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- Barisic, Vesna, et al.
(author)
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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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In: 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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Conference paper (other academic/artistic)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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| 2. |
- Derda, Patrycja, et al.
(author)
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Fate of Alkali Metals during Co-Combustion of Biodiesel Residues with Coal in a Semi-Industrial CFB Boiler
- 2008
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In: 9th International Conference on Circulating Fluidized Beds, CFB 2008, in Conjunction with the 4th International VGB Workshop on Operating Experience with Fluidized Bed Firing Systems; Hamburg; Germany; 13 May 2008 through 16 May 2008. - 9783930400577
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Conference paper (peer-reviewed)abstract
- The use of biodiesel, especially of Rapeseed Methyl Ester (RME), has recently increased inthe European countries. This gives rise to an increasing amount of after production residues. Rapeseedcake is the main residue of the RME production process, and may become available in large amounts forenergy recovery. Since rapeseed cake contains high levels of alkali metals, it may cause bedagglomeration, deposit formation and corrosion upon combustion in fluidized beds.This paper presents the fate of alkali metals formed during co-combustion of coal and up to 25% ofrapeseed cake pellets in a 12 MW Circulating Fluidized Bed Boiler at Chalmers University ofTechnology (Sweden). Standard fuel analyses combined with sequential leaching and SEM/EDX, showedthe alkali entering the boiler. Gaseous emissions, bed samples, fly ash and deposits were analyzed inorder to monitor the alkali metals distribution. Gaseous alkali chlorides were measured upstream from theconvective pass at a flue gas temperature of 800 oC using an In-situ Alkali Chloride Monitor (IACM). Inthe same location, deposits were collected on a deposit probe fitted with rings for SEM/EDX analysis.Re-circulated bed material was analyzed as well.Two-day tests showed successful co-firing of up to 25% rapeseed cake on energy basis in the semiindustrialfluidized-bed boiler. Alkali metals were enriched in fly ash. No significant difference could benoticed in the distribution of alkali metals when increasing the share of rapeseed cake from 15% to 25%on energy basis. In the near future, further studies will be carried out to determine the influence oflimestone on the performed tests.
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| 3. |
- Piotrowska, Patrycja, et al.
(author)
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Fate of Alkali Metals and Phosphorous of Rapeseed Cake in Circulating Fluidized Bed Boiler Part 2: Cocombustion with Coal
- 2010
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In: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 24:8, s. 4193-4205
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Conference paper (peer-reviewed)abstract
- This paper is part 2 in a series of two papers describing the fate of alkali metals and phosphorus during cocombustion of rapeseed cake pellets with different fuels in a 12 MWth CFB boiler. In the first part (Piotrowska, P.; Zevenhoven, M.; Davidsson, K.; Hupa, M.; Åmand, L.-E.; Barišić, V.; Coda Zabetta, E. Energy Fuels 2010, 24, 333−345), wood was applied as a base fuel for the cocombustion tests. In this second paper, coal was used. Cocombustion with coal has been proven to be a strategy to improve the combustion of rapeseed cake. This paper presents the fate of alkali metals and phosphorus during successful cocombustion of up to 25% of rapeseed cake pellets on an energy basis with coal. Tests with and without addition of limestone were performed. The fuels were analyzed according to standard fuel analyses and chemical fractionation. Elemental analyses of outgoing streams were performed by means of wet chemical analysis. In addition, SEM/EDX analyses of outgoing ashes and deposit samples collected with a deposit probe were performed. The SO2 and HCl emissions were analyzed. Mass balances were calculated for all cocombustion tests. Gaseous alkali chlorides were measured before the convective pass at a flue gas temperature of 800 °C using an in situ alkali chloride monitor (IACM). At the same place HCl and SO2 were measured, and deposit samples were collected with a deposit probe. Rapeseed cake cocombustion caused an increase in alkali metals and phosphorus. However, no heavy bed agglomeration or deposits were observed. This is due to interactions between alkali metals and aluminum silicates from coal. No formation of gaseous alkali metal chlorides was detected in the beginning of the convection pass by means of IACM. Phosphorus was present in the deposit samples up to about 9wt% P2O5 in the leeward side of the deposit probe when no lime was supplied to the combustion chamber. Addition of limestone resulted in a higher deposition rate and lowered emissions of HCl and SO2.
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| 4. |
- Piotrowska, Patrycja, et al.
(author)
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Fate of phosphorus during co-combustion of rapeseed cake with wood
- 2009
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In: 20th International Conference on Fluidized Bed Combustion; Xian; China; 18 May 2009 through 21 May 2009. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 9787302201465 ; 2, s. 979-986
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Conference paper (peer-reviewed)abstract
- Recent studies show that deposit formation and agglomeration in fluidized bed boilers may be aggravated by a high phosphorus content besides alkali metals, chlorine and sulphur in a fuel. This paper presents the fate of phosphorus during co-combustion of wood chips and wood pellets with rapeseed cake pellets, a high phosphorus fuel in a 12MW CFB boiler. 12 hour tests with 12% and 18% (energy basis) of rapeseed cake with wood were performed with and without limestone addition. All fuels were characterised by means of standard fuel analyses combined with chemical fractionation. Retrieved ash samples were analysed using wet chemical analysis complemented with SEM/EDXA. Gaseous alkali metal chlorides as well as HCl and SO2 were measured upstream of the convective pass at a flue gas temperature of 800oC where also the deposit samples were collected with a deposit probe. The composition of deposits was studied with SEM/EDXA. Analyses of bed material particle cross-sections showed phosphorus compounds present within a K-silicates matrix between the agglomerated sand particles, indicating direct attack of gaseous potassium compounds on the bed surface followed by adhesion of rich in phosphorus ash particles. Build-up of the deposits took place mainly on the windward side of the probe; where up to 9 wt-% of phosphorus was present. SEM/EDXA shows that rapeseed cake addition caused an increase of K, Na besides P indicating presence of low melting phosphate salts in the deposits. During limestone addition in the deposit samples the increase of Cl could be noticed however no significant change in P content was observed. This paper shows that agglomeration and fouling when co-firing rapeseed cake may be linked to its high content of organically bonded phosphorus - phytic acid salts; together with high content of water soluble fraction of alkali metals chlorides and sulphates in the fuel mixture.
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