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  • 1. Agrell, J.
    et al.
    Birgersson, H.
    Boutonnet, Magali
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Steam reforming of methanol over a Cu/ZnO/Al2O3 catalyst: a kinetic analysis and strategies for suppression of CO formation2002In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 106, no 1-2, p. 249-257Conference paper (Refereed)
    Abstract [en]

    Steam reforming of methanol (CH3OH + H2O --> CO2 + 3H(2)) was studied over a commercial Cu/ZnO/Al2O3 catalyst for production of hydrogen onboard proton exchange membrane (PEM) fuel cell vehicles. A simple power-law rate expression was fitted to experimental data in order to predict the rates Of CO2 and H-2 formation under various reaction conditions. The apparent activation energy (E-a) was estimated to be 100.9 kJ mol(-1), in good agreement with values reported in the literature. Appreciable amounts of CO by-product were formed in the reforming process at low contact times and high methanol conversions. Being a catalyst poison that deactivates the electrocatalyst at the fuel cell anode at concentrations exceeding a few ppm, special attention was paid to the pathways for CO formation and strategies for its suppression. It was found that increasing the steam-methanol ratio effectively decreases CO formation. Likewise, addition of oxygen or air to the steam-methanol mixture minimises the production of CO. By shortening the contact time and lowering the maximum temperature in the reactor, CO production can be further decreased by suppressing the reverse water-gas shift reaction.

  • 2. Agrell, J.
    et al.
    Birgersson, H.
    Boutonnet, Magali
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Melian-Cabrera, I.
    Navarro, R. M.
    Fierro, J. L. G.
    Production of hydrogen from methanol over Cu/ZnO catalysts promoted by ZrO2 and Al2O32003In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 219, no 2, p. 389-403Article in journal (Refereed)
    Abstract [en]

    Production of H-2 from methanol by steam reforming, partial oxidation, or a combination thereof was studied over Cu/ZnO-based catalysts. The catalysts were characterized by a variety of techniques, including N2O chemisorption, X-ray photoelectron spectroscopy, X-ray diffraction, and temperature-programmed reduction/oxidation. The influence of feed composition, reaction temperature, and catalyst formulation on H-2 production rate, product distribution, and catalyst lifetime was investigated. Distinct differences between the processes were observed with respect to catalyst behavior. ZrO2-containing catalysts, especially Cu/ZnO/ZrO2/Al2O3, exhibit the best performance in the steam reforming reaction. During partial oxidation, however, a binary Cu/ZnO catalyst exhibits the lowest light-off temperature and the lowest level of CO by-product. The redox properties of the catalyst appear to play a key role in determining the pathway for H-2 production. In particular. the extent of methanol and/or H-2 combustion at differential O-2 conversion is strongly dependent on the ease of copper oxidation in the catalyst.

  • 3. Agrell, J.
    et al.
    Boutonnet, Magali
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Fierro, J. L. G.
    Production of hydrogen from methanol over binary Cu/ZnO catalysts - Part II. Catalytic activity and reaction pathways2003In: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 253, no 1, p. 213-223Article in journal (Refereed)
    Abstract [en]

    The activity for conversion of methanol into hydrogen was investigated over binary Cu/ZnO catalysts derived from precursors prepared by two different techniques, viz. oxalates formed in microemulsion and hydroxycarbonates formed in aqueous solution. Some distinct differences in the reaction pathways were observed. During partial oxidation of methanol under a sub-stoichiometric oxygen/methanol ratio, the microemulsion materials exhibited considerably higher combustion activity in the low-temperature region than a catalyst prepared in aqueous solution. Over the former, oxygen was quickly converted by methanol combustion, after which steam reforming was initiated, producing hydrogen at the expense of water and gradually decreasing the net heat of reaction. Hence, a reaction sequence for the partial oxidation reaction over microemulsion catalysts is proposed. consisting of consecutive methanol combustion and steam reforming, followed by decomposition when all oxygen has been consumed. Over the hydroxycarbonate catalyst, the reaction ignited at a higher temperature, directly producing hydrogen by partial oxidation of methanol. When the two types of catalysts were evaluated in the steam reforming reaction, all catalysts displayed the typical S-shaped dependence of methanol conversion on temperature. However, there was a downward shift in the temperature at which methanol reached complete conversion, favouring the hydroxycarbonate, material. Hydrogen was produced selectively over all catalysts, but carbon monoxide formation was more pronounced over the microemulsion materials. The differences in catalytic behaviour are discussed in terms of catalyst morphology and the valence state of Cu in the working catalyst.

  • 4. Agrell, J.
    et al.
    Boutonnet, Magali
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Melian-Cabrera, I.
    Fierro, J. L. G.
    Production of hydrogen from methanol over binary Cu/ZnO catalysts - Part I. Catalyst preparation and characterisation2003In: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 253, no 1, p. 201-211Article in journal (Refereed)
    Abstract [en]

    Mixed copper-zinc oxide catalysts (Cu/ZnO) were prepared by two different techniques, i.e. from hydroxycarbonate precursors formed in aqueous solution and from oxalate precursors formed in water-in-oil microemulsion. Their physicochemical properties were characterised by nitrogen adsorption-desorption, N2O chemisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and oxidation (TPO). The BET surface areas ranged from 34 to 87 m(2)/g, depending on the method of preparation. Cu surface areas between 6.6 and 22 m(2)/g were measured. It was a general observation that catalysts prepared by microemulsion technique had lower Cu dispersions than expected (3.4-5.7%), due to a proposed partial embedding of Cu in ZnO. The catalyst prepared by carbonate co-precipitation exhibited a significantly higher Cu dispersion (10.3%). In addition, this catalyst displayed better resistance to successive TPR/TPO than the microemulsion catalysts, which exhibited significant Cu crystallite growth. However, the microemulsion route provided well-mixed materials with a narrow particle size distribution and the possibility to obtain high BET surface areas (up to 87 m(2)/g) by controlling the water/surfactant ratio in the microemulsion. XPS measurements revealed the existence of Cu+ species on the surface of both types of catalysts after exposure to a O-2/CH3OH mixture. The surface composition of the hydroxycarbonate-derived sample was unaffected by reduction in hydrogen and exposure to O-2/CH3OH, while Zn-enrichment on the surface was observed in the microemulsion catalysts after reduction, indicating sintering of the Cu particles. These observations were consistent with the TPR/TPO measurements.

  • 5. Agrell, J.
    et al.
    Germani, G.
    Järås, Sven G.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Boutonnet, Magali
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Production of hydrogen by partial oxidation of methanol over ZnO-supported palladium catalysts prepared by microemulsion technique2003In: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 242, no 2, p. 233-245Article in journal (Refereed)
    Abstract [en]

    Selective production of hydrogen by partial oxidation of methanol, using air as oxidant, was studied over a series of ZnO-supported Pd catalysts. Microemulsion-assisted synthesis and conventional impregnation techniques were used for preparation of catalysts containing Pd particles of different sizes. Catalyst characterisation included BET, XRD and TEM analyses. The influence of Pd particle size on catalytic activity and product distribution was studied by carrying out activity measurements at temperatures between 230 and 300 degreesC using a stoichiometric feed composition. All catalysts performed well with respect to methanol conversion and hydrogen yield. Both methanol conversion and hydrogen selectivity increased with increasing reaction temperature, the latter at the expense of water formation. Oxygen conversion was complete throughout the examined temperature range. These selectivity trends, with a strong dependence of hydrogen and carbon monoxide selectivities on methanol conversion and reaction temperature, support a reaction scheme consisting of consecutive methanol combustion, steam reforming and decomposition. More importantly, a correlation between Pd particle size and carbon monoxide selectivity was found. When the microemulsion catalysts are compared, carbon monoxide formation increases with increasing particle size. This was not observed over the impregnated reference catalysts, which exhibited high carbon monoxide-levels throughout the examined temperature range. Bimetallic PdZn particles were detected in spent catalysts by means of XRD and it is suggested that the catalytic activity is dependent on the formation of PdZn, the catalytic function being different from that of Pd-0.

  • 6. Agrell, J.
    et al.
    Hasselbo, K.
    Jansson, K.
    Järås, Sven G.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Boutonnet, Magali
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Production of hydrogen by partial oxidation of methanol over Cu/ZnO catalysts prepared by microemulsion technique2001In: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 211, no 2, p. 239-250Article in journal (Refereed)
    Abstract [en]

    Production of hydrogen by partial oxidation of methanol, using air as oxidant. has been studied over a series of Cu/ZnO catalysts prepared by microemulsion technique. The catalytic activity was compared to that of a reference catalyst prepared by conventional co-precipitation. The BET surface areas of the microemulsion catalysts (30-70 wt.% Cu) ranged from 22 to 36 m(2)/g and were considerably lower than that of the reference (60 m(2)/g). Nevertheless, the microemulsion catalysts were more active in the partial oxidation reaction and exhibited high hydrogen and carbon dioxide selectivities. At a molar O-2/CH3OH ratio of 0.1, hydrogen production was initiated at about 185 degreesC over the microemulsion catalysts. Over the reference, hydrogen production began at 215 degreesC under the same conditions. The catalytic activity was Found to be strongly dependent on the partial pressure of oxygen, which also plays an important role in determining the product distribution. By increasing the O-2/CH3OH ratio, the methanol conversion and carbon dioxide selectivity increase. while production of water occurs at the expense of hydrogen. By TEM and TPR, it was observed that Cu is less well-dispersed in the microemulsion catalysts than in the reference. The higher catalytic activity is not expected considering the lower number of exposed Cu sites, i.e, the turnover frequencies are substantially higher over the microemulsion catalysts. It is possible that, a strong interaction between a small part of CuO and the ZnO lattice is responsible for the higher turnover frequencies of the microemulsion catalysts, or that particular crystallographic Cu planes or surface imperfections are the active sites of the reaction.

  • 7.
    Agrell, Johan
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Development of Methanol-Reforming Catalysts for Fuel Cell Vehicles2003Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Vehicles powered by proton exchange membrane (PEM) fuelcells are approaching commercialisation. Being inherently cleanand efficient sources of power, fuel cells constitute asustainable alternative to internal combustion engines to meetfuture low-emission legislation. The PEM fuel cell may befuelled directly by hydrogen, but other alternatives appearmore attractive at present, due to problems related to theproduction, transportation and handling of hydrogen.

    Fuelling with an alcohol fuel, such as methanol, which isoxidised directly at the anode, offers certain advantages.However, the efficiency of the direct-methanol fuel cell (DMFC)is still significantly lower than that of the conventionalhydrogen-fuelled PEM fuel cell, due to some technical problemsremaining unsolved. Hence, indirect fuelling by a reformedliquid fuel may be the most feasible option in the early stagesof the introduction of fuel cell vehicles.

    The work presented in this thesis concerns the developmentof catalysts for production of hydrogen from methanol bypartial oxidation, steam reforming or a combination thereof.The work contributes to the understanding of how thepreparation route affects catalyst morphology and howphysicochemical properties determine catalytic behaviour andreaction pathways.

    The thesis is a summary of seven papers published inscientific periodicals. The first paper (Paper I) reviews thecurrent status of catalytic hydrogen generation from methanol,focusing on the fuel cell application. Paper II investigatesthe partial oxidation of methanol over Cu/ZnO catalystsprepared in microemulsion and by a conventionalco-precipitation technique. The activity for methanolconversion in the low-temperature regime is found to besignificantly higher over the former materials and the workcontinues by determining the nature of possible Cu-ZnOinteractions in the catalysts by studying their physicochemicalproperties more thoroughly (Paper III). In Paper IV, thepathways for methanol conversion via both partial oxidation andsteam reforming are elucidated.

    In Paper V, partial oxidation of methanol is studied overPd/ZnO catalysts prepared by microemulsion technique and againcompared to conventional materials. This investigationdemonstrates that although possessing high methanol conversionactivity, palladium-based catalysts are not suitable forreforming in fuel cell applications due to the considerableamounts of carbon monoxide formed.

    In Paper VI, methanol reforming is investigated over acommercial Cu/ZnO/Al2O3 catalyst. The mechanisms for carbonmonoxide formation and strategies for its suppression arediscussed, as well as reactor design aspects. The study alsoincludes some simple kinetic modelling. Finally, Paper VIIdescribes the optimisation of catalyst composition and processconditions to reach high hydrogen production efficiency at lowoperating temperatures and with minimum carbon monoxideformation.

    Keywords:PEM fuel cells, hydrogen, methanol, reforming,(partial) oxidation, reaction pathways, carbon monoxide,catalyst, microemulsion, Cu/ZnO, Pd/ZnO, copper, redoxproperties, oxidation state

  • 8.
    Ahlroth, Mikael
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Analysis of closed cycle gas turbines for biomass fuel2000Licentiate thesis, comprehensive summary (Other scientific)
  • 9. Alander, E. M.
    et al.
    Uusi-Penttila, M. S.
    Rasmuson, Åke C.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Characterization of paracetamol agglomerates by image analysis and strength measurement2003In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 130, no 03-jan, p. 298-306Article in journal (Refereed)
    Abstract [en]

    Paracetamol is crystallized in different solvents and techniques are developed and used to characterize the product. The product particles from three different solvent compositions: ethylene glycol, acetone and an acetone-water mixture (30-70 wt.%) have been examined. Product properties visually observed are quantified by image analysis and evaluation of measured image descriptors with Principal Component Analysis (PCA). The agglomerate strength has been determined by crushing single agglomerates. Depending on the solvent, the content of single crystals and agglomerates differ. Agglomerates differ by the number and size of crystals grown together, as well as by the strength.

  • 10. Amezaga, J.
    et al.
    Baresel, C.
    Destouni, G.
    Göbel, J.
    Gren, I.-M.
    Hannerz, F.
    Larsén, L.
    Loredo, J.
    Malmström, Maria
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Nuttall, C.
    Santamaria, L.
    Veselie, M.
    Wolkersdorfer, C.
    Younger, P.
    Mining Impacts on the Fresh Water Environment: Technical and Managerial Guidelines for Catchment-Focused Remediation2004In: Mine Water and the Environment, ISSN 1025-9112, E-ISSN 1616-1068, Vol. S23, no 1, p. 1-80Article in journal (Refereed)
  • 11.
    Andrae, Johan
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Numerical Studies of Wall Effects of Laminar Flames2001Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Numerical simulations have been done with the CHEMKINsoftware to study different aspects of wall effects in thecombustion of lean, laminar and premixed flames in anaxisymmetric boundary-layer flow.

    The importance of the chemical wall effects compared to thethermal wall effects caused by the development of the thermaland velocity boundary layer has been investigated in thereaction zone by using different wall boundary conditions, walltemperatures and fuel/air ratios. Surface mechanisms include acatalytic surface (Platinum), a surface that promotesrecombination of active intermediates and a completely inertwall with no species and reactions as the simplest possibleboundary condition.

    When hydrogen is the model fuel, the analysis of the resultsshow that for atmospheric pressure and a wall temperature of600 K, the surface chemistry gives significant wall effects atthe richer combustion case (f=0.5), while the thermal andvelocity boundary layer gives rather small effects. For theleaner combustion case (f=0.1) the thermal and velocityboundary layer gives more significant wall effects, whilesurface chemistry gives less significant wall effects comparedto the other case.

    For methane as model fuel, the thermal and velocity boundarylayer gives significant wall effects at the lower walltemperature (600 K), while surface chemistry gives rather smalleffects. The wall can then be modelled as chemically inert forthe lean mixtures used (f=0.2 and 0.4). For the higher walltemperature (1200 K) the surface chemistry gives significantwall effects.

    For both model fuels, the catalytic wall unexpectedlyretards homogeneous combustion of the fuel more than the wallthat acts like a sink for active intermediates. This is due toproduct inhibition by catalytic combustion. For hydrogen thisoccurs at atmospheric pressure, but for methane only at thehigher wall temperature (1200 K) and the higher pressure (10atm).

    As expected, the overall wall effects (i.e. a lowerconversion) were more pronounced for the leaner fuel-air ratiosand at the lower wall temperatures.

    To estimate a possible discrepancy in flame position as aresult of neglecting the axial diffusion in the boundary layerassumption, calculations have been performed with PREMIX, alsoa part of the CHEMKIN software. With PREMIX, where axialdiffusion is considered, steady, laminar, one-dimensionalpremixed flames can be modelled. Results obtained with the sameinitial conditions as in the boundary layer calculations showthat for the richer mixtures at atmospheric pressure the axialdiffusion generally has a strong impact on the flame position,but in the other cases the axial diffusion may beneglected.

    Keywords:wall effects, laminar premixed flames,platinum surfaces, boundary layer flow

  • 12.
    Andrae, Johan
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Wall Related Lean Premixed Combustion Modeled with Complex Chemistry2002Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Increased knowledge into the physics and chemistrycontrolling emissions from flame-surface interactions shouldhelp in the design of combustion engines featuring improvedfuel economy and reduced emissions.

    The overall aim of this work has been to obtain afundamental understanding of wall-related, premixed combustionusing numerical modeling with detailed chemical kinetics. Thiswork has utilized CHEMKIN®, one of the leading softwarepackages for modeling combustion kinetics.

    The simple fuels hydrogen and methane as well as the morecomplex fuels propane and gasified biomass have been used inthe model. The main emphasis has been on lean combustion, andthe principal flow field studied is a laminar boundary layerflow in two-dimensional channels. The assumption has been madethat the wall effects may at least in principle be the same forlaminar and turbulent flames.

    Different flame geometries have been investigated, includingfor example autoignition flames (Papers I and II) and premixedflame fronts propagating toward a wall (Papers III and IV).Analysis of the results has shown that the wall effects arisingdue to the surface chemistry are strongly affected by changesin flame geometry. When a wall material promoting catalyticcombustion (Pt) is used, the homogeneous reactions in theboundary layer are inhibited (Papers I, II and IV). This isexplained by a process whereby water produced by catalyticcombustion increases the rate of the third-body recombinationreaction: H+O2+M ⇔ HO2+M. In addition, the water produced at higherpressures increases the rate of the 2CH3(+M) ⇔ C2H6(+M) reaction, giving rise to increased unburnedhydrocarbon emissions (Paper IV).

    The thermal coupling between the flame and the wall (theheat transfer and development of the boundary layers) issignificant in lean combustion. This leads to a sloweroxidation rate of the fuel than of the intermediatehydrocarbons (Paper III).

    Finally in Paper V, a well-known problem in the combustionof gasified biomass has been addressed, being the formation offuel-NOx due to the presence of NH3 in the biogas. A hybridcatalytic gas-turbine combustor has been designed, which cansignificantly reduce fuel-NOx formation.

    Keywords:wall effects, premixed flames, flamequenching, numerical modeling, CHEMKIN, boundarylayerapproximation, gasified biomass, fuel-NOx, hybrid catalytic combustor.

  • 13.
    Andrae, Johan
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Wall Effects of Laminar Hydrogen Flames over Platinum and Inert Surfaces2000In: AIChE Journal, ISSN 0001-1541, E-ISSN 1547-5905, Vol. 46, no 7, p. 1454-1460Article in journal (Refereed)
    Abstract [en]

    Different aspects of wall effects in the combustion of lean, laminar and stationary hydrogen flames in an axisymmetric boundary-layer flow were studied using numerical simulations with the program CRESLAF. The importance of the chemical wall effects compared to thermal wall effects caused by heat transfer to a cold wall was investigated in the reaction zone by using different combustion systems at atmospheric pressure. Surface mechanisms include a catalytic surface, an inert surface that promotes radical recombinations, and a completely inert wall used as reference was the simplest possible boundary condition. The analysis of the results show that for the richer combustion case ( = 0.5) the surface chemistry gives significant wall effects, while the thermal and velocity boundary layer gives rather small effects. But for the leaner combustion case ( = 0.1) the thermal and velocity boundary layer gives more significant wall effects, while surface chemistry gives less significant wall effects compared to the other case. As expected, the overall wall effects were more pronounced for the leaner combustion case.

  • 14.
    Andrae, Johan
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Edsberg, Lennart
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Numerical studies of wall effects with laminar methane flames2002In: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921, Vol. 128, no 1-2, p. 165-180Article in journal (Refereed)
    Abstract [en]

    Wall effects in the combustion of lean methane mixtures have been studied numerically using the CHEMKIN software. To gain a deeper understanding of the flame-wall interaction in lean burn combustion, and in particular the kinetic and thermal effects, we have simulated lean and steady methane/air flames in a boundary layer flow. The gas-phase chemistry is modeled with the GRI mechanism version 1.2. Boundary conditions include an inert wall, a recombination wall and catalytic combustion of methane. Different pressures, wall temperatures and fuel-air ratios are used to address questions such as which part of the wall effects is most important at a given set of conditions. As the results are analyzed it can be seen that the thermal wall effects are more significant at the lower wall temperature (600 K) and the wall can essentially be modeled as chemical inert for the lean mixtures used. At the higher wall temperature (1,200 K), the chemical wall effects become more significant and at the higher pressure (10 atm) the catalytic surface retards homogeneous combustion of methane more than the recombination wall because of product inhibition. This may explain the increased emissions of unburned fuel observed in engine studies, when using catalytic coatings on the cylinder walls. The overall wall effects were more pronounced for the leaner combustion case (phi = 0.2). When the position of the reaction zone obtained from the boundary layer calculations is compared with the results from a one-dimensional premixed flame model, there is a small but significant difference except at the richer combustion case (phi = 0.4) at atmospheric pressure, where the boundary layer model may not predict the flame position for the given initial conditions.

  • 15.
    Andrae, Johan
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Edsberg, Lennart
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Eriksson, L-E
    Volvo Aero Corporation.
    A Numerical Study of Sidewall Quenching with Propane/Air Flames2002In: Proceedings of the Combustion Institute, ISSN 0082-0784, E-ISSN 1878-027X, Vol. 29, p. 789-795Article in journal (Refereed)
    Abstract [en]

    The head-on (i.e., stagnation) configuration has generally been used to numerically and experimentally characterize the flame-wall interaction with complex chemistry and multicomponent transport. Other studies have treated the transient case of a flame propagating toward a wall, and combustion in a boundary layer has also been dealt with. In this paper, a two-dimensional stationary model has been used to study the sidewall quenching,of laminar propane/air flames in a boundary-layer flow. This geometry may be described as a flame parallel to the wall that is swept away with a laminar boundary-layer flow while propagating toward and interacting with the wall. The main purpose has been to examine the extent to which the flame can propagate toward the cooled wall for lean flames compared to stoichiometric flames. A detailed kinetic model is used to examine the oxidation of both the fuel and the intermediate hydrocarbons (IHCs). For stoichiometric and near stoichiometric mixtures, the thermal coupling between the flame and the wall is small but significant. However, for very lean flames, the thermal coupling between the flame and the wall is found to be very significant. The intermediate hydrocarbons are the dominant emissions for stoichiometric and near-stoichiometric flames in contrast to the leaner flames in which the fuel becomes more significant. This implies that the IHCs are very important for the overall hydrocarbon emissions from flame quenching; as a result detailed kinetics of complex fuels should be used when determining the unburned hydrocarbon emissions.

  • 16.
    Andrae, Johan
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Edsberg, Lennart
    Eriksson, L-E
    Kinetic and Transport Effects of Pressurized Methane Flames in a Boundary Layer2003In: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921, Vol. 133, no 4, p. 503-506Article in journal (Refereed)
    Abstract [en]

    We have recently modeled combustion of lean methane-air [1] mixtures in a boundary layer flow using the program CRESLAF [2, 3 and 4]. A uniform fuel-air mixture above the auto-ignition temperature was introduced at the inlet edge of the wall, which gave an arrested flame zone, propagating in the upstream direction with a local flame speed that is equal and opposite to the local flow velocity. We compared the interaction of this flame with three model wall materials representing three idealized cases from a chemical point of view, a completely inert wall, a radical recombining wall, and a wall supporting catalytic combustion.

    Here we report on an analogous study of a flame geometry that may be considered a combination of a one-dimensional flame propagating towards a wall and the combustion of a uniform fuel-air mixture in a boundary layer flow. In contrast to our previous work [1] where we had a uniform inlet flow composition consisting of unburnt gas, here there is only unburnt gas close to the walls while there is burnt gas in the center of the channel. The present study concerns lean pressurized methane flames propagating toward hot isothermal walls where chemistry on the wall is considered important.

    The main purpose is to compare the results with those obtained in Ref. [1], which enables us, for the same flow field (boundary layer flow), to compare the effect of flame geometry on the wall effects. We have found and have been able to explain theoretically that such subtle changes of the flame geometry, which would be rather difficult to study experimentally, may have surprisingly significant effects on the combustion process.

  • 17.
    Andrae, Johan
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Glarborg, P
    A Design Concept to Reduce Fuel NOx in Catalytic Combustion of Gasified Biomass2003In: AIChE Journal, ISSN 0001-1541, E-ISSN 1547-5905, Vol. 49, no 8, p. 2149-2157Article in journal (Refereed)
    Abstract [en]

    A reactor concept was studied to reduce the fuel NOx at conditions relevant to catalytic combustion of gasified biomass containing ammonia. A hybrid reactor is modeled with passive and active channels, where only part of the fuel is combusted catalytically in the active channels. The completion of the reactions is carried out in the subsequent homogeneous zone. The air-fuel ratio is found to be the most important parameter for the NOx emission level. When the primary zone is operated fuel-lean, no favorable conditions are established for selective noncatalytic reduction reactions in the homogeneous zone, and the fuel nitrogen is largely oxidized to NO. However, if the air supply to the monolith is staged rich-lean, a 95% reduction in NO is possible. The NO reduction is facilitated by the remaining fuel components, CO and H-2.

  • 18.
    Andrae, Johan C. G.
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Johansson, A.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Rosen, A.
    OH desorption energies for a palladium catalyst characterised by kinetic modelling and laser-induced fluorescence2004In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 563, no 03-jan, p. 145-158Article in journal (Refereed)
    Abstract [en]

    A kinetic model for the H-2/O-2 reaction on a polycrystalline palladium catalyst has been constructed using CHEMKIN in order to understand the coverage-dependent OH desorption energy. Each adsorbed oxygen atom was modelled to cover four I'd surface sites. The yield of OH and the water production were measured with laser-induced fluorescence (LIF) and microcalorimetry respectively as a function of the relative hydrogen concentration, alpha(H2). The temperature of the catalyst was 1300 K, the total pressure was 13 Pa and the flow was set to 100 SCCM. In fitting the model to the experimental data, the OH desorption energy E-OH(d) was found to have a first-order coverage dependence according to: E-OH(d)(theta) = E-OH(d)(0) - Btheta, where B is a constant set to 92 kJ/mol. The desorption energy at zero coverage E-OH(d)(0) was determined to be 226 kJ/mol. The model could also qualitatively and quantitatively reproduce the apparent desorption energy as a function of alpha(H2); therefore it is believed that the coverage could be predicted by the model. The values for E-OH(d)(theta) were calculated as a function of alpha(H2). From the results of a sensitivity analysis and rate of production calculations' there are strong reasons to believe that the main water-forming reaction on Pd at 1300 K is the hydrogen addition reaction, H + OH reversible arrow H2O. Enthalpy diagrams for the water-forming reactions are also presented.

  • 19.
    Anheden, Marie
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Analysis of chemical-looping combustion systems for power generation1997Licentiate thesis, comprehensive summary (Other scientific)
  • 20.
    Anheden, Marie
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Analysis of gas turbine systems for sustainable energy conversion2000Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Increased energy demands and fear of global warming due tothe emission of greenhouse gases call for development of newefficient power generation systems with low or no carbondioxide(CO2) emissions. In this thesis, two different gasturbine power generation systems, which are designed with theseissues in mind, are theoretically investigated and analyzed.Inthe first gas turbine system, the fuel is combusted using ametal oxide as an oxidant instead of oxygen in the air. Thisprocess is known as Chemical Looping Combustion (CLC). CLC isclaimed to decrease combustion exergy destruction and increasethe power generation efficiency. Another advantage is thepossibility to separate CO2without a costly and energy demanding gasseparation process. The system analysis presented includescomputer-based simulations of CLC gas turbine systems withdifferent metal oxides as oxygen carriers and different fuels.An exergy analysis comparing the exergy destruction of the gasturbine system with CLC and conventional combustion is alsopresented. The results show that it is theoretically possibleto increase the power generation efficiency of a simple gasturbine system by introducing CLC. A combined gas/steam turbinecycle system with CLC is, however, estimated to reach a similarefficiency as the conventional combined cycle system. If thebenefit of easy and energy-efficient CO2separation is accounted for, a CLC combined cyclesystem has a potential to be favorable compared to a combinedcycle system with CO2separation.

    In the second investigation, a solid, CO2-neutral biomass fuel is used in a small-scaleexternally fired gas turbine system for cogeneration of powerand district heating. Both open and closed gas turbines withdifferent working fluids are simulated and analyzed regardingthermodynamic performance, equipment size, and economics. Theresults show that it is possible to reach high power generationefficiency and total (power-and-heat) efficiency with thesuggested system. The economic analysis reveals that the costof electricity from theEFGT plant is competitive with the moreconventional alternatives for biomass based cogeneration in thesame size range (<10 MWe).

    Keywords:power generation, Chemical Looping Combustion,CO2separation, oxygen carrier, biomass fuel, closedcycle gas turbine, externally fired gas turbine

  • 21.
    Arnerdal, Klas
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Transport of Heavy Metals in Soil Subjected to an Electric Field -A Study of the Transport of Copper in Bentonite Clay2002Licentiate thesis, monograph (Other scientific)
    Abstract [en]

    This licentiate thesis addressesphosphorus release from sewage sludge, which is the first stepin phosphorus recovery. The concept ofphosphorus recovery maybe seen as a part of sustainable sludge handling in that it isa means of recycling resources without supplying harmfulsubstances to humans or the environment. Independent of whichdirection the future development in the water and wastewatersector turns, phosphorus recovery as a part of the wholewastewater system is presumably to be included.

    In order to obtain moreinformation about different ways of phosphorus release fromsewage sludge experiments have been carried out. The results ofthe experiments on phosphorus release using acid and base arepresented. Fractionation of sludge is an important step torelease different components from the sludge, includingphosphorus. With the addition of acid, a large fraction of theinorganic material can be dissolved, and thereby also sludgebound phosphorus compounds. In particular, fractionation byusing acid treatment on digested sludge releases a considerableamount of phosphorus.

    The method of phosphorus removalin a conventional wastewater treatment plant has an impact onthe chemicals required for phosphorus recovery. A comparison oftechnology for the phosphorus recovery systems is highlydependent on the composition of the sludge, which is the rawmaterial for recovery of phosphorus, and different localconditions.

    The results of the performedexperiments concerning chemical demand for phosphorus releaseare compared with calculations based on a study of chemicaldemand of different technology systems for phosphorus recoveryat present operational conditions at Henriksdal wastewatertreatment plant. Overall, experiment and theory seem to be ingood agreement. Thermal technology and addition of acid torelease phosphorus lead to high chemical demand. The essentialfactor is the incoming iron content of the sludge, as given asthe quotient iron/phosphorus.

    Another possible method torelease phosphorus may be to use supercritical water oxidation,followed by phosphorus recovery. Studies of the Aqua Reciprocess, which uses this principle, have recently begun and theprocess is under development. Experiments have been performedto give information about recovery of phosphorus from sewagesludge, with application to digested sludge from biologicaltreatment and chemical precipitation with iron. Experimentsperformed on sludge residue from supercritical water oxidationare presented in this thesis.

    The results show that phosphatewas leached out more easily with acid (hydrochloric acid) atroom temperature than with base (sodium hydroxide), howeverheavy metals show slightly higher leaching percentage with acidthan with base at room temperature. Also, the leachingexperiment showed that the phosphate is leached out before theiron, in both cases. The iron content seems to be leached outto a somewhat greater degree with acid than with base. This maydisturb the further process to obtain a valuable purephosphorus product. The results also indicate that phosphorusis more easily leached out with acid from the sludge residuefrom supercritical water oxidation than from ash viaco-incineration with sewage sludge and household wastes.Supercritical water oxidation followed by phosphorus recoverymay be seen as an option to incineration of sludge andphosphorus recovery from ash.

    Keywords:Chemical demand, phosphorus recovery, sludgefractionation, supercritical water oxidation, sustainablesludge handling

  • 22.
    Assefa, Getachew
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Frostell, Björn
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Social Impact Assessment within Life Cycle Technology Assessment2004In: 4th SETAC World Congress, 2004Conference paper (Refereed)
    Abstract [en]

    Life cycle technology assessment provides a conceptual structure for different ecological, economic and social impact assessment (SIA) tools for acting together in determining the importance, size, or value of ecological, economic and social impacts of technology - doing and making things with materials and energy. In compatibly incorporating SIA with Material /Substance Flow Analysis, Life Cycle Assessment and Life Cycle Costing, different views of SIA are studied. An important difference between this exercise and conventional SIAs is that in the former case, there is no official plan or intention of implementing the technology in a specific time and place. This poses operational difficulty due to the poor knowledge about the community that will be affected by the technology in question. Besides, compatibility with LCA adds complexity associated with a requirement for the SIA to account for a number of communities associated with each portion of the life cycle. Thorough analysis of the opportunities and challenges involved led to the use of zooming analogy. Based on this analogy, in the absence of knowledge of detailed spatial and temporal coordinates of a specific community that will be affected by the technology, a reasonable level of zooming out is done. This enables identification and characterization of the most important social impact variables for the given technology in the zoomed out area ( e.g. say a country or region of a country). As an illustration, one variable from each of five categories of SIA variables will be used to characterize the social impacts of energy technologies in small municipalities in Sweden. These categories are population impacts; community and institutional arrangements; communities in transition; individual and family impacts; and community infrastructure needs. The knowledge from damage-based weighting of environmental impact categories using concepts such as Disability Adjusted Life Years (DALY) will be tested in characterizing the variables.

  • 23.
    Assefa, Getachew
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Frostell, Björn
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Technology Assessment: A framework for combination of tool2004In: 24th International Conference of IAIA - Impact Assessment for Industrial Development: Whose Business is it?, Vancouver, Canada: International Association of Impact Assessment , 2004Conference paper (Refereed)
  • 24.
    Assefa, Getachew
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Wennersten, Ronald
    KTH, Superseded Departments, Chemical Engineering and Technology.
    The Impact of Flows of Resources and Products ( imports, exports, and aid) between north and south: Case study: the flow between EU and East Africa2004In: Proceedings of the African Roundtable on Sustainable Consumption and Production, 2004Conference paper (Refereed)
  • 25.
    Aulin, Cecilia
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Transport, degradation and immobilisation processes in a landfill1998Licentiate thesis, comprehensive summary (Other scientific)
  • 26.
    Bartlett, Michael
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Developing Humidified Gas Turbine Cycles2002Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    As a result of their unique heat recovery properties,Humidified Gas Turbine (HGT) cycles have the potential todeliver resource-effective energy to society. The EvaporativeGas Turbine (EvGT) Consortium in Sweden has been studying thesetypes of cycles for nearly a decade, but now stands at acrossroads, with commercial demonstration remaining. Thisthesis binds together several key elements for the developmentof humidified gas turbines: water recovery and air and waterquality in the cycle, cycle selection for near-term, mid-sizedpower generation, and identifying a feasible niche market fordemonstration and market penetration. Moreover, possiblesocio-technical hinders for humidified gas turbine developmentare examined.

    Through modelling saltcontaminant flows in the cycle andverifying the results in the pilot plant, it was found thathumidification tower operation need not endanger the hot gaspath. Moreover, sufficient condensate can be condensed to meetfeed water demands. Air filters were found to be essential tolower the base level of contaminant in the cycle. This protectsboth the air and water stream components. By capturing airparticles of a similar size to the air filters, the humidifieractually lowers air stream salt levels. Measures to minimisedroplet entrainment were successful (50 mg droplets/kg air) andmodels predict a 1% blow down from the water circuit issufficient. The condensate is very clean, with less than 1 mg/lalkali salts and easily deionised.

    Based on a core engine parameter analysis for three HGTcycle configurations and a subsequent economic study, asteam-cooled steam injected cycle complemented with part-flowhumidification is recommended for the mid-size power market.This cycle was found to be particularly efficient at highpressures and turbine inlet temperatures, conditions eased bysteam cooling and even intercooling. The recommended HGT cyclegives specific investment costs 30- 35% lower than the combinedcycles and cost of electricity levels were 10-18% lower.Full-flow intercooled EvGT cycles give high performances, butseem to be penalised by the recuperator costs, while stillbeing cheaper than the CC. District heating is suggested as asuitable niche market to commercially demonstrate the HGTcycle. Here, the advantages of HGT are especially pronounceddue their very high total efficiencies. Feasibility prices forelectricity were up to 35% lower than competing combinedcycles. HGT cycles were also found to effectively include wasteheat sources.

    Keywords:gas turbines, evaporative gas turbines,humidification, power generation, combined heat and powergeneration.

  • 27.
    Bartlett, Michael A.
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Westermark, Mats O.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    An evaluation of the thermodynamic potential of high-pressure part-flow evaporative gas turbine cycles2004In: Energy-Efficient, Cost-Effective and Environmentally-Sustainable Systems and Processes, Vols 1-3 / [ed] Rivero, R; Monroy, L; Pulido, R; Tsatsaronis, G, 2004, p. 1053-1066Conference paper (Refereed)
    Abstract [en]

    Evaporative gas turbine cycles (EvGT) are advanced gas turbine cycles which utilise an air-water mixture as the working fluid in the turbine expander. The EvGT cycles studied in this article are further characterised by their use of humidification towers to introduce water vapour to the compressed working fluid. This article examines the thermodynamic potential of intercooled EvGT cycles, with the focus on working pressures over 50 bar and part-flow configurations. Along with known evaporative cycles, a new configuration is introduced and studied: the so-called high-pressure part-flow EvGT cycle (HP-PEvGT). The study found that all intercooled evaporative gas turbine cycles have efficiency optimums at pressures well over 40 bar for relevant firing temperatures, with the pressure optimum defined by internal cycle dynamics. The novel part-flow configuration and self-recuperative humidification circuit of the HP-PEvGT allow this cycle to reach higher pressures and efficiencies than conventional evaporative cycle configurations. Boilers should be utilised where the gas turbine exhaust temperatures are high to enable the humidification tower to operate more effectively. While a triple pressure combined cycle was found to be more efficient than evaporative cycles at current gas turbine operating pressures (20-40 bar), the HP-PEvGT cycle has a significantly higher efficiency potential, Furthermore, much higher power densities are found for evaporative cycles, especially when they are simulated at high pressure. Despite the technical challenges of high-pressure evaporative cycles, the gains in efficiency and power density plus the more compact heat recovery system may make such a development worthwhile.

  • 28.
    Behm, Mårten
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Electrochemical generation of polysulfide liquor and sodium hydroxide from white liquor1998Doctoral thesis, comprehensive summary (Other scientific)
  • 29.
    Behm, Mårten
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Simonsson, Daniel
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Electrochemical production of polysulfides and sodium hydroxide from while liquor .2. Electrolysis in a laboratory scale flow cell1997In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 27, no 5, p. 519-528Article in journal (Refereed)
    Abstract [en]

    Electrochemical production of polysulfide-containing white liquor and pure sodium hydroxide solution was investigated at 90 degrees C in a laboratory scale flow cell. A mixed iridium-tantalum oxide coated titanium electrode was used as the anode and the two electrolyte compartments were separated by a cation-exchange membrane. The process was demonstrated at current densities up to 5 kA m(-2), resulting in high current efficiencies for both products. The previously reported autocatalytic effect of polysulfide ions was confirmed, and its technical implications on the use of three-dimensional electrodes were demonstrated and discussed. The current efficiency was found to depend strongly on the degree of conversion of sulfur(-II) to sulfur(0). The anode material showed favourable properties, with respect to activity and selectivity, but suffered from limited durability.

  • 30.
    Behm, Mårten
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Simonsson, Daniel
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Electrochemical production of polysulfides and sodium hydroxide from white liquor .1. Experiments with rotating disc and ring-disc electrodes1997In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 27, no 5, p. 507-518Article in journal (Refereed)
    Abstract [en]

    Electrochemical oxidation of white liquor in a membrane cell is a process of great potential for the pulp and paper industry. The process produces polysulfide-containing white liquor in the anode chamber, and pure sodium hydroxide solution in the cathode chamber. The anode reaction has been investigated using cyclic voltammetry at temperatures between 25 and 90 degrees C on rotating disc and ring-disc electrodes. It was further investigated using chronoamperometry on rotating disc electrodes at 90 degrees C. The experiments, which were mainly run in dilute alkaline sulfide solutions, using platinum electrodes, show that the electrochemical production of polysulfide ions, at lower anode potentials (-0.1 to +0.1 V vs SCE), proceeds via formation of elemental sulfur on the electrode surface. The sulfur is dissolved by hydrosulfide and polysulfide ions producing (longer-chain) polysulfide ions. The rate of dissolution, and thus the overall reaction rate, increases strongly with temperature. Polysulfide ions have an autocatalytic effect on the anode reaction due to their ability to dissolve adsorbed sulfur. At higher anode potentials (greater than or equal to 0.2 V vs SCE), a change of reaction mechanism is observed. In this region the reaction rate depends on electrode potential and is not catalysed by polysulfide ions.

  • 31.
    Behm, Mårten
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Simonsson, Daniel
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Graphite as anode material for the electrochemical production of polysulfide ions in white liquor1999In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 29, no 4, p. 521-524Article in journal (Refereed)
  • 32.
    Behm, Mårten
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Simonsson, Daniel
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Nickel as anode material for the electrochemical production of polysulfides in white liquor1999In: Journal of New Materials for Electrochemical Systems, ISSN 1480-2422, Vol. 2, no 1, p. 11-18Article in journal (Refereed)
    Abstract [en]

    This paper is concerned with new anode materials for the electrochemical oxidation of white liquor. This electrosynthesis process is run in a membrane cell where polysulfide ions are produced in the white liquor of the anode chamber, while a pure sodium hydroxide solution is generated in the cathode chamber: If the noble metal oxide coated anodes that were used in a previous investigation could be successfully replaced by nickel, important reductions in investment costs would be possible. The stability and catalytic activity of nickel as anode material were investigated using cyclic voltammetry and chronoamperometry on rotating disc electrodes, combined with surface analysis. Furthermore, porous nickel was tested in a flow cell, with galvanostatic electrolysis. The results show that nickel has good activity for sulfide oxidation, but a nickel oxide/sulfide surface layer is formed which deactivates the electrode at E greater than or equal to -0.2 V, probably due to the increasing proportion of poorly conducting Ni(II) oxide. Carbon precipitation, and peeling of a thin film of the metal were observed with SEM. High current efficiency and an overpotential of less than 0.2 V were obtained with a porous nickel electrode at a geometric current density of 3 kA m(-2). Corrosion did not appear to be a problem, and nickel should also be suitable as substrate material for more active anode coatings.

  • 33.
    Bellais, Michel
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Davidsson, K.O.
    Liliedahl, Truls
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Sjöström, Krister
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Pettersson, J. B. C.
    Pyrolysis of large wood particles: a study of shrinkage importance in simulations2003In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 82, no 12, p. 1541-1548Article in journal (Refereed)
    Abstract [en]

    Shrinkage models have been developed and included in a model for the pyrolysis of large wood particles. Shrinkage is modelled in three different ways: uniform shrinkage, shrinking shell and shrinking cylinders. These models and a reference model without shrinkage are compared with experimental data for mass loss versus time during pyrolysis of birch cylinders at different temperatures. In the experiments a wood particle was introduced into a pyrolysis furnace held at constant temperature. The particle mass and volume were recorded using a balance and a video camera. Uniform shrinkage slows down the pyrolysis whereas shrinking shell and cylinder models enhance the pyrolysis rate. The effect was sufficiently small to be neglected given the uncertainty about some wood physical properties.

  • 34.
    Bellais, Michel
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Liliedahl, Truls
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Sjöström, Krister
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Influence of different shrinkage models and fuel geometry on heat transfer during rapid pyrolysis of solid biofuels2002In: Proceedings of the Finnish-Swedish FlameDays: Adapting Combustion Technology to New Fuels and Fuel Mixtures,september 2002, Vaasa, Finland: The Finnish and Swedish National Committees of The International Flame Research Foundation, IFRF, 2002Conference paper (Refereed)
  • 35. Berg, M.
    et al.
    Johansson, E. M.
    Järås, Sven G.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Catalytic combustion of low heating value gas mixtures: comparison between laboratory and pilot scale tests2000In: Catalysis Today, ISSN 0920-5861, E-ISSN 1873-4308, Vol. 59, no 02-jan, p. 117-130Article in journal (Refereed)
    Abstract [en]

    Catalytic combustion of low heating value fuels is a promising method for electricity production combining the use of a renewable fuel with ultra-low emissions. In the present work, catalytic combustion of a low heating value gas has been studied over monolithic catalysts in an atmospheric 30 kW pilot catalytic combustor connected to a wood pellet gasifier. The results have been compared to similar tests with a model gas mixture and a series of test in a laboratory scale reactor for monolithic samples. Various catalyst configurations have been tested, such as precious metal-based catalyst impregnated on modified alumina washcoats and hexaaluminate washcoats. Cordierite monoliths with various cells per square inch were used as supports, but hexaaluminate extruded monoliths were also used. The catalysts were combined in different segment series. The results show that it is possible to ignite the low heating value gas at compressor outlet temperatures without the use of pre-burners over precious metal catalysts. Generally, trends and phenomena obtained in laboratory reactor operating close to isothermal could be confirmed in the pilot operating at close to adiabatic conditions. Further results, such as deactivation by sulphur compounds, fuel-NOx conversion and emissions of carbon monoxide and total hydrocarbons, are addressed in the paper.

  • 36.
    Berg, Magnus
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Catalytic Oxidation of Emissions from Residential Wood fired boilers2001Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The European Commission has set a target of doubling theenergy supply from renewable sources from 6% in 1997 to 12% in2010. An increased usage of biofuels will play an importantrole in meeting this target. The Swedish government is alsoactively supporting a changeover from nuclear power to anincreased use of biofuels but have at the same time set "cleanair" environmental goals that must not be obstructed by theincreased usage of biofuels. To be able to simultaneously meetthese objectives, the development of new and improvedtechnologies for low emission equipment must be continued.

    Biofuels are today utilised in large-scale combined heat andpower plants as well as in residential heating, especially thelatter is often connected with high levels of harmfulemissions. This thesis describes the utilisation of oxidationcatalysts for the abatement of emissions from residentialboilers, which is one promising technique for the developmentof low emission boilers. The overall aim has been to developthis technique to the stage of commercial manufacture ofcatalytic boilers.

    The first part of the thesis reviews the use of biofuels inresidential heating with special emphasis on the emissions fromsuch appliances. Some general aspects of applied catalysis arediscussed and previous experience from the use of oxidationcatalysts in wood fired stoves are summarised.

    The second part of the thesis consists of a summary anddiscussion of the experimental work on oxidation catalysts inwood fired boilers, papersI-VI. Three different boilers were used for theseinvestigations, a traditional over-fired boiler based onnatural draught, a down-draught boiler using forced airsupplyand a modern down-draught boiler equipped with a flue gas fan.In paperIpellet based catalysts were evaluated, papersII-Vfocused on monolithic catalysts and in paperVIthe use of net-based catalysts were evaluated.

    The conclusion is that the integration of monolithiccatalysts in modern down-draught boilers has a large potentialfor the development of low emission wood fired boilers. It isshown that the emissions of carbon monoxide and hydrocarbons,with the exception of methane, is oxidised effectively over thecatalyst. A number of important aspects for optimal integrationof the catalyst in the boiler are demonstrated, as well as theeffect of combining primary measures with oxidation catalysts.The technology is at a stage where field trials are the nextstep for answering the main remaining issue, the lifetime ofthe catalyst.

    Keywords:biomass, wood, combustion, residentialboilers, applied catalysis, catalytic oxidation, VOC, carbonmonoxide

  • 37. Bergman, B.
    et al.
    Lagergren, Carina
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Lindbergh, Göran
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Schwartz, S.
    Zhu, B. H.
    Contact corrosion resistance between the cathode and current collector plate in the molten carbonate fuel cell2001In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 148, no 1, p. A38-A43Article in journal (Refereed)
    Abstract [en]

    The corrosion layer Formed in the contact between the cathode and the current collector is one factor limiting the cathode performance in molten carbonate fuel cells (MCFC). In order to investigate the contribution to the total polarization of the contact resistance, electrochemical experiments were performed in a laboratory-scale fuel cell unit with a specially designed current collector. Two cathode materials, NiO and LiCoO2, were investigated to elucidate the impact of the cathode material on the formed corrosion layer. Polarization measurements as well as electrochemical impedance spectroscopy were used. The method works well for NiO electrodes. However, due to the poor electronic conductivity in the LiCoO2 electrode, the experimental results become difficult to evaluate due to a nonuniform potential distribution. The contact resistance between the cathode and the current collector contributes with a large value to the total cathode polarization. The corrosion layer in case of the LiCoO2 cathode was iron-rich and has a thickness of about 20 mum after 8 weeks operation of the fuel cell. Ln the case of the NiO cathode, a nickel-rich corrosion layer of about 15 mum was formed after 5 weeks operation of the fuel cell.

  • 38. Birgersson, E.
    et al.
    Nordlund, J.
    Ekstrom, H.
    Vynnycky, M.
    Lindbergh, Göran
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Reduced two-dimensional one-phase model for analysis of the anode of a DMFC2003In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 150, no 10, p. A1368-A1376Article in journal (Refereed)
    Abstract [en]

    An isothermal two-dimensional liquid phase model for the conservation of mass, momentum, and species in the anode of a direct methanol fuel cell (DMFC) is presented and analyzed. The inherent electrochemistry in the DMFC anode active layer is reduced to boundary conditions via parameter adaption. The model is developed for the case when the geometry aspect ratio is small, and it is shown that, under realistic operating conditions, a reduced model, which nonetheless describes all the essential physics of the full model, can be derived. The significant benefits of this approach are that physical trends become much more apparent than in the full model and that there is considerable reduction in the time required to compute numerical solutions, a fact especially useful for wide-ranging parameter studies. Such a study is then performed in terms of the three nondimensional parameters that emerge from the analysis, and we subsequently interpret our results in terms of the dimensional design and operating parameters. In particular, we highlight their effect on methanol mass transfer in the flow channel and on the current density. The results indicate the relative importance of mass-transfer resistance in both the flow channel and the adjacent porous backing.

  • 39.
    Birgersson, Erik
    et al.
    KTH, Superseded Departments, Mechanics.
    Nordlund, Joakim
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Vynnycky, Michael
    KTH, Superseded Departments, Mechanics.
    Picard, Cyril
    KTH, Superseded Departments, Mechanics.
    Lindbergh, Göran
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Reduced two-phase model for analysis of the anode of a DMFC2004In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 151, no 12, p. A2157-A2172Article in journal (Refereed)
    Abstract [en]

    An isothermal two-phase ternary mixture model that takes into account conservation of momentum, mass, and species in the anode of a direct methanol fuel cell (DMFC) is presented and analyzed. The slenderness of the anode allows a considerable reduction of the mathematical formulation, without sacrificing the essential physics. The reduced model is then verified and validated against data obtained from an experimental DMFC outfitted with a transparent end plate. Good agreement is achieved. The effect of mass-transfer resistances in the flow field and porous backing are highlighted. The presence of a gas phase is shown to improve the mass transfer of methanol at higher temperatures (>30 degreesC). It is also found that at a temperature of around 30 degreesC, a one-phase model predicts the same current density distribution as a more sophisticated two-phase model. Analysis of the results from the two-phase model, in combination with the experiments, results in a suggestion for an optimal flow field for the liquid-fed DMFC.

  • 40.
    Birgersson, Henrik
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Development of a regeneration procedure for commercial automotive three-wy catalysts2004Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Car exhaust catalysts were introduced in the early 1980’s, to limit the release of pollutants such as hydrocarbons, carbon monoxides and nitrogen oxides. These catalysts contain noble metals such as palladium (Pd), platinum (Pt) and rhodium (Rh) and are able to simultaneously abate all three of the above-mentioned pollutants, hence the name three-way catalyst (TWC). The exposure to high temperatures (800-1000 °C) during operation and the presence of additives in petrol such as lead, calcium, silicon, magnesium, manganese, chromium, sulphur and phosphorus will after a certain time start to lower the overall effectiveness of the catalyst. These effects are either of a mechanical or a chemical nature. High temperatures reduce the active area by causing the noble metals to agglomerate and sinter whereas the additives alter the activity by either fouling the pores of the support material (phosphorus) or by interacting with the metals (sulphur and lead).

    The main objective of this work was to develop a method to redisperse the catalytically active sites, comprising Pd, Pt and Rh on the washcoat surface, in an effort to regain lost catalyst activity. For this purpose, a wide spectrum of different commercial car exhaust catalysts containing varying noble metal loadings, aged under various driving conditions and with mileages ranging from 30 to 100 000 km were evaluated.

    The influence of a thermal treatment in a controlled gas atmosphere, such as oxygen or hydrogen and a redispersing agent, e.g. chlorine, on the activity of TWC was investigated by means of laboratory-scale activity measurements. Several complementary characterisation methods such as SEM/TEM, XRD, BET and TPR were used to verify the effects of the regeneration treatments on the catalyst morphology (Paper I). Partial regeneration of catalyst activity and noble metal dispersion was achieved after thermal treatment in an oxygen-chlorine rich atmosphere at temperatures below 500 °C.

    Finally, an investigation of the effects of an oxy-chlorine thermal treatment for regeneration of a ‘full-scale’ commercial automotive three-way catalyst was performed. Catalyst activity and performance prior to and after the oxy-chlorine thermal treatment was measured on a test vehicle in accordance with the European driving cycle (EC2000). The catalyst surface was further characterised using XRD and EDX (Paper II). Improved catalyst activity for a high mileage catalyst could be observed, with emissions lowered by approximately 30 to 40 vol% over the EC2000 driving cycle

  • 41.
    Birgersson, Henrik
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Boutonnet, Magali
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Järås, Sven G.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Eriksson, L.
    Deactivation and regeneration of spent three-way automotive exhaust gas catalysts (TWC)2004In: Topics in catalysis, ISSN 1022-5528, E-ISSN 1572-9028, Vol. 30-1, no 1-4, p. 433-437Article in journal (Refereed)
    Abstract [en]

    The effect of oxidation, oxy-chlorination and reduction treatments at elevated temperatures on the dispersion of palladium (Pd) and rhodium (Rh) for commercially aged three-way automotive exhaust gas catalysts (TWC) has been investigated. The catalytic activity of treated samples was compared with a reference sample, which was taken from the corresponding aged TWC and tested using a 'mini-cuts' reactor simulating real driving conditions. In the case of oxygen, the improvement of the noble metal dispersion on the catalysts was dependent on the noble metal loading and the degree of metal sintering. Adding chlorine to the oxygen atmosphere facilitates the restructuring of the metals with an improved increase in the noble metal dispersion. The temperature and the composition of the gas used during these thermal treatments proved to be of importance not only to increase the metal dispersion, but also to prevent possible losses of noble metals, in the form of volatile MOxCly compounds. TEM-EDS techniques indicated changes in the size of the largest noble metal agglomerates of Lip to 100 nm in size after thermal gas treatment. BET porosity and XRD analyses were employed to investigate restructuring of the washcoat and showed a decrease in pore size distribution and an increase in surface area.

  • 42.
    Birgersson, Henrik
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Eriksson, L
    Boutonnet, Magali
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Järås, Sven
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Thermal gas treatment to regenerate spent automotive three-way exhaust gas catalysts (TWC)2004In: Applied Catalysis B: Environmental, ISSN 0926-3373, E-ISSN 1873-3883, Vol. 54, p. 193-200Article in journal (Refereed)
    Abstract [en]

    The effect of regeneration on the metal dispersion and catalyst activity of commercial automotive three-way catalysts (TWC) in oxygen, hydrogen and oxy-chlorine at elevated temperatures has been investigated. In addition, characterisation of the catalysts has been performed using XRD, TEM, TPR, CO chemisorption and BET surface area measurements. Activity tests on monolith fragments were conducted in a micro-reactor supplied with real exhaust gases. An increase in activity was observed with oxygen treatment on catalysts showing heavy sintering as well as a high noble metal loading. Hydrogen proved to be an ineffective treatment procedure, whereas the addition of chlorine to the oxygen stream resulted in an activity increase even on catalysts less sintered and with lower noble metal contents. A comparison of the XRD and BET profiles showed no or small changes in the washcoat structure compared to fresh catalysts after successful regeneration. The TEM, TPR and CO chemisorption measurements suggest a decrease in the size of the largest noble metal agglomerates on the catalyst surface, as well as some Pd and RhO restructuring. The oxy-chlorine regeneration procedure is shown to be the most efficient, both regarding the catalyst activity and the metal dispersion. An increase in the amount of noble metal particles with a size of 20-70 nm, coupled with a decrease in size of larger clusters up to 100 nm in size, was observed for this treatment.

  • 43.
    Björklund, Anna
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Environmental System Analysis of Waste Management: Experiences from Applications of the ORWARE Model2000Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Waste management has gone through a history of shiftingproblems, demands, and strategies over the years. In contrastto the long prevailing view that the problem could be solved byhiding or moving it, waste is now viewed as a problem rangingfrom local to global concern, and as being an integral part ofseveral sectors in society. Decisive for this view has beensociety’s increasing complexity and thus the increasingcomplexity of waste, together with a general development ofenvironmental consciousness, moving from local focus on pointemission sources, to regional and global issues of more complexnature.

    This thesis is about the development and application orware;a model for computer aided environmental systems analysis ofmunicipal waste management. Its origin is the hypothesis thatwidened perspectives are needed in waste managementdecision-making to avoid severe sub-optimisation ofenvironmental performance. With a strong foundation in lifecycle assessment (LCA), orware aims to cover the environmentalimpacts over the entire life cycle of waste management. It alsoperforms substance flow analysis (SFA) calculations at a ratherdetailed level of the system.

    Applying orware has confirmed the importance of applyingsystems perspective and of taking into account site specificdifferences in analysis and planning of waste manage-ment,rather than relying on overly simplified solutions. Somefindings can be general-ised and used as guidelines to reduceenvironmental impact of waste management. Recovery of materialand energy resources from waste generally leads to netreductions in energy use and environmental impact, because ofthe savings this brings about in other sectors. Waste treatmentwith low rate of energy and materials recovery should thereforebe avoided. The exact choice of technology however depends onwhat products can be recovered andhow they are used.

    Despite the complexity of the model and a certain degree ofuser unfriendliness, involved stakeholders have expressed thevalue of participating in orware case studies. It providesimproved decision-basis, but also wider understanding of thecomplexity of waste management and of environmental issues ingeneral.

    The thesis also contains a first suggestion of a frameworkto handle uncertainty in orware, based on a review of types ofuncertainty in LCA and tools to handle it.

  • 44.
    Björklund, Anna
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Environmental systems analysis waste management: with emphasis on substance flows and environmental impact1998Licentiate thesis, comprehensive summary (Other scientific)
  • 45.
    Björklund, Anna
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Survey of Approaches to Improve Reliability in LCA2002In: The International Journal of Life Cycle Assessment, ISSN 0948-3349, E-ISSN 1614-7502, Vol. 7, no 2, p. 64-72Article in journal (Refereed)
    Abstract [en]

    Limitations of data quality and difficulties to assess uncertainty are long since acknowledged problems in LCA. During recent years a range of tools for improvement of reliability in LCA have been presented, but despite this there is still a lack of consensus about how these issues should be handled. To give basic understanding of data quality and uncertainty in LCA, key concepts of data quality and uncertainty in the context of LCA are explained. A comprehensive st~rvey of methods and approaches for data quality management, sensitivity analysis, and uncertainty analysis published in the LCA literature is presented. It should serve as a guide to further reading for LCA practitioners interested in improving data quality management and uncertainty assessment in LCA projects. The suitability of different tools for addressing different types of uncertainty and future needs in this field is discussed.

  • 46.
    Björklund, Anna
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Bjuggren, Charlotte
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Waste Modelling Using Substance Flow Analysis and Life Cycle Assessment1998In: Proceedings of the Air & Waste Management Association’s Annual Meeting, Stockholm: KTH , 1998, p. 15pp-Conference paper (Refereed)
    Abstract [en]

    Computer models of municipal waste management have been developed initially to focus on cost minimization. As focus in local planning changed, the objective of these models now include environmental optimization. The development of life-cycle assessment (LCA) as a standard means to quantify environmental impact, and of substance flow analysis (SFA) as a means to track down causes of environmental problems has offered new possibilities in this field. The ORWARE (ORganic WAste REsearch) connects LCA and SFA for evaluation of environmental impact in waste planning. Despite the holistic approach of waste planning models, they do not necessarily facilitate decision making.

  • 47.
    Björklund, Anna
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Bjuggren, Charlotte
    Dalemo, Magnus
    Sonesson, Ulf
    Planning biodegradable waste handling in StockholmManuscript (preprint) (Other academic)
  • 48.
    Björklund, Anna
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Bjuggren, Charlotte
    Dalemo, Magnus
    Sonesson, Ulf
    Planning Biodegradable Waste Management in Stockholm1999In: Journal of Industrial Ecology, ISSN 1088-1980, E-ISSN 1530-9290, Vol. 3, no 4, p. 43-58Article in journal (Refereed)
    Abstract [en]

    The environmental impact of the management of biodegradable waste in Stockholm, based mainly on incineration and landfilling, was compared to systems with significant nutrient recycling; large-scale composting, anaerobic digestion, and separate collection and utilization of urine. The systems' emissions, residual products, energy turnover, and resource consumption were evaluated from a life-cycle perspective, using a computerized model, ORWARE (ORganic WAste REsearch model).

    Transportation was of relatively low importance to overall environmental impact, even at high rates of nutrient recycling. This is remarkable considering the geographical setting of Stockholm, with high population density and little nearby farmland. Ancillary systems, such as generation of electricity and district heating, were crucial for the overall outcome.

    Increased recycling of nutrients in solid biodegradable waste in Stockholm can reduce net environmental impact, whereas separation of human urine to be spread as fertilizer cannot yet be introduced without increased acidification. Increased nutrient recycling from solid biodegradable waste inevitably increases spreading of metals on arable land. Urine is by far the least contaminated residual product. Spreading of all other residuals would be limited by their metal content.

  • 49.
    Björklund, Anna
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Bjuggren, Charlotte
    Dalemo, Magnus
    Sonesson, Ulf
    System boundaries in waste management models-Comparing different approaches1998In: Systems engineering models for waste management : proceedings from the international workshop held in Gothenburg, Sweden 25-26 February 1998 / [ed] Sundberg, Johan, 1998Conference paper (Refereed)
  • 50.
    Björklund, Anna
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Dalemo, Magnus
    Sonesson, Ulf
    Evaluating a municipal waste management plan using ORWARE1999In: Journal of Cleaner Production, ISSN 0959-6526, E-ISSN 1879-1786, Vol. 7, no 4, p. 271-280Article in journal (Refereed)
    Abstract [en]

    Environmental consequences of implementing Uppsala's waste management plan have been analysed using ORWARE, a computerized static substance flow model based on life cycle assessment methodology. Normalizing emissions from waste management to total emission loadings in the municipality was tested as a means to improve the evaluation. It was found that anaerobic digestion of biodegradable waste can reduce net environmental impact, while large-scale composting either increases environmental impact or gives less reduction than anaerobic digestion. In either case, metal contamination of digester sludge or compost may limit the feasibility of the systems. Increased materials recycling has the potential of reducing environmental impact, provided that processing of recycled materials causes equal or less environmental impact than extraction and processing of virgin raw materials. Normalization showed that all impact categories were of roughly equal importance. It was shown that easy accessible data published by a Swedish municipality were sufficient to do a relatively comprehensive normalization.

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