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  • 1. Davidsson, K.O.
    et al.
    Åmand, L.-E.
    Elled, A.-L.
    University of Borås, School of Engineering.
    Leckner, B.
    Effect of Cofiring Coal and Biofuel with sewage Sludge on Alkali Problems in a Circulating Fluidized Bed Boilder2007In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 21, no 6, p. 3180-3188Article in journal (Refereed)
    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.

  • 2.
    Elled, Anna-Lena
    et al.
    University of Borås, School of Engineering.
    Åmand, Lars-Erik
    Eskilsson, David
    The fate of zinc during combustion of demolition wood in a fluidized bed boiler2007In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 22, no 3Article in journal (Refereed)
    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.

  • 3. Hashemi, Seyed Sajad
    et al.
    Karimi, Keikhosro
    Nosratpour, Mohammad Javad
    Sárvári Horváth, Ilona
    University of Borås, Faculty of Textiles, Engineering and Business.
    Efficient Biogas and Ethanol Production from Safflower Straw Using Sodium Carbonate Pretreatment2016In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 30, no 12, p. 10592-10601Article in journal (Refereed)
  • 4.
    Moradian, Farzad
    et al.
    University of Borås, School of Engineering.
    Pettersson, Anita
    University of Borås, School of Engineering.
    Richards, Tobias
    University of Borås, School of Engineering.
    Bed Agglomeration Characteristics during Cocombustion of Animal Waste with Municipal Solid Waste in a Bubbling Fluidized-Bed Boiler: A Thermodynamic Modeling Approach2014In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 28, no 3, p. 2236-2247Article in journal (Refereed)
    Abstract [en]

    ABSTRACT: Full-scale waste combustion tests showed that adding animal waste (AW) to municipal solid waste (MSW) prevented bed agglomeration, and the reason for this fi nding was not fully understood. This study uses thermodynamic modeling to investigate the composition of equilibrium products for two combustion scenarios: monocombustion of MSW (the reference case) and cocombustion of AW with MSW (the AW case). The modeling was performed using FactSage, and experimental data obtained during the full-scale combustion tests were used as input data for the calculations. The results of equilibrium modeling, together with information extracted from ternary phase diagrams, suggest higher bed temperature as the primary cause for formation of bed agglomerates in the reference case. In addition, melt-induced agglomeration is suggested as the bed agglomeration mechanism in this case. In the AW case, however, reduced bed temperature, as well as enriched calcium phosphate and sulfate in the bottom ashes are considered to signi fi cantly decrease the slagging tendency.

  • 5.
    Moradian, Farzad
    et al.
    University of Borås, Faculty of Textiles, Engineering and Business.
    Pettersson, Anita
    University of Borås, Faculty of Textiles, Engineering and Business.
    Richards, Tobias
    University of Borås, Faculty of Textiles, Engineering and Business.
    Thermodynamic Equilibrium Model Applied to Predict Fouling Tendency in a Commercial Fluidized-Bed Boiler, Combusting Solid Waste2015In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 29, no 5, p. 3483-3494Article in journal (Refereed)
    Abstract [en]

    A thermodynamic equilibrium model, combined with an advanced fuel analysis, was applied to predict the fouling tendency in a commercial bubbling fluidized-bed (BFB) boiler, combusting a mixture of solid waste. In order to enhance the performance of the model, further modifications were made, considering the combustion pattern in the fluidized-bed system and also the temperature profile in the combustion zone. The modeling was performed using Factsage, and experimental data obtained during the full-scale measurements were used as input for the model, simulating the deposit formation in the real boiler. The simulation results were then compared with the results obtained during the full-scale combustion tests to estimate the accuracy and validity of the applied model. The thermodynamic equilibrium modeling proved to be a reliable tool for predicting the fouling in the BFB boiler, thus determining the fraction of the melt in the deposited salts formed on the heat transfer surfaces during the flue gas condensation. The calculations showed that the ratio of the SO2 to alkali chloride concentration in the flue gas was the decisive factor that affected the rate of the deposit formation in the boiler. Both the simulation and the experimental results indicated that lower bed temperatures and cocombustion of P-rich fuels decrease the deposition buildup in the boiler. © 2015 American Chemical Society.

  • 6.
    Tchoffor, Placid
    et al.
    SP Technical Research Institute of Sweden, SE-501 15 Borås, Sweden.
    Moradian, Farzad
    University of Borås, Faculty of Textiles, Engineering and Business.
    Pettersson, Anita
    University of Borås, Faculty of Textiles, Engineering and Business.
    Kent, Davidsson
    SP Technical Research Institute of Sweden, SE-501 15 Borås, Sweden.
    Thunman, Henrik
    Chalmers University of Technology, 412 58 Gothenburg, Sweden.
    Influence of Fuel Ash Characteristics on the Release of Potassium, Chlorine, and Sulfur from Biomass Fuels under Steam-Fluidized Bed Gasification Conditions2016In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 30, p. 10435-10442Article in journal (Refereed)
    Abstract [en]

    Steam-fluidized bed gasification of biomass, which produces combustible gases from which transportation fuels can be synthesized, is a promising option for replacing the use of fossil fuels in the transportation sector. Similar to other thermal conversion processes, the release of potassium (K), chlorine (Cl), and sulfur (S) from biomass fuels to the gas phase during this process may be conducive to ash-related problems. Catalytic tar and char conversion by K has also been observed. In addition to operational conditions, the extent to which these elements are released to the gas phase may be affected by fuel ash characteristics such as the ash composition and the speciation (or association) of ash-forming elements in the fuel matrix. In the present work, the influence of these fuel ash characteristics on the extent to which K, Cl, and S are released from biomass fuels to the gas phase was studied under steam-fluidized bed gasification. The aim was to assess whether these fuel ash characteristics provide information that could be useful in making a quick judgment as to what extent K, Cl, and S would be released to the gas phase. To this end, the release of K, Cl, and S from forest residues and wheat straw during devolatilization and steam gasification of the char was quantified in a laboratory-scale bubbling fluidized bed reactor. The speciation of these elements in the virgin fuels was studied with chemical fractionation. The results reveal that the extent to which S is released from biomass fuels to the gas phase mainly depends on its speciation in the fuel matrix. While both the ash composition (mainly the Cl/K molar ratio) of the fuel and the speciation of K in the fuel matrix are relevant for the release of K, they appear to be unimportant with respect to the release of Cl.

  • 7.
    Teghammar, A.
    et al.
    University of Borås, School of Engineering.
    del Pilar Castillo, M.
    Ascue, J.
    Niklasson, C.
    Sárvári Horváth, Ilona
    University of Borås, School of Engineering.
    Improved Anaerobic Digestion by the addition of paper Tube residuals: Pretreatment, Stabilizing and Synergetic effects2013In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 27, no 1, p. 277-284Article in journal (Refereed)
    Abstract [en]

    This study deals with the addition of paper tube residuals to a nitrogen rich mixture of organic waste obtained from industrial and municipal activities. This nitrogen rich mixture, called buffer tank substrate (BTS) in the following text, is utilized in a large scale biogas plant. The effects were investigated in semi-continuous co-digestion processes and variations in operational conditions were studied. The addition of paper tubes had stabilizing effects and prevented the failure of the process and made it possible to decrease the hydraulic retention time from 25 to 20 days. Furthermore, synergetic effects were found, with 15-34% higher methane yields, when paper tubes were co-digested with BTS. Moreover, steam explosion pretreatment of the paper tube waste with the addition of 0-2% NaOH were evaluated by batch digestion experiments. Increasing the NaOH concentrations used in the pretreatment resulted in increasing methane yields, with the highest of 403 Nml/gVS methane production corresponding to an increase by 50% compared to that when untreated paper was digested (268 Nml/gVS). The long-term effects of this best pretreatment were further investigated by continuous co-digestion experiments leading to higher methane yield when pretreated paper tubes were utilized in the co-digestion process compared to untreated.

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