Reactivities of Blair Athol and Nang Tong coals in relation to their behavior in PFBC boiler

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.     

Kinetic modeling and simulation: Pyrolysis of Jatropha residue de-oiled cake

An improved kinetic model based on thermal decomposition of biomass constituents, i.e. cellulose, hemicellulose and lignin, is developed in the present study. The model considers the independent parallel reactions of order n producing volatiles and charcoal from each biomass constituent. While estimating the kinetic parameters, the order of degradation of biomass constituents is also checked and found to be matching with the order of degradation reported in the literature. The results of thermo-gravimetric analysis of Jatropha de-oiled cakes are used to find the kinetic parameters. The experimental runs are carried out using a thermo-gravimetric analyzer (TGA 4000, Perkin Elmer). TGA study is performed in a nitrogen atmosphere under non-isothermal conditions at different heating rates and the thermal decomposition profiles are used. The model is simulated using finite difference method to predict the pyrolysis rate. The corresponding parameters of the model are estimated by minimizing the square of the error between the model predicted values of residual weight fraction and the experimental data of thermogravimetry. The minimization of square of the error is performed using non-traditional optimization technique logarithmic differential evolution (LDE).     

Pyrolysis kinetics and multi-objective inverse modelling of cellulose at the microscale

The chemistry of pyrolysis, together with heat transfer, drives ignition and flame spread of biomass materials under many fire conditions, but it is poorly understood. Cellulose is the main component of biomass and is often taken as a surrogate for biomass. Its chemistry of pyrolysis is simpler and dominates the pyrolysis of biomass. Many reaction schemes with corresponding kinetic parameters can be found in the literature for the pyrolysis of cellulose, but their appropriateness for fire is unknown. This study investigated inverse modelling and blind predictions of six reaction schemes of different complexities for isothermal and non-isothermal thermogravimetric experiments. We used multi-objective optimisation to simultaneously and separately inverse model the kinetic parameters of each reaction scheme to several experiments. Afterwards we tested these parameters with blind predictions. For the first time, we reveal a set of equally viable solutions for the modelling of pyrolysis chemistry of different experiments. This set of solutions is called a Pareto front, and represents a trade-off between predictions of different experiments. It stems from the uncertainty in the experiments and in the modelling. Parameters derived from non-isothermal experiments compared well with the literature, and performed well in blind predictions of both isothermal and non-isothermal experiments. Complexity beyond the Broido-Shafizadeh scheme with seven parameters proved to be unnecessary to predict the mass loss of cellulose; hence, simple reaction schemes are most appropriate for macroscale fire models. Modellers should, therefore, use simple reaction schemes to model pyrolysis in macroscale fire models.     

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.     

Resistance of blended cement pastes subjected to organic acids: Quantification of anhydrous and hydrated phases

Concrete for agricultural construction is often subject to aggressive environmental conditions. Ground granulated blast furnace slag (GGBFS) or metakaolin (MK) largely improve the chemical resistance of the binder. Anhydrous particles seem particularly resistant to the acid solution. The purpose of this study is to quantify anhydrous particles in blended cement pastes as a function of acid exposition time in order to evaluate their acid resistance.Cement pastes were moist cured for 28 days and then immersed in an acetic acid solution for 2 months. The quantification of the anhydrous phases was carried out using ²⁹Si MAS NMR, selective dissolution and back-scattered electron (BSE) images analysis, while the hydrated phases content was evaluated by TGA. After 28 days of hydration, 60% of OPC, 44% of GGBFS and 76% of MK particles were hydrated. The amount of anhydrous particles drops for all materials during acid immersion. After 2 months of immersion, the amount of anhydrous particles drops by 49%, 23% and 15% for OPC, GGBFS, and MK respectively. This study confirms that GGBFS and MK anhydrous and hydrates phases present higher acid resistance than OPC.     

Tribopolymerization of n-butyl acrylate on the steel–steel rubbing surface

Antiwear property of n-butyl acrylate (BA) in hexadecane for steel–steel friction elements was studied. Scanning electronic microscopy (SEM) images of worn scars of balls, and width measurements of worn tracks of disks indicate that BA has good antiwear property.Tribopolymerization (polymerization initiated by the rubbing surface) tests of BA used as lubricant instead of an additive were conducted, to classify antiwear mechanisms. Infrared spectroscopy (IR) of washing solution and thermogravimetry (TG) traces of wear debris confirmed that tribopolymers were generated on steel–steel interface in situ. Also considerable wear products were precipitated from vacuum-condensed worn fluids with methanol as the non-solvent, characterized by IR, gel permeation chromatography (GPC), nuclear magnetic resonance (NMR) spectroscopy, showing that the precipitates were poly(n-butyl acrylate) (PBA) with very high molecular weight.To study tribopolymerization mechanisms of BA, effects of sliding velocities and adding 1 wt% n-butyl alcohol to BA fluids on the mass of tribopolymers were investigated, respectively. Expectedly, the mass of tribopolymers dramatically enhanced with the sliding velocity increasing, showing that the tribopolymers were generated just due to friction processes. Additionally, tribopolymerization of styrene (easy to thermopolymerize) was studied. Unexpectedly—but not unreasonably—no substantial worn products were precipitated from vacuum-condensed worn fluids. Based on these experimental results, an exoelectron-radical-tribopolymerization mode, consistent with some Kajdas’ tribochemistry theories, for BA was proposed.     

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.     

Thermogravimetry‐FTIR Analysis of Pyrolysis of Pyrolytic Lignin Extracted from Bio‐Oil

Pyrolytic lignin is attributed to the instability of bio‐oil but is a potential chemical material. To improve the stability and increase the economic viability of bio‐oil, high‐ and low‐molecular‐mass pyrolytic lignin (HMM and LMM) were obtained using solvent extraction. The microstructure of pyrolytic lignin was examined by Fourier transform infrared spectrometry (FTIR). The dissimilar absorption intensities indicated the different content of corresponding functional groups in HMM and LMM. The pyrolysis behavior of HMM and LMM was studied by thermogravimetry coupled with FTIR. Obviously pyrolytic lignin undergoes three weight loss stages.     

Microalgae Chlorella as a potential bio-energy feedstock

Microalgae are promising biomass species owing to their fast growth rate and high CO₂ fixation ability as compared to terrestrial plants. Microalgae have long been recognized as potentially good source for biofuel production because of their high oil content and rapid biomass production. In this study Chlorella sp. MP-1 biomass was examined for its physical and chemical characteristics using Bomb calorimeter, TGDTA, CHN and FTIR. The proximate composition was calculated using standard ASTM methodology. Chlorella sp. MP-1 biomass shows low ash (5.93%), whereas high energy (18.59 MJ/kg), carbohydrate (19.46%), and lipid (28.82%) content. The algal de-oiled cake was characterized by FTIR spectroscopy and thermogravimetric study at 10 °C/min and 30 °C/min to investigate its feasibility for thermo-chemical conversion. The present investigation suggests that within the realm of biomass energy technologies the algal biomass can be used as feedstock for bio and thermo-chemical whereas the de-oiled cake for thermo-chemical conversion thereby serving the demand of second generation biofuels.     

The use of thin layer activation in high-temperature cyclic oxidation studies

Thin layer activation (TLA) has been applied to a study of the high-temperature cyclic oxidation behaviour of pure and yttrium-implanted chromium, taking advantage of the high area selectivity of the technique.On pure chromium, two different sample areas, i.e. corners and the central part of a large surface area, were selected for activation. Due to this area selectivity, it was possible to distinguish the spallation behaviour of the oxide scale formed on flat from that formed on highly curved surfaces. In particular, the TLA data showed that the oxide scale formed during high-temperature cyclic oxidation near corners and edges was more prone to cracking and spallation.In the case of yttrium-implanted specimens, activation was performed only at the centre of the implanted zone, avoiding the distorting effect of the non-implanted parts of the sample. The area selectivity of TLA made it possible to study more accurately the beneficial effect of ion implantation on the cyclic oxidation behaviour than by conventional thermogravimetry. Due to the complementary character of TLA with respect to the conventional thermogravimetry, a more complete and better understanding of the cyclic oxidation performance of materials can be obtained.