Lignite Ash Research Articles

Studies on slag deposit formation in pulverized-coal combustors. 4. Comparison of sticking behaviour of minerals and low-temperature and ASTM high-temperature coal ash on medium carbon steel substrates

Sticking test results indicate that high-temperature melts containing iron sulphide (pyrrhotite) spread well over an oxidized mild steel surface and the adhesion forces are comparatively high even at low metal temperatures. This sulphide phase originates in the coal as pyrite. Alkalis substituted in the clay structure of both illite and montmorillonite led to the formation of lower-melting slag drops compared to kaolinite. Potassium and chlorine present in the slag drops, formed from the low-temperature ash (LTA) of a Wilcox belt Texas lignite, also led to enhanced sticking properties. The sticking behaviour of slag drops formed by the rapid melting of coal minerals, either LTA residue or synthetic mineral combinations, differed from that of the ASTM ash or synthetic metal oxide mixtures. Any tests, including the sticking test using the bulk minerals or ash composition of a specific coal, may not correlate with slag deposit formation in a utility boiler, as indicated by non-agreement between the test results with the Upper Freeport ash residues and operating experience at Keystone Generating Station.

Determination of germanium in coal ashes by hydride generation and flame atomic-absorption spectrophotometry

This paper describes the determination of germanium by atomic-absorption spectrophotometry with direct introduction into a dinitrogen oxide-acetylene flame of the germanium(IV) hydride generated by reducing with sodium tetrahydroborate(III) solution. A comparative study of the sensitivity of the germanium determination has been carried out and a study of interferences from lead(II), arsenic(III) and -(V), iron(II) and -(III), tellurium(IV), selenium(IV), antimony(III), tin(II), tartrates, oxalates and fluorides is described. The sensitivity of the proposed method is 0.012 µg ml–1 and the detection limit is approximately 100 times better than obtained with silica tube atomisation at a wavelength of 265.14 nm. The method has been applied to the determination of germanium in lignite ashes with an average germanium recovery of 97.65% and a relative standard deviation of 2.87%.

Recovery of uranium from lignites

There is a renewed interest in lignites as a source of fuel and for the possible by-product recovery of uranium. This paper summarizes the experimental work carried out at Oak Ridge National Laboratory during 1952 to 1954 that deals with the sulfuric acid leaching of lignite ash for uranium recovery. A discussion of the possible utilization of sulfur dioxides in flue gases should be of value to those companies planning to process lignites.

Closure to “Discussion of ‘Sulphur Neutralization by Lignite Ash: Pilot-Scale Combustion Experiments’” (1979, ASME J. Eng. Power, 101, p. 619)

Closure to “Discussion of ‘Sulphur Neutralization by Lignite Ash: Pilot-Scale Combustion Experiments’” (1979, ASME J. Eng. Power, 101, p. 619)

Discussion: “Sulphur Neutralization by Lignite Ash: Pilot-Scale Combustion Experiments” (Brown, T. D., Lee, G. K., and Bambrough, H. A., 1979, ASME J. Eng. Power, 101, pp. 615–619)

Discussion: “Sulphur Neutralization by Lignite Ash: Pilot-Scale Combustion Experiments” (Brown, T. D., Lee, G. K., and Bambrough, H. A., 1979, ASME J. Eng. Power, 101, pp. 615–619)

Sulphur Neutralization by Lignite Ash: Pilot-Scale Combustion Experiments

A pilot-scale research boiler (750 kg steam/hr) has been used to study the degree of sulphur neutralization during combustion experiments with three lignites. A series of four closely controlled experiments showed that sulphur balances close to 100 percent could be achieved in the pilot-scale system burning Gascoyne lignite; in these experiments the sulphur retained in solid phase residues varied between 21 and 24 percent of the input sulphur. It was also demonstrated with Utility lignite that external recirculation of flue-gas was moderately effective in reducing nitric oxide emissions at the expense of major increased in the carry-over of unburnt carbon. However, sulphur dioxide neutralization by the coal-ash cations remained essentially unchanged as the recirculation ratio increased. Enhancement of sulphur neutralization by dry lime addition to Poplar River lignite was only found to be effective at addition rates above 1/2 percent lime by weight. The effectiveness of the lime was found to increase as the excess-air level increased.

Element concentrations in aqueous equilibrates of coal and lignite fly ashes

A survey was conducted of the concentration of arsenic, boron, molybdenum, phosphorus, and selenium in aqueous equilibrates of fly ashes derived from a number of soft coals and lignites. concentrations of boron were much higher than those of the other elements. The concentrations of water-soluble boron and molybdenum in the soft coal ashes and water-soluble selenium in the lignite ashes showed a high degree of correlation (p<0.01) with the total element concentrations in the respective ash samples.

Catalysis of carbon-steam gasification by ash components from two lignites

Ash transfer from a reactive to a less reactive coal is an interesting possibility for improving and equalizing gasification characteristics of coals. To assess the catalytic action of coal impurities in the steam gasification of carbon, three approaches were used. In the first series, the effects of different coal ashes on the gasification kinetics of graphite were compared. A parallel study was made by adding lignite ash to a coal of low reactivity. Finally, gasification rates of chars prepared from demineralized coals were measured. While it was found that ash from reactive coals can significantly enhance the gasification rates of chars derived from coals of lesser reactivity, it was not possible to distinguish clearly between a catalytic lowering of the activation energy and an increase in the number of gasification sites. The gasification enhancement by lignite ash may open practical possibilities for blending coals of different reactivity, and warrants further study to identify the constituents associated with this effect.

A Proposed Mechanism for Ash Fouling Burning Northern Great Plains Lignite

Fouling of boiler heat transfer surfaces by lignite ash continues to be a problem that reduces boiler efficiency and availability. The present study evaluates the fouling mechanism in a microscopic sense. It endeavors to establish a relationship between the identity and mode of occurrence of mineral matter in lignite and the resultant ash deposits. Severe fouling conditions are believed caused by the formation of a melted phase binding material within the deposit. Sodium, volatilized from coal and reacted in the flue gas to form sulfate or carbonate, reacts with a fly ash subspecies (termed matrix parent) to form the integrative matrix within ash deposits. The reactive subspecies (matrix parent) is derived from the inherent ash present in each burning coal particle. However, only inherent ash having elemental compositions lying within a given range is fluxable by sodium to form a sticky, deposit-integrating material. The major elements comprising the matrix are Na, Ca, Al, and Si. A chemical solution to the lignite fouling problem must alter the fluxing sodium or the fluxable matrix parent.

The Plant Availability of Potassium in Fly Ash

AbstractThe availability of K in fly ash obtained from nine coal burning power generating plants was evaluated by greenhouse and laboratory procedures. The total K content of the samples of fly ash ranged from 0.65 to 3.14%. Eight of the samples were bituminous coal ashes, and one was lignite coal ash. The samples of bituminous coal fly ash neutralized less than 0.25 meq H3O+/g, whereas the sample of lignite coal fly ash neutralized 3.05 meq H3O+/g. Application of three samples of the bituminous coal fly ash and the sample of lignite coal fly ash increased K uptake by corn plants (Zea mays L.) grown on Davidson clay loam. Potassium uptake was higher from application of 158 mg K as KCl to 2,100 g of the soil than from application of a higher rate of K as the four samples of fly ash. Equivalent K uptake by corn plants occurred from application of 79 mg K as KCl and 207 mg K as the lignite fly ash. However, yield was lower where the ash was applied. Tissue analyses indicated that B toxicity limited yield on the latter treatment. Application of certain of the fly ash samples increased Mg uptake by corn plants. This increase in Mg uptake probably caused a decrease in K uptake by plants grown in the fly ash‐soil mixtures.

Sample preparation and electron microprobe examination of lignite ash deposits

A suitable technique was developed for preparation of lignite ash deposits for electron microprobe examination. Prepared samples were analyzed for concentrations and distribution relationships of seven elements at four separate positions in the bulk deposit. Fortytwo discrete groups of these elements were identified, each of which may represent more than one chemical compound.

Determination of Trace Elements in Lignite Ashes

Two spectrographic methods for the quantitative determination of trace elements in lignite ashes and shales are described. The involatile elements are determined in a controlled atmospher of carbon dioxide gas that suppresses cyanogen bands, improves line to background ratio, and provides a more precise technique for the simultaneous determination of a large number of elements. Lutecium oxide in calcium carbonate and fused potassium sulfate (1 + 1) is used as the internal standard The volatile elements are determined in an ordinary d.c. arc, using a pellet technique to increase the limit of detection and rate of volatilization. Antimony and cadmium potassium sulfate are used as internal standards. Analyses of U. S. Geological Survey standard rock samples G1 and W1 show that the method can be extended to other silicate rocks. An additional application of the controlled carbon dioxide atmosphere is the determination of boron and gallium.