Behavior Of Sulfur And Chlorine In Coal During Combustion And Boiler Corrosion Technical Report December 1 1992 February 28 1993
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| Total Pages | : 23 |
| Release | : 1993 |
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The goals of this project is to investigate the behavior of sulfur and chlorine during pyrolysis and combustion of Illinois coals, the chemistry of boiler deposits and the process of ash formation, and remedial measures to reduce the sulfur and chlorine compounds in combustion gases. The chemistry of boiler deposits provides information about the behavior of sulfur, chlorine, and ash particles during coal combustion. We report results obtained during this quarter on mineralogical and chemical compositions of twelve samples of boiler deposits collected from superheater and reheater tubes of an Illinois power plant. Scanning electron microscopy shows microscopic calcium sulfate droplets on cenospheres. There is a considerable variation of chemical composition among the samples. While eight out of twelve samples consist predominantly of quartz, mullite, and glass; the remaining four contain an appreciable amount additional phases (calcium sulfate and alkali iron sulfate) . The chlorine content in the samples is determined by neutron activation analysis. one sample contains 37 ppM chlorine, and the chlorine concentration is below the detection limit in other eleven samples (
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| Total Pages | : 782 |
| Release | : 1995 |
| Genre | : Power resources |
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| Total Pages | : 38 |
| Release | : 1993 |
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The goals of this project are to investigate the behavior of sulfur and chlorine during pyrolysis and combustion of Illinois coals, the chemistry and mineralogy of boiler deposits, the effects of combustion gases on boiler materials, and remedial measures to reduce the sulfur and chlorine compounds in combustion gases. Replicate determinations of chlorine and sulfur evolution during coal pyrolysis-gas combustion were conducted using a pyrolysis apparatus in conjunction with a quadrupole gas analyzer. HCl is the only gaseous chlorine species measured in combustion gases. Pyrolysis of coal IBC-109 spiked with NaCl solution shows a strong peak of HCl evolution above 700C. The absence of this peak during pyrolysis of Illinois coal indicates that little chlorine in Illinois coal occurs in the NaCl form. Evolution of sulfur during coal pyrolysis was studied; the sulfur evolution profile may be explained by the sulfur forms in coal. To determine the fate of sulfur and chlorine during combustion, a set of six samples of boiler deposits from superheater and reheater tubes of an Illinois power plant was investigated. Scanning electron microscopy shows microscopic calcium sulfate droplets on cenospheres. Superheater deposits are high in mullite, hematite, and cristobalite, whereas a reheater deposit is enriched in anhydrite. The chlorine content is very low, indicating that most of the chlorine in the feed coal is lost as volatile HCl during he combustion process. The profiles of SO2 released during combustion experiments at 825 C indicate that calcium hydroxide added to the coal has a significant effect on reducing the SO2 vapors in combustion gases.
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| Total Pages | : 26 |
| Release | : 1993 |
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The evolution of HCl during coal pyrolysis and its relation to chlorine forms in raw coal were studied using a temperature-programmed pyrolysis and gas combustion in conjunction with a quadrupole gas analyzer (QGA). Using a new filament source in the QGA significantly improved the sensitivity of HCl detection. The major peak at 445°C showed an increased intensity and a new HCl evolution peak at 600°C was observed during pyrolysis of Illinois coal IBC-109. Pyrolysis of coal IBC-109 spiked with NaCl solution showed a strong peak of HCl evolution above 700°C. In the study of boiler deposits, several sample preparation procedures for X-ray diffraction analysis were developed and six minerals were unambiguously determined in superheater and heater deposits from a power plant in Illinois. Effects of composite gases containing 0.2% HCl on six metals were tested at 600°C and 200°C, and at 100°C with moisture for 400 hours. Similar tests were conducted with a composite gas containing no HCl at 600°C and 200°C. The results allow us to assess the factors controlling the corrosion rate: Boiler materials, temperature, concentration of HCl in combustion gases, and chloride condensate on metal surfaces.
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| Total Pages | : 24 |
| Release | : 1992 |
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The goal of this project is to study the evolution of gaseous sulfur and chlorine species during temperature-controlled pyrolysis and combustion and their effect on boiler corrosion. We have been developing two techniques for determining the gas evolution profiles of sulfur and chlorine during coal pyrolysis and combustion. First, using a pyrolysis-combustion system in combination with a quadrupole gas analyzer, the evolution of sulfur dioxide (SO2) in combustion gas during temperature-programmed coal pyrolysis-combustion was monitored. When the atmosphere of the combustion chamber was changed to a reducing condition, gaseous COS and H2S were also detected in the combustion gas. Detection of hydrogen chloride by QGA has been improved by using a larger-diameter (75?m) capillary tubing. The HC1 evolution profile during the pyrolysis of coal IBC-109 was determined by QGA and by a chloride ion selective electrode for quantitative purposes. Second, the technique of thermogravimetry (TG) in conjunction with Fourier transform infrared (FTIR) spectroscopy was used to characterize gaseous species during coal pyrolysis. Gas evolution profiles of sulfur (SO2 and COS), chlorine (HC1), and nitrogen (NH3 and HCN) species were determined for coal IBC-109. Similar release profiles of HCI and NH3 supported an interpretation that chlorine gnd nitrogen are closely associated in coal. COS may be formed by reaction of CO with H2S in the gas phase. A mass balance study of chlorine evolution from coal IBC-109 in a TG-FTIR experiment was completed; the chloride dissolved in solutions was determined by an ion chromatographic technique.
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| Total Pages | : 1442 |
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| Total Pages | : 16 |
| Release | : 1994 |
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Limited literature and use history data have suggested that some high-chlorine Illinois coals do not cause boiler corrosion while extensive data developed by the British correlate corrosion with chlorine content and other parameters related to the coal and boiler. The differences in corrosivity in coals may be due to the coal properties, to blending of coals, or to the boiler parameters in which they were burned. The goals of this study focus on coal properties and are: (1) to characterize chlorine and other constituents in coals which have been reported to behave differently with respect to corrosion problems during combustion; (2) to determine the evolution profiles of chlorine-containing compounds in coals during pyrolysis and oxidation; and (3) to examine the behavior of Cl-, S-, N-, O-containing compounds in coal during pyrolysis. Proximate, ultimate, and ash composition analyses for all of the British and Illinois coal samples were completed in this quarter. Analysis of the acid-soluble sodium and potassium in coals is in progress. These data, along with ash composition data, will be used to assess a coal's relative corrosion potential. The HCl evolution profiles obtained from oxidation of the five Illinois coal samples were examined. The results indicate that temperatures of maximum HCl evolution range were 430°C to 450°C.
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| Total Pages | : 24 |
| Release | : 1992 |
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Four replicate experiments of pyrolysis with quadrupole gas analyzer and ion selective electrode were conducted to monitor the release of chlorine and sulfur from a high-chlorine Illinois coal IBC-109 (0.42% chlorine on dry basis). The chlorine in coal is released solely as HCl, and the HCl release profile shows a broad peak between 250°C and 600°C with a maximum at 445°C. In contrast, the sulfur release profile shows three peaks; the sulfur released around 370°C may be derived from a labile (possibly aliphatic) component of organic sulfur, the main peak at 475°C corresponds to the release of the main component (thiophenic) of organic sulfur, and the third peak at 600° results from the decomposition of pyrite. Sulfur dioxide (SO2) is the major sulfur species under an oxidizing condition in the combustion gas; additional gaseous sulfur species (COS and H2S) are observed when the atmosphere is changed to a reducing condition. Sodium and chlorine contents in char residues determined by neutron activation analysis showed that 98% of chlorine in coal was volatilized during pyrolysis to 800°C, and all the sodium is retained in the chars. The thermogravimetry-Fourier transform infrared (FTIR) spectroscopy experiments were carried out to characterize gaseous species during pyrolysis of four Illinois coals (IBC-103, -105, -106, and -109). Gas evolution profiles of sulfur (H2S, S02, and COS), chlorine (HCl), and nitrogen (NH3 and HCN) species were determined. Similar release profiles of HCl and NH3 supported an interpretation that chlorine and nitrogen are closely associated in coal. COS may be formed by reaction of CO with H2S in the gas phase.
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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.
| Author | : C.-L. Chou |
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| Release | : 1993 |
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