John L. Schaefer

Dry triboelectrostatic beneficiation of fly ash

A laboratory-scale triboelectrostatic separation system in conjunction with analytical techniques was used to study fly ash beneficiation. Fly ash samples were characterized by size analysis and carbon content and then subjected to dry triboelectrostatic separation. Due to differences in the surface physical and chemical properties of the carbon and ash, particles of unburnt carbon and fly ash were triboelectrically charged to opposite polarity and then separated by passing them through a static electric field. Ash fractions deposited on the positive and negative electrodes were collected, analysed for carbon content and subjected to SEM and petrographic analyses. The results indicate that the physical and chemical properties of the ash dictate the maximum carbon-ash separation that would be possible. In addition, the potential of dry separation technology for removing unburnt carbon from coal ash was demonstrated.

Particle tribocharging characteristics relating to electrostatic dry coal cleaning

Abstract The velocity, number density and size of representative coal mineral matter particles were measured using laser phase Doppler velocimetry subsequent to their triboelectrification and while flowing through a constant electric field. For 60 μm diameter silica particles, the accumulated negative charge, q, could be represented by a normal distribution having an average value which was linearly dependent on the gas velocity in the tribocharger, V, and represented by qSi = [2.6V + 4] × 10−14C. The width of the distribution increased with increasing gas velocity. Physical mixtures of similar sized silica and glassy carbon, and coal, were also subjected to electrostatic separation while being monitored by the non-intrusive laser optical technique. The purity of the carbon separated from silica was >90%, and dependent on the accumulation of either positive charge or no charge on the silica. For a high volatile A, Elswick seam, Pike County, Kentucky coal, the removal of mineral matter was comparable to that obtainable by wet processes, decreasing mineral matter content from 6.4% to 3.7% at a 72% combustible recovery.

Maceral/microlithotype partitioning through triboelectrostatic dry coal cleaning

Abstract Three eastern Kentucky and two Illinois Basin coals were tested in a bench scale triboelectrostatic separation unit. The three eastern Kentucky samples provided a rank series of petrographically comparable coals. The Illinois Basin bituminous coals were lower rank and had high vitrinite ( ∼ 80%) and sulfur contents in comparison to the other three coals. Triboelectrostatic beneficiation provides efficient maceral and mineral partitioning in the high volatile A and B bituminous coals tested, with vitrinite, as vitrite and vitrinite-enriched microlithotypes, reporting to the clean fractions and the inertinites, liptinites, and minerals reporting to the tails. The high volatile C bituminous Springfield coal had a lower separation efficiency than the petrographically similar, but higher rank, Herrin coal. The decreased separation efficiency in the behavior of the Springfield coal may be a response to its higher moisture content. Compared to bench-scale fuel oil agglomeration of some of the same coals, triboelectrostatic separation provides clearer partitioning of mineral matter, sulfur, and macerals.

Triboelectrostatic Cleaning of Coal In-Line Between Pulverizers and Burners at Utilities

Pulverized coal combustors are the principal means for converting coal to electricity in the United States. Coals used in these combustors have to be beneficiated because of escalating specifications on fuel quality that help to increase boiler efficiency and decrease acid gas emmissions. Because coal is pulverized before its combustion in PC boilers, during which time substantial mineral liberation occurs, it may be beneficial to remove mineral matter from the combustibles by using dry beneficiation techniques after the pulverizers and within the burner pipes leading to the coal burners. One such technique is based on triboelectrostatics. It relies on establishing a differential charge on coal and mineral matter and then separating this charged mixture in an electrostatic field. This paper presents data obtained at a utility site that quantify the charge imparted on coal during pulverization and transport in a burner pipe, and compares these values to data obtained within a laboratory setting. The electr...

Non-intrusive measurement of particle charge: Electrostatic dry coal cleaning

A test apparatus utilizing a Phase Doppler Particle Analyzer was developed to non-intrusively determine charge on small particles. Optimum operating conditions for the system were determined using highly characterized silica spheres with an average particle diameter of 60{mu} in a dry N{sub 2} gas. The silica spheres were triboelectrically charged, and passed through a high intensity electric field. The charged particle trajectories, diameter, and number density were monitored using a two component laser PDPA. From this data and known operating parameters charge magnitude was determined.

Triboelectrostatic Coal Cleaning

This research has shown that both pressurized and suction configurations for utility pulverizers impart substantial and differential charge on mineral matter and combustible material in coal. The absolute value of the average charge per unit mass was the same order of magnitude for both utility systems and was in agreement with values obtained within a laboratory system. This differential charge can be utilized to beneficiate combustibles and mineral matter in-line between the pulverizers and burners under conditions typical to that of coal transport in the utility.

Partitioning and behavior of coal macerais during dry coal cleaning

Publisher Summary Fine-coal cleaning is studied using dry, triboelectrostatic experimentation. The 45–75 μn coals are pneumatically transported through a Cu-loop tribocharger and then transported through a 100–200 kV/m electric field. Positively charged coal is deflected to the negative electrode and negatively charged minerals are deflected to the positive electrode. Samples are retrieved and subjected to petrographic analysis. Petrographic analysis of these samples showed that for high volatile A and B bituminous coals, vitrinite macerals are significantly enhanced in the clean coal, whereas the fusinite + semifusinite + exinite maceral are enhanced in the tailings/minerals. For a high volatile C bituminous coal, this trend in enhancement is not observed. The vitrinite partitioning, greater for dry processing than for wet processing, may be related to differences in surface chemical and physical properties of the coals.

Mild Temperature, Fluidized Bed Gasification of Coal/Phosphoric Acid Mixtures: Partitioning Coal Sulfur to the Gas as H2S

1. Abstract The processing of high sulfur, Illinois basin coal using fluidized bed mild temperature gasification of coal/phosphoric acid mixtures is described. It is part of an overall coal utilization process which can minimize the production of wastes and maximize the synthesis of value-added products. Comparisons of product slates and the extent of desulfurization as a consequence of using the novel process are compared to traditionally practiced mild temperature gasification. It is shown that high sulfur coal can be desulfurized at temperatures as low as 500°C that the sulfur partitions to the gas phase as H 2 S. Product yields and their characteristics important for application are discussed.