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1.
A 400 kW, dual distributor type fluidized bed gasifier was used to investigate the production rate and composition of the gas produced from wheat straw at various equivalence ratios (0.17, 0.20, 0.25, 0.35) and fluidization velocities (0.28, 0.33 and 0.37 m s). The results showed that the equivalence ratio was the major parameter affecting the gas composition. The equivalence ratio of 0.25 appeared to be the optimum with respect to the quality of the gas. The mole fractions of the combustible components reached their maximum values at this equivalence ratio. A typical gas composition at the equivalence ratio of 0.25 was 7% H2, 7% hydrocarbons (CH4, C2H2, C2/H4 and C2H6), 14% C02, 22% CO and 50% N2. The higher heating value of the produced gas (6.3–7.3 MJ Nm−3) obtained at this equivalence ratio appeared to be higher than most values reported in the literature for several types of biomass fuels.  相似文献   

2.
Thermochemical and kinetic evaluations of the very rapid elementary radical reactions consuming the C2H2 produced in a chlorine catalyzed polymerization of CH4 are presented. An earlier examination of the data and mechanism leading to C2H2 supports a methyl and chloromethyl recombination path to C2 hydrocarbons. The relative yield of CH3 and CH2Cl depends on the excess of methane.

In the CH4, system consumption of C2 species to ultimately form benzene is shown to proceed by a stepwise addition of CH3 radicals to CnHm species. When n is even the dominant species is an unsaturated polyolefin molecule. When n is odd the dominant species is a conjugated, unsaturated radical such as allyl, pentadienyl, benzyl, etc. Mono-olefins or saturated molecules are rapidly stripped to these species by radical catalyzed dehydrogenations. In the current system chloromethyl radicals are equivalent kinetically to methyl and play a dominant role. Their addition to unsaturated species produces chlorinated radicals that dechlorinate rapidly or recombine with chloromethyl to produce dichlorohydrocarbons that dehydrochlorinate very rapidly.

A very important reaction in the sequence is the isomerization of propenyl and chloropropenyl radicals to allyl and chlorallyl by a 1–3 H (or Cl) atom shift. Its high pressure Arrhenius parameters at 1300 K are estimated to be log [k(sec−1)] = 13.7 − 37/θ = 13.7 - 37/0 where 0 = 2.303 RT in kcal/mol. It appears likely that benzene conversion to soot also proceeds via a CH3/CH2Cl radical, sequential addition mechanism.

Stoichiometry considerations applied to the product yield distribution support the role of methyl and chloromethyl predicted by the proposed mechanism. Ionic pathways are shown to be insignificant in the formation of aromatics.  相似文献   


3.
Concentraion profiles of N2O, NO, and N2 from atmospheric pressure, flat-flame burner experiments are presented. Axial profiles of species and temperature are described for CH4-air and H2---O2---Ar flames doped with either NH3, NO, or N2O.

Species concentrations were determined by microprobe sampling and direct analysis by gas chromatography or chemiluminescence analysis, for flames ranging in temperature from 1300 to 2000 K. Burner surface temperatures were also estimated for these flames, using heat transfer analysis and an optical method. Nitrogen-atom balances were achieved in each of the H2---O2---Ar flames to within experimental error and better than 6%.

Axial profiles of N2O were similar for all flames. At sampling locations nearest to the burner (0.5–1.0 mm), N2O concentrations were highest. Concentrations decreased monotonically in the downstream direction, with N2O destruction essentially complete in the postflame region (height greater than 3 mm) for all flames except the one at the lowest temperature (1300 K). With NH3 as dopant, early-flame and postflame N2O concentration varied inversely with temperature. The lowest early-flame N2O concentration was observed with NO as dopant, and the highest was observed with direct N2O addition. Increased initial concentrations of NH3 led to higher early-flame N2O concentrations. With N2O as dopant, product branching to NO and N2 in the postflame region is approximately 8% and 92%, respectively. An NO removal process involving NHi is active in lean, NO-doped flames.  相似文献   


4.
Decomposition of nitrous oxide at medium temperatures   总被引:4,自引:0,他引:4  
Flow reactor experiments were done to study the decomposition of N2O at atmospheric pressure and in a temperature range of 600–1000°C. Dilute mixtures of N2O with H2, CH4, CO with and without oxygen with N2 as carrier gas were studied. To see directly the relative importance of the thermal decomposition versus the destruction by free radicals (i.e.: H, O, OH) iodine was added to the reactant mixture suppressing the radicals’ concentrations towards their equilibrium concentrations. The experimental results were discussed using a detailed chemistry model. This work shows that there are still some uncertainties regarding the kinetics of the thermal decomposition and the reaction between N2O and the O radical. Using the recommendations applied in this work for the reaction N2O + M ↔ N2 + O + M and for N2O + O ↔ products, a good agreement with the experimental data can be obtained over a wide range of experimental conditions. The reaction between N2O and OH is of minor importance under present conditions as stated in latest literature. The results show that N2O + H ↔ N2 + OH is the most important reaction in the destruction of N2O. In the presence of oxygen it competes with H + O2 + M ↔ HO2 + M and H + O2 ↔ O + OH, respectively. The importance of the thermal decomposition (N2O + M ↔ N2 + O + M) increases with residence time. Reducing conditions and a long residence time lead to a high potential in N2O reduction. Especially mixtures of H2/N2O and CO/H2O/N2O in nitrogen lead to a chain reaction mechanism causing a strong N2O reduction.  相似文献   

5.
Comparisons of computed and measured premixed charge engine combustion   总被引:4,自引:0,他引:4  
Comparisons are presented of computed and measured cylinder pressure in a reciprocating engine with a pancake combustion chamber and premixed propane/air charges. Engine operating conditions range over volumetric efficiency of 30–60%; equivalence ratio of 0.87–1.1; and rpm of 1000–1500. The computations start from the actual spark times and simulate the growth of the flame kernel into a fully developed turbulent flame by taking into account the increasing influence of turbulent eddies on the growing flame kernel. A k-ε submodel is used for turbulence. The species conversion submodel assumes that the species (C3H8, O2, H2O, CO2, CO, H2, and N2) concentrations approach their local thermodynamic equilibrium values with a characteristic conversion time that is a combination of a turbulent mixing time and a chemical conversion time in laminar propane---air flames. In all cases computed and measured cylinder pressure agree well in trends and magnitudes during the entire duration of combustion. The difference in magnitudes generally is much less than 8%. The main conclusion is that laminar flame processes must be explicitly accounted for in order to reproduce certain elements of premixed charge engine combustion.  相似文献   

6.
生物质发酵法制备甲烷存在甲烷收率低、CO2含量高等问题。本研究以纤维素为原料,在温和条件下采用水热催化转化的方法制备甲烷。对一系列催化剂进行了考察,发现Ru/C对该反应的催化活性最高。采用Ru/C催化剂进一步考察了一系列反应条件,结果表明,升高反应温度、延长反应时间、增加催化剂用量以及提高氢气初始压力对甲烷的生成具有促进作用。在1 MPa H2、220℃、12 h反应条件下,甲烷碳摩尔收率最高,达88%,反应过程中无CO2产生。采用TEM、BET、XRD和FT-IR等对催化剂进行了表征,结果表明,Ru/C催化剂的高催化活性可能与催化剂本身比表面积大、钌粒子颗粒小且分散均匀的特性有关。本研究采用的催化转化方法具有甲烷收率高、CO2排放量小(<5%)、反应条件更为温和等特点。  相似文献   

7.
Emission factors of wood and charcoal-fired cookstoves   总被引:1,自引:0,他引:1  
In the developing countries, energy required for cooking often has the biggest share in the total national energy demand and is normally met mostly by biomass. This paper presents the results of experimental studies on emission conducted on a number of traditional and improved cookstoves collected from different Asian countries using wood and charcoal as fuel. The emission factors from this study are comparable to those reported in the literature. In the case of wood combustion, CO2 emission factor is in the range of 1560–1620 g kg−1. The emission factors for pollutants CO, CH4, TNMOC and NOx were in the ranges 19–136, 6–10, 6–9 and 0.05–0.2 g kg−1, respectively. In the case of charcoal combustion, CO2 emission factor is in the range of 2155–2567 g kg−1. The emission factors for pollutants CO, CH4, TNMOC were in the ranges 35–198, 6.7–7.8, 6–10 g kg−1, respectively.

Comparison between wood and charcoal fired stoves shows that, CO2 and CO emission factor values for wood are lower as compared to charcoal. CH4 and TNMOC emission factors for wood are with the same range as compared to charcoal. Emission factors for NOx using wood is slightly lower than charcoal. The emission of all the pollutants per unit of useful heat was found to decrease with increasing stove efficiency for both wood and charcoal fired stoves.  相似文献   


8.
Lin Erda  Li Yue  Dong Hongmin 《Applied Energy》1997,56(3-4):423-432
China's agriculture accounts for about 5–15% of total national emissions of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Land-use changes related to agriculture are not major contributors of greenhouse gas emissions in China.

Mitigation options are available that could result in significant decrease in CH4 and N2O emissions from agricultural systems, and are likely to increase crop and animal productivity. Implementation has the potential to decrease CH4 emissions from rice paddies, ruminants, and animal waste by 4–40%. Improving the efficiency of plant utilization of fertilizer N could decrease N2O emissions from agriculture by almost 20%. Analyses of several of the proposed options show positive economic as well as environmental benefits.  相似文献   


9.
Production of hydrogen gas from novel chemical hydrides   总被引:1,自引:0,他引:1  
Six ligand-stabilized complexes have been synthesized and tested for use as hydrogen storage media for portable fuel cell applications. The new hydrides are: [HC(3,5-Me2pz)3]LiBH4 (1), {[H2C(3,5-Me2pz)2]Li(BH4)}2 (2) (pz = pyrazolyl), [(TMEDA)Li(BH4)]2 (3) (TMEDA = (CH3)2NCH2CH2N(CH3)2), [HC(pz)3]LiBH4 (4), {[H2C(pz)2]Li(BH4)}2 (5) and Mg(BH4).2 3THF (6) (THF = tetrahydrofuran). Hydrolysis reactions of the compounds liberate hydrogen in quantities which range from 56 to 104 (± 5%) percent of the theoretical yield. Gas chromatographic analysis of the product gases from these reactions indicate that hydrogen is the only gas produced. Thermally initiated reactions of the novel compounds with NH4Cl were unsuccessful. Although the amount of hydrogen energy which can be theoretically obtained per unit weight is lower than that of the classical hydrides such as LiBH4 and NaBH4, the reactions are less violent and hydrolysis of compounds 1, 2, 4, 5 and 6 releases less heat per mole of hydrogen generated.  相似文献   

10.
Methane was produced from H2 and CO2 using the acclimated-mixed methanogens in a 3.71 fermentor in batch culture at pH 7.2 and 37°C. The Fermentation kinetics parameter for the growth of methanogens, overall mass transfer coefficient of the reactor, and the conversion rate of H2 and CO2 to CH4 by the acclimated-mixed culture were determined using the technique of Vega et al. The maximum specific growth rate (μmax) and H2 specific consumption rate (qmax) were found to be 0.064(h−1) and 104.8 (mmol h−1 g−1) respectively. Monod saturation constants for growth (Kp) and for inhibition (Kp) were found to be 3.54 (kPa) and 0.57 (kPa), respectively. These findings indicate that without very low dissolved H2 levels, the fermentations are carried out under μmax, and the specific uptake rate (q) was almost not affected at any dissolved H2 level in the range studied. The yield of CH4 (Yp/s) was calculated to be 0.245 (mol CH4 mol−1 H2), which is near the stoichiometric value of 0.25. DH2 was also measured using the Teflon tubing method and was in good agreement with those estimated by kinetic calculations.  相似文献   

11.
Regular observations of atmospheric mixing-ratios of carbon dioxide and methane in the urban atmosphere, combined with analyses of their carbon-isotope composition (δ13C, δ14C), provide a powerful tool for assessing both the source strength and source partitioning of those gases, as well as their changes with respect to time. Intense surface fluxes of CO2 and CH4, associated with anthropogenic activities result in elevated levels of these gases in the local atmosphere as well as in modifications of their carbon-isotope compositions. Regular measurements of concentration and carbon-isotope composition of atmospheric CO2, carried out in Krakow over the past two decades, were extended to the period 1995–2000 and also to atmospheric mixing-ratios of CH4 and its carbon-isotope composition. Radiocarbon concentrations (δ14C) in atmospheric CO2 recorded at Krakow are systematically lower than the regional background levels. This effect stems from the addition of 14C-free CO2 into the local atmosphere, originating from the burning of fossil fuels. The fossil-fuel component in the local budget of atmospheric carbon calculated using a three-component mixing model decreased from ca. 27.5 ppm in 1989 to ca. 10 ppm in 1994. The seasonal fluctuations of this component (winter–summer) are of similar magnitude. A gradually decreasing difference between the 14CO2 content in the local atmosphere and the regional background observed after 1991 is attributed to the reduced consumption of 14C-free fuels, mostly coal, in southern Poland and the Krakow municipal area. The linear regression of δ13C values of methane plotted versus reciprocal concentration, performed for the data available for Krakow sampling site, yields the average δ13C signature of the local source of methane as being equal to −54.2‰. This value agrees very well with the measured isotope signature of natural gas being used in Krakow (−54.4±0.6‰) and points to leakages in the distribution network of this gas as the main anthropogenic source of CH4 in the local atmosphere.  相似文献   

12.
The profiles of the species H, OH, CH, NH, CN, NCO, NO2, and CH3O are compared in a series of five premixed stoichiometric 15-torr CH4/O2/NO2/N2 flames with NO2 comprising between 0% and 40% of the oxidizer. Relative species concentrations were measured by laser-induced fluorescence (LIF) and these results are compared with calculations using measured temperature profiles. The reaction mechanism of Miller and Bowman incorrectly predicts the standoff from the burner in flames containing more than 20% NO2; addition of several reactions involving NO2 and HONO produces excellent agreement with experiment for most species. The reaction CH3 + NO2 → CH3O + NO is found to be particularly important in the reaction mechanism. LIF profiles of CH3O show this species to be present in far larger quantities in the NO2 supported flames than in the CH4/O2 system. The nitrogen-containing intermediates CN, NCO, and NH are all overpredicted by a factor of two in the 40% NO2 flame relative to the 10% NO2 flame. This indicates an inaccuracy in either the reburn reactions or the fuel nitrogen chemistry when large amounts of NO are present. The kinetic modeling shows that in the 40% NO2 flame, the dominant pathway to N2 formation is through N2O, which is produced primarily by the reaction of NCO with NO. Comparison of emission profiles of NO2* for the various flames indicates that the appearance of an orange-yellow luminous zone at the base of NO2 supported flames is caused by thermal excitation of NO2, not by a chemiluminescence mechanism.  相似文献   

13.
搭建生物质与废塑料共气化动力学模型,并用实验数据对其进行验证。选用6种生物质和聚丙烯作为共气化反应物,以水蒸气为气化剂,计算气化温度在300~1000℃之间、气化压强在0.1~0.8 MPa之间、聚丙烯和松木锯末质量比例在0.5~2.5之间,以及不同生物质类型等对生物质和聚丙烯共气化产气特性的影响。结果表明:松木锯末气化中添加聚丙烯后,最高产气量和最大产气速率增加,最高产气总流量提高21.46%,最高产气速率提高4.64%,H2和CO最高产量分别提高54.27%和79.51%;压强增加不利于提高共气化产气的H2和CO含量,有利于提高CH4含量;6种常见生物质和聚丙烯共气化产氢量大小顺序为:果皮>棉花秆≈玉米秸秆>杨树木屑>稻秆>条浒苔;聚丙烯掺混比率增加有利于提高H2、CO和CH4等组分产量。  相似文献   

14.
Reducibility of a NiAl2O4 containing catalyst was studied. On a measurement of NiAl2O4 concentration in a catalyst, a peak area ratio of NiAl2O4 in XRD analysis was verified to express the NiAl2O4 concentration. The reducibility of NiAl2O4 was confirmed to be dependent on the calcining temperature to form NiAl2O4, not dependent on the calcining time. The catalyst containing NiAl2O4 was ascertained to be reduced under convenient conditions to actual plant operations; H2/N2 = 30/70 at 1023K for 1 h + steam/CH4 = 6 at 1023K for 17 h.  相似文献   

15.
The electrochemical and structural characteristics of the metal oxide-coated spinel were investigated in the range of 2.5–4.2 V. Metal oxide coating on commercial spinel powder (LiMn2−xMxO4, M=Zr, Nikki, Japan) was carried out using the sol–gel method. Al2O3/(PtOx or CuOx)-coated spinel exhibited improved cyclability compared to bare spinel. Impedance analysis results indicated that electrochemical resistance value was not consistent with cycle performance. The improved cycle performance of metal oxide-coated spinel may be due to formation of a new Li2Mn4O9, Li2MnO3 phase, which is expected to have stability to phase transition (Jahn–Teller distortion).  相似文献   

16.
The oxidation of HCN and NH3 with CO, CH4, or H2 addition has been studied in the temperature range between 600 to 1000°C. In most of the tests 10% oxygen was used. The experiments were carried out under well-defined conditions in a flow tube reactor made of quartz glass. The effects of NO addition and oxygen level have been tested. To study the importance of O/H radicals in the reaction mechanism and to confirm previous studies, iodine was added in some tests. A detailed chemical kinetic model was used to analyze the experimental data. In general, the model and experimental results are in good agreement. The results show that under the conditions tested CO significantly promotes NO and N2O formation during HCN oxidation. During NH3 oxidation carbon-containing gaseous species such as CO and CH4 are important to promote homogeneous NO formation. In the system with CH4 addition, the conversion of HCN to N2O is lower compared to the other systems. In the HCN/NO/CO/O2 system NO reduction starts at 700°C and the maximum reduction of approx. 40% is obtained at 800°C. For the NH3/NO/CO/O2 system the reduction starts at 750°C and the maximum reduction is 50% at 800°C. Iodine addition shifts the oxidation of HCN, NO, and N2O formation as well as NO reduction to higher temperatures. Under the conditions tested, it was found that iodine mainly enhances the recombination of the O-radicals. No effect on NO formation was found in the HCN/CH4/O2 system when oxygen was increased from 6% to 10%, but when oxygen was increased from 2% to 6% NO formation decreased. The role of hydrocarbon radicals in the destruction of NO is likely to become important at low oxygen concentrations (2%) and at high temperatures (1000°C).  相似文献   

17.
Undoped and aluminium-doped zinc oxide films have been prepared by thermal evaporation of zinc acetate [Zn(CH3COO)2 2H2O] and aluminium chloride [AlCl3] onto a heated glass substrate. The structural and optoelectrical properties of the films have been studied. The effects of heat treatment for the as-deposited films in air and vaccum are investigated. Highly transparent films with conductivity as low as 2×10−3 Ω cm can be produced by controlling the deposition parameters. The electron carrier densities are in the range 0.2–7×1019 cm−3 with mobilities of 22–58 cm2 V−1 s−1.  相似文献   

18.
用传统湿式浸渍法制备La2O3掺杂的商业γ-Al2O3负载的沼气重整催化剂Ni-Co/La2O3-γ-Al2O3,通过对NiCo双金属催化剂上沼气重整制氢在常压下的宏观动力学分析,得出该催化剂上CH4与CO2消耗、H2与CO生成时的表观反应速率方程.通过改变进料中CH4与CO2的分压,求出各物质的反应分级数,确定总反应...  相似文献   

19.
Solid oxide fuel cells (SOFCs) with NiO–ScSZ and Ni0.9Mg0.1O–ScSZ-based anodes were operated by directly feeding a fuel mixture of CH4, CO2 and N2 (CH4 to CO2 ratio of 3:2). Stable operation under constant current load (200 mA cm−2) was achieved with a NiO–ScSZ type anode during 200 h operating hours at 900 °C. Less stable operation occurred with a Ni0.9Mg0.1O–ScSZ type anode. In the case of SOFC with Ni0.9Mg0.1O–ScSZ as the anode, the methane reforming activity was higher than that with NiO–ScSZ. This was explained by change in the microstructure promoting reforming reactions. However, the addition of MgO resulted in degradation of electrochemical performance due to increase in ohmic resistance of the anode material during operation.  相似文献   

20.
A comparative analysis of the properties of LiNi0.5Mn0.5O2 and Li1+xNi0.5Mn0.5O2 (0.2 ≤ x ≤ 0.7) powders, obtained by the freeze drying method, was performed. Lattice parameters of Li1+xNi0.5Mn0.5O2 decreased considerably with growing amounts of Li until x = 0.3; at x > 0.5 trace amounts of Li2MnO3 are observed by X-ray diffraction (XRD) patterns. X-ray photoelectron spectroscopy (XPS) analysis displayed an increase of Ni3+/Ni2+ ratio at 0.3 < x < 0.5, while Mn 2p spectra were almost identical in all samples. Rechargeable capacity values (V = 2.5–4.6 V) increased systematically with x reaching its maximum (185–190 mAh g−1) at x = 0.5. Samples with superstoichiometric lithium content also demonstrated good C rate characteristics.  相似文献   

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