World’s renewed focus on decarbonization is affecting the Offshore Upstream industry. Today, many operators are taking voluntary steps by committing to a reduction in the overall carbon footprint from their assets. Looking at deep water projects, power generation is the biggest emission contributor on a Floating, Production, Storage, and Offloading (FPSO) plant, with more than 60% of the total greenhouse gas (GHG) emitted during lifecycle.
A recent trend is to consider Combined Cycle or Cogeneration Gas Turbines (CCGT) as an alternative to the traditional Open Cycle Gas Turbines (OCGT).
OCGTs are usually employed in Offshore due to their simplicity of operation, large references, low weight and compact footprint. A trend is to adopt larger and more efficient Gas Turbines to increase topside power density and therefore reduce footprint. In this way, typical electrical efficiency can go up to 40% depending on ambient conditions and gas turbines size.
As an alternative to OCGTs, a CCGT plant consists in:
- a conventional Gas Turbine Generation (GTG) system as Topping Cycle,
- a Steam Bottoming Cycle composed by a steam generator, usually of Once Through type, for waste heat recovery by means of steam production, and a Steam Turbine Generator coupled with a Condenser and balance of plant.
Leveraging its process and plant design competences, on top of its experience as OCGT supplier, in this paper Baker Hughes describes key technical considerations that shall be considered for a CCGT plant on a FPSO. Baker Hughes is currently engaged on several CCGT plants for FPSO and is executing world’ first of such a kind.
The CCGT solution drastically improves electrical efficiency as it is capable to reduce by 20% or more the overall emitted CO2 per MWh produced. Thanks to the most recent carbon pricing schemes, in certain regions set to achieve or exceed $50/ton of CO2 emitted, this reduction in carbon emission can even become an additional source of revenue for the project.
However, while improving efficiency a CCGT plant increases the complexity of the FPSO and therefore requires careful consideration since the project Conceptual phase. Both the Gas Turbine selection and the Steam Bottoming Cycle architecture can drastically affect plant performances, flexibility, footprint and weight. To properly select the CCGT, thermal and power demand have to be considered during entire project life as an input for the correct balance between efficiency gain and costs.
Baker Hughes developed several improvements which can help find the proper trade-off in performances and flexibility while reducing weight, footprint, CAPEX and OPEX.
