D12.3 Calcium Looping CO2 capture for the cement industry – Demonstration of fluidized bed CaL at 200 kW scale and research on entrained flow CaL

In this report, the findings of experimental research regarding Calcium Looping CO2 capture for the cement industry are presented. The Calcium Looping process using the fluidized bed technology was demonstrated at semi-industrial scale at USTUTT’s 200 kWth Calcium Looping pilot facility investigating comprehensively a field of operation conditions relevant to the technology’s application in the clinker production process, such as high make-up ratios up to 1 molCaO/molCO2, CO2 concentrations up to 33 vol%wet, carbonator temperatures between 600 to 710 °C, looping ratios up to 20 molCaO/molCO2, two different reactor configurations (CFB-CFB and BFB-CFB) and two limestone qualities. CO2 capture applying an alternative Calcium Looping concept using entrained flow reactors has been investigated at CSIC’s electrically heated drop tube reactor.
High CO2 capture rates in the carbonator (up to 98 %) have been demonstrated at industrially relevant conditions (TRL6). The high make-up ratios that are feasible when applying the Calcium Looping technology to the cement industry result in increased bed activity which enhances the CO2 capture performance. The high make-up feed rates of uncalcined material require however the provision of an increased thermal power in the calciner compared to Calcium Looping systems for power plant application. This needs to be addressed by a suitable calciner design.
Carbonator CO2 capture rates of 90 % and above were achieved at carbonator temperatures below 650 °C and looping ratios above 8 molCaO/molCO2 for make-up ratios around 0.7 molCaCO3/molCO2. To reach the same capture rate with a make-up ratio of 0.2 molCaCO3/molCO2, a looping ratio of 10.5 molCaO/molCO2 was estimated.
Regarding the experimental testing of CO2 capture by CaO carbonation under entrained flow reactor conditions, CSIC has completed additional test campaigns measuring the extent of carbonation conversion in gas-solid contact time scales between 1-6 seconds at different concentrations of CO2, carbonation temperatures, initial activity of the material and different types of CaO precursors. It has been confirmed that the carbonation reaction follows a pseudo-homogeneous kinetic model, first order in respect to CO2, with a small positive effect of water vapour in the gas. The rate of reactions are shown to be linearly dependent of the CO2 carrying capacity of the material, Xave, irrespective of the nature of the calcined material. A first screening of calcination conditions in a TG apparatus, regarding this new important aspect identified during the CEMCAP project, was included in D12.2. The results in EF conditions presented in this report confirm that, in order to understand the progress of carbonation reaction in integrated CaL systems, it will be essential to anticipate the value of Xave resulting after calcination, taking into account the competitive reactions (i.e. belite formation) that are present during calcination of cement raw meals and that tend to reduce Xave.