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The present study investigates the impact of biomass origin on the properties of biochar and its interaction with different treatment conditions, CO2 adsorption, and regeneration ability. The bioch...

The coadsorption of Hg⁰ and SO₃ on pure and Cu/Mn doped CeO₂(110) surfaces were investigated using the Density Functional Theory (DFT) method. A p (2 × 2) supercell periodic slab model with seven atomic layers was constructed to represent the CeO₂(110) surface. The results indicated that Hg⁰ physically adsorbed on the CeO₂(110) surface, while Hg⁰ chemically adsorbed on the Cu/Mn doped CeO₂(110) surface, which agree well with the experimental results that Cu and Mn doped CeO₂ greatly improved the Hg⁰ adsorption capacity of the adsorbent. The calculated results suggested that SO₃ more easily adsorbs on the above three surfaces than Hg⁰ due to the higher adsorption energy. The adsorption configurations and electronic structures indicated SO₃ reacted with O atoms of the surface to form SO₄²– species. Hence, SO₃ inhibits Hg⁰ adsorption on the CeO₂(110) surface by competing with Hg⁰ for surface lattice oxygen. In addition, SO₃ decreased the activity of the surface O atoms, which directly caused the negative effect on Hg⁰ adsorption.

The present study discusses a novel biochar activation technique consisting of physical modification using low frequency ultrasound and chemical functionalization with individual amines and their b...

It is known that NO in the flue gas can be effectively converted to NO2 by O3. The objective of this work is to investigate the feasibility of simultaneously abating NO2 and SO2 from flue gas by liquid-phase conversion. A suite of cost-effective additives for enhancing NO2 absorption through enriching the concentration of sulfite ion, SIV, in the liquid phase has been evaluated under pH similar to traditional flue-gas desulfurization (FGD). Experiments were conducted in a lab-scale washing tower with CaSO3 slurry, including metal and non-metal additives: FeSO4, FeCl2, Fe2(SO4)3, MnSO4, MnCl2, MgSO4, MgCl2, (NH4)2SO4, and NH4Cl. All of these additives enhance the absorption efficiency of NO2. Ferrous sulfate, FeSO4, is the most effective additive, with absorption efficiency reaching 95%, but the loss of additive is high because of the oxidation of FeII into FeIII. Ammonium sulfate, (NH4)2SO4, has similar absorption efficiency but shows lower loss during absorption. Its absorption efficiency improves with a...

Polar solvents are known to swell coal, break hydrogen bonds in the macromolecular structure, and enhance coal liquefaction efficiencies. The effects of the pretreatment of coal using supercritical CO{sub 2} on its physical structure and combustion properties have been studied at the bench-scale level. Emphasis has been placed on NO reburning, NO emissions during air-fired and oxy-fired combustion, and loss on ignition (LOI). Pretreatment was found to increase porosity and to significantly alter the fuel nitrogen reaction pathways. Consequently, NO reduction during reburning using bituminous coal increased, and NO emissions during oxidation of lignite decreased. These two benefits were achieved without negative impacts on LOI.

It is known that polar solvents swell coal, break hydrogen-bonds in the macromolecular structure, and enhance coal liquefaction efficiencies. The effects of drying, interaction with supercritical CO2 and degassing on the physical structure of coal have been studied using gas sorption technique and a scanning electron microscope (SEM). Both drying and interaction with supercritical CO2 drastically change the micropore and mesopore surface area, absolute volume, and volume distribution in both bituminous coal and lignite. Degassing removes debris in the pore space which allows for better analysis of the changes in the morphology that were induced by drying and exposure to supercritical CO2. SEM reveals that interaction of bituminous coal with supercritical CO2 results in an abundance of carbon structures similar to the maceral collinite.

In a recent study, we discovered that oxygen from the gas phase, organic portions of the coal, and minerals in the coal have profound influence on the formation and desorption of stable surface oxides in the early stages of coal combustion. In an attempt to isolate the effects of minerals, demineralized coals (DMC) are oxidized in O{sub 2} with a contact time less than 1 s, and the amount and strength of stable surface oxides are characterized by temperature-programmed desorption (TPD) up to 1650{sup o}C. Young chars derived from both demineralized lignite and bituminous coals show low and flat TPD profiles over a wide temperature range, signifying the minerals' catalytic activities in forming stable surface oxides for both coals. Indeed, the oxidation rates of chars from both bituminous coals and lignite, estimated based on the O{sub 2} concentrations entering and exiting the Al{sub 2}O{sub 3} reactor, were higher than their DMC counterparts. Moreover, graphite, containing no minerals and organically bound oxygen, has an even lower oxidation rate. Similar to those for the raw coals, the combined oxygen balance and elemental analysis of chars from DMC suggests that the oxygen in the organic portion of the lignite activates oxygen turnover andmore » carbon oxidation during its combustion; neither chars from raw nor demineralized bituminous coals possess these properties. X-ray photoelectron spectroscopy (XPS) of raw and demineralized bituminous coals and their char show peaks at around 532.0 eV in the O(1s) difference spectrum, suggesting the possible existence of intercalated stable surface oxides. 35 refs., 7 figs., 4 tabs.« less

To obtain representative temperature-programmed desorption (TPD) profiles of young oxidized chars up to 1650 °C with minimal reactor wall interferences, the chemistry and physics of four ceramic materials has been critically reviewed. A two-staged experimental apparatus is then uniquely designed to produce chars in an Al2O3 flow reactor with 1−21% O2 followed by in situ TPD with a SiC tube. Comparison of TPD profiles of oxidized chars with those from pyrolyzed chars and ashes suggests early-stage char oxidation is profoundly influenced by oxygen from three sources: organics oxygen, mineral matters, and gas phase O2. Young chars oxidized at 1000 °C with less than 0.3 s residence time shows CO desorption peaks during TPD at three distinct temperatures: 730, 1280, and 1560 °C. The peaks at 730 °C are mainly caused by incomplete devolatilization. The peaks at 1280 °C mainly represent desorption of stable surface oxides and incomplete devolatilization. Increasing the gas phase oxidants notably increases the am...

This paper reports our first study on the deactivation of young chars in flame conditions. The quantity and strength of surface oxides on young chars are monitored in situ by temperature-programmed desorption (TPD) up to 1700 °C. Young chars contain more abundant surface oxides than old chars over a wide range of temperature. Lignite chars possess more oxides than chars derived from a bituminous coal. Chars oxidized at 629 °C show desoprtion products at three distinct temperatures: 725, 1430, and 1700 °C. The TPD peaks around 725 °C correspond to activation energies in the range of 107-170 kJ/mol and have been well-documented in the literature. CO desorbed at around 1430 °C corresponds to activation energies over 300 kJ/mol, signifying the possible roles of strongly bound oxides on the basal planes of carbon. Search of the oxygen source for the huge amount of CO production at 1700 °C reveals that commonly adopted alumina tubes and support materials decompose to Al 2 O (g) and emit a notable amount of O 2 at temperatures above 1300 °C. Moreover, alumina tube and support materials react with CO and form CO 2 ; they also react with carbon and form CO and aluminum oxycarbides. SiC tube, on the other hand, is oxidized by O 2 , CO 2 , and H 2 O and forms SiO (g) , SiO 2(s) , Si-(OH) 4(g) , and CO above 650 °C. Moreover, Si can also form through a secondary reaction of SiC and SiO 2 . Thus, alumina appears suitable for the oxidation part of the experiments, where up to 120 ppm of O 2 emission is acceptable at a temperature of 1700 °C. SiC appears acceptable for TPD, though a small amount of SiC may be oxidized by the TPD product, CO 2, at temperatures above 900 °C. Oxidation of SiC prior to TPD should be avoided.

The breakage of coal particles into smaller fragments during the devolatilization stage mostly occurs randomly due to the heterogeneous structure of coal, thereby necessitating a stochastic approach for modeling. In the present work, the master equation approach has been proposed for predicting the statistics of the size distribution of the coal particles during their stepwise degradation. The particle-size distribution has been lumped into a limited number of states, each representing a particular volume range. The master equation and the equations for the means, variances, and covariances of the random variables, each representing the number of particles in the individual states in the system, have also been derived from the stochastic population balance. Simulation has been performed with a stiff differential equation solver to predict the dynamic particle number statistics at any time. By fitting the model to experimental data, the transition intensity function is found to be inversely proportional to the square of particle radius.

The effect of reburning fuel type on the partitioning of fixed-nitrogen species in the fuel-rich stage of reburning was studied in a bench scale flow reactor. Methane, hexane, benzene, bituminous coal, and lignite were used as reburning fuels. A simulated flue gas consisting of CO 2 (16.8%), 0 2 (1.95%), NO (1000ppm), and helium was used for experiments at 1100 o C and ca. 0.2s residence time. The total fixed nitrogen (TFN) speciation was found to depend strongly on fuel type ans stoichiometric ratio (SR). Rich stoichiometries promoted conversion of NO to HCN, whereas conversion of HCN to N 2 was promoted by lean stoichiometries. In this stimulated reburning stage, the optimum stoichiometry of TFN production for gaseous fuels was ca. SR=0.95

In this work, the dispersion of CO and CO 2 from temperature-programmed desorption of char before they reach the mass spectrometer is sequentially examined by a set of methods