Pyrolysis Of Fuels Research Articles

Плазменная переработка урансодержащих твердых топлив: термодинамический анализ и эксперимент

This paper presents the results of thermodynamic and experimental studies of plasma processing of uranium-containing solid fuels on the example of Nizhne Illi brown coal with an ash content of 12% and Estonian dictionem shale with an ash content of 88%. The essence of plasma processing of uranium-containing solid fuel is to convert its organic mass into synthesis gas with simultaneous gasification of uranium-containing compounds and subsequent condensation of uranium-containing components from the gas phase. Thermodynamic analysis showed that at a temperature of 1800 K, the uranium-containing compounds completely pass into the gas phase in the form of uranium oxides. At this temperature, the gas phase of the products of plasma pyrolysis and steam gasification of solid fuels consists of more than 95% synthesis gas. Experiments on plasma pyrolysis and steam gasification of dictionem shales were conducted in a flow-type plasma reactor. In the case of plasma-steam gasification of shale, the yield of synthesis gas was 86%, the degree of carbon gasification was 70.4%, and the degree of uranium release into the gas phase was 83.6%. The results of the research show that the plasma processing technology is not susceptible to the quality of the fuels used. It is shown that the integral parameters of plasma gasification of uranium-containing fuels are higher than in their plasma pyrolysis.

PAH formation from jet stirred reactor pyrolysis of gasoline surrogates

Soot particles and their precursor polycyclic aromatic hydrocarbon (PAH) species, formed during combustion, are responsible for particulate emissions in gasoline direct injection (GDI) engines. To better understand the effects of fuel composition on formation of soot in GDI engines, the pyrolysis of several gasoline surrogates was studied in a jet-stirred reactor across a broad temperature range at atmospheric pressure and 1 s residence time. Fuel and intermediate species, including aromatics up to naphthalene, were measured using gas chromatography (GC). PAH concentrations from pyrolysis of surrogate fuels were compared to gain insight into the effects of fuel composition on PAH formation. In addition, synergistic effects were observed in pyrolysis experiments of binary blends. A detailed kinetic model, recently developed at Lawrence Livermore National Laboratory (LLNL), successfully captured the effects of blending and the concentration of major PAHs. Major reaction pathways are discussed, as well as the role of important intermediate species, such as acetylene, and resonantly stabilized radicals such as allyl, propargyl, cyclopentadienyl, and benzyl in the formation of PAH.

Simultaneous analysis of light gases and heavy pyrolyzates evolved from lignite and hard coal by pyrolysis–GC/MS–GC/TCD

The pyrolysis of solid fossil fuels and biomass is of great relevance, because it influences the combustion kinetics of these fuels, and the pyrolysis products are potential raw materials for further chemical processing. The aim of this work was to develop a pyrolysis system able to separate the whole variety of pyrolysis products during one pyrolysis experiment without the need to replace GC columns for improved resolution. A conventional pyrolysis system equipped with a coupled gas chromatography (GC)/mass spectrometry (MS) detector was extended by a second GC with a fused-silica capillary column and a thermal conductivity detector (TCD). The coupled pyrolysis–GC/MS–GC/TCD system was used to investigate the evolved pyrolysis products of two lignites and a hard coal enabling the qualitative detection of pyrolyzates (GC/MS) while simultaneously quantifying the light gases (TCD). Benzofuran, catechol, and a preference for even-numbered hydrocarbon pyrolyzates in addition to a higher pristene/heptadecane ratio were found to be characteristic for the two studied German lignites in comparison to the Columbian hard coal as well as a higher release of especially oxygen-containing light gases.

Investigation of pyrolysis effect on convective heat transfer characteristics of supercritical aviation kerosene

By utilizing airborne hydrocarbon fuels working as coolant, active regenerative cooling method is a significant method for maintaining the reliability of the scramjet engine components. At high temperatures, the pyrolysis of hydrocarbon fuels occurs and provides extra heat absorption capacity. Investigation on coupled heat transfer and pyrolysis of fuels is essential for the design of cooling channels. This paper aims to study the pyrolysis effects on convective heat transfer of supercritical aviation kerosene RP-3 in vertical upwards. Firstly, a simple molecular kinetic model was proposed for RP-3 pyrolysis. Then the performance of two Reynolds-averaged Navier-Stokes turbulence models with three constant turbulent Prandtl numbers in predicting the fluid-thermal behaviors of reacting flow were evaluated. At last, the mechanisms of pyrolysis effect on heat transfer in the heat transfer deterioration region and the cracked region were investigated. The results showed that the pyrolysis affected heat transfer from two aspects: providing heat absorb or release capacity through the endothermic (exothermic) pyrolysis reactions, changing the fuel properties by the variations in composition. In the heat transfer deterioration region, the effect of heat absorption dominants over the effect of additional decreased in density and specific heat capacity by pyrolysis on the heat transfer, thus a lower wall temperature and larger heat transfer coefficients were observed when considering pyrolysis. In the cracked region, under the present condition, the competitive outcome of the above two led to an improved heat transfer by pyrolysis, and the improved effect first increased and then decreased as the fuel conversion increasing. This work provides a fundamental understanding of the behaviors of hydrocarbon fuel inside the cooling channels, which is valuable for the cooling structure design.

Comparison of pyrolysis of live wildland fuels heated by radiation vs. convection

During wildland fires, which include both planned (prescribed fire) and unplanned (wildfire) fires, live and dead plants may be subject to both radiative and convective heat transfer mechanisms. In this study, the pyrolysis of 14 live plant species native to the forests of the southern United States was investigated using a flat-flame burner (FFB) apparatus under three heating modes in order to mimic pyrolysis of plants during wildland fires. The heating modes were: (1) radiation-only, where the plants were pyrolyzed under a moderate heating rate of 4 °C s−1 (radiative flux of 50 kW m−2); (2) convection-only, where the FFB apparatus was operated at a high heating rate of 180 °C s−1 (convective heat flux of 100 kW m−2); and (3) a combination of convection and radiation, where the plants were exposed to both convective and radiative heat transfer mechanisms. Data were also compared with slow heating experiments (0.5 °C s−1). During the experiments, the pyrolysis products were collected and analyzed using GC–MS for the analysis of tars and GC-TCD for the analysis of light gases. The results indicate that the highest light gas and tar yields were obtained from the combined mode, which was performed at a higher pyrolysis temperature and heating rate. CO, CO2, CH4, and H2 were the major light gas species in all three heating modes. The radiation-only mode led to formation of primary tars and a few secondary tars consisting of aliphatic and 1–2 ring aromatic compounds with 1 to 3 attachments, including alkyl, hydroxyl, and methoxy groups.

In situ determination of the equivalence ratio in a methane/air flow field by femtosecond filament excitation

The equivalence ratio is a key parameter in understanding pyrolysis, combustion and gasification of fuels for improving combustion efficiency and lowering net pollution emissions. In this study, we investigate the feasibility of measuring the local equivalence ratio in a gaseous flow field using femtosecond filament excitation. We demonstrate that quasi-collimated-beam-induced filamentation in a premixed methane/air flow can produce a long and uniform free-of-atomic-line emission channel, and that the intensity ratios of the molecular emissions in this channel, such as methylidyne radical (CH) (331 nm)/N2 (337 nm), CH (331 nm)/N2 (357 nm), and CH (331 nm)/CN (388 nm), are all linear correlations to the equivalence ratios of the methane/air flow. Our results provide a possibility for the in situ measurement of long-range and multi-dimensional equivalence ratio of flow fields with femtosecond filament excitation.

One-Step Densification of Carbon/Carbon Composites Impregnated with Pyrolysis Fuel Oil-Derived Mesophase Binder Pitches

Carbon/carbon (C/C) composites are conventionally manufactured by liquid-phase impregnation (LPI), in which the binder pitches and phenolic resins are impregnated into the composites, and by chemical vapor infiltration (CVI). However, CVI has certain limitations in that expensive gases, such as methane and propane, are used and a long reaction time is required. Therefore, LPI is more widely used, as it employs economical pitches. In this study, the effects of one-step preparation on mechanical properties of C/C composites impregnated with mesophase binder pitches and phenolic resins have been investigated. The C/C composites containing four types of 20 wt.% mesophase binder pitches had differences in softening point (SP) and quinoline insoluble (QI) contents. After conducting trials on mesophase formation using different heat treatment temperatures and times, the best density and mechanical properties of the C/C composites were achieved using the mesophase binder pitches with 170 °C SP. However, when SP 200 °C was used, the density of the C/C composites was not further improved. This is because the binder pitches were not properly impregnated into the composites due to the high viscosity and QI of the binder pitches. Furthermore, the C/C composites fabricated with 20 wt.% pitch 2 exhibited the highest mechanical properties.

Structure and Activity of Ni2P/Desilicated Zeolite β Catalysts for Hydrocracking of Pyrolysis Fuel Oil into Benzene, Toluene, and Xylene

The effects of desilication (DS) of the zeolite β on the hydrocracking of polycyclic aromatics were investigated using the Ni2P/β catalysts. The Ni2P/β catalysts were obtained by the temperature-programmed reduction (TPR) method, and the physical and chemical properties were examined by N2 physisorption, X-ray diffraction (XRD), 27Al magic angle spinning–nuclear magnetic resonance (27Al MAS NMR), extended X-ray absorption fine structure (EXAFS), isopropyl amine (IPA) and NH3 temperature-programmed desorption (TPD), CO uptake, and thermogravimetric analysis (TGA). The catalytic activity was examined at 653 K and 6.0 MPa in a continuous fixed bed reactor for the hydrocracking (HCK) of model compounds of 1-methylnaphthalene (1-MN) and phenanthrene or a real feedstock of pyrolysis fuel oil (PFO). Overall, the Ni2P/DS-β was observed as more active and stable in the hydrocracking of polycyclic aromatics than the Ni2P/β catalyst. In addition, the Ni2P/β suffered from the coke formation, while the Ni2P/DS-β maintained the catalytic stability, particularly in the presence of large polycyclic hydrocarbons in the feed.

Photocatalytic oxidation removal of elemental mercury from flue gas. A review

Air pollution caused by mercury emissions from combustion and pyrolysis of fossil fuels, biomass, and solid wastes is a major health issue. Elemental mercury (Hg0), the dominant species in flue gas, is poorly captured by actual control equipments because Hg0 has a high volatility and is insoluble in water. Alternatively, photocatalytic processes can oxidize Hg0 into Hg compounds that are easier to remove. Here we review the recent research on oxidative removal of Hg0 by photocatalysts, with focus on titanium dioxide, bismuthides, silver compounds and hybrid photocatalysts. We discuss the Hg0 removal performances and mechanisms of catalytic oxidation. The TiO2 photocatalyst often suffers from low absorption of solar energy and easy recombination of photoinduced electron–hole couples. BiOIO3 appears as a promising photocatalyst due to its high Hg0 oxidation activity under visible light irradiation. Silver carbonates and silver halides are newly developed visible-light-responsive photocatalysts for Hg0 removal. Fast separation and transformation of photogenerated electrons and holes control the performance of Hg0 removal by photocatalysts.

Comparison of Growth Characteristics and Properties of CVD TiN and TiO2 Anti-Coking Coatings

Coating metals with anti-coking materials inhibit their catalytic coking and are especially beneficial in the pyrolysis of hydrocarbon fuels. It is believed that growth characteristics and properties may play a pivotal role in the anti-coking performance of chemical vapor deposition (CVD) coatings. In this study, TiN and TiO2 coatings were obtained by CVD using TiCl4–N2–H2 and TiCl4–H2–CO2 systems, respectively. The effects of deposition time, residence time, and partial pressure were examined, and the coating microstructure was characterized by scanning electron microscopy (SEM). The results reveal that the effect of deposition parameters on the growth characteristics of TiN and TiO2 coatings is very different. The growth of the TiN coating shows characteristics of the island growth model, while the TiO2 coating follows the layer model. In general, the growth rate of the star-shaped TiN crystals is higher than that of crystals of other shapes. For the TiO2 coating, the layer mode growth characteristics indicate that the morphology of the TiO2 coating does not change significantly with the experimental conditions. Coking tests showed that the morphology of non-catalytic cokes is not only affected by the temperature, pressure, and coking precursor, but is also closely related to the surface state of the coatings. Both TiN and TiO2 coatings can effectively prevent catalytic coking and eliminate filamentous cokes. In some cases, however, the N or O atoms in the TiN and TiO2 coatings may affect common carbon deposits formed by non-catalytic coking, such as formation of needle-like and flaky carbon deposits.

Modeling of High Density Polyethylene Regression Rate in the Simulation of Hybrid Rocket Flowfields

Numerical analysis of hybrid rocket internal ballistics is carried out with a Reynolds-averaged Navier–Stokes solver integrated with a customized gas–surface interaction wall boundary condition and coupled with a radiation code based on the discrete transfer method. The fuel grain wall boundary condition is based on species, mass, and energy conservation equations coupled with thermal radiation exchange and finite-rate kinetics for fuel pyrolysis modeling. Fuel pyrolysis is governed by the convective and radiative heat flux reaching the surface and by the energy required for the propellant grain to heat up and pyrolyze. Attention is focused here on a set of static firings performed with a lab-scale GOX/HDPE motor working at relatively low oxidizer mass fluxes. A sensitivity analysis was carried out on the literature pyrolysis models for HDPE, to evaluate the possible role of the uncertainty of such models on the actual prediction of the regression rate. A reasonable agreement between the measured and computed averaged regression rate and chamber pressure was obtained, with a noticeable improvement with respect to solutions without including radiative energy exchange.

Kinetics and modeling of supercritical pyrolysis of endothermic hydrocarbon fuels in regenerative cooling channels

Endothermic hydrocarbon fuel (EHF) is used as on-board coolant quenching the combustors of advanced aircrafts through sensible and endothermic pyrolysis reactions. The supercritical pyrolysis of EHFs was experimentally investigated under conditions (3.5 MPa, 525–600 °C) in a stainless steel mini-tubular reactor heated by a fluidized sand bath system. A simplified molecular reaction kinetic model (16 species and 11 reactions) was proposed based on the primary/secondary pyrolysis mechanism and the residence time estimation using computational fluid dynamics simulations. The experimental and predicted results using the developed kinetics model agree very well with the errors less than 10% under the conversion up to 70%. The pyrolysis model was also used in modeling EHF flowing and pyrolysis in an electrically heated tube showing the conversion prediction errors less than 15% and the fuel and wall temperature prediction deviations less than 20 K, which is a significant improvement on the previous model (Energy Fuels 2013, 27, 2563).

High temperature volatile yield and nitrogen partitioning during pyrolysis of coal and biomass fuels

Nitrogen oxides (NOx) are atmospheric pollutants specifically targeted by legislation which imposes limits on emissions from large scale plant. During combustion, part of the Nitrogen fuel will be released as a component of the volatile matter compounds and as volatile nitrogen, while part will remain in the char. Thus, the fate of volatile-N and char-N becomes crucial for the formation of NOx and, consequently, for determining the concentrations of NO in solid fuels combustion systems. In pulverized fuel combustion, major routes for conversion of the volatile-N are either NO or N2, while char-N reacts through a set of heterogeneous reactions as the char is oxidized. Measuring high temperature char nitrogen content of the fuels directly reduces the likely uncertainty in NOx emissions from solid fuels on modern power stations using deep furnace air staging High temperature volatile-N and char-N partitioning is investigated by pyrolyzing fuels in a high temperature (1600 °C) wire mesh apparatus (HTWM) and analyzing the resulting char. White wood biomass, olive waste, torrefied wood, two bituminous coals and one anthracite coal were used on this study. The volatile yield at high temperatures has been obtained for each sample. The fate of nitrogen released during the pyrolysis as volatile matter and the nitrogen retained in the char has been evaluated for different biomass samples. The nitrogen in the char was measured using a total nitrogen analyzer. Results show a large change in on the volatile yield compared with proximate analysis values for both coals. Only moderate change was observed on the volatile yield for both of the woody biomass that already have high values on proximate analysis, and just a slight increase was obtained on the volatile yield for the olive waste. Differences were found on the fate of nitrogen retained in the char that would lead to NOx formation. The biomass samples release most of their fuel-nitrogen as volatile (between 80 and 95%) while on the coals the volatile nitrogen is wide more variable depending on the coal sample.

A comparative applicability study of model-fitting and model-free kinetic analysis approaches to non-isothermal pyrolysis of coal and agricultural residues

Comparative applicability of model-fitting and model-free kinetic methods to pyrolysis of two coals and four agricultural residues was analyzed by using two models from each class of methods. The two model-fitting methods were Arrhenius and Coats-Redfern while Friedman and Vyazovkin were selected from the model-free category. According to kinetic analysis by all four models, the fuels could be arranged in following order of activation energy, CC > DC > SD > RH > FS > CH. The two model-fitting methods exhibited different kinetic parameters (E and reaction mechanism). All fuels were found to have a third order reaction mechanism (F3) by using Arrhenius model. In the case of Coats-Redfern model, the CC and RH displayed 3-dimensional diffusion mechanism (D3) whereas CH, SD and FS exhibited third order reaction mechanism (F3). DC was found to decompose according to 2-dimensional diffusion mechanism (D2). The percentage difference between the values of activation energy found from the Arrhenius and Coats-Redfern models was in the range of 6.24–21.64%. The percentage difference between the values of activation energy from two isoconversional models was not more than 3.29% for coals and 4.91% for agricultural residues in the fractional conversion range of 0.1–0.7. Isoconversional models were found to be more reliable and accurate for estimation of non-isothermal kinetics for pyrolysis of solid fuels compared with model-fitting methods.

A New Method for Direct Determination of Char Yield during Solid Fuel Pyrolysis in Drop-Tube Furnace at High Temperature and Its Comparison with Ash Tracer Method

A drop-tube furnace with a novel double-tube configuration was successfully developed to directly determine char yields during the pyrolysis of a wide range of solid fuels (mallee wood; mallee leaf; rice husk; biosolid; and subbituminous, bituminous, and anthracite coal) at a gas temperature of 1573 K. The char yield from pyrolysis of mallee wood and mallee leaf is 85%. This study shows using total ash as ash tracer results in 45–220% overestimation of char yields for biomass fuels and 13–27% for coals due to partial evaporation of ash. Similarly, selecting Na and K results in overestimation of biomass char yields by at least 2.5 times and selecting P leads...

Effects of endothermic hydrocarbon fuel composition on the pyrolysis and anti-coking performance under supercritical conditions

N-dodecane (C12) and decahydronaphthalene (DHN) were considered as the model compounds of alkanes and cycloalkanes, respectively. Pyrolysis of C12, DHN and C12-DHN binary fuels with different mass ratios of C12/DHN was performed on a supercritical cracking experimental apparatus equipped with a tubular reactor under supercritical conditions (3.5 MPa and 700 °C). The coke amount deposited on the inner surface of the tubular reactor was determined by weight method using an electronic analytical balance with a high measurement precision. Effects of EHF composition on the pyrolysis and anti-coking performance were studied. It was observed that there were reciprocal inhibition and competition effects during the co-pyrolysis of C12 and DHN. The increasing ratio of C12/DHN exerted a positive effect on gas yields of EHFs, but hardly on selectivities of H2 and alkenes (≤C4). Heat sink of EHFs depended largely on the gas yields representing thermal cracking level. C12/DHN ratio greatly affected the coke amount and morphologies of EHFs. Proper ratios of alkanes/cycloalkanes for advanced EHFs should not be less than 3/7 in terms of anti-coking performance. Inherent consistency could be obtained among carbon deposition, coking precursors, elements distribution and morphologies of coke. The results could provide a significant guidance on the design and development of advanced EHFs.

Characterization of pyrolysis products from slow pyrolysis of live and dead vegetation native to the southern United States

Prescribed (i.e., controlled) burning is a common practice used in many vegetation types in the world to accomplish a wide range of land management objectives including wildfire risk reduction, wildlife habitat improvement, forest regeneration, and land clearing. To properly apply controlled fire and reduce unwanted fire behavior, an improved understanding of fundamental processes related to combustion of live and dead vegetation is needed. Since the combustion process starts with pyrolysis, there is a need for more data and better models of pyrolysis of live and dead fuels. In this study, slow pyrolysis experiments were carried out in a pyrolyzer apparatus under nitrogen atmosphere in two groups of experiments. In the first group, the effects of temperature (400–800 °C), a slow heating rate (5–30 °C min−1), and carrier gas flow rate (50–350 ml min−1) on yields of tar and light gas obtained from pyrolysis of dead longleaf pine litter were investigated to find the optimum condition which results in the maximum tar yield. The results showed that the highest tar yield was obtained at a temperature of 500 °C, heating rate of 30 °C min−1, and sweep gas flow rate of 100 ml min−1. In the second group of experiments, 14 plant species (live and dead) native to forests in the southern United States, were heated in the pyrolyzer apparatus at the optimum condition. A gas chromatograph equipped with a mass spectrometer (GC–MS) and a gas chromatograph equipped with a thermal conductivity detector (GC-TCD) were used to study the speciation of tar and light gases, respectively. The results showed that the tar composition is dominated by oxygenated aromatic compounds consisting mainly of phenols. The light gas analysis showed that CO and CO2 were the dominant light gas species for all plant samples on a dry wt% basis, followed by CH4 and H2.

Numerical modeling of homogeneous gas and heterogeneous char combustion for a wood-fired hydronic heater

Abstract The pyrolysis of woody fuels produces two main products - pyrolysis gases and solid residue char which undergo homogeneous and heterogeneous reactions, respectively. Recent experimental measurements using a two-stage hydronic heater indicate the oxidization of these two products occur at distinctly different time scales with the pyrolysis gases burning immediately, and the majority of the char oxidization occurring later. In this study, these two oxidation pathways are explicitly accounted for in a numerical model that considers a non-homogeneous mixture of product flue gases. The model is based on a three-zone description of the heater which accounts for combustion and heat transfer using well-stirred reactor theory. The first zone describes the gasification of the wood fuel and burning of both pyrolysis gases and char. The second zone represents an after-burning stage. The last stage accounts for the transport of gases out the flue. Model predictions of O 2 , C O 2 , C O , H 2 O and temperature are compared to experimental measurements showing good overall agreement. Furthermore, the dual oxidation pathway description of combustion is shown to be critical to account for the dual-peak C O time signature. The first peak is associated with the burning of pyrolysis gases and the second corresponds to char oxidation.

Characterization of Toluene- and Quinoline-Insoluble Extracted from Pyrolysis Fuel Oil-Derived Pitch for Manufacture of C/C Composites

We herein report extraction and characterization of toluene-insoluble (TI) and quinoline-insoluble (QI) from pyrolyzed fuel oil (PFO) derived-pitch. The X-ray diffraction patterns demonstrated that QI component exhibited a more crystalline character than TI component. In addition, analysis by Fourier transform infrared spectroscopy (FT-IR) indicated the presence of signals at 3060 cm-1 for both TI components and QI components, which corresponded to the stretching of aromatic C-H bonds. As the intensity of this signal was greater than that of the peak at 2943 cm-1 corresponding to the stretching of aliphatic C-H bonds, it was clear that these components contained higher quantities of aromatic components than the original pitch sample. Furthermore, thermogravimetric analysis (TGA) indicated that the TI and QI components improved thermal stabilities and residues compared to the pitch sample (i.e., TI 75 wt% and QI 65 wt% at 850 oC). Finally, scanning electron microscopy (SEM) images confirmed that TI components were surrounded by β-resin (quinoline solubles in TI components) between the QI regions, which were themselves composed of aggregated grain-like spheres.

Understanding benzene formation pathways in pyrolysis of two C6H10 isomers: Cyclohexene and 1,5-hexadiene

To explore the fuel isomeric effects on the benzene formation pathways, the pyrolysis of two C6H10 isomers, cyclohexene (cC6H10) and 1,5-hexadiene (C6H10-15), was investigated by using molecular-beam mass spectrometry with tunable synchrotron radiation as the ionization source. The isomer-resolved pyrolysis intermediates, including some key radicals, were clearly identified and quantified at different temperatures for both fuels. A new kinetic model was developed and validated against the experimental results. The fuel-specific intermediates pools, the dominant fuel destruction pathways, as well as specific reactions channels leading towards benzene formations under pyrolysis conditions were revealed through experimental and modeling efforts. The elimination reaction (cC6H10 = C2H4 + C4H6) and the bond fission (C6H10-15 = C3H5-A + C3H5-A) dominate the consumption of cC6H10 and C6H10-15, respectively. Although the fuel structures of cC6H10 and C6H10-15 and their corresponding intermediate pools are quite different, the stepwise dehydrogenation reactions via cyclohexadiene isomers contribute to the majority of the benzene formation in the pyrolysis of both fuels. The recombination between the propargyl radical (C3H3) and allyl radical (C3H5-A) also contributes to benzene formation in the case of C6H10-15, while the C4 + C2 pathway provides a small amount of benzene in the case of cC6H10.