Calcium looping process integrated with a concentrated solar power system: assessment of limestone performance

The use of Carbon Capture and Sequestration (CCS) technologies and the exploitation of renewable sources are two of the main strategies to strongly reduce the CO2 emissions. Among them, the Calcium Looping (CaL) cycle is an important post-combustion technology for CCS that has reached the maturity of the demonstration stage, while the Concentrated Solar Power (CSP) system is a fast-growing renewable technology which relies on the use of solar energy and that owns some unquestionable advantages with respect to the most developed photovoltaic technology. The integration between a CSP system and a CaL cycle, in order to use a renewable source to supply the energy required by the calciner, would improve the performance of the CaL technology by overcoming most of its major drawbacks (e.g., an auxiliary fuel and an air separation unit would not be needed anymore). However, the role that high concentrated radiation can have on the sorbent properties in the CaL cycle is still matter of concern. In this work, the solar CaL process has been investigated by means of experimental tests through the use of a directly irradiated fluidized bed reactor. The solar simulation task is carried out by three short-arc Xe-lamps of 4 kWel each, coupled with elliptical reflectors, capable of producing a concentrated solar beam on the fluidized bed surface with a peak flux of nearly 3000 kW m–2 and a total power of nearly 3 kW. Several calcination and carbonation tests have been performed on samples of commercial limestone, in order to establish the evolution of the CO2 capture capacity of the sorbent with increasing number of cycles. A comparison between results obtained with and without the use of the solar simulator has also been performed, to better understand and optimize the exploitation of concentrated solar radiations.