Showing papers in "Energy & Fuels in 1992"

Chemical percolation model for devolatilization. 3. Direct use of carbon-13 NMR data to predict effects of coal type

Abstract: ~~ ~~ ~ ~ ~~ The chemical percolation devolatilization (CPD) model describes the devolatilization behavior of rapidly heated coal based on the chemical structure of the parent coal. Percolation lattice statistics are employed to describe the generation of tar precursors of finite size based on the number of cleaved labile bonds in the infinite coal lattice. The chemical percolation devolatization model described here includes treatment of vapopliquid equilibrium and a cross-linking mechanism. The cross-linking mechanism permits reattachment of metaplast to the infinite char matrix. A generalized vapor preasure correlation for high molecular weight hydrocarbons, such as coal tar, is proposed based on data from coal liquids. Coal-independent kinetic parameters are employed. Coal-dependent chemical structure coefficients for the CPD model are taken directly from 13C NMR measurements, with the exception of one empirical parameter representing the population of char bridges in the parent coal. This is in contrast to the previous and common practice of adjusting input coefficients to precisely match measured tar and total volatiles yields. The CPD model successfully predicts the effects of pressure on tar and total volatiles yields observed in heated grid experiments for both bituminous coal and for lignite. Predictions of the amount and characteristics of gas and tar from many different coals compare well with available data, which is unique because the majority of model input coefficients are taken directly from NMR data and are not used as empirical fitting coefficients. Predicted tar molecular weights are consistent with size-exclusion chromatography (SEC) data and field ionization mass spectrometry (FIMS) data. Predictions of average molecular weights of aromatic clusters as a function of coal type agree with corresponding data from NMR analyses of parent coals. The direct use of chemical structure data as a function of coal type helps justify the model on a mechanistic rather than an empirical basis.

Opportunities for biomass pyrolysis liquids production and upgrading

Abstract: Considerable work has been carried out on flash pyrolysis processes for liquid fuel production from biomass. The crude pyrolysis liquid may be used directly to substitute for conventional fuels or in more demanding applications such as turbines where the quality may not be sufficiently high to ensure trouble-free operation. In this latter case, upgrading to a higher quality fuel may be necessary, and two routes are available: hydrotreating and zeolite synthesis of hydrocarbons

Measuring CO2 Minimum Miscibility Pressures: Slim-Tube or Rising-Bubble Method?

Abstract: Determinations of carbon dioxide minimum miscibility pressures (MMP) using a slim-tube apparatus were compared with those using a rising-bubble apparatus (RBA). MMPs were determined for 12 different oils, with gravities varying from 34 to 51 °API. The results were found to compare very well when using a specific criterion for the slim-tube MMP. Although the slim-tube method is often referred to as the industry standard, there is no standard design, no standard operating procedure, and no standard criterion for determining MMPs with the slim tube. It is shown that the RBA is faster and more reliable than the slim tube for determining MMP. Bubble behavior is described for both the vaporizing and condensing gas processes.

Studies on the reduction of nitric oxide by carbon: the nitric oxide-carbon gasification reaction

Abstract: The heterogeneous reduction od NO by carbon was studied in a thermogravimetric analysis system, employing both pseudosteady and transient reaction methods. The reaction was studied at temperatures from near ambient up to 1073 K, and at NO partial pressures in the range 1.01-10.1 kPa. A relatively pure carbon derived from phenolic resin was studied. gaseous products of rection were measured. The gasification of carbon by NO involves two parallel processes: (1) somewhat slow desorption of relatively stable surface complexes; (2) processes involving NO attack on active unoccupied sites that results in essentially immediate desorption of gaseous products. The first process controls the overall gasification rate at lower temperatures and is governed by a distribution of desorption activation energies, involving mainly surface oxides that yield CO upon desorption

Semi-quantitative FTIR analysis of a coal tar pitch and its extracts and residues in several organic solvents

Abstract: The infrared spectra from 650 to 4000 cm −1 and their semiquantative analysis for a coal tar pitch and extracts and residues obtained when this coal tar pitch was treated with organic solvents are discussed. This analysis supplies excellent information on the concentration of the several functionalities in the samples. The treatment with solvents provides carbonaceous materials with different concentrations of the same functionalities which can be very useful in the study of relationships between composition, properties, and behavior. The different aromaticity of the samples, in relation with the hydrogen, are discussed. A preponderance of aromatic hydrogens, distributed mainly in structures containing four neighboring aromatic C-H bonds, and an appreciable amount of hydrogens attached to saturated carbon atoms, even in the insoluble fractions, can be observed

Computer simulation of the molecular structure of bituminous coal

Abstract: Molecular modeling techniques have been used to study the three-dimensional structure and the energetics of the Given, Wiser, Solomon, and Shinn molecular models of bituminous coal. These studies demonstrate the importance of van der Waals (vdW) interactions and hydrogen bonding in the formation and stabilization of coal macromolecular structure. VdW interactions are responsible for most of the stabilization in these models, and a tendency for the relative importance of vdW interactions to increase with increasing rank is indicated

Coal devolatilization during rapid transient heating. 2. Secondary pyrolysis

Abstract: This study utilizes the radiant coal flow reactor described in part 1 in an operating mode which independently regulates the extent of secondary pyrolysis. Product distributions for transient secondary pyrolysis at nominal heating rates of 10 4 K/s are reported for subbituminous and hvA bituminous coals, to characterize the transformations involving oxygen, nitrogen, and aliphatic functional groups as coal volatiles are pyrolyzed into soot. They show that the sum of the yields of tar, oils, and soot remains invariant at the ultimate yields of tar plus oils for primary devolatilization

Structural features of Alberta oil sand bitumen and heavy oil asphaltenes

Abstract: Ru ion catalyzed oxidation (RICO) has been used to probe the structural details of asphaltene molecules from Athabasca bitumen. The ability of RICO to remove nearly quantitatively aromatic carbons while leaving aliphatic and naphthenic structures essentially unaffected has been exploited for the quantitative determination of the following structural features : (1) the distribution of n-alkyl chains attached to aromatic carbons with respect to chain length, total number of n-alkyl chains and the number of carbon atoms in them; (2) the distribution of polymethylene bridges connecting two aromatic units with respect to bridge length, total number of bridges, and the number of carbon atoms in them; (3) the fractional amount of total sulfur present as saturated sulfides

Development of zinc ferrite sorbents for desulfurization of hot coal gas in a fluid-bed reactor

Abstract: Advanced integrated gasification combined cycle (IGCC) power generation systems require the development of high-temperature, regenerable, desulfurization sorbents capable of removing hydrogen sulfide from coal gasifier gas to very low levels. Fluidized-bed desulfurization reactors offer significant potential advantages in IGCC systems compared to fixed- and moving-bed reactors because of their ability to control the highly exothermic regeneration involved. However, a durable, attrition-resistant sorbent in the 100- to 300-μm-size range is needed. Thus, the objective of this investigation was to identify and demonstrate methods for enhancing the long-term chemical reactivity and mechanical strength of zinc ferrite, a leading regenerable sorbent, for fluidized-bed applications

Chemical structure of bituminous coal and its constituting maceral fractions as revealed by flash pyrolysis

Abstract: To study the relationships between the chemical structures of coals, coal macerals, and their precursors (plant tissues), a high-volatile bituminous Upper Carboniferous coal and its constituting maceral fractions, cutinite, resinite, sporinite, vitrinite, pseudovitrinite, semifusinite, and fusinite, were investigated by Curie point pyrolysis−gas chromatography and Curie point pyrolysis−gas chromatography−mass spectrometry

A structural model for lignin-derived vitrinite from high-volatile bituminous coal (coalified wood)

Abstract: Using data from elemental analyses, solid-state 13 C NMR, and pyrolysis/gas chromatography/mass spectrometry, a structural model for coalified wood of high-volatile bituminous coal rank was constructed. Considering the fact that the vitrinite was derived from lignin, we utilized a model of lignin as a template upon which the coal structure is based. The chemical structural information derived from comparisons among coalified gymnospermous wood samples ranging in rank from subbituminous to high-volatile C bituminous coal provided the basis for constructing the model

Coal devolatilization during rapid transient heating. 1. Primary devolatilization

Abstract: Our new flow experiment heats entrained coal suspensions by radiation from a near-blackbody enclosure, not by a preheated stream. Since the entrainment stream is transparent to radiation, it can be made to remain much cooler than the suspension. Pristine products which have been quenched as soon as they were expelled can be recovered or, alternatively, the extent of secondary chemistry can be regulated at will. The furnace system also includes rapid quenching to resolve reaction times on a scale of several milliseconds, aerodynamic segregation of particulate, aerosol, and gaseous products, and analyses for C 1 −C 4 hydrocarbons, oils, CO, CO 2 , H 2 O, NO, and HCN

Effects of ion-exchanged calcium on brown coal tar composition as determined by Fourier transform infrared spectroscopy

Abstract: In order to investigate the effect of ion-exchanged metals on the yield and composition of coal tar, we have pyrolyzed raw and calcium-exchanged Yallourn brown coal in a fluidized bed reactor at temperatures of 600 to 1000°C and have analyzed the product tars by Fourier transform infrared (FTIR) spectroscopy. At the lower temperatures (600-800°C), tar yields are lower for the calcium form coal than for the raw coal, indicating that the calcium either promotes tar conversion to char or tightens the coal structure and makes it difficult for larger tar molecules to escape

Carbon monoxide oxidation in supercritical water : the effects of heat transfer and the water-gas shift reaction on observed kinetics

Abstract: Oxidation in a supercritical water environment is an efficient method for treating wastes without formation of harmful byproducts. Complete oxidation of organics can be limited by conversion of carbon monoxide to carbon dioxde. The kinetics of carbon monoxide oxidation has been studied previously (Helling, R. K.; Tester, J. W. Energy Fuels 1987, 1, 417), but efforts to establish kinetic parameters for the direct oxidation pathway (CO+1/2O 2 →CO 2 ) were complicated by the reaction of carbon monoxide with water via the water-gas shift reaction pathway (CO+H 2 O→CO 2 +H 2 ) during preheating of the reactor feeds

Activated carbons from Spanish coals. 1. Two-stage carbon dioxide activation

Abstract: A two-stage (pyrolysis and CO 2 activation) treatment of Spanish coals has been studied in relation to the preparation of activated carbons. The paper analyzes three different aspects : (i) coal precursor effect (from anthracite to high-volatile bituminous), (ii) mineral matter content, and (iii) pore volume and surface area development upon activtion. The coal rank influences the pyrolysis behavior, the characteristics of the char (e.g., porosity), the rate of activation, and the characteristics of the resulting activated carbon. The pyrolysis and combustion behavior of the chars, deduced from TG-DTA curves, have been related to the subsequent porosity development upon activation. Chars showing a uniform combustion are better precursors than those presenting a bifurcated DTA peak and two TG steps

Effects of refinery processes on biological markers

Abstract: Concentrations of biomarkers remaining in straight-run refinery products of crude oil feedstock are mainly controlled by relative volatility. Thermal cracking exerts a second-order control on biomarker compositions of these products. Factors controlling biomarker concentrations and distributions in processed materials are more complex and include volatility, thermal stability, generation from heavier precursors, and the effects of catalysts and hydrogen pressure. Differential volatility of compounds within each biomarker class and sharp temperature gradients defining each distillation cut complicate interpretation of source- and maturation-dependent biomarker parameters used by petroleum exploration geochemists

In situ x-ray absorption fine structure spectroscopy investigation of sulfur functional groups in coal during pyrolysis and oxidation

Abstract: Sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy has been utilized to conduct the first direct characterization and quantification of sulfur functional groups in coal during in situ high-temperature oxidation and pyrolysis. The behavior of all major sulfur forms during such treatments was derived for two US bituminous coals and a low-rank Australian brown coal from least-squares analysis of sulfur K-edge XANES spectra taken at constant temperatures up to 600°C. During pyrolysis, pyrite began to convert to pyrrhotite at temperatures above 400°C

Single-Pulse Excitation 13C NMR Measurements on the Argonne Premium Coal Samples

Abstract: In view of the results of this study and the well-documented inherent problems with cross-polarization (CP) 13 C NMR concerning quantification for coals, it is now clear that the more time-consuming single-pulse excitation (SPE) or Bloch decay measurements are essential for obtaining aromaticities and other carbon skeletal parameters for coals. SPE 13 C NMR has been carried out on the Argonne Premium Coal Samples at both a low and a high field strength (25 and 75 MHz, respectively), high-speed magic angle spinning (13 kHz) being used to suppress spinning sidebands at the higher field

Composition of heavy petroleums. 4. Significance of the extended atmospheric equivalent boiling point (AEBP) scale

Abstract: The first two papers in this series (Energy fuels 1987, 1, 2; 1988, 2, 597) discussed the variation of the chemical composition of heavy petroleum fractions with increasing atmospheric equivalent boiling point (AEBP) up to about 760 o C (1400 o F). The third paper (this issue) described three correlations developed for the calculation of AEBPs from molecular weight and one more measurement, either specific gravity or H/C ratio or refractive index. In this paper we discuss the value of extending the AEBP scale to encompass the entire heavy crude oil, down to the «bottom of the barrel». The AEBP distribution curves, extending up to approximately 1650 o C (3000 o F), allow the comparison of heavy petroleums and their fractions on a common, rational basis

Fouling of convection heat exchangers by lignitic coal ash

Abstract: Ash deposits formed at moderate temperatures (1100-1300 K) in the convective sections of utility boilers firing coals containing lignitic ash are associated with the formation of sticky particles following condensation of sodium sulfate from the vapor phase at 1200-1300 K The deposits are enriched in calcium, due to the abundance of calcium among the particles impacting and sticking and the low melting temperature of mixtures of calcium, magnesium, and sodium sulfates Because the formation of these deposits occurs only in a limited range of gas temperatures, approximately from the dew point to the melting temperature of sodium sulfate, they are not observed during experiments in which deposition is accelerated by increasing the temperature to values typical of furnace exit gas or higher

Composition of heavy petroleums. 3. An improved boiling point-molecular weight relation

Abstract: The first two papers in this series (Energy Fuels 1987, 1, 2; 1998, 2, 597) introduced the concept of extended atmospheric equivalent boiling point (AEBP) to molecular distillates of petroleum residues. In this paper we describe three correlations between AEBP and M n (number average molecular weight) by means of a third variable, where the latter may be (a) specific gravity, (b) H/C ratio, or (c) refractive index. These correlations, we believe, are better than earlier ones between mid-boiling point, molecular weight (MW), and specific gravity. By applying them to atmospheric residue fractions obtained by moelcular distillation we have doubled the range from a previous upper limit of less than 450 to 950 MW, or from about 1000 o to over 1300 o F AEBP

An empirical model for coal fluidity based on a macromolecular network pyrolysis model

Abstract: We have developed a phenomenological model for coal fluidity based on a macromolecular network model for the decomposition and condensation of the network under the influence of bond breaking and cross-linking reactions. The macromolecular network model is the previously published FG-DVC model of coal pyrolysis. Its employs a network consisting of aromatic ring clusters linked by bridges. The bond scissions are described by a single first-order reaction with a distribution of activation energies

Maturation of petroleum source rocks. 1. Changes in kerogen structure and composition associated with hydrocarbon generation

Abstract: Kerogens ranging from immature to overmature with respect to hydrocarbon generation have been analyzed by various solid-state spectroscopy techniques, by pyrolysis/gas chromatography, and pyrolysis/gas chromatography/mass spectrometry in order to characterize changes in molecular composition. The kerogens analyzed were isolated from organic-rich calcareous shales of the Upper Devonian Duvernay Formation of Western Canada and represent marine Type II kerogens

Determination of kerogen activation energy distribution

Abstract: An experimental procedure for determining the activation energy distribution of isolated organic matter from source rocks is described. The method uses a nonisothermal pyrolysis technique coupled with computer analysis of the data. The computer analysis allows three options for the unkown distribution: a single activation energy for homogeneous organic matter, a log normal distribution, or a discrete distribution. In the majority of cases, the discrete distribution is superior to both the single-energy treatment and log normal distribution. Estimation of the discrete distribution is mathematically an ill-posed problem, and attention is given to an algorithm that combats the numerical difficulties

Catalytic steam gasification of coals

Abstract: Two bituminous and one subbituminous coals have been gasified with steam in the presence of calcium-potassium oxide or calcium-sodium oxide catalysts at 900 K. The coals gasify at better rates than the corresponding chars or than graphite and at better rates than in the presence of alkali-metal oxides (KO x or NaO x ). Hydrogen and carbon dioxide are the primary gaseous products with only traces of methane found. The catalyst is used in amounts of about 1% of the carbon in the coal and may not have to be recovered from the ash. The catalytic gasification mechanism is believed to be the same for all carbonaceous material (coals, chars and graphite) gasified in this and previous work

Alkali metal catalyzed CO2 gasification of carbon

Abstract: The mechanisms for CO 2 gasification of carbon with alkali metal catalysts were investigated with pulse reaction and temperature-programmed desorption techniques. Details of oxygen-transfer reactions between oxidant and alkali metal, and between alkali metal oxygen complex and carbon, were discussed. It is suggested that two processes are involved in both catalyst oxidation and catalyst reduction steps. The two active sites, alkali metal cluster (or aggregated metal) and dispersed alkali metal which is a precursor for the cluster, exist for all alkali metals. On these sites, fast and slow oxidation and reduction cycles proceed. However, the characteristics of these sites are quite different among the alkali metals

Spectroscopic Analyses of Aromatic-hydrocarbons Extracted From Naturally and Artificially Matured Coals

Abstract: Experimental simulation of Mahakam delta (Indonesia) coals maturation has been carried out in a confined system under pressure. Chloroformic extracts have been fractionated by liquid chromatography. Aromatic hydrocarbons have been concentrated and analyzed by FTIR spectroscopy (Nicolet 20 SX B), high-resolution proton NMR (Brucker AM 500 MHz), and synchronous excitation-emission UV fluorescence (Perkin-Elmer LS 50). Band assignment was made in order to take into account the evolution of the proton NMR, FTIR, and synchronous UV fluorescence spectra with respect to bibliographic data and spectral resolution. Results have been compared to those of a natural homogeneous series of coals of increasing rank. The corrected organic carbon content (% COC = % C x 100/(% C + % H + % O + % N)) was chosen as a common maturity index for both natural and artificial series. The progressive removal of aliphatic chains, the increase in the proton aromaticity, and the structural rearrangement are similar for both series. However, some significant discrepancies are noticed between the artificial and natural series. They mostly concern the rate of aromatization, the intensity of ring condensation, and the amount of extractable hydrocarbons.

Flash pyrolysis of coal following thermal pretreatment at low temperature

Abstract: A new and simple pyrolysis method is presented in which the coal preheated at 150-200 o C for 1 h is pyrolyzed successively without exposure to air. This method was developed based on the experimental fact that the hydrogen bond of coal is broken thermally at 150-200 o C. When eight coals of different rank were pyrolyzed in an inert atmosphere using a Curie-point pyrolyzer, the conversion and the tar yield increased by 3-4% for several lower rank coals as compared with the nontreated coals. These increases were found to be brought about by the suppression of water forming cross-linking reactions, which were effected by the breakage of the hydrogen bond prior to the pyrolysis. A Japanese coal was also pyrolyzed by use of a free-fall pyrolyzer in an inert atmosphere, in which the coal preheated at 200 o C while traveling a screw feeder was continuously fed to the pyrolyser

Effect of sulfur dioxide removal by limestone on nitrogen oxide (NOx) and nitrous oxide emissions from a circulating fluidized bed combustor

Abstract: The effect of limestone addition for SO 2 removal on emissions of NO x and N 2 O was evaluated with a laboratory-scale circulating fluidized bed combustor. It was found that NO x emission increased with increasing SO 2 removal whereas N 2 O emission decreased. The rates of HCN oxidation, NH 3 oxidation, NO reduction by CO, N 2 O decomposition, and SO 2 removal over limestone were evaluated with a fired bed reactor. The major product of HCN oxidation was NO. N 2 O formation was observed slightly among the product of HCN oxidation