Oxy-fuel Calciner Research Articles

Clinker based on calcium looped meals from the Cleanker Project.

The Cleanker (CLEAN clinKER production by Calcium Looping process) project, financed in the framework of Horizon 2020 EU funding program, has demonstrated the feasibility of the integrated CaL concept at industrial scale in a new demo system realised in the Buzzi Unicem cement plant in Vernasca (IT). The Calcium Looping (CaL) CO2 capture process exploits the reversible reaction of limestone calcination/carbonation (CaCO3 ↔ CaO + CO2). The Cleanker pilot plant consists of the coupling of a carbonator and an oxyfuel calciner. When the flue gases from kiln (containing CO2) flow through the carbonator together with calcined meal, which acts as a CO2 sorbent, carbonation takes place and CO2 is fixed in calcium carbonate. CaO is then regenerated in the calciner, where the opposite reaction takes place, and the captured CO2 is released. When the lime/limestone looping is carried out through a carbonator and a calciner operated in oxyfuel, a concentrated CO2 stream is obtained that can be efficiently addressed towards CCS or CCUS processes. In the Cleanker Project, the possibility to use raw meal for clinker production has been exploited and the meals sampled at the outlet of the oxyfuel calciner have been characterised and used for producing clinker at a lab scale. Calcium looped (CaL) meals collected at different sampling point during the operation of the CaL plant were characterised by means of X-ray fluorescence spectroscopy, X-ray diffraction and particle size distribution. Electron scanning microscopy revealed significant differences in the surface of particles of the looped meals with respect to the original one, resulting from the loading and unloading of CO2 during the looping cycles. The meals were burnt in a laboratory furnace and the obtained clinkers have been characterised on a chemical, mineralogical and microscopical point of view, revealing the good burnability of all the meals and attesting the possibility to reintegrate the materials in the clinker production process. A lower alite/belite ratio in the clinker produced from the looped meals was observed: actually, the depletion of calcium during the recirculation of the meal in the calciner/carbonator system led to a reduction of the lime saturation factor influencing the mineralogical composition of the product.

Techno-economic optimization and off-design analysis of CO2 purification units for cement plants with oxyfuel-based CO2 capture

This paper evaluates the technical and economic performance, as well as the direct/indirect CO2 emissions of the CO2 Purification Unit (CPU) for cement plants equipped with oxyfuel-based CO2 capture. Two configurations, targeting two different outlet CO2 specifications (‘moderate’ 95% purity and ‘high’ 99.9% purity) are designed, modelled and optimized in order to minimize the incremental clinker production cost for different values of the carbon tax. Mass and energy balances are simulated with Aspen Plus, while the operating conditions are numerically optimized with Matlab. Results show that moderate purity can be achieved with an increased cost of clinker of 16.3 €/tclk (CO2 recovery 99.3%), while the base high purity configuration leads to a 19.3 €/tclk increase (CO2 recovery 96.1%). Sensitivity analyses are carried out on design parameters (fuel and air infiltrations in the oxyfuel calciner line) and exogenous factors (carbon tax, CO2 intensity of electricity). Air infiltration rate has the highest impact on the incremental cost of clinker (increased by 25% when air leakage grows from 0 to 10%) and on the selection of optimal operational conditions. Off-design analyses aimed at assessing the impact of air infiltration changing over time highlight the relevance of designing the CPU for the scenario with air infiltrations, while selecting reasonable temperature differences (e.g. 5K) to avoid operability issues in the cold box heat exchanger. For the base case CPU, the cost of clinker increases by 3 €/tclk when moving from zero to 10% air infiltration.

Techno-Economic and Off-Design Analysis of Two CO2 Purification Units for Low-Carbon Cement Plants with Oxy-Fuel Calcination

This paper presents the techno-economic assessment of the CO2 Purification Unit (CPU) included in cement plants based on CO2 capture via oxy-fuel calcination. Two configurations, targeting two different outlet CO2 specifications (‘moderate’ and ‘high’ purity), have been optimized in order to minimize the increase in the clinker production cost due to this process unit. Air infiltration rate is the parameter with the highest impact on the operational conditions (e.g. separation pressure) and on the incremental cost of clinker due to the CPU (up to 20% for the worst case considered). The work has been carried out within the framework of the CLEANKER project.

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

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. The 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. The 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. The 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. The 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.

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

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.

Sorbent steam reactivation and methane-concentrated calcination for calcium-looping carbon capture: Compatibilities and limitations

This paper investigates the equilibrium performance of CaO hydration and CaCO3/Ca(OH)2 co-calcination in calcium-looping processes. A novel lime hydration configuration is proposed, introducing saturated steam as the reactivating reagent and direct-heat-removal medium. The proposed hydrator generates a substantial amount of superheated steam, used elsewhere as required. The slaked lime and limestone are calcined simultaneously in a methane-concentrated oxy-fuel calciner. The equilibrium performance of the co-calciner is studied at different reactor temperatures, operating pressures, solid/gas feed ratios and feed compositions. A correlation is proposed which estimates the required gaseous feed composition for autothermal, coke-free and complete sorbent regeneration using this novel technology.

Calcium Looping technology demonstration in industrial environment: the CLEANKER project and status of the CLEANKER pilot plant

The CLEANKER (CLEAN clinKER production by calcium looping process) project got EC support from October 2017 to September 2021 under the Horizon 2020 call LCE 29 – 2017. CLEANKER (www.cleanker.eu) aims at demonstrating at TRL7 (Technology Readiness Level) the Calcium Looping (CaL) concept in a configuration highly integrated with the cement production process, making use of entrained flow reactors. There are currently no feasible methods to produce clinker, and thus cement, without releasing CO2 from CaCO3, and, given the lifetime of a cement plant, the technologies to be developed have to be retrofittable. In addition to oxyfuel combustion and post-combustion solvent-based capture technologies, which have attracted most of the research efforts up to now, Calcium Looping is recognized as another very promising emerging technology for CO2 capture in cement plants. The core activity of the 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. The CLEANKER implementation plan spans four years from October 2017 to September 2021.The project is in its crucial phase: the erection of the demo plant is going to be completed by the end of August 2020 and the experimental campaigns will start immediately after.

Intensified steam methane reforming coupled with Ca-Ni looping in a dual fluidized bed reactor system: A conceptual design

This study presents an inclusive conceptual design of an intensified steam methane reforming technology coupled with in situ CO2 capture and chemical looping operating in two interconnected fluidized bed reactors. Simulations were run using Aspen Plus® and both the hydrodynamic and kinetic phenomena of the reactors were properly implemented through correlations and kinetic models of literature. High-purity H2 was generated in a bubbling bed reformer, while regeneration occurred at temperatures near 900 °C in a fast fluidization reactor due to the generated CO2 that impeded thermodynamically the calcination in lower temperatures. Simulation results had a satisfactory agreement with experiments in a bench-scale fixed bed apparatus, with both being close to equilibrium. A parametric study including the number of stages that the reformer is divided, the NiO/CaO and CaO/C molar ratios and the type of oxidant (O2/air) of regenerator was conducted. Increasing the NiO/CaO ratio led to lower thermal requirements at the expense of lower H2 yield and no alteration of the CH4 conversion in contrast to thermodynamics. Air utilization in the regenerator avoided the harsh operational conditions but led to the CO2 isolation with lower purity. It was proposed to reduce the energy requirements by incorporating Ni reoxidation with an oxy-fuel calciner.

A semi-industrial preparation procedure of CaO-based pellets with high CO2 uptake performance

A semi-industrial preparation procedure of CaO-based sorbent pellets was developed for the calcium looping process. First, Ca12Al14O33, was incorporated into CaO-based sorbents to enhance the cyclic stability via a wet mixing method. Then, spray-drying technology, was chosen to obtain well-mixed precursor powders quickly and efficiently in an industrialized mode. Finally, the CaO-based pellets were fabricated via an extrusion-spheronization method for practical industrial application and doped with three novel types of pore formers (urea, polyethylene glycol and polyvinyl alcohol). It is found that the sorbent pellets with 5 wt% urea possess the optimal CO2 uptake. Even under the oxy-fuel calcination condition, the sorbent pellets still held a 0.29 g CO2/g sorbent capacity at the 25th cycle, which was approximately 10 times as high as that of limestone pellets. Moreover, the sorbent pellets exhibited a high anti-attrition capacity, with a weight loss of below 0.8% after 3000 rotations. Therefore, the sorbent pellets derived from the foregoing semi-industrial synthesis procedure can simultaneously satisfy the requirements of cyclic sorption performance, industrial production and practical industrial application. This work provides a possibility for the production of highly efficient CaO-based sorbent pellets, to some extent, which can pave the way for the application of calcium looping process.

CLEANKER – Clean Clinker by Calcium Looping Process for Low-CO2 Cement Production

The CLEANKER project got EC support from October 2017 to September 2021 under the Horizon 2020 call LCE 29 – 2017 . CLEANKER (www.cleanker.eu) aims at demonstrating at TRL7 the Calcium Looping (CaL) concept in a configuration highly integrated with the cement production process, making use of entrained flow reactors. The cement industry is a key-sector for the reduction of CO2 emissions. CO2 generation in cement production processes in fact, cannot be disregarded due to the calcination of limestone (CaCO3 dissociated to CaO and CO2), the most important raw material. Around 60% of the direct CO2 emissions from the clinker burning process are due to this reaction. In addition, there are the emissions from combustion of mostly fossil fuels, as well as the generation of electric power required by the process (e.g. grinding), as indirect CO2 emissions. Cement production is thus responsible for about 27% of global anthropogenic CO2 emissions from industrial sources worldwide and for 5% of anthropogenic global CO2 emissions . According to IEA and ZEP studies, cement industry should contribute to the largest CO2 emission reduction through CCS in Europe, in order to meet the target of 2°C of global temperature increase (IEA 2DS scenario). There are currently no feasible methods to produce clinker, and thus cement, without releasing CO2 from CaCO3, and, given the lifetime of a cement plant (30-50 years), the technologies to be developed have to be retrofittable. In addition to oxyfuel combustion and post-combustion solvent-based capture technologies, which have attracted most of the research efforts up to now, Calcium Looping is recognized as another very promising emerging technology for CO2 capture in cement plants. Calcium looping (or carbonate looping) is a regenerative process, which takes advantage of the capacity of calcium oxide-based sorbents to capture CO2 at high temperatures. The process is divided in two basic steps: (1) the capture of CO2 by “carbonation” of CaO to form CaCO3 in a reactor operating around 650°C; and (2) oxyfuel calcination in a reactor operating above 900-920°C, which makes the CaO available again and releases a gas stream of nearly pure CO2. The highly integrated Calcium Looping process configuration allows achieving high-energy efficiency, with CO2 capture efficiency target over 90%. The overall energy consumption can be kept low by proper integration with raw meal preheating and heat recovery from the kiln flue gases. The adoption of entrained flow gas-solid reactors is particularly suitable for this Calcium Looping configuration, because in such reactors, the same very fine raw material can be used for clinker production (CaO) and for CO2 sorption without additional milling requirements. Moreover, entrained flow reactors are already commonly used in cement plants. The core activity of the 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. Other activities will include: (i) screening of different raw meals to assess their properties as CO2 sorbent, (ii) reactors and process modelling, (iii) scale-up study, (iv) economic analysis, (v) life cycle assessment, (vi) CO2 transport, storage and utilization study, (vii) demonstration of the complete value chain, including mineral carbonation of waste ash with the CO2 captured in the pilot system, (viii) exploitation study for the demonstration of the technology at TRL>7 and for its first commercial exploitation based on CO2 transport and storage opportunities. It integrates the research of 13 organizations: • Representatives from the academia: Politecnico di Milano (Italy), Tallinn University of Technology (Estonia), Lappeenranta University of Technology (Finland); University of Stuttgart (Germany) and Tsinghua University (China); • Research centres: LEAP (Italy), CSIC (Spain) and VDZ (Germany); • SME: Quantis (Switzerland); • Technology provider: IKN (Germany); • End users: Buzzi Unicem and Italcementi – Heidelberg Group (Italy); • Environmental organization: Amici della Terra (Italy). Thus including all the necessary expertise and access to the industrial facilities to reach the ambitious aim of the project. The project is coordinated by LEAP. Acknowledgements: This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 764816. This work is supported by the China Government (National Natural Science Foundation of China) under contract No. 91434124 and No. 51376105. Disclaimer: The European Commission support for the production of this publication does not constitute endorsement of the contents which reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

Impacts and Action Mechanism of Coal Ash on CaO-Based Sorbents for CO2 Capture under an Oxy-fuel Calcination Environment

The emerging calcium looping (CaL) process, basing on the reversible reactions between CaO and CaCO3, is considered to be a potential midterm mitigation solution in capturing CO2 from coal-fired power plants. Normally, the efficient regeneration of sorbents is realized through oxygen-enriched combustion of coal above 900 °C. However, the minerals in coal will potentially affect the CO2 capture ability of sorbents and the effect could gradually intensify as the temperature increases. Therefore, in this work, effects of ash with a series of variables under a more practical oxy-fuel calcination condition are evaluated, and the action mechanism of ash on the sorption process is especially studied. Using a combination of testing approaches, both physical and chemical contributions are observed and identified for the effect of coal ash on the CO2 capturing of CaO-based sorbents. The physical influence, caused by ash deposition and following grain aggregation, on CaO-based sorbents for CO2 capture is found to be...

The effect of HCl and steam on cyclic CO2 capture performance in calcium looping systems

Calcium looping is CO2 capture technology that is considered to be technically feasible at an industrial scale using a variety of fuels such as natural gas, coals, biomass, refuse derived fuels, and biofuels. Unfortunately, many of these fuels contain significant quantities of chlorine which principally converts to gaseous HCl during combustion or gasification. To date, very few studies have examined the effect of HCl on sorbent CO2 capture performance using calcium-based sorbents under realistic carbonation and calcination conditions. In this work, experiments were conducted using thermogravimetric analysis and fixed bed reactor testing to determine the effect of HCl addition during carbonation and calcination over repeated cycles using a Canadian limestone. The presence of HCl was found to increase sorbent reactivity towards CO2 capture when steam was injected during calcination. The resulting decomposition of CaCl2 to CaO during calcination caused changes in the particle morphology, which in turn decreased the CO2 diffusional resistance during carbonation. Fixed bed test results provided confirmation of full sorbent dechlorination under typical oxy-fuel calcination conditions. It was shown that both particle surface area and pore volume were higher during tests where HCl was present during carbonation and that greater than 99% HCl capture could be achieved without adversely affecting sorbent CO2 capture performance when steam was present during both carbonation and calcination.

Investigation of novel naturally occurring manganocalcite for CO2 capture under oxy-fuel calcination

The rapid capacity decay of CaO-based sorbents from limestone is one of the key issues for post-combustion CO2 removal using calcium looping process. Finding other naturally occurring Ca-containing minerals instead of limestone has been proved to be an effective way to acquire sorbents with highly improved cyclic CO2 capture performance. In the current work, a novel naturally occurring manganocalcite mineral was employed to produce CaO-based sorbent. EDS mapping has demonstrated that the inert solid support of Ca2MnO4 are homogeneously dispersed among the ultrafine active specie of CaO particles. As a result, calcined manganocalcite exhibits an obviously enhanced 20-cycle performance compared to calcined limestone when pure N2 calcination is used. Even under oxy-fuel calcination atmosphere, the sorbent still holds a surprisingly high conversion of ∼40% at the 20th cycle, 3.1 times as high as that of calcined limestone. Besides, the calcined manganocalcite is superior to calcined limestone for capturing CO2 under SO2-presence carbonation and oxy-fuel calcination. Coal combustion process during calcination stage was also investigated through employing synthetic char to simulate coal to burn with manganocalcite. It has been found that 0.5wt.% addition of synthetic char is the optimal ratio for manganocalcite in this study.

The Calcium Looping Process for Low CO2 Emission Cement Plants

The aim of this work is investigating the application of the Calcium looping process in cement plants with CO2 capture. A novel configuration with oxyfuel calciner and a carbonator integrated in the raw meal suspension preheater has been assessed by means of process simulations. The results obtained show a high potential of the proposed process, with equivalent avoided CO2 emissions (i.e. accounting for credits associated to electric power export) of about 94%, vs. 76% obtained for a competitive oxyfuel cement plant.

Effect of Sulfation during Oxy-Fuel Calcination Stage in Calcium Looping on CO2 Capture Performance of CaO-Based Sorbents

Sulfation of calcium-based sorbent is bound to occur during carbonation or calcination of the sorbent in a calcium looping system if SO2 is present in the system, and it will influence the CO2 capture capacity of the sorbent. While the effect of sulfation during the carbonation stage on the CO2 capture capacity has been studied by some researchers, the effect of sulfation during the calcination stage has not been studied extensively. In this study, the effect of sulfation during the calcination stage under oxy-fuel combustion conditions on the CO2 capture capacity of two calcium-based sorbents was investigated. The results showed that the calcination temperature and O2 concentration of 5-20% had little effect on the sulfation of the sorbents, while SO2 concentration and the presence of H2O greatly influenced the cyclic performance of the sorbents. Furthermore, reducing calcination time seems to be an effective way to limit sulfation during calcination, because the sulfation rate is slow in the initial induction stage of the gas-solid reaction.

Process design and energy requirements for the capture of carbon dioxide from air

A process to capture carbon dioxide from air to reduce its atmospheric concentration and to mitigate climate change is studied. It is based on the absorption of carbon dioxide in a sodium hydroxide solution, its precipitation as calcium carbonate, and its release as pure gas stream through oxy-fuel calcination. The process utilizes existing commercial technologies wherever possible, particularly in the case of the absorber, whose design is carried out in detail. The analysis allows deriving material and energy balances for the whole process and determining energy demands that can be used for a technical, economical, and environmental feasibility evaluation of the technology. In particular, it indicates that the real specific energy demand is larger than the heat released to emit the same amount of CO 2 by the combustion of coal, and smaller than that of methane.