Summary This paper will discuss novel technologies for increasing the energy efficiency of offshore oil and gas platforms. Three case studies are in progress that are based on actual oil-producing platforms--two on the Norwegian Continental Shelf (NCS) and one in the Brazilian basin. The current focus is on developing compact, novel bottoming cycles for recovery of waste heat from the gas turbine and heat recovery from the compressor train for gas export. The technologies under investigation use steam and alternative working fluids, such as carbon dioxide (CO2) and hydrocarbons. All the fluids investigated in this project are natural working fluids; hence, they will not cause any unexpected environmental issues in the future. A case study was performed that considered an 18-year period of operation on an actual platform and a scenario in which one gas turbine was removed and replaced with a CO2 bottoming cycle by use of the exhaust heat from a different gas turbine. The beauty of this scenario is that it would not increase the weight on the platform because the crate containing the gas turbine to be removed was of a weight similar to that of the crate containing the CO2 bottoming cycle. The substitution would not affect the ability to cover the heat demand on the platform because a waste-heat-recovery unit (WHRU) could be installed on the platform's other gas turbine. The case study indicates a significant reduction in CO2 emissions of 22% (63 000 t/a), and does not involve adding additional weight or volume to the platform. If operating on the NCS, the annual savings in reduced fuel costs and CO2 tax from implementing this scenario would be USD 17 million, although much lower in other territories.

The cost of CO2 removal from natural gas with subsequent storage is estimated and the results show that it can be very close to an economically viable process. The cost of removing CO2 from a natural gas stream(sweetening) using the MDEA process is 30% lower than cost of conventional amine MEA technology for CO2 capture from flue gas, putting this project at a much lower cost than capture from most other industrial CO2 sources. The cost of CO2 removal is as low as 35€/tonne. In addition natural gas sweetening projects will capture potentially larger volumes of CO2 than many industrial projects if new large gas fields are developed. The large scale could provide the necessary amount and steady supply of CO 2 needed to kick-start the deployment of CCS. This could happen either by allowing a large-scale offshore central CO 2 storage or offshore EOR projects. Large scale storage would reduce the storage cost for CO 2 improving the cost benefit situation for a CCS project. A large scale EOR project could create a market for CO 2 in the Nordic region that also land-based industry can sell to thereby reducing their costs for CCS sufficiently to allow industrial CCS projects to start.

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In this work different concepts are investigated for combined heat and power production (CHP) from offshore gas turbines. Implementation of such technology could improve energy efficiency of offshore oil and gas production and lead to reduced fuel consumption and resulting CO2 emissions. Offshore electric power is in most cases generated by gas turbines operating in a simple cycle. However it would be desireable to increase energy efficiency by adding steam or CO2 bottoming cycles to produce power from the exhaust heat. However part of the heat from the gas turbine exhaust is normally used for onboard process heat for the oil/water separation process among others, this must be taken into consideration when estimating capacity for additional power production. Different CHP concepts will be evaluated at different operating conditions while running the turbines in both design and off-design mode The results show that it is possible to produce an additional 6–8 MW of electrical power from a 32 MW turbine (depending on the conditions) while using 15 MW of heat from the exhaust for on-board processing.

This paper describes design and optimization of a Waste Heat Recovery Unit (WHRU) for a power cycle which uses CO2 as a working fluid. This system is designed for offshore installation to increase gas turbine efficiency by recovering waste heat from the exhaust for production of additional power. Due to severe constraints on weight and space in an offshore setting, it is essential to reduce size and weight of the equipment to a minimum. Process simulations are performed to optimize the geometry of the WHRU using different objective functions and thermal-hydraulic models. The underlying heat exchanger model used in the simulations is an in-house model that includes the calculation of weight and volume for frame and structure for the casing in addition to the thermal-hydraulic performance of the heat exchanger core. The results show that the for a set of given process constraints, optimization with respect to minimum total weight or minimum core weight shown similar results for the total installed weight, although the design of heat exchanger differs. The applied method also shows how the WHRU geometry can be optimized for different material combinations.