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00547 Evolution of volatile species from the combustion of coal pyrolysis volatiles
09
Combustion
(burners, combustion systems)
affected by natural and/or forced convection, which in turn affects the ignition mechanism and temperature. The ignition temperature decreased with the volatile matter content of coal under negligible and natural convection. Under forced convection, however, the ignition temperature remained more or less constant and temperatures under negligible and forced convections seem to converge at low volatile matter contents, suggesting a point of transition from homogeneous to heterogeneous ignition. The effect of particle size was almost the same in all three conditions where ignition temperatures increased with increasing particle size. The converging trend was not observed on varying particle size, indicating volatile matter content is the main factor in determining the ignition mechanism.
Development of a drop tube furnace based method 9a/oo537 for assessment of the effects of coal reactivity on the propensity for reduction of NO, emissions during pf (pulverized fuel) combustion King, M. J. et al. DGMK Tagungsber., 1997, 9703, (Proceedings ICCS ‘97, Volume 2), 1095-1098. Various coals were investigated via combustion in a pilot-scale optical access drop tube furnace (OA-DTF) and a laminar flat flame burner (LFFB) with regard to their reactivity. The OA-DTF consisted of an electrically heated furnace with a central ceramic tube and pre-heated Nz or air flew through this tube while coal was introduced into the hot gas stream. The LFFB consisted of a premixed Hz/OzINz flame into which coal particles were injected and the cooling of the burner body prevented particle preignition. The combustion gases from both furnaces were collected and analysed for NO, and Oz content, and the burnout of the coals was determined by the analysis of the ash. NO, concentration reduction was achieved at a temperature of 1400°C and a residence time of 400 ms. Drop tube investigations into coal particle combus98100538 tion at elevated temperatures and pressures Scherello, A. et al. DGMK Tagungsber., 1997, 9703, (Proceedings ICCS ‘97, Volume 2). 999-1002. Coal particle (loo-125 /Im) combustion was investigated via drop tube investigations performed at temperatures up to 1500°C and pressures up to 20 bar. New methods of in silu particle observation like phase-shift Doppler anemometry and high-resolution video CCD monitoring were developed. The study determined velocity distributions and surface temperatures of burning particles and velocity and the extent of devolatilization were found to be strongly reduced at high pressures. Significant pressure dependence was observed in the apparent reaction rate coefficients. Drop-tube studies on combustion of coal at high 98100539 temperatures and pressures Bonn, B. et al. VDI-Ber., 1997, 1313, (Verbrennung und Feuerungen), 8388. (In German) Equipped with phase-Doppler anemometry and charge-coupled cameras for observation of pulverized coal combustion, a high-temperature highpressure drop-tube reactor was developed. The rate degree of combustion are both strongly reduced due to the pressure coefficient of the reaction rate. Effect of alkali and alkaline earth metals on nitro98100540 gen release during temperature programmed pyrolysis of coal Ohtsuka, Y. et al. Fue1, 1997, 76, (14/1S), 1361-1367. During fixed-bed pyrolysis at 10K min-‘, the formation of HCN, NH3, and Nz has been studied using coal samples after partial demineralization followed by addition of metal hydroxides from aqueous systems. Without additives, NHs is the predominant product at 700°C showing the two peaks in the formation rate profile, whereas Nz is the only product at 2 800°C. Between 450 and 600°C. NH3 formation is considerably promoted by the presence of NaOH, KOH and Ca(OH)z, but HCN formation is suppressed. The Ca shows the largest effect on both the promotion and suppression. It is likely that the NH3 increased by Ca addition arises partly from HCN, but mainly from secondary reactions of tar-N. These hydroxides affect Nz formation in quite different ways, which are discussed in terms of solidphase reactions of alkali metal carbonates with char-N and secondary decomposition reactions of tar-N on CaQ particles. As a result, total conversion of coal-N to HCN. NHa and N? up to 1000°C increases in the sequence of Na < none < K < Ca. Effect of lateral and extended fins on heat transfer 98iOO541 in a circulating fluidized bed Reddy, B. V. and Nag, P. K. Int. J. Heat Mass Transfer, 1998, (Pub. 1997) 41, (1) 139-146. The effect of lateral, and lateral and extended fins together on heat transfer coefficient and on the rate of heat transfer in a hot circulating fluidized bed unit was experimentally studied. A mathematical model is proposed to predict the heat transfer coefficient to a water-wall test section with lateral and extended fins. Comparisons of the model results with the present experimental data and also with those of published literature found good agreement.
46
Fuel and Energy Abstracts January 1998
98loo542 Effect of maceral content on volatile release and char combustion reactivity Cai, H. Y. er al. DGMK Tagungsber., 1997, 9703, (Proceedings ICCS ‘97, Volume 2) 1011-1014. As a result of their lower overall volatile release, high inertinite coals are known to give rise to flame stability problems in the near burner zone in pfcombustion. Furthermore, levels of carbon found in fly ash have often been associated with the presence and levels of inertinite in the feed coal. Therefore coals high in inertinite content are less expensive, as they are less desirable for electricity generation. However, available data on the relative combustion reactivity of chars derived from different macerals, have not always supported the hypothesis of the inferiority of inertinite. This paper examines the effect of maceral content (particularly inertinite) on volatile release from coals and the relative combustion reactivities of their pyrolysis chars. 98/00543 Effect of mineral matter content on combustion kinetics of some Turkish lignites Haykiri-Arma. H. ef al. DGMK Tagungsber., 1997, 9703, (Proceedings ICCS ‘97, Volume 2). 915-918. In order to obtain the kinetic data related to coal combustion, nonisothermal thermogravimetry was applied. To determine the effect of mineral matter content on the combustion kinetics, original and demineralized lignite samples were used. The burning profiles of 10 lignite samples were obtained by heating from room temperature to 1273 K with a heating rate of 40 Kimin. Using a computer program in BASIC which permits regression analysis, the kinetic analysis of these profiles was achieved and 20 different model equations of possible solid-state rate controlling mechanism were considered. For all samples, the best fit was provided by Prout-Tumpkins Mode. Different calculated activation energy and frequency factor values were found for each sample. 98100544 Effects of particle density and sulfur forms on pyrolysis desulfurization in rapid heating of coals Sugawara, K. et al. Energy Fuels, 1997, 11, (6) 1272-1277. A free-fall reactor was implemented in the rapid pyrolysis of four kinds of coal particles, having the same average diameter (69989% C daf). Pyrolysis took place at atmospheric pressure under a nitrogen stream at a terminal temperature of 1253 K in order to clarify pyrolysis desulfurization and volatilization behaviour. There was poor correlation between the extent of organic sulfur removal in the rapid pyrolysis and the carbon content of raw coal. The same sample particles were subsequently separated by density into three groups with a sink-float method. In the rapid pyrolysis of each group, volatile yield and extent of organic sulfur removal increased linearly with decreasing average density of the group, with exception of a high-rank coal. X-ray absorption near-edge structure analysis indicated that the Iowdensity group contained sulfide and sulfoxide, which could contribute to the high extent of organic sulfur removal. The efficient removal of organic sulfur from the densest group in a high-rank coal by rapid pyrolysis actually resulted in decomposition and/or vaporization of elemental sulfur which was apparently regarded as organic sulfur according to the ASTM (D2492). 98100545 Evaluation of precombustion control of mercury emissions from coal combustion by mild pyrolysis in a Rijke pulse combustor Keener, T. C. ef al. DGMK Ta,gungsber., 1997, 9703, (Proceedings ICCS ‘97, Volume 2) 573-576. I _ As an approach to mitigating mercury emissions, mild pyrolysis before combustion was explored. The pilot facility consisted of a pyrolysis reactor constructed as a dual screw feeder, that feeds a Rijke combustor. Coal was feed by the inner of the concentric screws and CaO was conducted in reverse flow by the outer crew to absorb Hg from the pyrolysis gas. As the pyrolysis temperature exceeded 400°C a substantial reduction in the amount of Hg released was observed.
98100546
Evaluation of the combustion characteristic of pulverized coal by using TG-DTA-T-DTG and EGD-GC Chen, Q. er al. Huadong Ligong Dame Xuebao, 1997, 23, (3). 286-291. (In Chinese) Simultaneous implementation of the TG-DTA-T-DTG and DTA-TEGDlevolved gas detectionl-GC methods, at a heating rate of 2O”Cimin was used to stidy combustion properties of five types oflpulverized coal. A regular change with the rank of coal is clarified. Demineralized coal was also studied. The effects of mineral and pore structure on combustion reactivity are discussed. 98/00547 Evolution of volatile species from the combustion of coal pyrolysis volatiles Ledesma, E. B. et al. DGMK Tagungsber., 1997, 9703, (Proceedings ICCS ‘97, Volume 2), 939-942. Pyrolysis of an Australian bituminous coal took place under Ar at 600°C in a fluidized bed reactor to produce volatiles. Combustion of the volatiles was examined at 900 and 1000°C in a quartz two-stage reactor. The reactor consisted of a tubular flow reactor in series with a fluidized bed reactor. HNCO was found as a significant N-containing product at low 0: concentrations, while the concentration of the other volatile N-containing compounds decreased in comparison to the volatile feed. An increase of carbonyl functionality was observed with increasing Oz concentration in the condensable fraction.
Combustion
(burners, combustion systems)
affected by natural and/or forced convection, which in turn affects the ignition mechanism and temperature. The ignition temperature decreased with the volatile matter content of coal under negligible and natural convection. Under forced convection, however, the ignition temperature remained more or less constant and temperatures under negligible and forced convections seem to converge at low volatile matter contents, suggesting a point of transition from homogeneous to heterogeneous ignition. The effect of particle size was almost the same in all three conditions where ignition temperatures increased with increasing particle size. The converging trend was not observed on varying particle size, indicating volatile matter content is the main factor in determining the ignition mechanism.
Development of a drop tube furnace based method 9a/oo537 for assessment of the effects of coal reactivity on the propensity for reduction of NO, emissions during pf (pulverized fuel) combustion King, M. J. et al. DGMK Tagungsber., 1997, 9703, (Proceedings ICCS ‘97, Volume 2), 1095-1098. Various coals were investigated via combustion in a pilot-scale optical access drop tube furnace (OA-DTF) and a laminar flat flame burner (LFFB) with regard to their reactivity. The OA-DTF consisted of an electrically heated furnace with a central ceramic tube and pre-heated Nz or air flew through this tube while coal was introduced into the hot gas stream. The LFFB consisted of a premixed Hz/OzINz flame into which coal particles were injected and the cooling of the burner body prevented particle preignition. The combustion gases from both furnaces were collected and analysed for NO, and Oz content, and the burnout of the coals was determined by the analysis of the ash. NO, concentration reduction was achieved at a temperature of 1400°C and a residence time of 400 ms. Drop tube investigations into coal particle combus98100538 tion at elevated temperatures and pressures Scherello, A. et al. DGMK Tagungsber., 1997, 9703, (Proceedings ICCS ‘97, Volume 2). 999-1002. Coal particle (loo-125 /Im) combustion was investigated via drop tube investigations performed at temperatures up to 1500°C and pressures up to 20 bar. New methods of in silu particle observation like phase-shift Doppler anemometry and high-resolution video CCD monitoring were developed. The study determined velocity distributions and surface temperatures of burning particles and velocity and the extent of devolatilization were found to be strongly reduced at high pressures. Significant pressure dependence was observed in the apparent reaction rate coefficients. Drop-tube studies on combustion of coal at high 98100539 temperatures and pressures Bonn, B. et al. VDI-Ber., 1997, 1313, (Verbrennung und Feuerungen), 8388. (In German) Equipped with phase-Doppler anemometry and charge-coupled cameras for observation of pulverized coal combustion, a high-temperature highpressure drop-tube reactor was developed. The rate degree of combustion are both strongly reduced due to the pressure coefficient of the reaction rate. Effect of alkali and alkaline earth metals on nitro98100540 gen release during temperature programmed pyrolysis of coal Ohtsuka, Y. et al. Fue1, 1997, 76, (14/1S), 1361-1367. During fixed-bed pyrolysis at 10K min-‘, the formation of HCN, NH3, and Nz has been studied using coal samples after partial demineralization followed by addition of metal hydroxides from aqueous systems. Without additives, NHs is the predominant product at 700°C showing the two peaks in the formation rate profile, whereas Nz is the only product at 2 800°C. Between 450 and 600°C. NH3 formation is considerably promoted by the presence of NaOH, KOH and Ca(OH)z, but HCN formation is suppressed. The Ca shows the largest effect on both the promotion and suppression. It is likely that the NH3 increased by Ca addition arises partly from HCN, but mainly from secondary reactions of tar-N. These hydroxides affect Nz formation in quite different ways, which are discussed in terms of solidphase reactions of alkali metal carbonates with char-N and secondary decomposition reactions of tar-N on CaQ particles. As a result, total conversion of coal-N to HCN. NHa and N? up to 1000°C increases in the sequence of Na < none < K < Ca. Effect of lateral and extended fins on heat transfer 98iOO541 in a circulating fluidized bed Reddy, B. V. and Nag, P. K. Int. J. Heat Mass Transfer, 1998, (Pub. 1997) 41, (1) 139-146. The effect of lateral, and lateral and extended fins together on heat transfer coefficient and on the rate of heat transfer in a hot circulating fluidized bed unit was experimentally studied. A mathematical model is proposed to predict the heat transfer coefficient to a water-wall test section with lateral and extended fins. Comparisons of the model results with the present experimental data and also with those of published literature found good agreement.
46
Fuel and Energy Abstracts January 1998
98loo542 Effect of maceral content on volatile release and char combustion reactivity Cai, H. Y. er al. DGMK Tagungsber., 1997, 9703, (Proceedings ICCS ‘97, Volume 2) 1011-1014. As a result of their lower overall volatile release, high inertinite coals are known to give rise to flame stability problems in the near burner zone in pfcombustion. Furthermore, levels of carbon found in fly ash have often been associated with the presence and levels of inertinite in the feed coal. Therefore coals high in inertinite content are less expensive, as they are less desirable for electricity generation. However, available data on the relative combustion reactivity of chars derived from different macerals, have not always supported the hypothesis of the inferiority of inertinite. This paper examines the effect of maceral content (particularly inertinite) on volatile release from coals and the relative combustion reactivities of their pyrolysis chars. 98/00543 Effect of mineral matter content on combustion kinetics of some Turkish lignites Haykiri-Arma. H. ef al. DGMK Tagungsber., 1997, 9703, (Proceedings ICCS ‘97, Volume 2). 915-918. In order to obtain the kinetic data related to coal combustion, nonisothermal thermogravimetry was applied. To determine the effect of mineral matter content on the combustion kinetics, original and demineralized lignite samples were used. The burning profiles of 10 lignite samples were obtained by heating from room temperature to 1273 K with a heating rate of 40 Kimin. Using a computer program in BASIC which permits regression analysis, the kinetic analysis of these profiles was achieved and 20 different model equations of possible solid-state rate controlling mechanism were considered. For all samples, the best fit was provided by Prout-Tumpkins Mode. Different calculated activation energy and frequency factor values were found for each sample. 98100544 Effects of particle density and sulfur forms on pyrolysis desulfurization in rapid heating of coals Sugawara, K. et al. Energy Fuels, 1997, 11, (6) 1272-1277. A free-fall reactor was implemented in the rapid pyrolysis of four kinds of coal particles, having the same average diameter (69989% C daf). Pyrolysis took place at atmospheric pressure under a nitrogen stream at a terminal temperature of 1253 K in order to clarify pyrolysis desulfurization and volatilization behaviour. There was poor correlation between the extent of organic sulfur removal in the rapid pyrolysis and the carbon content of raw coal. The same sample particles were subsequently separated by density into three groups with a sink-float method. In the rapid pyrolysis of each group, volatile yield and extent of organic sulfur removal increased linearly with decreasing average density of the group, with exception of a high-rank coal. X-ray absorption near-edge structure analysis indicated that the Iowdensity group contained sulfide and sulfoxide, which could contribute to the high extent of organic sulfur removal. The efficient removal of organic sulfur from the densest group in a high-rank coal by rapid pyrolysis actually resulted in decomposition and/or vaporization of elemental sulfur which was apparently regarded as organic sulfur according to the ASTM (D2492). 98100545 Evaluation of precombustion control of mercury emissions from coal combustion by mild pyrolysis in a Rijke pulse combustor Keener, T. C. ef al. DGMK Ta,gungsber., 1997, 9703, (Proceedings ICCS ‘97, Volume 2) 573-576. I _ As an approach to mitigating mercury emissions, mild pyrolysis before combustion was explored. The pilot facility consisted of a pyrolysis reactor constructed as a dual screw feeder, that feeds a Rijke combustor. Coal was feed by the inner of the concentric screws and CaO was conducted in reverse flow by the outer crew to absorb Hg from the pyrolysis gas. As the pyrolysis temperature exceeded 400°C a substantial reduction in the amount of Hg released was observed.
98100546
Evaluation of the combustion characteristic of pulverized coal by using TG-DTA-T-DTG and EGD-GC Chen, Q. er al. Huadong Ligong Dame Xuebao, 1997, 23, (3). 286-291. (In Chinese) Simultaneous implementation of the TG-DTA-T-DTG and DTA-TEGDlevolved gas detectionl-GC methods, at a heating rate of 2O”Cimin was used to stidy combustion properties of five types oflpulverized coal. A regular change with the rank of coal is clarified. Demineralized coal was also studied. The effects of mineral and pore structure on combustion reactivity are discussed. 98/00547 Evolution of volatile species from the combustion of coal pyrolysis volatiles Ledesma, E. B. et al. DGMK Tagungsber., 1997, 9703, (Proceedings ICCS ‘97, Volume 2), 939-942. Pyrolysis of an Australian bituminous coal took place under Ar at 600°C in a fluidized bed reactor to produce volatiles. Combustion of the volatiles was examined at 900 and 1000°C in a quartz two-stage reactor. The reactor consisted of a tubular flow reactor in series with a fluidized bed reactor. HNCO was found as a significant N-containing product at low 0: concentrations, while the concentration of the other volatile N-containing compounds decreased in comparison to the volatile feed. An increase of carbonyl functionality was observed with increasing Oz concentration in the condensable fraction.