Investigation of mineral transformations and ash deposition during staged combustion. Quarterly technical progress report, October 1, 1996--December 31, 1996

The key issues addressed this quarter were related to operational problems in the coal feed system, namely, the inability to accurately measure all of air entering the system, and plugging of coal in the feed lines due to poor entrainment. Both of these problems caused unacceptable uncertainty and/or fluctuations in the operating conditions and therefore required solutions. The coal entrainment problem was solved by installing a new educator designed for entraining solids in gas streams. All of the air entering the reactor now flows through the educator, either as motive air or through the suction air inlet. This ensures that the coal is entrained at relatively high velocity, so that it will flow to the reactor without forming slugs in the lines. A new feeder shroud was also installed with an air jet directed towards the auger to sweep off the tip in order to reduce pulsations when feeding coal. The problems associated with accurately metering the air have been somewhat more difficult to resolve. New strategies for completely closing the system have been tested and look promising. A new flowmeter was also purchased with cost sharing funds to directly measure the air flow rate of the two phase stream (after the coal injection point). If the system can be operated without leaks, then the changes will provide two independent measurements of the air flow to ensure accuracy. If the system cannot be sealed, the new flowmeter will still provide reliable measurement of the air flow and permit proper operation of the combustor. Consequently, we feel that the problems have been resolved and we look forward to a productive next quarter

Investigation of mineral transformations and ash deposition during staged combustion. Quarterly technical progress report, April 1, 1997--June 30, 1997

This report describes work performed in the fifteenth quarter of a fundamental study to examine the effect of staged combustion on ash formation and deposition. Efforts this quarter included addition of a new cyclone for improved particle sampling and modification of the existing sampling probe. Particulate samples were collected under a variety of experimental conditions for both coals under investigation. Deposits formed from the Black Thunder coal were also collected. Particle size and composition from the Pittsburgh No. 8 ash samples support previously reported results. In addition, the authors ability to distinguish char/ash associations has been refined and applied to a variety of ash samples from this coal. The results show a clear difference between the behavior of included and excluded pyrite, and provide insight into the extent of pyrite oxidation. Ash samples from the Black Thunder coal have also been collected and analyzed. Results indicate a significant difference in the particle size of {open_quotes}unclassifiable{close_quotes} particles for ash formed during staged combustion. A difference in composition also appears to be present and is currently under investigation. Finally, deposits were collected under staged conditions for the Black Thunder coal. Specifically, two deposits were formed under similar conditions and allowed to mature under either reducing or oxidizing conditions in natural gas. Differences between the samples due to curing were noted. In addition, both deposits showed skeletal ash structures which resulted from in-situ burnout of the char after deposition

Investigation of mineral transformations and ash deposition during staged combustion. Quarterly technical progress report, October 1, 1996--December 31, 1996

The key issues addressed this quarter were related to operational problems in the coal feed system, namely, the inability to accurately measure all of air entering the system, and plugging of coal in the feed lines due to poor entrainment. Both of these problems caused unacceptable uncertainty and/or fluctuations in the operating conditions and therefore required solutions. The coal entrainment problem was solved by installing a new educator designed for entraining solids in gas streams. All of the air entering the reactor now flows through the educator, either as motive air or through the suction air inlet. This ensures that the coal is entrained at relatively high velocity, so that it will flow to the reactor without forming slugs in the lines. A new feeder shroud was also installed with an air jet directed towards the auger to sweep off the tip in order to reduce pulsations when feeding coal. The problems associated with accurately metering the air have been somewhat more difficult to resolve. New strategies for completely closing the system have been tested and look promising. A new flowmeter was also purchased with cost sharing funds to directly measure the air flow rate of the two phase stream (after the coal injection point). If the system can be operated without leaks, then the changes will provide two independent measurements of the air flow to ensure accuracy. If the system cannot be sealed, the new flowmeter will still provide reliable measurement of the air flow and permit proper operation of the combustor. Consequently, we feel that the problems have been resolved and we look forward to a productive next quarter

Investigation of mineral transformation and ash deposition during staged combustion. Final report, October 1, 1993--September 30, 1997

The purpose of this report is to document a recently completed four-year study to examine the impact of low-NOx firing technologies on ash formation and deposition while firing pulverized coal. Low-NOx burners and staged combustion inhibit NOx formation by restricting the amount of oxygen available to form a fuel-rich zone in which nitrogen compounds are reduced to molecular nitrogen (N{sub 2}) rather than oxidized. Additional oxygen is provided downstream for complete combustion. Consequently, coal and mineral particles encounter different temperatures and oxygen concentrations when they are burned under low-NOx firing conditions than they do in conventionally-fired units. Two coals with distinctly different inorganic contents and ash characteristics were fired in a pilot-scale laboratory combustor under both conventional and staged combustion conditions. Ash and deposit samples were collected at various locations in the reactor and analyzed in order to assess the influence of staged combustion. This report is organized as follows. First, a background section provides the foundation needed in order to understand the motivation for and the results of the experimental program. The next section presents a description of the experimental apparatus and procedures, including the development the analytical methods critical to the study. Results of the analyses of coal, ash and deposit samples are then presented and discussed for each of the two coals. Finally, the report ends with a short summary and statement of conclusions

Investigation of mineral transformations and ash deposition during staged combustion. Quarterly technical progress report, April 1, 1996--June 30, 1996

This report describes work completed during the eleventh quarter of a DOE-funded study of mineral transformations and ash deposition during staged combustion. Accomplishments included repairs and improvements to the laboratory combustor, collection of deposits and observation of deposition behavior as a function of operating conditions, and analysis of deposit samples collected under both staged and conventional conditions. The water cooling shell for the brass burner was rebuilt this quarter. It was necessary to rebuild the cooling shell because of frequently occurring leaks which could no longer be repaired. No new leaks have occurred since the repairs were made. Deposits were collected for several stoichiometries between SR=0.65 and SR=0.75. A changeover from carbon-rich deposits to deposits which contained little carbon was observed at about SR=0.73 for the coal and natural gas feed rates used the experiments. However, even deposits which contained relatively little carbon had a carbon- enriched layer at the tube surface. This layer was due to carbon which did not burn out completely after impaction. A similar type of carbon layer may affect deposit formation in utility boilers. One of the key contributions this quarter was the analysis of deposit samples collected under both staged and conventional conditions. These initial results indicate that deposits formed during staged combustion of a Pittsburgh No. 8 are similar to those formed during conventional combustion. Some small differences were observed and it is not yet known how significant these differences may be. However, substantial differences between the deposits and ash samples were observed. These differences were apparent in both the bulk compositions and ``species`` distributions. Continuing work will focus on clarifying and quantifying the effect of staged combustion on deposit formation and strength development

Investigation of mineral transformations and ash deposition during staged combustion. Quarterly technical progress report, January 1, 1996--March 31, 1996

Progress during the tenth quarter of a three-year study of ash formation and deposition was made in several areas. One of the key contributions this quarter was the development of an algorithm to distinguish between ash particles that are associated with char particles (included) and ash particles which are excluded. This algorithm was used to determine the extent to which pyrite transformations are influenced by whether the pyrite grains are included or excluded. The results indicate that pyrite oxidation is slower for included pyrite grains. Replicate experiments were also performed for the Pittsburgh No. 8 coal (washed) under both staged and conventional conditions. An objective of these experiments was to validate the effect of staged combustion on the size distribution of ash particles as reported for the previous quarter. Analysis of the new samples and repeat analyses of previous samples showed no significant difference in the ash particle size for samples collected at stoichiometric ratios of 0.75 (before the stage) and 1.04. The number of points in the new analyses was considerably higher than in previous analyses, resulting in greater confidence. The similarity in the ash composition for samples collected under staged and conventional conditions was also verified this quarter with replicate samples and analyses. The net result is that staged combustion does not appear to have a significant impact on either ash size or composition for the Pittsburgh No. 8 coal. Finally, numerical simulations of the temperature distribution in the laboratory combustor were performed and evaluated. Also, a paper documenting the classification algorithm developed last quarter was presented at the March ACS meeting in New Orleans and published in the ACS Division of Fuel Chemistry Preprints

Investigation of mineral transformations and ash deposition during staged combustion. Quarterly technical progress report, January 1, 1995--March 31, 1995

Progress during the sixth quarter of a three-year study was made in two task areas: (1) parametric testing of the target coals, and (2) analysis of samples from the combustion tests. A new microanalysis system was acquired (no cost to DOE) and is now functional, although development of analysis routines for the system is still in progress. This system has significantly increased our analytical throughput and has provided increased reliability. Parametric testing of the Pittsburgh No. 8 coal (weathered) was initiated this quarter. Initial analytical results from these tests show sulfur release and iron transformations as a function of test conditions and sampling location. A new supply of Pittsburgh No. 8 coal has been shipped and will be used to contrast behavior between the oxidized (weathered) and unoxidized Pittsburgh fuels. Finally, specific tasks for the next quarter have been identified and reported

The Deepest Radio Study of the Pulsar Wind Nebula G21.5-0.9: Still No Evidence for the Supernova Shell

We report on sensitive new 1.4-GHz VLA radio observations of the pulsar wind nebula G21.5-0.9, powered by PSR J1833-1034, and its environs. Our observations were targeted at searching for the radio counterpart of the shell-like structure seen surrounding the pulsar wind nebula in X-rays. Some such radio emission might be expected as the ejecta from the <~ 1000 yr old supernova expand and interact with the surrounding medium. We find, however, no radio emission from the shell, and can place a conservative 3-sigma upper limit on its 1-GHz surface brightness of 7 x 10^-22 W/m^2/Hz/sr, comparable to the lowest limits obtained for radio emission from shells around other pulsar-wind nebulae. Our widefield radio image also shows the presence of two extended objects of low-surface brightness. We re-examine previous 327-MHz images, on which both the new objects are visible. We identify the first, G21.64-0.84, as a new shell-type supernova remnant, with a diameter of ~13' and an unusual double-shell structure. The second, G21.45-0.59, ~1' in diameter, is likely an HII region.Comment: 8 Pages, submitted to MNRA

Chandra and Suzaku observations of the Be/X-ray star HD110432

We present an analysis of a pointed 141 ks Chandra high resolution transmission gratings observation of the Be X-ray emitting star HD110432, a prominent member of the gamma Cas analogs. The Chandra lightcurve shows a high variability but its analysis fails to detect any coherent periodicity up to a frequency of 0.05 Hz. The analysis of the Chandra HETG spectrum shows that, to correctly describe the spectrum, three model components are needed. Two of those components are optically thin thermal plasmas of different temperatures (kT~8-9 and 0.2-0.3 keV respectively). Two different models seem to describe well the third component. One possibility is a third hot optically thin thermal plasma at kT=16-21 keV with an Fe abundance Z~0.3Zo, definitely smaller than for the other two thermal components. Alternatively, the third component can be described by a powerlaw with a photon index Gamma=1.56. In either case, the Chandra HETG spectrum establishes that each one of these components must be modified by distinct absorption columns. The analysis of a non contemporaneous 25 ks Suzaku observation shows the presence of a hard tail extending up to at least 33 keV. The Suzaku spectrum is described with the sum of two components: an optically thin thermal plasma at kT ~ 9 keV and a very hot second plasma with kT ~33 keV or, alternatively, a powerlaw with photon index Gamma=1.58. The analysis of the Si XIII and S XV He like triplets present in the Chandra spectrum point to a very dense (n_e ~ 10^13 cm^-3) plasma located either close to the stellar surface (r<3R_*) of the Be star or, alternatively, very close (r ~1.5R_WD) to the surface of a (hypothetical) WD companion. We argue, however, that the available data supports the first scenario.Comment: 13 pages, 21 Figures. Accepted for publication in Ap