Co-combustion of low rank coal/waste biomass blends using dry air or oxygen

Biomass species such as the rice husk and the olive milling residue, and a low quality Turkish coal, Soma Denis lignite, were burned in a thermal analyzer under pure oxygen and dry air up to 900 °C, and differential thermal analysis (DTA) and derivative thermogravimetric (DTG) analysis profiles were obtained. Co-combustion experiments of lignite/biomass blends containing 5–20 wt% of biomass were also performed. The effects of the oxidizer type and the blending ratio of biomass were evaluated considering some thermal reactivity indicators such as the maximum burning rate and its temperature, the maximum heat flow temperature, and the burnout levels. FTIR (Fourier transform infrared) spectroscopy and SEM (scanning electron microscopy) were used to characterize the samples, and the variations in the combustion characteristics of the samples were interpreted based on the differences in the intrinsic properties of the samples.     

Investigation of gasification characteristics of some coals in Turkey by the thermogravimetric analysis method

When the coal is heated, conversion process starting with moisture loss passes through pyrolysis, burning and gasification processes depending on the atmosphere, temperature rise rates, final temperature and other parameters. Since coal has a heterogeneous structure, interpretation of these phases is difficult. Thermogravimetric analysis, on the other hand, has a wide range of applications and allows valid approaches to the physical and chemical properties of coal. Therefore, the thermogravimetric analysis makes it possible to analyze the characteristics of the coal gasification phase in a practical and rapid manner.

In this study, the gasification characteristics of coal samples taken from Ilg?n, Ermenek and Zonguldak regions in Turkey were determined. Conversion time and gasification rates of Ilg?n and Ermenek coals were investigated using thermogravimetric analyzer at 700°C, 750°C, 800°C and 850°C in CO₂ atmosphere and comparisons were made between samples. In addition, conversion and gasification rates of coal samples taken from Zonguldak region at 1150°C were investigated. It was observed that the conversion time of the Ilg?n coal at 800°C and the Ermenek coal at 850°C was shorter than the other temperatures. When the 80% conversion rates of Ilg?n coal at 800°C, Ermenek coal at 850°C, and Zonguldak at 1150°C, are compared; it is observed that there exist a 1,2 min difference between Ilg?n-Zonguldak, 1,05 min between Ilg?n-Ermenek and 1,96 min between Ermenek and Zonguldak coals.     

Pyrolysis characteristics of Turkish lignites in N2 and CO2 environments

Pyrolysis characteristics and kinetic parameters of two Turkish lignites having different ash contents (Orhaneli as low ash and Soma as high ash sample) were studied under N₂ and CO₂ atmospheres by means of thermogravimetric analysis. The isoconversional kinetic methods of Flynn?Wall??Ozawa, Kissinger??Akahira??Sunose, and Friedman were employed to estimate the activation energy and pre-exponential factors. The experiments were conducted at four different heating rates of 5, 10, 15, and 20°C/min within the temperature range of 50??950ºC. The obtained results indicated that changing the pyrolysis ambient had no significant effect on the devolatilization region up to 700°C. The char formation region in N₂ atmosphere was due to the CaCO₃ decomposition and was more significant for Soma lignite due to its high ash content. However, in CO₂ atmosphere, the gasification reaction took place at temperatures higher than 700°C. The decomposition process of CaCO₃ in CO₂ atmosphere was hampered up to temperatures higher than 900°C. The estimated activation energies were found to have approximately similar trends under different atmospheres. For Orhaneli lignite, the average activation energy values were higher in CO₂ environment. However, for Soma lignite due to decomposition of CaCO₃, the activation energy values were higher in N₂ atmosphere. The mean uncertainty values were assessed for the activation energy values obtained for all test cases.     

Pyrolysis Kinetics of Blends of Yeni Çeltek Lignite and Sugar Beet Pulp

Abstract

Pyrolysis kinetics of the Yeni Çeltek lignite/sugar beet pulp blends prepared at different ratios (100:0, 80:20, 60:40, 40:60, 20:80, and 0:100) were investigated by thermogravimetric analysis in the present study. All the experiments were carried out in nitrogen atmosphere under non-isothermal conditions with a heating rate range of 30 K/min in the pyrolysis temperature interval of 298–1,173 K. The Arrhenius model is applied to determine the kinetic parameters from TG/DTG curves. Apparent activation energies of the lignite and sugar beet pulp were calculated as 51.55 kJ/mol and 97.27 kJ/mol, respectively. Activation energies of the blends were also calculated and were found to vary between 54.87 and 74.83 kJ/mol. Effects of blending ratio of lignite to sugar beet pulp on kinetic parameters were investigated and the results were discussed.     

Air and oxy-fuel combustion kinetics of low rank lignites

The air and oxy-fuel combustion processes of two low-grade lignite coals were investigated by thermogravimetric analysis (TGA) method. Coals were provided from two different coal mines in the Aegean region of Turkey. Oxy-fuel combustion experiments were carried out with three different gas mixtures of 21% O₂–79% CO₂; 40% O₂–60% CO₂ and 50% O₂–50% CO₂ at 950 °C and heating rates of 10 °C/min, 20 °C/min and 40 °C/min. The kinetics of the oxy-fuel combustion of coals were studied by using four different methods namely, Coats-Redfern (model-fitting method), Friedman (FR), Flynn–Wall–Ozawa's (FWO) and Kissinger–Akahira–Sunose's (KAS) methods. The apparent activation energies of combustion process calculated by FWO method are slightly but systematically higher than that calculated by the KAS and FR methods for the oxy-fuel atmospheres. Combustion behavior of both coals in the oxy-fuel combustion environment could vary significantly, likely due to their characteristics such ash and volatile matter contents.     

Petrographic composition of the ex-situ lignite gasification residues

The article presents the results of the petrographic analysis of the lignite from Turów deposit and the residues formed during its ex-situ gasification. The analysis used seven spot samples, representing different transformation areas, collected from the residues. The obtained results, compared with the lignite before the gasification, have shown that changes in the petrographic composition correspond to the temperature distribution during the process. The highest amounts of gasified particles, represented by inertoid-type chars, were observed in samples collected from areas where the temperature exceeded 600°C. The unchanged lignite macerals dominated in samples from areas where the temperature was below 200°C.     

Influence of Heating Rate on the Burning Profiles of Hazelnut Shell

Abstract

In this study, hazelnut shell was subjected to thermogravimetric analysis to establish burning profiles in a dynamic dry air atmosphere. The Turkish hazelnut shell with a particle size of ?0.250 mm was heated up to 1,173 K by heating rates of 5, 10, 20, 30, 40, and 50 K/min. This study revealed that heating rate during oxidation is an important parameter affecting thermal behavior of hazelnut shell. A strong relation was determined between the heating rate and the intensity of the peaks on the burning profiles.     

Fixed-Bed Pyrolysis of Hazelnut (Corylus Avellana L.) Bagasse: Influence of Pyrolysis Parameters on Product Yields

Fixed-bed slow pyrolysis experiments have been conducted on a sample of hazelnut bagasse to determine particularly the effects of pyrolysis temperature, heating rate, particle size and sweep gas flow rate on the pyrolysis product yields. The temperature of pyrolysis, heating rate, particle size and sweep gas flow rate were varied in the ranges 350–550° C, 10 and 50° C/min, 0.224–1.800 mm and 50–200 cm³/min, respectively. Under the various pyrolysis conditions applied in the experimental studies, the obtained char, liquid, and gas yield values ranged between 26 and 35 wt%, 23 and 34.40 wt%, and 25 and 32 wt%, respectively. The maximum biooil yield of 34.40% was obtained at the final pyrolysis temperature of 500°C, with a heating rate of 10° C/min, particle size range of 0.425–0.600 mm and a sweep gas flow rate of 150 cm³/min.     

Optimization study of sub/supercritical water liquefication of lignite: Fast liquefaction for high bio-oil yield

Sub/supercritical water liquefication (SCWL) is a water-based thermochemical technology as well as an environmentally friendly treatment by converting wet feedstock into bioenergy. In the present study, a systematic investigation of SCWL of lignite was carried out covering a temperature range between 320 and 440 °C when residence time increased from 5 min to 40 min. The highest bio-oil oil yield of 34.3% with solid residue of 52.7% was obtained at 440 °C for 5 min. Phenol derivatives, carboxylic acids, long chain hydrocarbons, ketones, and naphthalene were the main bio-oil composition through FTIR and GC-MS analysis. Gas yields and their exact compositions were also determined and CO₂ was the dominate gas product but the percentage of CH₄ became significant at severe SCWL conditions. A conclusion was drawn that fast liquefaction (e.g. 5 min) at relative higher temperature (e.g. 400 °C) which avoid excessive gasification and repolymerization reactions was an optimization strategy for high yield bio-oil production from SCWL of lignite.     

Nanosized Zn–Sn metal composite oxide: a new anode material for Li ion battery

Abstract

The morphological evolution of nanosized Zn–Sn composite oxides, synthesised by the decomposition of ZnSn(OH)₆ precursor at temperature ranged from 300 to 800°C was investigated by using XRD and high resolution TEM. The precursor was also studied by thermal analysis. The electrochemical performance of Zn–Sn composite oxides as anode materials for Li ion batteries was measured in the form of Li/Zn–Sn composite oxides cells. The results reveal that the samples calcined at low temperatures (300 and 500°C) were amorphous Zn₂SnO₄ and SnO₂, and the samples calcined at high temperatures (720 and 800°C) were crystal Zn₂SnO₄ and SnO₂. All the samples have a high reversible specific capacity of over 800 mAh g^?1, and the first charge specific capacity is up to 903 mAh g^?1 for the sample calcined at 500°C. The charge capacity and cyclability were sensitive to the structure and composition of the electrode active materials; the samples calcined at phase transition temperature rage exhibited relatively worse electrochemical properties.     

CO2 gasification characteristics of nascent pyrolyzed particles from coals and oil shale

In this work, the co‐pyrolysis characteristics of oil shale with two typical coals, bitumite and lignite, and the co‐gasification characteristics of the mixture pyrolyzed fuels were studied via thermo‐gravimetric analysis. The individual fuels and mixture fuels were first pyrolysis in N₂ atmosphere to specified temperature (450, 550, and 620 °C) at the heating rate of 20, 30 and 40 °C/min, respectively, and then maintained at the given temperature for 20 min before converted to CO₂ ambient to conduct the CO₂ gasification tests. The kinetic behavior and effects of both fuel types and pyrolysis temperature were investigated. The shoulder peak at around 550 °C observed in the derivative of weight loss derivative thermogravimetry analysis (DTG) curve during the pyrolysis of oil shale has confirmed the existence of specific reactions of oil shale at around 550 °C that leads to a sharp trough in the differential curves of co‐pyrolysis with coals and the unusual change in activation energies of gasification. In isothermal pyrolysis stage, oil shale lost its vast majority of organic matters at the temperature lower than 550 °C. The escape of pyrolysis gas and liquids in the coals is much harder than that in oil shale. The interaction between oil shale and bitumite was too weak to discriminate both in the pyrolysis and CO₂ gasification process. The variation of the particle surface structure caused by the releasing of volatile gases is strongly affected by the reaction rate and temperature. Quick volatile decomposition and gas releasing lead to the increase of surface area, decrease of the average pore diameter as well as the uniformization of the pore structure, while the higher temperature results in the blockade and merging of fine pores. The two factors lead to the greatest mass loss rate in the pyrolyzed particles obtained at 550 °C in temperature programmed CO₂ gasification stage. Two model‐free methods, Friedman method and Flynn–Wall–Ozawa method, were used to extract kinetic parameters from the experimentally determined pyrolyzed fuel conversions. The volatile contend has a significant influence on the fixed carbon conversion during the partially pyrolyzed particles' CO₂ gasification. In this study, significant interactions existed in co‐thermal utilization, both pyrolysis and CO₂ gasification, of oil shale and lignite. It is therefore surmised that co‐gasification of pyrolyzed lignite and oil shale may represent a feasible, practical route to high‐efficiency utilization of these fuels. Copyright © 2017 John Wiley & Sons, Ltd.     

Attrition of lignite char in a spouted bed combustor

The generation of carbon fines by attrition during burning of Thai lignite char has been studied experimentally by means of a 92 mm i.d. continuous spouted bed combustor at different values of spouting gas velocity, bed temperature, and char feed size. Both inert particle size and static bed depth were fixed for all experimental runs. The collected data were used to analyse size distributions of both in-bed particles and elutriated fines, and to generate the suitable correlations for carbon attrition rate. Results obtained showed that attrition rate in the spouted bed is proportional to the excess of gas velocity above the minimum spouting gas velocity and the overall bed carbon surface exposed to attrition. The attrition rate constant is slightly dependent on operating bed temperature. Its values for the char studied were 1.6511 × 10^?6 for 707°C operating bed temperature, and 1.1222 × 10^?6 for 850°C, with the average for all tested runs being 1.224 × 10^?6.     

CFB combustion of low-grade lignites: Operating stability and emissions

This work presents the results of a comprehensive experimental investigation on the combustion of the low grade Turkish lignites in a 30 kW_th circulating fluidized bed combustor. This is the first study of this kind has ever been undertaken on these coals. Eighteen lignite samples procured from various lignite sites of Turkey have been burned under similar combustion conditions in order to access to their combustion stability and to determine the emissions of the major pollutants such as CO, NO_X and SO₂ in the flue gas from combustor. The qualities of lignites were evaluated based on van Krevelen graph which was highly scattered and diverse in respect to the degree of ageing. A steady and stable combustion was observed in the temperature range of 725–950 °C with an average operating temperature of around 850 ± 50 °C for all lignites. Under the operating condition applied in the study, CO, NO_X and SO₂ emissions varied mostly in the ranges of 120–600 mg/Nm³, 90–420 mg/Nm³ and 1100 mg/Nm³ - 18000 mg/Nm³, respectively. From the experimental results it seems that the most challenging problem may be faced during the CFB combustion of most of these lignites will be SO₂ emissions.     

Carbonization of Eight Bamboo Species of Northeast India

Abstract

Eight bamboo species of northeast India were carbonized in a laboratory-scale fixed bed reactor at temperature ranging from 300°C to 600°C with a heating rate of 5°C/min, and their mass balance experiments of decomposition products were done at 600°C. At this temperature, the yields of charcoal, tar, gas, and condensable liquid ranged from 23.35–28.25%, 6.46–8.85%, 6.93–10.05%, and 51.98–57.96%, respectively. Fixed carbon content of the charcoal samples varied from 62.10–67.52% indicating their suitability only for domestic use or as a fuel for gasification and not for metallurgical use.     

Biodesulfurization of Cayirhan Lignites

In this study, the lignite was improved oxidizing sulfur compounds by Thiobacillus thiooxidans and Thiobacillus ferrooxidans bacteria. Experiments in the batch reactors have been carried out 20% aqueous suspension of coal samples. Sugar beet molasses was used as the bacterial substrate. The maximum removal of combustible sulfur was obtained as 78.2% under the following conditions; addition 5% of T. thiooxidans and 5% T. ferrooxidans into coal suspension, 0.2 g molasses/g coal change, pH value of 3, at shaking rate of 70 rpm and at 40°C for 5 days.     

Highly dense and chemically stable proton conducting electrolyte sintered at 1200 °C

The BaCe_0.7Zr_0.1Y_0.2?xZn_xO_3?δ (x = 0.05, 0.10, 0.15, 0.20) has been synthesized by the conventional solid state reaction method for application in protonic solid oxide fuel cell. The phase purity and lattice parameters of the materials have been studied by the room temperature X-ray diffraction (XRD). Scanning electron microscopy (SEM) has been done for check the morphology and grain growth of the samples. The chemical and mechanical stabilities have been done using thermogravimetric analysis (TGA) in pure CO₂ environment and thermomechanical analysis (TMA) in Argon atmosphere. The XRD of the materials show the orthorhombic crystal symmetry with Pbnm space group. The SEM images of the pellets show that the samples sintered at 1200 °C are highly dense. The XRD after TGA in CO₂ and thermal expansion measurements confirm the stability. The particles of the samples are in micrometer ranges and increasing Zn content decreases the size. The conductivity measurements have been done in 5% H₂ with Ar in dry and wet atmospheres. All the materials show high proton conductivity in the intermediate temperature range (400–700 °C). The maximum proton conductivity was found to be 1.0 × 10^?2 S cm^?1 at 700 °C in wet atmosphere for x = 0.10. From our study, 10 wt % of Zn seems to be optimum at the B-site of the perovskite structure. All the properties studied here suggest it can be a promising candidate of electrolyte for IT-SOFCs.     

Temperatures of Coal Particle During Devolatilization in Fluidized Bed Combustion Reactor

The purpose of this study was to investigate the thermal behavior of coal during devolatilization in fluidized bed. Temperatures in the center of single coal particle were measured by thermocouple. Two coals were tested (brown coal Bogovina and lignite Kosovo), using dry coal particle, shaped into spherical form of diameters 7 and 10 mm, in temperature range from 300 to 850°C. Unsteady behavior of coal particle during heating and devolatilization in fluidized bed was described by a model that takes into account heat transfer between bed and particle surface, heat transfer through particle and an endothermic chemical reaction of first-order. Based on the mathematical model analysis and compared with experimental results, values of heat conductivity (λ _c ) and heat capacity (C _p ) of coal were determined. The best agreement was obtained for constant thermal properties, for brown coal λ _c = 0.20 W/mK and C _p = 1200 J/kgK and for lignite λ _c = 0.17 W/mK and C _p = 1100 J/kgK.     

Reactivity of pulverized coals during combustion catalyzed by CeO2 and Fe2O3

Effects of CeO₂ and Fe₂O₃ on combustion reactivity of several fuels, including three ranks of coals, graphite and anthracite chars, were investigated using thermo-gravimetric analyzer. The results indicated that the combustion reactivity of all the samples except lignite was improved with CeO₂ or Fe₂O₃ addition. It was interesting to note that the ignition temperatures of anthracite were decreased by 50 °C and 53 °C, respectively, with CeO₂ and Fe₂O₃ addition and that its combustion rates were increased to 15.4%/min and 12.2%/min. Ignition temperatures of lignite with CeO₂ and Fe₂O₃ addition were 250 °C and 226 °C, and the combustion rates were 12.8% and 19.3%/min, respectively. When compared with those of lignite without catalysts, no obvious catalytic effects of the two catalysts on its combustion reactivity were revealed. The results from the combustion of the three rank pulverized coals catalyzed by CeO₂ and Fe₂O₃ indicated significant effects of the two catalysts on fixed carbon combustion. And it was found that the higher the fuel rank, the better the catalytic effect. The results of combustion from two kinds of anthracite chars showed obvious effects of anthracite pyrolysis catalyzed by CeO₂ and Fe₂O₃ on its combustion reactivity.     

Optimization of manufacturing conditions for activated carbon from Turkish lignite by chemical activation using response surface methodology

The purpose of this research is to obtain optimal processing conditions for activated carbon from lignite by chemical activation with K₂CO₃ using response surface methodology (RSM). The activated carbons produced were characterized by carbon yield (%), BET surface area, porosity development (total pore volume and micropore fraction). RSM based on a five-variable central composite rotatable design was used to determine the effect of chemical ratio (ranging from 0 to 4) and activation temperature (ranging from 500 °C to 900 °C) on the responses levels. Each response has been described by a second order model that was found to be appropriate to predict most of the responses in every experimental region. The most influential factor on each experimental design response have been identified from the analysis of variance (ANOVA). The optimum conditions for manufacturing of activated carbon from Turkish lignite, which were based on response surface and contour plots, were found as follows: chemical ratio of 2.05 and carbonization temperature of 800 °C.     

Pyrolysis of Some Indigenous Tree Species of Northeast India: Effect of Pyrolysis Temperature and Heating Rate on the Products Yield and Char Quality

Abstract

Seven indigenous tree species of northeast India were pyrolyzed at temperatures ranging from 300°C–800°C with two different heating rates, 3°C/min and 20°C/min, and the effect of heating temperature and heating rate on the products yield and char quality were analyzed and discussed. Among all the species, E. acuminata, M. bombycina and Q. griffithii were found to yield higher percentages of char with better quality, whereas A. lucida yielded the highest percentage of tar.