Eric G. Eddings

Experimental formulation and kinetic model for JP-8 surrogate mixtures

Jet A and JP-8 are kerosene fuels used in aviation and consist of complex mixtures of higher order hydrocarbons, including alkanes, cycloalkanes, and aromatic molecules. The objectives of the current work are to develop a surrogate mixture to represent JP-8 fuels and to discuss a general detailed chemical kinetic model for jet fuels, which is suitable for future reduction. Asurrogate blend of six pure hydrocarbons is found to adequately simulate the distillation and compositional characteristics of a practical JP-8. A hierarchically constructed kinetic model already available for the oxidation of alkanes and simple aromatic molecules (benzene, toluene, ethylbenzene, xylene, etc.) is extended to include methylcyclohexane and tetralin as new reference fuel components. The kinetic model is validated through comparisons with experimental data for the pure components and it is also used to verify and predict the structures of laminar premixed flames of different pure components as well as conventional kerosene fuels.

Char nitrogen conversion: implications to emissions from coal-fired utility boilers

Abstract The contribution of nitrogen present in the char on the production of nitrogen oxides during char combustion was analyzed. A literature review summarizes the current understanding of the mechanisms that account for the formation of NO and N2O from the nitrogen present in char. The review focused on: (1) the functionalities in which nitrogen is present in the coal and how they evolve during coal devolatilization; (2) the mechanism of nitrogen release from the char to the homogeneous phase and its further oxidation to NO; and (3) the reduction of NO on the surface of the char. The critical analysis of these three issues allowed identification of uncertainties and well-founded conclusions observed in the literature for this system. The existing models for the production of nitrogen oxides from char-N were also reviewed. A critical analysis of the assumptions made in these models and how they affect the final predictions is presented. Finally, a simplified version of these models was used to perform a parametric analysis evaluating the impact of several parameters on the total conversion of char-N to NO. These parameters include: (1) the rate of NO reduction on the char surface; (2) the rate of carbon oxidation; and (3) early vs. late nitrogen release during the char oxidation process. The results underscore the importance of the reaction of NO reduction on the char surface to the final conversion of char-N to NO.

Formulation of a surrogate for the simulation of Jet fuel pool fires

ABSTRACT The simulation of pool fires involving complex hydrocarbon fuels requires the development of a simplified surrogate with a limited number of compounds having known oxidation mechanisms. A series of six-component surrogates was developed for the simulation of JP-8 pool fires, and experiments were carried out with a 30-cm-diameter pool fire to allow comparison of the surrogate fuel behavior to that of the jet fuel. The surrogate was shown to simulate the burning rate, radiant heat flux, and sooting tendency of jet fuel under steady-state pool fire conditions. This study also illustrated the transient nature of batch pool fire experiments and highlighted the difficulties associated with formulating an appropriate surrogate to mimic jet fuel behavior over the lifetime of a batch pool fire. These difficulties were shown to arise from fuel compositional changes, with preferential destruction of lighter components and accumulation of heavier components during the course of the fire.

Emissions from Syngas Combustion

Gasification technology has matured to the point that previously-held hesitations regarding performance and availability have given way to acceptance of the technology for energy generation. Indeed, the past few years have seen a significant increase in the number of gasifiers installed for generation of power and heat, and the number of installations is expected to increase dramatically over the next several decades as demand for efficient and environmentally sound energy generation increases. It is valuable to consider the environmental impact of this new generation of energy production systems, specifically release of gaseous emissions from combustion of the synthesis gas produced by gasification. Emissions from syngas combustion in turbines, engines and boilers are discussed in this review. The types of emissions considered include the unburned fuel components and partially oxidized species, nitrogen and sulfur-containing gases, volatile organic compounds, and other trace elements. Combustion of synthesis gas, in general, produces lower emissions for heat and power generation than conventional liquid and solid fuels. The composition of the syngas strongly influences the level of emissions. Hydrogen and carbon monoxide in synthesis gases results in elevated combustion temperature that facilitates the thermal formation of NO and NO2. In contrast, higher temperatures promote complete combustion and reduce the emission of organic volatiles, which are formed mainly from minor fractions of hydrocarbons in synthesis gases. Particulate matter, metallic compounds and other undesired pollutants are usually removed before firing synthesis gases for heat and power production. Therefore, integrated gasification and combined cycle systems are more environmentally friendly than conventional power generation systems.

Fundamental studies of metal behavior during solids incineration

Abstract An experimental apparatus was constructed which allows investigation of the vaporization behavior of metal contaminants during incineration of their host substrate. Comparisons were made between equilibrium predictions and experimental observations for a number of different melals in chlorinated, inert, and reducing environments between 150°C and 650°C. The equilibrium predictions for Pb vaporization were found to show the greatest deviation from experimental observations. Comparisons showed that a knowledge of elements associated with the initial metal species, as well as omission of PbCl4 from the calculations, can be important for the equilibrium predictions. Experimental results showed that the formation of volatile PbCl4 predicted by equilibrium was not kinetically favorable under the conditions studied. Subsequent vaporization studies involving PbCl2 deposited on a silica substrate demonstrated an influence of initial concentration on the amount of Pb vaporization observed. The extent of va...

Kinetics of Enol Formation from Reaction of OH with Propene

Kinetics of enol generation from propene has been predicted in an effort to understand the presence of enols in flames. A potential energy surface for reaction of OH with propene was computed by CCSD(T)/cc-pVDZ//B3LYP/cc-pVTZ calculations. Rate constants of different product channels and branching ratios were then calculated using the Master Equation formulation (J. Phys. Chem. A 2006, 110, 10528). Of the two enol products, ethenol is dominant over propenol, and its pathway is also the dominant pathway for the OH + propene addition reactions to form bimolecular products. In the temperature range considered, hydrogen abstraction dominated propene + OH consumption by a branching ratio of more than 90%. Calculated rate constants of enol formation were included in the Utah Surrogate Mechanism to model the enol profile in a cyclohexane premixed flame. The extended model shows consistency with experimental data and gives 5% contribution of ethenol formation from OH + propene reaction, the rest coming from ethene + OH.

Determination of metal behavior during the incineration of a contaminated montmorillonite clay

The goal of this study was to develop an understanding of metals behavior during thermal treatment. Clay samples, contaminated with metals to obtain a surrogate waste, were analyzed prior to and following thermal treatment using nitric acid and/or hydrogen fluoride digestion, followed by inductively coupled plasma emission spectrophotometry analysis. Techniques were used to examine particle surface and metal distribution within cross sections. Lead, cadmium, and chromium results are discussed. With hydrogen fluoride-digested samples, the results indicated that vaporization increased slightly with increasing temperature for cadmium and lead. Chromium did not show increased vaporization. At higher temperatures, the nitric acid digestions did not completely remove the metals. Scanning electron microscope pictures showed that, at higher temperatures, the particle structure became compact and glassy; the electron microprobe results indicated that lead and cadmium were located in regions with high silicon, suggesting reactions with the silicon. Chromium distribution remained uniform, suggesting that chromium was immobilized due to structural changes not reactions. 40 refs., 11 figs., 2 tabs.

Evaluation of Organometallic Fuel Additives for Soot Suppression

Abstract In this work, we investigate the utility of the smoke lamp for evaluating the soot-reducing potential of additives, by comparing it to a more complex liquid-fed laminar diffusion flame. The additives, ferrocene (bis(cyclopentadienyl) iron-Fe(C5H5)2), ruthenocene (bis(cyclopentadienyl)ruthenium-Ru(C5H5)2), iron naphthenate (a 12% iron salt of naphthenic acid, which is a mixture of fatty carboxylic acids, some of which may include a cyclopentane ring), and MMT (Methylcyclopentadienyl manganese tricarbonyl-CH3C5H4Mn(CO)3) are evaluated at various concentrations in the jet fuel JP-8. Although the smoke lamp is a simple, inexpensive, and widely-available test for evaluating the sooting potential of liquid fuels, it does not provide an effective measure of soot suppression by metal-containing additives. The drop-tube reactor more accurately captures the physical conditions and processes—droplet vaporization, ignition, and rich vs. lean operation—typically found in more complex systems. We find in the smoke lamp that ferrocene, and to a lesser degree ruthenocene, are effective soot suppressors when used in JP-8, and that their effectiveness increases with increasing concentration. In the smoke lamp, MMT and iron naphthenate have minimal effect. On the other hand, in the drop-tube reactor, all four additives are quite effective, especially at fuel lean conditions, where soot suppression reaches 90–95%. Under fuel-rich conditions, where in some cases the additives elevate the yield of soot aerosol slightly, we find a significant increase in the production of the soluble organic fraction of the aerosol, i.e., tar. In order to understand why the smoke lamp sometimes fails to indicate a soot suppressing potential (i.e., from MMT and iron naphthenate), soot samples were collected from a wick lamp burning ferrocene and iron naphthenate additives in JP-8. These samples, as well as several from the drop-tube reactor, were analyzed by X-Ray Fluorescence (XRF) in order to determine their metal content, and we find that the soot aerosol produced by the wick lamp using ferrocene-containing fuel had roughly 30 times the iron content of the soot aerosol produced by the wick lamp using iron-naphthenate-containing fuel. This difference in metal content is not found in samples produced in the drop-tube reactor. We conclude that the poor performance of iron naphthenate in the smoke lamp is likely the result poor vaporization of the additive from the wick, a consequence of its high molecular weight (average 465).

Modeling the vaporization of ash constituents in a coal-fired boiler

Emissions of fine particulate and trace toxic metals are being subjected to increasing regulation. This paper addresses how the emission of these compounds can be influenced by changes in combustion conditions, particularly those selected to minimize NOx emissions. The vaporization and condensation of refractory oxides dominate submicron aerosol formation during the combustion of bituminous coals. The vaporization of these oxides is augmented by the reduction of refractory oxides to suboxides or metals. We used available drop tube furnace data to develop and test models for the vaporization of aluminum and iron. The vaporization of alumina is found to occur primarily via reduction of the alumina to Al2O. Although other paths are recognized to be important, the vaporization of iron is approximated by a mechanism involving FeO reduction. The models for aluminum and iron vaporization, together with previously developed models for the other refractory metals, are incorporated into a computational fluid dynamics code to determine the impact of different oxidation-temperature histories in a utility boiler. The vaporization of refractory oxides is calculated for conditions corresponding to the operation of the boiler before and after retrofitting with low-NOx burners and overfire air ports. The results show that the vaporization of refractory oxides is diminished under low-NOx operating conditions and that the different oxygen-temperature histories of particles lead to significant differences in the vaporization of oxides for particles originating from different burners. The vaporization is found to occur primarily in regimes where temperature and CO concentration are high.

Trends in predicting and controlling ash vaporization in coal-fired utility boilers

Abstract The past decade has seen a dramatic increase in the use of computational fluid dynamics (CFD) in the solution of problems related to the design and operation of pulverized coal-fired utility boilers. These tools have been increasingly used to simulate the performance of utility boilers, primarily for NOx control and associated problems of unburned carbon in fly ash and in water-wall corrosion. These models are extended to calculate the emissions of submicron particles by the vaporization and condensation of ash constituents. A single particle model for the vaporization of minerals in coal was first calibrated with results for vaporization of 14 coals in a laboratory reactor. The calibrated model was then applied in the simulation of the ash vaporization in a 500-MW opposed-wall fired boiler with 12 burners on each of the front and rear walls, and for cases before and after retrofitting the boiler with burner technology to reduce NOx emissions. The simulations showed that the ash vaporization occurred primarily during short intervals along particle trajectories when the particle temperatures increased above 1800 K. The ash vaporization decreased slightly on retrofitting the boiler, and the contributions by different burners to the total amount vaporized varied widely, particularly after the low-NOx retrofit.