Showing papers in "Energy & Fuels in 1993"

Catalytic upgrading of pyrolysis oil

Abstract: The upgrading of a fast pyrolysis bio-oil and its two fractions was studied at atmospheric pressure using HZSM-5 as catalyst. The two fractions were pyrolytic lignin (which remained after removing water-soluble components from the whole bio-oil) and resid oil (which remained after separating phenolic fraction from the whole bio-oil). The upgrading was done in the temperature range of 340-410°C in a fixed bed microreactor. The objective was to maximize the desired organic distillate product with a high concentration of aromatic hydrocarbons. The maximum organic distillate from the upgrading of whole bio-oil was 19 wt% of bio-oil and the highest concentration of aromatic hydrocarbons in the distillate was 83 wt%

Hydrogen production by steam reforming glucose in supercritical water

Abstract: Results of the steam reforming of glucose in supercritical water at 34.5 MPa and temperatures between 450° and 650°C are presented. At 600°C and above glucose is completely gasified (no observable char or tar product) in less than one minute. The gas consists primarily of hydrogen and carbon dioxide, and a small amount of carbon monoxide and methane. Phase separation of the products exiting the reactor makes the gas available at very high pressure.

Relation between functional forms of coal nitrogen and formation of nitrogen oxide (NOx) precursors during rapid pyrolysis

Abstract: The formation of NO x precursors during rapid pyrolysis was investigated for 20 coals covering wide ranks at temperatures of 853-1488 K to elucidate the influence of coal properties on NO x formation during coal combustion. It was found that the main compositions of volatile nitrogen are HCN, NH 3 , and N 2 under these experimental conditions. Their yields are strongly dependent on coal types and pyrolysis temperature. By analyzing functional forms of coal nitrogen in parent coals and chars after pyrolysis using X-ray photoelectron spectroscopy, the relation between nitrogen functionality and formation of nitrogen-containing species has been further demonstrated. Three nitrogen functional forms of pyrrole type, pyridine type, and quaternary nitrogen are observed for all coals

Influence of char surface chemistry on the reduction of nitric oxide with chars

Abstract: The reactions of brown coal chars with nitric oxide, oxygen, and their mixture were carried out at 300 °C. The copper-catalyzed char-NO reaction was remarkably enhanced by the presence of O 2 . The formation of reactive surface intermediates (C(O)) and stable carbon-oxygen complexes (C-O) during these reactions was investigated by the combination of transient kinetics and temperature-programmed desorption techniques. The majority of the carbon-oxygen complexes generated during the reactions were the stable C-O species. The concentration of reactive C(O) was increased by the presence of both O 2 and Cu catalyst

Sulfur and nitrogen evolution in the Argonne coals. Experiment and modeling

Abstract: Sulfur and nitrogen evolution from the Argonne Premium coals has been studied using thermogravimetric analysis with measurement of evolved products by Fourier transform infrared spectroscopy (TG-FTIR) The method combines temperature-programmed pyrolysis and combustion H 2 S and tar sulfur were monitored by measuring SO 2 after oxidation of volatile products The SO 2 evolution curves produced with volatile oxidation erhibit two main evolution peaks and one smaller high-temperature evolution peak For each peak, the temperature of the maximum evolution rate (T max ) increases with increasing rank The individual evolution curves of the organic and pyritic sulfur were identified, and their evolution kinetics were derived

Pyrolysis kinetics and maturation of coals from the San Juan basin

Abstract: Temperature-programmed pyrolysis was used to analyze 18 coals and coaly shales from the San Juan Basin of the southwestern U.S., giving temperatures of maximum evolution rate (T max ) and pyrolysis yields. T max values increased with maturity (as measured by vitrinite reflectance [%R m ]). The pyrolysis yields remained constant or increased slightly with increasing maturity until a value for %R m of approximately 1.0 was reached, after which the yields declined rapidly. Pyrolysis-gas chromatography and pyrolysis-FTIR showed that alkane and alkene yields followed similar trends. A subgroup of coals from the Fruitland seam of the San Juan Basin was also analyzed by micropyrolysis at several constant heating rates to determine laboratory pyrolysis kinetics

Nitrogen oxide (NO) reduction by activated carbons. 1. The role of carbon porosity and surface area

Abstract: The results of an investigation are reported concerning the NO reduction activity of 10 different carbons and activated carbons, covering a wide range of surface areas and pore size distributions. These samples were subjected to temperature-programmed reaction (TPR) and isothermal reaction (at 600 °C) studies in a flow microreactor at a constant feed NO partial pressure of 0.404 kPa. It was found that, even though these carbons exhibited a wide range of reactivity, their qualitative behavior in the TPR experiments was quite similar, with the exception of samples that contained significant levels of potassium

Role of moisture in coal structure and the effects of drying upon the accessibility of coal structure

Abstract: This paper is concerned with the colloidal gel nature of coals and what impacts this has upon several properties of practical significance. Water is shown to be a good swelling agent for coals ranging in rank from lignites up to high-volatile bituminous, and the coals shrink when dried from the as-mined state. Shrinkage upon drying is correlated by volumetric shrinkage (%) = 0.863 (moisture content, wt%)-0.162. Shrinkage of this magnitude suggests that measurements of «surface areas» of dried coals will provide an erroneous estimate of true accessibility of coal structure. In addition, the presence of moisture in the structure of coals serves to significantly enhance the rate of uptake of solvents by the coal

Pyrolytic Degradation Studies of a Coal-Derived and a Petroleum-Derived Aviation Jet Fuel

Abstract: The future high-Mach aircraft requires advanced jet fuel with high stability in rigorous thermal environments. In this work high-temperature thermal stability of two JP-8 type jet fuels, a petroleum-derived JP-8P and a coal-derived JP-8C was studied by stressing in closed reactors at 450°C under 0.7 MPa of N 2 for periods ranging from 0.5 to 16 h. The extents of fuel degradation in terms of liquid depletion, gas formation, and solid deposition were always higher with JP-8P than with JP-8C. There appeared an induction period for solid formation, which was longer for JP-8C than for JP-8P

Activated Carbons from CO2 Partial Gasification of Eucalyptus Kraft Lignin

Abstract: The behavior of eucalyptus kraft lignin as activated carbon precursor is investigated. The development of porosity upon C02 partial gasification at 1073 and 1123 K of low-temperature precarbonized kraft lignin has been studied. Increase of micropore volume and broadening of micropore size distribution takes place as activation proceeds. At intermediate burn-off, corresponding to an overall yield of about 25 % , a substantial development of mesoporosity is already observed. Macroporosity becomes important at higher activation degrees. The development of apparent surface area compares favorably, in an overall yield basis, with the reported for lignocellulosic materials upon physical activation. In the case of kraft lignin, the evolution of porosity shows a different pattern with a higher contribution of meso and macroporosity. The presence of S in the activated carbons is negligible, and the final ash content is easily reduced up to below 2 % by simply washing with dilute H&O4 aqueous solution. The reactivity curves for C02 gasification of low-temperature precarbonized kraft lignin have been obtained at differenttemperatureswithin the 1023-1173 K range. The reactivity values are indicative of significant catalytic effect which can be attributed to the presence of finely distributed Na, the major metallic component of the inorganic impurities. This effect becomes more relevant at high conversion values where a higher Na/C atomic ratio is reached. No saturation is observed at least up to X - 0.95, most probably as the result of the aforementioned fine distribution of Na. Apparent activation energy values in the range of 212-239 kJ/mol have been obtained, the lower values corresponding to higher conversions.

Simulation of ash deposit growth in a pulverized coal-fired pilot scale reactor

Abstract: A model has been developed to relate the deposition behavior of ash under slagging conditions to boiler operating conditions and coal composition data. This model has been incorporated into a comprehensive combustion code and used to investigate the effects of ash deposition rate, thermal conditions, and ash chemistry on slag growth in a pilot-scale combustor. Results for simulated deposits from a coal blend fired at 3.7 MBtu/h showed a relatively high liquid fraction corresponding to denser and presumably stronger deposits. The same coal blend fired at a lower rate produced deposits which were less dense because of the lower temperatures and heat flux levels in the combustor, as well as the lower ash deposition rates

Nondestructive determination of trace element speciation in coal and coal ash by XAFS spectroscopy

Abstract: The environmental impact of specific trace element species in coal utilization and waste disposal depends not only on the abundance but also on the form(s) of occurrence of the element present in coal and coal ash. While there are a number of analytical methods for determining the abundance of trace elements in coal and ash, there are very few methods available for determining the form of occurrence (speciation) of a trace element in such materials at abundances as low as 10 ppm. In this report, the potential of XAFS spectroscopy for trace element speciation is demonstrated by means of measurements on two environmentally important trace elements, arsenic and chromium, in coal and ash

Nickel and Vanadyl Porphyrins in Saudi Arabian Crude Oils

Abstract: This study reports the isolation and characterization of nickel and vanadyl porphyrins in the residue (535 °C+) and asphaltenes from Arabian Heavy crude oil. The residue was obtained by distillation of crude oil, whereas the asphaltenes were precipitated by n-heptane from the crude oil. Metalloporphyrins were first extracted from the residue and the asphaltenes. The nickel porphyrins were separated from vanadyl porphyrins by means of adsorption chromatography on silica gel and alumina using solvents of increasing polarity. The chromatographic separation process was monitored by ultraviolet-visible spectrophotometry. Both nickel and vanadyl porphyrins were identified and characterized by ultraviolet-visible spectrophotometry and mass spectrometry

Pyrite removal from kerogen without altering organic matter: the chromous chloride method

Abstract: The standard hydrochloric/hydrofluoric acid treatment used to remove most minerals in kerogen preparation often leaves abundant pyrite. This pyrite is a major obstacle to establishing elemental composition and functional group distributions in kerogen by both chemical and spectroscopic techniques. Quantitative pyrite removal by other conventional means such as nitric acid, lithium aluminum hydride, and sodium borohydride has not been possible without objectionable alterations of the organic matter. Experiments reported here demonstrate that acidic chromous chloride reduction can remove pyrite quantitatively without causing significant alteration of the organic matter

Structural characterization of coal-tar and petroleum pitches

Abstract: «Average structure» data for coal-tar and petroleum (Ashland A-240) pitches are reported, based on NMR spectroscopy combined with elemental and molecular weight analyses. The average structure of both coal-tar and A-240 pitches indicates that they have similar sized aromatic units. The major difference is the much higher degree of aromatic substitution in petroleum pitch. The «average» petroleum pitch molecule contains two methyl and one ethyl group, with one in two molecules containing a ring-joining methylene group. However, the average coal-tar pitch molecule contains only one methyl and one ring-joining methylene group for every two molecules

An upgrading process through cavitation and surfactant

Abstract: Catalytic cracking is the most effective procedure for upgrading heavy oil in industrial practices, but high temperatures (400-500 °C) and high pressures (maybe up to 100 atm) are still necessary. They place constraints and limitations on the reactor material and on safety considerations. Asphaltenes, contained in the heavy oil, are not only refractory for cracking but can also deactivate the catalyst. In this investigation, we address a process to convert asphaltenes into gas oil and resins at room temperature and atmospheric pressure. Ultrasound provides the high temperature and pressure at localized cavitation centers, and surfactant prevents the agglomeration of the asphaltenes

NO and N2O formation for coal combustion in a fluidized bed: Effect of carbon conversion and bed temperature

Abstract: The conversion of fuel nitrogen to NO and N 2 O have been determined in a small-scale fluidized bed. Small batches of coal particles were used, permitting the separation of the formation reactions within individual particles from subsequent destruction or re-formation on other particles. From time-resolved measurements of the concentrations of NO, N 2 O, CO 2 , CO, and CH 4 , the instantaneous fractional conversions of coal nitrogen to NO and N 2 O as a function of fractional char burnout were obtained for bed temperatures between 975 and 1148 K. The conversion to N 2 O decreases with increasing temperature, whereas that to NO erhibits a maximum between 1023 and 1095 K. As a particle burns out, the instantaneous conversion to N 2 O decreases, whereas the reversed trend is seen for NO

Characterization of intermediates in the microbial desulfurization of dibenzothiophene.

Abstract: The desulfurization of dibenzothiophene by Rhodococcus rhodochrous IGTS8 gave several microbial products which were isolated by extraction from the culture media. Two key compounds that were proposed as intermediates in the 4S pathway, for dibenzothiophene desulfurization, are 2'-hydrorybiphenyl-2-sulfinic acid and 2'-hydrorybiphenyl-2-sulfonic acid. By utilizing a gas chromatographic/Fourier transform infrared/mass spectrometry (GC/FTIR/MS) system, these compounds were identified in the sultine form, dibenz[c,e] [1,2]orathiin 6-oxide, and sultone form, dibenz[c,e]-[1,2] oxathiin 6,6-dioxide, respectively

A comprehensive three-dimensional model for simulation of combustion systems: PCGC-3

Abstract: A generalized, three-dimensional combustion model has been developed to simulate large-scale, steady-state, gaseous and particle-laden, reacting and nonreacting systems. The model, which is based on an earlier two-dimensional model, has been applied to turbulent, combustion systems, including pulverized-coal systems. It uses an Eulerian framework for the gas phase and a Lagrangian framework for the particles. The code assumes equilibrium gas-phase chemistry and couples the turbulent flow field with the chemical reactions by integrating the equations over a probability density function. The model uses advanced numerics and a differencing scheme capable of solving the large computational meshes required to simulate practical furnaces. Convective and radiative heat transfer are also modeled

Effect of pyrolysis conditions on the macropore structure of coal-derived chars

Abstract: The effect of pyrolysis heating rate and particle size on the macropore structure of coal-derived chars was studied and quantified. A procedure combining optical microscopy with digital image analysis was developed first to characterize macropores with sizes larger than 1 μm. With the new approach, the macroporosity and the total macropore surface area of char samples can be measured without any restricting assumptions about the geometrical shape of the pores. The digital imaging procedure was then applied to analyze the structural properties of char samples produced from Illinois No. 6 and lignite coals

Turbulent dispersion of particles: The STP model

Abstract: A mathematical description of the stochastic transport of particles (STP) model for particle dispersion in turbulent flows is presented. The STP model is based on established theories of stochastic process modeling. The parameters of the model include physical properties of the particle (diameter and mass) and a description of the turbulent characteristics (mean velocities with rms fluctuations and their residence-time correlations) of the fluid phase in which the particles are dispersed. The model includes no adjustable parameters in the sense of calibration factors. It is independent of any particular turbulence model, but estimates of its parameters from information available from the common k-{var_epsilon} turbulence model are presented. Elements of the STP model are compared with exact solutions of the diffusion equation, alternative dispersion models, and experimental data collected under well-defined conditions. The STP model reproduces the exact solutions when both are based on consistent assumptions. Suggested approximated terms in the model also reproduce the experimental data nearly within its error under simple flow conditions. The STP model describes the origin of more complex behavior (counter-gradient diffusion, for example) and has the potential of describing it if sufficient detail about the gas-phase turbulence is known.

Predicting ash behavior in utility boilers

Abstract: In recent years, significant advances have been made in the development of methods to predict ash behavior in utility boilers. This paper provides an overview of methods used to assess and predict ash formation and deposition. These prediction methods are based on a detailed knowledge of ash formation and deposition mechanisms that has been obtained through bench, pilot, and field testing and detailed coal and ash characterization. The paper describes advanced methods of coal and ash analyses and the advantages of these methods over conventional methods. The advanced coal characterization methods provide sufficient data to predict size and composition distribution of fly ash

Analysis of Sulfur Compound Types in Asphalt

Abstract: The project evaluated analytical methods for determination of sulfur compound types in asphalt and to obtain results on asphalts from the SHRP (Strategic Highway Research Program) Reference Library. Methods were applied to whole asphalts and fractions obtained through liquid chromatographic separations. The distribution of sulfur types varied with asphalt source and within fractions from a given asphalt. Sulfur types determined were as follows: sulfoxides (infrared ); aliphatic sulfides (tetrabutylammonium periodate oxidation); aromatic sulfides (total sulfides - aliphatic sulfides); and thiophenes (by difference; or direct via oxidation with hydrogen peroxide). Sulfur types present at negligible concentrations in the asphalts tested include thiols, sulfones, and sulfonic acids.

Development of a gas-sweep facility for the direct capture of pyrolysis tars in a variable heating rate high-pressure wire-mesh reactor

Abstract: A variable heating rate high-pressure wire-mesh pyrolysis/hydropyrolysis reactor has been configured to permit the continuous passage of gas through the sample holder in order to remove volatiles away from the reaction zone. The introduction of the gas-sweep facility, hitherto not available at elevated pressures, was made possible by the development and installation of a flow-smoothing section beneath the sample holder. This served to reduce turbulence within the gas stream and even out heat transport from the wire-mesh to the flowing gas. Positive tar recovery was achieved at pressures between 2.5 and 150 bar, at heating rates ranging from 1 to 2500 K s −1 and temperatures up to 850 °C

Structure and dispersion of iron-based catalysts for direct coal liquefaction

Abstract: Mossbauer spectroscopy, XAFS spectroscopy, and a number of complementary techniques have been used to investigate the structure and size dispersion of a variety of ultrafine iron-based DCL catalysts. In the as-prepared state, iron that was chemically incorporated into the coal exhibited an FeOOH structure, while iron catalysts prepared separately had the Fe 2 O 3 structure. The Mossbauer spectra exhibited pronounced superparamagnetic relaxation effects. The relaxation spectra could be analyzed at several temperatures to determine size distributions for the catalyst particles. The resulting size distributions were in the nanometer range and agreed reasonably well with size information obtained by SQUID magnetometry, STEM, and XRD

Nitrogen chemistry of kerogens and bitumens from x-ray absorption near-edge structure spectroscopy

Abstract: X-ray absorption near-edge structure (XANES) spectroscopy studies have been conducted on several different kerogens and bitumens to identify all the different nitrogen chemical structures present. Virtually all of the nitrogen is present in aromatic forms; pyrroles are the most dominant type, followed by pyridines, pyridones, and aromatic amines. A considerable amount of porphyrinic nitrogen, characterized by significant spectral effects, is found in one of the bitumens. The pyridone fraction in the kerogens and bitumens is much larger than in petroleum asphaltenes, suggesting that petroleum generation is accompanied by the loss of pyridone, possibly by conversion to pyridines

Linear eddy modeling of turbulent combustion

Abstract: The use of the linear eddy mixing model in application to reacting flows is discussed for several different combustion geometries. The unique feature of this model is the explicit distinction made among the various physical processes (convection, diffusion, and reaction) at all scales of the flow. This is achieved by resolving all relevant scales of motion through a reduced, one-dimensional statistical description of the scalar field in a linear domain. The advantages of this modeling approach over other conventional modeling approaches are pointed out. Applications to both «stand-alone» formulations and subgrid formulations for use in large eddy simulation (LES) are discussed

Geochemical origins of sedimentary benzoporphyrins and tetrahydrobenzoporphyrins

Abstract: Complex mixtures of metalloporphyrins are associated with organic-rich sediments Although some of these petroporphyrins have been correlated with known biological pigments, the origins of certain structures are obscure Benzoporphyrins and tetrahydrobenzoporphyrins, two minor families of geological tetrapyrroles, have been isolated from numerous oil shales and petroleums but the origins of these molecular fossils are poorly understood A number of possible pathways for the geochemical formation of benzo- and tetrahydrobenzoporphyrins are discussed The data presently available favors a Diels-Alder cycloaddition mechanism between putative divinylchlorophyll and quinone precursors for the formation of these compounds

Relevance of cleavage of strong bonds in coal liquefaction

Abstract: Almost ten years ago we proposed that cleavage of bonds too strong to undergo simple thermolysis but which are cleaved by the mediation of solvent or solvent-derived radicals may be an important contributor to the liquefaction of coals. In this paper we discuss the process implications of this revised view. We show how this picture continues to help rationalize many otherwise inexplicable observations in fossil fuel conversion technology. These observations include the breaking of nonhomolyzable bonds in grafted and doped coals, the ineffectiveness (in liquefaction) of nonhydroaromatic radical scavengers, the effectiveness of nondonor polycyclic aromatic hydrocarbons (PAH), the «activation» of cyclic aliphatics by PAH, increasing hydrogen utilization efficiency observed with added PAH, and the decrease in gas formation observed at lower temperatures or with added PAH

Determination of nonprotonated aromatic carbon concentrations in coals by single pulse excitation carbon-13 NMR

Abstract: It is now generally accepted that single pulse excitation (SPE) or Bloch decay measurements are essential for obtaining reliable aromaticity values for coals by solid-state 13 C NMR although such measurements are considerably more time consuming than cross-polarization (CP). Just as with normal CP, SPE can be combined with dipolar dephasing (DD) to derive nonprotonated aromatic carbon concentrations. This approach has been applied to four of the Argonne premium coal samples (APCS, N. Dakota lignite, Wyodak, Illinois no. 6, and Pocahontas), two vitrinite concentrates from UK bituminous coals, and an anthracite. The results have been compared with those obtained from CP and, for the APCS, nonprotonated aromatic carbon concentrations derived indirectly from FTIR and 1 H CRAMPS