| 1. |
- Johnsson, Jan-Erik, et al.
(författare)
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Modeling N2O Reduction and Decomposition in a Circulating Fluidized Bed Boiler
- 1996
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Ingår i: Energy & Fuels. - 1520-5029 .- 0887-0624. ; 10:4, s. 970-979
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Tidskriftsartikel (refereegranskat)abstract
- The N2O concentration was measured in a circulating fluidized bed boiler of commercial size. Kinetics for N2O reduction by char and catalytic reduction and decomposition over bed material from the combustor were determined in a laboratory fixed bed reactor. The destruction rate of N2O in the combustion chamber and the cyclone was calculated taking three mechanisms into account: reduction by char, catalytic decomposition over bed material, and thermal decomposition. The calculated destruction rate was in good agreement with the measured destruction of N2O injected at different levels in the boiler. The conclusion is that in the bottom part of the combustor, where the solids concentration is about 1000 kg/m3 (voidage 0.6) and the char content in solids 2 wt %, heterogeneous reactions were the most important N2O destruction mechanisms. Reduction by char accounted for 80% of the N2O destruction, 20% was due to catalytic decomposition over bed material, and homogeneous thermal decomposition was negligible. However, at higher levels in the combustor, the solids concentration is lower: at the top 60% of the N2O destruction was due to thermal decomposition and in the cyclone heterogeneous destruction of N2O was insignificant. It was estimated that more than one-half of the formation of N2O in the combustion chamber takes place above the secondary air inlet.
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| 2. |
- Johnsson, Jan-Erik, et al.
(författare)
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Modelling of N2O reduction in a circulating fluidized bed boiler
- 1996
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Ingår i: Proc of the 5th International Conference on Circulating Fluidized Bed. ; 5, s. 338-343
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Konferensbidrag (refereegranskat)abstract
- The N2O was measured in a circulating fluidized bed boiler of commercial size. Kinetics of N2O reduction and decomposition by char and over bed material from the combustor were determined in a laboratory fixed bed reactor. A mathematical model of the N2O chemistry in the combustor was set up, and the results from the simulation of N2O destruction were in good agreement with measurements of the N2O destruction from injection at different levels in the furnace of the boiler.
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| 3. |
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| 4. |
- Kassman, H., et al.
(författare)
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Influence of air-staging on the concentration profiles of NH3 and HCN in the combustion chamber of a CFB boiler burning coal
- 1999
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Ingår i: 15th Int. Conf. on Fluidized Bed Combustion / Reuther, R.B..
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Konferensbidrag (refereegranskat)abstract
- The characterisation of the concentration profiles of NH3 and HCN are of great importance for increasing the knowledge of the formation and destruction pathways of NO and N2O in a fluidized bed boiler. Further improvements of the sampling methods for the determination of both NH3 and HCN in the combustion chamber in full-scale CFB boilers are also needed. A gas-sampling probe connected to a Fourier Transform Infra Red (FTIR) instrument and a gas-quenching (GQ) probe in which the sample is quenched directly in the probe tip by a circulating trapper solution were used. The FTIR technique is based on analysis of hot combustion gases, whereas the trapper solutions from the GQ probe were analysed by means of wet chemistry.The tests were performed during coal combustion in a 12 MW CFB boiler, which was operated at three air-staging cases with the addition of limestone for sulphur capture. The concentration profiles of NH3 and HCN in the combustion chamber showed a different pattern concerning the influence of air-staging. The highest levels of NH3 were observed during reducing conditions (severe air-staging), and the lowest were found under oxidising conditions (no air-staging). The levels of HCN were much lower than those measured for NH3. The highest levels of HCN were observed for reversed air-staging and severe air-staging showed almost no HCN. The potential reactions involving NH3 and HCN in the combustion chamber as well as the potential measurement errors in each sampling technique are discussed for the three air-staging cases.
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| 5. |
- Kassman, Håkan, 1962, et al.
(författare)
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Secondary effects in sampling ammonia during measurements in a circulationg fluidised-bed combustor
- 1997
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Ingår i: Journal of the Institute of Energy. ; :70, s. 95-101
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Tidskriftsartikel (refereegranskat)abstract
- A previous paper presented the results of measuring the ammonia (NH3) concentration in the combustion chamber of a circulating fluidised-bed (CFB) boiler. Two sampling techniques were used: a gas-quenching (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. In this paper, an attempt is made to estimate the influence of potential secondary reactions with NH3 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.
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| 6. |
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| 7. |
- Knöbig, T, et al.
(författare)
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Are measurements in small-scale combustors representative of the performance of large-scale combustors with circulating fluidized bed?
- 1997
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Ingår i: VDI Berichte 1314: Wirbelschichtfeurungen: Erfahrungen und Perspektiven. - 3180913142 ; 1314, s. 281-296
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Comparative combustion experiments were performed in an industrial-scale combustor at the Chalmers University of Technology and in a lab-scale facility at the Technical University of Hamburg-Harburg. A comparison between the axial profiles of the concentrations of O2, CO NO, N2O and NH3 along the riser height, which were obtained during combustion of wood, peat and coal, shows basic similarity, which indicates that lab-scale combustors of suitable dimensions may be a valuable tool for the investigation of combustion phenomena. However, some significant deviations caused by three-dimensional effects in the large-scale combustor and indicate the limitations of small-scale experiments.
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| 8. |
- Knöbig, T., et al.
(författare)
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Comparison of large- and small-scale circulating fluidized bed combustors with respect to pollutant formation and reduction for different fuels
- 1998
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Ingår i: Fuel. ; 77, s. 1635-1642
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Tidskriftsartikel (refereegranskat)abstract
- To investigate the scale-up problem of circulating fluidized bed combustors with particular respect to emissions, comparative combustion experiments have been performed in an industrial-size combustor (12 MWth, height 14 m, cross-sectional area 1.6 m X 1.6 m) and in a lab-scale facility (height 16 m, inner diameter 100 mm). A comparison of the axial concentration profiles of oxygen, carbon monoxide, nitric oxide, nitrous oxide and ammonia along the riser height, obtained during the combustion of wood, peat and coal under conditions of equal fuel bed material, solid holdup and gas residence time, shows a basic similarity. This indicates that suitably sized and operated lab-scale combustors may indeed be valuable tools for the investigation of combustion phenomena. However, some significant deviations of the profiles can be recognized, too. These deviations are caused by three-dimensional effects in the large-scale combustor and indicate the limitations of small-scale experiments.
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| 9. |
- Lyngfelt, Anders, 1955, et al.
(författare)
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Low N2O, NO and SO2 emissions from circulating fluidized bed boilers
- 1995
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Ingår i: Proc. Int. Conf. Fluid. Bed Combustion. - 0197-453X. - 0791813053 ; 13, s. 1049-1057
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A new method, reversed staging, for decreasing N2O without increasing the emission of the other pollutants, NOx and SO2, was investigated in the 12 MW circulating fluidized bed boiler at Chalmers University of Technology. It was possible to reduce the emission of N2O to one fourth (25 ppm), NO to half (about 40 ppm) compared to normal staging and normal temperature, without significantly affecting the sulphur capture efficiency (about 90%). Air staging, which is normally used in circulating fluidized bed boilers means that only a part of the combustion air, primary air, is added to the bottom zone, resulting in a lower oxygen concentration in the bottom part, while the secondary air results in more oxidizing conditions in the upper part of the combustion chamber and the cyclone. The principal idea of reversed staging is to reverse the conditions in top and bottom, i.e. to decrease the oxygen concentration in the upper part and to increase it in the bottom part. Such a reversal is accomplished by adding air in the bottom corresponding to an air ratio of approximately unity. No secondary air is added to the combustion chamber which means that the oxygen concentration will be low in the upper part of the combustion chamber and the cyclone. Air for final combustion is added in the cyclone outlet.
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| 10. |
- Lyngfelt, Anders, 1955, et al.
(författare)
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Methods for reducing the emission of nitrous oxide from circulating fluidized bed combustion
- 1996
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Ingår i: Energy Conversion and Management. - : Elsevier BV. - 0196-8904. ; 37:6-8, s. 1297-1302
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Tidskriftsartikel (refereegranskat)abstract
- Abstract - Two methods for the reduction of nitrous oxide emissions, afterbuming and reversed air staging, are investigated in a 12 MW circulating fluidized bed boiler. With afterburning the N2O emission can be reduced by 90% or more, using an amount of secondary fuel corresponding to 10% of the total energy input. With reversed air staging it is possible to reduce the emission of N2O to one fourth (25 ppm), without significantly affecting the other emissions. With reversed air staging no secondary air is used in the combustor and an air-ratio of about unity is maintained throughout the combustion chamber. Air for final combustion is added in the cyclone outlet.
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