Experimental investigation of the calcination reactor in a tail-end calcium looping configuration for CO2 capture from cement plants

• Published in: Fuel (Guildford) 2021-01, Vol.284, p.118927, Article 118927
• Main Authors: Hornberger, Matthias, Moreno, Joseba, Schmid, Max, Scheffknecht, Günter
• Format: Article
• Language: English
• Subjects: Boundary conditions; Calcium; Calcium carbonate; Calcium looping; Carbon dioxide; Carbon sequestration; CCS; Cement; Cement industry; Cement plants; Clinker; CO2 capture; Combustion; Data integration; Electric power generation; Flue gas; Fossil fuels; Gases; High temperature; Industrial plants; Integration; Limestone; Manufacturing industry; Nuclear fuels; Oxy-fuel; Oxy-fuel calciner; Oxygen; Power plants; Regeneration; Roasting; Sorbents; Sulfation; Sulfur dioxide; Technology; Temperature profiles
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2020.118927

The calcium looping process is a high temperature post-combustion CO2 capture technology using limestone or a calcium containing sorbent to separate CO2 from flue gases. Hence, it is expected to be a particularly suitable CO2 capture technology for the decarbonisation of cement plants. Sharing a common feedstock, CaCO3, enables the reutilisation of purged calcium looping sorbent (i.e. CaO) in the cement clinker manufacturing process. Thus, allowing the operation with large amounts of sorbent make-up and setting new beneficial boundary conditions for the calcium looping process. So far, calcium looping CO2 capture has been demonstrated at semi industrial scale for fossil fuelled power plants but not yet for cement plants. In this work, results obtained from University of Stuttgart’s 200 kW calcium looping pilot plant investigating the so called tail-end calcium looping cement plant integration are presented focusing on the operation of the oxy-fuel calciner. Different integration levels between the cement plant and the calcium looping process have been assessed with make-up ratios up to 0.9 mol mol−1 and CO2 flue gas concentrations up to 0.35 m3 m−3. The calcination performance covering a broad range of sorbent make-up rates was assessed using the active space time approach adapted to the calcium looping calciner. The calcination performance was minorly influenced by the calcination temperature in the investigated temperature range (895 °C–932 °C). An active space time of approx. 37 s was sufficient to achieve a regeneration efficiency of 0.9 mol mol−1. Uniform temperature profiles without major hotspots were obtained throughout the experiments operating with recirculation rates as low as 20% and oxygen inlet concentrations as high as 0.56 m3 m−3 on a wet basis. The calciner’s flue gas showed an increased formation of NOx associated to the combustion in a lime bed ranging from 500 × 10−6 m3 m−3 to 750 × 10−6 m3 m−3 increasing linearly with increasing excess oxygen concentration. Contrarily, SO2 emissions were significantly decreased averaging around 10 × 10−6 m3 m−3, due to beneficial desulphurisation conditions (i.e. high Ca/S ratio and optimal oxy-fuel sulphation temperature). Based on the obtained results CO2 purities around 0.95 m3 m−3 can be anticipated for the calciner’s flue gas.