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The first objective of this work was to compare the pyrolysis behavior of coals coming from different geographic locations (South Africa, South America, Europe, Australia, and North America). This preliminary study was limited to the kinetics of methane and tar evolution, with data on additional species to be reported in a separate publication. The second objective was to examine the possible relationship between tar and methane evolution during pyrolysis. This study was done by employing a thermogravimetric analyzer coupled with a Fourier-transform infrared spectrometer (TG-FTIR). The evolution curves for 35 coals of different elemental compositions were measured at three different heating rates (10, 30, and 100 K/min). Pyrolysis kinetics were described using a simple first-order reaction model. The technique, first proposed by Kissinger, is based on the variation of the temperature at which a volatile species evolution rate is a maximum (Tmax) as a function of the heating rate. The TG-FTIR data for tar evolution reveal a generally consistent behavior for coals from different parts of the world, showing increasing activation energies with increasing coal rank. The same correlation is also true for methane, although the slope of the activation energy versus carbon content curve is rather flat, at least up to about 90% carbon content. The values of activation energies for methane evolution were found to be lower in the case of the Argonne coals, as compared with the non-US coals. A study of the temperatures at which the evolution of methane and tar begins (Tini), and the temperatures at which the evolution rates reach a maximum (Tmax), reveals a correlation between the Tini for methane and Tmax for tar. This may be due to the fact that both tar and methane evolve as a result of similar reactions involved in the breakup and recombination of the coal macromolecular network.

The subject of this paper is mitigation of the undesirable side-effects of selective non-catalytic reduction (SNCR) and selective catalytic reduction (SCR): ammonia slip, residual NO x , and N 2 O emissions. The use of microwave-plasma discharge within the flue gas was explored as a potential pollution-control method. The key issues addressed were: (1) N 2 O, NH 3 , and NO removal efficiencies; and (2) sustaining a stable plasma at atmospheric, or close to atmospheric, pressure. In non-oxidizing atmospheres, removal efficiencies were always close to 100% for all species. In the presence of oxygen, however, appreciable amounts of nitric oxide and ammonia were formed. Methods leading to preventing these undesirable effects were examined. In a number of runs, stable plasma operation was attained at pressures close to atmospheric.

Over the next decade there will be a renewed emphasis on the use of biomass as a fuel and the cofiring of coal and biomass materials. In view of the tremendous diversity of biomass feedstocks, a great need exists for a robust, comprehensive model that could be utilized to predict the composition and properties of pyrolysis products as a function of feedstock characteristics and process conditions. The objective of this work was to adapt an existing coal pyrolysis model, the Functional Group-Depolymerization, Vaporization Crosslinking (FG-DVC) model, and make it suitable for the pyrolysis of biomass. The soundness of this approach is based on numerous similarities between biomass and coal. However, there are important differences, which preclude direct application of the coal model. This work involved: (1) selection of a set of materials representing the main types of biomass, (2) development of a classification scheme, (3) development of a modeling approach based on an extension of a coal pyrolysis model, (4) calibration of the model for a set of standard materials against pyrolysis data taken over a range of heating rates, and (5) validation of the model against pyrolysis data taken under higher heating rate conditions. A streamlined version of the FG-DVC coal pyrolysis model was successfully developed for whole biomass samples and demonstrated to have predictive capability when extrapolated to high heating rate conditions (103 °C/sec). Improvements will be needed in the model to properly account for mineral effects and secondary reactions, and the model has not yet been tested under the very high heating rates that may exist in some combustion devices (104–105 °C/sec).

Radiation pyrometry and thermometry combined with fiber optics provide sensors for determining surface and gas temperatures in otherwise inaccessible locations. However several applications require that temperature measurements be made in the long-wavelength infrared (LWIR) where widely used silica fibers are nontrasmissive. This study involved the development and testing of hollow sapphire fiber-optic radiometric temperature sensors that operate in the LWIR. Hollow sapphire waveguides are suitable for use at high temperatures and transmit in the LWIR: no currently available solid-core fiber offers this combination of features. A prototype fiber-optic radiometric temperature sensor was assembled for the LWIR spectral region, and several experiments were performed to demonstrate the feasibility of developing a system that could be used in gas turbine applications. Open-tip and closed-tip hollow sapphire waveguides were used as the sensor probes and were coupled to an FT-IR spectrometer using hollow glass waveguides. Both types of sensors were tested in laboratory facilities and the closed-tip configuration was also used in a jet engine test rig. The principal findings can be summarized as follows: (1) Open-tip hollow sapphire waveguides were demonstrated to be useful sensors for remote pyrometric temperature measurements in the LWIR. Analysis of calibration data predicted an error level of less that 1% of the reading at 800°C. (2) Closed-tip hollow sapphire waveguides were demonstrated to be useful sensors for radiometric gas temperature measurements in the LWIR. (3) It was determined that interference ence caused by hot H2O and CO2 emission in the open-tip configuration could be eliminated through careful selection of the analyzed spectral region. (4) It was found that interference caused by heating of the waveguide walls in either configuration could be eliminated by limiting the throughput of the optical system.

There have been several studies on the devolatilization of large coal particles under laboratory conditions simulating large-scale fluidized or fixed-bed combustion conditions, all of which demonstrate that the process of devolatization of large coal particles occurs over a much longer timescale than that of pulverized coals under the same conditions. This paper reports the development of a model for large coal particle devolatilization under fluidized and fixed-bed combustion conditions. The model combines a heat transfer model with a general and comprehensive coal devolatilization model, FG-DVC. It inherits the generality of FG-DVC and can be applied to coals of various types without extensive prior knowledge of the coals. This model includes a detailed treatment of coal pyrolysis reactions including the yields of individual gas species, tar yields, and tar molecular weight distributions. The changes in coal physical properties are modeled with the application of Merrick's coal physical property submodels for specific heat and thermal conductivity. Both the convective and radiative heat transfer between the gas phase and coal particles are considered and Gunn's correlation for the surface heat transfer coefficient is used. Model predictions are compared with the data of large coal particle devolatilization measured in fluidized beds and tubular reactors, for particle thermal response, total weight loss, and individual gas evolution rates. In general, the agreement with the data is very good for the particle center temperature and weight loss curves and is fair for the individual gas evolution curves.

An interpolation method was proposed to correlate the input parameters of a coal devolatization model[functional group-depolymerization, vaporization, cross-linking (FG-DVC)] to coals of a wide range of ranks, and it conceptually applicable to other devolatilization models. This method uses a set of well-defined coals (library coals) to form a triangular mesh in the van Krevelen diagram. If an unknown coal is within a triangle formed by three library coals, the model input parameters for this unknown coal can be interpolated from those of the three library coals based solely on the elemental composition. This method extends the FG—DVC model to be able to model any coal that can be interpolated, without the requirement for any additional characterization of the coal. It is also easy to accommodate more library coals so that a wider range of coal types can be covered. The validity of this method was demonstrated by comparing the tar yield measurements and the predictions for 27 coals over a wide range of pressures and heating rates. For most of the coals, the predictions compare very well with the data. For selected coals, data were available on the variation of the yield of total volatiles with pressure and heating rate, and again, good agreement was obtained. The model could be improved by using additional parameters to describe the exchangeable cation content, sulfur content, and/or the maceral composition.

Pyrolysis of lignin is one approach that has been investigated to upgrade this material into higher value products. However, there have been relatively few efforts to quantitatively model these reactions. This paper describes a methodology for modeling lignin pyrolysis which has been extensively developed for related materials like coal. The samples are characterized using pyrolysis experiments under a standard set of conditions, where the products are analyzed by Fourier Transform Infrared (FT-IR) Spectroscopy and Field Ionization Mass Spectrometry (FIMS). Solvent extraction experiments are done to determine the extractables yields and elemental analysis is done to further constrain the model. One lignin, produced from ethanol/water extraction of mixed hardwoods, was selected for the application of this modeling approach. The model was able to qualitatively predict the tar molecular weight distributions and quantitatively predict the variations of the gas and tar evolution rates and yields with heating rate for the calibration set of experiments. The model can be improved by more precise information on lignin structure, crosslinking chemistry, and tar transport mechanisms. It also needs to be validated by simulation of pyrolysis conditions at high heating rates and/or high pressures for which data is currently not available.

A test instrument was developed and used to characterize the changes in the thermal and optical properties of charring polymeric materials when exposed to radiative heat fluxes. The system is based on a bench-top emissometer apparatus, which was developed originally to simultaneously measure the surface temperature and spectral properties of materials at elevated temperatures and was modified in this work to study charring polymers. An advantage of using a modified emissometer is that the front surface temperature is measured optically instead of with a thermocouple. Time-resolved measurements of the front surface temperature, along with thermocouple measurements of the interior and back surface temperatures can provide information on the changes in thermal conductivity and thermal diffusivity with the extent of charring, assuming that the heat of gasification is known. In addition, this apparatus measures the changes in the material's spectral emissivity and functional group composition as it chars. Data are presented for experiments on two different samples of 3.2-mm-thick polyurethane, heated using radiant fluxes from 22 to 32 kW/m2. Analysis of the surface temperature and emissivity data indicates that the samples undergo a transition from a volume to a surface absorber during initial irradiation. Quantification of this behavior will be a critical element in predicting the flammability limits of these materials.

This paper considers the development of a predictive macromolecular network decomposition model for coal conversion which is based on a variety of modern analytical techniques for coal characterization. Six concepts which are the foundation of the functional group-depolymerization-vaporization-cross-linking (FG-DVC) model are considered: 1. (1) The decomposition of functional group sources in the coal yields the light gas species in thermal decomposition. The amount and evolution kinetics can be measured by t.g.-FT-i.r., the functional group changes by FT-i.r. and n.m.r. 2. (2) The decomposition of a macromolecular network yields tar and metaplast. The amount and kinetics of the tar evolution can be measured by t.g.-FT-i.r. and the molecular weight by f.i.m.s. The kinetics of metaplast formation and destruction can be determined by solvent extraction, by Gieseler plastometer measurements and by proton magnetic resonance thermal analysis (p.m.r.t.a.). 3. (3) The molecular weight distribution of the metaplast depends on the network coordination number (average number of attachments on aromatic ring clusters). The coordination number can be determined by solvent swelling and n.m.r. 4. (4) The network decomposition is controlled by bridge breaking. The number of bridges broken is limited by the available donatable hydrogen. 5. (5) The network solidification is controlled by cross-linking. The changing cross-link density can be measured by solvent swelling and n.m.r. Cross-linking appears to occur with evolution of both CO2 (before bridge breaking) and CH4 (after bridge breaking). Thus low-rank coals (which evolve much CO2) cross-link before bridge breaking and are thus thermosetting. High-volatile bituminous coals (which form little CO2) undergo significant bridge breaking before cross-linking and become highly fluid. Weathering, which increases the CO2 yield, causes increased cross-linking and lowers fluidity. 6. (6) The evolution of tar is controlled by mass transport in which the tar molecules evaporate into the light gas or tar species and are carried out of the coal at rates proportional to their vapour pressure and the volume of light species. High pressures reduce the volume of light species and hence reduce the yield of heavy molecules with low vapour pressures. These changes can be studied with f.i.m.s. The paper describes how the coal kinetic and composition parameters are obtained by t.g.-FT-i.r., solvent swelling, solvent extraction and Gieseler plastometer data. The model is compared with a variety of experimental data in which heating rate, temperature and pressure are all varied. There is good agreement with theory for most of the data available from the authors' laboratory and in the literature.

The main objective of the current work was to develop a char reactivity submodel that could be used in a comprehensive code for entrained coal combustors and gasifiers. The requirement of a char reactivity model is to predict the reactivity of chars from a wide range of coals, over a wide range of temperatures, and for various degrees of burnoff. In order to predict intrinsic reactivity, correlations of reactivity with char hydrogen content, coal oxygen content and coal mineral content were used. A random pore model (high rank coals) and a volumetric model (low rank coals) were included to predict variations of intrinsic reactivity with burnoff. The correlations combined with those models gave good predictions of reactivity (within a factor of 2 to 4) and reactivity variations with burnoff (within 20%) for the range of chars studied. In the pore diffusion regime, the model uses the Thiele modulus to calculate the reaction rate as a function of the intrinsic rate (obtained using the correlations) and char properties such as porosity, tortuosity and mean pore radius. Predictions of reactivity required an estimate of the tortuosity and the mean pore radius. The tortuosity was kept constant at a value of 2. Using a value of 6(corresponding to the size of micropores) for the mean pore radius led to good predictions of the onset of diffusion limitations for low heating rate, fluid chars. For high heating rate chars, pore size distribution measurements showed that values of approximately 100were more appropriate. The corresponding predictions using this value gave a fairly good fit of the literature data investigated. This analysis shows that it may be possible to extend a low temperature reactivity model to high temperatures.

We have developed a TG-FT-IR instrument which combines thermogravimetric analysis (TGA) with evolved product analysis by Fourier Transform Infrared (FT-IR) spectroscopy. FT-IR analysis of evolved products has an advantage over mass spectroscopy in allowing analysis of very heavy products, and over gas chromatography in speed. This paper describes the most recent improvements in the apparatus and presents its application in characterizing coal. The emphasis in this work is on employing the TG-FT-IR system to obtain kinetic rates for species evolution under easily obtained laboratory conditions. These rates can then be extrapolated to predict the conversion behavior of the hydrocarbon at higher heating rates and temperatures in practical conversion processes or at lower heating rates and temperatures in geological conversion processes. For several coal samples, a kinetic analysis was applied to species evolution data collected at several different heating rates. For coal, there is a systematic variation in rate with rank for almost all volatile species. Extrapolation to high temperatures shows excellent agreement with high temperature coal pyroloysis data. Extrapolation to low temperatures is consistent with the expected changes induced by bed temperatures over geological times.

Several groups have considered statistical network fragmentation models to describe coal thermal decomposition. In these models, the coal macromolecule is viewed as a collection of fused aromatic rings (monomers) linked by bridges. During thermal decomposition, existing bridges break and new bridges are formed. The parameters of the models are the geometry of the network, which is expressed as the number of attachments per monomer (the coordination number, σ + 1), and the chemistry of bridge breaking and formation. Given σ + 1 and the instantaneous number of unbroken and formed bridges, the molecular weight distribution can be predicted. The different groups have employed both Monte Carlo methods and percolation theory to describe the network statistics. The former approach has advantages in terms of describing both the depolymerization and crosslinking processes in coal decomposition, since it does not require a constant coordination number. The latter method provides closed form solutions and is computationally less demanding. The models differ in the geometry of the network, the chemistry of bridge breaking and bridge formation (crosslinking) and the mass transport assumptions. This paper considers for three such models: the mathematical schemes; the assumed network geometries; the assumed bond breaking and bond formation chemistries; and the mass transport assumptions. The predictions of three models were compared by comparing the oligomer populations as a function of the number of unbroken bridges per ring cluster. This paper also presents results from a new model which combines the geometry, chemistry and mass transport assumptions of the FG-DVC model with the mathematics of a modified percolation theory.

A new ignition phenomenon has been observed during studies of coal combustion. The experiment, which was described in a recent publication [1], injects coal particles suspended in a roomtemperature carrier gas as a jet into a flowing preheated air stream. The new phenomenon is shown in Fig. 1, which is a photograph of several ignited particles traveling upward. The particles of interest are at the edge of the cold particle stream and have first contact with the surrounding hot preheated gas stream. They ignite and appear to burn on the particle's surface, as indicated by the fact that the width of the luminosity is roughly that of the particle diameter. The particles become hotter with increasing distance. The new ignition phenomenon occurs after the particles have burned for a short time. Under these conditions there is often a secondary ignition event. To the unaided eye, it looks like a bright flash of light at the end of a long luminous trajectory. When viewed through a microscope, this event has the following characteristics.