Open (i.e., simple) cycle gas turbines (GTs) have been the preferred means of power generation on floating, production, storage, and offloading (FPSO) vessels over the past two decades. GT-based packages offer several advantages over other widely used power solutions, such as gas engines and diesel gensets - including high power density, increased availability, and reduced greenhouse gas (GHG) emissions. In recent years, however, with many offshore operators establishing targets for environmental footprint reductions, new pathways for decarbonization are being evaluated. Combined cycle (i.e., the addition of a steam bottoming cycle to an open cycle GT) is a concept that has been widely employed in onshore industrial applications and is now garnering more interest in the offshore segment.
This paper discusses the benefits combined cycle power plants can provide when compared to open cycle GTs and outlines installation and operability considerations for both greenfields and brownfields. In certain applications, the combined cycle power plant design may allow compression duties to be met with electric motors instead of gas turbines. Aside from operational advantages, such as increased availability and efficiency, and better turndown capabilities, this provides the added benefit of centralizing and optimizing emissions on the facility. It also enables more effective emissions monitoring and control.
The paper will also discuss how digital monitoring and control systems can be applied to ensure that gas turbines are running at optimal setpoints relative to ambient conditions and current power demand. In this way, all GTs in the power plant can be operated (collectively) in the most fuel-efficient manner, thus contributing to further emissions reductions.