摘要:

The distribution of wettability of as-received and oxidized coal particles was determined by film flotation with a series of aqueous methanol solution of different surface tensions. The mean critical wetting surface tension of coal particles (y¯) obtained from the distribution shows that in general the hydrophobicity of coal particles decreases upon oxidation and that low-rank coals are more susceptible to oxidation than high-rank coals. The increase in y¯ can be correlated quite well with the oxygen uptake during oxidation and the acidic oxygen function group concentration on coal surface, and with the water retention capacity and the salt flotation yield of coals. This study further demonstrates that y¯cof coal can be used as a reliable parameter for correlating the wetting behavior of coals with their composition, rank and degree of oxidation and for predicting the behavior of coal particles in fine coal beneficiation.

ISSN:0734-9343    

DOI:10.1080/07349349208905189

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The contact angle of water on fine coal particles was measured on a flat surface formed by pressing the coal powder into a highly compacted disc. A model that considers solid particles and pores as major disc consituents was employed. The fractional area of pores on the disc surface was postulated being equal to the disc bulk porosity under the assumption of uniform porosity within the disc and of negligible plastic deformation and crushing action on the particles on the disc surface. The predominant effect of disc porosity on the contact angle was corrected using the Cassie-Baxler equation.

ISSN:0734-9343    

DOI:10.1080/07349349208905190

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The distribution of the wettability of coals of different rank was determined by measurements of contact angles for individual particles. The contact angle was estimated from the equilibrium partitioning of a particle at the water/air interface. Using this technique contact angles were determined for a larger number of particles from a given sample and a frequency distribution of contact angle was obtained. The contact angle distribution was broad for all the coals tested with included an anthracite, a hvA bituminous and a sub-bituminous coal. In comparison, spherical particles of polymethylmethacrylate gave a much narrower distribution. The distribution for irregular polyethylene particles was somewhat broader than that for the polymethylmethacrylate spheres but broader than that for the polymethylmethacrylate spheres but considerably narrower than that for coal. The broader wetting distribution for coal was attributed to differences in surface chemical properties.

ISSN:0734-9343    

DOI:10.1080/07349349208905191

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A flow calorimetric method was developed for comparing the strength and/or extent of acid-base bonding in the outer surface and subsurface regions of fine coal particles. This method was applied to an ultrafine sample of a low-sulfur, low-ash bituminous coal. Information about the acid-base bonding in the outer surface region of the fine particles was deduced from heats of interaction of 4-tert.-butylpyridine dissolved in 2.2,4-trimethylpentane (“"isooctane”). The penetration of this basic probe molecule into the particles is limited by its tert.-butyl group. The acid-base character of the subsurface region was deduced from heals of interaction with acetone and pyridine. good coal penetrants/swelling agents. The results suggest that the outer surface of the low-sulfur, low-ash coal studied is H-bonded to a considerably greater extent than the subsurface region. Such results are rationalized on the basis of mild oxidative weathering conditions, which may render the outer surface of coals richer in ether oxygens than the subsurface region. Once formed, such oxygens are expected to H-bond to acidic protons from contiguous portions of the coal.

ISSN:0734-9343    

DOI:10.1080/07349349208905192

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Scanning electron microscope-based automated image analysis (SEM-AIA) is a technique of characterizing particles for size and shape from SEM images and for elemental composition from energy-dispersive X-ray spectra, and because it is automated it can provide data for a statistically significant number of particles. It was used to characterize the association of mineral matter with organic coal components in order to predict cleanability for both density-based and surface-based cleaning processes. Selected samples of coals from Pittsburgh No. 8, Upper Freeport, and Illinois No. 6 seams, ground by two different research groups to a nominal 200-mesh particle size, were characterized using this technique. SEM-AIA results indicated significant differences in the overall particle size distributions between the Pittsburgh No. 8 coal samples from the two groups, which were reflected in the association of coal and mineral matter. Coal and mineral phases within composite coal-mineral particles were characterized in cross section for phase size and identity. The amount of phases present within each composite particle and the combined amount of mineral phases present on the exposed perimeter were also measured as indicators of association with regard to density- and surface-based cleaning processes, respectively. For the three coals ground at the same place to comparable sizes, the Upper Freeport appeared to be the most cleanable by density-based processes, followed by the Illinois No. 6 and then the Pittsburgh No. 8 coal. For the same coals, the SEM-AIA results also predicted significantly less cleanability for surface-based processes; at high levels of coal recovery and mineral reduction, 10-20% less mineral reduction was predicted at the same level of coal recovery. These differences are apart from any surface chemistry considerations and involve only the association, i.e., the distribution of coal and mineral matter within the particles. The coals exhibited the same relative ranking of cleanability by density- or surface-based processes.

ISSN:0734-9343    

DOI:10.1080/07349349208905193

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Diffuse and specular reflectanceFTIRanalysis both fossil resin (resinite) and coal has been carried out to study surface oxidation reactions which occur during the selective flotation of fossil resin from coal by ozone conditioning. It was found from theFTIRspectra that ozonation of both fossil resin and coal causes an increase in the peak intensity associated with stretching vibrational frequencies of certain oxygen functional groups such as hydroxyls (3400 cm−1’) and carbonyls (1700 cm−1).

ISSN:0734-9343    

DOI:10.1080/07349349208905194

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

In order to develop appropriate desulfurization strategies, the organic sulfur species and their distribution in coal need to be characterized. Peroxyacetic acid oxidation has been developed to render coal soluble, allowing for the subsequent GC-FID/FPD and GC-MS analysis of sulfur compounds. Four Illinois Basin coals and samples of sporinite, vitrinite and semifusinite isolated from them have been examined. Between 20 and 50% of the organic sulfur in these coals is associated with relatively few compounds detected in the volatile oxidation products. Of these, methylsulfonic acid is the most abundant, which, from model compound studies, results from oxidation of either methyl disulfide or simple thiophene structures in the coals. Although the species detected are commonly occurring among the majority of the coal and maceral fractions, their distribution varies considerably from sample to sample. By fractionating the oxidation products, a fraction was obtained that had a sulfur content of 18%. This fraction represents nearly 50% of the total organic sulfur but only 10% of the weight of the coal. Using peroxyacetic acid to desulfurize coal, it has been demonstrated that all pyrite and sulfate can be removed at room temperature and at least 25% of the organic sulfur at slightly higher temperatures.

ISSN:0734-9343    

DOI:10.1080/07349349208905195

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The Pittsburgh Energy Technology Center (PETC) recently completed an interlaboratory test program (ITP) involving eight laboratories that are currently performing washability analyses of coals finer than 500-microns top size using a centrifugal float-sink technique.

ISSN:0734-9343    

DOI:10.1080/07349349208905196

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

This paper presents the results of an experimental study undertaken to demonstrate the feasibility of using silica sand as a grinding media in stirred ball mills for ultra-fine coal grinding. Laboratory butch as well as bench scale continuous tests indicate that when fracturing silica sand is substituted for steel media, then superior energy savings on the order of 50% and more can be realized. Moreover, this approach has been found to eliminate the disadvantages observed with grinding using steel media such as high replacement cost, contamination of coal through media wear, greater degree of coal oxidation due to higher slurry temperature and greater level of noise dissipation. Additionally, coal-sand attrition system reduces the manpower time because steel media after grinding needs precautionary measures to be taken such as thorough cleaning and their storage in inert atmosphere to avoid rust and corrosion problems.

ISSN:0734-9343    

DOI:10.1080/07349349208905197

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A 5-horsepower Pitt Mill prototype has been used to develop information on the effects of coal characteristics and of mill design and operation on the cost of grinding coal to the 10 microns size range. Grinding media wear is the largest cost factor in fine grinding of coal using stirred bed technology. The specific media loss rate, pounds of media per kW-hour energy input to the grinding bed, more than doubles and the cost per pound of replacement media increases by a factor of four as the chrome steel grinding media ball size is reduced from 3/8 inch to 3/16 inch diameter. The specific media loss rate has been found to be directly related to the ash level of the coal. Estimates of the cost to grind 50 HGI coal to sizes between 10 and 20 µm in the Pitt Mill range from $29 to $10 per ton respectively.

ISSN:0734-9343    

DOI:10.1080/07349349208905198

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor