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  • 1.
    Claesson, Frida
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Skrifvars, B-J
    Elled, Anna-Lena
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Johansson, A
    Chemical characterization of waste fuel for fluidized bed combustion2009Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

  • 2. Davidsson, K.O.
    et al.
    Åmand, L.-E.
    Elled, A.-L.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Leckner, B.
    Effect of Cofiring Coal and Biofuel with sewage Sludge on Alkali Problems in a Circulating Fluidized Bed Boilder2007Inngår i: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 21, nr 6, s. 3180-3188Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cofiring experiments were performed in a 12 MW circulating fluidized bed boiler. The fuel combinations were biofuel (wood+straw), coal+biofuel, coal+sewage sludge+biofuel, and sewage sludge+biofuel. Limestone or chlorine (PVC) was added in separate experiments. Effects of feed composition on bed ash and fly ash were examined. The composition of flue gas was measured, including on-line measurement of alkali chlorides. Deposits were collected on a probe simulating a superheater tube. It was found that the fuel combination, as well as addition of limestone, has little effect on the alkali fraction in bed ash, while chlorine decreases the alkali fraction in bed ash. Sewage sludge practically eliminates alkali chlorides in flue gas and deposits. Addition of enough limestone to coal and sludge for elimination of the SO2 emission does not change the effect of chlorine. Chlorine addition increases the alkali chloride in flue gas, but no chlorine was found in the deposits with sewage sludge as a cofuel. Cofiring of coal and biofuel lowers the alkali chloride concentration in the flue gas to about a third compared with that of pure biofuel. This is not affected by addition of lime or chlorine. It is concluded that aluminum compounds in coal and sludge are more important than sulfur to reduce the level of KCl in flue gas and deposits.

  • 3. Davidsson, K.O.
    et al.
    Åmand, L.-E.
    Steenari, B.-M.
    Elled, A.-L.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Eskilsson, D.
    Leckner, B.
    Countermeasures against alkali-related problems during combustion of biomass in a circulating fluidized bed boiler2008Inngår i: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 63, nr 21, s. 5314-5329Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The purpose of this work was to study different ways to mitigate alkali-related problems during combustion of biomass in circulating fluidized beds. Wood chips and wood pellets were fired together with straw pellets, while the tendency to agglomerate and form deposits was monitored. In addition to a reference case, a number of countermeasures were applied in related tests. Those were addition of elemental sulphur, ammonium sulphate and kaolin to a bed of silica sand, as well as use of olivine sand and blast-furnace slag as alternative bed materials. The agglomeration temperature, composition and structure of bed-ash samples were examined. The flue-gas composition, including gaseous alkali chlorides, was measured in the hot flue gases and in the stack. Particles in the flue gas were collected and analysed for size distribution and composition. Deposits were collected on a probe in hot flue gases and their amount and composition were analysed. Addition of kaolin was found to be the best method to counteract the agglomeration problem. The deposition problem is effectively counteracted with addition of ammonium sulphate, while kaolin is too expensive to be used commercially against deposits, and sulphur is less effective than ammonium sulphate.

  • 4.
    Elled, A.-L.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Combustion of sludge with wood in a fluidised bed boiler- the fate of trace elements and sulphur performance2005Rapport (Annet vitenskapelig)
  • 5.
    Elled, Anna-Lena
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Co-combustion of biomass and waste fuels in a fluidised bed boiler: fuel synergism2008Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    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.

  • 6.
    Elled, Anna-Lena
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Davidsson, K.O.
    Åmand, L.E.
    Sewage sludge as a deposit inhibitor when co-fired with high potassium fuels2010Inngår i: Biomass and Bioenergy, ISSN 0961-9534, E-ISSN 1873-2909, Vol. 34, nr 11, s. 1546-1554Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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.

  • 7.
    Elled, Anna-Lena
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Åmand, Lars-Erik
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Andersson, Bengt-Åke
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Leckner, B.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Phosphorus 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 model2005Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

  • 8.
    Elled, Anna-Lena
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Åmand, Lars-Erik
    Eskilsson, David
    The fate of zinc during combustion of demolition wood in a fluidized bed boiler2007Inngår i: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 22, nr 3Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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.

  • 9.
    Elled, Anna-Lena
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Åmand, Lars-Erik
    Leckner, Bo
    Andersson, Bengt-Åke
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    The fate of trace elements in fluidised bed combustion of sewage sludge and wood2006Inngår i: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 86, nr 5-6, s. 843-852Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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.

  • 10.
    Elled, Anna-Lena
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Åmand, L.-E.
    Leckner, B.
    Andersson, Bengt-Åke
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Influence of phosphorus on sulphur capture during co-firing of sewage sludge with wood or bark in a fluidised bed2006Inngår i: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 85, nr 12, s. 1671-1678Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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.

  • 11.
    Pettersson, Anita
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Elled, Anna-Lena
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Möller, A
    Steenari, B-M
    Åmand, L-E
    The impact of zeolites during co-combustion of municipal sewage sludge with alkali and chlorine rich fuels2009Inngår i: Proceedings of the 20th International Conference on Fluidized Bed Combustion, Springer Berlin Heidelberg , 2009, s. 902-909Konferansepaper (Fagfellevurdert)
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