| 1. |
- Claesson, Frida, et al.
(författare)
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Chemical characterization of waste fuel for fluidized bed combustion
- 2009
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Konferensbidrag (refereegranskat)abstract
- Combustible waste is very heterogeneous and the variation in chemical composition is of great significance for the performance of the combustors in terms of boiler availability and power efficiency. For example, the content of alkali, Chlorine and sulfur affect agglomeration, fouling and corrosion mechanisms, which often limits the steam data and requires counteracts such as soot blowing and outages. An increased knowledge on favorable levels and ratios of fuel components are therefore highly important when developing waste combustors, both existing and future. However, to be able to make good predictions of reactions, reliable fuel analyses are a necessity and they are difficult to perform because of the heterogeneity of waste. As a consequence, it is also difficult to complete pro-active measure to reduce unwanted reactions. This work has investigated the composition of the fuel during one year in a 40 MW commercial BFB waste plant. Twelve samples have been performed in order to estimate the variation of key components. The fuel samples were analyzed chemically for alkali and several other components of interest, such as Cl and S. Moreover, thermo-chemical multi-phase equilibrium calculations were performed for prediction of the chemical composition of the furnace in the temperature range 400-1000 ºC. In this temperature range NaCl and PbClx are formed as well as gas phase HCl and solid silicates. Furthermore, the calculations show that the chemistry is very sensitive to the input chemical composition, suggesting that already a minor shift in fuel mineral matter may change the behavior of the fuel radically in terms of its fouling and corrosion tendency.
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| 2. |
- Davidsson, Kent, 1967, et al.
(författare)
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Countermeasures against alkali-related problems during combustion of biomass in a circulating fluidized bed boiler
- 2008
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Ingår i: Chemical Engineering Science. ; 63, s. 5314-5329
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this work was to study different ways to mitigate alkali-related problems during combustionof biomass in circulating fluidized beds. Wood chips and wood pellets were fired together withstraw pellets, while the tendency to agglomerate and form deposits was monitored. In addition to areference case, a number of countermeasures were applied in related tests. Those were addition of elementalsulphur, ammonium sulphate and kaolin to a bed of silica sand, as well as use of olivine sand andblast-furnace slag as alternative bed materials. The agglomeration temperature, composition and structureof bed-ash samples were examined. The flue-gas composition, including gaseous alkali chlorides, wasmeasured in the hot flue gases and in the stack. Particles in the flue gas were collected and analysed forsize distribution and composition. Deposits were collected on a probe in hot flue gases and their amountand composition were analysed. Addition of kaolin was found to be the best method to counteract theagglomeration problem. The deposition problem is effectively counteracted with addition of ammoniumsulphate, while kaolin is too expensive to be used commercially against deposits, and sulphur is lesseffective than ammonium sulphate.
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| 3. |
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| 4. |
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| 5. |
- Elled, Anna-Lena, 1975
(författare)
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Co-combustion of Biomass and Waste Fuels in a Fluidised Bed Boiler - Fuel Synergism
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The objective of this work was to study co-combustion of biomass and waste fuels in a circulating fluidised bed boiler and to detect synergy effects with respect to flue gas composition and ash formation during boiler operation. It was also the aim to perform supplementary thermodynamic equilibrium calculations in order to support the experimental results. The base fuel used was either wood or bark pellets and the additional fuels included municipal sewage sludge, sludge from the pulp and paper industry and demolition wood. In some of the tests, additives were supplied to the boiler to enhance any effects from substances of special interest. Examples of such additives are zinc oxide, PVC, ammonium sulphate, kaolin and zeolites.The 12 MWth circulating fluidised bed boiler situated at Chalmers University of Technology was central to the investigation. All combustion tests were performed in this boiler and it provided operating data, flue gas composition and samples of fuel, ash and deposits under required combustion conditions. Great effort was put into the analyses of ashes and deposits and in excess of conventional techniques, time-of-flight secondary ion mass spectrometer (TOF-SIMS), scanning electron microscopy energy dispersive x-ray (SEM EDX) and x-ray diffraction (XRD) were applied to several of the samples to create a more complete scan of the constituents. The thermodynamic equilibrium calculations were performed using the computer program FactSage and the module EQUILIB. The thermodynamic data was collected from the database FACT.The focus of the investigation was directed towards three main areas: sulphur capture performance by lime addition to the bed, distribution of heavy metals in ashes and flue gas, and formation of deposits on heat transfer surfaces in the convective pass and the use of municipal sewage sludge as a preventive additive.The relatively high content of phosphorus in municipal sewage sludge interferes with the sulphur capture by lime and decreases the sulphur capture performance. Phosphorus reacts with calcium, which otherwise is available for reaction with sulphur, and forms compounds such as calcium phosphates. The formation was supported by equilibrium calculations and proved by analysing the ashes with TOF-SIMS. The decreased lime efficiency must be taken into account when sulphur capture strategies are decided for the reduction of SO2 emissions from co-combustion of municipal sewage sludge. Further, the use of bark pellets as base fuel during co-combustion with sulphur containing wastes reduces the sulphur emissions due to their relatively high content of calcium and potassium in connection with its low content of sulphur.The supply of heavy metals to the combustion increases dramatically when wood is replaced by municipal sewage sludge under otherwise constant conditions. The heavy metals are to a large extent recovered in the ash and captured by the flue gas cleaning system. Even the most volatile species, such as mercury, are captured and enriched in the fine fly ash. The effective metal capture is partly due to the sludge ash and partly to the bag filter. The amount of ash in the boiler increases with the sludge and the fine fly ash fraction constitutes a high particle surface area which enhances the capture of volatile metals. Further, the ash contains large amounts of several elements known to retain trace elements such as aluminium, calcium, carbon and silicon. Especially the presence of zeolites in the sludge is likely to contribute to the capture of mercury. Further, the enrichment ratios of metals in the filter ash indicate the necessity of including bag-filters in the flue gas cleaning system in order to achieve sufficient removal of toxic heavy metals.Zinc, and its effect on deposit formation, was given special attention since the metal is commonly present in demolition wood. The result showed that combustion of demolition wood contaminated with zinc alone generates only a modest amount of deposits. Demolition wood contaminated with both zinc and chlorine gives rise to more severe deposit formation. The main reason for this is the formation of alkali chlorides but also zinc chlorides in the flue gas. The formation of zinc chlorides is, under reducing conditions, thermodynamically favoured between 450 and 850°C. Under oxidising conditions, the formation is initiated at 400°C and gradually increased with the temperature.Municipal sewage sludge is not only a waste that must be disposed of, it can also be regarded as an additive to prevent deposit formation during combustion of high alkali biomass. The sludge reduces the concentration of KCl in the flue gas, impedes the deposit formation and eliminates the content of chlorine in the deposits. The occurrence is clear of though the fuel is contaminated with chlorine. The effect is partly due to sulphation of potassium and partly to potassium sequestration by the sludge ash.
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| 6. |
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| 7. |
- Elled, Anna-Lena, 1975, et al.
(författare)
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Composition of agglomerates in fluidized bed reactors for thermochemical conversion of biomass and waste fuels Experimental data in comparison with predictions by a thermodynamic equilibrium model
- 2013
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 111, s. 696-708
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Tidskriftsartikel (refereegranskat)abstract
- Controlled combustion tests of biomass were performed in the 12 MWth circulating fluidized bed (CFB) boiler located on the campus of Chalmers University of Technology. The aim was twofold: to investigate the composition of agglomerated material and also to highlight the reasons for sintering and agglomeration during thermochemical conversion of biomass and wastes in fluidized bed reactors using quartz sand as bed material. Bed ash from three different tests regarding fuel or fuel mixtures (wood with straw, bark, and bark with refused derived fuel) was analysed to determine the ash elements using: (a) inductive coupled plasma (ICP) equipped with optical emission spectroscopy (OES) and (b) scanning electron microscopy equipped with an electron dispersive X-ray spectrometer (SEM-EDX). Chemical equilibrium calculations were also performed to support the interpretation of the experimental findings. It was found that the combination of (i) well controlled full-scale tests in a fluidized bed boiler, (ii) the use of line-scans by the EDX spectrometer of the SEM on bed samples and (iii) thermodynamic equilibrium modelling is a powerful tool in understanding the phenomena of bed agglomeration using quartz sand.
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| 8. |
- Elled, Anna-Lena, 1975, et al.
(författare)
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Influence of phosphorus on sulphur capture during co-firing
- 2006
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Ingår i: Fuel. ; 85, s. 1671-1678
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Tidskriftsartikel (refereegranskat)abstract
- Interference from phosphorus on sulphur capture during co-firing of sludge with wood has been investigated in a circulating fluidised bed boiler.Chemical equilibrium analyses were performed on the combustion system to complement the experimental results. It was found that the relativelyhigh content of phosphorus in municipal sewage sludge interferes with the sulphur capture by occupying calcium, which otherwise would beavailable for reaction with sulphur. This fact must be taken into account when sulphur capture strategies are decided for reduction of sulphurdioxide emissions from sewage sludge as an additional fuel.q 2006 Elsevier Ltd. All rights reserved.
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| 9. |
- Elled, Anna-Lena, et al.
(författare)
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Influence of phosphorus on sulphur capture during co-firing of sewage sludge with wood or bark in a fluidised bed
- 2006
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Ingår i: Fuel. - 0016-2361 .- 1873-7153. ; 85:12, s. 1671-1678
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Tidskriftsartikel (refereegranskat)abstract
- Interference from phosphorus on sulphur capture during co-firing of sludge with wood has been investigated in a circulating fluidised bed boiler. Chemical equilibrium analyses were performed on the combustion system to complement the experimental results. It was found that the relatively high content of phosphorus in municipal sewage sludge interferes with the sulphur capture by occupying calcium, which otherwise would be available for reaction with sulphur. This fact must be taken into account when sulphur capture strategies are decided for reduction of sulphur dioxide emissions from sewage sludge as an additional fuel.
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| 10. |
- Elled, Anna-Lena, et al.
(författare)
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Phosphorous in ash from co-combustion of municipal sewage sludge with wood in a CFB boiler: a comparison of experimental data with predictions by a thermodynamic equilibrium model
- 2005
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Ingår i: In Proceedings of the 18th International Conference on Fluidized Bed Combustion--FBC2005 held in Toronto, Ontario, Canada, May 22-25, 2005. - 0791837556 ; 18, s. FBC2005-78072
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Konferensbidrag (refereegranskat)abstract
- Combustion tests have been carried out in a circulating fluidised bed (CFB) boiler co-firing wood and municipal, digested and mechanical dewatered sewage sludge from two Swedish wastewater treatment plants, using either iron sulphate or aluminium sulphate as precipitating chemicals. Experimental data on the concentration of various phosphorous compounds in the ashes are compared with theoretical equilibrium predictions. A clear relationship is not found between the employed precipitation chemical and the formation of phosphorous compounds in the ash. Hematite (Fe2O3(s)) is predicted to be the stable iron compound, and even in the sludge precipitated by iron sulphate, the aluminium content is sufficient to form aluminium phosphate (AlPO4(s)) in similar amounts as in the sludge precipitated by aluminium sulphate. Lime addition to the bed gives a decreased formation of AlPO4(s) in favour of calcium orthophosphate (Ca3(PO4)2(s)), which interferes with the sulphur capture efficiency of lime.
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| 11. |
- Elled, Anna-Lena, 1975, et al.
(författare)
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Sewage sludge as a deposit inhibitor when co-fired with high potassium fuels
- 2010
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Ingår i: Biomass and Bioenergy. - : Elsevier BV. - 1873-2909 .- 0961-9534. ; 34:11, s. 1546-1554
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this work is to survey the fate of potassium in the gas phase of a fluidised bed boiler and gain deeper understanding of the involved mechanisms during co-firing of municipal sewage sludge with biomass containing high amounts of potassium and chlorine. The results show that formation of alkali chlorides in the flue gas and corrosive deposits on heat transfer surfaces can be controlled by addition of municipal sewage sludge even though the fuel is highly contaminated with chlorine. The beneficial effects are partly due to the content of sulphur in the sludge, partly to the properties of the sludge ash. The sludge ash consists of both crystalline and amorphous phases. It contains silica, aluminium, calcium, iron and phosphorus which all are involved in the capture of potassium. (c) 2010 Elsevier Ltd. All rights reserved.
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| 12. |
- Elled, Anna-Lena, et al.
(författare)
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The fate of trace elements in fluidised bed combustion of sewage sludge and wood
- 2006
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Ingår i: Fuel. - : Elsevier. - 0016-2361 .- 1873-7153. ; 86:5-6, s. 843-852
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Tidskriftsartikel (refereegranskat)abstract
- Combustion tests have been carried out in a fluidised bed boiler to investigate the fate of trace elements during co-combustion of wood and municipal sewage sludge. The approach was to collect fuel and ash samples and to perform thermodynamic equilibrium calculations for gasification (reducing) and combustion (oxidising) conditions. Trace elements are found in the ash. Even most of the highly volatile Hg is captured in the bag filter ash. The bag filter ash offers higher surface area than the secondary cyclone ash and enhances the capture of Hg. There is no obvious correlation between capture and parameters investigated (sludge precipitation agent and lime addition). As, Cd, Hg, Pb, Se, Sb and Tl are predicted by equilibrium calculations to be volatile in the combustion chamber under oxidising conditions and Hg even at the filter temperature (150°C). Reducing conditions promote, in some case more than others, the volatility of As, Cd, Pb, Sb, Se, Tl and Zn. The opposite effect was observed for Cu and Ni. Data points to the necessity of including bag-filter in the gas cleaning system in order to achieve good removal of toxic trace elements.
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| 13. |
- Elled, Anna-Lena, et al.
(författare)
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The fate of trace elements in fluidised bed combustion of sewage sludge and wood
- 2007
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Ingår i: Fuel. ; 86:5-6, s. 843-852
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Tidskriftsartikel (refereegranskat)abstract
- Combustion tests have been carried out in a fluidised bed boiler to investigate the fate of trace elements during co-combustion of wood and municipal sewage sludge. The approach was to collect fuel and ash samples and to perform thermodynamic equilibrium calculations for gasification (reducing) and combustion (oxidising) conditions. Trace elements are found in the ash. Even most of the highlyvolatile Hg is captured in the bag filter ash. The bag filter ash offers higher surface area than the secondary cyclone ash and enhances the capture of Hg. There is no obvious correlation between capture and parameters investigated (sludge precipitation agent and lime addition).As, Cd, Hg, Pb, Se, Sb and Tl are predicted by equilibrium calculations to be volatile in the combustion chamber under oxidising conditions and Hg even at the filter temperature (150°C). Reducing conditions promote, in some case more than others, the volatility of As, Cd, Pb, Sb, Se, Tl and Zn. The opposite effect was observed for Cu and Ni. Data points to the necessity of including bag filter in thegas cleaning system in order to achieve good removal of toxic trace elements.
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| 14. |
- Elled, Anna-Lena, et al.
(författare)
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The fate of zinc during combustion of demolition wood in a fluidized bed boiler
- 2007
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Ingår i: Energy & Fuels. - : American Chemical Society. - 0887-0624 .- 1520-5029. ; 22:3
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Tidskriftsartikel (refereegranskat)abstract
- Demolition wood can be used as a fuel in heat and power plants. However, it may contain elevated amounts of zinc, originating from white paint, which can cause problems related to deposit formation and corrosion on heat transfer surfaces. In this work, combustion tests with zinc addition were carried out in a fluidized bed boiler to investigate its effect on deposit formation. Thermodynamic equilibrium calculations were performed to complement the experimental data. The results show that combustion of demolition wood only contaminated with zinc generates a modest amount of deposit. Combustion of demolition wood contaminated with both zinc and chlorine promotes the deposit formation due to the increased amount of submicron particles in the flue gas. The thermodynamic equilibrium analyses show further that reducing conditions increase the release of zinc to the flue gas. On the other hand, in the case of oxidizing conditions, the retention of zinc in the ash is strong. Zinc, in combination with chlorine, gives rise to formation of zinc chloride in the flue gas. The formation is, at reducing conditions, thermodynamically favored between 450 and 850 °C. At oxidizing conditions, the formation is initiated at 400 °C and gradually increased with the temperature.
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| 15. |
- Pettersson, Anita, 1965, et al.
(författare)
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The impact of zeolites during co-combustion of municipal sewage sludge with alkali and chlorine rich fuels
- 2009
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Ingår i: Proceedings of the 20th International Conference on Fluidized Bed Combustion in Xi:an, China May 18-20, 2009. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 9787302201465 ; 2, s. 903-909, s. 902-909
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Konferensbidrag (refereegranskat)abstract
- Municipal sewage sludge has proven to eliminate alkali metals and chlorine related problems during combustion of straw and refuse derived fuels (RDF). However, the mechanisms involved have not been clarified. The aim of this work was to gain more knowledge about the behaviour of sewage sludge and detergent zeolites in combustion and about their effects on alkali metal chemistry. Co-combustion tests with combinations of municipal sewage sludge, wood and straw were carried out in a 12 MW fluidised bed (FB) boiler. In addition, a detergent zeolite, Doucil A24, was used as additive during co-combustion of wood and straw. The chemical characteristics of fuels and fly ashes were studied using several methods, such as chemical fractionation and scanning electron microscopy with element analysis by energy dispersive fluorescence detection (SEM-EDX) and X-ray diffraction (XRD). In the co-combustion tests involving sewage sludge no KCl was found in the flue gas prior to the convection pass. The zeolite addition was less effective but the KCl concentration was reduced to some degree in favour of HCl compared to the reference case. Both SEM-EDX and XRD confirmed the presence of potassium-aluminium-silicates in the fly ash fraction in all cases. In addition, the laboratory study showed that Doucil A24 had the ability to capture potassium and KCl at temperatures in the range of 700-900°C.
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