CO2-Free Power Generation: A Study of Three Conceptually Different Plant Layouts

Ever since the release of the Kyoto protocol the demand for CO2-free processes have been increasing. In this paper three different concepts with no or a very small release of CO₂ to the atmosphere are evaluated and compared concerning plant efficiency and investment cost. A novel approach to biomass gasification is proposed to provide fuel for a combined gas turbine cycle, where the biomass is considered to be a renewable fuel with zero impact regarding CO₂ in the exhaust gases. The gasification concept used is a Dual Pressurised Fluidised Bed Gasifier (DPFBG) system, using steam and recycled product gas as fluidising agent in the gasification reactor. In the separate combustion reactor air is used as fluidising agent. The second cycle is a hybrid fuelled Humid Air Turbine (HAT) cycle with post-combustion CO₂-separation. Steam used for regenerating the amines in the separation plant is produced using a biomass boiler, and natural gas is used as fuel for the humid air turbine. With this fuel mix the net release of CO₂ can even be less than zero if the exhaust gas from the steam generator is mixed and cleaned together with the main exhaust gas flow. The third cycle proposed is a combined cycle with postcombustion CO₂-separation and the steam generation for the CO₂-separation integrated in the bottoming steam cycle. All power cycles have been modelled in IPSEpro™, a heat and mass balance software, using advanced component models developed by the authors. An equilibrium model is employed both for the gasification and the separation of CO₂ from exhaust gases. All three power cycles show efficiencies around 45%, which is high for a biomass gasification cycle. The HAT and the combined cycle show efficiency drops of about 8 percentage points, due to the post-combustion treatment of exhaust gases.