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81.
Explosions of gas-dust hybrid mixtures have long been considered as particular cases encountered in specific industrial contexts. However, it should be reminded that during the explosion of an organic powder, the presence of a hybrid mixture composed of the dust itself and its pyrolysis gases is compulsory. On these premises, an experimental study to determine the role of cellulose pyrolysis products (gaseous, condensable and solid) on the global phenomenon is presented. Hybrid mixture explosion tests were exploited to carry out the investigation. The G-G furnace and the 20 L sphere were employed. Several experimental strategies were chosen to demonstrate the impact of pyrolysis reaction on the explosion of organic powders: i) the fuel equivalence ratio of the reactive mixture (case 1), or ii) the mass of reactants (case 2) were respectively kept constant, iii) the effects of water vapor, char and tar were tested. They were next compared to identify the most suitable one. The two first experimental approaches lead to significantly different results: only case 2 keeps the maximum explosion pressure almost constant, but maximum rate of pressure rises and deflagration index greatly decrease when the pyrolysis gases concentration decreases, which highlights the importance of the pyrolysis reaction on the explosion kinetics. It should also be stressed that the maximum explosion severity is not obtained for the pure gases but when a small dust content is added. The same evolution is observed when a small amount of char is introduced to pyrolysis gases, which underlines the influence of the radiative transfer. Adding small amounts of tar to cellulose tends to increase its explosion severity. However, this impact is less than that generated by the addition of pyrolysis gases. 相似文献
82.
Animal manures generally contain high levels of heavy metals that may pose a significant threat to soil and groundwater qualities. Pyrolysis as means of reducing metal availability in such feed stocks is recently encouraged, but systematic studies are currently lacking. The aim of this study was to assess the impact of pyrolysis temperature on the availability of Cu and Zn by chemical extraction, to determine the speciation of Cu and Zn by synchrotron-based X-ray spectroscopy, and finally to investigate the phase distribution of metal species in the carbonaceous materials by combining acid–base extractions and absorption spectroscopy data. The results showed that both Cu and Zn in the swine manure were mainly bound to organic functional groups. Cu (II) reduction and Cu (I)–S complexes were observed during the pyrolysis process. Zn species resembling ZnAc2 was still dominant, being 60.8–69.2%, and ZnS increased by 6.6–21.8% in the carbonaceous materials. The distribution of Cu and Zn in the mineral, carbonized and non-carbonized organic phases varied greatly with the pyrolysis temperature. The higher the temperature, the more the metals existed in the mineral phase and carbonized organic phase. The decrease of EDTA extractable Cu and Zn with pyrolysis temperature was due to the increase of metals in the carbonized organic phase and mineral phase. It is suggested that pyrolysis at the relatively higher temperature is a better choice for metal-containing manure according to the metal speciation, solubility and availability. 相似文献
83.
84.
Toshiro Tsuji Yoshiki Tanaka Hironori Itoh 《Journal of Material Cycles and Waste Management》2001,3(1):2-7
Plastic pellets of polyethylene (PE), polypropylene (PP), and polystyrene (PS) were gasified in a two-stage thermal degradation
process. The first stage is the conversion of polyolefins to distilled oils using a melting vessel. In the second stage, the
oils from the first stage are gasified using a tubular reactor. The distilled oil yields of PE, PP, and PS in the first stage
were 84, 89, 92 wt%, respectively, each at 470°C. The total gas yields of PE, PP, and PS in the second stage were 80, 74,
and 6.2 wt%, respectively, each at 800°C. The main components of the product gas for PE and PP were methane and olefins such
as ethene and propene. Some aromatic oils, including benzene, toluene, and xylene, were also produced as by-products. The
amount of carbonaceous residue, or coke, was very low (less than 1 wt%). By dividing the process into two stages, the coking
rate was considerably reduced compared with direct gasification of the polyolefins.
Received: July 19, 2000 / Accepted: September 17, 2000 相似文献
85.
Tao Jiang Joeri Kaal Jiang Liu Jian Liang Yaoling Zhang Dingyong Wang 《环境科学学报(英文版)》2020,32(4):146-156
Soil dissolved organic matter(DOM) plays an essential role in the Three Gorges Reservoir(TGR) as a linkage between terrestrial and aquatic systems.In particular,the reducing capacities of soil DOM influence the geochemistry of contaminants such as mercury(Hg).However,few studies have investigated the molecular information of soil DOM and its relationship with relevant geochemic al reactivities,including redox properties.We collected samples from eight sites in the TGR areas and studied the link between the molecular characteristics of DOM and their electron donation capacities(EDCs) toward Hg(II).The average kinetic rate and EDC of soil DOM in TGR areas were(0.004±0.001) hr~(-1) and(2.88±1.39) nmol e~-/mg DOM_(bulk),respectively.Results suggest that higher EDCs and relatively rapid kinetics were related to the greater electron donating components of ligninderived and perhaps pyrogenic DOM,which are the aromatic constituents that influenced the reducing capacities of DOM in the present study.Molecular details revealed that even the typical autochthonous markers are important for the EDCs of DOM as well,in contrast to what is generally assumed.More studies identifying specific DOM molecular components involved in the abiotic reduction of Hg(II) are required to further understand the relations between DOM sources and their redox roles in the environmental fate of contaminants. 相似文献
86.
Kuniyasu Kawaguchi Kazutada Miyakoshi Kiyoshi Momonoi 《Journal of Material Cycles and Waste Management》2002,4(2):102-110
It is important to investigate the pyrolysis processes of municipal solid waste (MSW) in the same way as for any mixture
comprised of multiple substances. In this article, a two-reaction model for a variety of MSW mixtures is proposed to predict
mass changes due to pyrolysis. In order to formulate the model based on pyrolysis kinetics, we conducted experiments to determine
the kinetic model parameters. By thermal analysis of the typical components of MSW, mass changes attributable to the pyrolysis
reaction were found at about 350°C for paper, 400°–500°C for plastics, and 200°–400°C for garbage (dry condition). Activation
energies were obtained by the Ozawa method based on the mass changes in pyrolysis. Thus, the pyrolysis behavior is formulated
as a function of temperature. Then the pyrolysis mass change of the mixture can be predicted by using a weighted sum of the
individual components. The model proved useful in experiments with real waste (refuse-derived fuels). Furthermore, the weight
yields (pyrolysis gas, tars, solid residues) of the mixture can be calculated by their additive property after measuring the
mass balance of each component.
Received: May 11, 2001 / Accepted: November 16, 2001 相似文献
87.
88.
Conversion of leather wastes to useful products 总被引:1,自引:0,他引:1
Onur Ylmaz I. Cem Kantarli Mithat Yuksel Mehmet Saglam Jale Yanik 《Resources, Conservation and Recycling》2007,49(4):436-448
The main objective of the present study is to investigate the production of useful materials from different kinds of leather waste. Three different types of tannery wastes (chromium- and vegetable-tanned shavings, and buffing dust) were pyrolyzed in a fixed bed reactor at temperatures of 450 and 600 °C under N2 atmosphere. Gas, oil, ammonium carbonate and carboneous residue were obtained by pyrolysis. The effect of temperature and type of leather waste on product distribution of pyrolysis was investigated. Buffing dust gave the highest yield of oil (ca. 23%), while other wastes recorded yields of ca. 9%. Results of elemental analysis and column chromatography showed that pyrolysis oils could be used as fuel or chemical feedstock after re-treatment. The yields of carboneous residue (chars) were between 37.5% and 48.5% and their calorific value was between 4300 and 6000 kcal kg−1, suitable for use as solid fuel. In addition, these chars were activated by CO2 to obtain the activated carbon. The activated carbon having highest surface area (799.5 m2 g−1) was obtained from chromium-tanned shavings. Activated carbons prepared from chromium-tanned leather were presented as an adsorbant for the adsorption of dyes from aqueous solution. 相似文献
89.
This paper describes a mathematical model for the pyrolysis of a small dry pine wood cylinder. The computational domain is axisymmetric and involves the heating chamber, with the wood cylinder vertically situated in the centre of the chamber. The model simulates the laminar flow around the particle and the laminar flow inside the wood/char matrix by applying a two-phase transport model where the solid wood/char matrix acts as one phase and the various gases produced from the pyrolysis process is assembled in the other phase. Convective, conductive and thermal radiation transfer modes are included in the model. A two-step pyrolysis reaction scheme is used for the modelling of the conversion from wood to tar and gas. Both the thermal conductivity and the permeability of the wood/char matrix are modelled anisotropically in order to capture the directional differences in heat and mass transport, existing in real wood. Results from simulations are compared with measurements from literature for the centre core solid temperature and the conversion from wood to char, tar and pyrolysis gas in the particle during heating. The results show very good agreement with the measured temperature profile. The simulated conversion profile shows an overall good agreement with the measurements, however with discrepancies in the early stage of the process. Besides the successful validation with the experimental data, it provides us with all the details of the distribution of the migrating pyrolysis gas and tar, the temperature, the velocity flow field and pressure in the wood/char cylinder. 相似文献
90.