Glenn A. Norton

Catalytic effects observed during the co-gasification of coal and switchgrass

We are investigating catalytic gasification of coal char using biomass-derived potassium salts. Alkali metal salts, especially those containing potassium, are excellent promoters of gasification reactions but are generally considered too expensive for commercial use. Fast-growing biomass, which contains large quantities of potassium, may prove to be an excellent source of inexpensive gasification catalyst. A series of CO2-char gasification tests were performed in a thermogravimetric analyzer (TGA) to evaluate the catalytic activity of alkali-rich biomass-derived materials. Both switchgrass char and switchgrass ash displayed catalytic activity in mixtures with coal char produced from Illinois No. 6 coal. The results obtained with switchgrass ash were especially impressive, with an almost eight-fold increase in coal char gasification rate at 895°C in a 10:90 mixture of coal char and switchgrass ash. These results give encouragement that biomass could be the source of inexpensive, coal gasification catalysts.

Heterogeneous oxidation of mercury in simulated post combustion conditions

Heterogeneous mercury oxidation was studied by exposing whole fly ash samples and magnetic, nonmagnetic, and size-classified fly ash fractions to elemental mercury vapor in simulated flue gas streams. Fly ash from sub-bituminous Wyodak–Anderson PRB coal and bituminous Blacksville coal were used. Scanning electron microscopy, X-ray diffraction, thermogravimetric analyses, and BET N2 isothermal sorption analyses were performed to characterize the fly ash samples. Mercury speciation downstream from the ash was determined using the Ontario Hydro method. Results showed that the presence of fly ash was critical for mercury oxidation, and the surface area of the ash appears to be an important parameter. However, for a given fly ash, there were generally no major differences in catalytic oxidation potential between different fly ash fractions. This includes fractions enriched in unburned carbon and iron oxides. The presence of NO2, HCl, and SO2 resulted in greater levels of mercury oxidation, while NO inhibited mercury oxidation. The gas matrix affected mercury oxidation more than the fly ash composition.

Morphological and chemical characterization of iron-rich fly ash fractions.

Fly ash samples collected from the electrostatic precipitator of a coal-fire power plant were separated into relatively magnetic and nonmagnetic fractions. The magnetic portions of these samples were examined by scanning electron microscopy, optical microscopy, and X-ray diffraction. The fly ash particles in the magnetic concentrates were predominately spherical and were generally solid in cross section, although vesicular particles were common in the larger sizes (e.g., >50 ..mu..m). The larger particles also exhibited the most diversity with respect to internal morphology. A variety of dendritic growths were among the features observed. X-ray diffraction analyses revealed that the magnetic fly ash fraction was composed primarily of magnitude and less amounts of hematite. Results of this study suggest a potential for increasing ash density and purity by selecting a particle size range that will optimize these parameters. This in turn could make it more suitable for use as a heavy medium in physical coal beneficiation. 22 references, 9 figures.

Rapid dissolution technique for colorimetric determination of nitrogen in coals

Abstract A simple and rapid method for the colorimetric determination of total nitrogen in coal has been tested on several coals digested under various conditions. The method consists of initial carbonization of the coal sample with H 2 SO 4 followed by digestion using continuous-flow addition of a mixture of 50% H 2 O 2 plus concentrated H 2 SO 4 . Nesslers reagent is added for colour development for the subsequent spectrophotometric determination of ammonia nitrogen. Maximum nitrogen recovery was obtained by using boiling times of 4 min or more during sample carbonization, H 2 O 2 :H 2 SO 4 ratios of 4:1 to 9:1, and digestion reagent volumes of 20–40 cm 3 . Altering the heat setting on the digestion apparatus substantially changed digestion times but did not significantly affect nitrogen values obtained. Using the optimum digestion conditions, results for nitrogen in seven different coal samples were comparable with those obtained by conventional determinations using an instrumental ‘CHN’ analyser. The precision of this rapid dissolution technique was good and appeared to be better than that of the instrumental analyser for many of the coals studied.

Experimental electron beam microanalytical procedure for determining oxygen in coal

Abstract The standard ASTM procedure for determining levels of organic oxygen in coal is an indirect determination which has cumulative errors. As yet, there is no fast, simple, accurate, direct method for determining the organic oxygen content of coal. Although various techniques employing oxidation, reduction or fast-neutron activation (FNA) are currently used to determine organic oxygen in coal, these methods can be time consuming or relatively complex. In addition, corrections must often be made for the inorganic oxygen from the mineral matter. In this study, the organic oxygen levels in coal are directly determined by scanning electron microscopy coupled with wavelength-dispersive X-ray analysis (SEM-WDX). Previously, a similar technique has been used successfully to quantify organic sulphur levels in coal. The SEM-WDX method provides data for the organic oxygen content after chemical screening with energy-dispersive X-ray analysis to avoid the inorganic oxygen components. Four coals were analysed for oxygen by the SEM-WDX method and results were compared with values from the ASTM and FNA methods. One coal gave SEM-WDX results similar to the ASTM and FNA values, while the other three coals gave results significantly lower than the ASTM or FNA values. Sample volatilization, oxygen standards, matrix correction routines and other analytical conditions are discussed as potential causes for the lower SEM-WDX results.

EFFECTS OF FLY ASH ON MERCURY OXIDATION DURING POST COMBUSTION CONDITIONS

Tests were performed in simulated flue gas streams using two fly ash samples from the electrostatic precipitators of two full-scale utility boilers. One fly ash was derived from a Powder River Basin (PRB) coal, while the other was derived from Blacksville coal (Pittsburgh No. 8 seam). The tests were performed at temperatures of 120 and 180 C under different gas compositions. Elemental mercury (Hg) streams were injected into the simulated flue gas and passed over filters (housed in a convection oven) loaded with fly ash. The Ontario Hydro method was used to determine the total amount of Hg passing through the filter as well as the percentages of elemental and oxidized Hg collected. Results indicated that substantial amounts of Hg oxidation did not occur with either fly ash, regardless of the temperature used for testing. When oxidation was observed, the magnitude of the oxidation was comparable between the two fly ashes. These results suggest that the gas matrix may be more important than the ash components with respect to the distribution of Hg species observed in gaseous effluents at coal-fired power plants.

Development of Mercury and Hydrogen Chloride Emission Monitors for Coal Gasifiers

The gas conditioning issues involved with coal gasification streams are very complex and do not have simple solutions. This is particularly true in view of the fact that the gas conditioning system must deal with tars, high moisture contents, and problems with NH{sub 3} without affecting low ppb levels of Hg, low levels (low ppm or less) of HCl, or the successful operation of conditioner components and analytical systems. Those issues are far from trivial. Trying to develop a non-chemical system for gas conditioning was very ambitious in view of the difficult sampling environment and unique problems associated with coal gasification streams. Although a great deal was learned regarding calibration, sample transport, instrumentation options, gas stream conditioning, and CEM design options, some challenging issues still remain. Sample transport is one area that is often not adequately considered. Because of the gas stream composition and elevated temperatures involved, special attention will need to be given to the choice of materials for the sample line and other plumbing components. When using gas stream oxidation, there will be sample transport regions under oxidizing as well as reducing conditions, and each of those regions will require different materials of construction for sample transport. The catalytic oxidation approach worked well for removal of tars and NH{sub 3} on a short term basis, but durability issues related to using the catalyst tube during extended testing periods still require study.

Precipitation of iron, sodium, and potassium impurities from synthetic solutions modeling spent acid streams from a chemical coal cleaning process

ABSTRACT Experiments on treating model spent acid streams from a chemical coal cleaning process by double salt precipitation indicated that simple heating of solutions containing Fe2(SO4)3, Na2SO4, and K2SO4 caused jarosite (KFe3(SO47)2(OH)6) to form preferentially to natrojarosite (NaFe3(SO4)2(OH)6), and precipitate yields were higher than when Na2SO4 was the only alkali sulfate present. Virtually all of the K, about 90% of the Fe, and about 30% of the SO4 2− could be precipitated at 95°C, while little or no Na was removed. However, simply heating Fe2(SO4)3/Na2SO4 solutions up to 95°C for <12 hours did not produce adequate precipitate yields. When Na was the only alkali metal present, the Fe concentration in the solution had to be increased to avoid formation of undesirable iron compounds. Increasing the Fe concentration to about 6 g/L by adding excess Fe2(SO4)3 suppressed the formation of undesirable iron salts and increased natrojarosite yields significantly, but the amount of precipitate obtained was...

AN EXAMINATION OF ASTM PROCEDURES FOR DETERMINING SULFUR FORMS IN COAL

ABSTRACT Several raw coals of various ranks were used to examine the effects of some of the variations in ASTM procedures on analytical results obtained for total sulfur and sulfur forms. ASTM procedures were also used to determine pyritic sulfur in two coals cleaned by selective agglomeration processes.In addition, organic sulfur values obtained by the indirect ASTM procedure were compared to those obtained directly by leaching coal with hot HNO3 followed by total sulfur determinations on the coal residue. Differences in the ASTM leaching procedure with HNO3 did not significantly affect the pyritic sulfur results for any of the coals. However, small differences between the referee (leaching coal with HNO3) versus alternate (leaching coal ash with HCl) ASTM procedures for determining pyritic sulfur were observed.Neithei: procedure was consistently higher than the other.