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- Lyngfelt, Anders, 1955, et al.
(author)
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Dependence of Sulphur Capture Performance on Air Staging in a 12 MW Circulating Fluidised Bed Boiler
- 1993
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In: Gas Cleaning at High Temperatures, Eds. R. Clift and J.P.K. Seville, Blackie Academic & Professional, Glasgow, ISBN 0 7514 0178 1.. - 0751401781 ; , s. 470-491
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Book chapter (other academic/artistic)abstract
- Three cases of air staging were examined in a 12 MW circulating fluidised bed boiler: i) no staging, ii} normal staging and iii) intensified staging. The conditions inside the combustion chamber were investigated by zirconia cell measurements of the oxygen partial pressure, 0.35, 0.65 and 8 m above the bottom air distributor plate. A significant effect of the degree of staging was seen in the two lower locations: At 0.65 m height the fraction of time under substoichiometric conditions was low in the no-staging case (2-35%), at normal staging it was 70-90%, whereas at intensified staging it was 100Y.. At 0.35 m height, i.e. in the dense bed, a similar effect was seen, although the fraction of time under reducing conditions was lower. The fraction of time under reducing conditions was low in the top of the combustion chamber in all three cases . The increase in the fraction of time under reducing conditions with a higher degree of staging is associated with a decrease in sulphur capture. It is assumed that a release of SO2 from CaSO4 takes place during the transitions between oxidising and reducing conditions. Thus, the rapid alternations between oxidising and reducing conditions, as seen with the zirconia cell, offer an explanation of the reductive decomposition and, accordingly, of the dependence of sulphur capture on temperature and on the extent of staging.
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| 2. |
- Lyngfelt, Anders, 1955, et al.
(author)
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Low N2O, NO and SO2 emissions from circulating fluidized bed boilers
- 1995
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In: Proc. Int. Conf. Fluid. Bed Combustion. - 0197-453X. - 0791813053 ; 13, s. 1049-1057
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Conference paper (other academic/artistic)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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| 3. |
- Lyngfelt, Anders, 1955, et al.
(author)
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Methods for reducing the emission of nitrous oxide from circulating fluidized bed combustion
- 1996
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In: Energy Conversion and Management. - : Elsevier BV. - 0196-8904. ; 37:6-8, s. 1297-1302
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Journal article (peer-reviewed)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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| 4. |
- Lyngfelt, Anders, 1955, et al.
(author)
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Nitrous oxide from fluidized bed boilers
- 1998
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In: Ecyclopedia of Environment Analysis and Remeditation / Meyers, R.A.. ; 5, s. 3053-3062
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Book chapter (other academic/artistic)
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| 5. |
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| 6. |
- Lyngfelt, Anders, 1955, et al.
(author)
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Progress of combustion in the furnace of a circulating fluidised bed boiler
- 1996
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In: Twenty-sixth Symposium (International) on Combustion. ; , s. 3253-3259
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Conference paper (peer-reviewed)abstract
- Gas concentrations were measured in the combustion chamber of a circulating fluidized bed boiler(FBB ). Sieved fractions of solid material sampled at different heights were analyzed 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. High concentrations of combustible gases and low concentrations of oxygen Were found in the bottom part, indicating that the bed material to a large extent is subject to reducing conditions. From the gas concentration profile, the degree of combustion/fuel conversion versus boiler height was deduced. This procedure, however, involves a major error since measured concentrations gin, 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. A correction for the hn1ass flow was attempted, which increases the 02 concentration in the lowest position from 2.5 to 11%. This correction compared favorably with the fuel conversion versus height, derived from the distribution of solid combustibles (char) in the combustion chamber. The results show that the concentrations measured in the bottom part of the combustion chamber do not represent the flow and cannot, accordingly, be directly used in mass balanees. This misrepresentation has consequences for the interpretation of gas measurements in the bottom part of FBBs.
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| 7. |
- Lyngfelt, Anders, 1955, et al.
(author)
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Reduction of N2O Emissions from Fluidised Combustion by Reversed Air Staging
- 1995
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In: Second International Conference on Combustion and Emissions Control, The Institute of Energy, London. ; , s. 89-100
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Conference paper (peer-reviewed)abstract
- A new method, reversed air staging, for decreasing N2O from fluidised bed combustion, was investigated in a 12 MW circulating fluidised bed boiler. Previous measurements, showing that the N2O is decreased to one fourth (25 ppm), and NO to half(40 ppm) with maintained sulphur capture, were confirmed. Supplementary information on reversed air staging was obtained from additional measurements. By adjusting the temperature and the air ratio it was possible to reduce the CO emission. Thus, the N2O emission can be reduced to the level of 25 ppm, with the emissions of NO, SO2 and CO maintained at about same level as with normal air staging. Low load in combination with reversed air staging resulted in:further reduced emissions. The effect of reversed air staging on the emissions from peat is similar to that of bituminous coal. There is no negative effect of reversed air staging on the combustion efficiency.
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| 8. |
- Lyngfelt, Anders, 1955, et al.
(author)
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Reversed air staging - a method for reduction of N2O emissions from fluidized bed combustion of coal
- 1998
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In: Fuel. ; 77:9-10, s. 953-959
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Journal article (peer-reviewed)abstract
- Reversed air staging, a method for reduction of N2O emissions, was studied in a 12 MW circulating fluidized bed boiler. The effect of combustor air-ratio, bed temperature, load and limestone addition ratio was investigated. The results indicate that if only the air distribution is changed, the emission of N2O can be decreased to one fourth compared to normal air staging at a temperature of 850°C, with maintained low emissions of NO,´SO2 and CO. With increased bed temperature, 870°C, in combination with increased limestone addition, from Ca/S molar ratio = 3 to 4, it was possible to reduce N2O by 90 vol% with low emissions of NO, SO2 and CO. The method was less efficient at low load, because of the lower cyclone temperature. Also the effect of redistribution of some of the air added in the cyclone outlet to the cyclone inlet was studied. This did not, however, give any improvement in the boiler used compared to adding all of the air in the cyclone outlet. There was no significant difference in combustion efficiency between reversed air staging and normal air staging.
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| 9. |
- Lyngfelt, Anders, 1955, et al.
(author)
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Reversed air staging - a method to reduce nitrous oxide emissions from circulating fluidized bed boilers
- 1997
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In: Proceedings of the 7th International Workshop on Nitrous Oxide Emissions, Cologne, Ber. Bergische Univ. Gesamthochsch. Wuppertal Fachbereich 9 Phys. Chem.. ; :41, s. 75-82
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Conference paper (peer-reviewed)abstract
- Reversed air staging is a method to reduce nitrous oxide (N2O)emissions from circulating fluidized bed boilers (FBBs). Tests in a 12 MW circulating FBB show that the N20 emission can be lowered to one fourth without affecting the emissions of NO,SO2 or CO and without adverse effects on the combustion efficiency. The focus of the paper is on the conditions in the combustion chamber. Measurements inside the combustion chamber reveal how the combustion conditions are affected by reversed air staging compared to normal air staging. These measurements confirm the working principle of reversed air staging, namely to provide more oxidizing conditions in the lower part of the combustion chamber and lower stoichiometry in the upper part of the combustion chamber.
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| 10. |
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