- Email: [email protected]
01723 Molecular transport effects on turbulent flamepropagation and structure
09 Combustion (burners, combustion systems) temperature 850-1000 K. The ignition and oxidation of n-heptane are predicted using a reaction mechanism consisting of 34 species and 56 steps• The mixture fraction is computed separately as a passive species, the diffusion coefficient, of which is equal to the local thermal diffusion coefficient. From these computations, the transient structure of the flamelet, including ignition, is obtained• The results are compared with those obtained with the unity Lewis number assumption. The implications of the unity Lewis number assumption on the predicted ignition characteristics are discussed.
05•01718 Effects of NOx, -Fe203, -Fe~03, and HCI on mercury transformations in a 7-kW coal combustion system Galbreath, K. C. et al. Fuel Processing Technology, 2005, 86, (4), 429448. Bench-scale investigations indicate that NO, NO2, hematite ( a - F e 2 0 3 ) , maghemite (7 -Fe203), and HC1 promote the conversion of gaseous elemental mercury (Hg °) to gaseous oxidized mercury (Hg z+) and/or particle-associated mercury (Hg[p]) in simulated coal combustion flue gases. In this investigation, the effects of NOx, c~-FezO3, 3' -F%O3, and HCI on Hg transformations were evaluated by injecting them into actual coal combustion flue gases produced from burning subbituminous Absaloka and lignitic Falkirk coals in a 7-kW down-fired cylindrical furnace. A bituminous Blacksville coal known to produce an Hg2+-rich combustion flue gas was also burned in the system. The American Society for Testing and Materials Method D6784-02 (Ontario Hydro method) or an online Hg analyser equipped to measure Hg 0 and total gaseous mercury (Hg[tot]) was used to monitor Hg speciation at the baghouse inlet (160-195°C) and outlet (110-140°C) locations of the system. As expected the baseline Blacksvflle flue gas was composed predominantly of Hg- (Hg2+/ Hg[tot]=0.77), whereas Absaloka and Falkirk flue gases contained primarily Hg O (Hg 0 /Hg[tot] = 0.84 and 0.78, respectively). Injections of NO2 (80-190 ppmv) at 440-880°C and c~-Fe203 (15 and 6 wt%) at 450°C into Absatoka and Falkirk coal combustion flue 2g+ases did not significantly affect Hg speciation. The lack of Hg ° to H g conversion suggests that components of Absaloka and Falkirk combustion flue gases and/or fly ashes inhibit heterogeneous Hg°-NOx-c~-Fe203 reactions or that the flue gas quench rate in the 7-kW system is much different in relation to bench-scale flue gas simulators. An abundance of Hg 2+, HCI, and 7 - F e 2 0 3 in Blacksville flue gas and the inertness of injected a - F e 2 0 3 with respect to heterogeneous Hg ° oxidation in Absaloka and Falkirk flue gases suggested that 7 - F e 2 0 3 catalyses Hg 2+ formation and that HC1 is an important Hg ° reactant. The filtration of Absaloka and Falklrk combustion flue gases at I50°C through fabric filters with ~60 g/m 2 7 - F e 2 0 3 indicated that about 30% of the Hg ° in Absaloka and Falkirk flue gases was converted to Hg 2 + and/or Hg(p). HCI injection (100 ppmv) into the Absaloka combustion flue gas converted most of the Hg ° to Hg 2+, whereas HC1 injection into the Falkirk flue gas converted most of the Hg ° and Hg 2 + to Hg(p). Additions of -Fe203 and HC1 did not have a synergistic effect on Hg ° oxidation. The filtration of Absaloka and Falkirk flue gases through much greater fabric filter loadings of 475 g/m ~-7 -Fe203 essentially doubled the baghouse Hg[tot] removal efficiency to about 50%. Results from this investigation demonstrate the importance of evaluating potential Hg ° reactants and oxidation catalysts in actual coal combustion flue gases. •
•
'
7 +
05•01719 Effects of strain rate on high-pressure nonpremixed n-heptane autoignition in counterflow Liu, S. et al. Combustion andFlame, 2004, 137, (3), 320-339. The effect of steady strain on the transient autoignition of n-heptane at high pressures is studied numerically with detailed chemistry and transport in a eounterflow configuration. Skeletal and reduced nheptane mechanisms are developed and validated against experiments over a range of pressure and stoiehiometries. Two configurations are investigated using the skeletal mechanism• First, the effect of strain rate on multistage n-heptane ignition is studied by imposing a uniform temperature for both the fuel and the oxidizer streams. Second, a temperature gradient between the fuel and the oxidizer streams is imposed. The global effect of strain on ignition is captured by a Damk6hler number based on either the heat-release rate or the characteristic chain-branching rate. Results show that for low to moderate strain rates, both the low- and intermediate-temperature chemistries evolve in a manner comparable to that in homogeneous systems, including the negative temperature coefficient regime, but with somewhat slower evolution attributable to diffusive losses. At high strain rates diffusive losses inhibit ignition; for two-stage ignition, it is found that ignition is inhibited during the second, intermediatetemperature stage. The imposition of an overall temperature gradient further inhibits ignition because reaction zones for key branching reactions with large activation energies are narrowed. For a fixed oxidizer stream temperature that is not sufficiently high, a higher fuel temperature results in a shorter ignition delay provided that the heptyl radicals are mainly oxidized by low-temperature chemistry. As expected, an increase in pressure significantly increases reaction rates
and reduces ignition delay time. However, with increasing pressure there is a shift toward single-stage low-temperature-dominated ignition which serves to delay ignition.
05/01720 Experimental studies on low-temperature pyrolysis of municipal household garbage-temperature influence on pyrolysis product distribution Yan, W. et al. Renewable Energy, 2005, 30, (7), 1133-1142. The low-temperature pyrolysis of the mixture of nine typical components from municipal household garbage has been experimentally studied in an externally heated fixed-bed pyrolyser, at temperatures ranging from 300 to 700°C. The yields of final pyrolysis product varying with temperatures are presented in this paper. The solid product yield decreases with the increase of temperature in the test temperature range, and reduces quickly at 300-550°C but very slowly at 550-700°C. However, the pyrolysis liquid yield increases with the increase of temperature, but reaches the maximum at 550°C, and afterwards begins to decline. Among liquid product, cream-shaped tar is found, the yield of which also reaches the maximum at 550°C. The pyrolysis gas yield steadily increases with the increase of temperature at the whole test temperature range. The above-mentioned experimental results could be helpful to the practical application of low-temperature pyrolysis of municipal household garbage.
05•01721 Investigations into the pyrolytic behaviour of coal/biomass blends using thermogravimetric analysis Vuthaluru, H. B. Bioresource Technology, 2004, 92, (2), 187-195. Investigations into the pyrolytic behaviour during co-pyrolysis of coal, biomass materials and coal/biomass blends prepared at different ratios (10:90, 20:80, 30:70 and 50:50) have been conducted using a thermogravimetric analysis (TGA) apparatus. The coal sample selected was Collie sub-bituminous coal from Western Australia, while wood waste (WW) and wheat straw (WS) were used as biomass samples. Three thermal events were identified during the pyrolysis. The first two were dominated by the biomass pyrolysis, while the third was linked to the coal pyrolysis, which occurred at much higher temperatures. No interactions were seen between the coal and biomass during copyrolysis. The pyrolytic characteristics of the blends followed those of the parent fuels in an additive manner. Among the tested blends, 20:80 blends showed the lowest activation energies of 90.9 and 78.7 kJ mol a for coal/WW and coal/WS blends respectively. The optimum blend ratio for pyrolysis of coal/WS was 50:50 with a high degradation rate in ali the thermal events and a higher mass loss over the course of the copyrolysis compared to coal/WW blends examined. The reaction orders in these experiments were in the range of 0.21-1.60, thus having a significant effect on the overall reaction rate. Besides the pyrolysis of coal alone, the 50:50 coal/biomass blends had the highest reaction rate, ranging 1 × 109-2 x 101. The experimental results may provide useful data for power generation industries for the development of co-firing options with biomass.
05•01722 Modeling of soot particles growth in fuel-rich premixed flame Oknyama, M. et al. International Journal of Heat and Mass Transfer, 2004, 47, (21), 4625-4635.~ The soot formation process and the structure of a fuel-rich premixed flame stabilized in the downstream side of a porous medium have been investigated by experimental measurements and numerical analysis. In the numerical analysis, a modified Tesner's model for the reaction rate of soot formation has been introduced through a comparison between measured and calculated distributions of the temperature and the species mole fractions. Furthermore, a novel model for soot growth is developed, taking both surface and coalescence growths into account. On the basis of this model, the following results are obtained. Surface growth becomes dominant immediately after the beginning of soot formation. In the downstream side, the soot particle increases due to grow by the coalescence with smaller soot particles, and decrease as a result of collision with radicals and coalescence with larger soot particles.
05/01723 Molecular transport effects on turbulent flame propagation and structure Lipatnikov, A. N. and Chomiak, J. Progress in Energy and Combustion Science, 2005, 31, (3), 1-73. Various experimental and DNS data show that premixed combustion is affected by the differences between the coefficients of molecular transport of fuel, oxidant, and heat not only at weak but also at moderate and high turbulence. In particular, turbulent flame speed increases with decreasing the Lewis number of the deficient reactant, the effect being very strong for lean hydrogen mixtures. Various concepts; flame instability, flame stretch, local extinction, leading point, that aim at describing the effects of molecular transport on turbulent flame propagation and structure are critically discussed and the results of relevant studies of perturbed laminar flames (unstable flames, flame balls, flames in vortex tubes) are reviewed. The crucial
Fuel and Energy Abstracts July 2005 253
09 Combustion (burners, combustion systems) role played by extremely curved laminar flamelets in the propagation of moderately and highly turbulent flames is highlighted and the relevant physical mechanisms are discussed.
05101724 Pretreated olivine as tar removal catalyst for biomass gasifiers: investigation using naphthalene as model biomass tar Devi, L. et al. Fuel Processing Technology, 2005, 86, (6), 707-730. Biomass is considered as a potential source of renewable energy. One of the major problems for biomass gasification is the presence of tar in the product gas. This study investigated the catalytic behaviour of olivine as a prospective bed additive for biomass gasifiers for tar removal. In the present paper, the pretreatment of olivine was investigated to improve its activity. Pretreatment method includes heating olivine at 900°C in the presence of air for different treatment times. The catalytic activity of olivine was investigated via steamreforming reaction of naphthalene as model biomass tar compound. Improvement in naphthalene conversion of around 30% was observed with 1 h of pretreatment. Also effect of pretreatment time was investigated. With increasing pretreatment time, conversion increased; more than 80% naphthalene conversion was observed with 10 h of pretreatment time for olivine. Both steam and dry reforming reaction of naphthalene formed more than 50% gaseous products over 10 h pretreated olivine. Besides the gaseous products and light tars, polymerization reactions occured producing higher tars in small quantity. Naphthalene conversion under syngas mixture was somewhat lower than that of only in steam and CO2. Apparent activation energy of 187 kJ mo1-1 was determined for 10 h pretreated olivine under gasification-gas mixture.
05•01725
Pyrolytic behavior of waste corn cob
Cao, Q. et al. Bioresource Technology, 2004, 94, (1), 83 89. The powder of the agricultural waste corn cob was pyrolysed in a tubetyped stainless steel reactor of 200 ml volume under N2 atmosphere. The compositions of the gases and liquid obtained at different pyrolytic temperatures below 600°C at the heating rate of 30 K/rain were analysed. With the increment of the pyrolytic temperature, the yields of the solid and the liquid products were decreased, but the yield of gas products was increased. The liquid products were approximately 3440.96% (wt%), the gas products were 27-40.96% (wt%) and the solid products 23.6-31.6% (wt%). There were tess changes for the yields of these products above 600°C. The gas products were analysed by gas chromatography (GC) as CO2, CO, H2, CH4, C2H4, C3H6, C3H8, etc. When the temperature was 350-400°C, the gases had CO2 and CO 8095% (v/v). When the temperature increased continuously, yields of H2, CH4, C2H4, C3H6 and C3Hs gradually increased. The liquid products were identified by GC-MS as phenols, 2-furanmethanol, 2-cyclopentanedione, etc. The Fourier transform infra-red spectrophotometer (FTIR) analysis of the liquid product showed a strong - O H group absorption peak. Differential thermogravimetric analysis (DTG) showed that thermal decomposition process involves two steps. The heating rate affects not only the activation energy of the decomposition reaction, but also the path of the reaction. With the increment of the heating rate, the maximum rate temperature of the decomposition reaction was shifted to a higher temperature, and the order and activation energy of the total decomposition reaction were decreasing.
05•01726 Reductive pyrolysis of Miocene-aged lignite lithotypes using MS and GC/MS detection systems for analysis of organic sulphur groups Stefanova, M. et al. Fuel, 2005, 84, (1), 71-79. The atmospheric pressure temperature programmed reduction (APTPR) technique, an approach for organic sulfur speciation, was extended by mass spectral detection. The coupling gave ground for precise assignment of sulfur compounds in flue gases of lignite lithotypes pyrolysed in H2 atmosphere. A broad range of suifur compounds was determined, i.e. thiols, dimethylsulphide, dimetbyldisulphide, CS2, thiophenes, benzothiophenes and their alkylated homologues. Certain peculiarities in organic sulfur distribution in lithotypes under study were noticed. Humovitrain was the lithotype with the highest organic sulfur content. A preponderance of aliphatic sulfur, thiols and dimethylsulfides were determined for both homogeneous lithotypes (xylain and humovitrain). In humovitrain, additionally thiophenes were also identified. For heterogeneous lithotypes, liptain and humoclarain, a dominance of disulphides and an almost lack of sulphides was observed. This is an indication that with coalification a gradual loss of aliphatic sulfur functions has proceeded, where more resistant disulphides sulfur bridges turned out to be present. Thiophenes are the most abundant aromatic structures, dominating in humoclarain. Some amounts of oxidized organic sulfur compounds (1% up to 4.1% of Sorg) were semi-quantitative determined in lithotypes using AP-TPR-MS.
254 Fuel and Energy Abstracts
July 2005
05/01727 Size and charge of soot particles in rich premixed ethylene flames Maricq, M. M. Combustion and Flame, 2004, 137, (3), 340-350. A nano differential mobility analyser (DMA) is used to measure both the size and electrical charge distributions of soot particles generated during rich premixed combustion. The size distributions are bimodal. One mode peaks at diameters below the 3 nm lower limit of the nano DMA and falls off nearly exponentially with increasing particle diameter. The intensity of this mode persists with increasing height above the burner suggesting that it represents the continued formation of new particles. The second mode is lognormal in shape. Its intensity decreases and the mean diameter increases with increasing height above the burner due to coagulation and surface growth as the particles rise in the flame. The DMA measurements show that a substantial fraction of the soot particles are electrically charged in the flame, predominantly with a single charge per particle and with essentially equal numbers of positive and negative particles. These charged particles belong solely to the upper mode, whereas the lower mode remains charge neutral, suggesting that ions do not act as soot nuclei. Following soot inception, the fraction of charged particles quickly increases with height above the burner and stabilizes at ~30% of the upper mode for each polarity.
05•01728 Sulphur functionality study of steam pyrolyzed 'Mequinenza' lignite using reductive pyrolysis technique coupled with MS and GC/MS detection systems Marinov, S. P. et al. Fuel Processing Technology, 2005, 86, (5), 523-534. Atmospheric pressure-temperature programmed reduction (AP-TPR) and its analogous in oxidative atmosphere coupled 'on-line' with a mass spectrometer (MS) were used to study the behaviour of organic sulfur forms of 'Mequinenza' lignite during their mild steam pyrolysis. The obtained data were confirmed and completed by the AP-TPR-GC/MS 'off-line' analysis. Samples under study were pyrolysed at different processing parameters (temperature and flow gas). Some peculiarities in the distribution of non-thiophenic sulfur forms depending on experimental conditions were found. Namely, their amounts decreased with temperature increase at the steam treatment. The experiment performed at 500°C in water vapour flow proved the C-S bond splitting in dibenzothiophene with biphenyl formation. Sulphonic acid compounds were also systematically removed. At higher temperature of the steam pyrolysed treatment, this effect was more pronounced. At the same time, a relative increase in sulphones was found. The following organic sulfur species in demineralized lignite were detected by the 'offqine' AP-TPR-GC/MS technique: methyl- and benzenethiols; mono- and disulphides; alkylthiolanes; alkenyl thiophenes; alkylbenzo[b]thiophenes and alkyldibenzo[bd]thiophenes. Their relative intensities as a function of temperature were followed. A strong preponderance of benzo[b]thiophene and its alkytated homologues above 450°C were observed. Thiophene presence was temperature independent.
05/01729 Tracer-LIF diagnostics: quantitative measurement of fuel concentration, temperature and fuel/air ratio in practical combustion systems Schulz, C. and Sick, V. Progress in Energy and Combustion Science, 2005, 31, (1), 75-121. The safe, clean, and reliable operation of combustion devices depends to a large degree on the exact control of the fuel/air mixing process prior to ignition. Therefore, quantitative measurement techniques that characterize the state of the fresh gas mixture are crucial in modern combustion science and engineering. This paper presents the fundamental concepts for how to devise and apply quantitative measurement techniques for studies of fuel concentration, temperature, and fuel/air ratio in practical combustion systems, with some emphasis on internal combustion engines. The paper does not attempt to provide a full literature review of quantitative imaging diagnostics for practical combustion devices; rather it focuses on explaining the concepts and illustrating these with selected examples. These examples focus on application to primarily gaseous situations. The photophysies of organic molecules is presented in an overview followed by discussions on specific details of the temperature-, pressure-, and mixturedependence of the laser-induced fluorescence strength of aliphatic ketones, like acetone and 3-pentanone, and toluene. Models that describe the fluorescence are discussed and evaluated with respect to their functionality. Examples for quantitative applications are categorized in order of increased complexity. These examples include simple mixing experiments under isothermal and isobaric conditions, fuel/air mixing in engines, temperature measurements, and mixing studies where fuel and oxygen concentrations vary. A brief summary is given on measurements of fuel concentrations in multiphase systems, such as laser-induced exeiplex spectroscopy. Potentially adverse effects that added tracers might have on mixture formation, combustion, and the faithful representation of the base fuel distribution are discussed. Finally, a brief section describes alternative techniques to tracer-based measurements that allow studies of fuel/air mixing processes in
05•01718 Effects of NOx, -Fe203, -Fe~03, and HCI on mercury transformations in a 7-kW coal combustion system Galbreath, K. C. et al. Fuel Processing Technology, 2005, 86, (4), 429448. Bench-scale investigations indicate that NO, NO2, hematite ( a - F e 2 0 3 ) , maghemite (7 -Fe203), and HC1 promote the conversion of gaseous elemental mercury (Hg °) to gaseous oxidized mercury (Hg z+) and/or particle-associated mercury (Hg[p]) in simulated coal combustion flue gases. In this investigation, the effects of NOx, c~-FezO3, 3' -F%O3, and HCI on Hg transformations were evaluated by injecting them into actual coal combustion flue gases produced from burning subbituminous Absaloka and lignitic Falkirk coals in a 7-kW down-fired cylindrical furnace. A bituminous Blacksville coal known to produce an Hg2+-rich combustion flue gas was also burned in the system. The American Society for Testing and Materials Method D6784-02 (Ontario Hydro method) or an online Hg analyser equipped to measure Hg 0 and total gaseous mercury (Hg[tot]) was used to monitor Hg speciation at the baghouse inlet (160-195°C) and outlet (110-140°C) locations of the system. As expected the baseline Blacksvflle flue gas was composed predominantly of Hg- (Hg2+/ Hg[tot]=0.77), whereas Absaloka and Falkirk flue gases contained primarily Hg O (Hg 0 /Hg[tot] = 0.84 and 0.78, respectively). Injections of NO2 (80-190 ppmv) at 440-880°C and c~-Fe203 (15 and 6 wt%) at 450°C into Absatoka and Falkirk coal combustion flue 2g+ases did not significantly affect Hg speciation. The lack of Hg ° to H g conversion suggests that components of Absaloka and Falkirk combustion flue gases and/or fly ashes inhibit heterogeneous Hg°-NOx-c~-Fe203 reactions or that the flue gas quench rate in the 7-kW system is much different in relation to bench-scale flue gas simulators. An abundance of Hg 2+, HCI, and 7 - F e 2 0 3 in Blacksville flue gas and the inertness of injected a - F e 2 0 3 with respect to heterogeneous Hg ° oxidation in Absaloka and Falkirk flue gases suggested that 7 - F e 2 0 3 catalyses Hg 2+ formation and that HC1 is an important Hg ° reactant. The filtration of Absaloka and Falklrk combustion flue gases at I50°C through fabric filters with ~60 g/m 2 7 - F e 2 0 3 indicated that about 30% of the Hg ° in Absaloka and Falkirk flue gases was converted to Hg 2 + and/or Hg(p). HCI injection (100 ppmv) into the Absaloka combustion flue gas converted most of the Hg ° to Hg 2+, whereas HC1 injection into the Falkirk flue gas converted most of the Hg ° and Hg 2 + to Hg(p). Additions of -Fe203 and HC1 did not have a synergistic effect on Hg ° oxidation. The filtration of Absaloka and Falkirk flue gases through much greater fabric filter loadings of 475 g/m ~-7 -Fe203 essentially doubled the baghouse Hg[tot] removal efficiency to about 50%. Results from this investigation demonstrate the importance of evaluating potential Hg ° reactants and oxidation catalysts in actual coal combustion flue gases. •
•
'
7 +
05•01719 Effects of strain rate on high-pressure nonpremixed n-heptane autoignition in counterflow Liu, S. et al. Combustion andFlame, 2004, 137, (3), 320-339. The effect of steady strain on the transient autoignition of n-heptane at high pressures is studied numerically with detailed chemistry and transport in a eounterflow configuration. Skeletal and reduced nheptane mechanisms are developed and validated against experiments over a range of pressure and stoiehiometries. Two configurations are investigated using the skeletal mechanism• First, the effect of strain rate on multistage n-heptane ignition is studied by imposing a uniform temperature for both the fuel and the oxidizer streams. Second, a temperature gradient between the fuel and the oxidizer streams is imposed. The global effect of strain on ignition is captured by a Damk6hler number based on either the heat-release rate or the characteristic chain-branching rate. Results show that for low to moderate strain rates, both the low- and intermediate-temperature chemistries evolve in a manner comparable to that in homogeneous systems, including the negative temperature coefficient regime, but with somewhat slower evolution attributable to diffusive losses. At high strain rates diffusive losses inhibit ignition; for two-stage ignition, it is found that ignition is inhibited during the second, intermediatetemperature stage. The imposition of an overall temperature gradient further inhibits ignition because reaction zones for key branching reactions with large activation energies are narrowed. For a fixed oxidizer stream temperature that is not sufficiently high, a higher fuel temperature results in a shorter ignition delay provided that the heptyl radicals are mainly oxidized by low-temperature chemistry. As expected, an increase in pressure significantly increases reaction rates
and reduces ignition delay time. However, with increasing pressure there is a shift toward single-stage low-temperature-dominated ignition which serves to delay ignition.
05/01720 Experimental studies on low-temperature pyrolysis of municipal household garbage-temperature influence on pyrolysis product distribution Yan, W. et al. Renewable Energy, 2005, 30, (7), 1133-1142. The low-temperature pyrolysis of the mixture of nine typical components from municipal household garbage has been experimentally studied in an externally heated fixed-bed pyrolyser, at temperatures ranging from 300 to 700°C. The yields of final pyrolysis product varying with temperatures are presented in this paper. The solid product yield decreases with the increase of temperature in the test temperature range, and reduces quickly at 300-550°C but very slowly at 550-700°C. However, the pyrolysis liquid yield increases with the increase of temperature, but reaches the maximum at 550°C, and afterwards begins to decline. Among liquid product, cream-shaped tar is found, the yield of which also reaches the maximum at 550°C. The pyrolysis gas yield steadily increases with the increase of temperature at the whole test temperature range. The above-mentioned experimental results could be helpful to the practical application of low-temperature pyrolysis of municipal household garbage.
05•01721 Investigations into the pyrolytic behaviour of coal/biomass blends using thermogravimetric analysis Vuthaluru, H. B. Bioresource Technology, 2004, 92, (2), 187-195. Investigations into the pyrolytic behaviour during co-pyrolysis of coal, biomass materials and coal/biomass blends prepared at different ratios (10:90, 20:80, 30:70 and 50:50) have been conducted using a thermogravimetric analysis (TGA) apparatus. The coal sample selected was Collie sub-bituminous coal from Western Australia, while wood waste (WW) and wheat straw (WS) were used as biomass samples. Three thermal events were identified during the pyrolysis. The first two were dominated by the biomass pyrolysis, while the third was linked to the coal pyrolysis, which occurred at much higher temperatures. No interactions were seen between the coal and biomass during copyrolysis. The pyrolytic characteristics of the blends followed those of the parent fuels in an additive manner. Among the tested blends, 20:80 blends showed the lowest activation energies of 90.9 and 78.7 kJ mol a for coal/WW and coal/WS blends respectively. The optimum blend ratio for pyrolysis of coal/WS was 50:50 with a high degradation rate in ali the thermal events and a higher mass loss over the course of the copyrolysis compared to coal/WW blends examined. The reaction orders in these experiments were in the range of 0.21-1.60, thus having a significant effect on the overall reaction rate. Besides the pyrolysis of coal alone, the 50:50 coal/biomass blends had the highest reaction rate, ranging 1 × 109-2 x 101. The experimental results may provide useful data for power generation industries for the development of co-firing options with biomass.
05•01722 Modeling of soot particles growth in fuel-rich premixed flame Oknyama, M. et al. International Journal of Heat and Mass Transfer, 2004, 47, (21), 4625-4635.~ The soot formation process and the structure of a fuel-rich premixed flame stabilized in the downstream side of a porous medium have been investigated by experimental measurements and numerical analysis. In the numerical analysis, a modified Tesner's model for the reaction rate of soot formation has been introduced through a comparison between measured and calculated distributions of the temperature and the species mole fractions. Furthermore, a novel model for soot growth is developed, taking both surface and coalescence growths into account. On the basis of this model, the following results are obtained. Surface growth becomes dominant immediately after the beginning of soot formation. In the downstream side, the soot particle increases due to grow by the coalescence with smaller soot particles, and decrease as a result of collision with radicals and coalescence with larger soot particles.
05/01723 Molecular transport effects on turbulent flame propagation and structure Lipatnikov, A. N. and Chomiak, J. Progress in Energy and Combustion Science, 2005, 31, (3), 1-73. Various experimental and DNS data show that premixed combustion is affected by the differences between the coefficients of molecular transport of fuel, oxidant, and heat not only at weak but also at moderate and high turbulence. In particular, turbulent flame speed increases with decreasing the Lewis number of the deficient reactant, the effect being very strong for lean hydrogen mixtures. Various concepts; flame instability, flame stretch, local extinction, leading point, that aim at describing the effects of molecular transport on turbulent flame propagation and structure are critically discussed and the results of relevant studies of perturbed laminar flames (unstable flames, flame balls, flames in vortex tubes) are reviewed. The crucial
Fuel and Energy Abstracts July 2005 253
09 Combustion (burners, combustion systems) role played by extremely curved laminar flamelets in the propagation of moderately and highly turbulent flames is highlighted and the relevant physical mechanisms are discussed.
05101724 Pretreated olivine as tar removal catalyst for biomass gasifiers: investigation using naphthalene as model biomass tar Devi, L. et al. Fuel Processing Technology, 2005, 86, (6), 707-730. Biomass is considered as a potential source of renewable energy. One of the major problems for biomass gasification is the presence of tar in the product gas. This study investigated the catalytic behaviour of olivine as a prospective bed additive for biomass gasifiers for tar removal. In the present paper, the pretreatment of olivine was investigated to improve its activity. Pretreatment method includes heating olivine at 900°C in the presence of air for different treatment times. The catalytic activity of olivine was investigated via steamreforming reaction of naphthalene as model biomass tar compound. Improvement in naphthalene conversion of around 30% was observed with 1 h of pretreatment. Also effect of pretreatment time was investigated. With increasing pretreatment time, conversion increased; more than 80% naphthalene conversion was observed with 10 h of pretreatment time for olivine. Both steam and dry reforming reaction of naphthalene formed more than 50% gaseous products over 10 h pretreated olivine. Besides the gaseous products and light tars, polymerization reactions occured producing higher tars in small quantity. Naphthalene conversion under syngas mixture was somewhat lower than that of only in steam and CO2. Apparent activation energy of 187 kJ mo1-1 was determined for 10 h pretreated olivine under gasification-gas mixture.
05•01725
Pyrolytic behavior of waste corn cob
Cao, Q. et al. Bioresource Technology, 2004, 94, (1), 83 89. The powder of the agricultural waste corn cob was pyrolysed in a tubetyped stainless steel reactor of 200 ml volume under N2 atmosphere. The compositions of the gases and liquid obtained at different pyrolytic temperatures below 600°C at the heating rate of 30 K/rain were analysed. With the increment of the pyrolytic temperature, the yields of the solid and the liquid products were decreased, but the yield of gas products was increased. The liquid products were approximately 3440.96% (wt%), the gas products were 27-40.96% (wt%) and the solid products 23.6-31.6% (wt%). There were tess changes for the yields of these products above 600°C. The gas products were analysed by gas chromatography (GC) as CO2, CO, H2, CH4, C2H4, C3H6, C3H8, etc. When the temperature was 350-400°C, the gases had CO2 and CO 8095% (v/v). When the temperature increased continuously, yields of H2, CH4, C2H4, C3H6 and C3Hs gradually increased. The liquid products were identified by GC-MS as phenols, 2-furanmethanol, 2-cyclopentanedione, etc. The Fourier transform infra-red spectrophotometer (FTIR) analysis of the liquid product showed a strong - O H group absorption peak. Differential thermogravimetric analysis (DTG) showed that thermal decomposition process involves two steps. The heating rate affects not only the activation energy of the decomposition reaction, but also the path of the reaction. With the increment of the heating rate, the maximum rate temperature of the decomposition reaction was shifted to a higher temperature, and the order and activation energy of the total decomposition reaction were decreasing.
05•01726 Reductive pyrolysis of Miocene-aged lignite lithotypes using MS and GC/MS detection systems for analysis of organic sulphur groups Stefanova, M. et al. Fuel, 2005, 84, (1), 71-79. The atmospheric pressure temperature programmed reduction (APTPR) technique, an approach for organic sulfur speciation, was extended by mass spectral detection. The coupling gave ground for precise assignment of sulfur compounds in flue gases of lignite lithotypes pyrolysed in H2 atmosphere. A broad range of suifur compounds was determined, i.e. thiols, dimethylsulphide, dimetbyldisulphide, CS2, thiophenes, benzothiophenes and their alkylated homologues. Certain peculiarities in organic sulfur distribution in lithotypes under study were noticed. Humovitrain was the lithotype with the highest organic sulfur content. A preponderance of aliphatic sulfur, thiols and dimethylsulfides were determined for both homogeneous lithotypes (xylain and humovitrain). In humovitrain, additionally thiophenes were also identified. For heterogeneous lithotypes, liptain and humoclarain, a dominance of disulphides and an almost lack of sulphides was observed. This is an indication that with coalification a gradual loss of aliphatic sulfur functions has proceeded, where more resistant disulphides sulfur bridges turned out to be present. Thiophenes are the most abundant aromatic structures, dominating in humoclarain. Some amounts of oxidized organic sulfur compounds (1% up to 4.1% of Sorg) were semi-quantitative determined in lithotypes using AP-TPR-MS.
254 Fuel and Energy Abstracts
July 2005
05/01727 Size and charge of soot particles in rich premixed ethylene flames Maricq, M. M. Combustion and Flame, 2004, 137, (3), 340-350. A nano differential mobility analyser (DMA) is used to measure both the size and electrical charge distributions of soot particles generated during rich premixed combustion. The size distributions are bimodal. One mode peaks at diameters below the 3 nm lower limit of the nano DMA and falls off nearly exponentially with increasing particle diameter. The intensity of this mode persists with increasing height above the burner suggesting that it represents the continued formation of new particles. The second mode is lognormal in shape. Its intensity decreases and the mean diameter increases with increasing height above the burner due to coagulation and surface growth as the particles rise in the flame. The DMA measurements show that a substantial fraction of the soot particles are electrically charged in the flame, predominantly with a single charge per particle and with essentially equal numbers of positive and negative particles. These charged particles belong solely to the upper mode, whereas the lower mode remains charge neutral, suggesting that ions do not act as soot nuclei. Following soot inception, the fraction of charged particles quickly increases with height above the burner and stabilizes at ~30% of the upper mode for each polarity.
05•01728 Sulphur functionality study of steam pyrolyzed 'Mequinenza' lignite using reductive pyrolysis technique coupled with MS and GC/MS detection systems Marinov, S. P. et al. Fuel Processing Technology, 2005, 86, (5), 523-534. Atmospheric pressure-temperature programmed reduction (AP-TPR) and its analogous in oxidative atmosphere coupled 'on-line' with a mass spectrometer (MS) were used to study the behaviour of organic sulfur forms of 'Mequinenza' lignite during their mild steam pyrolysis. The obtained data were confirmed and completed by the AP-TPR-GC/MS 'off-line' analysis. Samples under study were pyrolysed at different processing parameters (temperature and flow gas). Some peculiarities in the distribution of non-thiophenic sulfur forms depending on experimental conditions were found. Namely, their amounts decreased with temperature increase at the steam treatment. The experiment performed at 500°C in water vapour flow proved the C-S bond splitting in dibenzothiophene with biphenyl formation. Sulphonic acid compounds were also systematically removed. At higher temperature of the steam pyrolysed treatment, this effect was more pronounced. At the same time, a relative increase in sulphones was found. The following organic sulfur species in demineralized lignite were detected by the 'offqine' AP-TPR-GC/MS technique: methyl- and benzenethiols; mono- and disulphides; alkylthiolanes; alkenyl thiophenes; alkylbenzo[b]thiophenes and alkyldibenzo[bd]thiophenes. Their relative intensities as a function of temperature were followed. A strong preponderance of benzo[b]thiophene and its alkytated homologues above 450°C were observed. Thiophene presence was temperature independent.
05/01729 Tracer-LIF diagnostics: quantitative measurement of fuel concentration, temperature and fuel/air ratio in practical combustion systems Schulz, C. and Sick, V. Progress in Energy and Combustion Science, 2005, 31, (1), 75-121. The safe, clean, and reliable operation of combustion devices depends to a large degree on the exact control of the fuel/air mixing process prior to ignition. Therefore, quantitative measurement techniques that characterize the state of the fresh gas mixture are crucial in modern combustion science and engineering. This paper presents the fundamental concepts for how to devise and apply quantitative measurement techniques for studies of fuel concentration, temperature, and fuel/air ratio in practical combustion systems, with some emphasis on internal combustion engines. The paper does not attempt to provide a full literature review of quantitative imaging diagnostics for practical combustion devices; rather it focuses on explaining the concepts and illustrating these with selected examples. These examples focus on application to primarily gaseous situations. The photophysies of organic molecules is presented in an overview followed by discussions on specific details of the temperature-, pressure-, and mixturedependence of the laser-induced fluorescence strength of aliphatic ketones, like acetone and 3-pentanone, and toluene. Models that describe the fluorescence are discussed and evaluated with respect to their functionality. Examples for quantitative applications are categorized in order of increased complexity. These examples include simple mixing experiments under isothermal and isobaric conditions, fuel/air mixing in engines, temperature measurements, and mixing studies where fuel and oxygen concentrations vary. A brief summary is given on measurements of fuel concentrations in multiphase systems, such as laser-induced exeiplex spectroscopy. Potentially adverse effects that added tracers might have on mixture formation, combustion, and the faithful representation of the base fuel distribution are discussed. Finally, a brief section describes alternative techniques to tracer-based measurements that allow studies of fuel/air mixing processes in