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Title: Simulating the transformation of heavy metals during coal or sewage sludge combustion

Abstract

A mathematical model (FPM) is presented to predict the transformation of heavy metals in the downstream of combustor or incinerator. The model accounts for the transformation of heavy metals through the combined effect of condensation, nucleation, coagulation, external force and thermophoresis force. The calculation of heavy metals is embodied in the post-processor appended to Fluent software. Before the simulation, velocity, temperature, PbCl{sub 2} concentration and other initial parameters are obtained by experiment. In addition, the transformation of PbCl{sub 2} is also experimentally studied. The comparison of experimental and predicted results indicate that the fine particle model (FPM) is valid for predicting the transformation of heavy metals in the downstream of incinerator or combustor.

Authors:
; ; ; ; ;  [1]
  1. Huazhong University of Science & Technology, Wuhan (China)
Publication Date:
OSTI Identifier:
20862100
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Environmental Science and Health, Part A: Toxic Hazardous Substances and Environmental Engineering; Journal Volume: 42; Journal Issue: 2
Country of Publication:
United States
Language:
English
Subject:
01 COAL, LIGNITE, AND PEAT; 09 BIOMASS FUELS; COMBUSTION; COAL; SEWAGE SLUDGE; MATHEMATICAL MODELS; METALS; COMPUTERIZED SIMULATION; LEAD CHLORIDES; PARTICULATES

Citation Formats

Han, J., Xu, M., Yao, H., Furuuchi, M., Sakano, T., and Kim, H.J.. Simulating the transformation of heavy metals during coal or sewage sludge combustion. United States: N. p., 2007. Web. doi:10.1080/10934520601011395.
Han, J., Xu, M., Yao, H., Furuuchi, M., Sakano, T., & Kim, H.J.. Simulating the transformation of heavy metals during coal or sewage sludge combustion. United States. doi:10.1080/10934520601011395.
Han, J., Xu, M., Yao, H., Furuuchi, M., Sakano, T., and Kim, H.J.. Mon . "Simulating the transformation of heavy metals during coal or sewage sludge combustion". United States. doi:10.1080/10934520601011395.
@article{osti_20862100,
title = {Simulating the transformation of heavy metals during coal or sewage sludge combustion},
author = {Han, J. and Xu, M. and Yao, H. and Furuuchi, M. and Sakano, T. and Kim, H.J.},
abstractNote = {A mathematical model (FPM) is presented to predict the transformation of heavy metals in the downstream of combustor or incinerator. The model accounts for the transformation of heavy metals through the combined effect of condensation, nucleation, coagulation, external force and thermophoresis force. The calculation of heavy metals is embodied in the post-processor appended to Fluent software. Before the simulation, velocity, temperature, PbCl{sub 2} concentration and other initial parameters are obtained by experiment. In addition, the transformation of PbCl{sub 2} is also experimentally studied. The comparison of experimental and predicted results indicate that the fine particle model (FPM) is valid for predicting the transformation of heavy metals in the downstream of incinerator or combustor.},
doi = {10.1080/10934520601011395},
journal = {Journal of Environmental Science and Health, Part A: Toxic Hazardous Substances and Environmental Engineering},
number = 2,
volume = 42,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • The behavior of Cd, Cr, Cu, Co, Mn, Ni, Pb, Zn, and Hg during the combustion tests of a dry granular sewage sludge on a fluidized bed combustor pilot (FBC) of about 0.3 MW was evaluated. The emissions of these heavy metals from mono-combustion were compared with those of co-combustion of the sludge with a bituminous coal. The effect of the addition of limestone was also studied in order to retain sulphur compounds and to verify its influence on the retention of heavy metals (HM). Heavy metals were collected and analyzed from different locations of the installation, which included themore » stack, the two cyclones, and the material removed from the bed. The results showed that the volatility of metals was rather low, resulting in emissions below the legal limits of the new directive on incineration, with the exception of Hg during the mono-combustion tests. The partitioning of metals, except for Hg, appeared to follow that of ashes, amounting to levels above 90% in the bed streams in the mono-combustion case. For co-combustion, there was a lower fixation of HM in the bed ashes, mostly originating essentially from the sewage sludge, ranging between 40% and 80%. It is believed that in this latter case, a slightly higher temperature could have enhanced the volatilization, especially of Cd and Pb. However these metals were then retained in fly ashes captured in the cyclones. In the case of Hg, the volatilisation was complete. The bed ashes were free of Hg and part of Hg was retained in the cyclones and the rest was emitted either with fine ash particles or in gaseous forms. In mono-combustion the Hg emissions from the stack (particles and gas) accounted, for about 50%. This appeared to have significantly decreased in the case of co-combustion, as only about 75% has been emitted, due to the retention effect of cyclone ashes.« less
  • Emission of airborne P-bearing particulates from combustion of both coal and sewage sludge samples has been studied in a lab-scale drop tube furnace. The results indicate that both the organically bound fraction of phosphorus and its inorganic species in a complex form containing Si, Al, Ca, Fe, P and O at non-stoichiometric ratios appear to vaporize readily. The resultant phosphorus vapors undergo oxidation, chemical reactions with other metallic vapors including Na/K/Zn, nucleation, and homogeneous/heterogeneous coagulation to form a mixture of their oxides and phosphates with particle sizes smaller than 1.0 {mu}m. On the other hand, phosphorus in the larger fractions,more » {gt}1.0 {mu}m, mainly consist of apatite and condensed melting phases, which may have been formed through the direct liberation of inherent apatite in raw fuels and the shedding of melting P-bearing particles from the char surface. The amounts of phosphorus in each fraction of PM10 vary considerably with fuel type and combustion conditions. 15 refs., 10 figs., 2 tabs.« less
  • Co-combustion tests of dry sewage sludges with coal were performed in a pilot bubbling FBC aiming at the characterization of ashes and determining the behaviour of heavy metals in the process. The tests showed compliance with the regulatory levels as far as heavy metal emissions were concerned. The bottom ashes, which accounted for about 70% of the total ash production, were obtained in a granular form, with diameters ranging from 0.5 to 4 mm. The heavy metals were distributed in ashes obtained from different locations of the installation and their concentrations were found to vary depending on the location ofmore » capture. The increase in heavy metals content in bottom ashes was not found to lead to higher leachability and ecotoxicity compared to sewage sludges, suggesting that there could be opportunities for their further use. Mercury suffered vaporisation inside the reactor, thus leaving bottom ashes free of contamination by it. However, there was observed a strong retention of mercury in cyclone ashes due to the presence of unburned carbon which probably acted as an adsorbent. The effluent mercury was also found to be mostly associated with the particulate fraction, being less than 20% emitted in gaseous forms. The results suggested that the combustion of the sewage sludge could successfully be carried out and the amount of unburned carbon leaving the combustor but captured in cyclone was large enough to ensure substantial retention of mercury at low temperatures, hence could contribute to an improvement of the mercury release which still remains an issue of great concern to resolve during combustion of waste materials.« less
  • The speciation of heavy metals in soils determines the availability of metals for plant uptake and the potential for contamination of groundwater following the application of municipal sewage sludge to agricultural land. Methods used to characterize heavy metals in the solid phase of sludges and sludge-amended soils include chemical extractions, elutriation, and filtration, while chromatographic techniques and computer calculations are frequently applied to the solution phase. Such studies have shown metals to be predominantly associated with the solid phase; soluble and exchangeable species generally represent < 10% of total metals. Speciation in sludge-amended soils initially reflects that of the sludgemore » itself, although changes with time have been observed. It is apparent, however, that more refined interpretation of analytical data obtained by current speciation techniques is required to further characterize heavy metals. In addition, certain techniques used to speciate metals in other matrices may have applications for sludges and sludge-amended soils.« less
  • Sewage sludge from Baltimore, Md. was compared to that of Washington, D. C. in terms of the tendency to release heavy metals under a variety of circumstances. Total and 1.0N HCl-extractable concentrations of Cd, Cu, Pb, and Zn were determined by atomic absorption spectrophotometry. Fractionation of the metals by leaching columned samples of Baltimore sludge, with either a CaCl/sub 2/ solution or H/sub 2/O over extended periods of time, showed Cd and especially Zn were more leachable than Cu and Pb. Except for Pb, leachability of the metal was much lower in the sludge from Washington, D.C. than in themore » Baltimore sludge. Regarding the sign of charge of Cu species as a function of the progression of leaching of Baltimore sludge, anionic and, especially amphoteric species increased, as cationic ones decreased. When aqueous sludge leachates were stored for 13 months at 5/sup 0/C, amphoteric Cu strongly increased, while all other Cu species decreased. In contrast, nearly all Zn species in the stored leachates were cationic. When sludge samples were subjected to simulated weathering by stirring with either H/sub 2/O/sub 2/ in a number of concentrations, or H/sub 2/O followed by steambath drying, the extractability of heavy metals with H/sub 2/O and 0.01N HCl increased. Extractability of Cu increased more than that of Cd or Zn, suggesting that the stability of the amphoteric Cu species depended strongly on acidity. Because of the H/sub 2/O/sub 2/ treatements, the cation exchange capacity of the sludges diminished by 15 to 25 percent depending on their origin, although no C was lost. Compared with Washington, D.C. sewage sludge, Baltimore sludge has a greater heavy metal contaminating potential for soil amended with it.« less