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02478 Activated carbon made from semi-coke powder and comparison with coal-based carbon
04 i3y-products related to fuels
One of the highest exposures to polycyclic aromatic hydrocarbons (PAHs) in the working environment is found in coke-oven production. Genotoxic effects of PAHs on the top-side of a coke oven battery were evaluated by the ‘single cell gel assay’ (comet assay), detecting the DNA single strand breaks and alkali-labile sites (biomarkers of exposure). Individual susceptibility to PAH exposure was analysed by glutathion S-transferase Ml (GSTMI) polymorphism and N-acetyl transferase 2 (NAT-2) polymorphism detection (biomarkers of suseptibility). The study included 24 subjects from coke ovens, 12 control subjects from iron works, and another 16 subjects from town. Exposure to PAHs was determined by personal exposure monitoring 8 h before the collection of blood and urine samples. Coke-oven workers were exposed to carcinogenic PAH median concentrations (range in parentheses) during the shift of 18.7 &m3 (5.1-300.2 pLp/ m3), controls from iron works 0.41 m3 (0.12-1.22 pg/m3, and controls from town 0.58 &m3 (0.09-1.64 &rn-). The following comet parameters were evaluated in peripheral lymphocytes (100 images/sample): percentage of DNA in comet trail (%T) and comet tail length (TL) in pm. The highest levels of %T and TL were observed in controls from the iron works 14.5 (6.1-15.7) and 23.5 (11.6-35.8) vs. 6.2 (3.2-15.4) and 11.4 (7.4-29.5) in coke-oven workers versus 5.9 (3.8-11.0) and 10.9 (8.4-20-o) in controls from town, respectively. No differences were seen either using the coefficient of dispersion. No effects of smoking or GSTMI or NAT-2 polymorphism were observed for any of comet parameters. According to these results, it seems that if peripheral lymphocytes were used, the comet assay in the peripheral lymphocytes of coke-oven workers was not a particularly sensitive technique to determine the effects of carcinogenic PAHs at the DNA level.
p4
04
BY-PRODUCTS TO FUELS
RELATED
00102477 In situ measurements of the thermal conductivity of ash deposits Robinson, A. L. et 01. Svmp. (Inr.) Comhusr., [Proc.], 1998, 2, 172771735. The heat transfer rates to heat transfer surfaces in coal-fired power plants including furnace walls and super-heater tubes, can be reduced by ash deposits. The effective thermal conductivity of a porous ash deposit is one vital parameter for determining the magnitude of this reduction. This paper reports on the in siru, time-resolved measurements of the effective thermal conductivity of ash deposits formed under conditions that closely replicate those found in the convective pass of a commercial boiler. Illinois No. 6 coal and a blend of Illinois No. 6 coal and wheat/straw were used in experiments to determine the thermal conductivity of highly porous deposits. For deposits formed while firing both fuels, the measured thermal conductivity of loose, unsintered deposits is 0.15 W/(m K). almost a factor of three greater than that of air under these conditions.
00102478 Activated carbon made from semi-coke powder and comparison with coal-based carbon Cui, Y. er al. Meifan Zhuanhua, 1998. 21, (4) 91-94. (In Chinese) To examine the feasibility of the production of activated carbon from semicoke powder, the raw material selected had a grain size of l-3 mm. The study includes the manufacture of granular activated carbon by direct activation and that of cylindrical one through carbonization and activation. The test indicates that this is a feasible path of process and utilization, enabling to realize the reutilization of waste. Comparisons made with cylindrical carbon produced from the coal, demonstrated that it has different characters during activation, plus, it has the feature that both the macropore and mesopore are enriched.
00102479 Activated carbons from bituminous coal: effect of mineral matter content Linares-Solano, A. Fuel, 2000, 79, (6), 635-643. A bituminous coal from Puertollano Basin (Spain) was selected on the basis of previous study as the most suitable raw precursor to prepare activated carbons. In fact, this coal gave the best results among a total of 10 different Spanish coals that covered a wide range of coal rank. Its initial ash level (19 wt%) was decreased in the coal mine facilities by different intensive hydropneumatic washing,yielding fractions with 12 and 8 wt% ash. Another fraction was also obtained from the original coal with 5 wt% ash by an HCI/ HF washing treatment. These four coals were carbonized at 850°C and activated at 850°C for different activation times in steam and carbon dioxide, to analyse the effect of ash level on the porosity development of the resulting carbons. Contrary to what might be expected (catalysis effect, pore blocking and impediment of suitable porosity development), the initial ash level does not affect the porosity development. Those samples with a lower ash (at the same burn-off degree) yield higher micropore volumes. But when the results are presented in term of dry ash free basis, the same porosity development is attained regardless of the initial ash level. Comparing the behaviour of steam and carbon dioxide as activating agents, the pore structure and pore volumes attained are quite similar, though the pore sizes of steam samples are slightly wider than those of carbon dioxide
samples. The Dubinin-Stoeckli equation applied to experimental adsorption isotherm was used to follow the porosity development during activation for each reactive gas.
00102480 An AFM-SEM investigation of the effect of silica fume and fly ash on cement paste microstructure Papadakis, V. G. ef 01. J. Marer. Sci., 1999, 34, (4), 683-690. Particle shape and surface texture details of normal portland cement and supplementary cementing materials (silica fume, low-calcium fly ash, and high-calcium fly ash) was observed by atomic force microscopy (AFM). The latter materials mixed with cement were examined after prolonged hydration. Significant innovative informatton on particle shape and hydrated paste microstructure was obtained. Conventional microscopy techniques, such as SEM, cannot provide such detailed images and surface texture characteristics of the fine materials and of the product microstructure. AFM showed, for the first time, that silica fume particles are primarily composed of two complimentary parts (hemispheres or semi-cylinders). Nano-size particles were found in all materials. A relatively smooth product surface was observed in the hydrated cement paste. The hydrated surface of the addition-cement pastes presented small spheroid bulges, giving an additional roughness as measured by AFM.
00102481 Apparatus and method for incinerator. flue gas treatment Ito, A. and Oku, T. Jpn. Kokai Tokkyo Koho JP 11 137,949 [99 137,949] (Cl. BOlD53/34), 25 May 1999, Appl. 97/305,373. 7 Nov 1997. 6. (In Japanese) The authors describe the apparatus for blowing flue gases from refuse incinerators through bag filters in order to trap fly ashes containing heavy metals, calcium and HCI. Filtering the washing wastewaters means adding NaOH solution into the filtrate to convert CaClz into Ca(OH)z, melting and solidifying the CaClz-free ashes with cement to prevent leachates of heavy metals in landfill disposal, and feeding the final filtrate into an electrolysis tank to regenerate NaOH for reuse.
00102482 Ash formation in circulating fluidised bed combustion of coal and solid biomass Lind, T. VTT Pub/.. 1999, 378, I-166. Experiments were made in full-scale boilers on the fly and bottom ash formation mechanisms in circulating fluidized bed combustion of a bituminous coal and two solid biomass fuels. The biomass fuels were forest residue and willow (Salix). Main ash formation mechanisms are discussed for coal and biomass combustion. Ash formation was studied using traditional ash sampling and aerosol technology methods. Using traditional ash sampling methods, ash samples were collected from different boiler ash streams. Collection streams included fuel feed, sorbent or bed material feed, boiler bottom ash and fly ash collected in an electrostatic precipitator. Aerosol technology methods sampled particles directly from flue gas flows. In this way, particle size distributions were determined and particle elemental content was analysed to obtain concentrations of ash compounds in flue gas. Aerosol instrumentation included low-pressure impactors, cyclones, a differential mobility analyser combined with a condensation nucleus counter and an electric low-pressure impactor. Particle morphology was analysed by SEM. In coal combustion, limestone sorbent captured SOz; no additional bed material was used. Bottom ash consisted mainly of coal minerals and unfragmented sorbent particles. Coal minerals agglomerated during combustion forming bottom ash particles with a wide range of compositions. Sorbent particles captured SOz and were mainly present as CaSO., and CaO. During biomass combustion, quartz sand was fed into the furnace to maintain an adequate bed inventory; no sorbent was used. The bottom ash was formed by ash adhesion to sand particles and the subsequent growth of bed particles. Ash compounds adhered to sand particles by two mechanisms: adhesion of non-volatile ash compounds as particles on the sand surface; and diffusion of volatile ash compounds into the quartz sand and subsequent chemical reaction. Ash particles formed a or when sticky layer on the sand particles which, at high temperatures grown sufficiently thick, might have caused agglomeration and deposition problems in the bed and in the upper parts of the furnace and in cyclone loop. Fly ash size distributions were bimodal with all fuels. The fine mode was formed in a sub-micron size range by volatilization and subsequent nucleation of volatilized species; these particles grew by condensation. Fine particle mass consisted 0.3% of total mass of fly ash particles during coal combustion, 2% during forest residue combustion, and 8% during willow combustion. Major fractions of the mass in the fine mode consisted of HCI with coal, KCI with forest residue, and KaS04 with willow. Coarse fly ash particles (residual ash) were formed mainly from ash compounds that did not volatilize during combustion. Coal minerals formed agglomerates with a few minerals in one particle. In addition, a major proportion of the limestone sorbent fragmented and escaped the furnace as fly ash. Biomass combustion coarse fly ash particles were large agglomerates comprised of mainly sub-micron-sized primary particles up to several thousand in number. The gas-to-particle conversion of volatilized species was affected by particle agglomerate shape, consequently, the resulting concentration size distributions were different from those for spherical particles. Condensation of the volatilized species resulted in enrichment of condensed species in the fine particles whereas gas-to-particle conversion by a chemical surface reaction concerned the volatilized species that did not depend on particle size at all.
Fuel and Energy Abstracts
September
2000
279
One of the highest exposures to polycyclic aromatic hydrocarbons (PAHs) in the working environment is found in coke-oven production. Genotoxic effects of PAHs on the top-side of a coke oven battery were evaluated by the ‘single cell gel assay’ (comet assay), detecting the DNA single strand breaks and alkali-labile sites (biomarkers of exposure). Individual susceptibility to PAH exposure was analysed by glutathion S-transferase Ml (GSTMI) polymorphism and N-acetyl transferase 2 (NAT-2) polymorphism detection (biomarkers of suseptibility). The study included 24 subjects from coke ovens, 12 control subjects from iron works, and another 16 subjects from town. Exposure to PAHs was determined by personal exposure monitoring 8 h before the collection of blood and urine samples. Coke-oven workers were exposed to carcinogenic PAH median concentrations (range in parentheses) during the shift of 18.7 &m3 (5.1-300.2 pLp/ m3), controls from iron works 0.41 m3 (0.12-1.22 pg/m3, and controls from town 0.58 &m3 (0.09-1.64 &rn-). The following comet parameters were evaluated in peripheral lymphocytes (100 images/sample): percentage of DNA in comet trail (%T) and comet tail length (TL) in pm. The highest levels of %T and TL were observed in controls from the iron works 14.5 (6.1-15.7) and 23.5 (11.6-35.8) vs. 6.2 (3.2-15.4) and 11.4 (7.4-29.5) in coke-oven workers versus 5.9 (3.8-11.0) and 10.9 (8.4-20-o) in controls from town, respectively. No differences were seen either using the coefficient of dispersion. No effects of smoking or GSTMI or NAT-2 polymorphism were observed for any of comet parameters. According to these results, it seems that if peripheral lymphocytes were used, the comet assay in the peripheral lymphocytes of coke-oven workers was not a particularly sensitive technique to determine the effects of carcinogenic PAHs at the DNA level.
p4
04
BY-PRODUCTS TO FUELS
RELATED
00102477 In situ measurements of the thermal conductivity of ash deposits Robinson, A. L. et 01. Svmp. (Inr.) Comhusr., [Proc.], 1998, 2, 172771735. The heat transfer rates to heat transfer surfaces in coal-fired power plants including furnace walls and super-heater tubes, can be reduced by ash deposits. The effective thermal conductivity of a porous ash deposit is one vital parameter for determining the magnitude of this reduction. This paper reports on the in siru, time-resolved measurements of the effective thermal conductivity of ash deposits formed under conditions that closely replicate those found in the convective pass of a commercial boiler. Illinois No. 6 coal and a blend of Illinois No. 6 coal and wheat/straw were used in experiments to determine the thermal conductivity of highly porous deposits. For deposits formed while firing both fuels, the measured thermal conductivity of loose, unsintered deposits is 0.15 W/(m K). almost a factor of three greater than that of air under these conditions.
00102478 Activated carbon made from semi-coke powder and comparison with coal-based carbon Cui, Y. er al. Meifan Zhuanhua, 1998. 21, (4) 91-94. (In Chinese) To examine the feasibility of the production of activated carbon from semicoke powder, the raw material selected had a grain size of l-3 mm. The study includes the manufacture of granular activated carbon by direct activation and that of cylindrical one through carbonization and activation. The test indicates that this is a feasible path of process and utilization, enabling to realize the reutilization of waste. Comparisons made with cylindrical carbon produced from the coal, demonstrated that it has different characters during activation, plus, it has the feature that both the macropore and mesopore are enriched.
00102479 Activated carbons from bituminous coal: effect of mineral matter content Linares-Solano, A. Fuel, 2000, 79, (6), 635-643. A bituminous coal from Puertollano Basin (Spain) was selected on the basis of previous study as the most suitable raw precursor to prepare activated carbons. In fact, this coal gave the best results among a total of 10 different Spanish coals that covered a wide range of coal rank. Its initial ash level (19 wt%) was decreased in the coal mine facilities by different intensive hydropneumatic washing,yielding fractions with 12 and 8 wt% ash. Another fraction was also obtained from the original coal with 5 wt% ash by an HCI/ HF washing treatment. These four coals were carbonized at 850°C and activated at 850°C for different activation times in steam and carbon dioxide, to analyse the effect of ash level on the porosity development of the resulting carbons. Contrary to what might be expected (catalysis effect, pore blocking and impediment of suitable porosity development), the initial ash level does not affect the porosity development. Those samples with a lower ash (at the same burn-off degree) yield higher micropore volumes. But when the results are presented in term of dry ash free basis, the same porosity development is attained regardless of the initial ash level. Comparing the behaviour of steam and carbon dioxide as activating agents, the pore structure and pore volumes attained are quite similar, though the pore sizes of steam samples are slightly wider than those of carbon dioxide
samples. The Dubinin-Stoeckli equation applied to experimental adsorption isotherm was used to follow the porosity development during activation for each reactive gas.
00102480 An AFM-SEM investigation of the effect of silica fume and fly ash on cement paste microstructure Papadakis, V. G. ef 01. J. Marer. Sci., 1999, 34, (4), 683-690. Particle shape and surface texture details of normal portland cement and supplementary cementing materials (silica fume, low-calcium fly ash, and high-calcium fly ash) was observed by atomic force microscopy (AFM). The latter materials mixed with cement were examined after prolonged hydration. Significant innovative informatton on particle shape and hydrated paste microstructure was obtained. Conventional microscopy techniques, such as SEM, cannot provide such detailed images and surface texture characteristics of the fine materials and of the product microstructure. AFM showed, for the first time, that silica fume particles are primarily composed of two complimentary parts (hemispheres or semi-cylinders). Nano-size particles were found in all materials. A relatively smooth product surface was observed in the hydrated cement paste. The hydrated surface of the addition-cement pastes presented small spheroid bulges, giving an additional roughness as measured by AFM.
00102481 Apparatus and method for incinerator. flue gas treatment Ito, A. and Oku, T. Jpn. Kokai Tokkyo Koho JP 11 137,949 [99 137,949] (Cl. BOlD53/34), 25 May 1999, Appl. 97/305,373. 7 Nov 1997. 6. (In Japanese) The authors describe the apparatus for blowing flue gases from refuse incinerators through bag filters in order to trap fly ashes containing heavy metals, calcium and HCI. Filtering the washing wastewaters means adding NaOH solution into the filtrate to convert CaClz into Ca(OH)z, melting and solidifying the CaClz-free ashes with cement to prevent leachates of heavy metals in landfill disposal, and feeding the final filtrate into an electrolysis tank to regenerate NaOH for reuse.
00102482 Ash formation in circulating fluidised bed combustion of coal and solid biomass Lind, T. VTT Pub/.. 1999, 378, I-166. Experiments were made in full-scale boilers on the fly and bottom ash formation mechanisms in circulating fluidized bed combustion of a bituminous coal and two solid biomass fuels. The biomass fuels were forest residue and willow (Salix). Main ash formation mechanisms are discussed for coal and biomass combustion. Ash formation was studied using traditional ash sampling and aerosol technology methods. Using traditional ash sampling methods, ash samples were collected from different boiler ash streams. Collection streams included fuel feed, sorbent or bed material feed, boiler bottom ash and fly ash collected in an electrostatic precipitator. Aerosol technology methods sampled particles directly from flue gas flows. In this way, particle size distributions were determined and particle elemental content was analysed to obtain concentrations of ash compounds in flue gas. Aerosol instrumentation included low-pressure impactors, cyclones, a differential mobility analyser combined with a condensation nucleus counter and an electric low-pressure impactor. Particle morphology was analysed by SEM. In coal combustion, limestone sorbent captured SOz; no additional bed material was used. Bottom ash consisted mainly of coal minerals and unfragmented sorbent particles. Coal minerals agglomerated during combustion forming bottom ash particles with a wide range of compositions. Sorbent particles captured SOz and were mainly present as CaSO., and CaO. During biomass combustion, quartz sand was fed into the furnace to maintain an adequate bed inventory; no sorbent was used. The bottom ash was formed by ash adhesion to sand particles and the subsequent growth of bed particles. Ash compounds adhered to sand particles by two mechanisms: adhesion of non-volatile ash compounds as particles on the sand surface; and diffusion of volatile ash compounds into the quartz sand and subsequent chemical reaction. Ash particles formed a or when sticky layer on the sand particles which, at high temperatures grown sufficiently thick, might have caused agglomeration and deposition problems in the bed and in the upper parts of the furnace and in cyclone loop. Fly ash size distributions were bimodal with all fuels. The fine mode was formed in a sub-micron size range by volatilization and subsequent nucleation of volatilized species; these particles grew by condensation. Fine particle mass consisted 0.3% of total mass of fly ash particles during coal combustion, 2% during forest residue combustion, and 8% during willow combustion. Major fractions of the mass in the fine mode consisted of HCI with coal, KCI with forest residue, and KaS04 with willow. Coarse fly ash particles (residual ash) were formed mainly from ash compounds that did not volatilize during combustion. Coal minerals formed agglomerates with a few minerals in one particle. In addition, a major proportion of the limestone sorbent fragmented and escaped the furnace as fly ash. Biomass combustion coarse fly ash particles were large agglomerates comprised of mainly sub-micron-sized primary particles up to several thousand in number. The gas-to-particle conversion of volatilized species was affected by particle agglomerate shape, consequently, the resulting concentration size distributions were different from those for spherical particles. Condensation of the volatilized species resulted in enrichment of condensed species in the fine particles whereas gas-to-particle conversion by a chemical surface reaction concerned the volatilized species that did not depend on particle size at all.
Fuel and Energy Abstracts
September
2000
279