and the distribution system, in each subprocess and in each process unit, is calculated. This was done for two dates, with two years in between. In addition, the possibility for installing a combined cycle is studied. The exergy analysis of the oil and gas processing platform is also compared to another exergy analysis of a North Sea oil platform performed by Voldsund et al. (Voldsund M. , Ertesvåg, He, & Kjelstrup, 2013). The specific power consumption was 31 kWh/Sm3/ 40 kWh/Sm3 and the exergetic efficiency was 36.6 %/ 38.9 % for the whole oil and gas processing process at the platform. The highest losses were related to compression and cooling of gas in the recompression train and the reinjection train and throttling in the production manifolds. Also heating and cooling in the separation train and export system contributed a lot, respectively. The exhaust gas from the mechanical drive turbine does not have enough heat to cover the electricity demand via a steam cycle. However, if one utilizes the heat from one of the generator drive gas compressors at part load in addition, the electricity demand is covered. The total exergy destruction is reduced with 5.8 MW/ 10.0 MW. We see the advantage of analyzing exergy destruction and exergetic efficiency of the process. These parameters show other features of the processes, in addition to the industry?s own measures of performance.

Place, publisher, year, edition, pages
Institutt for energi- og prosessteknikk , 2013. , 188 p.
URN: urn:nbn:no:ntnu:diva-22003Local ID: ntnudaim:9603OAI: diva2:646741
Available from: 2013-09-09 Created: 2013-09-09 Last updated: 2013-09-09Bibliographically approved

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