Edwin J. Hippo

Reactivity of heat-treated coals in carbon dioxide at 900 °C

Abstract 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.

Enhancement of lignite char reactivity to steam by cation addition

Abstract 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.

Combustion characteristics of selected whole coals and macerals

Abstract 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.

Catalytic activity of calcium for lignite char gasification in various atmospheres

Abstract 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.

Chemical coal cleaning using selective oxidation

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.

Selective oxidation pretreatments for the enhanced desulfurization of coal

Abstract 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.

Characterization and Selective Removal of Organic Sulfur from IIIinois Basin Coals

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...

Aspects of sporinite chemistry

Abstract 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.

Microscopic characterization of coal residues from supercritical desulfurization of Illinois coal

Abstract 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.

Supercritical desulfurization kinetics of illinois no. 5 coals

Abstract 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.