Modeling the carbonator of a Ca-looping process for CO2 capture from power plant flue gas

Techno-Economic Analyses of the CaO/CaCO3 Post-Combustion CO2 Capture From NGCC Power Plants

Calcium looping is a post-combustion technology that enables CO2 capture from the flue gases of industrial processes. While considerable studies have been performed at various levels from fundamental reaction kinetics to the overall plant efficiency, research work on techno-economic analyses of the calcium looping processes is quite limited, particularly for the Natural Gas Combined Cycle (NGCC). Earlier work has shown that theoretically, a high thermal efficiency can be obtained when integrating calcium looping in the NGCC using advanced process configurations and a synthetic CaO sorbent. This paper presents an investigation of calcium looping capture for the NGCC through a techno-economic study. One simple and one advanced calcium looping processes for CO2 capture from NGCC are evaluated. Detailed sizing of non-conventional equipment such as the carbonator/calciner and the solid-solid heat exchanger are performed for cost analyses. The study shows that the CO2 avoided cost is 86–95 €/tCO2, avoided, which is considerably more expensive than the reference amine (MEA) capture system (49 €/tCO2, avoided). The calcium looping processes considered have thus been found not to be competitive with the reference MEA process for CO2 capture from NGCC with the inputs assumed in this work. Significant improvements would be required, for example, in terms of equipment capital cost, plant efficiency and sorbent annual cost in order to be make the calcium looping technology more attractive for capturing CO2 from NGCC plants.

Nano-TiO2 promoted CaO-based high-temperature CO2 sorbent: influence of crystal level properties on the CO2 sorption efficiency

This work investigates the multi-cycle CO₂ sorption and the kinetics of the carbonation reaction of nano-TiO₂ promoted CaO synthesized from commercially available micron sized CaCO₃.

Comparison of Technologies for CO2 Capture from Cement Production—Part 1: Technical Evaluation

A technical evaluation of CO2 capture technologies when retrofitted to a cement plant is performed. The investigated technologies are the oxyfuel process, the chilled ammonia process, membrane-assisted CO2 liquefaction, and the calcium looping process with tail-end and integrated configurations. For comparison, absorption with monoethanolamine (MEA) is used as reference technology. The focus of the evaluation is on emission abatement, energy performance, and retrofitability. All the investigated technologies perform better than the reference both in terms of emission abatement and energy consumption. The equivalent CO2 avoided are 73–90%, while it is 64% for MEA, considering the average EU-28 electricity mix. The specific primary energy consumption for CO2 avoided is 1.63–4.07 MJ/kg CO2, compared to 7.08 MJ/kg CO2 for MEA. The calcium looping technologies have the highest emission abatement potential, while the oxyfuel process has the best energy performance. When it comes to retrofitability, the post-combustion technologies show significant advantages compared to the oxyfuel and to the integrated calcium looping technologies. Furthermore, the performance of the individual technologies shows strong dependencies on site-specific and plant-specific factors. Therefore, rather than identifying one single best technology, it is emphasized that CO2 capture in the cement industry should be performed with a portfolio of capture technologies, where the preferred choice for each specific plant depends on local factors.

Effect of SO2and steam on CO2capture performance of biomass-templated calcium aluminate pellets

Four types of synthetic sorbents were developed for high-temperature post-combustion calcium looping CO₂capture using Longcal limestone. Pellets were prepared with: lime and cement (LC); lime and flour (LF); lime, cement and flour (LCF); and lime, cement and flour doped with seawater (LCFSW). Flour was used as a templating material. All samples underwent 20 cycles in a TGA under two different calcination conditions. Moreover, the prepared sorbents were tested for 10 carbonation/calcination cycles in a 68 mm-internal-diameter bubbling fluidized bed (BFB) in three environments: with no sulphur and no steam; in the presence of sulphur; and with steam. When compared to limestone, all the synthetic sorbents exhibited enhanced CO₂capture performance in the BFB experiments, with the exception of the sample doped with seawater. In the BFB tests, the addition of cement binder during the pelletisation process resulted in the increase of CO₂capture capacity from 0.08 g CO₂per g sorbent (LF) to 0.15 g CO₂per g sorbent (LCF) by the 10^thcycle. The CO₂uptake in the presence of SO₂dramatically declined by the 10^thcycle; for example, from 0.22 g CO₂per g sorbent to 0.05 g CO₂per g sorbent in the case of the untemplated material (LC). However, as expected all samples showed improved performance in the presence of steam, and the decay of reactivity during the cycles was less pronounced. Nevertheless, in the BFB environment, the templated pellets showed poorer CO₂capture performance. This is presumably because of material loss due to attrition under the FB conditions. By contrast, the templated materials performed better than untemplated materials under TGA conditions. This indicates that the reduction of attrition is critical when employing templated materials in realistic systems with FB reactors.

Use of steel slag for CO2 capture under realistic calcium-looping conditions

CaO derived from steel slag pretreated with acetic acid can be regenerated in short residence times at 900 °C and its capture capacity is greatly improved.

Effect of dolomite decomposition under CO2 on its multicycle CO2 capture behaviour under calcium looping conditions

The mechanism of dolomite decomposition under CO₂ is responsible for its superior CO₂ capture performance as compared to limestone.

Crystallographic transformation of limestone during calcination under CO2

The calcination of limestone under CO₂ is determined by a topotactic transformation.

Relevant influence of limestone crystallinity on CO₂ capture in the Ca-looping technology at realistic calcination conditions

We analyze the role of limestone crystallinity on its CO2 capture performance when subjected to carbonation/calcination cycles at conditions mimicking the Ca-looping (CaL) technology for postcombustion CO2 capture. The behavior of raw and pretreated limestones (milled and thermally annealed) is investigated by means of thermogravimetric analysis (TGA) tests under realistic sorbent regeneration conditions, which necessarily involve high CO2 partial pressure in the calciner and quick heating rates. The pretreatments applied lead to contrasting effects on the solid crystal structure and, therefore, on its resistance to solid-state diffusion. Our results show that decarbonation at high CO2 partial pressure is notably promoted by decreasing solid crystallinity. CaO regeneration is fully achieved under high CO2 partial pressure at 900 °C in short residence times for the milled limestone whereas complete regeneration for raw limestone requires a minimum calcination temperature of about 950 °C. Such a reduction of the calcination temperature and the consequent mitigation of multicyclic capture capacity decay would serve to enhance the efficiency of the CaL technology. On the other hand, the results of our study suggest that the use of highly crystalline limestones would be detrimental since excessively high calcination temperatures should be required to attain full decarbonation at realistic conditions.

Acoustic streaming enhances the Multicyclic CO2 capture of natural limestone at Ca-looping conditions

The Ca-Looping (CaL) process, based on the multicyclic carbonation/calcination of CaO at high temperatures, is a viable technology to achieve high CO2 capture efficiencies in both precombustion and postcombustion applications. In this paper we show an experimental study on the multicyclic CO2 capture of a natural limestone in a fixed bed at CaL conditions as affected by the application of a high-intensity acoustic field. Our results indicate that sound promotes the efficiency of CO2 sorption in the fast carbonation phase by enhancing the gas-solids mass transfer. The fundamentals of the physical mechanism responsible for this effect (acoustic streaming) as well as the technical feasibility of the proposed technique allows envisaging that sonoprocessing will be beneficial to enhance multicyclic CO2 capture in large-scale applications.