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1.
L. Chen C. Zeng X. Guo Y. Zhang W. Li H. Zhu V. Zamansky 《Fuel Processing Technology》2010,91(8):848-852
Quantitative gas evolution kinetics of coal primary pyrolysis at high heating rates is critical for developing predictive coal pyrolysis models. This study aims to investigate the gaseous species evolution kinetics of a low rank coal and a subbituminous coal during pyrolysis at a heating rate of 1000 °C s− 1 and pressures up to 50 bar using a wire mesh reactor. The main gaseous species, including H2, CO, CO2, and light hydrocarbons CH4, C2H2, C2H4, C2H6, C3H6, C3H8, were quantified using high sensitivity gas chromatography. It was found that the yields of gaseous species increased with increasing pyrolysis temperature up to 1100 °C. The low rank coal generated more CO and CO2 than the subbituminous coal under similar pyrolysis conditions. Pyrolysis of the low rank coal at 50 bar produced more gas than at atmospheric pressure, especially CO2, indicating that the tar precursor had undergone thermal cracking during pyrolysis at the elevated pressure. 相似文献
2.
Hydrogen production via gasification of meat and bone meal in two-stage fixed bed reactor system 总被引:1,自引:0,他引:1
Gasification of meat and bone meal followed by thermal cracking of tar was carried out at atmospheric pressure using a two-stage fixed bed reaction system in series. The first stage was used for the gasification and the second stage was used for thermal cracking of tar. In this work, the effects of temperature (650-850 °C) of both stages, equivalence ratio (actual O2 supply/stoichiometric O2 required for complete combustion) (0.15-0.3) and the second stage packed bed height (40-100 mm) on the product (char, tar and gas) yield and gas (H2, CO, CO2, CH4, C2H4, C2H6, C3H6, C3H8) composition were studied. It was observed that the two-stage process increased hydrogen production from 7.3 to 22.3 vol.% (N2 free basis) and gas yield from 30.8 to 54.6 wt.% compared to single stage. Temperature and equivalence ratio had significant effects on the hydrogen production and product distribution. It was observed that higher gasification (850 °C) and cracking (850 °C) reaction temperatures were favorable for higher gas yield of 52.2 wt.% at packed bed height of 60 mm and equivalence ratio of 0.2. The residence time of tar and product gases was varied by varying the packed bed height of second stage. The tar yield decreased from 18.6 wt.% to 14.2 wt.% and that of gas increased from 50.6 wt.% to 54.6 wt.% by changing the packed bed height of second stage from 40 to 100 mm while the gross heating value (GHV) of the product gas remained almost constant (16.2-16.5 MJ/m3). 相似文献
3.
Capucine Dupont Jean-Michel Commandré Guillaume Boissonnet Daniel Schweich 《Fuel》2008,87(7):1155-1164
Experiments are performed in an entrained flow reactor to better understand the kinetic processes involved in biomass pyrolysis under high temperatures (1073-1273 K) and fast heating condition (>500 K s−1). The influence of the particle size (0.4 and 1.1 mm), of the temperature (1073-1273 K), of the presence of steam in the gas atmosphere (0 and 20 vol%) and of the residence time (between 0.7 and 3.5 s for gas) on conversion and selectivity is studied. Under these conditions, the particle size is the most crucial parameter that influences decomposition. For 1.1 mm particles, pyrolysis requires more than 0.5 s and heat transfer processes are limiting. For 0.4 mm particles, pyrolysis seems to be finished before 0.5 s. More than 70 wt% of gas is produced. Forty percent of the initial carbon is found in CO; less than 5% is found in CO2. The hydrogen content is almost equally distributed among H2, H2O and light hydrocarbons (CH4, C2H2, C2H4). Under these conditions, the evolution of the produced gas mixture is not very significant during the first few seconds, even if there seems to be some reactions between H2, the C2 and tars. 相似文献
4.
Pyrolysis products of uncoated printing and writing paper of MSW 总被引:1,自引:0,他引:1
Uncoated printing and writing paper, one of the principal waste papers in Taiwan, was pyrolyzed with a thermogravimetric analysis (TGA) reaction system. The pyrolysis experiments were carried out in nitrogen environment at a constant heating rate of 5 K min−1. The gaseous products and the residues were collected at room temperature (300 K) and analyzed by gas chromatography (GC) and elemental analyzer, respectively. The major gaseous products investigated included non-hydrocarbons (H2, CO, CO2, and H2O) and hydrocarbons (C1-3, C4, C5, C6, 1-ring, C10-12, levoglucosan, C13-15, and C16-18). The cumulated masses and the instantaneous concentrations of gaseous products were obtained under the experimental conditions. The yields of non-hydrocarbon gases and of hydrocarbon gases were about 10.46 and 0.49% at 623 K, 33.68 and 0.89% at 700 K, 64.52 and 1.05% at 788 K, and 79.10 and 1.63% at 938 K, respectively. The estimation of the mass of tar, yielded at various pyrolysis temperatures was also made. The results of this study might be useful for the design of pyrolysis process as well as for determining the pyrolysis mechanisms of the uncoated printing and writing paper. 相似文献
5.
The influence of poisoning of Pt catalyst by CO on the kinetics and mechanism of H2 oxidation reaction (HOR) at Pt/C electrode in 0.5 mol dm−3 HClO4, saturated with H2 containing 100 ppm CO, was examined with rotating disc electrode (RDE) at 22 °C. Commercial carbon black, Vulcan XC-72 was used as support, while Pt/C catalyst was prepared by modified polyol synthesis method in an ethylene glycol (EG) solution. The kinetically controlled current (Ik) for the HOR at Pt/C decreases significantly at CO coverage (ΘCO) > 0.6. For ΘCO < 0.6 the HOR takes place through Tafel-Volmer mechanism with Tafel reaction as rate-determining step at the low CO coverage, while Volmer step controls the overall reaction rate at the medium CO coverage. When CO coverage is higher then 0.6, Heyrovsky-Volmer mechanism is operative for the HOR with Heyrovsky as the rate-determining step (rds). 相似文献
6.
Experiments on pyrolysis of C2Cl4 with hydrogen in argon bath gas (C2Cl4: H2: AR=0.5:7:92.5) were performed in a laboratory scale flow reactor, to determine reaction paths and kinetic parameters, plus to observe hydrogen as a source to convert chlorocarbons into hydrocarbons and HCl. The reaction was carried out at 1 atmosphere total pressure in the tubular flow reactor, over temperature ranges from 575 to 850 °C, with average residence times in the range of 0.3 to 1.2 s. The major reaction products were C2HCl3, CH2CCl2, C2H6, C2H4 and HCl. Trace intermediates including CH4, C2H2, C3H6, C3H4, C4H8, C4H6, C4H4, C2H3Cl, C2HCl, trans-CHClCHCl, cis-CHClCHCl C2Cl2 and aromatic compounds were found. The equation for overall loss of C2Cl4 (k (s−1)) was 1.35×106exp(−27055/RT). This study shows that C2H4 became the major product for reaction temperatures higher than 700 °C, and became one of the final products together with HCl.A detailed kinetic mechanism consisting of 202 elementary reactions with 59 species was developed to model the results obtained from the experiments. Sensitivity analyses were performed to rank the significance of each reaction in the mechanism. Modeling and sensitivity analysis revealed that C2Cl4+H→C2HCl3+Cl, C2Cl4+H→C2Cl3+Cl, and C2Cl4→C2Cl3+Cl are the primary reactions for the decomposition of C2Cl4. 相似文献
7.
Carlos A. Alzate Carlos F. Valdés Arturo Berrio Javier De La Cruz Carlos A. Londoño 《Fuel》2009,88(3):437-529
A pelletization process was designed which produces cylindrical pellets ∼8 mm in length and 4 mm in diameter. These ones were manufactured using a blend of Pinus Patula and Cypress sawdust and coal in proportions of 0%, 5%, 10%, 20%, and 30% v/v of coal of rank sub-bituminous extracted from the Nechí mine (Amagá-Antioquia). For this procedure, sodium carboxymethyl cellulose (CMC) was used as binder at three different concentrations. The co-gasification experiments were carried out with two kinds of mixtures, the first one was composed of granular coal and pellets of 100% wood and the second one was composed of pulverized wood and granular coal pellets. All samples were co-gasified with steam by using an electrical heated fluidized-bed reactor, operating in batches, at 850 °C. The main components of the gaseous product were H2, CO, CO2, CH4, and N2 with approximate quantities of 59%, 6.0%, 20%, 5.0%, and 9.0% v/v, respectively, and the higher heating values ranged from between 7.1 and 9.5 MJ/Nm3. 相似文献
8.
CO tolerance of H2-air single cell with phosphoric acid doped polybenzidazole (PA-PBI) membrane was studied in the temperature range 140-180 °C using either dry or humidified fuel. Fuel composition was varied from neat hydrogen to 67% (vol.) H2-33% CO mixtures. It was found that poisoning by CO of Pt/C and Pt-Ru/C hydrogen oxidation catalysts is mitigated by fuel humidification. Electrochemical hydrogen oxidation at Pt/C and Pt-Ru/C catalysts in the presence of up to 50% CO in dry or humidified H2-CO mixtures was studied in a cell driven mode at 180 °C. High CO tolerance of Pt/C and Pt-Ru/C catalysts in FC with PA-PBI membrane at 180 °C can be ascribed to combined action of two factors—reduced energy of CO adsorption at high temperature and removal of adsorbed CO from the catalyst surface by oxidation. Rate of electrochemical CO oxidation at Pt/C and Pt-Ru/C catalysts was measured in a cell driven mode in the temperature range 120-180 °C. Electrochemical CO oxidation might proceed via one of the reaction paths—direct electrochemical CO oxidation and water-gas shift reaction at the catalyst surface followed by electrochemical hydrogen oxidation stage. Steady state CO oxidation at Pt-Ru/C catalyst was demonstrated using CO-air single cell with Pt-Ru/C anode. At 180 °C maximum CO-air single cell power density was 17 mW cm−2 at cell voltage U = 0.18 V. 相似文献
9.
Sylvie Valin Julien Cances Pierre Castelli Anthony Dufour Guillaume Boissonnet 《Fuel》2009,88(5):834-4128
Biomass gasification at temperatures below 1273 K produces gas which contains methane and too much tar for Fischer-Tropsch synthesis. The aim of this study is to investigate methane conversion at high temperature. Experimental tests were performed between 1273 and 1773 K, with a mixture of gas representative of wood pyrolysis at 1100 K (main components only: CO, CO2, CH4, H2, H2O). Two different kinetic schemes were used to predict the gas composition, and PAH molecules formation. For a residence time of 2 s in the reactor, the gas must be heated to at least 1650 K to reach a methane conversion rate of 90%. A parametric study was performed at 1453 K, by varying the initial methane, steam and hydrogen contents, so as to find out which components are the most influent on methane conversion and soot production. 相似文献
10.
Yijun Zhao Hao Zhou Rui Sun Hongming Tian Jiyi Luan Juan Qian 《Fuel Processing Technology》2010,91(8):910-914
Experiments were performed in an entrained-flow reactor to better understand the processes involved in biomass air gasification. Effects of the reaction temperatures (700 °C, 800 °C, 900 °C and 1000 °C), residence time and the equivalence ratio in the range of 0.22-0.34 on the gasification process were investigated. The behavior of biomass gasification was discussed in terms of composition of produced gas. Four parameters, i.e. the low heating value, fuel gas production, carbon conversion and cold gas efficiency were used to evaluate the gasification. The results show that CO, CO2 and H2 are the main gasification products, while hydrocarbons (CH4 and C2H4) are the minor ones. With the increase of the reaction temperature, the concentration of CO decreases, while the concentrations of CO2 and H2 increase. The concentrations of CH4 and C2H4 reach their maximum value when the reaction temperature is 800 °C. The optimal reaction temperature is considered to be 800 °C and the optimal equivalence ratio is 0.28 in that the low heating value of the produced gas, carbon conversion and cold gas efficiency achieve their maximum values. The kinetic parameters of sawdust air gasification are calculated basing on the Arrhenius correlation. 相似文献
11.
U. Balachandran 《Fuel》2006,85(2):150-155
Novel cermet (i.e. ceramic-metal composite) membranes have been developed to separate hydrogen from mixed gases, particularly product streams generated during coal gasification and/or methane reforming. Hydrogen separation with these membranes is non-galvanic, i.e. it does not use electrodes or an external power supply to drive the separation, and hydrogen selectivity is nearly 100% because the membranes contain no interconnected porosity. The hydrogen permeation rate has been measured as a function of temperature (500-900 °C), membrane thickness (≈22-210 μm), and partial pressure of hydrogen (0.04-1.0 atm) in the feed gas. The hydrogen flux varied linearly with the inverse of membrane thickness, and reached ≈20 cm3(STP)/min cm2 for a membrane with a thickness of ≈22 μm at 900 °C with 100% H2 (at ambient pressure) as the feed gas. The results indicate that the hydrogen flux is limited by bulk diffusion and might be higher for a thinner (<22 μm) membrane. Some of the membranes were tested in a simulated syngas mixture containing H2, CO, CO2, and CH4, and showed no degradation in performance. Hydrogen flux measurements made in H2S-containing atmospheres for times approaching ≈270 h showed that a 200-μm-thick cermet membrane was stable in gases containing up to ≈400 ppm H2S. While longer-term studies are needed, these results suggest that the cermet membranes may be suitable for practical hydrogen separation applications. 相似文献
12.
A two-step process to generate H2 gas; first by milling polystyrene (PS) or poly(vinyl alcohol) (PVA) with Ni(OH)2 and Ca(OH)2, followed by heating of the milled product in the second-step was performed in this work. Polymer and hydroxide mixtures obtained after milling for 60 min and heating to 700 °C showed H2, CH4, H2O, CO, and CO2 as the main gaseous products with H2 as the dominant gas generated between 350 and 500 °C. Analysis of the gaseous products by TG-MS and gas-chromatography, and solid products by TG-DTA and XRD shows that CO2 gas was fixed as CaCO3 at temperatures between 350 to 600 °C allowing generation of H2 gas with concentrations over 95% for PS and over 98% for PVA. The results in this study show that milling of solid based hydrocarbon compounds with nickel and calcium hydroxides allows dispersion of nickel to hydrocarbon surfaces and facilitates C-C bond rupture in polymer(s) during heating at temperatures below 500 °C, at the same time calcium adsorbs CO2. This process could be developed to treat hydrocarbon based wastes such as plastics, biomass or combinations at low temperatures avoiding syngas purification and separation steps. 相似文献
13.
The combustion mechanism of asphalt binder was investigated by using thermogravimetric analyzer coupled with Fourier transform infrared spectrometer (TG-FTIR) in a mixed gas environment of 21% oxygen and 79% nitrogen. The results show that the combustion process of asphalt binder consists of three main consecutive stages at a low heating rate. The combustion reaction becomes more and more intense from the 1st to 3rd stage. The release of volatiles occurs mainly at 300-570 °C, and the gaseous products in each stage are different. The main products in the 1st stage are CO2, CO, H2O, hydrocarbons, formaldehyde, tetrahydrofuran, formic acid, aromatic compounds, etc. In the next stage, the combustion products mentioned above keep on increasing, but some new volatiles such as alcohols, phenols, styrene, etc. are present. In the last stage, the CH and CO bonds continue to fracture and aromatization reaction occurs, and the release amount of CO2, CO, and H2O reaches the maximum. But the content of other products decreases or even disappears due to burning. Among the above volatiles, CO2 is the dominant gaseous product in the whole combustion process. The concentration of CO2 and CO keeps increasing, and reaches the maximum intensity at about 520 °C. The evolution of H2O, CH4, and formic acid exhibits the trend of increase first, and then decrease. Over 570 °C, there are few products released at the end of the combustion process. Asphalt binder combustion process includes two modes of complete and incomplete combustion, and the latter may be main combustion mode of asphalt binder. 相似文献
14.
The 30-cell nickel-yttria stabilized zirconia (Ni-YSZ) hydrogen electrode-supported planar solid oxide electrolyzer (SOE) stack modules were manufactured and tested at 800 °C in steam electrolysis mode for hydrogen production. The electrolysis efficiency of the stack modules was higher than 100% at a total steam and hydrogen flow of 2.1 sccm cm−2, a H2O/H2 ratio of 80/20, and a current density of <0.2 A cm−2. The electrolysis efficiency, current efficiency, and actual hydrogen production rate of the stack modules increased with increasing H2O/H2 ratio at a constant current density. However, the electrolysis and current efficiencies decreased steadily at high current densities. During hydrogen production, the stack modules were operated at 800 °C and a constant current density of 0.15 A cm−2 for up to 1100 h. A steam conversion rate of 62% and current efficiency of 87.4% were obtained; the actual hydrogen production rate reached as high as 103.6 N L h−1. Post-mortem analysis showed that delamination of the LSM–YSZ oxygen electrode mainly occurred in the steam and air inlet area of the 10×10 cm2 cells. 相似文献
15.
The growth of carbon nanofibers from Fe-Cu catalyzed decomposition of CO/C2H4/H2 mixtures at temperatures over the range 500-650 °C has been investigated. Based on analysis of the gas phase and solid products it is apparent that co-adsorption of CO and C2H4 induces major perturbations in the surfaces of the bimetallic catalyst particles. These features are reflected in an increase in the yield of solid carbon and subtle changes in the structural characteristics of the carbon nanofibers. Optimum performance with respect to the yield of carbon nanofibers is found for iron-rich particles treated in CO/C2H4/H2 (1:3:1) at 600 °C. Deactivation of the catalyst is observed to occur with high Cu concentrations and at reaction temperatures in excess of 600 °C. It is suggested that under these conditions the surface of the particles in contact with the reactant gas mixture become enriched in Cu, which does not possess the ability to dissociatively chemisorb either CO or C2H4. 相似文献
16.
Wen-Yueh Yu Wen-Sheng Lee Chien-Pang Yang Ben-Zu Wan 《Journal of the Chinese Institute of Chemical Engineers》2007
By simulating CO and H2 oxidations at thermodynamic equilibrium and studying the catalytic oxidations over Au/TiO2, preferential oxidation of CO in a H2 rich stream (PROX) was investigated. During the simulation, at least two cases under different gaseous feeds, H2/CO/O2/N2 = 50/1/0.5/48.5 or 50/1/1/48 (vol.%) were examined under the assumption of an ideal gas and one atmosphere pressure in the reactor. It was found that the addition of 1% O2 (the latter case) effectively reduced CO concentration to less than 100 ppm in the temperature range between 0 and 90 °C. This range narrowed to between 0 and 50 °C with the addition of 3% H2O and 15% CO2 in the feed. The thermodynamic study suggests that 1% CO in a H2 rich system can be decreased to below 100 ppm within those low temperature ranges, if there is no substantial adsorptions onto the catalyst surface and the reactions rapidly reach equilibrium. During the catalysis reaction study, a well-pH adjusted Au/TiO2 catalyst was found very active for PROX. CO conversions at the reactor outlet were close to those at equilibrium. Au/TiO2 used in this work was prepared via deposition-precipitation (DP) method. The influence of gold colloid pH (at 6) adjustment time on gold loading, gold particle size and chloride residue on TiO2 surface was detected by atomic absorption (AA), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). A pH adjustment time of at least 6 h for the preparation of gold colloids at room temperature was demonstrated to be essential for the high catalytic activity of Au/TiO2. This was attributed to the smaller gold particle and the less chloride residue on the catalyst surface. 相似文献
17.
Elisa Barbosa-Coutinho 《Carbon》2003,41(9):1707-1714
The preparation of carbon membranes by pyrolysis of polyetherimide hollow fibers and the influence of process variables on the final membrane morphology using a statistical experimental design are described in this work. The characterization of polymers and membranes was carried out by thermal analysis and scanning electron microscopy (SEM). The carbonization process was accompanied by mass spectroscopy to monitor the products formed. Similar to carbonization of others polymers, H2O, CO2 and CO evolution from 420 to 680 °C, and hydrogen evolution from 450 to 800 °C, indicate the formation of crosslinking of polymeric chains and formation of a graphite-like structure. These experiments permitted the production of thermostable carbon hollow fibers and selection of best treatment conditions. The extent of membrane exposure under oxidizing atmosphere and the maximum temperature of stabilization were decisive in the final membrane morphologic characteristics and properties. When the stabilization temperature was above 500 °C an intensive degradation of the fiber was observed. An initial exposure to an oxidizing atmosphere seems to be fundamental in order to control the final membrane properties. In this atmosphere, heating rates as low as 1 °C min−1 during stabilization reduce cracks in the surface of final membranes. 相似文献
18.
A precipitated iron catalyst containing sulfur for Fischer-Tropsch (F-T) synthesis was prepared by means of a novel method using a ferrous sulfate as precursor. Both fixed bed reactor (FBR) and continues stirred tank slurry reactor (STSR) were used to test long-term F-T reaction behaviors over the catalyst. A stability test (1600 h) in FBR showed that the catalyst was active even after 1500 h of time-on-stream with CO conversion of 78% and with C5+ hydrocarbon selectivity of 72 wt% at 250 °C, 2.0 MPa, 2.0 NL/g-cat/h, and H2/CO=2.0. The test (550 h) in STSR indicated that the catalyst exhibited relatively high activity with CO conversion of 70-76% and C5+ selectivity of 83-86 wt% in hydrocarbon products under the conditions of 260 °C, 2.0 MPa, 2.0 NL/g-cat/h, and H2/CO=0.67. The deactivation rate of the catalyst was low, accompanied by surprisingly low methane selectivity of 2.0-2.9 wt%. It is shown that a small amount of sulfur (existing as SO42−) may promote the catalyst by increasing activity and improving the heavier hydrocarbon selectivity. It is also comparable with other typical iron catalysts for F-T synthesis. 相似文献
19.
Five German hard coals of 6–36 wt% volatile matter yield (maf) were pyrolysed at pressures up to 10 MPa, using two different apparatuses, which mainly differ in the heating rates. One consists of a thermobalance where a coal sample of ≈ 1.5 g is heated at a rate of 3 K min ?1 under a gas flow of 3 I min?1. The other apparatus is constructed for rapid heating (102?103 K s?1) of a small sample of ≈10 mg of finely-ground coal distributed as a layer between the folded halfs of a stainless-steel screen, heated by an electric current. The product gas composition was determined by quantitatively analysing for H2, CH4, C2H4, C2H6, CO, CO2 and H2O. The amounts of tar and char were measured by weighing. The heating rate, pressure and gas atmosphere were varied. Under an inert gas atmosphere, high heating rates result in slightly higher yields of liquid products, e.g. tar. The yields of light hydrocarbon gases remain the same. With increasing pressure, the thermal cracking of tar is intensified resulting in high yields of char and light hydrocarbon gases. Under H2, pyrolysis is influenced strongly at elevated pressure. Additional amounts of highly aromatic products are released by hydrogenation of the coal itself, particularly between 500 and 700°C. This reaction is less effective at higher heating rates because of the shorter residence time and diffusion problems of H2. The yield of light gaseous compounds CH4 and C2H6 increases markedly under either heating condition owing to gasification of the reactive char. 相似文献
20.
Reforming of pure glycerol, crude glycerin, and methanol (pure and in the presence of Na2CO3) in supercritical water was investigated. Continuous experiments were carried out at temperatures between 450 and 650 °C, residence times between 6 and 173 s, and feed concentrations of 3-20 wt%. For methanol the gas products are mainly H2, CO2, and CO. The carbon-to-gas efficiency and the observed activation energy for pure methanol are higher than for methanol with Na2CO3. This can be explained by assuming different decomposition mechanisms for pure methanol and methanol with Na2CO3. For glycerol, H2, CO, CO2, CH4, and higher hydrocarbons are produced. The carbon-to-gas efficiencies of crude glycerin and pure glycerol are comparable. Overall, 2 of the 3 carbon atoms present in glycerol end up in carbon oxides, while 1 carbon atom becomes CxHy. The overall mechanism of glycerol decomposition involves the dehydration of 1 mole of H2O/mole glycerol. For both, methanol and glycerol at carbon-to-gas efficiencies below 70%, the gas yields (mole/mole feed) and carbon-to-gas efficiency correlate well. 相似文献