Mild Pyrolysis Of Selectively Oxidized Coals Technical Report September 1 1991 August 31 1992
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| Total Pages | : 34 |
| Release | : 1992 |
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The primary objective of this study was to evaluate selective oxidation as a pretreatment for the enhanced desulfurization of Illinois Basin coals using a variety of mild thermal/chemical processes. Both an Illinois No. 6 and an Indiana No. 5 coal were selectively oxidized with peroxyacetic acid in the pretreatment step. The products were then treated with many hydroxide and carbonate bases using either water, methanol or ethanol as the solvent system. Other reaction variables investigated include reaction temperature, reaction time, pyrolysis pressure, particle size of the coal and the level of oxidation in the pretreatment step. Throughout the study the selectively oxidized coals were compared to unoxidized control coals. Model compounds were also studied. The results of these studies overwhelmingly show that selective oxidation with peroxyacetic acid significantly enhances the level of desulfurization obtained with subsequent chemical/thermal treatments. Indeed, every process investigated, including simple pyrolysis experiments, showed sulfur removal in the pretreatment step and the subsequent step to be substantially additive. In addition, considerable enhancement in the reactivity of the sulfur in the coal was obtained by the selective oxidation pretreatment. Sulfur contents lower than 0.25% were obtained for selectively oxidized coals. This represents an overall sulfur reduction of around 95%. This is beyond the level required for compliance with Clean Air Act legislation. No unoxidized coal, regardless of the desulfurization treatment, approached this level of sulfur removal.
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| Total Pages | : 20 |
| Release | : 1991 |
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The primary objective of this study is to investigate the removal organic sulfur from selectively oxidized Illinois coals using mild thermal/chemical processes. Work completed this quarter includes the investigation of the mild pyrolysis of unoxidized coals plus a selection of selectively oxidized coals. In addition the effect of particle size and extent of oxidation on pyrolysis was investigated. Some preliminary data concerning pyrolysis under vacuum and ambient pressure was also obtained. Work completed this quarter supports the following conclusions: (1) Desulfurization of unoxidized coals increases with increasing pyrolysis temperature and correlates with the loss of volatile matter. (2) Particle size did not influence the extent of desulfurization significantly. (3) Removing pyrite prior to pyrolysis helps to achieve a lower sulfur product beyond that expected from the removal of pyrite alone. (4) The extent of selective oxidation in teh pretreatment step did not effect the level of desulfurization obtained by pyrolysis alone. However this factor was important in the desulfurization obtained with supercritical methanol (SCM)/base. (5) Up to 84% of the sulfur has been removed from the IBC 101 coal by combining selective oxidation and SCM/base reactions. (6) Evidence for regressive reactions between volatilized sulfur compounds and partially desulfurized products was obtained by studying how changes in pyrolysis pressure effected the product sulfur content.
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| Total Pages | : 526 |
| Release | : 1994-04 |
| Genre | : Power resources |
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| Total Pages | : 24 |
| Release | : 1992 |
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The primary objective of this study is to investigate the removal organic sulfur from selectively oxidized Illinois coals using mild thermal/chemical processes. Work completed this quarter primarily concerned the investigation of the desulfurization of the selectively oxidized coals using aqueous or alcoholic base mixtures. Model compound studies were initiated. Results were: Levels of desulfurization obtained in this study are at, or very close to, the 90% removal levels required for these coals to be in compliance with the Clean Air Act legislation; Up to 89.4% of the sulfur in the IBC 101 coal and 88.9% of the sulfur in the IBC 106 coal has been removed by combining selective oxidation and alcoholic/base reactions; Overall, selective oxidation pretreatment always led to a lower sulfur product than the untreated sample; Substantial enhancement in the reactivity of the sulfur in the coal has been achieved by the selective oxidation pretreatment; The highest levels of desulfurization obtained so far all involve bases as additives; The water/Na2CO3 combination, was superior than any of the aqueous hydroxide bases. Possible synergistic interactions between the alcohol and the base are suspected. Over 70% of the sulfur in the IBC 101 coal can be removed by performing vacuum pyrolysis on the selectively oxidized coal. Lower sulfur contents are obtained by lowing the pyrolysis pressure.
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| Total Pages | : 23 |
| Release | : 1992 |
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The primary objective of this study is to investigate the removal organic sulfur from selectively oxidized Illinois coals using mild thermal/chemical processes. Work completed this quarter primarily concerned establishing the level of selective oxidation required for successful desulfurization in subsequent treatments. Many desulfurization reactions were performed on pretreated as well as unoxidized coal. The results obtained support the following new conclusions: (1) The extent of selective oxidation in the pretreatment step does not effect the level of desulfurization obtained by pyrolysis alone. However this factor was important in the desulfurization obtained with supercritical methanol (SCM)/base. (2) Up to 84% of the sulfur in the IBC 106 coal and 86% of the sulfur in the IBC 106 coal has been removed by combining selective oxidation and SCM/base reactions. (3) Most desulfurizations at 250°C did not produce significant levels of desulfurization. However as the temperature was increased levels of desulfurization increased considerably. (4) Although aqueous base was successful in removing sulfur from both pretreated and untreated samples, the most pronounced desulfurizations were obtained for the untreated samples. This is explained primarily by the dissolution of pyrite in the untreated samples. (5) The best desulfurizations involved SCM and base. Possible synergistic interactions between the methanol and the base are suspected. (6) Overall, selective oxidation pretreatment always led to a lower sulfur product. The severity of desulfurization is reduced by selective oxidation pretreatment.
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| Total Pages | : 698 |
| Release | : 1994 |
| Genre | : Science |
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| Total Pages | : 1224 |
| Release | : 1994 |
| Genre | : Government publications |
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| Release | : 2005 |
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An integrated method consisting of physical coal cleaning, mild gasification (MG) and low temperature oxidation (LTO) is proposed to produce chars with SO[sub 2] emissions at least 50% lower than those of their parent coals. Mild gasification and char desulfurization studies are conducted in both a batch fluidized-bed reactor and in a continuous rotary kiln reactor. MG chars were subjected to a LTO step to remove additional sulfur. Under non-optimized conditions, SO[sub 2] emissions of the MG chars were decreased 657%, representing on average over 60% reduction in SO[sub 2] emissions from the coals. Physical coal cleaning, mild gasification and char desulfurization reduced the SO[sub 2] emissions of IBC-104 and IBC-105 coals about 71%. LTO chars prepared from four of the six coals tested had SO[sub 2] emissions of less than 2.5 lbs SO[sub 2]/MMBtu. The VM contents of LTO chars were about 18%, which includes contributions from stable C-0 complexes formed by adsorption of oxygen on the surface of the chars. The average yield of low sulfur char obtained after MG and LTO was nearly 64% by weight of the original coal. A series of LTO optimization tests were conducted using IBC-102 coal. Results suggest that the greatest reduction in SO[sub 2] emissions was obtained using smaller particle diameters, steam during both MG and LTO, a higher temperature and higher oxygen partial pressure. The order of importance of process variables on SO[sub 2] emissions reduction of coals was: particle diameter> steam pyrolysis> oxygen partial pressure> steam oxidation [much-gt] temperature.
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| Total Pages | : 38 |
| Release | : 1992 |
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Laboratory-scale research conducted at Southern Illinois University at Carbondale (SIUC) has shown that coal pyrolysis in the presence of CH4/O2 in a 97:3 mole ratio (the METHOXYCOAL process) can produce high yields of liquids and valuable chemical feedstocks, particularly phenols, cresols, and xylenols (PCX). The addition of magnesia, coal ash, or clays have been shown to further enhance coal conversion to these chemicals. The goal of this two-year project was to build upon that laboratory research by conducting continuous bench-scale tests at IGT. Tests were conducted with IBC-101 and IBC-105 coals under N2, CH4, and CH4/O2 blends, with and without mineral additives, at temperatures and pressures up to 1000°F and 200 psig. These tests have provided data valuable to further development efforts on the process. In the first year, fluidized-bed tests were conducted using inert bed diluents (coke and sand) to retard agglomeration. PCX yields of 0.99 wt% maf coal were achieved in CH4 atmosphere, tripling the yield in N, atmosphere, while overall liquid yields were 18--20 wt% maf in either atmosphere. However, control of caking was difficult in spite of a very high bed dilution ratio of 4.5:1. During the second year, agglomeration was controlled by slurry impregnation of the coal with coal ash, magnesia, or montmorillonite at levels as low as 10 wt%. Thirteen continuous tests were conducted in 2-inch fluidized-bed and moving-bed reactors at test conditions of 900°--1000°F and 120 psig.
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| Total Pages | : 34 |
| Release | : 1992 |
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Using the pyrolysis-QGA system, samples of coal were heated from ambient temperature to 800°C at a rate of 20°C/min in the pyrolysis chamber under a nitrogen atmosphere. The volatile products were carried with the nitrogen flow to the combustion chamber which was maintained at 850°C under a constant flow of oxygen. For Illinois coals (IBC-101, 103, and -109), HCl was the only chlorine species identified by the QGA. The HCl release profiles for the coals showed a broad peak between 250°C and 600°C with a maximum at 445°C. Neutron activation analysis of pyrolysis residues showed that 98 percent of the chlorine in raw coal was volatilized. Thus, it may be inferred that the chlorine in Illinois coals is released rapidly as HCl, not as sodium chloride (NaCl), during combustion in a utility/industrial boiler. In contrast to chlorine, the sulfur release profile for IBC-109 showed three peaks: the first sulfur peak at about 350°C was probably derived from elemental sulfur, the main peak at 475°C corresponded to the release of organic sulfur, and the third peak at 600°C resulted from the decomposition of pyrite. The low-temperature peak was absent for fresh samples. Sulfur dioxide (SO2) was the major sulfur species in combustion gases under an oxidizing condition; additional gaseous sulfur species (COS and H2S) were observed when the atmosphere was changed to a reducing condition.
