[Show abstract][Hide abstract] ABSTRACT: The partitioning of trace elements and the influence of the feed conditions (50:50 coal/pet-coke feed blend and limestone addition) was investigated in this study. To this end feed fuel, fly ash and slag samples were collected under different operational conditions at the 335 MW Puertollano IGCC power plant (Spain) and subsequently analysed. The partitioning of elements in this IGCC plant may be summarised as follows: (a) high volatile elements (70–>99% in gas phase): Hg, Br, I, Cl and S; (b) moderately volatile elements (up to 40% in gas phase and ⩾60% in fly ash): As, Sb, Se, B, F, Cd, Tl, Zn and Sn; (c) elements with high condensation potential: (>90% in fly ash): Pb, Ge, Ga and Bi; (d) elements enriched similarly in fly ash and slag 30–60% in fly ash: Cu, W, (P), Mo, Ni and Na; and (e) low volatile elements (>70% in slag): Cs, Rb, Co, K, Cr, V, Nb, Be, Hf, Ta, Fe, U, Ti, Al, Si, Y, Sr, Th, Zr, Mg, Ba, Mn, REEs, Ca and Li. The volatility of As, Sb, and Tl and the slagging of S, B, Cl, Cd and low volatile elements are highly influenced by the fuel geochemistry and limestone dosages, respectively.
[Show abstract][Hide abstract] ABSTRACT: The relevance of Al-Si glass in a number of fly ash applications, such as use as a pozzolanic material, zeolite synthesis, and geopolymer production, necessitated research towards investigation of methods for an easy and consistent determination of the glass content in this coal (co)-combustionby-products. A glass standard-addition X-ray powder diffraction (XRD)-based method is proposed in this study as an alternative to the non straightforward procedure of conventional methods for determining the amorphous components, mainly by difference of the total mass and the addition of quantified crystalline species. A >99% Al-Si glass slag sample was selected as a standard for glass. A number of glass standard/fly ash mixtures were performed on Fluidized Bed Combustion (FBC) and pulverized coal combustion (PCC) fly ashes and subsequently analyzed by XRD. The method provides results closer to quantitative proportions of the Al-Si amorphous material of this (co)-combustion by-product, with a range of values <3% when compared with those obtained by the conventional Reference Intensity Method (RIM) method, demonstrating suitability and consistence of the procedure. Furthermore, by the proposed method, the requirement of previous determination of the mineral phases of conventional techniques is avoided. Coupled with the easy calculations, this allowed a fast determination of the glass content of (co)-combustion fly ash. The mineralogy of FBC and PCC fly ash was also investigated using the RIM method. The occurrence and proportions of the crystalline components in fly ash are in line with the combustion technology and their inherent operational parameters, especially the (co)-combustion temperature. The FBC fly ash shows the highest content of relic phases from feed coal (quartz, illite, calcite, and feldspars) and lower contents of amorphous components. The PCC fly ash are characterized by the highest proportions of mullite and Al-Si glass and low contents of quartz an other relict phases. The occurrence and distribution of anhydrite and Fe-oxide species appears to be related to the content of Ca and Fe in the feed fuels, showing slightly higher contents in FBC than in PCC fly ash. (c) 2009 Elsevier Ltd. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: The (co)-firing of low-cost alternative fuels is expected to increase in the forthcoming years in the EU because of the economic and environmental benefits provided by this technology. This study deals with the impact of the different coal/waste fuel ratio of the feed blend on the mineralogy, the chemical composition and especially on the leaching properties of fly ash. Different blends of coal, petroleum coke, sewage sludge, wood pellets, coal tailings and other minor biomass fuels were tested in PCC (pulverised coal combustion) and FBC (fluidized bed combustion) power plants. The co-firing of the studied blends did not drastically modify the mineralogy, bulk composition or the overall leaching of the fly ash obtained. This suggests that the co-firing process using the alternative fuels studied does not entail significant limitations in the re-use or management strategies of fly ash.
[Show abstract][Hide abstract] ABSTRACT: The environmental characteristics of coal gangue dumps in Yangquan (Shanxi Province, China) were investigated. The amounts of coal gangue are very high in this coal region given the large coal production. As a result, widespread spontaneous coal gangue combustion gives rise to serious environmental problems. Coal gangue (including bulk gangue and specific lithologies, such as coal, kaolinite-rich material, sandstone, carbonate minerals, and sulfide mineralizations), fired coal gangue and condensate products from gas vents were fully characterized with respect to mineralogy, chemistry and leaching potential. The mineral paragenesis of the fired coal gangue (cristobalite, mullite, hematite, trydimite, cordierite) showed that the combustion temperature could reach 1200 °C. This was also corroborated by laboratory calcination tests. During this combustion some elements such as C, Cl, F, S, N, As, Cd, Hg, Pb, Sn, Ge and Se are emitted into the atmosphere. However, condensation processes accounted for the partial trapping of gaseous emissions of As, S, N, Hg and Se. Thus, condensate mineralizations of elemental sulfur and ammonium salts enriched in Se, As and other trace elements are frequent in the gas vents. The leaching potential of trace elements in the fresh coal gangue was relatively low, but the leaching of weathered coal gangue and the gas vents condensates could give rise to environmental problems, as these materials produce acidic leachates and yield relatively high leachable levels of a number of elements.
[Show abstract][Hide abstract] ABSTRACT: Co-firing of coal with inexpensive secondary fuels such as petroleum coke is expected to increase in the near future in the EU given that it may provide certain economic and environmental benefits with respect to coal combustion. However, changes in the feed fuel composition of power plants may modify the bulk content and the speciation of a number of elements in fly ash and slag. Consequently, leachability of these byproducts also can be modified. This study is focused on identifying the changes in the environmental quality of co-fired fly ash and slag induced by a modification of the petcoke/coal ratio. Petcoke was found to increase the leachable content of V and Mo and to enhance the mobility of S and As. However, with the exception of these elements, the addition of this secondary fuel did not drastically modify the bulk composition or the overall leachability of the resulting fly ash and slag.
Environmental Science and Technology 09/2007; 41(15):5330-5. · 5.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The co-combustion of coal is becoming increasingly important owing to the environmental and economical benefits that it supposes. However, it may have environmental implications such as the potential increase in the volatility of some trace pollutants or changes in the speciation. Since the new environmental regulations in the European Union (EU), novel alternatives in co-combustion are being applied. However, no previous studies are available determining how emissions and combustion products could be modified. In this study the effect of co-combustion of coal and pet coke on the partitioning of trace pollutants during co-combustion of coal in a power plant was investigated. The results revealed an increase of the volatile behaviour of Tl (75 % increased), Sn and B (30 % increased), Cl, F and Se (over 10 %) and S and Hg (over 5 %) when up to 30 % of petcoke is added in feed fuel blends, with respect when 96/4 coal/petcoke blends were used. Furthermore V, Ni and Mo are enriched in FA. This adjustment of the partitioning has to be attributed to the major organic affinity in pet coke, which assists the volatilization of S, Cl, F, B, V, Ni and Mo. Therefore, a high volatile fraction of these elements may promotes the occurrence of high volatile Tl, Sb, Sn and Se chlorides and volatile F and B species, explaining their high volatile behaviour. The high volatility of S, V, Ni and Mo result in a high occurrence of sulphates species and V-Ni-Mo free oxides or salts in fly ash (FA), with potential implications in the leachable fractions of these metals.
2nd World of coal ash conference (WOCA), Cincinnati, Kentucky, USA; 05/2007