Calcination Heating Research Articles

The Characteristics of Calcium-Based Sorbent Burning Pore Structure and Simulation of Gas-Solid Mass Transfer in Vulcanization

The experimental is carried out in the normal air atmosphere by calcining CaCO3 and using the scan electricity speculum and N2 adsorption apparatus to research the ventage structure of the calcinate CaO at 860°C.Analyzing on fractal dimension of different calcination temperature, heating rate and residence time. Thorough the pore structure of CaO which is a porous substance, using “dynamic pervasion modulus” to analyse the Calcium-based sorbent’s gas-solid pervasion transferring quality reaction when it is calcined in the furnace. Using the “dynamic pervasion modulus” and revising the expression of the SO2 adsorption quality in vulcanizing reaction.

Photocatalytic performance of S doped TiO2 in relation to processing conditions: calcination temperature and heating rate

The effect of different heating profiles on the photocatalytic performance of sulphur doped TiO2 photocatalysts is reported. The photocatalysts were synthesised by a sol–gel method using thiourea as the dopant precursor and characterised using X-ray diffraction, elemental analysis and reflection measurements. The degradation of dichloroacetic acid, under indirect sunlight and visible light irradiation, was used to determine the photocatalytic performance of the synthesised materials. A number of different commercial photocatalysts were used as comparative standards. In all the studied specimens, anatase TiO2 was the dominant crystalline type. Additionally, compared with undoped TiO2 and commercial standards, significant absorption into the visible region (400–470 nm) was observed for the modified TiO2.

Effect of heat treatment on particle growth and magnetic properties of electrospun Sr0.8La0.2Zn0.2Fe11.8O19 nanofibers

Sr0.8La0.2Zn0.2Fe11.8O19/poly(vinyl pyrrolidone) (PVP) composite fiber precursors were prepared by the sol–gel assisted electrospinning. Subsequently, the M-type ferrite Sr0.8La0.2Zn0.2Fe11.8O19 nanofibers with diameters about 120 nm were obtained by calcination of these precursors at different heat treatment conditions. The precursor and resultant Sr0.8La0.2Zn0.2Fe11.8O19 nanofibers were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectrometer and vibrating sample magnetometer. With the calcination temperature increased up to 1,000 °C for 2 h or the holding time prolonged to 12 h at 900 °C, the Sr0.8La0.2Zn0.2Fe11.8O19 particles gradually grow into a hexagonal elongated plate-like morphology due to the dimensional control along the nanofiber length. These elongated plate-like particles will be linked one by one to form the nanofiber with a necklace-like morphology. The magnetic properties of the Sr0.8La0.2Zn0.2Fe11.8O19 nanofibers are closely related to grain sizes, impurities and defects in the ferrite, which are influenced by the calcination temperature, holding time and heating rate. After calcined at 900 °C for 12 h with a heating rate of 3 °C/min, the optimized magnetic properties are achieved with the specific saturation magnetization 75.0 A m2 kg−1 and coercivity 426.3 kA m−1 for the Sr0.8La0.2Zn0.2Fe11.8O19 nanofibers.

Structure and Novel Optical Characteristics of SrSi2O2N2:Ce3+/Tb3+Oxynitride Phosphors

A microwave-assisted hydrothermal route was developed for preparing (Sr1−x−yCexTby)Si2O2−δN2+μ phosphors. Both the required calcination temperatures and heating duration were markedly reduced as compared with the solid-state reaction. With a rise in the calcination temperatures, the emission intensity of Ce3+-doped phosphors decreased due to the thermal quenching effects. For Tb3+-doped phosphors, the emission intensities of the splitting peaks were influenced by the thermal interaction between the Tb3+ energy levels. It is found that the Ce3+- and Tb3+-doped SrSi2O2N2 phosphors demonstrate great absorption in the vacuum ultraviolet region and are therefore suitable for application in plasma display panels. While Ce3+ and Tb3+ were codoped into SrSi2O2N2, the emission spectra exhibited the combination of the Ce3+ and Tb3+ emission peaks. The energy transfer process from Tb3+ to Ce3+ via the electrostatic interaction was also investigated in detail.

10.2478/s11814-009-0198-3

The CO2 capture from flue gases by a small fluidized bed reactor was experimentally investigated with limestone. The results showed that CO2 in flue gases could be captured by limestone with high efficiency, but the CO2 capture capacity of limestone decayed with the increasing of carbonation/calcination cycles. From a practical point of view, coal may be required to provide the heat for CaCO3 calcination, resulting in some potential effect on the sorbent capacity of CO2 capture. Experiment results indicated that the variation in the capacity of CO2 capture by using a limestone/coal ash mixture with a cyclic number was qualitatively similar to the variation of the capacity of CO2 capture using limestone only. Cyclic stability of limestone only undergoing the kinetically controlled stage in the carbonation process had negligible difference with that of the limestone undergoing both the kinetically controlled stage and the product layer diffusion controlled stage. Based on the experimental data, a model for the high-velocity fluidized bed carbonator that consists of a dense bed zone and a riser zone was developed. The model predicted that high CO2 capture efficiencies (>80%) were achievable for a range of reasonable operating conditions by the high-velocity fluidized bed carbonator in a continuous carbonation and calcination system.

Characterization and activity of visible-light driven TiO2 photocatalyst doped with tungsten

This research aimed to expand the activity of TiO(2) down to the visible light region by modifying the sol-gel conditions and doping with tungsten. The optimum conditions for calcination temperature, acid type, and heating rate were 200°C, HNO(3), and 1°C/min, respectively. The undoped TiO(2) synthesized under these conditions could significantly absorb the visible light whereas the commercial Degussa P-25 could not. The absorptivity decreased sequentially as the wavelength increased from 400 to 700 nm. Within 6 h of 2-W blue-light illumination, 23% of 0.1 mM 2-chlorophenol was removed. The XRD result showed that the crystalline was anatase phase. The visible-light absorption property of the TiO(2) became even better when doped with tungsten. At the optimum W to TiO(2) ratio of 0.5%, the degradation of 0.1 mM 2-chlorophenol increased to 53% indicating a higher photocatalytic activity. Both crystalline and amorphous TiO(2) could exhibit the photocatalytic activity under the visible light region.

Effects of rapid calcination on properties of calcium-based sorbents

The calcination process may influence subsequent fragmentation, sintering and swelling when CaO derived from limestone acts as a CO 2 or SO 2-sorbent in combustion, gasification and reforming. Sorbent properties are affected by CO 2 partial pressure, total pressure, temperature, heating rate, impurities and sample size. In this study, the effect of calcination heating rate was investigated based on an electrically heated platinum foil. The effects of heating rate (up to 800 °C/s), calcination temperature (700–950 °C), particle size (90–180 μm) and sweep gas velocity were investigated. Higher initial heating rates led to lower extents of limestone calcination, but the extents of carbonation of the resulting CaO were similar to each other. Calcium utilization declined markedly during carbonation or sulphation of CaO after calcination by rapid heating. Experimental results show that carbonation and calcium utilization were most effective for carbonation temperatures between 503 and 607 °C. Increasing the extent of calcination is not the best way to improve overall calcium utilization due to the vast increase in energy consumption.

CO2 capture from flue gases using a fluidized bed reactor with limestone

The CO2 capture from flue gases by a small fluidized bed reactor was experimentally investigated with limestone. The results showed that CO2 in flue gases could be captured by limestone with high efficiency, but the CO2 capture capacity of limestone decayed with the increasing of carbonation/calcination cycles. From a practical point of view, coal may be required to provide the heat for CaCO3 calcination, resulting in some potential effect on the sor- bent capacity of CO2 capture. Experiment results indicated that the variation in the capacity of CO2 capture by using a limestone/coal ash mixture with a cyclic number was qualitatively similar to the variation of the capacity of CO2 capture using limestone only. Cyclic stability of limestone only undergoing the kinetically controlled stage in the carbonation process had negligible difference with that of the limestone undergoing both the kinetically controlled stage and the product layer diffusion controlled stage. Based on the experimental data, a model for the high-velocity fluidized bed carbonator that consists of a dense bed zone and a riser zone was developed. The model predicted that high CO2 capture efficiencies (>80%) were achievable for a range of reasonable operating conditions by the high-velocity fluidized bed carbonator in a continuous carbonation and calcination system.

Structures and Properties of Lead-Free NKN Piezoelectric Ceramics

In this work, the preparation of sodium potassium niobate (Na0.5K0.5)NbO3 (NKN) ceramics were carried out by the conventional method. The effect of calcination temperatures, dwell time and heating rate on phase formation was investigated. Earlier work reported that to achieve the density of NKN ceramic over 95% of its theoretical density is rather difficult. In this work, firing conditions and heating and cooling rates were carefully varied to fabricate the NKN ceramics. X-ray diffraction (XRD) techniques were used to investigate the phase evolution of the calcined powders and sintered bodies. Microstructures of sintered pellets were studied by the scanning electron microscopic (SEM) techniques. Dielectric and ferroelectric properties were also investigated and reported.

Structure and catalytic activity of Al-MCM-48 materials synthesised at room temperature: Influence of the aluminium source and calcination conditions

MCM-48 aluminosilicates with different aluminium contents were synthesised by a room temperature procedure using tetraethoxysilane and aluminium sulfate, isopropoxide or tert-butoxide as metal sources. The samples were characterised by X-ray diffraction, nitrogen adsorption at 77 K, and 27Al MAS NMR and the catalytic activity tested in the reaction of 1-butene double bond position isomerisation. The influence of the synthesis time and calcination conditions, such as heating rate and time at final temperature, on the structural and catalytic properties of the materials was also evaluated. Aluminium isopropoxide and sulfate allowed the preparation of well structured Al-MCM-48 materials, with high specific pore volume and uniform pore size, and with the majority of the aluminium incorporated in tetracoordinated environment after calcination, at least down to Si/Al of 15. The highest initial conversions were found for samples with Si/Al = 20 and 30 prepared with aluminium isopropoxide and calcined using a heating rate of 3 K min −1, with those of samples prepared with aluminium sulfate being slightly lower. Al-MCM-48 materials with high specific pore volume and uniform size were also synthesised using aluminium tert-butoxide, but the materials were less well ordered, presented a higher proportion of hexa- and pentacoordinated Al species and exhibited lower initial conversions, independently of the synthesis time or calcination conditions tested. It is concluded that aluminium isopropoxide and sulfate are more adequate metal sources than aluminium tert-butoxide to prepare Al-MCM-48 catalysts by this room temperature method and a calcination heating rate of 3 K min −1 instead of 1 K min −1 produces more effectively active catalysts.

Platinum species in the pores of NaX, NaY and NaA zeolites studied using EPR, XAS and FTIR spectroscopies

The results of X-band EPR, X-ray absorption and Fourier transform infrared spectroscopy on Pt(NH(3))(4)(2+) exchanged NaX, NaY and NaA zeolites reveal after oxygen calcination at 573 K that diamagnetic Pt(2+) is not the only product. Calcination provides Pt(3+) cations, but depending on the heating rate, the decomposition of amino groups during calcination also produces hydrogen that reduces Pt(3+) to Pt(2+) and Pt(+). NaX (Si/Al = 1.23) has a more negative framework charge than NaY (Si/Al = 2.31), so Pt(3+) can be stabilized only in NaX, whereas lower oxidation states of Pt such as Pt(+) can be stabilized in both, NaX and NaY, and neither of the paramagnetic Pt cations are stabilized in NaUSY (Si/Al = 3). The autoreduction process allows controlling the number of Pt(3+) and Pt(+) in the NaX zeolite by changing the calcination heating rate: a heating rate of 1.25 K min(-1) gives only Pt(+), but 0.5 K min(-1) gives a Pt(3+)/Pt(+) ratio close to 1. The structure of the support is also important for the synthesis of Pt species. While isolated paramagnetic Pt ions were stabilized in faujasite zeolites (NaX and NaY), a paramagnetic Pt dimer was obtained in a Linde type A zeolite (LTA, Si/Al = 1) by applying the same preparation methods. The fraction of paramagnetic Pt species which were characterized by X-band EPR spectroscopy amounts to 2-18% of the total Pt in the zeolites, the remaining Pt must be diamagnetic.

Rapid calcination of high quality mesostructured MCM-41, MSU-X, and SBA-15 silicate materials: A step towards continuous processing?

Rapid calcination of high quality silicate mesostructures is possible at rates at least up to 100 °C min −1. Some ’fine-tuning’ of the mesopore structure is possible by controlling the rate of heating during the calcination process and lower temperatures might be used to calcine the non-ionically templated SBA-15 and MSU-X materials. High calcination heating rates produce a distortion of the Si-MCM-41 hexagonal repeat unit and some form of phase transition in the 3-D disordered Si-MSU-X. At the calcination heating rates used here (2, 5, 10, 20, 100 °C min −1) the overall structural integrity of siliceous mesostructured materials is maintained while some structural collapse is observed in Al- and Ti-substituted MCM-41. SBA-15 materials appear to benefit from an elevated temperature aging period prior to high temperature calcination. The results suggest that for siliceous mesostructures it might be possible to use continuous processing methods at least in the calcination step.

Preparation and characterization of high-surface-area titanium dioxide by sol-gel process

One of the important ways to improve photocatalytic efficiency is to prepare catalyst with enhanced surface area. In this work, titanium dioxide (TiO2) nanoparticles having enhanced surface area were synthesized under the interference of SiO2. The mixed oxide, SiO2-TiO2 (10% mol% Si), was prepared by a sol-gel procedure using titanium tetra-n-butoxide as Ti-precursor. The commercial SiO2 nanoparticles were added into the TiO2 sols after hydrolysis. After condensation and calcination heat treatment, the SiO2-TiO2 nanoparticles were obtained. To achieve the purpose of obtaining the high-surface-area TiO2, the SiO2 was removed subsequently by aqueous NaOH solution. The TiO2 products were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), electron spectroscopy for chemical analysis (ESCA), and by N2 adsorption-desorption isotherm. A fine mesoporous structure was formed for as-prepared TiO2 after calcination at 400∘C and the average pore diameter was about 7 nm. The porous TiO2 products possess mixing phases of anatase and rutile. Phase transformation from anatase to rutile occurred when the samples were calcined. The phase transition temperature is sensitive to the silicon content. The particle size of ∼43 nm remained constant upon calcinations from 500 to 700∘C. The specific surface area was increased up to 66% compared to regular TiO2 samples that were prepared by the similar sol-gel procedure. The porous TiO2 nanostructures exhibited enhanced photocatalytic performance to decompose methylene blue under UV irradiation.

Dehydration of sodium carbonate monohydrate with indirect microwave heating

In this study, dehydration of sodium carbonate monohydrate (Na 2CO 3·H 2O) (SCM) in microwave (MW) field with silicon carbide (SiC) as an indirect heating medium was investigated. SCM samples containing up to 3% free moisture were placed in the microwave oven. The heating experiments showed that SCM is a poor microwave energy absorber for up to 6 min of irradiation at an 800 W of microwave power. The heat for SCM calcination is provided by SiC which absorbs microwave. The monohydrate is then converted to anhydrous sodium carbonate on the SiC plate by calcining, i.e. by removing the crystal water through heating of the monohydrate temperatures of over 120 °C. The calcination results in a solid phase recrystallization of the monohydrate into anhydrate. In the microwave irradiation process, dehydration of SCM in terms of indirect heating can be accelerated by increasing the microwave field power.

New MOD solution for the preparation of high Jc REBCO superconducting films

High quality REBa2Cu3Ox (RE=Y,Eu,Gd) films have been successfully fabricated by metalorganic deposition method using dichloroacetic acid. Metal acetates or oxide powders were dissolved in dichloroacetic acid and blue-colored get was obtained by drying. Coating solution was prepared by diluting blue gel in methanol. Coating solution was coated on single crystal (001) LaAlO3(LAO) by dip coating method. Processing parameters such as oxygen partial pressure, water vapor, ramping rate and pyrolysis temperature etc were controlled in order to obtain a good epitaxial film. 0.5μm-thick film was obtained by single coating and with no crack after calcination heat treatment. Oxygen partial pressure was varied in the range of 100–1000ppm and conversion heat treatment was carried out at the temperature range of 725–765°C. A critical transition temperature (Tc0) of 90K and a critical transport current density (Jc) of >0.5MA/cm2 (77K and self-field) were demonstrated for the GdBCO film grown on LAO single crystal substrate with a thickness of 0.5μm. Ic was determined by utilizing a transport measurement. SEM observations showed that the growth behavior of Y123 grains is different from that of TFA–MOD process.

Effect of Calcination Procedure on the Electrocatalytic Activities of Ti/IrO<sub>2</sub> Electrodes in Acidic Aqueous Solution

The influence of the calcination procedure on electrocatalytic properties for oxygen evolution at Ti/IrO2, electrodes was investigated by using cyclic voltammetry (CV) and anodic polarization tests. Thermal decomposition at single temperature of 500 degrees C for each layer (conventional method) was adopted as the standard procedure. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and electrochemical impedance spectroscopy (EIS) show the standard procedure leads to compact oxide coatings, with large grain distributing on coatings and high resistance of obtained electrodes. Both applying the lower temperatures in first three under-layers (step-method) and the programming heating in each layer can, to some extent, overcome the disadvantages of the conventional procedure, and thereby improve the electrochemical activities of electrodes. By using the modified procedures, the electrode resistance is found to decrease due to the inhibition of substrate oxidation. When using the controlled programming calcination (heating rate), the coating becomes more porous and rugged.

Nitrogen oxide (NOx) emission reduction during pellet induration by fuel addition to the green pellets and decreased excess air

A research project was undertaken to determine if coal addition to fluxed-magnetite prefired pellets would reduce nitrogen oxide (NOx) emissions during pellet induration. Iron-oxidation-rate tests, coal-oxidation-rate tests and calcinations-rate tests were conducted in a laboratory furnace to determine the amount of coal necessary to provide adequate heat for limestone calcination without producing detrimental effects to magnetite oxidation. Pilot-scale pot-grate tests were then performed both with and without coal in the prefired pellets to verify pellet-quality parameters and nitrogen oxide emissions. The off-gas during each pot-grate test was analyzed for NOx, CO2, CO, SO and O2. There was approximately a 10% reduction in NOx emissions with coal addition during the normal pot-grate firing cycle. There was a 75% reduction in NOx emissions during firing cycles that used 25% to 75% excess air during firing rather than the normal 300% excess air.

The Effect of Heating Rate and Gas Atmosphere on Template Decomposition in Silicalite-1

Template evolution from TPABr/silicalite powder was studied in a thermogravimetric analyzer as a function of heating rate and gas atmosphere to determine the maximum rate of weight loss and the temperature at which the rate of weight loss was a maximum. Through the application of TPD theory, the activation energies of the thermal decomposition reactions in various gaseous atmospheres (helium, oxygen, air, ozone/air mixture) were also calculated. The results of these investigations showed that an increased calcination heating rate had a direct correlation with an increased rate of weight loss. The template removal reaction in an inert atmosphere (helium) was endothermic; however, the presence of oxidizing components in the gas atmosphere gave rise to significant exothermic reactions. We found that the least stressful conditions for template removal occurred with a heating rate of 0.5 K/min in an atmosphere containing a mixture of air and ozone (1%). For these conditions, the maximum rate of weight loss was 0.061%/min, and the temperature at maximum weight loss was 487 K; the template was fully removed at a final temperature of ca 723 K.

Filter sand for municipal water supply

This work presents DEM-CFD simulations of the transient processes occurring in an industrial scale PFR-kiln. DEM allows the numerical simulation of the moving and reacting limestone bed in the kiln and is coupled with a 3-dimensional CFD simulation describing the interstitial gas phase.A PFR-kiln consists of two vertical shafts and a connecting crossover channel. The two shafts periodically switch their function at regular intervals of about 15 min. While one shaft calcines the product in parallel flow with gas temperatures above 900 °C, the other preheats the stones in counter flow.The model has been applied to an industrial PFR-kiln of 18 m height. A realistic particle size distribution of the limestone with particles ranging from 50 to 90 mm has been set. Methane combustion provides the heat for calcination and is simulated by a two-step mechanism. Simulation results show a nearly uniform temperature distribution in the calcination zone but significant inner particle temperature gradients. The calcination degree depends on the particle location within the kiln and decreases towards the outer kiln walls. Measured and simulated temperatures are compared. Maximum temperature values as well as its characteristic oscillation induced by the periodic kiln operation could be reproduced by the simulation, especially keeping in mind the difficulties of thermocouple measurements under the harsh conditions in industrial reality.