Coal-derived unburned carbons in fly ash: A review

Hower, James C.; Groppo, J.G.; Graham, Uschi M.; Ward, Colin R.; Kostova, I.; Maroto‐Valer, M. Mercedes; Dai, Shifeng

doi:10.1016/j.coal.2017.05.007

Cited by 184 publications

(106 citation statements)

References 161 publications

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“…The fine monazite and other minerals are entrained in glass in the fly ash [20][21][22][23]. REEs are also associated with nano-scale carbons surrounding the fly ash glass and spinels [20,24].In Phase I of this study [21], several ashes (four pulverized coal combustion (PCC) ashes and one fluidized bed combustion (FBC) ash) were beneficiated on a bench-scale array involving froth flotation of the carbons, magnetic separation of the Fe-spinels (magnetite), and screening to produce a <200-mesh (<75-µm) Al-Si-rich ash product. Additional testing was conducted on the ponded ash from one of the PCC plants, which was a retired 1950 s-vintage, four-unit plant.…”

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Distribution of Lanthanides, Yttrium, and Scandium in the Pilot-Scale Beneficiation of Fly Ashes Derived from Eastern Kentucky Coals

et al. 2020

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In this study, Central Appalachian coal-derived fly ashes from two power plants were beneficiated in a pilot-scale facility in order to produce a product with a relatively consistent concentration of rare earth elements (REE). The <200-mesh final fly ash product was produced by removing the carbon- and Fe-rich particles prior to screening at 200 mesh (75 µm). The Plant D fly ash had high concentrations of CaO and SO3, which were diminished through the two months when the ash was being beneficiated, representing a consequence of the heat, humidity, and excessive rainfall in the Kentucky summer. The high CaO and SO3 concentrations through the early runs likely contributed to the lower REE in the <200-mesh products of those runs. Of the non-REE minor elements, Ba, V, Mn, Zn, and As showed the greatest between-run variations within the runs for each plant. The overall REE concentrations proved to be similar, both on a between-run basis for the individual fly ash sources and on a between-plant basis. Variations in fly ash quality will occur in larger-scale operations, so on-going attention to the fly ash quality and the response of the fly ash to beneficiation is necessary. Changes in the Plant D fly ash with time imply that both the freshness of the original ash and the length and conditions of its storage at the site of beneficiation could be factors in the quality and consistency of the processed fly ash.

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Distribution of Lanthanides, Yttrium, and Scandium in the Pilot-Scale Beneficiation of Fly Ashes Derived from Eastern Kentucky Coals

et al. 2020

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“…The RUC reached the maximum of 80.89% at the conditioning speed of 1200 rpm. The UC collected from the FA could be used as some industrial materials or fed back to the boiler as fuel energy [53]. The optimal conditioning-flotation results were obtained with an LOI of 3.32%, a yield of 78.69% and an RUC of 80.89% when the conditioning speed was 1200 rpm.…”

Section: Effect Of the Conditioning Speed On The Loi And Yield Of Flomentioning

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The Process of the Intensification of Coal Fly Ash Flotation Using a Stirred Tank

Zhu

et al. 2018

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Pulp preconditioning using a stirred tank as a pretreatment process is vital to the flotation system, which can be used to improve the flotation efficiency of mineral particles. The kinetic energy that is dissipated in the stirred tank could strengthen the interaction process between mineral particles and flotation reagents to improve the flotation efficiency in the presence of the preconditioning. In this paper, the effect of the conditioning speed on the coal fly ash flotation was investigated using numerical simulations and conditioning-flotation tests. The large eddy simulation coupled with the Smagorinsky-Lilly subgrid model was employed to simulate the turbulence flow field in the stirred tank, which was equipped with a six blade Rushton turbine. The impeller rotation was modelled using the sliding mesh. The simulation results showed that the large eddy simulation (LES) well matched the previous experimental data. The turbulence characteristics, such as the mean velocity, turbulent kinetic energy, power consumption and instantaneous structures of trailing vortices were analysed in detail. The turbulent length scale (η) decreased as the rotation speed increased, and the minimum value of η was almost unchanged when the rotation speed was more than 1200 rpm. The conditioning-flotation tests of coal fly ash were conducted using different conditioning speeds. The results showed that the removal of unburned carbon was greatly improved due to the strengthened turbulence in the stirred tank, and the optimal results were obtained with an LOI of 3.32%, a yield of 78.69% and an RUC of 80.89% when the conditioning speed was 1200 rpm.

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“…Sulfur emissions are mitigated through dry/wet desulphurization technologies [9,10], which provide promising achievements also for some other elements, such as Hg, As, Se, Cl and Br [11]. Due to its toxicity and volatility, world-wide attention is paid to Hg retention from flue gas, revealing good results for activated carbon [12], unburned carbon [13][14][15][16], manganese-based adsorbents [17], etc.…”

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Behavior of Pb During Coal Combustion: An Overview

et al. 2019

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Despite the progress in understanding heavy metals behavior during coal combustion, mitigation of heavy metals emissions is still a tough challenge due to a complex character of this phenomenon. Several lists of potentially toxic elements have been presented; in most cases, Pb belongs to the elements with the greatest environmental and human-health concern. The review paper is focused upon the behavior of Pb during coal combustion. with particular attention paid to decreasing its emissions. It summarizes the dominant parameters affecting its redistribution among coal combustion streams. As gaseous emissions can quite easily pass through the particulate control device, attention was paid primarily to Pb distribution between condensed and volatilized phases. A crucial factor enhancing Pb volatility is the presence of organic or inorganic chlorides, which is discussed in detail, including their chlorination mechanisms and interactions with other fuel/flue gas species. Components decreasing Pb volatility and promoting the formation of condensed phases are also discussed (higher levels of moisture, Na, O2 etc.). Factors enhancing Pb volatility, as well as factors facilitating Pb retention, are discussed with the view of fluidized-bed combustion, pulverized-fuel combustion, or co-combustion of coal with wastes.

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Coal-derived unburned carbons in fly ash: A review

Cited by 184 publications

References 161 publications

Distribution of Lanthanides, Yttrium, and Scandium in the Pilot-Scale Beneficiation of Fly Ashes Derived from Eastern Kentucky Coals

Distribution of Lanthanides, Yttrium, and Scandium in the Pilot-Scale Beneficiation of Fly Ashes Derived from Eastern Kentucky Coals

The Process of the Intensification of Coal Fly Ash Flotation Using a Stirred Tank

Behavior of Pb During Coal Combustion: An Overview

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