Thermodynamic Equilibrium Simulation Research Articles

A detailed speciation of iron on FCC catalysts based on an integrated use of advanced characterisation methods and thermodynamic equilibrium simulation

This paper aims to characterise six spent and equilibrated catalysts (Ecats) collected from two different fluid catalytic cracking (FCC) units. Apart from bench-scale facilities including Mӧssbauer spectroscopy, XPS, XRD and SEM–EDS, synchrotron X-ray Adsorption Spectroscopy (XAS) was used to investigate the speciation of iron (Fe), vanadium (V) and sulphur (S), their spatial distribution across each single catalyst and variation between the two refineries. Additionally, thermodynamic equilibrium calculations were performed to elaborate the probable formation mechanisms. As have been confirmed, the oxidation state of iron varies greatly between top surface and bulk of each catalyst, and between the samples collected from different refineries. Fe2+ is predominant in the catalysts collected from the refinery with a partial combustion regenerator. It is also in higher concentration inside a catalyst than on the surface, and preferentially combined with other metallic contaminants on the Al3+-centred active sites, causing the deactivation of the catalysts.

Behaviour of mercury during Co-incineration of sewage sludge and municipal solid waste

Co-incineration is promising for disposal of sewage sludge (SS) and municipal solid waste (MSW) with energy recovery, although mercury (Hg) emission in this process is non-negligible. In this work, a series of experimental and simulation works was conducted to provide knowledge about the distribution, ecological toxicity, and transformation of Hg during co-incineration of SS and MSW. The experimental results show that co-incineration can increase the Hg content in incineration ash and reduce the amount of Hg released into the atmosphere. The optimal blending ratio for Hg enrichment was 54 wt% SS and 46 wt% MSW. A modified three-step sequential extraction method was used to investigate the chemical species of Hg in incineration ash. It was found that when SS accounted for 50 wt% ∼75 wt% of the feedstock, the direct toxicity risk of Hg in incineration ash was reduced because of the presence of less hazardous chemical forms of Hg. Thermodynamic equilibrium simulation was also conducted on incineration flue gas. The results show that co-incineration caused more gaseous Hg0 to be oxidized to Hg2+ during the cooling process, leading to less environmental risk to the atmosphere. It is hoped that this work can help develop better co-incineration strategies and guide downstream Hg control technology, to dispose of and recover energy from SS and MSW with a cleaner approach.

Effect of initial compositions on boron carbide synthesis and corresponding growth mechanism

ABSTRACTThe yield of boron carbide (B4C) synthesised by carbothermal reduction (CTR) is low (40–50%) owing to the inappropriate initial composition. In this paper, thermodynamic equilibrium simulations for effects of initial compositions on B4C synthesis were performed, while initial compositions on the quality and yield of B4C synthesised by CTR from B2O3-C mixture at atmospheric pressure were systemically investigated. The reaction mechanisms for B4C synthesis process were thermodynamically analysed. Moreover, growth mechanisms for B4C particles were speculated based on the thermodynamic and experimental results. The results show that the simulations agree well with experimental results, and optimal initial composition is 1.906 (B2O3/C weight ratio). Under optimal condition, B4C powder prepared at 1973 K is high-quality with well crystallinity, purity of 93.58% and yield of 90.05%. Additionally, the prepared B4C particles show two types of morphologies, aggregate of small equiaxed particles and needle-like particle, which are formed through different reaction mechanisms, respectively.

Sequential mineral transformation during underground coal gasification with the presence of coal partings

Underground coal gasification (UCG) can be adopted to convert unminable coal resources into synthesis gas for use in the production of electricity, fuels, and chemicals. UCG is a promising technology with many health, safety, and environmental advantages over conventional mining techniques. It is of great scientific significance to study the mineral transformation and identify the typical minerals in certain process conditions, because it may help to ensure the stable operation of the gasification processes and improve the utilization efficiency of coal seams. The presence of coal partings has an important impact on mineral transformation. In this paper, the UCG process has been subdivided into pyrolysis, reduction, and oxidation stages, and the progressive coal conversion products were prepared. Ulanqab lignite was used as the test coal. The minerals in the coal transformation products were identified by X-ray diffraction (XRD) and scanning electron microscopy coupled with an energy-dispersive spectrometer (SEM-EDS). The thermodynamic equilibrium simulation software, FactSage 7.2, was used to calculate the relevant phase diagram to assist in understanding the mineral transformations. The experimental results indicate that the different iron-bearing minerals occur in raw coal and non-coal partings which are nontronite (Na0.3Fe2Si4O10(OH)2.4H2O) and glauconite (K (Fe, Al)2(Si, Al)4O10(OH)2) respectively. Pyrrhotite is the main iron-bearing mineral in the pyrolysis products. In the reduction stage, the relative content of Al2O3 is increased due to the presence of non-coal partings, which reacts with FeO to produce hercynite (FeAl2O4) at a temperature above 1100 °C. When the temperature increases to 1300 °C, hercynite is converted to the thermodynamically-stable cordierite (Fe2Al4Si5O18). In the oxidation stage, mullite (Al6Si2O13) is produced when the oxidation temperature reaching 1300 °C, which could be used to reflect the underground reaction conditions in the coal seam. The phase diagram of (SiO2)6.2Al2O3-CaO-Fe2O3 proves that mullite and anorthite (CaAl2Si2O8) are the dominant minerals when the mole fraction of (SiO2)6.2Al2O3 is above 0.7. In addition, the ash melting point rises with an increase of Si and Al content in the presence of non-coal partings.

Monochromatic and mean radiative properties of astrophysical plasma mixtures in nonlocal thermodynamic equilibrium regime

Radiative‐hydrodynamics and radiative transfer simulations of astrophysical plasmas require the determination of radiative properties. However, most of the plasma radiative properties are calculated assuming the plasma in coronal equilibrium or local thermodynamic equilibrium regimes that is often not the case for many scenarios. In this work, we present nonlocal thermodynamic equilibrium calculations of radiative opacities of Fe and S and of an astrophysical plasma mixture for temperatures larger than 100 eV. We also analyze the departure from local thermodynamic equilibrium simulations.

Thermodynamic Equilibrium Simulations of Thallium Distributions in Interactions with Chlorine, Sulfur, Phosphorus, and Minerals During Sludge Co-combustion

Effects of interactions among chlorine (Cl), sulfur (S), phosphorus (P), and minerals on thallium (Tl) distributions were simulated using thermodynamic equilibrium conditions during the sludge co-combustion. Our results showed that Tl mainly existed in the forms of Tl2O3(s) and Tl(g) and did not react with SiO2, Al2O3, CaO, Fe2O3, and TiO2. Cl generated TlCl(g) and Tl(g) which in turn promoted Tl volatilization. S produced Tl2SO4(s), thus inhibiting Tl volatilization. P existence had no influence on Tl volatilization. With the couplings of Cl + S, S + P, and Cl + S + P, the reactions between single minerals and Tl were mainly controlled by S but P and Cl. With the Cl + P coupling, Cl controlled the reactions between the minerals and Tl, while P and the minerals had no significant impact. With the coupled minerals of SiO2 + CaO + Al2O3, S exerted a more influence than did Cl and P on the distributions of Tl, thus preventing Tl emissions.

Effect of inherent minerals on sewage sludge pyrolysis: Product characteristics, kinetics and thermodynamics

Inherent minerals in sludge influence sludge pyrolysis behaviors and the final products. In this study, the effects of inherent minerals on sewage sludge pyrolysis were systematically investigated by studying the pyrolysis behaviors of raw sewage sludge (RS) and HCl-washed sludge (WS), and in combination with thermodynamic equilibrium simulations for the hypothetical mineral-free sludge (AS) assumed. The pyrolysis of RS and WS was performed with a novel online thermogravimetric analyzer equipped with an infrared spectrometer and a gas chromatograph coupled with a mass spectrometer (TG-IR-GC/MS). It was found that inherent minerals influenced both the release of volatile products as a function of pyrolysis temperature, and the development of the physicochemical properties of the derived char. In the temperature range of 300–500 °C, hydrocarbons with more than 4 carbon atoms as well as aromatic compounds showed an increased release during WS pyrolysis, with respect to RS, while hydrocarbons with less than 3 carbon atoms such as CH4 and C3H6 exhibited a decreased release. In addition, the inherent minerals enhanced the release of HCN and NH3, both leading to increased NO2 release, and the release of H2S and COS was also promoted while the release of CH3SH, SO2 and CS2 was mitigated. Kinetic analysis confirmed that a catalytic effect induced by the inherent minerals decreased the activation energy at 300–500 °C. Thermodynamic simulations suggested that inherent minerals influenced sludge pyrolysis and the derived products formation by increasing the total Gibbs energy of the sludge pyrolysis system. Therefore, considerations of sludge inherent minerals should be taken into account during pyrolysis for the purpose of value-added commodity production and pollutant mitigation.

Prediction of gaseous products from Dachengzi oil shale pyrolysis through combined kinetic and thermodynamic simulations

The characteristics of gas evolution from Dachengzi oil shale pyrolysis under different temperatures were experimentally investigated using a fixed bed reactor and then were evaluated by integrating thermodynamic equilibrium simulation employing HSC Chemistry program and Sandia PSR kinetics simulation in this paper. The experiment results indicate that the non-condensable gases contain much higher CO2, CH4 and H2 and lower CO and C2–C4 hydrocarbons in terms of volume percentages, and mainly consist of CO2 and CH4 as well as some minor gases in terms of mass distribution. CO2, CO and H2 are firstly produced followed by the generation of light hydrocarbons. The HSC calculation results present that some C2 and C2+ hydrocarbons disappear in the predicted gaseous products thermodynamically, and the nitrogen- and sulfur-containing gases mainly are N2 and H2S, respectively. Then, the normalized HSC species are inputted into the Sandia PSR code by three methods, i.e., the CHO input method, the regional input method and the individual input method, considering the potential kinetic constraints. Some C2 and C2+ hydrocarbons appear in the predicted gaseous products based on the three methods. The regional input method demonstrates that more H2 and CO are produced at higher temperature, which agrees with the experimental results. And more C2H4 and C2H2 release at higher temperature depending on the enhanced secondary gas cracking reactions. The peak concentration of every gas product is obtained at higher temperature with lower value compared to the experimental results possibly due to ignoring the effect of the shale ash. The individual input method indicates that C2 and C3 hydrocarbons are generated after the formation of CH4, CO, CO2 and H2. The change trends of CO2, CO and H2 obtained from the experiment and simulation with rising temperature are very similar, but those for CH4 are different, due to most likely certain limitations of a fixed bed reactor as a reaction system. Combining the HSC and PSR calculations, the obtained gas products are closer to the realistic situation.

Arsenic Partitioning Behavior During Sludge Co-combustion: Thermodynamic Equilibrium Simulation

Using the computation method of thermodynamic equilibrium, effects of sewage sludge (SS) co-combustion conditions and interactions with Fe2O3, SiO2, CaO and Al2O3 on migration and transformation of arsenic (As) were simulated in oxy-fuel (CO2/O2) and air (N2/O2) atmospheres. Arsenic mainly existed as As(s), As4(g), As2O5(s), As4O6(g) and AsO(g) and volatilized more easily in reducing than oxidizing atmosphere. Increased O2 concentration slowed down the formation rate of AsO(g), thus reducing the volatilization rate of As. With the increased pressure, the conversion rate of As2O5(s) into As4O6(g) accelerated. In the multi-chemical system of SiO2, Al2O3 and CaO, As reacted with CaO and Al2O3 to form AlAsO4(s) and Ca3(AsO4)2(s) which inhibited As volatilization. SiO2 prevented As from reacting with CaO to generate Ca3(AsO4)2(s). Fe2O3 affected reactions between Al2O3(CaO) and As which inhibited As volatilization. In the whole SS co-combustion system, As reacted with O2 but had a weak affinity with Cl and with no arsenic chlorides observed.

A study of the in-situ CO2 removal pyrolysis of Chinese herb residue for syngas production

The in-situ CO2 removal pyrolysis of Chinese herb residue was studied by thermodynamic equilibrium simulation and experimental methods. The effects of temperature, pressure, and CaO loading on the gas composition, heating value and yield were determined. The simulation results indicate that the heating value of product gas increases with the increase of Ca/H and pressure, and slightly decreases with the increase of temperature. The simulation results were verified by the experiments conducted with a micro fixed-bed reactor. Under the simulated reaction conditions including atmospheric pressure, reaction temperature of 700 °C and the Ca/H of 0.65, the CO2 in the product gas was effectively removed, resulting the syngas with a high heating value. The product gas was mainly composed of H2, CO, CO2 and CH4 with the contents of 47.52, 22.04, 9.01 and 14.02 respectively by experiment. And the lower heating value of the product gas reached 18.1 MJ/Nm3.

Chlorosilane Interactions with Iron at High Temperatures

Chlorosilane species are commonly used at high temperatures in the manufacture and refinement of ultra-high purity silicon and silicon materials. They are highly corrosive in these processes, necessitating the use of high cost alloys for the construction of reactors, pipes, and vessels required to handle and produce them. In this study, iron, the primary alloying component of low cost metals, was exposed to a variety of silicon tetrachloride-hydrogen-hydrogen chloride vapor streams at industrially-relevant times (0-100 hours), temperatures (500-700°C), and compositions. Post exposure analyses including FE-SEM, EDS, XRD, and gravimetric analysis revealed formation and growth of stratified silicide and chloride surface layers, which vary as a function of time, temperature and gas composition. Additionally, there was evidence for various regimes of diffusion-limited and reaction-limited surface layer growth. Speculated mechanisms to explain these observations were supported by thermodynamic equilibrium simulations of experimental conditions. This study furthers the understanding of metals in chlorosilane environments, which is critically important for manufacturing the high purity silicon required for silicon-based electronic and photovoltaic devices.

High-Temperature (550–700°C) Chlorosilane Interactions with Iron

Chlorosilane species are commonly used at high temperatures in the manufacture and refinement of ultra-high purity silicon and silicon materials. The chlorosilane species are often highly corrosive in these processes, necessitating the use of expensive, corrosion resistant alloys for the construction of reactors, pipes, and vessels required to handle and produce them. In this study, iron, the primary alloying component of low cost metals, was exposed to a silicon tetrachloride-hydrogen vapor stream at industrially-relevant times (0–100 hours), temperatures (550–700°C), and vapor stream compositions. Post exposure analyses including FE-SEM, EDS, XRD, and gravimetric analysis revealed formation and growth of stratified iron silicide surface layers, which vary as a function of time and temperature. The most common stratification after exposure was a thin FeSi layer on the surface followed by a thick stoichiometric Fe3Si layer, a silicon activity gradient in an iron lattice, and finally, unreacted iron. Speculated mechanisms to explain these observations were supported by thermodynamic equilibrium simulations of experimental conditions. This study furthers the understanding of metals in chlorosilane environments, which is critically important for manufacturing the high purity silicon required for silicon-based electronic and photovoltaic devices.

The influence of air and oxy-fuel combustion on fly ash and deposits

This article summarizes the results on the influence of combustion conditions (air, oxy-fuel) on deposit and ash formation and transformation and their implications on plant operation. The investigations involved thermodynamic equilibrium simulations as well as experiments at IFK's 20kWth and 0.5MWth combustion test rigs and Vattenfall's 30MWth oxy-fuel pilot plant “Schwarze Pumpe”. Comparative air and oxy-fuel experiments with Lusatian lignite showed a considerable increase of sulfur in ash and deposits and a 12 percentage point lower sulfur release to SO2 in oxy-firing. One reason for this is the higher SO2 partial pressure in oxy-fuel combustion that stabilizes sulfates. Therefore, sulfates can form at higher temperatures and more extensively. Oxy-fuel deposits may be more sintered by sulfates and therefore more difficult to remove by soot blowing. However, the experimental and theoretical considerations presented here support the conclusion that SO2 levels and therefore sulfate stability in oxy-fuel combustion of low sulfur coals is comparable to conditions experienced in air-firing of high sulfur fuels. Thus, it can be expected that problems associated with sulfatic deposits (e.g.: fouling) in low sulfur coal oxy-fuel combustion can be handled by standard techniques (e.g. soot blowing). For high sulfur fuels with considerable sulfur capture potential (e.g.: high Ca), this may not be true and additional measures may be required for a reliable plant operation.

Characterization of zinc vapor condensation in fly ash particles using synchrotron X-ray absorption spectroscopy

Heavy metals released from municipal solid waste incinerators have become a major environmental concern. A comprehensive knowledge of metal vapor condensation in fly ash particles during incineration is essential for alleviating heavy metal toxicity, and for optimizing incineration process parameters and flue-gas cleaning systems. In this paper, the condensation of zinc vapor during flue-gas cooling in a 200 t/d fluidized bed incinerator and a 150 t/d moving grate incinerator was characterized and comparatively studied using high resolution synchrotron X-ray absorption spectroscopy (XAS). Principal component analysis, target transformation, and linear combination fitting were employed to identify zinc species directly from size fractionated fly ash particles. The chemical reaction behaviors of different zinc species were described by thermodynamic equilibrium simulations. Consistent with previous theoretical analysis and laboratory scale tests, the condensation behavior of zinc in an industrial incineration system is mainly affected by the sulfur/chlorine ratio and the inorganic particulates. It is found that zinc chloride is the major zinc species in a moving grate incinerator but willemite dominates in the fluidized bed incinerator. The high sulfur and silica/alumina particle concentration in the fluidized bed system changes the condensation propensity of vapors of Zn compounds. Adjusting the concentrations of SO2 in flue-gas can inhibit the formation of zinc chlorides. Silica, alumina, aluminosilicates, and calcium-based compounds are potential sorbents for transforming zinc to less harmful species. To prevent toxic zinc species contained in fine particles from escaping into the atmosphere, wet scrubbers are more suitable for cleaning flue-gases in moving grate incineration systems, while improving the efficiency of dust removal is more important for fluidized bed incineration systems.

Organization of lipids in the tear film: a molecular-level view.

Biophysical properties of the tear film lipid layer are studied at the molecular level employing coarse grain molecular dynamics (MD) simulations with a realistic model of the human tear film. In this model, polar lipids are chosen to reflect the current knowledge on the lipidome of the tear film whereas typical Meibomian-origin lipids are included in the thick non-polar lipids subphase. Simulation conditions mimic those experienced by the real human tear film during blinks. Namely, thermodynamic equilibrium simulations at different lateral compressions are performed to model varying surface pressure, and the dynamics of the system during a blink is studied by non-equilibrium MD simulations. Polar lipids separate their non-polar counterparts from water by forming a monomolecular layer whereas the non-polar molecules establish a thick outermost lipid layer. Under lateral compression, the polar layer undulates and a sorting of polar lipids occurs. Moreover, formation of three-dimensional aggregates of polar lipids in both non-polar and water subphases is observed. We suggest that these three-dimensional structures are abundant under dynamic conditions caused by the action of eye lids and that they act as reservoirs of polar lipids, thus increasing stability of the tear film.

Effect of oxygen and steam on gasification of palm oil wastes

The distribution of gas products released from palm oil waste gasification was investigated. The combustion of palm oil wastes (empty fruit bunches, palm fibre and shell) was studied using thermogravimetric analysis and the results showed that fibre and EFB easily ignite with a single peak while three peaks were observed for palm shell. The fibre gasification was conducted under different air and steam ratios, and it was found that gasification mainly occurs at 220–500°C. The mass loss rate of fibre increases with oxygen input. The maximum yield of carbon monoxide occurs for an air ratio of 0·13. Steam input impacts only at high temperatures, with high amounts of carbon monoxide and carbon dioxide and a significantly high hydrogen yield. Thermodynamic equilibrium simulation showed that the contributions of oxygen from steam and oxygen have different influences on hydrogen yield: the hydrogen yield increases with steam input, but decreases with oxygen input.

Long-term cement corrosion in chloride-rich solutions relevant to radioactive waste disposal in rock salt – Leaching experiments and thermodynamic simulations

Low- and intermediate-level radioactive wastes are frequently solidified in a cement matrix. In a potential repository for nuclear wastes, the cementitious matrix is altered upon contact with solution and the resulting secondary phases may provide for significant retention of the radionuclides incorporated in the wastes. In order to assess the secondary phases formed upon corrosion in chloride-rich solutions, which are relevant for nuclear waste disposal in rock salt, leaching experiments were performed. Conventional laboratory batch experiments using powdered hardened cement paste in MgCl2-rich solutions were left to equilibrate for up to three years and full-scale cemented waste products were exposed to NaCl-rich and MgCl2-rich solutions for more than twenty years, respectively. Solid phase analyses revealed that corrosion of hardened cement in MgCl2-rich solutions advanced faster than in NaCl-rich solutions due to the extensive exchange of Mg from solution against Ca from the cementitious solid. Thermodynamic equilibrium simulations compared well to results at the final stages of the respective experiments indicating that close to equilibrium conditions were reached. At high cement product to brine ratios (>0.65gmL−1), the solution composition in the laboratory-scale experiments was close to that of the full-scale experiments (cement to brine ratio of 2.5gmL−1) in the MgCl2 systems. The present study demonstrates the applicability of thermodynamic methods used in this approach to adequately describe full-scale long-term experiments with cemented waste simulates.

Simulation of spectrum of doped Ar in indirectly driven implosion target

X-ray spectrum of tracer in ICF implosion target is usually used to infer electron temperature, density and mix of fuel. As the plasma in fuel is in non-local thermodynamic equilibrium (non-LTE), a line transfer code Alpha is developed. Taking the electron temperature and density provided by radiation hydrodynamic as input condition, atomic kinetics and radiation transfer equation are self-consistently solved with the detailed configuration atom (DCA) model. The opacity for specified frequency intervals is obtained, and X-ray spectrum in the image plane is also presented.As application of Alpha program, the spectrum of doped Ar in implosion target on SG Ⅱ laser facility is simulated. The effect of self-absorption of K α line is studied. And it is shown that self-absorption of K α line affects both the intensity and shape of the spectrum, and it should be considered in simulating X-ray spectrum of Ar. And as the spectrum of local thermodynamic equilibrium (LTE) simulation gives large intensity and different shapes compared with the non-LTE results, non-LTE simulation is necessary in such a simulation.

Mechanisms of particle agglomeration and inhibition approach in the existence of heavy metals during fluidized bed incineration

Agglomeration occurring during fluidized bed incineration not only causes the fluidization characteristics to change and the system to unexpectedly shut down, but it also leads to the generation of secondary pollutants such as heavy metals. Accordingly, the aim of this study is to estimate the mechanisms of particle agglomeration in fluidized bed incineration. Experiments are carried out, including a pilot-scale fluidized bed test and a laboratory furnace test. Thermodynamic equilibrium simulations are also considered. In addition, the speciation of agglomerates is determined from the analysis of the laboratory furnace using X-ray diffraction (XRD), electron spectroscopy for chemical analysis (ESCA), and field emission scanning electron microscopy/energy dispersive spectrometry (FESEM–EDS). The experimental results reveal that higher concentrations of metals are emitted when defluidization occurs. When we compare the results from two different agglomeration inhibitors, the Al-based additive is shown to achieve higher levels of inhibition versus a Ca-based additive. In addition, the results from our simulation illustrate that the heavy metals Pb, Cr, and Cd have different affinities with Na, Si, Al, and Ca, which causes different emission behaviors during the agglomeration inhibition processes. Good agreement is observed among the experimental data, the agglomerate characterization, and the thermodynamic equilibrium simulations. The primary mechanisms of both particle agglomeration and the emission of heavy metals are also established.

Effects of Agglomeration Processes on the Emission Characteristics of Heavy Metals under Different Waste Compositions and the Addition of Al and Ca Inhibitors in Fluidized Bed Incineration

The agglomeration that occurs in a fluidized bed incineration system results in the unexpected shutdown of the system and causes secondary pollutants such as heavy metals to be generated. Addition of Al- and Ca-based additives is an efficient method to control the particle agglomeration. However, emission behavior of heavy metals in incineration processes could be influenced by the addition of agglomeration inhibitors due to both chemical reaction with metals and the fluidization behavior being changed. Accordingly, the aim of this study is to show the emission characteristics of heavy metals (Pb, Cr, and Cd) under various waste compositions (Cl and S) and the addition of agglomeration inhibitors (Al and Ca) during the defluidization process. A thermodynamic equilibrium simulation was used to predict heavy metal formation and to compare the experimental results. The results showed that the emission concentration of heavy metals increased as a result of the reduction of combustion efficiency caused by Al a...