Energy Optimization on Offshore Installations with Emphasis on Offshore Combined Cycle Plants

Abstract

Abstract Increasing fuel cost and concern regarding emissions have incurred focus on energy conservation on offshore oil and gas installations. On the Norwegian continental shelf there has been an increased commercial value of natural gas and a CO2-tax on fuel consumption the last 10 years. For the time being the alternative value of natural gas is in the range 0 to 0.08 EUR/Sm3 and consumption of fuel is taxed with approx. 0.1 EUR/Sm3 burned. This has brought forward significant changes in operational procedures and technology development on the Norwegian oil and gas installations compared to installations in other oil and gas regions throughout the world. Focus has increased on keeping the power requirement down, avoiding unnecessary fuel consumption and designing more energy efficient systems. The most efficient way of achieving this is by installing cold process flares and steam cycles on existing or new gas turbines to form Combined Cycles (CC). In Norway three steam cycle plants fueled by gas turbine exhaust are under completion on offshore oil and gas installations. The overall electrical efficiency of these plants is around 50%. When steam is extracted for process heat the overall thermal efficiency is higher. Compared to conventional simple cycles the combined cycle reduces consumption of fuel gas and emissions of CO2 and NOX with minimum 25%. When designed as alternative to conventional simple cycle solutions, a combined cycle represents an alternative investment reducing the size and/or the number of gas turbines needed. This gives a good contribution to the overall Life Cycle evaluation in favor of the combined cycle option when compared to the simple cycle option.