Calcium Looping Technology Demonstration in Industrial Environment: Status of the CLEANKER Pilot Plant

Abstract

Calcium Looping (CaL) is recognized as one of the most promising emerging technology for CO2 capture in cement plants. The highly integrated Calcium Looping process configuration enables CO2 capture with an efficiency target over 90% and high-energy efficiency. \n \nThe core activity of the CLEANKER project is the design, construction and operation of a CaL demonstration system including the entrained-flow carbonator (the CO2 absorber) and the entrained-flow oxyfuel calciner (the sorbent regenerator). This demonstration system, connected to the Buzzi Unicem kiln of the Vernasca cement plant (Italy), will capture the CO2 from a portion of the flue gases of the kiln, using as CO2 sorbent the same raw meal that is used for clinker production. \n \nThe CLEANKER implementation plan spans four years and half, from October 2017 to March 2022 (an extension of six months has been requested due to the pandemic situation). The first two years have been devoted to the (i) detailed design of the CaL demonstration system, the (ii) characterization of raw meals as CO2 sorbents and the (iii) erection of the demonstrator. \n \nThe pilot plant has been commissioned in October 2020 and then will be demonstrated by means of several short and long steady-state tests (during spring and summer 2021), with the aim of optimizing the operational parameters governing the CO2 capture process and of bringing the integrated CaL technology at TRL7. The pilot plant and the conventional kiln operations will be deeply integrated: the CaL calciner will be fed by the same kind of raw meal used in the kiln for producing clinker, whereas the carbonator will treat the effluents coming from the cement plant. The CaL calciner will be fired in a recirculated oxy-fuel combustion mode, where a heavy fuel oil will be burnt with oxygen and a fraction of the CO2-rich exhausts will be recirculated to control the oxidant composition. Before being recycled to the CaL calciner inlet, this CO2-rich stream will be properly cooled in a regenerative riser-cyclone stage, designed to preheat the fresh raw meal-based sorbent fed to the pilot, minimizing the additional fuel supplied to run the calcium looping process. In the carbonator, the amount of sorbent (FCa/FCO2) will be tuned either by increasing the raw meal exchanged with the CaL calciner or by internally recycling a fraction of sorbent from the carbonator outlet to the inlet. First short campaigns will be carried out by specialized Buzzi Unicem operators (assisted by CLEANKER partners such as, Politecnico di Milano, Laboratorio Energia e Ambiente Piacenza, IKN, University of Stuttgart and VDZ) to test the process performances as a function of the type of raw meal, the amount of sorbent (solid to gas ratio in the carbonator) and the carbonation/calcination operating temperatures. \n \nThe experimental activity will prove the stability and the effectiveness of the process by running over hundreds of hours the optimal experimental configuration, capable of achieving a constant carbon capture rate higher than 90%. Besides the continuous monitoring of process temperatures, flow rates and gas compositions, the experimental campaigns will be supported by post-processing sorbent analysis, in order to evaluate the capture capacity of the raw meal and the extent of side reactions. Test results will be exploited to validate simulation models and to improve the future scale-up and the design of an industrial size CaL plant.