| 1. |
- 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. |
- Lindmark, Hampus, 1992, et al.
(author)
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A material degradation study of novel FeCrAl alloys, stainless steels and nickel base alloy in fluidized bed heat exchangers of a waste-fired CFB boiler
- 2023
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In: Fuel. - : Elsevier BV. - 0016-2361. ; 338
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Journal article (peer-reviewed)abstract
- This study aimed to evaluate the material degradation resistance of two newly developed FeCrAl alloys exposed within the loop seal region of an 85 MWth waste-fired CFB boiler in Sweden. In addition to the FeCrAl alloys, two commercial austenitic stainless steel and one nickel base (Ni-base) alloy were also studied. The samples were exposed for 6 and 12 months by clamping half-moon rings onto tubes of the installed superheater bundle, achieving a material temperature of 500–520 °C. The material degradation of the samples was assessed by evaluating material loss using an ultrasonic thickness gauge in combination with a scanning electron microscope (SEM). Microstructural analysis was carried out using SEM coupled with Energy-dispersive X-ray spectroscopy (EDX). Both FeCrAl alloys showed promising results achieving material losses in the same range as the investigated austenitic stainless steels and the Ni-base alloy. A thin inward-growing Cr/Al-rich and thick outward-growing Fe-rich oxide were present for the FeCrAl alloys, and an internal nitridation zone was formed in the material matrix close to the metal/oxide interphase. The material loss and extent of the corrosion attack for the austenitic stainless steels varied depending on the alloy composition. However, the corrosion attack remained similar, as all the austenitic steels suffered from internal and intergranular corrosion. For the Ni-base alloy, the attack was defined by an internal Cr-rich oxide formation with no intergranular corrosion. This study suggests that the novel FeCrAl alloys provide satisfying resistance towards corrosion and erosion of the fluidized bed heat exchangers in the loop seal region of a waste-fired boiler. In addition, the stainless steel SX and the Ni-base alloy Sanicro® 69 performed well. Furthermore, the results revealed that corrosion rather than erosion was the dominating degradation process of the investigated samples, as deposit formation was observed on most of the samples as well as corrosion product layers. Thus, the erosive aspect of the attack was expected to be minor.
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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 Alkali Metals and Phosphorus of Rapeseed Cake in Circulating Fluidized Bed Boiler Part 1: Cocombustion with Wood
- 2010
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In: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 24:1, s. 333-345
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Journal article (peer-reviewed)abstract
- This paper is part I in it series of two describing the fate of alkali metals and phosphorus during cocombustion of rapeseed cake pellets in a 12 MW thermal CFB boiler. In paper I the results of using the mixture of wood chips and wood pellets as a base fuel are described. Up to 45% on energy basis of rapeseed cake was cocombusted during it 4 h test. Two approximately 12 h tests with energy fractions of rapeseed cake of 12 and 18% were performed with limestone as a varying parameter. Fuels were characterized by means of chemical fractionation and standard methods. Elemental mass balances were calculated for ingoing and Outgoing streams of the boiler. In addition SEM/EDX analyses of ashes were performed. Gaseous (KCl + NaCl) its well its HCl and SO2 were Measured upstream of the convection pass, where deposit samples were also collected with deposit probe. The deposit samples were analyzed semiquantitatively by means of SEM/EDX. The elemental mass balances Show accumulation of alkali metals and phosphorus ill the boiler. Analyses of bed material particle cross sections show the presence of phosphorus Compounds within it K-silicates matrix between the agglomerated sand particles, indicating it direct attack of gaseous potassium compounds on the bed surface followed by adhesion of ash particles rich in phosphorus. Build-up of deposit during the cocombustion tests mainly took place on the windward side of the probe; where in increase of K, Na, and P has been observed. Addition of limestone prevented formation of K-silicates and increased retention of phosphorus in the bed, most probably due to formation of high-melting calcium phosphates. During the tests with limestone,,in increase of potassium chloride upstream of the convection pass and it decrease of phosphorus in the fly ash fraction could be noticed. Agglomeration and slagging/fouling when cofiring wood with rapeseed cake may be linked to its high content of organically bonded phosphorus-phytic acid salts-together with high contents of water-soluble alkali metals chlorides and sulfates in the fuel mixture.
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| 5. |
- 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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