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| 2. |
- Boëlle, A., et al.
(author)
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Coal Comminution Characterization for Industrial Scale Circulating Fluidized Bed
- 2002
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Reports (other academic/artistic)abstract
- The management of the bed solids inventory and particle size distribution in fluidized bed combustors has long been recognized as a key factor for the efficient and trouble-free operation of industrial scale fluidized bed ombustors. From a coal particle to an ash particle getting out the circulating loop, the particle size reduction factor can be hundred. Detailed pilot scale test observations related to the size of circulating particles and ash particles, show very different behaviours for different coals. In order to describe those behaviours related to a large particle size spectrum, a general frame work is proposed based on several concepts. The key concept is represented by the Primary Ash Particle Size Distribution (PAPSD). According to this concept, Primary Ash Particles are liberated from the carbon matrix under the combined action of Combustion and Primary Attrition of the mother fuel particles. By Primary Attrition it is meant here a complex of particle comminution phenomena closely associated with the progress of reactions (devolatilization/char combustion), along pathways and with mechanisms that are extensively discussed by Chirone et al. (1991). Further (Secondary) attrition of ash particles can occur after char combustion is complete and is not associated with the parallel progress of chemical reactions but to mechanical attrition only. Those concepts are associated with coal characterization procedures in order to have information on the size reduction of a coal particle and the final size istribution of ash. The measurement obtained on a lab scale is validated by the analysis of some results of industrial-scale tests. In association with procedure definition, a qualitative approach allows prediction and inter-coal comparison. A modelisation work is also presented considering however that quantitative predictions of the particle size distribution inside a CFBC is still a far objective.
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| 5. |
- Hansson, Karl-Martin, 1973, et al.
(author)
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Formation of HNCO, HCN, and NH3 from the pyrolysis of bark and nitrogen-containing model compounds
- 2004
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In: Combustion and Flame. - 1556-2921 .- 0010-2180. ; 137, s. 265-277
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Journal article (peer-reviewed)abstract
- Bark pellets have been pyrolyzed in a fluidized bed reactor at temperatures between 700 and 1000C. Identifiednitrogen-containing species were hydrogen cyanide (HCN), ammonia (NH3), and isocyanic acid (HNCO). Quantification of HCN and to some extent of NH3 was unreliable at 700 and 800C due to low concentrations. HNCO could not be quantified with any accuracy at any temperature for bark, due to the low concentrations found. Since most of the nitrogen in biomass is bound in proteins, various protein-rich model compounds were pyrolyzed with the aim of finding features that are protein-specific, making conclusions regarding the model compounds applica-ble for biomass fuels in general. The model compounds used were a whey protein isolate, soya beans, yellow peas,and shea nut meal. The split between HCN and NH3 depends on the compound and temperature. It was found that the HCN/NH3 ratio is very sensitive to temperature and increases with increasing temperature for all compounds, including bark. Comparing the ratio for the different compounds at a fixed temperature, the ratio was found to decrease with decreasing release of volatile nitrogen. The temperature dependence implies that heating rate andthereby particle size affect the split between HCN and NH3. For whey, soya beans, and yellow peas, HNCO was also quantified. It is suggested that most HCN and HNCO are produced from cracking of cyclic amides formed as primary pyrolysis products. The dependence of the HNCO/HCN ratio on the compound is fairly small, but the temperature dependence of the ratio is substantial, decreasing with increasing temperature. The release of nitrogen-containing species does not seem to be greatly affected by the other constituents of the fuel, and proteins appear to be suitable model compounds for the nitrogen in biomass.
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| 6. |
- Hansson, Karl-Martin, 1973, et al.
(author)
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Pyrolysis of poly-L-leucine under combustion-like conditions
- 2003
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In: Fuel. - 0016-2361. ; 82, s. 653-660
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Journal article (peer-reviewed)abstract
- The protein poly-L-leucine has been used as a model compound for the nitrogen in biomass fuels. It was pyrolysed in a fluidised bed at 700 and 800C and the pyrolysis gases were analysed with a FT-IR spectrometer. HCN, NH3 and HNCO were identified as the main nitrogen-containing species, while neither NO nor N2O were found among the pyrolysis gases. At 700C, as much as 58% of the nitrogen content was converted into HCN and 31% into NH3. The HCN/NH3 ratio increased from about 1.9 at 700C to above 2.2 at 800C. Pyrolysis of another protein, poly-L-proline, at 800C gave a HCN/NH3 ratio close to 10. This revealed that the protein’s amino acid composition has a marked impact on the composition of the pyrolysate.
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| 8. |
- Hansson, Karl-Martin, 1973, et al.
(author)
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The temperature’s influence on the selectivity between HNCO and HCN from pyrolysis of 2,5-diketopiperazine and 2-pyridone
- 2003
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In: Fuel. - 0016-2361. ; 82, s. 2163-2172
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Journal article (peer-reviewed)abstract
- Two cyclic amides, 2-pyridone and 2,5-diketopiperazine (DKP), were pyrolysed at temperatures ranging from 700 to 1100C. Pyridone is the only one of the four main nitrogen functionalities found in coal that is likely to form HNCO under pyrolysis. DKP is a primary pyrolysis product from proteins, which are the main nitrogen source in biomass. The formation of HNCO from biomass has been suggested to originate from DKP and other cyclic amides. The aromatic 2-pyridone was thermally more stable than the non-aromatic DKP. Both amides formed HCN, HNCO and NH3. The NH3 yields, about 3–4% for 2-pyridone and 10% for DKP, were almost independent of temperature. The HCN yield on the other hand showed strong temperature dependence and increased with temperature for both of the cyclic amides. The HNCO yield decreased with increasing temperature for DKP over the whole temperature interval. For 2-pyridone, the pyrolysis was incomplete at the lowest temperature in the investigation. Between 900 and 1100C, the pyrolysis of 2-pyridone was complete and the HNCO yield decreased with increasing temperature. The HNCO/HCN ratio for both of the cyclic amides decreased with increasing temperature over the whole investigated temperature range. The finding in literature that the HNCO formation from cracking of coal tars produced a maximum HNCO yield at an intermediate temperature, is explained by the thermal stability of pyridone at low temperatures and the selectivity towards HCN at high temperatures.
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| 9. |
- Kallio, S., et al.
(author)
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Sensitivity study of fluid dynamic effects on nitric oxide formation in CFB combustion of wood
- 2002
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In: Proc. of the 7th International Circulating Fluidized Bed. - 0920804985 ; , s. 757-764
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Book chapter (other academic/artistic)abstract
- The paper presents results from simulations by a 1.5D numerical model developed to study the formation of the NO and N2O emissions in a circulating fluidized bed combustor (CFBC) under different operating conditions and burning different fuels. A comprehensive kinetic scheme for the homogeneous chemistry and a single particle model for char combustion are used. Fluiddynamic factors, including gas mixing and release of volatiles, are investigated in the case of wood combustion under normal air staging conditions. The pattern of release of volatiles, the mixing of secondary air, and the lateral mixing of gas are observed to play significant roles in the formation of the relatively high NO emissions from combustion of wood. Comparisons are made with measurement data and also with coal combustion.
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| 10. |
- Kilpinen, P., et al.
(author)
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Towards a quantitative understanding of NOx and N2O emission formation in full-scale circulating fluidised bed combustors
- 2001
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In: In Proceedings of the 16th International Conference on Fluidized Bed Combustion--FBC01, held in Reno, Nevada, USA, May 13-16, 2001.
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Conference paper (peer-reviewed)abstract
- A mathematical tool is being developed for studying the nitrogen oxide emission formation in circulating fluidised bed combustors. The model is based on detailed homogeneous and heterogeneous chemical kinetics and a simplified, reasonable description of CFB hydrodynamics with presumed temperature distribution (Kilpinen et al, 1999a). With the model different fuels and fuel mixtures can be compared in regard to their nitrogen oxide emission formation tendency at typical CFBC conditions. In this paper the structure of the CFBC model and its submodels are shortly described in present form. The CFBC model is tested for nitrogen oxide prediction at normal air staging conditions in a 12 MW CFB with bituminous coal and wood chips as the fuel, respectively. Comparisons of modelling results with detailed gas concentration profiles measured inside the furnace are made. The relative importance of homogeneous and heterogeneous reactions on NO and N2O concentration profiles is illustrated based on a quantitative reaction rate analysis at different parts in the combustor. The importance of effects of radical removal on particle surfaces, and thus, a decreased CO burnout and, simultaneously, enhanced rates of catalytic bed/char reactions on nitrogen oxides’ destruction are discussed.
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