| 1. |
- Dam-Johansen, Kim, et al.
(författare)
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Influence of SO2 on the NO/N2O chemistry in fluidized bed combustion 2. Interpretation of full-scale observations based on laboratory experiments
- 1993
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Ingår i: Fuel. - 0016-2361. ; 72:4, s. 565-571
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Tidskriftsartikel (refereegranskat)abstract
- In circulating fluidized bed combustion of coal, significant interactions between desulfurization by limestone and emissions of nitrogen oxides (NO, N2O) are generally observed. In order to facilitate interpretation of experimental results obtained in a 12 MW circulating fluidized bed boiler, a series of laboratory tests have been carried out. The tests include homogeneous CO and HCN oxidation in the presence of different concentrations of SO2, CO oxidation catalysed by calcined and partly sulfated limestone particles, and formation and reduction of NO and N20 over bed material containing char. The presence of SO2 in the gas is shown to decrease the rate of homogeneous CO and HCN oxidation and thereby change the product distribution of the nitrogen-containing species. Unlike sulfated limestone, calcined limestone (CaO) is shown to be a good catalyst for oxidation of CO. A lower mean CO concentration is therefore expected in fluidized bed combustors during injection oflimestone. This indirectly influences the nitrogen chemistry. Finally, the influence of NO and O2 on the formation of N2O from char was studied.
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| 2. |
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| 3. |
- 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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| 4. |
- 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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| 5. |
- Johnsson, Jan-Erik, et al.
(författare)
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Modelling of NOx Formation in a Circulating Fluidized Bed Boiler
- 1990
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Ingår i: Proceedings 3rd International Conference on Circulating Fluidized Beds held October 15-18, 1990 in Nagoya, Japan.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A detailed kinetic model for the oxidation of NH3 and reduction of NO in FBC is used to model the NO concentration profile in an 8 MW CFB. Three different fuels were burned in the full scale tests: Bituminous coal, brown coal and petroleum coke. Kinetics were measured in a laboratory reactor using samples of char and bed material from the boiler. The simulation results show that char is an important catalyst for the oxidation of NH3 and reduction of NO when burning bituminous coal and petroleum coke. The char content in the brown coal bed is low and very active bed material with a high ash content is the important catalyst in this case. Homogeneous gas phase reactions were found to have only a minor influence. The levels of NO concentration calculated are in agreement with the experimental results. It is concluded that modelling the fuel-N conversion using kinetics measured for the specific chars and bed materials is a considerable step towards a better understanding of the formation and reduction of NO in FBC.
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| 6. |
- 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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| 7. |
- 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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| 8. |
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| 9. |
- 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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| 10. |
- 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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