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  • 51.
    Zhang, Xiaolei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Yang, Weihong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, Wlodzimierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Kinetics of levoglucosan and formaldehyde formation during cellulose pyrolysis process2012In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 96, no 1, p. 383-391Article in journal (Refereed)
    Abstract [en]

    The mechanisms and kinetics studies of the formation of levoglucosan and formaldehyde from anhydroglucose radical have been carried out theoretically in this paper. The geometries and frequencies of all the stationary points are calculated at the B3LYP/6-31+G(D,P) level based on quantum mechanics, Six elementary reactions are found, and three global reactions are involved. The variational transition-state rate constants for the elementary reactions are calculated within 450-1500 K. The global rate constants for every pathway are evaluated from the sum of the individual elementary reaction rate constants. The first-order Arrhenius expressions for these six elementary reactions and the three pathways are suggested. By comparing with the experimental data, computational methods without tunneling correction give good description for Path1 (the formation of levoglucosan); while methods with tunneling correction (zero-curvature tunneling and small-curvature tunneling correction) give good results for Path2 (the first possibility for the formation of formaldehyde), all the test methods give similar results for Path3 (the second possibility for the formation of formaldehyde), all the modeling results for Path3 are in good agreement with the experimental data, verifying that it is the most possible way for the formation of formaldehyde during cellulose pyrolysis.

  • 52.
    Zhang, Xiaolei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Yang, Weihong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, Wlodzimierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Kinetics study on thermal dissociation of levoglucosan during cellulose pyrolysis2013In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 109, p. 476-483Article in journal (Refereed)
    Abstract [en]

    The mechanisms and kinetics studies of the levoglucosan (LG) primary decomposition during cellulose pyrolysis have been carried out theoretically in this paper. Three decomposition mechanisms (C-O bond scission, C-C bond scission, and LG dehydration) including nine pathways and 16 elementary reactions were studied at the B3LYP/6-31 + G(D, P) level based on quantum mechanics. The variational transition-state rate constants for every elementary reaction and every pathway were calculated within 298-1550 K. The first-order Arrhenius expressions for these 16 elementary reactions and nine pathways were suggested. It was concluded that computational method using transition state theory (TST) without tunneling correction gives good description for LG decomposition by comparing with the experimental result. With the temperature range of 667-1327 K, one dehydration pathway, with one water molecule composed of a hydrogen atom from C3 and a hydroxyl group from C2, is a preferred LG decomposition pathway by fitting well with the experimental results. The calculated Arrhenius plot of C-O bond scission mechanism is better agreed with the experimental Arrhenius plot than that of C-C bond scission. This C-O bond scission mechanism starts with breaking of C1-O5 and C6-O1 bonds with formation of CO molecule (C1-O1) simultaneously. C-C bond scission mechanism is the highest energetic barrier pathway for LG decomposition.

  • 53.
    Zhou, Chunguang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Stuermer, T.
    Gunarathne, Rathnayaka
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Yang, Weihong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, Wlodzimierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Effect of calcium oxide on high-temperature steam gasification of municipal solid waste2014In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 122, p. 36-46Article in journal (Refereed)
    Abstract [en]

    Steam gasification of municipal solid waste (MSW) using a CaO additive was investigated in a batch-type fixed bed, to examine the effects of CaO addition on the heat transfer properties, the devolatilization characteristics of MSW, CO2 adsorption capacities of CaO, and char gasification in the presence of steam. Evolutionary behaviors of syngas molar compositions and individual gas flow rates at both MSW devolatilization and char gasification stages were examined at different CaO/MSW mass ratios with a fixed MSW mass. The effect of temperature varying from 700 to 900 C was also considered in this test. In both stages, hydrogen concentrations were found to increase and CaO was found to have a catalytic effect. Finally, using from the experimental observations and the results of SEM/EDS analyses of the obtained residues, the mechanism underlying the catalytic effects of calcium species in both reaction stages was discussed.

  • 54.
    Zhou, Chunguang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Yang, Weihong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Effect of heat transfer model on the prediction of refuse-derived fuel pyrolysis process2015In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 142, p. 46-57Article in journal (Refereed)
    Abstract [en]

    Heat transfer models using to estimate the effective thermal conductivity have been developed and included in a model for the pyrolysis of refuse-derived fuel or solid recovered fuel particles composed of cardboard and polyethylene. Both the predictions from the Kunii and Smith model and the Breitbach and Barthels model were presented and compared with the experimental data. The possible mechanisms of heat transfer in the porous solid particles were discussed. Compared to the conduction mode by solid matrix and gas phase, radiation heat flux between the neighboring voids and from particle surface and neighboring particle surface are considered as the main mechanisms at the temperatures presented in this paper. The porosity has been reported to serve as an important role in the accurate estimation of the radiation exchange factor for the radiation term in heat transfer model in a highly porous medium. Refuse-derived fuel particle with a high plastic concentration exhibits a rapid increase of porosity with the continuous thermal conversion of plastic. Thus, a coefficient as a function of porosity was applied to the radiation exchange factor in the Kunii and Smith model, which was constructed and based on a simplified model of heat transfer in packed bed. Moreover, the effect of the contact surface area between solid particles on the heat transfer of conduction mode was also considered in the Breitbach and Barthels model. Both modified models were further validated with experimental results obtained at different temperature, with different PE content and initial porosity.

12 51 - 54 of 54
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