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| 2. |
- Andersson, Sven B, 1952, et al.
(författare)
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N2O-Emissions from Fluidized Bed Combustion
- 1988
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Ingår i: Proceedings of IEA AFBC Technical Meting held in November 1988 in Amsterdam, The Netherlands.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Nitrous oxide, N20, is formed during combustion. In flames the N20 is removed because of the fast destruction at high temperatures. At the temperatures of fluidized bed combustion the destruction is much slower and N20 will leave the system, normally at a concentration of 50-200 ppm when burning coal. Using the results of the preliminary model in a CFB, it can be assumed that:- N20 is formed from char nitrogen in the bottom bed because of reactions in the pores of the particle. - Only some N20 is formed when NO is reduced during its journey up through the combustion chamber. - N20 is formed from HCN. This is a slow process (taking seconds) and it therefore takes place principally above the bottom bed.
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| 3. |
- Barisic, Vesna, et al.
(författare)
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The Role of Limestone in Preventing Agglomeration and Slagging during CFB Combustion of High-Phosphorous Fuels
- 2008
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Ingår i: Proceedings Poster Session for World BioEnergy 2008 Conference & Exhibition on Biomass for Energy, 27-29 May 2008, Jönköping - Sweden. ; , s. 259-263
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- ABSTRACT: This paper presents key observations on the role of limestone in preventing bed agglomeration during combustion of a high-phosphorous fuel in CFB boilers. Composition of the bed material samples was analyzed using X-ray fluorescence, and scanning electron microscope combined with an energy dispersive X-ray analyzer (SEM/EDXA). It has been demonstrated that during combustion of the high-phosphorous fuel in CFB conditions, addition of limestone reduces or prevents bed agglomeration and formation of slag by interfering with the ash chemistry, and not by simple dilution of the reacting system. The role of limestone can be summarized as: 1) to provide calcium for the reaction with phosphorous forming high-temperature-melting calcium phosphates instead of low-temperature-melting potassium phosphates, and 2) to coat silica particles preventing the reaction of potassium (calcium) phosphates and silica from fluidizing sand, which can form low-temperature-melting potassium (calcium) silicates, especially relevant for fluidized bed combustion conditions.
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| 4. |
- Boëlle, A., et al.
(författare)
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Coal Comminution Characterization for Industrial Scale Circulating Fluidized Bed
- 2002
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Rapport (övrigt vetenskapligt/konstnärligt)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. |
- Edvardsson, Elin, 1976, et al.
(författare)
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Solids Distribution and Gas Concentrations in the Furnace of a CFB Boiler during Co-Combustion of Bituminous Coal with Municipal Sewage Sludge
- 2006
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this work, bituminous coal was co-fired with municipal sewage sludge in a 12 MWth circulating fluidized bed (CFB) research boiler. The fraction of sewage sludge(both wet and dry) in the feed was varied in the range 0-67 % (on dry mass). The impact of co-combustion on ash leaving the boiler, bed material in the furnace and concentrations of O2, CO2, CO and total hydrocarbons throughout the furnace was studied. In order to evaluate the influence of the wide size distribution of the coal on the results, the coal was pre-sieved into a fine and a coarse size fraction and separately burned. The higher ash content in the sewage sludge resulted in increasing fly ash flows and lower combustible content in the fly ash with increasing fraction of sludge in the fuel mix. The bottom ash flow and combustible content were more sensitive to the feed coal size distribution than to the sludge supply. Compared to coal combustion, co-combustion of coal with sewage sludge was found to lead to a higher concentration of fine solids in the furnace, caused by attrition of sludge ash particles. Furthermore, as the density of sewage sludge ash is lower than that of coal ash, coarser sludge ash particles than coal ash particles could be entrained from the bottom bed. These two phenomena contributed to wider solids size distributions throughout the furnace in the case of co-combustion with sewage sludge. The effect of theentering coal size distribution on the size distribution of the inert ashes was negligible compared to the impact of the sludge fraction in the feed. The size distributions of the combustible solids in the bed material, on the other hand, were dependent on variations in feed size distribution of the coal rather than on sludge supply. Theintroduction of sewage sludge in the fuel mix resulted in greater measured concentrations of CO and total hydrocarbons in the furnace, leading to an increasedcombustion of volatiles above the bottom bed and higher temperatures in the top of the furnace.
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| 7. |
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| 8. |
- Herstad-Svärd, S., et al.
(författare)
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Ramprogram – Åtgärder för samtidig minimering av alkalirelaterade driftproblem, Etapp 2
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Combustion of an increasing amount of biofuel and waste woods has resulted in certainenvironmental advantages, including decreased emissions of fossil CO2, SO2 andmetals. On the other hand, a number of chloride and alkali related operational problemshave occurred which are related to combustion of these fuels.Alkali related operational problems have been studied in a project consisting of twoparts. The overall scope has been to characterise the operational problems and to studymeasures to minimise them. The first part was reported in Värmeforsk report 997 wherethe results were summarised in a table of different measures. In part two, additionalmeasures have been included in the test plan and initial corrosion has been studiedlinked to the different measures. The tests have also in part two been carried out at the12 MW CFB boiler at Chalmers. The effect of the selected measures has beeninvestigated concerning both deposit formation and bed agglomeration, and at the sametime emissions and other operational conditions were characterised.The second part of the project has among other things focused on:• To investigate measures which decrease the content of alkali and chloride in thedeposits, and consequently decrease the risk for corrosion (by investigating theinitial corrosion). Focus was also on trying to explain favourable effects.• To investigate if it is possible to combine a rather low dosage of kaolin and injectionof ammonium sulphate. This was done in order to reduce both bed agglomerationand problems from deposits during combustion of fuels rich in chlorine.• To investigate if co-combustion with sewage sludge, de-inking sludge or peat withhigh ash content, could give similar advantages as conventional additives.• Investigate if ash from PFBC is possible to use as an alternative bed material.By comparing the different measures in part two, it could be concluded that cocombustionof sewage sludge gave the best overall effect. The judgement was based onthe effects concerning bed agglomeration, level of alkali chloride in the flue gas,deposits and initial corrosion. Simultaneous addition of kaolin and ammonia sulphatealso had a favourable impact both in the bed and on the alkali chlorides in the gas phase.Dosage of kaolin did not reduce the effect of injected ammonium sulphate. Cocombustionof peat could also be a very attractive alternative, but it is critical to select asuitable peat type. It is of special concern to avoid peat with a high content of calcium,since it can increase the level of alkali chlorides by reacting with available sulphur.Change of bed material to ash from PFBC can decrease problems with bedagglomeration, but there is a risk of increased deposit formation and corrosion. A boileroperated with high steam data should consequently combine the change of bed materialwith injection of ammonium sulphate or another source of sulphur.Co-combustion of de-inking sludge from pulp and paper production can reduceproblems with bed agglomeration. There is, however, an increased chance of corrosiondue to the high content of calcium. Injection of sulphates may improve the situationconcerning corrosion. The results also showed that low potassium chlorine content in the flue gas decreasesthe risk of corrosion. Increased amount of potassium chlorine content in the flue gaswill not necessary give a high amount of chlorine content in the deposits if there is sulphur in the system.Key words: agglomeration, deposits, corrosion, alkali, kaolin, ammonium sulphate,sludge
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| 9. |
- 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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| 10. |
- Kallio, S., et al.
(författare)
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Sensitivity study of fluid dynamic effects on nitric oxide formation in CFB combustion of wood
- 2002
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Ingår i: Proc. of the 7th International Circulating Fluidized Bed. - 0920804985 ; , s. 757-764
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Bokkapitel (övrigt vetenskapligt/konstnärligt)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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