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04899 Relation between evaporation of minerals and coal ash deposition during coal combustion
09
oven for 105 days also showed no decrease in reactivity. Only when one of these samples had agglomerated did it show decreased reactivity, suggesting that the agglomeration process rather than duration is significant in promoting sintering and reducing the sulfate reactivity.
Relation between evaporation ash deoosition durina coal combustion .~
97104899
of minerals
and coal
Wang, B. et al. Ransh:o Kexue Yu Jishu., 1995, 1, (4), 305-311. (In Chinese) Both theoretical and experimental studies were conducted to explore the evaporation of coal minerals during combustion. The relationships between coal ash deposition and main mineral evaporation was analysed based on several empirical slagging indexes. New conclusions were reached concerning coal ash deposition.
97/04900 combustion
The
release
of
nitrogen
oxides
during
char
Thomas, K. M. Fuel, 1997, 76, (6). 457-473. During coal combustion, the release of nitrogen oxides has a major environmental impact. In low-NO, burners and fluidized bed combustors the char nitrogen is the major contributor to these emissions. This review considers the role of coal and char structural characteristics in the release of nitrogen oxides during coal combustion. The changes in the nitrogen functionality during the conversion of coal nitrogen to char nitrogen are discussed in detail. The results available in the literature are discussed in terms of the mechanisms for production of nitrogen oxides and their reduction in the pores or on the surface of the char.
A review of NO, formation and reduction 97104901 isms in combustion systems, with particular reference
mechanto coal
Williams. A. er al. J. Insritute of Energy, September 1997, 70, 102-113. Considerable reductions have been witnessed in recent years in the amount of NO, emitted by burners fired by natural gas, oil or pulverized coal. This has been brought about bv a number of aooroaches such as reducing the temperature aid fuel staging, both of which minimize the NO,-forming reactions in fuel-rich zones. In gaseous or light-fuel flames this reduction in NO, is considerable-EO-90%-but in the combustion of pulverised coal it is only about SO-60%. Thus there is considerable interest in reducing NO, further, and this is the subject of a number of collaborative research projects such as the current UK DTI-NO, project. In this review the NO,forming reactions are discussed, giving an indication of the way that they can be used for computational fluid dynamic (CFD) modelling of flames. A number of applications are considered, including natural-gas burners and staged oil-spray flames, where in both cases prompt-NO, becomes dominant at low NO, levels. However, particular attention is devoted to combustion of pulverized coal and some of the DTI-NO, project results from laboratory experiments. An ‘advanced coal model’ detailing some aspects of the work is outlined; in this, details of devolatilization of speciated volatiles, including HCN, are also included for a number of coals. The char left by the devolatilization process is a porous carbonaceous material, and a model is given for the formation of network char and cenospheres, and the subsequent reaction of the fuel-nitrogen compounds in the char to give NO,. The effect of coal composition, rank. and the nature of the nitrogen functionalities on NO, formation, and on residual carbon burn-out, are discussed. Methods of improving NO, are also considered.
97104902 Secondary effects in sampling ammonia measurements in a circulating fluidised-bed combustor
during
Kassman, H. ef al. J. Insritufe of Energy, September 1997, 70, 95-101. The results of measuring the ammonia (NH,) concentration in the combustion chamber of a circulating fluidized-bed (CFB) boiler were presented in a previous paper. Two sampling techniques were used: a gasquenching (GQ) probe where the sample is quenched directly in the probe tip by a circulating trapper solution, and a gas-sampling probe connected to a Fourier-transform infra-red (FTIR) instrument. The present namer attempts to estimate the influen‘ce of ‘potential secondary ‘reactions’ with NH2 in the GQ probe tip by means of a plug-flow model. The calculations showed that heterogeneous and homogeneous reactions could be of importance to the accuracy of the measurement. This contradicts the almost identical results relative to the parallel FTIR measurement, and the conversion of NH3 is probably overestimated by the model. In addition, transients obtained during the FTIR measurement were used to study the accuracy of the gas-sampling probe.
97104903 Seven years of operating experience with high dust-DENOX plants behind slag tap furnaces-consequences for tailing plants Schonrok, M. and Hein, M. VCR Tech. Ver. Grosskraffwerksbetr., [Tagungsber.] VGB-TB, 1997, 17, l-10. The operating conditions of two slag tap coal-fired cyclone combustors in the Staudinger power plant is reported with a discussion about the required retrofitting of the downstream DeNOx facility. The combustors have 100% fly ash recirculation, which is reintroduced into the combustor and molten down into slag.
97104904
char/carbon
Combustion
(burners, combustion
systems)
Simple method for calculating the burning rate of particles under oxygen concentration change.
Fu, W. and Zheng, S. Ranshao Kexue Yu Jishu., 1996, 2, (2), 104-I 10. (In Chinese) A simple method for calculating the burning rate of char/carbon particles under varying oxygen concentration is presented, suitable for application in engineering calculation.
97lO4905 The solution of regional power and ecology problems based on the new low-temperature vortex-type technology for solid fuel combustion Rundygin, Y. A. et al. Energy Environ., Proc. Inr. Conf., 1995 (Pub. 1996) 631-638. Edited by Chen, Z.-H. ef al., Begell House, New York. The new Low-Temperature Vortex-type (LTV) technology for low-quality fuel combustion is presented. The use of regional low-quality fuel and its associated problems are discussed. Attention is given to peculiarities of the LTV technology and fuel preparation system schemes. Characteristics of the fuel, which have been tested with LTV technology are given in the paper. Some practical results of LTV technology applications for peat, brown coal, oil shale and flammable industrial wastes combustion are presented.
97lQ4906
Soot in coal combustion
systems
Fletcher, T. H. et al. Prog. Energy Cornbust. Sci., 1997, 23, (3) 283-301. Soot is generated from coal when volatile matter, tar in particular, undergoes secondary reactions a high temperatures. A description of soot in coal flames allows better calculations of radiative transfer and temperatures in near-burner regions, which in turn allows more accurate predictions of NO. formation in coal-fired furnaces. Exoeriments examinmg the formation, agglomeration and properties of coal derived soot, including pyrolysis experiments and combustion experiments, are reviewed. This review includes the types of experiments performed, the soot yields obtained, the size of the soot particles and agglomerates, the optical properties of soot, the relationship between coal-derived soot and soot from simple hydrocarbons and attempts to model soot in coal flames.
97104907 Studies of combustion and slagging of anthracite blends with bituminous coal.
characteristics
Zeng, H. er al. Ranshao Kexue Yu Jishu., 1996, 2. (2). 181-189. (In Chinese) This study examines the combustion and slagging characteristics of bituminous coal blends with anthracite. The equivalent volatile matter and the optimum mixed ratio are determined and examined by hot tests,
97lO4909 Studies on the release of volatile mineral matter species during the high temperature, rapid heating of pulverized fuel under conditions relevant to low NO, burners British Coal Corporation Comm. Eur. Commttnifies, /Rep./ EUR, 1996, (EUR 15200) 124 pp. Boiler efficiency is decreased with ash deposition within pulverized coalfired boilers, derived from the mineral matter in the coal. If allowed to develop, these deposits may require expensive outages for their removal. It is therefore important to know how coal properties and boiler conditions affect ash deposition. Low NO, burners are installed in European coal-fired power stations in order to reduce the emissions of nitrogen oxides. During the early stages of combustion within these burners, oxygen concentrations and temperatures tend to be lower than in conventional burners and this may affect ash deposition. The sodium in coal has a major influence on ash deposition. Some of the sodium volatilizes in the flame and reacts with other flame components to form species which condense on the heat transfer surfaces of the boiler or the surface of the fly ash particles and act as a precursor to ash deposition. It is possible that the extent of release and form of the volatile sodium is not the same in low NO, burners as it is in conventional burners. The project aimed to compare the release of sodium from pulverized coal particles on a laboratory-scale, under conditions pertaining to low NO, and conventional burners.
97104909
Study of combustion of coal char by thermogravimetry
Li, W. and Baoqing, L. Meiton Zhuanhua, 1996, 19, (3). 76-81. (In Chinese) The use of thermogravimetry in studies of coal char combustion is under investigation. Topics include characterization of specific temperatures in the combustion process of coal char, and the dynamics of coal-char rnmh,,ct~_n
97lO4910 Study on burning rate of carbon particle under forced convection Xu, C. and Fu, W. Ranshao Kexue Yu Jishu., 1996, 2, (I), l-7. (In Chinese) A simplified calculation model is introduced, based on the burning process characteristics of a single carbon particle under forced convection (Rec200). Based on this model, the numerical simulation of burning process for carbon particle is conducted. Then both the burning rate of carbon particle under different conditions and the distributions of concentration and temperature in the boundary layer of carbon particle are obtained. The calculated results agreed well with experimental data, validating the feasiblity of the model.
Fuel and Energy Abstracts
November
1997
425
oven for 105 days also showed no decrease in reactivity. Only when one of these samples had agglomerated did it show decreased reactivity, suggesting that the agglomeration process rather than duration is significant in promoting sintering and reducing the sulfate reactivity.
Relation between evaporation ash deoosition durina coal combustion .~
97104899
of minerals
and coal
Wang, B. et al. Ransh:o Kexue Yu Jishu., 1995, 1, (4), 305-311. (In Chinese) Both theoretical and experimental studies were conducted to explore the evaporation of coal minerals during combustion. The relationships between coal ash deposition and main mineral evaporation was analysed based on several empirical slagging indexes. New conclusions were reached concerning coal ash deposition.
97/04900 combustion
The
release
of
nitrogen
oxides
during
char
Thomas, K. M. Fuel, 1997, 76, (6). 457-473. During coal combustion, the release of nitrogen oxides has a major environmental impact. In low-NO, burners and fluidized bed combustors the char nitrogen is the major contributor to these emissions. This review considers the role of coal and char structural characteristics in the release of nitrogen oxides during coal combustion. The changes in the nitrogen functionality during the conversion of coal nitrogen to char nitrogen are discussed in detail. The results available in the literature are discussed in terms of the mechanisms for production of nitrogen oxides and their reduction in the pores or on the surface of the char.
A review of NO, formation and reduction 97104901 isms in combustion systems, with particular reference
mechanto coal
Williams. A. er al. J. Insritute of Energy, September 1997, 70, 102-113. Considerable reductions have been witnessed in recent years in the amount of NO, emitted by burners fired by natural gas, oil or pulverized coal. This has been brought about bv a number of aooroaches such as reducing the temperature aid fuel staging, both of which minimize the NO,-forming reactions in fuel-rich zones. In gaseous or light-fuel flames this reduction in NO, is considerable-EO-90%-but in the combustion of pulverised coal it is only about SO-60%. Thus there is considerable interest in reducing NO, further, and this is the subject of a number of collaborative research projects such as the current UK DTI-NO, project. In this review the NO,forming reactions are discussed, giving an indication of the way that they can be used for computational fluid dynamic (CFD) modelling of flames. A number of applications are considered, including natural-gas burners and staged oil-spray flames, where in both cases prompt-NO, becomes dominant at low NO, levels. However, particular attention is devoted to combustion of pulverized coal and some of the DTI-NO, project results from laboratory experiments. An ‘advanced coal model’ detailing some aspects of the work is outlined; in this, details of devolatilization of speciated volatiles, including HCN, are also included for a number of coals. The char left by the devolatilization process is a porous carbonaceous material, and a model is given for the formation of network char and cenospheres, and the subsequent reaction of the fuel-nitrogen compounds in the char to give NO,. The effect of coal composition, rank. and the nature of the nitrogen functionalities on NO, formation, and on residual carbon burn-out, are discussed. Methods of improving NO, are also considered.
97104902 Secondary effects in sampling ammonia measurements in a circulating fluidised-bed combustor
during
Kassman, H. ef al. J. Insritufe of Energy, September 1997, 70, 95-101. The results of measuring the ammonia (NH,) concentration in the combustion chamber of a circulating fluidized-bed (CFB) boiler were presented in a previous paper. Two sampling techniques were used: a gasquenching (GQ) probe where the sample is quenched directly in the probe tip by a circulating trapper solution, and a gas-sampling probe connected to a Fourier-transform infra-red (FTIR) instrument. The present namer attempts to estimate the influen‘ce of ‘potential secondary ‘reactions’ with NH2 in the GQ probe tip by means of a plug-flow model. The calculations showed that heterogeneous and homogeneous reactions could be of importance to the accuracy of the measurement. This contradicts the almost identical results relative to the parallel FTIR measurement, and the conversion of NH3 is probably overestimated by the model. In addition, transients obtained during the FTIR measurement were used to study the accuracy of the gas-sampling probe.
97104903 Seven years of operating experience with high dust-DENOX plants behind slag tap furnaces-consequences for tailing plants Schonrok, M. and Hein, M. VCR Tech. Ver. Grosskraffwerksbetr., [Tagungsber.] VGB-TB, 1997, 17, l-10. The operating conditions of two slag tap coal-fired cyclone combustors in the Staudinger power plant is reported with a discussion about the required retrofitting of the downstream DeNOx facility. The combustors have 100% fly ash recirculation, which is reintroduced into the combustor and molten down into slag.
97104904
char/carbon
Combustion
(burners, combustion
systems)
Simple method for calculating the burning rate of particles under oxygen concentration change.
Fu, W. and Zheng, S. Ranshao Kexue Yu Jishu., 1996, 2, (2), 104-I 10. (In Chinese) A simple method for calculating the burning rate of char/carbon particles under varying oxygen concentration is presented, suitable for application in engineering calculation.
97lO4905 The solution of regional power and ecology problems based on the new low-temperature vortex-type technology for solid fuel combustion Rundygin, Y. A. et al. Energy Environ., Proc. Inr. Conf., 1995 (Pub. 1996) 631-638. Edited by Chen, Z.-H. ef al., Begell House, New York. The new Low-Temperature Vortex-type (LTV) technology for low-quality fuel combustion is presented. The use of regional low-quality fuel and its associated problems are discussed. Attention is given to peculiarities of the LTV technology and fuel preparation system schemes. Characteristics of the fuel, which have been tested with LTV technology are given in the paper. Some practical results of LTV technology applications for peat, brown coal, oil shale and flammable industrial wastes combustion are presented.
97lQ4906
Soot in coal combustion
systems
Fletcher, T. H. et al. Prog. Energy Cornbust. Sci., 1997, 23, (3) 283-301. Soot is generated from coal when volatile matter, tar in particular, undergoes secondary reactions a high temperatures. A description of soot in coal flames allows better calculations of radiative transfer and temperatures in near-burner regions, which in turn allows more accurate predictions of NO. formation in coal-fired furnaces. Exoeriments examinmg the formation, agglomeration and properties of coal derived soot, including pyrolysis experiments and combustion experiments, are reviewed. This review includes the types of experiments performed, the soot yields obtained, the size of the soot particles and agglomerates, the optical properties of soot, the relationship between coal-derived soot and soot from simple hydrocarbons and attempts to model soot in coal flames.
97104907 Studies of combustion and slagging of anthracite blends with bituminous coal.
characteristics
Zeng, H. er al. Ranshao Kexue Yu Jishu., 1996, 2. (2). 181-189. (In Chinese) This study examines the combustion and slagging characteristics of bituminous coal blends with anthracite. The equivalent volatile matter and the optimum mixed ratio are determined and examined by hot tests,
97lO4909 Studies on the release of volatile mineral matter species during the high temperature, rapid heating of pulverized fuel under conditions relevant to low NO, burners British Coal Corporation Comm. Eur. Commttnifies, /Rep./ EUR, 1996, (EUR 15200) 124 pp. Boiler efficiency is decreased with ash deposition within pulverized coalfired boilers, derived from the mineral matter in the coal. If allowed to develop, these deposits may require expensive outages for their removal. It is therefore important to know how coal properties and boiler conditions affect ash deposition. Low NO, burners are installed in European coal-fired power stations in order to reduce the emissions of nitrogen oxides. During the early stages of combustion within these burners, oxygen concentrations and temperatures tend to be lower than in conventional burners and this may affect ash deposition. The sodium in coal has a major influence on ash deposition. Some of the sodium volatilizes in the flame and reacts with other flame components to form species which condense on the heat transfer surfaces of the boiler or the surface of the fly ash particles and act as a precursor to ash deposition. It is possible that the extent of release and form of the volatile sodium is not the same in low NO, burners as it is in conventional burners. The project aimed to compare the release of sodium from pulverized coal particles on a laboratory-scale, under conditions pertaining to low NO, and conventional burners.
97104909
Study of combustion of coal char by thermogravimetry
Li, W. and Baoqing, L. Meiton Zhuanhua, 1996, 19, (3). 76-81. (In Chinese) The use of thermogravimetry in studies of coal char combustion is under investigation. Topics include characterization of specific temperatures in the combustion process of coal char, and the dynamics of coal-char rnmh,,ct~_n
97lO4910 Study on burning rate of carbon particle under forced convection Xu, C. and Fu, W. Ranshao Kexue Yu Jishu., 1996, 2, (I), l-7. (In Chinese) A simplified calculation model is introduced, based on the burning process characteristics of a single carbon particle under forced convection (Rec200). Based on this model, the numerical simulation of burning process for carbon particle is conducted. Then both the burning rate of carbon particle under different conditions and the distributions of concentration and temperature in the boundary layer of carbon particle are obtained. The calculated results agreed well with experimental data, validating the feasiblity of the model.
Fuel and Energy Abstracts
November
1997
425