Exergetic assessment of energy systems on North Sea oil and gas platforms

• North Sea oil and gas platforms are investigated and a generic model is developed.
• Exergy analysis of these offshore facilities is performed.
• Most of the total exergy destruction is attributable to the utility systems producing the electrical power required onsite.
• Rejection of the exhaust gases from the utility systems is the major exergy loss of this system.
• The highest thermodynamic performance is reached with low well-fluid content of water and gas.

Oil and gas platforms in the North Sea region are associated with high power consumption and large CO2-emissions, as the processing and utility plants suffer from significant changes in production rates and performance losses over the field lifespan. In this paper, a generic model of the overall offshore system is described: its thermodynamic performance is assessed by performing an exergy accounting and rules of thumb for oil and gas platforms are derived. Simulations are built and conducted with the tools Aspen Plus®, Dynamic Network Analysis and Aspen HYSYS®. 62–65% of the total exergy destruction of an offshore platform is attributable to the power generation and waste heat recovery system, and 35–38% to the oil and gas processing. The variability of the feed composition has little effect on the split of the thermodynamic irreversibilities between both plants. The rejection of high-temperature gases from the utility and flaring systems is the major contributor to the exergy losses. These findings suggest to focus efforts on a better use of the waste heat contained in the exhaust gases and on the ways in which the gas compression performance can be improved.