Process simulation and evaluation of options for heat and power generation on offshore oil and gas installations
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In the efforts of trying to reduce global greenhouse gas emissions, the Norwegian oil and gas industry is looking for ways to improve efficiencies when supplying heat and power offshore. By making a scenario of a platform with set heat and power requirements, this thesis tries to answer the question, What are good options for heat and power generation offshore and how do they perform in a lifetime analysis? To answer that question, the modelled platform scenario had varying ambient temperature according to North Sea weather data, and a typical heat and power profile, with a maximum power requirement of 60 MW and a maximum heat requirement of 22 MW. The platform s lifetime was assumed to be 20 years. 7 different cases were modelled and tested in the process simulation software, Ebsilon Professional, with the VTU gas turbine library. To evaluate the designs, focus was put upon lifetime CO2 emissions and flexibility. A case of two GE LM2500+G4 with WHRUs, the most common power technology used offshore, gave a total lifetime emission of 3.99 mega tonnes CO2. The best alternative for the modelled platform were thought to be a combination of a simple cycle and a combined cycle: One LM2500+G4 giving off heat to a WHRU while another LM2500+G4 providing heat to an OTSG that drives a steam extraction cycle. It had high flexibility and low lifetime emissions of 3.20 mega tonnes CO2. A case of electrifying the platform was also evaluated, with using a gas boiler to provide process heat. It was found that the results were highly dependent on assumed associated emission ratings to onshore electric power. With an assumption of marginal power coming from EU and predicted future emission rates, the electrification case gave off 3.60 mega tonnes CO2. The longer a platform operates or the later it is built; the more favourable electrification becomes due to predicted cleaner electric energy in the future.