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The production of high-purity hydrogen via steam gasification of coal has been investigated. The separation of CO from H2 in the gasification products is achieved by CO oxidation to CO2 followed by uptake of the CO2 by a suitable removal agent. This uptake of CO2 increases the extent of the water gas shift reaction and enhances the yield and purity of H2. In addition to the water gas shift reaction, the oxidation is enhanced by the use of a solid oxygen transfer agent (Fe2O3) in the hydrogen enrichment pass. Subsequently, the reduced oxygen transfer agent is reoxidized (and thus regenerated) in the presence of air and the heat liberated via the exothermic reaction is utilized to regenerate carbon dioxide removal agent. In this study, the effect of process variables on coal gasification and hydrogen enrichment has been evaluated. Fixed bed gasification studies using coal and coal−Fe2O3 and coal−CaO mixtures were conducted to evaluate the kinetics of gasification and separation effectiveness of the process....

Thermogravimetric analysis (TGA) of the reduction of Fe2O3 in a continuous stream of 100% CO was conducted at temperatures ranging from 800 to 900 °C. X-ray diffraction analysis of solids identified the presence of iron, graphite and a carbide of iron as the products of reactions. A kinetic model based on the first-order irreversible rate kinetics was developed and fitted to the TGA data so as to estimate the rate constants for each reduction reaction. The reaction pathways considered in this analysis involved reduction of iron oxides, Boudouard reaction and iron-carbide formation. The rate parameters were calculated and compared with data reported in literature.

The desulfurization of selectively oxidized coals and unoxidized control coals was investigated using mild pyrolysis and various base treatments. Both an Illinois No. 6 and an Indiana No. 5 coal were selectively oxidized with peroxyacetic acid in the pretreatment step and then treated with various hydroxide and carbonate bases, using either water, methanol or ethanol as the solvent. Reaction variables investigated include reaction temperature, reaction time, pyrolysis pressure, and the level of oxidation in the pretreatment step. In general, it was found that selective oxidation, when combined with subsequent desulfurization reactions, always led to greater sulfur removal. In addition, the reactivity of the sulfur in the coal towards desulfurization was apparently enhanced by the selective oxidation pretreatment. Thus, the severity of desulfurization conditions can be reduced by employing this pretreatment. Sulfur removals of up to 95% were obtained in some cases. Usually the most effective treatments involved carbonate bases under supercritical alcohol conditions. The desulfurization of some selectively oxidized, sulfur containing model compounds was also observed under similar reaction conditions.

The peroxyacetic acid oxidation products from a series of coals of organic sulfur content 0.5–9.8 wt% were examined. The distributions of organic S and N compounds were determined by gas chromatography with sulfur-selective flame photometric and nitrogen-selective thermionic specific detection respectively. A selected sample was also examined in greater detail using low-voltage high-resolution mass spectrometry. The distribution of organic sulfur compounds in the oxidation products was remarkably similar for all the coals. The number of sulfur compounds detected was small compared with that of organic nitrogen compounds detected. This suggests that the sulfur chemistry of coal is considerably simpler than its nitrogen chemistry. Analysis of the m.s. data, together with a comparison of sulfur-selective and nitrogen-selective chromatograms, indicated that a significant proportion of the heteroatomic species present in coal contain more than one heteroatom. This is significant, because few models of coal structure incorporate such species.

The primary objective of this study is to investigate the removal of both mineral and organic sulfur from Illinois coals using low temperature selective oxidation. This overall objective is to develop new methods for either physical/chemical or physical/microbial cleaning of Illinois coal. Innovative approaches to achieve deep cleaned products, containing both ash and sulfur contents less than 0.5 percent, will be considered. Experiments focus on developing cost-effective methods for the removal of organic sulfur and finely disseminated mineral impurities, especially fine pyrite particles, from coal. Rates and mechanisms for organic sulfur removal will be studied. Chemical reagent recycling and/or reagent wastes will be studied. Chemical reagent recycling and/or reagent wastes handling are included. Bench scale studies are performed.

The overall objective of this project was to determine the combustion properties of separated single coal maceral fractions from a rank series of coals and then to try to predict the combustion behaviour of various whole coals on the basis of their maceral compositions and rank. The combustion properties studied were based on the burning profile in a TGA apparatus. The results of this study indicate that most of the reactivity and combustion profile parameters varied significantly with coal rank and that all of the rank trends observed were best defined in the data from the single maceral samples which were more reproducible, more linear, and less variable. The variations in the combustion profiles and reactivities in different macerals from the same sample are of the same order of magnitude as the variations due to rank. It also appears that there are some maceral interactions during combustion and gasification that significantly affect these processes.

In order to develop appropriate desulfurization strategies, the organic sulfur species and their distribution in coal need to be characterized. Peroxyacetic acid oxidation has been developed to render coal soluble, allowing for the subsequent GC-FID/FPD and GC-MS analysis of sulfur compounds. Four Illinois Basin coals and samples of sporinite, vitrinite and semifusinite isolated from them have been examined. Between 20 and 50% of the organic sulfur in these coals is associated with relatively few compounds detected in the volatile oxidation products. Of these, methylsulfonic acid is the most abundant, which, from model compound studies, results from oxidation of either methyl disulfide or simple thiophene structures in the coals. Although the species detected are commonly occurring among the majority of the coal and maceral fractions, their distribution varies considerably from sample to sample. By fractionating the oxidation products, a fraction was obtained that had a sulfur content of 18%. This fractio...

The main objective of this study is to investigate the desulfurization behavior of individual coal macerals. The sporinite and vitrinite macerals which contain most of the organic sulfur in coal are more reactive toward desulfurization processes than any of the other materials that were studied. They also give the highest desulfurization levels. Since they are more reactive than whole coals or floated samples, the other constituents in the coal matrix must reduce sulfur removals. This phenomenon has not been reported previously. It implies that the inertinite macerals may behave in a manner similar to activated charcoal and chemically absorb copious amounts of sulfur during the desulfurization processes. The practical result of this phenomenon is that selection of coals on the basis of maceral composition could be necessary to optimize thermal-chemical desulfurization.

With the recent advent of the ability to separate coal into maceral concentrates of high purity, the individual constituents of coal can now be analyzed separately, without their mutual interference, giving a much better understanding of the macromolecular structure of coal. The sporinites from two Pennsylvanian age coal samples (Illinois Basin, U.S.A.) were studied, one from a vitrinite-rich high-volatile bituminous coal, the other from a liptinite-rich high-volatile butuminous coal of slightly higher rank. Sporinites were isolated from each coal by density gradient centrifugation. The sporinite of the vitrinite-rich coal was compared chemically and petrographically with the parent coal and with the sporinite of the liptinite-rich coal. The fluorescence spectrum of the sporinite from the liptinite-rich coal is shifted to the red end of the spectrum, which may be accounted for by the somewhat higher rank of the sample and/or by differences in the original assemblage of spores. The lack of chemical differences between the extracts of the sporinite and its whole coal reinforce the concept of bitumen as an homogeneous mobile phase pervading the coal. Thus, extract chemistry seems an unsuitable technique for distinguishing between macerals from the same coal. Hopane and sterane distributions in the sporinite and parent coal pyrolyzates are very similar, but the two materials can be readily distinguished by the distribution of tetracyclic diterpanes of the phyllocladane type, which are biological marker compounds derived from higher plant material. Overall, the sporinite is considerably more paraffinic in character and has a greater preponderance of straight-chain alkane moieties than the coal as a whole. In the case of the vitrinite-rich coal, the whole-coal structure appears significantly more polyaromatic than the sporinite. The distributions of thiophenic compounds differ in the pyrolyzates of the two materials. The sporinite from the liptinite-rich coal is even less polycondensed than the sporinite from the vitrinite-rich sample. The chemical and petrographic differences of the two sporinites probably reflect the different assemblages of spores in the original peats and their different diagenetic histories.

It is expected that in the 21st century the Nation will continue to rely on fossil fuels for electricity, transportation, and chemicals. It will be necessary to improve both the process efficiency and environmental impact performance of fossil fuel utilization. GE Global Research has developed an innovative fuel-flexible Unmixed Fuel Processor (UFP) technology to produce H{sub 2}, power, and sequestration-ready CO{sub 2} from coal and other solid fuels. The UFP module offers the potential for reduced cost, increased process efficiency relative to conventional gasification and combustion systems, and near-zero pollutant emissions including NO{sub x}. GE Global Research (prime contractor) was awarded a contract from U.S. DOE NETL to develop the UFP technology. Work on this Phase I program started on October 1, 2000. The project team includes GE Global Research, Southern Illinois University at Carbondale (SIU-C), California Energy Commission (CEC), and T. R. Miles, Technical Consultants, Inc. In the UFP technology, coal and air are simultaneously converted into separate streams of (1) high-purity hydrogen that can be utilized in fuel cells or turbines, (2) sequestration-ready CO{sub 2}, and (3) high temperature/pressure vitiated air to produce electricity in a gas turbine. The process produces near-zero emissions and, based on ASPEN Plus process modeling, has an estimated process efficiency of 6 percentage points higher than IGCC with conventional CO{sub 2} separation. The current RD it also provides a summary of program activities and accomplishments covering progress in tasks including lab-scale experimental testing, pilot-scale testing, kinetic modeling, program management and technology transfer.

GE Global Research is developing an innovative energy technology for coal gasification with high efficiency and near-zero pollution. This Unmixed Fuel Processor (UFP) technology simultaneously converts coal, steam and air into three separate streams of hydrogen-rich gas, sequestration-ready CO{sub 2}, and high-temperature, high-pressure vitiated air to produce electricity in gas turbines. This is the draft final report for the first stage of the DOE-funded Vision 21 program. The UFP technology development program encompassed lab-, bench- and pilot-scale studies to demonstrate the UFP concept. Modeling and economic assessments were also key parts of this program. The chemical and mechanical feasibility were established via lab and bench-scale testing, and a pilot plant was designed, constructed and operated, demonstrating the major UFP features. Experimental and preliminary modeling results showed that 80% H{sub 2} purity could be achieved, and that a UFP-based energy plant is projected to meet DOE efficiency targets. Future work will include additional pilot plant testing to optimize performance and reduce environmental, operability and combined cycle integration risks. Results obtained to date have confirmed that this technology has the potential to economically meet future efficiency and environmental performance goals.

Scanning Tunneling Microscope (STM) is a new tool for resolving surface topography and electronic states at the atomic level. STM excels over other microscopy techniques in its high lateral and vertical resolutions. Many forms of carbon including diamonds, fullerenes, isotropic porous carbons and glassy carbons have been studied extensively by STM. STM studies of basic carbon materials and surface adsorbed species on these carbon surfaces are essential as a foundation for future nanoscopic work involving more complex materials, such as carbon-carbon composites and coal structures, as well as the advancement of carbon inhibition/gasification technology. Our studies have shown that atomic structure of solvent deposited coal can be revealed and this will help in better understanding of the coal structure. The metal salts deposited on the graphite structure will help in a better understanding of the catalysis in carbon gasification. In this paper we have discussed some of the preliminary work performed on the materials deposited on the highly oriented pyrolytic graphite (HOPG) surface.

Carbon-gas reactions have been an important area of study over the past two decades. The basic mechanisms of carbon gasification are essential to understanding coal gasification. However, the studies of the inhibition and catalysis of carbon gasification have raised technical issues which have not been fully addressable until now. Some of these issues for catalytic gasification include: the effective particle size of the catalysts; the exact nature of bi-metallic catalysts; the interaction between carbon surfaces, gas, and catalyst; the percentage of the catalyst which is active; and catalyst deactivation mechanisms. The scanning tunneling microscope (STM) can address some of these issues. The purpose of this paper is to describe some preliminary work on applying STM to characterizing gasified carbon surfaces. Highly ordered pyrolytic graphite (HOPG) was gasified at 650° C for a net weight loss of 5 and 30%. The study has identified the tendency to develop high oxidation rate perpendicular to the basal plane despite the unfavorable thermodynamics of attack in this direction. The initial attack does not develop in the expected hexagonal pattern which develops after 5% burnoff. Oxygen on the surface can be identified by study of bond lengths in cross sectional analysis. Additional work is required to identify the exact nature of the oxygen structures, but the techniques developed in this study demonstrate that it is possible to follow gasification with the STM.

Publisher Summary This chapter discusses the liquefaction of coal/waste plastic mixtures. The results gathered are preliminary in nature, and it can be appreciated that the use of waste plastics in coal liquefaction processes has great potential. Synergistic conversions of coal/plastic mixtures are observed under many pyrolysis and liquefaction conditions. The strong interactions among the components of the system occur during coprocessing. A free radical hydrogen abstraction mechanism is responsible for much of the observed behavior, and the tetralin retards polyethylene (PE) and polypropylene (PP) decomposition through a radical capping or adduction mechanism. Liquefaction conversions are important because they are obtained using no added liquefaction catalyst, relatively low temperatures, low hydrogen pressures, and using a relative poor H-donor solvent (tetralin).

Gasification rates of a Texas lignite char, having calcium contents varying from 1.1 to 12.9 wt%, were measured in air, steam, CO 2 , and H 2 . Gasification rates increased rectilinearly with increase in calcium loading. The chemisorption of CO 2 at 298 K on the CaO present on the char surface was used to determine CaO particle dispersion. Knowing this dispersion, specific activities of calcium as a catalyst for the gasification reactions were calculated. The spread in specific activities in different atmospheres is large, it being a maximum when the char-air reaction is compared with the char -H 2 reaction.

The primary obstacle to overcome in the development of applications of structural carbons in high-temperature environments containing oxidants is the prevention of carbon gasification, which leads to weakening of mechanical properties and eventually to failure. Many factors effect the rate of carbon gasification. These include: environment temperature, sample temperature, oxidant, rate of oxidant flow, carbon type, pore volume and distribution, crystallite size, catalyst concentration, catalyst state, catalyst cluster size, catalyst spill-over rate, active surface area, and the presence of inhibitors. Because of the number and complexity of factors which influence gasification rates of carbon, there are many possible approaches to inhibiting carbon gasification rates. These approaches can be categorized into four groups: 1. 1) prevention of catalysis; 2. 2) retardation of gas access to the carbon; 3. 3) inhibition of the carbon gas reactions; and 4. 4) improvement in the carbon crystallite structure. This article considers the present state of these approaches as well as future trends. Emphasis will be placed on a novel approach to inhibition involving the reduction in the number of active sites available to oxidant adsorption by occupying various sites in graphitized carbons with thermally stable complexes.

Analytical data from a set of 66 coal samples, ranging in rank from lignitic to low-volatile bituminous, were used to define relationships between coal properties. Unusual care was taken in selecting, collecting, preparing and analysing this set of premium samples providing a high degree of confidence in the conclusions obtained. It was found that univariate relationships between properties, which might seem to convey useful information, are generally of limited operational value and can lead to erroneous conclusions. However, multivariate correlations can predict a number of properties. Specific energy, volatile matter yield, and density (by helium pycnometry) can be estimated from the elemental composition according to the following expressions: Btulb−1 = 145.9%C + 569.6%H − 53.89%O + 43.08%S − 6.3%Ash%VM = −0.408%C + 11.25%H + %O + 1.3%Sgml−1 = 0.01556%C − 0.04117%H + 0.02247%O + 0.02049%S + 0.0208%Ash The standard deviations of the residuals (estimated-experimental) for the above three correlations are 86 Btu lb−1, 1.5% VM and 0.013 g ml−1. The free-swelling index was found to correlate strongly with the oxygen content (for coals containing > 2 wt% oxygen, daf) and the petrographic composition according to the following expression: FSI = 5 + 4.68f(O) − 0.00395NPC2 + 0.0897NPC − 0.06LIP where f(O) = sin(0.2513Odaf + 0.9505)NPC = ashweight% + inertinite, volume% mineral-freeLIP = liptinite, volume%, mineral-free It is concluded that the elemental composition of coal can predict many physical properties and process responses. The petrographic composition must be considered when predicting plastic properties. Though petrographic composition influences other properties and process responses, microscopically obtained maceral percentages did not prove useful for quantitatively predicting properties or responses.

An investigation of the microscopic properties of residues produced from Illinois coal treated under various supercritical alcohol extraction conditions has been conducted. The objective of this investigation was to obtain a better understanding of the supercritical alcohol/coal desulfurization system. It was found that pyrite is converted progressively to pyrrhotite and then to troilite. Also, coal particles tended to become fluid and form coke. The degree of coke formation and size of anisotropic units (optical texture) were found to correspond to the extent of desulfurization. These correlations were found to be solvent dependent. Zoning effects were also observed in both the organic and inorganic phases. These effects appear to be mass or heat transfer limited and related to the operation of the batch reactors employed in obtaining samples for this study. The investigation is continuing, employing smaller reactors with improved heat and mass transport properties. Attempts will be made to determine if desulfurization is enhancing fluidity or if fluidity is enhancing desulfurization.

This paper describes a desulfurization process to remove both organic and inorganic sulfur from coal employing alcohols under supercritical conditions. The overall objective of this study was to gain a better understanding of the kinetics of the supercritical alcohol/coal desulfurization process. A microreactor system was developed to examine in detail the reaction kinetics of coal desulfurization under supercritical conditions. The microreactors provide a uniform temperature within the reactor and allow precise measurement of temperature. Desulfurization tests were conducted to obtain solid residues for sulfur analysis (% in product), as well as optical microscopic examination. The results of the analysis indicate that the desulfurization process is highly temperature dependent. Generally, with increased reaction temperature, desulfurization is increased. For all isothermal reactions there is at least one stage at which sulfur is reincorporated into the product. Pretreatment of coal with 5% KOH is desirable to prevent coke formation, but under the conditions studied, had little effect on ultimate desulfurization levels. Additions of KOH increased the rate at which ultimate desulfurization levels were reached.

Coal combustion experiments were carried out over the temperature range 25–900 °C using air at atmospheric pressure in a derivative thermogravimetric analysis system. Sixty-six coals high in vitrinite (> 80% mineral-matter-free basis) and low in inorganics (all but 12 samples < 10%) were examined as part of a coal characterization programme. The coals varied in rank from lignites (69% carbon on a dry, mineral-matter-free basis) to low-volatile bituminous (91% carbon). Combustion rates increased progressively with increasing temperature, passed through maxima and then declined. The rate data were fitted to an Arrhenius equation and plots showed four distinct regions of combustion. Apparent activation energies were calculated for each region and varied from ≈4 kJ mol−1 in the high-temperature, diffusion-controlled region to 290 kJ mol−1 in the chemical-reaction controlled, low-temperature region. The temperatures at which 50% of the sample had burned away (sol12-life) were rectilinearly related to oxygen and carbon contents (correlation coefficient squared values of 0.88 and 0.86, respectively).

Reactivities of sixteen 40 × 100 (U.S.) mesh U.S. coals charred to 1000 °C were measured in carbon dioxide at 900 °C. Chars derived from coals with less than 80% carbon, on a dry-ash-free basis, were the most reactive. These chars also gave the widest spread in reactivity. Plots of inorganic element content in the chars versus reactivity showed that magnesium and calcium are important to char reactivity. Six coals were acid-washed with hydrochloric acid and four coals were further demineralized with hydrofluoric acid. Most acid-treated coals showed a decrease in reactivity; but two coals of high rank increased in reactivity. This increase in reactivity is attributed to the creation of additional porosity as a result of mineral matter removal and thus a reduction in resistance to carbon dioxide diffusion to reactive sites. Two demineralized and two original coals were divided into four size ranges and chars were produced from each size of each coal. Gasification rates increased monotonically with decreasing particle size reacted.

Chars produced from lignites typically have much higher reactivities to gasification than those produced from bituminous coals. This has been attributed previously to the presence of carboxylate salts of inorganic constituents on the lignites. Upon charring of the lignites, the carboxylate salts decompose leaving behind well dispersed inorganic constituents which act as catalysts for gasification. In this study, a raw lignite has been treated with HCl and HF to demineralize it and to increase its carboxyl content prior to exchanging selected cations with the hydrogen on the carboxyl groups. Up to 2.14 mmol of calcium per g of coal could be added using this procedure. Addition of varying amounts of calcium to the lignite resulted in the production of chars containing calcium contents ranging from 1.1 to 12.9 wt %. Such addition resulted in a rectilinear increase in reactivity of the char to steam with increasing amount of calcium added. Maximum reactivity attained was over ten times the reactivity found for the char produced from the raw lignite. At comparable molar loadings of metal cations onto the acid-treated lignite, the chars subsequently produced had reactivities in steam in the order: K >Na ≈ Ca >Fe >Mg. Char reactivity could also be enhanced by the addition of cations to nitric acid-treated char which had been produced, in turn, from demineralized lignite.