Renewable-integrated flexible production of energy and methane via re-using existing offshore oil and gas infrastructure

Denmark has been extracting gas and oil from the North Sea since the 1970s. However, Denmark has recently committed to phasing out fossil fuel production by 2050 to meet the climate goals of the Paris Agreement. The decommissioning of the offshore infrastructure is going to be very expensive. Therefore, considering effective ways for its repurposing becomes of great interest. In parallel to this scenario, the energy transition towards renewable and sustainable energy supply has been boosting the construction of offshore wind farms (OWF) in the North Sea. In this context, the integration of OWF with offshore oil and gas (O&G) platforms could result in a better alternative to decommissioning. In this work, a novel zero-carbon emission energy system for both power generation and methane production is proposed. By utilizing surplus electricity from OWF, electrolysis can be used to split water into oxygen and hydrogen, which can be used in the Allam cycle for power generation and methanation according to the Sabatier reaction, respectively. In this novel integrated system, surplus electricity from wind farms, seawater, and CO₂ are converted into controllable electricity, methane, and oxygen. The synthesized methane can be partly stored or exported via existing natural gas pipelines. The portion to be stored/exported is defined as the storage ratio in this study. The integrated system has high flexibility since the Allam cycle and methanation unit can be operated separately or simultaneously. To validate the feasibility of the system, preliminary energy and exergy analysis are performed using Engineering Equation Solver (EES) software. 1% (45 ton/day) of the total daily Danish natural gas consumption is assumed as the baseline for the modeling. If all the synthesized methane is burned in the Allam cycle, 51.34 MW of electricity from wind farms can be transformed into 16.4 MW of controllable electricity. In this scenario, the integrated system can be regarded as an energy storage system, where the round-trip efficiency is about 32%.