Calcium looping in solar power generation plants

The use of a calcium looping based process as a thermal storage and transportation system for concentrated solar power plants is proposed in this work. This system exploits the reversible calcination carbonation reaction of limestone and lime. Concentrated solar heat is used to calcine CaCO3, which is then released as required by carbonating the resulting CaO. The CaO/CaCO3 system has a high energy density and its high temperature operation allows the use of a gas turbine for power production. This paper presents a first order evaluation of the potential of this application of calcium looping, with particular consideration given to carbonation activity of the sorbent. A model including a solar calciner and a pressurised fluidised bed carbonator feeding a gas turbine in an open Brayton cycle has been developed. Results from the model indicate that electric efficiencies of 40-50% could be achieved with sorbent carbonation activities between 15% and 40%. Higher sorbent activity levels do not affect efficiency, but would lead to lower capital costs. According to the model, CaO activity levels above 17% lead to significant reductions in the required storage volume over existing systems, such as molten salts. In principle, high efficiency and smaller footprint solar thermal power plants are possible with calcium looping. Such plants would have no process use of water and could be used as baseload, variable demand load or microgrid systems. (C) 2012 Elsevier Ltd. All rights reserved.