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03142 Progress of combustion in the furnace of a circulating fluidized bed boiler
08
Steam raising (boiler operation/design)
Materials for a steam generator with maximum 9aiO3137 steam conditions Hardt, R. Werkst. Energietech., Symp. 3, Werkst@voche ‘96, 1996 (Pub. 1997), 35-41. (In German). Edited by Gruenling, H. W., DGM Informationsgesellschaft, Oberursel, Germany. For use as a critical construction material for coal-fired steam power plants that operate at >7OO”C, the nickel superalloy Alloy 617 has great potential. Alloy C263 and Nimonic 90 are recommended for the steam collector. Method and arrangement for burning gas in a 90lQ3138 furnace Raiko, M. et al. PCT Int. Appl. WO 98 00,675 (Cl. F23G7106). 8 Jan 1998, FI Appl. 96/2,669, 28 Jun 1996, 15 pp. A method and arrangement for burning fuel gas in a furnace, particularly burning gases of low heating value in a boiler principally fired with a main fuel, is reported. The invention is based on feeding the product gas of a gasifier or other combustible gas into air-deficient conditions of the lower part of the furnace and the gas is combusted upper in the furnace at a desired level of combustion air infeed or alternatively at multiple infeed levels of the combustion air. A new combustion stabllity index CSI for utility 98103139 coal-fired boilers Cheng, H. et al. Gongcheng Rewuli Xuebao, 1997, 18, (4) 512-516. (In Chinese) The paper discusses the shortage of the general suitability of some existing assessment methods for relative combustion stability and a new combustion stability index (CSI) for utility coal-fired boilers is proposed. The index is based on the concepts of BIB0 stability theory. CSI was measured by the maximum disturbance ratio of fuel mass flow rate which can be overcome by stable combustion process. A combustion process with CSI being 0 or I corresponds to the lowest or highest combustion stability, respectively The results of dynamic combustion simulation of a utility boiler and experiments on two types of burner in a laboratory-scale single-burner furnace have proved initially the effectiveness of CSI. It can be expected that a comprehensive method will be established on assessing the relative combustion stability of industrial combustion processes. Practice of burning gasifier slags in fluid-bed boiler 98/03140 with water-cooled vortex internal separator and circulation Zhang, D. et al. Huafei Gongye, 1997, 24, (4), 33-36 (In Chinese) The paper presents the technical features of the fluidized bed boiler with a water-cooled vortex internal separator and fluid circulation in the combustion of coal-gasification slags. Design features, operation, and use in small nitrogen-type fertilizer plants are discussed.
Prediction of combustion behavior of coal blends 98103141 in industrial scale boilers from laboratory scale data Pisupati, S. V. and Scaroni, A. W. DGMK Tagungsber., 1997, 9703, (Proceedings ICCS ‘97, Volume 2). 1151-I 154. The authors obtained the burning profiles of blends of three different coals and a bituminous coal. The combustion efficiencies were determined in a 1000 lb/h research boiler and a good correlation was obtained between the initial temperature obtained in the thermogravimetric analysis and the combustion efficiency in the boiler. The burning profiles were shown to be useful tools to predict the carbon burnout of individual coals and blends in a practical combustor. Progress of combustion in the furnace of a 98103142 circulating fluidized bed boiler Lyngfelt, A. et al. Symp. (Int.) Cornbust., [Proc.], 1996, 26, (2), 3253-3259. In the combustion chamber of a circulating fluidized bed boiler (FBB), measurements were taken of the gas concentrations and the sieved fractions of solid material sampled at different heights were analysed for combustible matter. Together with the bulk density profile obtained from pressure drop measurements, these data were used to obtain the distribution of combustible matter in the combustion chamber. In the bottom part, high concentrations of combustible gases and low concentrations of oxygen were found, indicating that, to a large extent, the bed material is subject to reducing conditions. The gas concentration profile permitted the determination of the degree of combustion/fuel conversion vs boiler height. This procedure, however, involves a major error since measured concentrations give a misrepresentation of the concentrations of the gas flow. This is explained by a through flow of gas through bubbles or voids in the bottom bed with high velocity and high concentration of oxygen. An attempt was made to correct the bypass flow, which increases the 02 concentration in the lowest position from 2.5 to 11%. This correction compared favourably with the fuel conversion vs height, derived from the distribution of solid combustibles (char) in the combustion chamber. The concentrations measured in the bottom part of the combustion chamber do not represent the flow and cannot be directly used in mass balances. Consequently, this affects the interpretation of gas measurements in the bottom part of FBBs.
299
Fuel and Energy Abstracts
July 1998
gal031 43 Reduction of emissions of nitrogen oxides with flue gases of boiler TP-92 Ivasyk, Y. K. and Mysak, I. S. Ekotekhnol. Resursosberezhenie, 1996, (5/6), 70-73. (In Russian) The TP-92 boiler’s operation was studied before and after introduction of the three-stage combustion scheme for fuel (including natural gas and coal). Natural gas combustion at optimum boiler loading reduced the nitrogen oxides in flue gases by 45% and the burning of coal with natural gas addition led to a 70% reduction (accounting for heat, by 65%). Analysis of dependencies of the influence of the air surplus coefficient on the nitrogen oxide concentration in flue gases was obtained. 98103144 Reversed air staging. A method to reduce nitrous oxide emissions from circulating fluidized bed boilers Lyngfelt, A. er al. Ber. Bergische Univ., Gesamthochsch. Wuppertol, Fachbereich 9, Phys. Chem., 1997, (41). 75-82. Reverse air staging could lower N20 emissions by up to a quarter without affecting the emission of NO, SOz or CO and without adverse effects on the combustion efficiency, as shown by tests in a 12 MW circulating fluidized bed boiler. Combustion chamber measurements revealed how the combustion conditions were affected by reversed air staging compared to normal air staging. With normal air staging, the conditions were reducing in the bottom part and oxidizing in the upper part, but with reversed air staging, the difference between the upper and lower part were more moderate and the measured data indicated an increase in the fraction of time under reducing conditions with height. When reversed and normal air staging were compared, reversed air staging resulted in more oxidizing conditions in the bottom part and more reducing conditions in the upper part. Under reducing conditions in the upper part of the combustion chamber the fraction of time was very sensitive to small changes in the cornbuster air ratio, explaining why the emissions were very sensitive to small changes in the combustor air ratio. 98103145 Solubility and thermodynamics of sodium phosphate reaction products under hideout conditions in highpressure boilers Tremaine, P. R. et al. Off Proc. Int. Water Conf., 1996, 57, 207-217. The solid phases that form by reaction with magnetite under sodium phosphate hideout conditions in high pressure boilers have been identified with pressure vessel and flow experiments. Solubility and X-ray diffraction studies have provided new structural and thermodynamic data for the iron(II1) reaction product at temperatures up to 325°C. Several key factors controlling phosphate hideout are described by the results, 98103146 Study of modified calcium hydroxides for enhancing SOa removal during sorbent injection in pulverized coal boilers Adanez, J. et al. Fuel, 1997, 76, (3), 257-265. In order to obtain sorbents with enhanced SOz, removal capacity, several modified calcium hydroxides were prepared by lrme hydration using NaCI, KCI, calcium lignosulfonate, ethanol-water solutions and combinations of them. Characterization of the sorbents took place in a drop-tube reactor under conditions similar to those during sorbent injection in pulverized coal boilers. Calcium lignosulfonate additive or using aqueous EtOH solutions showed the greatest increases in SO1 retention during CaO hydration. Alkali promoters acted mainly on the product layer diffusivity. Calcium lignosulfonate modified the pore size distribution of the calcined hydrate and decreased the mean particle size of the modified Ca(OH)z by up to five times. The use of ethanol-water solutions during the hydration process decreased the mean particle size of the modified hydrate and improved the porous structure of the calcined hydrate, mainly by increasing the porosity. To combine the favourable effects of these additives, they were combined to produce several different sorbents. Sorbents modified by a combination of calcium lignosulfonate and hydration with aqueous EtOH solutions achieved the best sulfur retentions. The effect of the combination of additives on the sorbent properties was not the same as that of their action separate and their effect on sulfur retention was not cumulative. 90103147 Sulphur capture in circulating fluidised-bed boilers: decomposition of CaS04 under local reducing conditions Lyngfelt, A. and Leckner, B. J. Inst. Energy, March 1998, 71, 27-32. A 12 MW circulating fluidized bed boiler was used to study the reductive decomposition of CaSO+ Measurements were made inside the combustion chamber under normal operating conditions except that the bed material contained old, sulphated sorbent. Addition of limestone was stopped two days before the tests, in order to eliminate the effects of fresh sorbent. Gas concentrations were measured in the centre of the riser cross-section at different heights at two bed temperatures 850 and 920°C. At one height, measurements were also made in nine positions distributed over the horizontal cross-section. The data were compared with results obtained with a sand-bed. The results show that reductive decomposition takes place below 0.5 m height and that most of the released sulphur is recaptured in the splash zone immediately above the dense bottom bed. This means that most of the recapture occurs below the secondary air ports, indicating the important role of the dense bottom bed in the sulphur-capture process.
Steam raising (boiler operation/design)
Materials for a steam generator with maximum 9aiO3137 steam conditions Hardt, R. Werkst. Energietech., Symp. 3, Werkst@voche ‘96, 1996 (Pub. 1997), 35-41. (In German). Edited by Gruenling, H. W., DGM Informationsgesellschaft, Oberursel, Germany. For use as a critical construction material for coal-fired steam power plants that operate at >7OO”C, the nickel superalloy Alloy 617 has great potential. Alloy C263 and Nimonic 90 are recommended for the steam collector. Method and arrangement for burning gas in a 90lQ3138 furnace Raiko, M. et al. PCT Int. Appl. WO 98 00,675 (Cl. F23G7106). 8 Jan 1998, FI Appl. 96/2,669, 28 Jun 1996, 15 pp. A method and arrangement for burning fuel gas in a furnace, particularly burning gases of low heating value in a boiler principally fired with a main fuel, is reported. The invention is based on feeding the product gas of a gasifier or other combustible gas into air-deficient conditions of the lower part of the furnace and the gas is combusted upper in the furnace at a desired level of combustion air infeed or alternatively at multiple infeed levels of the combustion air. A new combustion stabllity index CSI for utility 98103139 coal-fired boilers Cheng, H. et al. Gongcheng Rewuli Xuebao, 1997, 18, (4) 512-516. (In Chinese) The paper discusses the shortage of the general suitability of some existing assessment methods for relative combustion stability and a new combustion stability index (CSI) for utility coal-fired boilers is proposed. The index is based on the concepts of BIB0 stability theory. CSI was measured by the maximum disturbance ratio of fuel mass flow rate which can be overcome by stable combustion process. A combustion process with CSI being 0 or I corresponds to the lowest or highest combustion stability, respectively The results of dynamic combustion simulation of a utility boiler and experiments on two types of burner in a laboratory-scale single-burner furnace have proved initially the effectiveness of CSI. It can be expected that a comprehensive method will be established on assessing the relative combustion stability of industrial combustion processes. Practice of burning gasifier slags in fluid-bed boiler 98/03140 with water-cooled vortex internal separator and circulation Zhang, D. et al. Huafei Gongye, 1997, 24, (4), 33-36 (In Chinese) The paper presents the technical features of the fluidized bed boiler with a water-cooled vortex internal separator and fluid circulation in the combustion of coal-gasification slags. Design features, operation, and use in small nitrogen-type fertilizer plants are discussed.
Prediction of combustion behavior of coal blends 98103141 in industrial scale boilers from laboratory scale data Pisupati, S. V. and Scaroni, A. W. DGMK Tagungsber., 1997, 9703, (Proceedings ICCS ‘97, Volume 2). 1151-I 154. The authors obtained the burning profiles of blends of three different coals and a bituminous coal. The combustion efficiencies were determined in a 1000 lb/h research boiler and a good correlation was obtained between the initial temperature obtained in the thermogravimetric analysis and the combustion efficiency in the boiler. The burning profiles were shown to be useful tools to predict the carbon burnout of individual coals and blends in a practical combustor. Progress of combustion in the furnace of a 98103142 circulating fluidized bed boiler Lyngfelt, A. et al. Symp. (Int.) Cornbust., [Proc.], 1996, 26, (2), 3253-3259. In the combustion chamber of a circulating fluidized bed boiler (FBB), measurements were taken of the gas concentrations and the sieved fractions of solid material sampled at different heights were analysed for combustible matter. Together with the bulk density profile obtained from pressure drop measurements, these data were used to obtain the distribution of combustible matter in the combustion chamber. In the bottom part, high concentrations of combustible gases and low concentrations of oxygen were found, indicating that, to a large extent, the bed material is subject to reducing conditions. The gas concentration profile permitted the determination of the degree of combustion/fuel conversion vs boiler height. This procedure, however, involves a major error since measured concentrations give a misrepresentation of the concentrations of the gas flow. This is explained by a through flow of gas through bubbles or voids in the bottom bed with high velocity and high concentration of oxygen. An attempt was made to correct the bypass flow, which increases the 02 concentration in the lowest position from 2.5 to 11%. This correction compared favourably with the fuel conversion vs height, derived from the distribution of solid combustibles (char) in the combustion chamber. The concentrations measured in the bottom part of the combustion chamber do not represent the flow and cannot be directly used in mass balances. Consequently, this affects the interpretation of gas measurements in the bottom part of FBBs.
299
Fuel and Energy Abstracts
July 1998
gal031 43 Reduction of emissions of nitrogen oxides with flue gases of boiler TP-92 Ivasyk, Y. K. and Mysak, I. S. Ekotekhnol. Resursosberezhenie, 1996, (5/6), 70-73. (In Russian) The TP-92 boiler’s operation was studied before and after introduction of the three-stage combustion scheme for fuel (including natural gas and coal). Natural gas combustion at optimum boiler loading reduced the nitrogen oxides in flue gases by 45% and the burning of coal with natural gas addition led to a 70% reduction (accounting for heat, by 65%). Analysis of dependencies of the influence of the air surplus coefficient on the nitrogen oxide concentration in flue gases was obtained. 98103144 Reversed air staging. A method to reduce nitrous oxide emissions from circulating fluidized bed boilers Lyngfelt, A. er al. Ber. Bergische Univ., Gesamthochsch. Wuppertol, Fachbereich 9, Phys. Chem., 1997, (41). 75-82. Reverse air staging could lower N20 emissions by up to a quarter without affecting the emission of NO, SOz or CO and without adverse effects on the combustion efficiency, as shown by tests in a 12 MW circulating fluidized bed boiler. Combustion chamber measurements revealed how the combustion conditions were affected by reversed air staging compared to normal air staging. With normal air staging, the conditions were reducing in the bottom part and oxidizing in the upper part, but with reversed air staging, the difference between the upper and lower part were more moderate and the measured data indicated an increase in the fraction of time under reducing conditions with height. When reversed and normal air staging were compared, reversed air staging resulted in more oxidizing conditions in the bottom part and more reducing conditions in the upper part. Under reducing conditions in the upper part of the combustion chamber the fraction of time was very sensitive to small changes in the cornbuster air ratio, explaining why the emissions were very sensitive to small changes in the combustor air ratio. 98103145 Solubility and thermodynamics of sodium phosphate reaction products under hideout conditions in highpressure boilers Tremaine, P. R. et al. Off Proc. Int. Water Conf., 1996, 57, 207-217. The solid phases that form by reaction with magnetite under sodium phosphate hideout conditions in high pressure boilers have been identified with pressure vessel and flow experiments. Solubility and X-ray diffraction studies have provided new structural and thermodynamic data for the iron(II1) reaction product at temperatures up to 325°C. Several key factors controlling phosphate hideout are described by the results, 98103146 Study of modified calcium hydroxides for enhancing SOa removal during sorbent injection in pulverized coal boilers Adanez, J. et al. Fuel, 1997, 76, (3), 257-265. In order to obtain sorbents with enhanced SOz, removal capacity, several modified calcium hydroxides were prepared by lrme hydration using NaCI, KCI, calcium lignosulfonate, ethanol-water solutions and combinations of them. Characterization of the sorbents took place in a drop-tube reactor under conditions similar to those during sorbent injection in pulverized coal boilers. Calcium lignosulfonate additive or using aqueous EtOH solutions showed the greatest increases in SO1 retention during CaO hydration. Alkali promoters acted mainly on the product layer diffusivity. Calcium lignosulfonate modified the pore size distribution of the calcined hydrate and decreased the mean particle size of the modified Ca(OH)z by up to five times. The use of ethanol-water solutions during the hydration process decreased the mean particle size of the modified hydrate and improved the porous structure of the calcined hydrate, mainly by increasing the porosity. To combine the favourable effects of these additives, they were combined to produce several different sorbents. Sorbents modified by a combination of calcium lignosulfonate and hydration with aqueous EtOH solutions achieved the best sulfur retentions. The effect of the combination of additives on the sorbent properties was not the same as that of their action separate and their effect on sulfur retention was not cumulative. 90103147 Sulphur capture in circulating fluidised-bed boilers: decomposition of CaS04 under local reducing conditions Lyngfelt, A. and Leckner, B. J. Inst. Energy, March 1998, 71, 27-32. A 12 MW circulating fluidized bed boiler was used to study the reductive decomposition of CaSO+ Measurements were made inside the combustion chamber under normal operating conditions except that the bed material contained old, sulphated sorbent. Addition of limestone was stopped two days before the tests, in order to eliminate the effects of fresh sorbent. Gas concentrations were measured in the centre of the riser cross-section at different heights at two bed temperatures 850 and 920°C. At one height, measurements were also made in nine positions distributed over the horizontal cross-section. The data were compared with results obtained with a sand-bed. The results show that reductive decomposition takes place below 0.5 m height and that most of the released sulphur is recaptured in the splash zone immediately above the dense bottom bed. This means that most of the recapture occurs below the secondary air ports, indicating the important role of the dense bottom bed in the sulphur-capture process.