Environmental applications of pyrogenic carbon, aka black carbon (BC), have been hampered due to the poor characterization and quantification of environmental BC. This dissertation was dedicated to the better characterization of environmental char/charcoal BC (char-BC), the most heterogeneous and the less identifiable group in the BC continuum. The analytical approach developed for char-BC was further incorporated with other BC methods in environmental samples for a comprehensive assessment of combustion-derived carbon inputs in different environmental systems. The present study firstly evaluated the feasibility of using levoglucosan, a marker derived from cellulose/hemocellulose combustion, to characterize and quantify char-BC in the environment. Levoglucosan was found exclusively in BC materials derived from biomass combustion albeit in highly variable yields across different char-BC. A further examination of synthetic chars showed that temperature is the most influential factor affecting levoglucosan yield in char. Notably, levoglucosan was only detectable in low temperature char samples (150-350 degrees C), regardless of plant species. These results demonstrated that levoglucosan could serve as a good qualitative indicator for the presence of char produced under low temperature conditions in soil, sediments, and aerosols. Results of lignin analysis on the synthetic chars further reveal that combustion can greatly decrease the yield of the eight major lignin phenols with no lignin phenols detected in any synthetic char produced at greater than or equal to 400 degrees C. The values of all lignin parameters show significant shifts with increasing combustion severity (temperature and/or duration), indicating that thermal alteration is an important abiotic lignin degradation process. Hence the input of char-BC in the environments represents a terrestrial organic matter source with highly altered lignin signatures. Finally, a multi-proxy approach, including elemental (soot-BC) and molecular (levoglucosan, polycyclic aromatic hydrocarbons (PAHs), and lignin oxidation products) proxies, was adopted to investigate the centennial-scale temporal distribution of combustion products in four sediment cores from Puget Sound basins, WA. The observed temporal trends of soot-BC and combustion PAHs fluxes reflect the evolution of energy consumption and the positive effects of environmental regulations. The distinct temporal patterns of soot and PAHs among cores demonstrate that urbanization is a crucial factor controlling the inputs of combustion byproducts to the environment. On the other hand, the trends of levoglucosan may be more relevant to the climate oscillation and thus show a regional distribution pattern. Our results demonstrate that environmental loading of combustion byproducts is a complex function of urbanization and land use, fuel usage, combustion technology, environmental policies, and climate changes.

Hydroxyl terminated polybutadiene (HTPB) based polyurethanes (PUs) are low modulus materials and degrade easily at low temperature. Polycarbodiimide (PCDI) and polysiloxane (PSi) are reactive-type fillers when formed by carbodimidzation and sol-gel process, respectively. During the combustion, PCDI and PSi give off non-toxic, non-corrosive volatile gases, and finally form carbonaceous and siliceous chars. In this study, modified PUs were prepared by incorporating PCDI or PSi into PUs to give high carbon, nitrogen and silicon materials. These modified PUs are kinds of organic-inorganic hybrids with higher modulus and higher thermal stability than HTPB-based PUs. In addition, new silicone based insulation materials were prepared by mixing two silicone rubber materials LSR-2670 and RTV-627 from GE Silicones, in order to improve the heat insulation and to reduce the ablation rate. These inhibitors can keep the rocket motor from the high temperature ablation for a long time, especially castable silicone based heat insulations for the case of the ramjet engines. The mechanical properties at room temperature and the thermal stability of these modified PUs and silicone rubbers were investigated using a tensile tester and a thermogravimetric analyzer (TGA). ATR/FTIR (Attenuated total reflectance / Fourier transform infrared) technique is applied to monitor the synthesis process of PCDI and to examine the change of surface chemistry of insulator before and after thermal degradation via TGA. TGA coupled with FTIR (TGA/FTIR) was used to analyze the kinetics and the mechanism of thermal degradation under nitrogen and/or air. The Friedman and Kissinger methods of analysis were used for calculating the activation energy of degradation from dynamic TGA. The modified PUs (HIPTD-40%Psi¤ÎHIPTD-30%PMPS-PSi) with average activation energy of 88 and 112 kcal/mole (0.5¡Õ£\¡Õ0.9, under N2) and the modified silicone rubber (LR-5%HTB) with activation energy of 46.2~67.0 kcal/mole (0.1¡Õ£\¡Õ0.9, under N2) and 34.0~59.1 kcal/mole (0.1¡Õ£\¡Õ0.9, under air).The maximum degradation temperature (Tmax) and char yield (CY) of thermal degradation were estimated from a series of experiments with heating rates of 1, 3, 5, 10, 20, 30, 40 and 50 ¢J/min, under nitrogen or air. It is apparent that the maximum degradation temperature is dependent on heating rate. By assuming the heating rate for the insulator used in a rocket operating environment is about 5000¢J/min, Tmax calculated for the modified PUs (HIPTD-40%PSi and HIPTD-30%PMPS-PSi under N2) are found as 538 and 562¢J and for the modified silicone rubber (LR-5%HTB under N2 and air) are found as 576 and 562¢J, respectively. CY calculated for the modified silicone rubber (LR-5%HTB under N2 and air) is found as 71.5% and 66.2%. The morphology of modified PUs and silicone rubbers before and after thermal degradation via TGA was observed by optical and scanning electron microscope (SEM).

Pyrolysis has been a useful procedure to treat waste-tire, which decomposes waste-tire at high temperature in the absence of oxygen. This thermal decomposition process generates pyrolysis oil, combustible gas, and char, which distribute in liquid phase, gas phase, and solid phase, respectively. Pyrolysis oil and combustible gas are fuels, while char is composed of carbon black and ash. Thus, char would be economically worth while to be treated before reuse. In this study, based on the resistivity difference between carbon black and ash, ash can be removed from char in the principle of electrostatic separation and thus increase the value of char. In this study, the objective was to separate ash from char by electrostatic separation process, different char including waste-tire pyrolytic char (raw char), low pressure re-pyrolytic char, ZnO-added char (12% ZnO mixed with 600 oC re-pyrolytic cahr) and man-made char (N600 carbon black mixed with 14.5% metallic oxide) were tested. The Electro-Static Separator (ESS) was designed and constructed with two types of discharge electrodes including a needle-plate electrode (NPE) and a needle-bar electrode (NBE) and two kinds of dust feeders to generate either fine or coarse particles. The results indicated that raw char had higher collection efficiency using the NBE system than the NPE system in the operating voltages of -7 kV to -15 kV because the surface area of the NBE system was less than the NPE system, thus led higher surface charge density for the NBE system than the NPE system, resulting in higher discharge current of the NBE system. In order to lower resistivity and reduce deposited pyrolysis oil on char, low pressure repyrolysis process was used. Because the removal efficiency of pyrolysis oil is proportional to repyrolysis temperature, more pyrolysis oil can be removed from the surface of char, resulting in more carbon blacks exposed on the char surface as conductive material. Thus, the collection efficiency of 600 oC repyrolytic char was less than that of 400 oC repyrolytic char. Furthermore, because particle charging quantity was proportional to particle size, fine char particles had less collection efficiency than coarse char particles. However, both raw char and repyrolytic char, the collection efficiency of carbon and ash had similar trends, suggesting that similar percentage of carbon and ash were collected on the plate and penetrated the ESS system. Therefore, the separation efficiency of carbon and ash were similar, same situation was observed for the ZnO-added char. In order to verify the feasibility of carbon and ash separation by electrostatic separation process, N660 carbon black mixing with 14.5% man-made ash (Al2O3, ZnO and CaO composed) to simulate man-made char, which was further used to proceed the electrostatic separation experiments in this study. The results indicated that the collection efficiency of man-made char increased with operating voltage, and the ash content seems to increase with voltage. Carbon black is a low resistivity material, which causing sparkover during the experiments, thus operating voltage cannot be regulated more than -8.25 kV. In order to verify the feasibility of carbon black and ash separation by the principle of electrostatic separation, this study applied non-linear regression to model the collection efficiency of man-made char, carbon black and ash, and further simulate the collection efficiency at higher electrical field strength. The simulated results indicated that the maximum collection efficiency of carbon and ash was approached around -10 kV/cm of carbon black and ash and their collection efficiencies were similar. The collection efficiency of ash was close to the ash content of man-made char (the collection efficiency of ash equal to the collected ash per mass of injected char), suggesting that most injected ash was collected by the ESS system. In addition, the ash content of penetration char was also simulated, the modeling results showed that the ash content of penetrated char were lower than 2%, while was relatively lower than the raw man-made char, and more than 75% injected char could penetrate the ESS system during the operation procedure. According to the modeling results, solid-solid separation technology could be more efficient if carbon and ash are independently separate particles, and lower resistivity materials would penetrate the ESS system and higher resistivity materials would be collected by the electrostatic separation process.

The conversion of coal and char nitrogen has been investigated during fuel rich combustion. The experiments were done with the objective of clarifying the roles of NO, HCN, and NH₃, and char nitrogen in the post-combustion gases in the first, fuel rich stage of a staged combustor. The experimental apparatus includes a downflow combustor of 15 cm internal diameter and 180 cm length constructed of fibrous alumina insulation surrounding a central tube composed of vacuum- formed alumina cylinders. The combustion gases and solids were sampled in situ with a water-cooled and -quenched probe. Neither the combustor nor the sample probe were found to be reactive towards NO. Temperatures of the gases and walls were measured with Type K thermocouples and the particle temperatures were determined with a seven wavelength infrared pyrometer. Gas compositions were measured chromatographically using a 5A molecular seive for permanent gases (H₂, O₂, N₂, CO, and CH₄) and Poropak T for polar gases (CO₂ and HCN). A chemiluminescent analyzer measured NO. NH₃ and HCN were measured in the quench water with ion electrodes. The C, H, N, ash compositions of the char were measured with an elemental analyzer. Experiments of the fuel rich conversion of char nitrogen show that at all stoichiometries (SR = 0.8, 0.4) the concentrations of HCN and NH₃ in the post-flame gases are small compared to the concentration of NO. Char nitrogen conversion was stoichiometric or greater. NO destruction was found to be controlled by a heterogeneous mechanism involving the char carbon surface. The mechanism is deactivated by oxygen, an effect demonstrated by others. The fuel rich conversion of coal nitrogen was investigated with a Utah bituminous coal. At moderate fuel rich conditions (SR = 0.8), the residual char nitrogen conversion is 90 percent or greater and NH₃ and HCN concentrations were less than 20 ppmv. NO peaked at 1200 ppmv (1850 K) and declined to 600 (1580 K) ppmv over 1.8 seconds. Coal nitrogen conversion is dominated by NO formation at this stoichiometry. At extreme fuel rich conditions (SR = 0.4), coal nitrogen conversion is 85 percent. The gas is dominated by HCN, NO, and NH₃. HCN decayed from 600 ppm to 300 ppmv, NO from 350 to 50, and NH₃ increased from 200 to 375 ppmv, indicating that interconversion reactions in the gas phase are dominating. The kinetics which govern the volatile nitrogen reactions can be described by global homogeneous kinetics as follows: UNFORMATTED TABLE/EQUATION FOLLOWS: r₁ = d/dt[HCN] = -5.5x10¹⁷ exp(-83.3 K/RT)[HCN][H₂O]/[H₂]¹/² mole/cm³s r₂ = d/dt[NO] = -2.2x10¹⁶ exp(-54.4 K/RT)[NO][NH₃]/[H₂]¹/² d/dt[NH₃] = d/dt[NO] - d/dt[HCN] UNFORMATTED TABLE/EQUATION ENDS These yield rates for free radical reactions very similar to those determined in gas flame experiments, lending credence to their validity. A one-dimensional combustor model has been formulated which accounts for the heterogeneous combustion and gasification of the coal and char. This model includes the devolatilization of the coal and homogeneous oxidation of carbon monoxide and devolatilized species. The water-gas shift reaction is assumed to be equilibrated. The model also includes the mass, momentum and energy balances of the particles but obviates the solution of the combustor heat balance by using the measured gas temperature in the solution. The model accurately predicts the gas and elemental conversions and particle temperatures observed in the experiments, and supports the homogeneous and heterogeneous kinetics of post-combustion fuel nitrogen conversion.

Σκοπός της παρούσας εργασίας είναι ο προσδιορισμός της ρύπανσης των ιζημάτων του Αλφειού ποταμού από στερεά σωματίδια, που προέρχονται από την εξόρυξη και την καύση του λιγνίτη Μεγαλόπολης. Βασικό αντικείμενο έρευνας αποτέλεσε η μικροσκοπική εξέταση του οργανικού μέρους, που είναι παρόν στα ιζήματα του Αλφειού ποταμού και η οργανική γεωχημική εξέταση επιλεγμένων δειγμάτων για την ανίχνευση πολυκυκλικών αρωματικών υδρογονανθράκων (polycyclic aromatic hydrocarbons, PAHs). Επιπλέον σε δείγματα λιγνίτη, ιπτάμενης τέφρας, τέφρας εστίας και τέφρας απόθεσης από το Λιγνιτικό Κέντρο Μεγαλόπολης πραγματοποιήθηκε μία σειρά εργαστηριακών προσδιορισμών, που περιέλαβε προσεγγιστική και άμεση ανάλυση, ανθρακοπετρογραφική εξέταση του λιγνίτη, καθώς και ορυκτολογικές και στοιχειακές αναλύσεις. Με βάση τις περιεκτικότητες του λιγνίτη και των παραπροϊόντων της καύσης του σε κύρια στοιχεία και ιχνοστοιχεία μπορεί να εκτιμηθεί η κινητικότητά τους κατά την καύση και το κατά πόσο αυτά διαφεύγουν στο περιβάλλον ή παραμένουν στο χώρο καύσης. Τα πιο ευκίνητα στοιχεία, που περιέχονται στο λιγνίτη Μεγαλόπολης, είναι τα Ba, Li, Mg, Rb και Sn, τα οποία μαζί με τα As και Pb, που συμμετέχουν στο λεπτόκοκκο τμήμα της ιπτάμενης τέφρας αποτελούν δυνητικούς ρυπαντές. Αντίθετα τα στοιχεία Ge, Mn, Th, Ti και Y είναι περιβαλλοντικά λιγότερο επικίνδυνα, καθώς συμμετέχουν στο τμήμα των παραπροϊόντων, που παραμένει στην τέφρα των ατμοηλεκτρικών σταθμών. Από μικροσκοπική παρατήρηση προέκυψε ότι το οργανικό υλικό, που είναι παρόν στα συγκεκριμένα ιζήματα αποτελείται κατά 78,4% κ.ό. από ανθρωπογενή σωματίδια, ενώ το υπόλοιπο 21,6% αποτελείται από φρέσκα φυτικά υπολείμματα. Το 81,5% κ.ό. του συνόλου των ανθρωπογενών σωματιδίων αποτελείται από κόκκους λιγνίτη και το 19,5% κ.ό. συνίσταται από εξανθρακώματα, που μεταφέρονται με την ιπτάμενη τέφρα και αποτίθενται στα ιζήματα. Τα ανθρακούχα σωματίδια στα ιζήματα του Αλφειού αντικατοπτρίζουν την ανθρακοπετρογραφική σύσταση του λιγνίτη Μεγαλόπολης, από την οποία εξαρτάται επίσης και η μορφή των εξανθρακωμάτων. Το επίπεδο των συγκεντρώσεων PAHs στα ιζήματα του Αλφειού είναι σχετικά χαμηλό (10-100 ng/g), ωστόσο η καύση του λιγνίτη συνεισφέρει σε ποσοστό 39,5% στην εκπομπή τους, ενώ το 23,5% προέρχεται από τον ίδιο το λιγνίτη. Η συμμετοχή των PAHs στα συγκεκριμένα ιζήματα φαίνεται να σχετίζεται ως ένα βαθμό με την παρουσία εξανθρακωμάτων, γεγονός που υποδεικνύει διεργασίες ρόφησης. Με την παρούσα εργασία αποδεικνύεται ότι η Οργανική Πετρολογία σε συνδυασμό με δεδομένα Οργανικής και Ανόργανης Γεωχημείας, μπορεί να αποτελέσει σημαντικό εργαλείο σε ό,τι αφορά στον προσδιορισμό της ρύπανσης ιζημάτων και εδαφών από την εκμετάλλευση γαιανθράκων. / The main target of the present study is the assessment of the contamination degree of Alfeios River sediments with solid particles deriving from mining and combustion of Megalopolis lignite. The objectives of the study were the microscopical examination of the organic matter present in these sediments, as well as the determination of the concentration of Polycyclic Aromatic Hydrocarbons (PAHs) in selected samples. Additionally in lignite, fly ash, bottom ash and ash deposit samples, were conducted a string of analyses including, proximate and ultimate analyses along with mineralogical and elemental determinations. The mobility of major and trace elements during the combustion of lignite can be estimated according to the concentration of these elements in bulk lignite and its combustion by-products. Based on these results the most mobile and thus more environmentally "sensitive" elements in Megalopolis lignite are As, Ba, Li, Mg, Pb, Rb and Sn, while Ge, Mn, Th, Ti and Y are the less mobile elements participating mostly in bottom ash. From the microscopical study of the organic matter present in Alfeios sediments it is evident that it consists of 78,4% of anthropogenic particles, while the remaining 21,6% consists of fresh plant remnants. The 81,5% of the anthropogenic particles consists of lignite particles deriving from mining and transportation processes and the remaining 19,5% consists of char particles transported and deposited as portion of the fly ash produced in Megalopolis Lignite Centre. The coal-petrographic composition of lignite particles is similar to the coal-petrographic composition of Megalopolis lignite. The latter is also responsible for the shape and texture of the char particles. The PAHs concentration level is rather low, ranging from 10-100 ng/g. Nevertheless lignite combustion along with the Megalopolis lignite itself are the main emission sources of such compounds accounting for 39,5% and 23,5% respectively. The presence of PAHs is related to the presence of char particles, probably via sortion procedures. The results of this study show that Organic Petrology can be a useful tool in environmental science and particularly in the field of contamination of soils and sediments from coal exploitation, if combined with Organic and Inorganic Geochemical data.

No description available.

It is recognised that the reactions with steam and CO2 are the rate limiting step during coal gasification, and a vast number of studies has been dedicated to the kinetics of these reactions. Most studies were carried out by using a single reactant (CO2 or H2O), either pure or diluted with an inert gas. Research using gas mixtures of CO2 and steam and their effects on gasification kinetics have been undertaken but are limited. The objective of this study is to determine the effects of CO2 on the steam gasification rate of a typical Highveld seam 4 coal. The South African medium ranked high volatile bituminous coal was charred at 950 °C. 2.0 g samples of ± 1 mm particles were analysed in a modified large particle thermo gravimetric analyser under various reactant gas concentrations. Experiments were conducted at atmospheric pressure (87.5 kPa) and temperatures from 775 to 900 °C, such that the conversion rate was controlled by chemical reaction. Reagent mixtures of steam-N2, steam-CO2 and CO2-N2 at concentrations of 25-75 mol%, 50-50 mol%, 75-25 mol% and 100 mol% were investigated. Arrhenius plots for steam and CO2 gasification produced activation energy values of 225 ± 23 kJ/mol and 243 ± 32 kJ/mol respectively. The calculated reaction orders with respect to reagent partial pressure were 0.44 ± 0.08 and 0.56 ± 0.07 for steam and CO2 respectively. Comparisons of the experimental data showed a higher reaction rate for the steam-CO2 mixtures compared to steam-N2 experiments. The semi empirical Wen model (m = 0.85) with an additive Langmuir-Hinshelwood styled rate equation predicted the mixed reagent gasification accurately. Reaction constants that were determined from the pure reactant experiments could directly be applied to predict the results for the experiments with mixtures of steam and CO2. The conclusion was made that under the investigated conditions steam and CO2 reacts simultaneously on different active sites on the char surface. / Thesis (MIng (Chemical Engineering))--North-West University, Potchefstroom Campus, 2013.

It is recognised that the reactions with steam and CO2 are the rate limiting step during coal gasification, and a vast number of studies has been dedicated to the kinetics of these reactions. Most studies were carried out by using a single reactant (CO2 or H2O), either pure or diluted with an inert gas. Research using gas mixtures of CO2 and steam and their effects on gasification kinetics have been undertaken but are limited. The objective of this study is to determine the effects of CO2 on the steam gasification rate of a typical Highveld seam 4 coal. The South African medium ranked high volatile bituminous coal was charred at 950 °C. 2.0 g samples of ± 1 mm particles were analysed in a modified large particle thermo gravimetric analyser under various reactant gas concentrations. Experiments were conducted at atmospheric pressure (87.5 kPa) and temperatures from 775 to 900 °C, such that the conversion rate was controlled by chemical reaction. Reagent mixtures of steam-N2, steam-CO2 and CO2-N2 at concentrations of 25-75 mol%, 50-50 mol%, 75-25 mol% and 100 mol% were investigated. Arrhenius plots for steam and CO2 gasification produced activation energy values of 225 ± 23 kJ/mol and 243 ± 32 kJ/mol respectively. The calculated reaction orders with respect to reagent partial pressure were 0.44 ± 0.08 and 0.56 ± 0.07 for steam and CO2 respectively. Comparisons of the experimental data showed a higher reaction rate for the steam-CO2 mixtures compared to steam-N2 experiments. The semi empirical Wen model (m = 0.85) with an additive Langmuir-Hinshelwood styled rate equation predicted the mixed reagent gasification accurately. Reaction constants that were determined from the pure reactant experiments could directly be applied to predict the results for the experiments with mixtures of steam and CO2. The conclusion was made that under the investigated conditions steam and CO2 reacts simultaneously on different active sites on the char surface. / Thesis (MIng (Chemical Engineering))--North-West University, Potchefstroom Campus, 2013.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.