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1.
A case study was carried out to investigate the bed agglomeration observed in a fluidized bed incinerator when burning blends of three wastes (carbon soot, biosludge and fuel oil). Several instrumental approaches were employed (i.e. XRF, SEM, XRD, and ICP-AES) to identify the bed materials (fresh sand and degrader sand) and clinkers formed in the full-scale incinerator tests. Several elements (V, Al, S, Na, Fe, Ni, P, and Cl), which normally are associated with the formation of low melting point compounds, were found in the waste blends at high content levels. The clinker bridges were identified to be associated with Al, Fe, V, K, Na, S, Ni, and Si elements.The effects of temperature and blending ratio were investigated in a muffle furnace. Carbon soot is believed to be more susceptible to the clinker formation than the other two fuels. Thermodynamic multi-phase multi-component equilibrium calculations predict that the main low melting point species could be Al2(SO4)3, Fe2(SO4)3, Na2SO4, NaCl, Na2SiO3 and V2O5. This information is useful to understand the chemistry of clinker formation. Also, it helps to develop methods for the control and possible elimination of the agglomeration problem for the design fuels.  相似文献   

2.
The sintering kinetics of nano grained tungsten carbide (n-WC) powders has been analyzed by non isothermal and isothermal sintering. Non isothermal sintering experiments reveal a multi staged sintering process in which at least three major sub-stages can be distinguished. The isothermal shrinkage strain also exhibits an asymptotic behavior with time indicating an end point density phenomenon in most of the temperature ranges. Combined microstructural and kinetic data analyses suggest that differences in the sinterability of inter and intra agglomerate pore phases introduce sub-stages in the sintering process which manifest as stagnant density regions in both the isothermal and non isothermal experiments. Kinetic analysis of the data reveals very low activation energies for sintering suggesting that particle rearrangement and agglomeration at low temperatures may be brought about by surface diffusion leading to neck growth and grain rotation. At higher temperatures rapid grain boundary diffusion by overheating along inter particle boundaries induced by sparking may be a dominant sintering mechanism. Although grain growth and densification in conventional WC powders generally obey an inverse relation to each other, in n-WC powders both can act synergistically to increase the net densification rate. In fact, complete densification cannot be achieved in n-WC powders without grain growth as one abets the other.  相似文献   

3.
Bed collapsing experiments were carried out in a cold-air transparent column 192 mm in diameter and 2 m high. Typical Fluid Catalytic Cracking (FCC) catalyst with a mean particle size of 76 μm and a density of 1400 kg/m3 was used. Both single and double-drainage protocols were tested. The local pressure drop and bed surface collapse height were acquired throughout the bed settling.Typical results were found regarding dense phase voidage of a fluidised bed and the bed surface collapse velocity. In addition, bubble fraction was calculated based on the collapse curve.Experimental results showed that windbox effect is significantly reduced compared to previous works since the volume of air within the windbox was reduced. The comparison of single/double-drainage protocols revealed a new period in the defluidisation of Geldart-A particles concerning gas compressibility. Through the temporal analysis of local pressure drop, the progress of the solid sedimentation front from bottom to top was determined, analysed and modelled.  相似文献   

4.
Miftahul Huda  Yozo Korai  Isao Mochida 《Fuel》2004,83(16):2151-2156
The combustion reactivities of Blair Athol (BA) and Nang Tong (NT) coals were measured by thermogravimetry to understand their different behaviors in the PFBC boiler. The reactivity of BA was much the same as that of NT coal but their chars showed different characteristics. BA char of higher surface area (25 m2/g) showed slightly higher reactivity than that of NT char of smaller surface area (7 m2/g). BA coal showed heterogeneous ignition even at its particle size of as large as +355 μm while NT coal showed homogeneous ignition at the average particle size over 75 μm heterogenous one occurring with finer particle size (−75 μm). Higher calorific value of BA volatile matter and higher reactivity of its char than those of NT coal causes of its heterogeneous ignition with an intense DTA peak, which may lead to local heating at its combustion and to yield reactive CaO from limestones causing of bed materials agglomeration in the PFBC.  相似文献   

5.
An alumina precursor was prepared by the aluminium sulphate (0.20 M) and excess urea reaction in boiling aqueous solution. The precursor was calcined at 900 °C for 2 h and then δ-Al2O3 powder having volumetric agglomeration degree of 80% was obtained. Cylindrical compacts having diameter of 14 mm were prepared under 32 MPa by axial pressing using oleic acid as binder. Each compact was fired isothermally at various temperatures between 950 and 1400 °C. The firing time was changed from zero to 2 h. The fired compacts were examined by scanning electron microscopy (SEM) and nitrogen adsorption techniques. The specific surface areas (S/m2 g− 1) of the samples were calculated using the Brunauer, Emmett, and Teller (BET) procedure. The rate constant (k) and mechanism-characteristic parameter (n) were obtained for different temperatures between 950 °C and 1150 °C from the application of the neck-growth sintering rate (NGRM) model on the surface area reduction data. An Arrhenius equation and the parameter n for the sintering were found in the forms of k = (7.648 × 106 h− 1) exp (− 186,234 J mol− 1 / RT) and n = 4.0 × 10− 7 T3-1.7 × 10− 3 T2 + 2.3 T − 1030.8 respectively. The parameter n changes in the interval 0.61 <  n < 1.34 with rising temperature having maximum at about 1025 °C. Based on the SEM images and NGRM data, the intra-particle sintering was discussed.  相似文献   

6.
《Ceramics International》2015,41(4):5648-5655
Lime mud is a kind of waste generated during causticization reaction of an alkali recycling process in paper industry. Lime mud and fly ash were reused as raw materials to fabricate anorthite ceramics through solid state reactions. Both sintering temperature and lime mud content influenced the crystalline phases in the prepared ceramics. Anorthite was the major phase in all samples (samples L36, L40, L50 and L60) and it was prominent in sample L36 (containing 36 wt% lime mud). The results also showed that anorthite ceramic can be synthesized at low sintering temperature (1100 °C). Gehlenite and wollastonite were formed in the samples possessing higher calcium (above 40 wt% lime mud) or at lower sintering temperatures. Bulk density, water absorption and compressive strength were measured. These ceramics were of light weight and had high water absorption. Recycling of lime mud and fly ash as raw materials of anorthite ceramic is a feasible approach to solve the solid wastes.  相似文献   

7.
Highly sinter-active nano crystalline composite powder of 2 mol% yttria doped tetragonal zirconia polycrystal (2Y-TZP) with 2 wt% alumina was synthesized by co-precipitation method. Crystallization temperature of the amorphous precursor powder, measured from simultaneous thermogravimetric (TG) and differential thermal analysis (DTA) techniques was found to be ∼470 °C. The powder was calcined at different temperatures in the range of 700-1000 °C. XRD patterns of the calcined powders revealed the presence of a single tetragonal phase. Particle size of the calcined powder measured by different techniques (X-ray line broadening, BET surface area and laser scattering technique) indicated an increase in the average particle size with calcination temperature. The study of compaction behaviour revealed the presence of soft agglomerates in the calcined powder. Pore size distribution of the green compacts obtained from a mercury porosimeter was found to be monomodal above a critical pressure. The onset temperature of sintering was found to increase with calcination temperature. Powders calcined at 800 °C and 900 °C had shown better sinterability at 1200 °C owing to the presence of finer pores with a narrow size distribution in the green compacts. Sintering behaviour of the powder calcined at 700 °C was found to be marginally poorer in comparison to the other samples, whereas the powder calcined at 800 °C had demonstrated best densification behaviour, especially when compacted at 300 MPa.  相似文献   

8.
In this work the use of chemical materials (additives) in order to reduce the biomass ash sintering tendency is investigated. A total of seven additives (kaolin, limestone, lime, dolomite, calcined dolomite, ophite and alumina) and silica utilised as reference material were mixed in different proportions with the ash of five different biomasses, and then a laboratory sintering test was performed on the mixtures to determine the effect of the additives on the sintering. The biomasses studied in this work were: thistle biomass, brassica carinata biomass, barley straw, almond shell and orujillo (olive oil extraction residue). The sintering decrease among the additives was studied using X-ray diffraction.Kaolin, lime, calcined dolomite and ophite are proved to be suitable to reduce the biomass sintering in all the considered cases. Dolomite, limestone and, particularly, the tabular alumina, offer poorer results. The dilution of the biomass ash is considered the main process involved in the decrease of the sintering for most of the additives, with the exception of kaolin whose chemical reactions could be more important than the dilution effect.  相似文献   

9.
Nijie Jing  Zhongyang Luo 《Fuel》2011,90(8):2645-2651
The sintering temperature of coal ash is studied to further understand ash behavior. The objective of this study is to obtain a detailed understanding of the effect of the reaction atmospheres on the sintering temperature under elevated pressure. A series of experiments and analyses have been completed using a pressurized pressure-drop measuring device and X-ray diffractometer (XRD) analyzer. The results show that the sintering temperatures decline markedly under all reaction atmospheres with the rise in pressure. The pressure influences the sintering temperatures by affecting the reaction rate and the mineral transformations undergone by the coal ash, as observed from the XRD patterns. The sintering temperatures measured under the reducing reaction atmospheres are lower than those for oxidizing atmospheres. The sintering temperature under N2 is lower than those under other oxidizing atmospheres. The sintering temperature under the gasification atmosphere is close to those under H2 and CO atmospheres, whereas the sintering temperature under a H2 atmosphere is lower than that under a CO atmosphere.  相似文献   

10.
Porcelain is a material produced from kaoline, quartz and potassium-feldspar. Recently, research of new materials, for example non-hazardous wastes, that are able to replace traditional fluxing agents without changing the process or quality of the final products has been realized. The aim of this work is to study the possibility of the use of glass powder waste and fly ash together for manufacturing porcelain. Instead of quartz, fly ash was used at the selected porcelain composition. The waste glass was added partially and fully in replacement of potassium-feldspar. Samples were fired in an electric furnace with a heating rate of 10 °C/min at 1100, 1150 and 1200 °C for a period of 1, 2, 3 and 5 h. The sintered samples were characterised by XRD (X-ray diffraction) and SEM (scanning electron microscopy). Sintering activation energies were determined based on the bulk density result. At 10, 15, 20 and 25 wt.% glass waste addition, the apparent activation energies were calculated to be 145, 113.5, 70.4 and 53.74 kJ/mol, respectively. It was found that the sintering activation energy decreased with increasing waste glass addition.  相似文献   

11.
This study focused on the effects of agglomeration/defluidization on the Cd, Pb and Cr distribution in bottom ash particles of different sizes. In this study we have incinerated artificial waste, which was a mixture of sawdust, polypropylene, selected metal solutions, and polyethylene. The experimental parameters included Na concentration, addition of Ca and Mg and operating temperature. The results indicated that particle size decreased by attrition and thermal impact in the absence of added Na. When Na was added to the system, this metal reacted with silica sand to form eutectics, which increased particle size. Further addition of Ca and Mg was found to prolong the operating time, with greater amounts of liquid eutectic accumulating, leading to increase particle size.The heavy metal concentrations in coarse and fine particles were greater than those present in particles of intermediate sizes over a range of experimental conditions. As the particle size decreased below 0.59 mm or increased above 0.84 mm, the heavy metal concentrations increased. As Ca and Mg were added, the heavy metal concentrations in particles of all sizes increased relative to those present in identical particles when no metals or only Na were added. Additionally, the ratio of Cd sorption to silica sand decreased with increasing Na concentration, but Cr sorption had the opposite tendency. Therefore, while the addition of Na tended to increase agglomeration, it also increased the tendency for heavy metals to remain in the sand bed of fluidized bed incinerators. Addition of Ca and Mg not only inhibited the agglomeration/defluidization process, resulting in increased operating time, but also enhanced the removal of heavy metals by silica sand, decreasing the concentration of heavy metals in reactor exhaust.  相似文献   

12.
In the food manufacturing and pharmaceutical industry several agglomeration technologies are applied: fluidised bed agglomeration, steam jet agglomeration, agglomeration during drying and pressure agglomeration like extrusion, roller compaction or tabletting. In addition, caking or sticking of amorphous substances, which is a kind of undesired agglomeration, is frequently observed.Any desired or undesired agglomeration of amorphous substances is dependent on the mechanical properties of the entire particle or the particle surface. Changes in the mechanical properties of the material are linked to changes in moisture and temperature and can be predicted by applying the glass transition concept. Using this concept it is possible to estimate the viscosity and the Young's modulus for a given amorphous substance while knowing their glass transition temperature in dependence on the water content.Knowing the viscosity and the Young's modulus and applying equations derived from the sintering technology or the theory of viscoelasticity it is possible to define suitable conditions for most of the agglomeration processes mentioned above.  相似文献   

13.
Particles agglomeration is obtained by spraying liquid over solid particles fluidized by hot air. The growth mechanism depends on the operating parameters (geometry and process conditions) and initial materials, influencing drying conditions and agitation, leading either to agglomeration or coating or wet quenching. It is linked to air temperature and/or humidity distributions appearing in the well-mixing system of the fluidized bed due to the penetration of the sprayed liquid jet.In this study, air temperatures distributions in a conical fluidized bed of model particles (glass beads) top sprayed with water were measured varying the initial particles load (250, 500, 750 g), the fluidizing air inlet temperature (60-70-80 °C), the liquid feed rate (2.65, 5.33, ) and the relative air spraying pressure (1,2,3 bars). Three thermal zones were identified (heat transfer, isothermal, wetting-active), with sizes and shapes related to particles circulation patterns and drying and spraying conditions influenced by the operating parameters. Subsequent agglomeration trials, were carried out with glass beads and soluble maltodextrin particles agglomerated, respectively, with an acacia gum solution and water. They showed a relationship between the air temperatures distribution and the resulting growth mechanism. Particularly, controlled agglomeration was obtained for a wetting-active zone occupying 18-30% of the fluidized bed.  相似文献   

14.
The mineral matter in typical feed coals used in South African gasification processes and the ash derived from gasifying such coals have been investigated using a variety of mineralogical, chemical and electron microscope techniques. The mineral matter in the feed coals consists mainly of kaolinite, with minor proportions of quartz, illite, dolomite, calcite and pyrite plus traces of rutile and phosphate minerals. The calcite and dolomite occur in veins within the vitrinite macerals, and are concentrated in the floats fraction after density separation. Some Ca and Ti also appear to be present as inorganic elements associated with the organic matter.Electron microscope studies show that the gasification ash is typically made up of partly altered fragments of non-coal rock, bonded together by a slag-like material containing anorthite and mullite crystals and iron oxide particles, with interstitial vesicular glass of calcic to iron-rich composition. Ash formation and characteristics thus appear to be controlled by reactions at the particle scale, allowing the different types of particles within the feed coal to interact with each other in a manner controlled mainly by the modes of mineral occurrence. Integration of such techniques provides an improved basis for evaluating ash-forming processes, based on quantitative phase identification, bulk and particle chemistry, and the geometric forms in which the different phases occur.  相似文献   

15.
This paper presents a study of the precipitation of ZnO and CuO crystals during the sintering of Cu-doped Ni-Zn ferrites. The nature of the resulting crystal precipitates were analysed using scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), confirming the findings of a previous paper (Part I). This study examines the influence of sintering temperature and sintering time of the thermal cycle on their formation, and on their microstructure and electromagnetic properties. The same two consecutive chemical reactions proposed in Part I can be used to explain the bulk precipitation and subsequent re-dissolution of the zinc and copper oxides observed during sintering. The effect of these crystal precipitates on the final properties of this type of soft ferrite was also analysed, revealing a deterioration in its electromagnetic performance.  相似文献   

16.
Yongbin Cui  John F. Stubington 《Fuel》2001,80(15):2235-2243
Char combustion parameters that significantly affect the in-bed combustion of char in PFBC were determined experimentally using a batch-fed PFBC. The ratio of carbon to oxygen consumed on the surface of a burning char particle was determined and it was concluded that CO was the only product of char combustion in PFBC.

Model simulations revealed that, for PFBC, mass transfer controlled the combustion of large char particles ≥2 mm, whereas the combustion of small char particles below 0.9–2 mm was controlled by both mass transfer and chemical kinetics.

System pressure influenced the char combustion via the interaction between chemical kinetics and the mass transfer of oxygen to the char. Char particle temperature varied markedly with oxygen partial pressure in the particulate phase, indicating a distribution of char particle combustion rates in PFBC. In modelling char combustion in PFBC, the temperature of char particles in the bed should be calculated at different locations based on a heat balance around the burning char particle taking into account the local bed oxygen concentration.  相似文献   


17.
H. Haykiri-Acma  S. Kucukbayrak 《Fuel》2010,89(10):3063-3068
Sintering temperatures and the initial deformation temperatures of ashes from Turkish Elbistan lignite, and biomass species such as hazelnut shell and rice husk were investigated up to 1450 °C by Heating Microscope Technique. Sintering temperatures were found 1300, 1269, and 1320 °C for hazelnut shell, rice husk, and lignite, respectively, while the initial deformation temperatures were >1450, 1370, and >1450 °C. Lignite/biomass blends were prepared by adding of biomass into coal in the ratios of 5 or 10 wt.%, and then effects of biomass presence on sintering temperature and the initial deformation temperature were tested. It was determined that the addition of potassium-rich hazelnut shell reduced the sintering temperatures to 919 and 730 °C for the blends of 5 and 10 wt.%, respectively. Also, initial deformation temperature dropped to 788 °C in case of the blend of 10 wt.%. Such a big antagonistic influence of hazelnut shell on the thermal behaviour of ash is attributed to the interaction of potassium from biomass with silicon compounds found in mineral matter of lignite. In addition, concentration of CaO may be another reason for this. On the other hand, the presence of rice husk showed limited effect on the sintering temperature as well the initial deformation temperature.  相似文献   

18.
Green compacts pressed by means of uniaxial compaction with Magnesia (MgO) powders precipitated from sea water and calcined at different temperatures were sintered under H2 atmosphere at 1700 °C. The calcination, carried out between 900 and 1200 °C had a great influence in the final density and the microstructure. The densification of MgO agglomerated powders seems to be predictably related to grain growth and thus coarsening kinetics. At calcination temperatures higher than 900 °C, the volume of large pores was increased notably suggesting that the inhibited grain growth adversely affected the thermodynamics of pore sintering. Relative densities between 74 and 98% of theoretical density were reached in compacts obtained at different compaction pressures. The microstructural differences were examined by Scanning Electron Microscopy (SEM).  相似文献   

19.
Phase development and changes in crystalline composition of LTCC material during the sintering process were investigated using in-situ X-ray diffraction (XRD) measurements. CeramTape GC was chosen as the chemically simplest model system composed of alumina particles and glass for the investigations. The chemical characterization and microstructural analyses of the tapes sintered with some representative firing profiles were performed by techniques such as (scanning) transmission electron microscope, energy-dispersive X-ray spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and XRD. Moreover, the porosification behavior of LTCC substrates fired at different peak temperatures was studied. These investigations are important for the subsequent wet chemical etching, representing an approach which allows to reduce locally the permittivity of LTCC tapes. Treatment with a KOH solution shows non-selective etching behavior for all substrates. In addition, highly porous silica structures corresponding to Ca and Al depletion from the anorthite phase were observed in all samples after etching treatment.  相似文献   

20.
《Ceramics International》2016,42(7):8005-8009
Slip-cast ceramic samples of the system (100−x) (ZrO2–3.5 mol% Y2O3)–xAl2O3 (abridged as (100−x) 3.5 YSZ/xAl2O3 composite, where x is expressed in wt%) were examined using dilatometry, isothermal sintering and electron microscopy methods. The shrinkage in the range 1100–1300 °C was found to be higher for the (100−x) 3.5 YSZ/xAl2O3 samples with prevailing fraction of PSZ than for the composites with a corundum matrix. When the weight fraction of corundum was increased, the relative shrinkage of the (100−x) 3.5 YSZ/xAl2O3 samples decreased and the open porosity of the ceramic materials grew. The effect of <gamma>-Al2O3 impurity on the sintering process and linear dimensions of ceramics is shown. Heat treatment of (50–40) 3.5 YSZ/(50–60) Al2O3 composites at 1300 °C are proposed as the optimum conditions for porous diaphragm formation.  相似文献   

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