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1.
The evolution of gases and volatiles during Sulcis coal pyrolysis under different atmospheres (N2 and H2) was investigated to obtaining a clean feedstock of combustion/gasification for electric power generation. Raw coal samples were slowly heated in temperature programmed mode up to 800 °C at ambient pressure using a laboratory-scale quartz furnace coupled to a Fourier transform infrared spectrometer (FTIR) for evolved gas analysis. Under both pyrolysis and hydropyrolysis conditions the evolution of gases started at temperature as low as 100 °C and was mainly composed by CO and CO2 as gaseous products. With increasing temperature SO2, COS, and light aliphatic gases (CH4 and C2H4) were also released. The release of SO2 took place up to 300 °C regardless of the pyrolysis atmosphere, whilst the COS emissions were affected by the surrounding environment. Carbon oxide, CO2, and CH4 continuously evolved up to 800 °C, showing similar release pathways in both N2 and H2 atmospheres. Trace of HCNO was detected at low pyrolysis temperature solely in pure H2 stream. Finally, the solid residues of pyrolysis (chars) were subjected to reaction with H2 to produce CH4 at 800 °C under 5.0 MPa pressure. The chars reactivity was found to be dependent on pyrolysis atmosphere, being the carbon conversions of 36% and 16% for charN2 and charH2, respectively.  相似文献   

2.
This study is devoted to investigating the continuous coal pyrolysis in a laboratory fluidized bed reactor that fed coal and discharged char continuously at temperatures of 750–980 °C and in N2-base atmospheres containing O2, H2, CO, CH4 and CO2 at varied contents. The results showed that the designed continuous pyrolysis test provided a clear understanding of the coal pyrolysis behavior in various complex atmospheres free of and with O2. The effect of adding H2, CO, CH4 or CO2 into the atmosphere on the tar yield was related to the O2 content in the atmosphere. Without O2 in the atmosphere, adding H2 and CO2 decreased the pyrolysis tar yield, but the tar yield was conversely higher with raising the CO and CH4 contents in the atmosphere. In O2-containing atmospheres, the influence from varying the atmospheric gas composition on the product distribution and pyrolysis gas composition was closely related to the oxidation or gasification reactions occurring to char, tar and the tested gas.  相似文献   

3.
Thermo-gravimetric technique was used to study the combustion characteristics of pulverized coal in different O2/CO2 environments. The effects of combustion environment, oxygen concentration, particle size and heating rate were considered and the differences of pulverized coal pyrolysis, combustion and gaseous compounds release under two environments were analyzed. Results show that the coal pyrolysis in CO2 environment can be divided into three stages: moisture release, devolatilization and char gasification by CO2 in higher temperature zone. In the lower temperature zone, the mass loss rate of coal pyrolysis in CO2 environment is lower than that in N2 environment. The burning process of pulverized coal in O2/CO2 environment is delayed compared with that in O2/N2 environment for equivalent oxygen concentrations. With the oxygen concentration increase or the coal particle size decrease, the burning rate of coal increases and burnout time is shortened. As the heating rate increases, coal particles are faster heated in a short period of time and burnt in a higher temperature region, but the increase in heating rate has almost no obvious effect on the combustion mechanism of pulverized coal. During the programmed heating process, species in flue gas including H2O, CO2, CO, CH4, SO2 and NO were determined and analyzed using the Fourier-transform infrared (FTIR) spectrometer. Compared with pulverized coal combustion in O2/N2 environment, much more CO is produced in O2/CO2 coal combustion process, but the releases of SO2 and NO are less than those released in O2/N2 environment. The present results might have important implications for understanding the intrinsic mechanics of pulverized coal combustion in O2/CO2 environment.  相似文献   

4.
To deeply understand the mechanism of inert gases in inhibiting coal spontaneous combustion, the effects of dry air, CO2, and N2 on coal spontaneous combustion were analyzed experimentally. To this end, bituminous coal prepared from Dongrong No. 2 Coal Mine was considered the research object. Based on the adsorption configuration of the oxygen-containing coal, the displacement behavior of O2 by CO2 /N2 was studied using the grand canonical Monte-Carlo (GCMC) and molecular dynamics (MD) methods. The obtained results show that the injection of CO2 and N2 reduces the ability of spontaneous combustion of coal. It is found that among the studied gases, CO2 has a stronger inhibition effect on coal spontaneous combustion, which increases the temperature of CO occurrence by 5℃, decreases the concentration of CO by 29.91%, and inhibits low-temperature oxidation of coal. From the microscopic point of view, CO2 /N2 gases can effectively displace O2 by diffusion and occupying adsorption sites. It is found that after the injection of CO2, the concentration of O2 molecules increases significantly in the vacuum layer. Compared with N2, injection of CO2 increases the diffusion activation of O2 by 5.89%. This indicates that the injection of an inert gas significantly reduces the oxygen absorption capacity of coal, thereby decreasing the coal-oxygen combination reaction and preventing the spontaneous combustion of coal. The performed analyses demonstrate that CO2 outperforms N2 in restraining the spontaneous combustion of coal.  相似文献   

5.
The choice of a solid reducer for hybrid propulsion is generally based on the quantity of gaseous combustible it can produce (expressed indirectly by the regression rate). For this reason, the studies focus on the use of additives or on the design of grain while the kinetic aspect is rarely of interest despite the chemistry drives the phenomena (chemical induction delay, heat absorption, and chemical composition). One-step mechanisms are first considered in this paper to quantify the effect of operating conditions on high density polyethylene (HDPE), polymethylmethacrylate (PMMA) and hydroxyl termination polybutadiene (HTPB). Then the chemical composition of pyrolysis products is determined for a large range of operating conditions with highly detailed mechanism for HDPE (1014 species and 7541 reactions). The heating rate applied to the reducer is investigated (from 1 K s−1 to 107 K s−1). Ethylene is found to be the major pyrolysis product. The timescale found over 1250 K and 11.11 bar is in agreement with the requirements of hybrid propulsion. The calculated data are compared to experimental ones. Finally, a short combustion study with detailed chemistry (over 700 species and 3000 reactions) is proposed because it impacts directly on the pyrolysis through the generated heat flux. It allows considering the oxidiser decomposition (hydrogen peroxide (H2O2) and nitrous oxide (N2O)). Pure oxygen (O2) is considered as reference data. The effect of atmosphere (inert or oxidative) on the pyrolysis is shown. The kinetic computations of N2O combustion give higher flame temperatures than for H2O2. Ignition times, below a few milliseconds, are obtained for all the reducers over 1250 K. Finally, the HDPE/H2O2 and HTPB/N2O couples are found to be the most interesting.  相似文献   

6.
In the present work, new CaO-based adsorbents were obtained by a fast solution combustion method and high-energy ball-milling process to study their CO2 capture behavior under different moderate pressure and temperature conditions. The as-prepared CaO products were characterized systematically using different analytical techniques such as X-ray diffraction, scanning electron microscopy and N2 physisorption measurements. The results showed that the CaO prepared by solution combustion and ball-milled during 2.5 h showed the maximum CO2 adsorption capacity of 9.31 mmol/g at 25 °C and 1 atm mainly via chemisorption with CaCO3 formation, which was corroborated by infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy studies. In general, the obtained results revealed that the synthesized CaO nanopowders from solution combustion that were treated by high-energy ball-milling enhanced their CO2 adsorption capacity due to improved structural and textural properties, and this CaO-based adsorbent can be used as a promising material for CO2 capture in post-combustion CO2 capture technologies on a large scale, under atmospheric pressure and temperature conditions.  相似文献   

7.
The effects of impregnated Cr3+ on sulfur removal during pyrolysis and hydropyrolysis of coal were investigated by loading CrCl3 into raw, demineralized and pyrite removed coal, respectively. The results indicate that Cr has no effect on the removal of pyrite. Cr affects the removal of total sulfur by forming Cr7S8 and affecting the removal of organic sulfur. Cr acts as the sulfur removing agent by promoting the decomposition of the unstable organic sulfur at low temperature. However, it behaves to be sulfur fixing agent between 400 and 700 °C so as to inhibit the evolution of H2S, even in hydropyrolysis. With the increase of temperature from 700 to 1050 °C, a certain ratio of Cr7S8 is converted into organic sulfur during pyrolysis; however, almost all the Cr7S8 is reduced into Cr at 1050 °C during hydropyrolysis. And Cr significantly promotes the removal of organic sulfur at high temperature within reducing atmosphere. The XPS results indicate that the sulfur is enriched on coke surface by Cr, which is attributable to the formation of Cr7S8 as well as the transfer of organic sulfur from bulk to surface during pyrolysis and hydropyrolysis.  相似文献   

8.
The construction, optimization and use of simple and inexpensive gas analyzer for real time measurement of sulfur dioxide in gas streams are described. The analyzer consisted of three main components (i) a custom fabricated hollow fiber membrane (HFM) gas contactor, (ii) carrier solution which absorbs SO2 molecules from the gas stream in the HFM gas contactor and (iii) a flow-through detector placed downstream which continuously measures the changes occurred to the carrier solution upon absorption of SO2 molecules. The significant acidic properties of the produced sulfurous acid suggested pH and conductivity detectors to monitor the decrease in pH or the increase in the conductivity which constituted the basis for quantification of SO2 in the gas line. Aqueous potassium oxalate (10? 1 mol/L) and hydrogen peroxide (10? 3 mol/L) were used as carrier solutions in combination with pH and conductivity detectors, respectively. The analyzer equipped with pH detector provided linear potentiometric response to SO2 concentration up to 1000 ppm with Nernstian slop of 61 mV/log[SO2]. Excellent SO2 recoveries (97–108%) were obtained in the presence of several folds of potentially interfering acidic gases, i.e., CO2 and H2S. The conductivity detector provided linear response up to 2500 ppm. Under optimized conditions, both detectors offered several favorable performance characteristics such as (i) fast response and recovery times, (ii) excellent signal stability and reproducibility (RSD = 0.5%), (iii) intrinsic high selectivity to most common neutral gases, e.g., CH4, N2, O2, CO, etc. The suggested analyzer was applied successfully in monitoring the removal of SO2 from SO2–N2 gas mixtures with hollow fiber membrane contactor using distilled water or aqueous sodium hydroxide as stripping solvents.  相似文献   

9.
We have determined the intrinsic gas transport properties of He, H2, O2, N2, CH4, and CO2 for a 6FDA-durene polyimide as a function of pressure, temperature and aging time. The permeability coefficients of O2, N2, CH4, and CO2 decrease slightly with increasing pressure. The pressure-dependent diffusion coefficients and solubility coefficients are consistent with the dual-sorption model and partial immobilization. All the gas permeabilities increase with temperature and their apparent activation energies for permeation increase with increasing gas molecular sizes in the order of CO2, O2, N2, and CH4.The percentages of permeability decay after 280 days of aging are 22, 32, 36, 40, 42, and 30% for He, H2, O2, N2, CH4, and CO2, respectively. Interestingly, except for H2 (kinetic diameter of 2.89 Å), the percentages of permeability decay increase exactly in the order of He (kinetic diameter of 2.6 Å), CO2 (3.30 Å), O2 (3.46 Å), N2 (3.64 Å), and CH4 (3.80 Å). The apparent activation energies of permeation for O2, N2, CH4, and CO2 increase with aging because of the increases in activation energies of diffusion and the decreases in solubility coefficients. The activation-energy increase for diffusion is probably due to the decrease in polymeric molar volume because of densification during aging. The reduction in solubility coefficient indicates the available sites for sorption decreasing with aging because of the reduction of microvoids and interstitial chain space.  相似文献   

10.
Oxidative pyrolysis of pine wood was studied by thermogravimetric analysis (TGA) coupled with mass spectrometer (MS) and differential scanning calorimetry (DSC) methods. The effects of oxygen concentration on pyrolysis behavior, carbon oxide production and heat properties were investigated. Several parameters were defined to evaluate the oxygen influence. It was found that oxygen dramatically promotes the oxidative degradation and char oxidation rate. The reactivity index was found to be proportional to the oxygen concentration, which suggested that oxidative degradation reactions were under increasingly kinetic control in elevated oxygen concentration environments. Carbon oxides evolution properties were investigated. There are two releasing peaks in MS curves for oxidative condition comparing with one peak under inert condition. They are related with oxidative degradation and char oxidation, respectively. Both total amounts and rates of carbon oxides emission were found to increase with oxygen concentration. The cumulative emission ratio of CO to CO2 first decreases then increases with oxygen concentration with 10% as turning point. It may be caused by different oxygen diffusion behaviors with variable oxygen concentrations. The absolute reaction heat value of oxidative pyrolysis (−7.23 MJ kg−1, 5% O2) is much larger than that of inert condition (+0.28 MJ kg−1). Increasing of oxygen concentration results in an increase of heat emission. Comparing with pine wood low heat value, the net heat emission efficiencies under different oxygen concentrations (5%, 10%, 15%, 21%) are 39.73%, 44.84%, 68.90% and 78.41%, respectively.  相似文献   

11.
Experimental bubble pressure, as well as liquid density of (CO2 + NO2/N2O4) mixtures are reported at temperatures ranging from (298 to 328.45) K. Experiments were carried out using a SITEC high-pressure variable volume cell. Transition pressures were obtained by the synthetic method and liquid density was deduced from measurement of the cell volume. Correlation of experimental results was carried out without considering chemical equilibrium of NO2/N2O4 system. (Liquid + vapour) equilibrium was found to be accurately modelled using the Peng–Robinson equation of state with classical quadratic mixing rules and with a binary interaction coefficient kij equal to zero. Nevertheless, modelling of liquid density values was unsatisfactory with this approach.  相似文献   

12.
The process of combustion produces minimal amounts of CO2 for conventional radiocarbon dating, making it difficult to estimate the age of the archaeological wood. Thus, the objective of this paper is to introduce a novel integrated pyrolysis-combustion process that will maximize the production of CO2. Degraded wood samples were assumed to be archaeological samples for this study, namely Karas (Aquilaria malaccensis), Meranti (Shorea acuminate) and Setumpol (Hydnocarpus spp.) were used for this process. The process of CO2 production was optimized by the application of design of experiment (DOE) and response surface method. The mathematical model was examined using the analysis of variance (ANOVA) at 5% level of significance. The temperature during the pyrolysis process, retention time and flow rates for the carrier gas (argon) were found to have a positive influence on the production of CO2. A second-order model was obtained to predict the production of CO2 as a function of temperature, retention time and flow rate. Optimum conditions for the production of CO2 were obtained at a pyrolysis temperature of 300 °C, 20 min retention and 980, 984 and 987.6 ml/min argon flow rate for Karas, Meranti and Setumpol, respectively. The optimized yields of carbon dioxide produced were 82.57, 79.7 and 84% for Karas, Meranti and Setumpol, respectively. The different yields of carbon dioxide were due to the carbon content in the individual samples.  相似文献   

13.
Emissions evolved from the pyrolysis and combustion of polyvinyl chloride (PVC) were studied at four different temperatures (500, 700, 850 and 1000 °C) in a horizontal laboratory tubular quartz reactor in order to analyse the influence of both temperature and reaction atmosphere on the final products from thermal and oxidative reactions. It was observed that the CO2/CO ratio increased with temperature. Methane was the only light hydrocarbon whose yield increased with temperature up to 1000 °C. Benzene was rather stable at high temperatures, but in general, combustion at temperatures above 500 °C was enough to destroy light hydrocarbons. Semivolatile hydrocarbons were collected in XAD-2 resin and more than 160 compounds were detected. Trends on polyaromatic hydrocarbon (PAH) yields showed that most had a maximum at 850 °C in pyrolysis, but naphthalene at 700 °C. Formation of chlorinated aromatics was detected. A detailed analysis of all isomers of chlorobenzenes and chlorophenols was performed. Both of them reached higher total yields in combustion runs, the first ones having a maximum at 700 °C and the latter at 500 °C. Pyrolysis and combustion runs at 850 °C were conducted to study the formation of polychlorodibenzo-p-dioxins (PCDDs) and polychlorodibenzofurans (PCDFs). There was more than 20-fold increase in total yields from pyrolysis to combustion, and PCDF yields represented in each case about 10 times PCDD yields.  相似文献   

14.
An experimental study on metastable equilibria at T=288 K in the quinary system Li2CO3 + Na2CO3 + K2CO3 + Li2B4O7 + Na2B4O7 + K2B4O7 + H2O was done by isothermal evaporation method. Metastable equilibrium solubilities and densities of the solution were determined experimentally. According to the experimental data, the metastable equilibrium phase diagram under the condition saturated with Li2CO3 was plotted, in which there are four invariant points; nine univariant curves; six fields of crystallization: K2CO3 · 3/2H2O, K2B4O7 · 5H2O, Li2B2O4 · 16H2O, Na2B2O4 · 8H2O, Na2CO3 · 10H2O, NaKCO3 · 6H2O. Some differences were found between the stable phase diagram at T=298 K and the metastable one at T=288 K.  相似文献   

15.
In this investigation, polymeric nanocomposite membranes(PNMs) were prepared via incorporating zinc oxide(ZnO) into poly(ether-block-amide)(PEBAX-1074) polymer matrix with different loadings. The neat membrane and nanocomposite membranes were prepared via solution casting and solution blending methods, respectively. The fabricated membranes were characterized by field emission scanning electron microscopy(FESEM) to survey cross-sectional morphologies and thermal gravimetric analysis(TGA)to study thermal stability. Fourier transform infrared(FT-IR) and X-ray diffraction(XRD) analyses were also employed to identify variations of the chemical bonds and crystal structure of the membranes, respectively. Permeation of pure gases, CO_2, CH_4 and N_2 through the prepared neat and nanocomposite membranes was studied at pressures of 3–18 bar and temperature of 25 °C. The obtained results showed that the fabricated nanocomposite membranes exhibit better separation performance compared to the neat PEBAX membrane in terms of both permeability and selectivity. As an example, at temperature of 25 °C and pressure of 3 bar, CO_2 permeability, ideal CO_2/CH_4 and CO_2/N_2 selectivity values for the neat PEBAX membrane are 110.67 Barrer, 11.09 and 50.08, respectively, while those values are 152.27 Barrer,13.52 and 62.15 for PEBAX/ZnO nanocomposite membrane containing 8 wt% ZnO.  相似文献   

16.
The catalytic oxidation of methane was studied over calcined and reduced Pt–Pd/γ-Al2O3 catalysts, in the presence and the absence of SO2 in the CH4–O2 reaction feed. The effect of sulfation (SO2 + O2 for 4 h at 500 °C) was also studied on the catalyst resistance to deactivation by sulfur poisoning. Sulfating the calcined Pt–Pd/γ-Al2O3 catalysts resulted in a strong deactivation for the CH4–O2 reaction. However, the catalytic activity of the reduced-sulfated Pt–Pd/γ-Al2O3 catalyst for CH4–O2 reaction remained rather unaffected in the presence and in the absence of SO2 in the reaction feed. XPS analysis revealed, over reduced-sulfated Pt–Pd/γ-Al2O3 catalysts, the presence of Pt(0) metallic surface species on which SO2 interactions may be faster related to Pd surface species. The presence of Pt(0) may be necessary to prevent the interactions between SO2 and Pd surface species. Long time catalytic tests showed that the activity of a reduced Pt–Pd/γ-Al2O3 catalysts for CH4–O2 reactions remained rather unaffected despite the presence of SO2 in the reaction feed.  相似文献   

17.
A complete, critical evaluation of all phase diagrams and thermodynamic data was performed for all condensed phases of the (NaCl + Na2SO4 + Na2CO3 + KCl + K2SO4 + K2CO3) system, and optimized parameters for the thermodynamic solution models were obtained. The Modified Quasichemical Model in the Quadruplet Approximation was used for modelling the liquid phase. The model evaluates first- and second-nearest-neighbour short-range order, where the cations (Na+ and K+) were assumed to mix on a cationic sublattice, while anions (CO32-,SO42-,andCl-) were assumed to mix on an anionic sublattice. The thermodynamic properties of the solid solutions of (Na,K)2(SO4,CO3) were modelled using the Compound Energy Formalism, and (Na,K)Cl was modelled using a substitutional model in previous studies. Phase transitions in the common-cation ternary systems (NaCl + Na2SO4 + Na2CO3) and (KCl + K2SO4 + K2CO3) were studied experimentally using d.s.c./t.g.a. The experimental results were used as input for evaluating the phase equilibrium in the common-cation ternary systems. The models can be used to predict the thermodynamic properties and phase equilibria in multicomponent heterogeneous systems. The experimental data from the literature are reproduced within experimental error limits.  相似文献   

18.
Metastable equilibrium solubilities and properties such as densities, conductivity, pH, refractive index, and viscosity of the solution were determined experimentally. According to the experimental data, the metastable equilibrium phase diagram was plotted. In the phase diagram, there are three invariant points, seven univariant curves, five fields of crystallization: Li2SO4 · H2O, K2SO4, Li2B4O7 · 3H2O, K2B4O7 · 4H2O, and K2SO4 · Li2SO4. The double salt K2SO4 · Li2SO4 was found in the quaternary system metastable equilibria. Lithium sulfate (Li2SO4) has the highest concentration and strong salting-out effects on other salts.Also, the relationship diagram between the properties and the ion concentration of solution was constructed. It can be seen from the relationship diagram that the equilibrium solution density values, viscosity values, and refractive index values are increased apparently with the rise of sulfate ion concentration, reaching the maximum values at eutonic point F3. Electrical conductivity values and pH values, however, fall down with the rise of ion concentration on the whole.  相似文献   

19.
A polymeric blend has been prepared using urea formaldehyde (UF) and epoxy (DGEBA) resin in 1:1 mass ratio. The thermal degradation of UF/epoxy resin blend (UFE) was investigated by using thermogravimetric analyses (TGA), coupled with FTIR and MS. The results of TGA revealed that the pyrolysis process can be divided into three stages: drying process, fast thermal decomposition and cracking of the sample. There were no solid products except ash content for UFE during combustion at high temperature. The total mass loss during pyrolysis at 775 °C is found to be 97.32%, while 54.14% of the original mass was lost in the second stage between 225 °C and 400 °C. It is observed that the activation energy of the second stage degradation during combustion (6.23 × 10−4 J mol−1) is more than that of pyrolysis (5.89 × 10−4 J mol−1). The emissions of CO2, CO, H2O, HCN, HNCO, and NH3 are identified during thermal degradation of UFE.  相似文献   

20.
《Fluid Phase Equilibria》2004,218(2):261-267
Gas solubility of carbon dioxide in an aqueous solution of 32.5 wt.% N-methyldiethanolamine and 12.5 wt.% diethanolamine with 4, 6, and 10 wt.% 2-amino-2-methyl-1-propanol has been measured, at 313.15, 343.15, and 393.15 K, over a range of pressure from 3 to 2000 kPa, using a chromatographic method for analysis of the liquid phase. The results of the gas solubility are given as the partial pressure of CO2 against its mole ratio α (mol CO2/mol alkanolamine) and its mole fraction at each temperature studied. The solubility of CO2 in all the systems studied decreases with an increase in temperature and increases with an increase in the partial pressure of CO2 at a given temperature and it is a function of the concentration of the mixture of alkanolamines in solution. The enthalpy of solution of CO2 has been calculated from the experimental solubility data.  相似文献   

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