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This paper presents a numerical study of the gas-liquid flow inside a novel Venturi carbonation reactor for red mud processing. The model is based on the Eulerian-Eulerian model, with population balance method being used to describe bubble size distribution. The validity of the model is confirmed through different applications. It is then used to analyze the flow and gas dispersion inside the reactor at different liquid flow rates. The numerical results reveal that the new reactor can produce periodic variations of fluid pressure and gas holdup with time. Correspondingly, the ascending liquid flow presents a vortex column, swinging periodically in the radial direction. This flow oscillation becomes more obvious at an increased liquid flow rate, promoting bubble refining and uniform distribution. The results of this study should be useful not only for better understanding the gas-liquid flow but also for designing and controlling this new reactor. [ABSTRACT FROM AUTHOR]

Amine-based absorption is the primary contender for postcombustion CO2 capture from fossil fuel-fired power plants. However, significant concerns have arisen regarding the formation and emission of toxic nitrosamine and nitramine byproducts from amine-based systems. This paper reviews the current knowledge regarding these byproducts in CO2 capture systems. In the absorber, flue gas NOx drives nitrosamine and nitramine formation after its dissolution into the amine solvent. The reaction mechanisms are reviewed based on CO2 capture literature as well as biological and atmospheric chemistry studies. In the desorber, nitrosamines are formed under high temperatures by amines reacting with nitrite (a hydrolysis product of NOx), but they can also thermally decompose following pseudo-first order kinetics. The effects of amine structure, primarily amine order, on nitrosamine formation and the corresponding mechanisms are discussed. Washwater units, although intended to control emissions from the absorber, can contribute to additional nitrosamine formation when accumulated amines react with residual NOx. Nitramines are much less studied than nitrosamines in CO2 capture systems. Mitigation strategies based on the reaction mechanisms in each unit of the CO2 capture systems are reviewed. Lastly, we highlight research needs in clarifying reaction mechanisms, developing analytical methods for both liquid and gas phases, and integrating different units to quantitatively predict the accumulation and emission of nitrosamines and nitramines. [ABSTRACT FROM AUTHOR]

NaNO3 modified MgO sorbents have a large theoretical CO2 capture capacity, but their practical capture performance at medium temperatures (350-400 °C) is poor for the high thermodynamic equilibrium partial pressure of CO2 at these temperatures. The thermodynamic limitations for NaNO3 modified MgO sorbents can be relaxed by adding alkali or alkaline earth carbonates, and the effective carbonation temperature can be shifted to the higher temperatures (350-400 °C) to satisfy the requirement of fast kinetic reactions. In this paper, the CO2 absorption characteristics of NaNO3 modified MgO with or without CaCO3 are compared experimentally to verify the promoting effects of CaCO3. Based on the CaCO3 promoting theory, the methods of stage heating during carbonation and partial decomposition during regeneration were adopted to improve the CO2 absorption ability of NaNO3 modified MgO sorbents at 350 °C. Combined with the composition of fuel gas, effects of increasing CO2 partial pressure and H2O were tested, and they both accelerated the carbonation rates of the sorbents, which forecasted the application potential of NaNO3 modified MgO sorbents. [ABSTRACT FROM AUTHOR]

Thedensity and viscosity of partially carbonated aqueous solutionsof either 2-dimethylaminoethanol or 2-diethylaminoethanol were measuredover a temperature range of (298.15 to 353.15) K with alkanolaminemass fractions of 0.15 to 0.45. Correlations were developed to representthe density and viscosity of these solutions as a function of amineconcentration, CO2loading, and temperature. For the density,the correlation represents the experimental data to within ±0.2 %, while the viscosity data were correlated to within ± 4%. The data and models reported in this paper will help facilitatea better understanding of the performance of these amines in CO2capture processes, especially in relation to mass transferand hydrodynamic calculations. [ABSTRACT FROM AUTHOR]

Theuse of a calcium looping cycle for the production of hydrogen(Ca-LHP) from biomass gasification syngas is a promising alternativeto the conventionally used catalytic water–gas shift process.The process takes place in two fluidized bed reactors connected bysolid CaO flow. In the first reactor (the carbonator), the water–gasshift reaction is enhanced by CO2capture via the carbonationreaction with CaO. In the second reactor (the regenerator), the capturedCO2is released. This paper presents results from a continuouslyoperated 20 kWthdual fluidized-bed facility using a syngas-likemixture obtained from biomass gasification. The influence of the mainprocess parameters, i.e., temperature in the carbonator (Tcarb), looping ratio (LR), and space time (τ) onthe H2concentration, and the CO conversion in the carbonatorwas investigated. A H2concentration of 84.4 vol %dryand a CO conversion of 76.4% were achieved for a carbonatortemperature of 639 °C, a looping ratio of 6 molCa/molCO+CO2, and a space time of 1.0 h. Additionally,experiments with different syngas compositions as obtained from variousbiomass fluidized bed gasification processes were performed and themechanical stability as well as the chemical sorbent activity werestudied. The potential of the calcium looping cycle for H2production could be shown by the experimental results obtained andtheir comparison with literature. [ABSTRACT FROM AUTHOR]

Steel production is one of the largest contributors to industrial CO2 emissions. This industry also generates large amounts of solid byproducts, such as slag and sludge. In this study, fine grained stainless-steel slag (SSS) is valorized to produce compacts with high compressive strength without the use of a hydraulic binder. This carbonation process is investigated on a pore-scale level to identify how the mineral phases in the SSS react with CO2, where carbonates are formed, and what the impact of these changes is on the pore network of the carbonated SSS compact. In addition to conventional research techniques, high-resolution X-ray computed tomography (HRXCT) is applied to visualize and quantify the changes in situ during the carbonation process. The results show that carbonates mainly precipitate at grain contacts and in capillary pores and this precipitation has little effect on the connectivity of the pore space. This paper also demonstrates the use of a custom-designed polymer reaction cell that allows in situ HRXCT analysis of the carbonation process. This shows the distribution and influence of water and CO2 in the pore network on the carbonate precipitation and, thus, the influence on the compressive strength development of the waste material. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The effects of different types of anionic polyacrylamide (PAM) on crystallization behavior of precipitated calcium carbonate (PCC) prepared via carbonation using calcium hydroxide and carbon dioxide gas. The percentage of aragonite phase increased higher reaction temperature. The use of anionic PAM resulted in the formation of larger PCC aggregates than in the case of PCC crystallized without anionic PAM. This outcome resulted from a contraction of the PAM coils due to the electrostatic screening and counterion condensation effects. The carbonate ions were combined with aggregated calcium ions. Furthermore, the carbonation reaction time could also be reduced by the addition of anionic PAM. [ABSTRACT FROM AUTHOR]