TG-FTIR pyrolysis of coal and secondary biomass fuels: Determination of pyrolysis kinetic parameters for main species and NOx precursors

Co-firing of secondary biomass fuels with coal in coal-fired pulverized fuel boilers is facing increased application in large-scale power production. Fundamental knowledge on the thermochemical behavior of biomass and waste fuels is still lacking, especially regarding the release of the fuel bound nitrogen. Characterization of chicken litter (CL), biomass mix (BM) and meat and bone meal (MBM) and an HV coal blend was performed using TG-FTIR analysis. Three heating rate profiles were applied (10, 30 and 100 °C/min), with a final temperature of 900 °C. NH₃ was found to be the major gaseous N-product, while HCN and HNCO were also released in substantial amounts. Kinetic parameters for the pyrolysis of biomass fuels were obtained using a model based on parallel first-order reactions with a Gaussian distribution of activation energies. Input files for the coal FG-DVC (functional group-devolatilization, vaporization, cross-linking) and FG-BioMass pyrolysis models were prepared. The fit of model parameters to TG-FTIR product-evolution data was found to be generally good, but the model-predicted yields for some species did not fit experimental data at all heating rates equally well. This problem can be overcome by improvements in the FG-BioMass model. The results of this study can be used to have an improved input of initial pyrolysis in CFD modeling of co-fired boilers.     

Preparation of microporous sorbents from cedar nutshells and hydrolytic lignin

Carbon nutshells and hydrolytic lignin were used as starting materials for the preparation of microporous active carbons. Optimum parameters for cedar nutshell carbonization have been selected (temperature of carbonization 700-800 °C, rate of heating less than 3 °C/min) for the preparation of microporous carbons (average pore width 0.56 nm). The textural characteristics of microporous carbons made from nutshell are similar to those of a ‘Coconut’ carbon molecular sieve, but the latter has both a higher CO₂ adsorption capacity and a higher coefficient of N₂/O₂ separation. The influence of carbonization and steam-activation parameters on the microtexture and molecular-sieve properties of granular carbons made from hydrolytic lignin was also investigated. A low rate of heating (less 3 °C/min) promotes the formation of micropores with average sizes around 0.56-0.58 nm at carbonization temperature 700 °C. At the same carbonization temperature the average sizes of micropores were 0.7-0.78 nm at rates of heating more than 3 °C/min. The activation of lignin-char with steam at 800 °C resulted in the formation of active carbons with more developed micropore volume (0.3-0.35 cm³ g⁻¹) and with micropores of widths around 0.6-0.66 nm which are able to separate He from a He-CH₄ mixture. The size of the micropores was varied as a function of burn off value.     

Determination of EMC isotherms and appropriate mathematical models for canola

Canola seed needs to be dried to minimize damage during subsequent unit operations. In order to optimize the drying and storage processes of seeds it is necessary to know the equilibrium moisture content at different air equilibrium relative humidities and temperatures. In the present work adsorption equilibrium moisture content isotherms were determined for a specific local canola variety at 25, 40 and 55 °C and seven air relative humidifies within the range of 11-90%. Experimental data were used to model the adsorption isotherm process using non-linear regression analysis. Thirteen available mathematical and semi empirical models were employed to find the best fit isotherm curve model. The Halsey model showed the best results at 25 and 40 °C and the values of coefficient of determination (R²), chi-square (χ²) and root of mean square error (RMSE) were 0.993, 0.122 and 0.295 at 25 °C and 0.994, 0.042 and 0.174 at 40 °C. Another best fit mode was the GAB model at 55 °C which resulted in the values of 0.997, 0.023 and 0.120 for R², χ² and RMSE respectively. The adsorption monolayer moisture content (m₀) was also evaluated using BET equation. The m₀ values at 25 °C, 40 °C and 55 °C were 0.017, 0.016 and 0.015 g H₂O/g solid and the corresponding constant values of the BET equation were found to be −4.733, −5.129 and −10.299 respectively.     

Formation of nanosize ZnO particles by thermal decomposition of zinc acetylacetonate monohydrate

Formation of ZnO particles by thermal decomposition of zinc acetylacetonate monohydrate in air atmosphere has been investigated using XRD, DTA, FT-IR, and FE-SEM as experimental techniques. ZnO as a single phase was produced by direct heating at ≥200 °C. DTA in air showed an endothermic peak at 195 °C assigned to the ZnO formation and exothermic peaks at 260, 315 and 365 °C, with a shoulder at 395 °C. Exothermic peaks can be assigned to combustion of an acetylacetonate ligand released at 195 °C. ZnO particles prepared at 200 °C have shown no presence of organic species, as found by FT-IR spectroscopy. Particles prepared for 0.5 h at 200 °C were in the nanosize range from ∼20 to ∼40 nm with a maximum at 30 nm approximately. The crystallite size of 30 nm was estimated in the direction of the a₁ and a₂ crystal axes, and in one direction of the c-axis it was 38 nm, as found with XRD. With prolonged heating of ZnO particles at 200 °C the particle/crystallite size changed little. However, with heating temperature increased up to 500 or 600 °C the ZnO particle size increased, as shown by FE-SEM observation. Nanosize ZnO particles were also prepared in two steps: (a) by heating of zinc acetylacetonate monohydrate up to 150 °C and distillation of water and organic phase, and (b) with further heating of so obtained precursor at 300 °C.     

Recrystallization studies on isotropic cold-crystallized PET: Influence of heating rate

The nanostructural changes associated to the multiple melting behaviour of isotropic cold-crystallized poly(ethylene terephthalate) (PET) have been investigated by means of simultaneous wide- and small-angle X-ray scattering, using a synchrotron radiation source. Variations in the degree of crystallinity, coherent lateral crystal size and long period values, as a function of temperature, for two different heating rates are reported for cold-crystallized samples in the 100-190 °C range. The Interface Distribution Function analysis is also employed to provide the crystalline and amorphous layer thickness values at various temperatures of interest. Results suggest that samples crystallized at both low (T_a = 100-120 °C) and high (T_a = 160-190 °C) temperatures are subjected to a nearly continuous nanostructural reorganization process upon heating, starting immediately above T_g (≈80 °C) and giving rise to complete melting at ≈260 °C. For all the T_a investigated, a melting-recrystallization mechanism seems to take place once T_a is exceeded, concurrently to the low-temperature endotherm observed in the DSC scans. For low-T_a and slow heating rates (2 °C/min), a conspicuous recrystallization process is predominant within T_a + 30 °C ≤ T ≤ 200 °C. In contrast, for high-T_a, an increasingly strong melting process is observed. For both, high- and low-T_a, an extensive structural reorganization takes place above 200 °C, involving the appearance of new lamellar stacks simultaneously to the final melting process. The two mechanisms should contribute to the high-temperature endotherm in the DSC scan. Finally, the use of a high heating rate is found to hinder the material's overall recrystallization process during the heating run and suggests that the high-temperature endotherm is ascribed to the melting of lamellae generated or thickened during the heating run.     

Study on the thermal behavior of a solution-cast liquid-crystalline polymer film by positron-annihilation lifetime spectroscopy

The thermal behavior of a solution-cast liquid-crystalline polymer (LCP) film was extensively studied by positron-annihilation lifetime spectroscopy (PALS). From the positronium (Ps) lifetimes of the first heating process from 40 to 250 °C at a heating rate of 2.5 °C/h, four characteristic temperatures (140, 170, 200, 235 °C) were observed. From a combined investigation with conventional differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA), the first three characteristic temperatures were found to correspond to reorientation, glass-transition, and softening temperatures, respectively. The fourth temperature was related to the commencement of crystallization, which was observed above about 235 °C from a decrease in the Ps lifetime. A low-temperature PALS experiment exhibited the γ-transition due to rotation of the phenyl moiety at about −53 °C.     

TG-FTIR characterization of coal and biomass single fuels and blends under slow heating rate conditions: Partitioning of the fuel-bound nitrogen

The devolatilization behavior of a bituminous coal and different biomass fuels currently applied in the Dutch power sector for co-firing was experimentally investigated. The volatile composition during single fuel pyrolysis as well as during co-pyrolysis was studied using TG-FTIR characterization with the focus on the release patterns and quantitative analysis of the gaseous bound nitrogen species. It was shown that all investigated biomass fuels present more or less similar pyrolysis behavior, with a maximum weight loss between 300 and 380 °C. Woody and agricultural biomass materials show higher devolatilization rates than animal waste. When comparing different fuels, the percentage of fuel-bound nitrogen converted to volatile bound-N species (NH₃, HCN, HNCO) does not correlate with the initial fuel-N content. Biomass pyrolysis resulted in higher volatile-N yields than coal, which potentially indicates that NO_x control during co-firing might be favored. No significant interactions occurred during the pyrolysis of coal/biomass blends at conditions typical of TG analysis (slow heating rate). Evolved gas analysis of volatile species confirmed the absence of mutual interactions during woody biomass co-pyrolysis. However, non-additive behavior of selected gas species was found during slaughter and poultry litter co-pyrolysis. Higher CH₄ yields between 450 and 750 °C and higher ammonia and CO yields between 550 and 900 °C were measured. Such a result is likely to be attributed to catalytic effects of alkali and alkaline earth metals present in high quantity in animal waste ash. The fact that the co-pyrolysis of woody and agricultural biomass is well modeled by simple addition of the individual behavior of its components permits to predict the mixture's behavior based on experimental data available for single fuels. On the other hand, animal waste co-pyrolysis presented in some cases synergistic effects in gas products although additive behavior occurred for the solid phase.     

Biosorption properties of dried Neurospora crassa for the removal of Burazol Blue ED dye

Biosorption potential of dried Neurospora crassa for Burazol Blue ED was studied with respect to pH, equilibrium time, biomass concentration and temperature to determine equilibrium and kinetic model parameters. The most suitable pH, equilibrium time and biomass concentration were determined as 1 ± 0.2, 60 min and 1.6 g L^− 1, respectively, at 20 °C ± 1.0. The equilibrium data was best described by the Langmuir isotherm model. The maximum biosorption capacity (q_m) of biomass obtained from the Langmuir fit was 110.1 mg g^− 1 biomass at 30 °C. The overall biosorption process was best described by the pseudo-second-order kinetic model. The biosorption process was found to be favored at higher temperatures.     

Estimation of thermal transitions in poly(ethylene naphthalate): Experiments and modeling using isoconversional methods

Thermal transitions of PEN, such as the glass transition temperature and those occurring during isothermal or nonisothermal crystallization were investigated based on careful experiments and modeling with isoconversional methods. The latter was applied to DSC data to determine the effective activation energy for the glass transition in PEN. Using the same data and different thermal methods the dynamic fragility of PEN was evaluated. The Lauritzen-Hoffman (LH) parameters K_g and U^∗ were estimated using the secondary nucleation theory from both PLM and isothermal DSC after self-nucleation measurements. Regime II to I and III to II transition at about 253 °C and 243 °C were concluded. Elliptical-shaped hedrite-like morphology was observed above 253 °C. Finally, isoconversional analysis was applied to both melt and glass non-isothermal crystallization data and the combined set of activation energies was found to be described by the theoretical Vyazovkin-Sbirrazzuoli equation using a single set of LH parameters coming from PLM measurements.     

Effect of two stage, tray and heat pump assisted-dehumidified drying on drying characteristics and qualities of dried ginger

Desorption isotherms for sliced gingers have been measured. A non-linear regression programme was used to fit four moisture sorption isotherm models to the experimental data. The Modified Halsey and Modified Oswin models gave the best fit for X_e = f(RH_e, T) and RH_e = f(X_e, T), respectively. Tray and heat pump dehumidified drying incorporated by single and two stage drying were conducted. It was found that the modified Page model was the most effective. The drying constant was fitted to drying air temperature using the Arrhenius model. Effective moisture diffusivities were determined using the drying data. The heat pump dehumidified drying incorporated by the two stage drying could reduce the drying time at 40 °C by 59.32% and increase 6-gingerol content by 6%. Quality evaluation by 6-gingerol content, rehydration ratio and ΔE* showed the best quality for dried sliced gingers in the heat pump dehumidified drying incorporated by the two stage drying at 40 °C.     

Preparation of carbon hollow fiber membranes by pyrolysis of polyetherimide

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.     

Pyrolysis and combustion kinetics of Fosterton oil using thermogravimetric analysis

Thermogravimetric analysis (TGA) was used to examine the thermal behavior of Fosterton oil mixed with reservoir sand. TGA experiments were performed in nitrogen and air atmospheres at the heating rate of 10 °C/min up to 800 °C. In this study, four sets of TGA runs were performed to examine the thermal behavior of Fosterton whole oil, and the coke sample derived from the whole oil. Similar to previous studies in the literature, we also observed low-temperature oxidation (LTO), fuel deposition (FD), and high-temperature oxidation (HTO) in the non-isothermal combustion experiment. Higher activation energy values were obtained in reaction regions at higher temperatures. The mean activation energy for whole oil in nitrogen and air atmospheres was 33 and 126 kJ/mol, respectively. Fresh coke samples derived from whole oil were subjected to isothermal combustion at different temperatures from 375 to 500 °C. Arrhenius model was used to obtain the kinetic parameters from the TGA data. From the model, the Arrhenius parameters such as activation energy (E = 127 kJ/mol) and the pre-exponential factor (A = 1.6 × 10⁸/min) were determined for the coke combustion. The results showed a close agreement between the kinetic model and experimental data for different combustion temperatures. It was observed that the apparent order of combustion reaction for different temperatures approach unity.     

Preparation of AlON ceramics via reactive spark plasma sintering

Al₂O₃ and AlN powder mixtures were used to synthesise AlON ceramics using the reactive spark plasma sintering (SPS) method at temperatures between 1400 and 1650 °C for 15-45 min at 40 MPa under N₂ gas flow. AlON phase formation was initiated in the samples sintered above 1430 °C, according to the X-ray analysis. The complete transformation of the initial phases (Al₂O₃ and AlN) into AlON was observed in the samples that were spark plasma sintered at 1650 °C for 30 min at 40 MPa. A high spark plasma sintering temperature together with a low heating rate produced a greater amount of AlON formation at a constant process time. The densification, microstructure and mechanical properties of the produced ceramics were analysed. The highest hardness value was recorded to be 16.7 GPa, and the fracture toughness of the sample with the highest AlON ratio was measured to be 3.95 MPa m^1/2.     

Thermomechanical and thermodilatometric analysis of green alumina porcelain

A modulated force thermomechanical analysis (mf-TMA) and thermodilatometric analysis (TDA) of the green ceramic mixture of kaolin (27 wt.%), Al₂O₃ (50 wt.%) and feldspar (23 wt.%) up to 1000 °C is presented. The mf-TMA reflects changes during heating the green ceramics with higher sensitivity than TDA. Discrepancies between mf-TMA and TDA revealed that the elastic behavior of the green porcelain samples is determined most importantly by processes on the crystal boundaries (escaping of the water molecules at the low temperatures up to 150 °C and solid state sintering at the temperatures above 450 °C). Processes in the crystal interiors (e.g. dehydroxylation) have a lesser function. Thermodilatometric results depend more on the processes which take place inside the crystals than on the processes on the crystal surfaces.     

An experimental study of biomass ignition

An experimental study has been conducted to determine the ignition temperature of biomass at 21% O₂, both under pulse ignition conditions and under thermogravimetric conditions. In the pulse ignition experiments, samples of about 2 g wheat straw were placed in an isothermal reactor. The ignition temperature was determined from the transient CO and CO₂ profiles to approximately 255 °C at a superficial gas velocity of 14 cm/s (STP). The ignition temperature increased for decreasing superficial gas velocity.Thermogravimetric experiments at 20% O₂ and heating rates of 5 °C/min with finely milled biomass indicated ignition temperatures of approximately 220 °C for wheat straw, 235 °C for poplar wood, and 285 °C for eucalyptus wood. These values are significantly lower than values obtained for coal under similar conditions and confirm the relationship between volatile matter content and ignition temperature previously reported for coal.A mechanistic model for ignition of biomass is proposed. We believe that the ignition process is initiated by oxidation reactions on the straw surface. These reactions raise the surface temperature above that of the surrounding gas and promote ignition of the volatiles. Once ignited, the volatiles may form a homogeneous diffusion flame away from the particle surface. The superficial gas velocity affects the particle heating rate as well as the transport of oxygen to the surface. For this reason the ignition process is not entirely controlled by kinetics at low temperatures.     

Sintering and characterization of flyash-based mullite with MgO addition

Mullite ceramics were fabricated at relatively low sintering temperatures (1500-1550 °C) from recycled flyash and bauxite with MgO addition as raw materials. The densification behavior was investigated as function of magnesia content and sintering temperature. The results of thermal analysis, bulk density and pore structure indicate that MgO addition effectively promoted sintering, especially above 1450 °C. Due to the presence of large interlocked elongated mullite crystals above 1450 °C, associated with enhanced densification, an improvement in mechanical strength was obtained for the samples containing magnesia. The addition of magnesia slightly decreases the LTEC at 1300 °C due to the formation of low-expansion α-cordierite, but slightly increases the LTEC above 1400 °C due to the formation of high expansion corundum and MgAl₂O₄ spinel.     

Low-temperature synthesis of superfine barium strontium titanate powder by the citrate method

Ba_0.6Sr_0.4TiO₃ powder was synthesized by a citrate method. The phase development was examined with respect to calcining temperature and heating rate during the calcining process. The results reveal a crucial role of the heating rate to the formation of a pure perovskite phase at low calcining temperatures. It was found that keeping relatively low heating rates ≤0.7 °C/min during the calcining process after 300 °C was favorable to a sufficient decomposition of (Ba,Sr)₂Ti₂O₅·CO₃ intermediate phase at low temperatures and consequently led to the formation of a pure perovskite phase at 550 °C. Ba_0.6Sr_0.4TiO₃ powder calcined at the temperature under the heating rate of 0.7 °C/min showed a superfine and uniform particle morphology and high sintering reactivity. As a result, the ceramic specimens prepared from the powder attained reasonable relative densities (94–95%) at sintering temperatures of 1250–1270 °C.     

Lignin-based carbon fibers: Oxidative thermostabilization of kraft lignin

The thermostabilization of lignin fibers used as precursors for carbon fibers was studied at temperatures up to 340 °C at various heating rates in the presence of air. The glass transition temperature (T_g) of the thermally treated lignin varied inversely with hydrogen content and was found to be independent of heating rate or oxidation temperature. A continuous heating transformation (CHT) diagram was constructed from kinetic data and used to predict the optimum heating rate for thermostabilization; a heating rate of 0.06 °C/min or lower was required in order to maintain T_g > T during thermostabilization. Elemental and mass analyses show that carbon and hydrogen content decrease during air oxidation at constant heating rates. The hydrogen loss is sigmoidal, which is consistent with autocatalytic processes. A net increase in oxygen occurs up to 200-250 °C; at higher temperatures, oxygen is lost. Spectroscopic analyses revealed the oxidation of susceptible groups within the lignin macromolecule to ketones, phenols and possibly carboxylic acids in the early stage of the reaction; the later stage involving the loss of CO₂ and water and the formation of anhydrides and possibly esters. Slower heating rates favored oxygen gain and, consequently, higher glass transition temperatures (T_g) as opposed to faster heating rates.     

In situ TEM investigations of reactions of Ni, Fe and Fe-Ni alloy particles and their oxides with amorphous carbon

Ni, Fe and Ni-Fe alloy particles were vapour deposited on thin films of amorphous carbon (a-C) inside a specially equipped transmission electron microscope, and reactions with the substrate were observed at elevated temperatures. The influence of oxidation of the particles was also investigated. In contrast to Ni, which was found in earlier work to graphitise the carbon at above 600 °C without bulk carbide being involved, pure Fe reacted with the a-C support at about 500 °C to Fe₃C, which graphitised the carbon similar to Ni, starting at about 600 °C. No carbide was formed from oxidised Fe particles. FeO decomposes above 500 °C, higher oxides (Fe₃O₄, Fe₂O₃) only above 750 °C. The remaining Fe particles graphitised the carbon support directly. Alloy particles with composition Ni80:Fe20 (permalloy) graphitised a-C in the same way as pure Ni, without any phase separation. Annealing of a mixed phase of finely dispersed Ni-Fe-oxide or deposition of Ni-Fe under oxygen at above 300 °C resulted in nucleation of three-dimensional crystallites of virtually pure Ni, which graphitised the carbon, while the remaining phase of small particles was converted to inactive Ni-ferrite, NiFe₂O₄.     

Pyrolysis of poly-l-leucine under combustion-like conditions

The protein poly-l-leucine has been used as a model compound for the nitrogen in biomass fuels. It was pyrolysed in a fluidised bed at 700 and 800 °C and the pyrolysis gases were analysed with a FT-IR spectrometer. HCN, NH₃ and HNCO were identified as the main nitrogen-containing species, while neither NO nor N₂O were found among the pyrolysis gases. At 700 °C, as much as 58% of the nitrogen content was converted into HCN and 31% into NH₃. The HCN/NH₃ ratio increased from about 1.9 at 700 °C to above 2.2 at 800 °C. Pyrolysis of another protein, poly-l-proline, at 800 °C gave a HCN/NH₃ ratio close to 10. This revealed that the protein's amino acid composition has a marked impact on the composition of the pyrolysate.