Gasification of fuel cane bagasse the waste residue from an energy crop known as Fuel Cane was carried out in an intensified 50 kWe air-blown downdraft gasifier. The main objective of this study was to evaluate the feasibility of fuelling solid oxide fuel cells (SOFCs) with the syngas generated during gasification of this feedstock. Optimal operation of the gasifier system was evaluated in terms of syngas heating value, syngas yield, equivalence ratio, stability of gasifier operating zones and cold gas efficiency. Mass balances were calculated to examine the reliability of the results generated. Contaminants in syngas were investigated to assess the possible impact of the syngas produced on the SOFC system. The effect of CaO as a primary measure and sulphonated PolyHIPE polymer (PHP) as a novel secondary treatment process on tar production and conversion during gasification were investigated. Optimal gasification occurred at an equivalence ratio of 0.26 producing syngas with a heating value of 5.7 ± 0.6 MJ Nm-3 and syngas yield of 3.2-3.9 Nm3 kg-1. The air/fuel ratio was 1.17 Nm3 kg-1 (dry basis), cold gas efficiency 77-85 % and mass balances closures ranged from 92-94 %. Increasing the moisture content in the lower oxidation zone increased H2 production generating a medium heating value syngas suitable for power, liquid fuels and chemicals production. Tar concentration in the syngas was 621 ± 11 mg Nm-3 of which Class 1 tars comprised 3 %, the remainder was dominated by Class 2 and 5 tars. In-bed 6 wt% CaO reduced the tar yield by 35 %, increased the syngas yield by 37 % and reduced the tar dew point to 30-32 oC whereas sulphonated PHP had no effect on syngas yield but reduced the tar yield by 77 % and the tar dew point to 72.6 oC. Chemical fractionation studies showed that 30 % of the K released to the syngas was ‗captured‘ by aluminosilicates in the feedstock and retained in the ash. Potassium, HCl and H2S concentrations in the gas phase were 371 ± 62 mg m-3, 27 ± 8 mg m-3 and 40 ± 7 ppmv respectively. It is evident therefore that syngas from fuel cane bagasse can be used to power SOFCs, however a high potential for fouling of the SOFC anodes exist. Therefore a combination of primary and secondary syngas treatment systems for removal of Class 1, 2 and 5 tars as well as alkali metal sorbents will be essential for commercial operation of fuel cane bagasse fuelled SOFCs.

The environmental, social and economic challenges facing society make sustainability and resource efficiency a necessity. To overcome these challenges in wastewater treatment, energy conservation and recovery are two central requirements. Microbial fuel cells (MFCs) as an energy producer could provide a sustainable solution to fulfil both objectives. A challenge for reliable and efficient use of microbial fuel cells is achieving low material costs due to the low power output especially when using wastewater as substrate. Low cost materials for the anode, cathode and membrane in MFCs were studied to increase the knowledge of reactions and interactions between microbiology and materials in a MFC and to try to increase the power performance and coulombic efficiencies when using complex wastewaters as substrate. Activated carbon cloth, as one of the anode materials tested, showed the greatest potential for high power performances from wastewater. It reached power densities of 67 mW m -2 during polarisation in a membrane-less reactor and 29±3.4 mW m under 1000 Ω external load using a radiation grafted ion exchange membrane based on ethylene tetrafluoroethylene (ETFE). Coulombic efficiencies (CE) observed reached 92±6% CE for reactors using ETFE radiation grafted membranes and 68±11% CE for membranes-less reactors with an interior biocathode opposite to the anode in the anode chamber. Both reactors used activated carbon cloth as anode material and carbon black as cathode catalyst. The low conductivity of the wastewater (1-2 mS cm -1 ) limited the power density achieved as it created high ohmic losses because of a high internal resistance in the reactors using 4 cm electrode spacing. Reducing the electrode distance to 2 mm decreased the internal resistance by a factor of ten. A simultaneous reduction in anode potential of 100 mV lead to lower power densities presumably due to oxygen diffusing into the anode chamber. With the exception of carbon cloth, the anode materials investigated showed low overpotential losses and charge transfer resistivities. The cathode was the more limiting influence in the system when a low costs separator (Rhinohide) was used as membrane. However when an ion exchange membrane (Nafion or a radiation grafted membrane based on ETFE) or membrane-less (carbon paper with an internal cathode) was used lower overpotential losses were observed on the carbon black cathode than the anode. The different membranes and separators tested showed a greater influence on the system than previously anticipated. Although durability studies of the activated carbon cloth as anode material and the different cathode materials over three and two month respectively showed a concerning decline in power performance, the coulombic efficiencies increased over time. So the high coulombic efficiencies achieved and a capability for high power densities using inexpensive materials give hope for the use of microbial fuel cell systems for economical energy generation from wastewater.

A technique that is becoming more widespread in usage and popularity, ball milling has been used successfully in the pretreatment of sodium lignosulphonate (NaLS), a waste biomass material. The ball milled material produced higher yields of commercially valuable aromatic products, particularly vanillin in an industry standard copper-catalysed aerobic oxidation reaction. Through the optimisation of the parameters of this pretreatment technique both for NaLS alone and NaLS with sodium hydroxide and calcium oxide as additives, the vanillin yield after oxidation of the pretreated material could be increased by over 100 %. The generation of vanillin in NaLS in the solid state during ball milling was also observed for the first time confirming that mechanochemical transformation of the NaLS was taking place. Despite the difficulties associated with the analysis of such a heterogeneous and complex biopolymer, SEM imaging, GPC analysis and 2-D NMR analysis were used to identify some of the major chemical and physical changes occurring in the material during mechanochemical pretreatment. An HPLC analytical method for accurate measurement of the main oxidation products was also developed. The effect of using milling media of a different material on the pretreatment and subsequent oxidation reactions revealed that this pretreatment is transferable between different types and scale of equipment but that the results are sensitive to both materials of construction and storage conditions for analytical samples. The extrapolation of this pretreatment technique to other reactions of NaLS, hydrogenolysis for example, and to other biomass substrates was also investigated but with varying degrees of success, indicating that the mechanochemical changes can be subtle and highly reaction specific. Initial attempts at providing more mechanistic information were made through the synthesis and transformations of some simple lignosulphonate model compounds. These provided confirmation that the mechanistic scenario is complex and that several pathways are likely to be operating in parallel in the transformations of both model and polymer substrates.

The work described in this Dissertation is a combined experimental and theoretical study of laminar diffusion flames leading to their structural characterisation. For this purpose, experiments were conducted on two laboratory laminar diffusion flames of methane and air, in which measurements of temperature, stable species concentrations and velocities were made. Analyses of the resulting species concentrations and temperature data from these experiments and of corresponding data from previous works are presented as correlations against a suitably defined conserved flame property, otherwise called mixture fraction. The mixture fraction is a mixing quantity and the presentation of data against a spatial coordinate defined by it, helps to examine and identify regions of these correlations characterising either diffusive flow or combined diffusive and chemically reactive flow. The reactive flow regime is examined in detail, using the experimental correlations as a basis for transforming the species conservation equations into explicit expressions for reaction rates of methane and carbon monoxide, in terms of measured quantities. Correlations of measured reaction rates are provided in the form of global kinetic rates. For the combustion of methane, the correlating global rate is: R_CH4 = 3.86 x 10¹⁶ exp (-30693/T) [CH₄] [H₂]^½ k moles m⁻³ sec⁻¹, with the concentrations in moles cm⁻³, over temperature range 1300 K ≤ T ≤ 2000 K and equivalence ratio 2.5 > φ > .39. This correlation is consistent with the rate given by the forward step of the kinetic mechanism CH₄ + H ↔ CH₃ + H₂, with equilibrium H according to H₂ ↔ H + H. The global rate for carbon monoxide oxidation is RCO oxi = 2.63 x 10¹⁴ exp (-15401/T) [C0][0₂]^¼[H₂O]^½ k moles m⁻³ sec⁻¹, with concentrations in moles cm⁻³, in the range .39 ≤ φ ≤ 1.08, 1300 K ≤ T ≤ 2000 K. The rates given by this correlation are consistent with the rates given by the main kinetic mechanism for carbon monoxide oxidation CO + OH = CO₂ + H, in which both the forward and reverse steps are significant, but the reaction proceeds by the dominance of the forward step; and using [H]/[OH] ↔ [H]/[OH] equilibrium with OH in equilibrium according to: 20H ↔ H₂O + ½O₂. A theoretical model is developed, based on the Shvab-Zeldovich similarity analysis and its extended version. This semi-empirical similarity model incorporates the experimental species correlations in the similarity equations of stoichiometry. The resulting equations which relate the major species concentrations and enthalpy to the mixture fraction, are combined with the momentum conservation equation and the conserved species equation, in a numerical computation of the aerothermodynamic field of the flame.

No description available.

No description available.

No description available.

No description available.

The mechanism of formation of sulphur trioxide in combustion gases has been investigated using liquid fuel firing combustor with laminar pre-mixed flame. The combustion chamber was constructed from a stainless steel tube for minimizing any affect of catalysis. A temperature controlled evaporating chamber was designed where liquid fuel was evaporated and mixed with total combustion air prior to entering the combustion zone. The vapour mixture then passed through a silica sintered disc and a flat flame was produced. Six sampling ports at 0.304m (1 ft) intervals along the combustion tube were used for sampling the gases for analysis and for the measurement of sulphur trioxide with respect to residence time. Diesel oil, Kerosine, Cyclohexane, n-hexane, and n-Pentane were used in the investigation: Sulphur content of these fuels were raised to 3.4% (wt.) by addition of appropriate amount of carbon disulphide (CS2) in each fuel. It was found that SO3 was only formed when there was an excess oxygen in the combustion gases and under sub-stoichiometric conditions, no SO3 could be detected. An increase in the quantity of combustion air in excess of stoichiometric requirement lead to an increase in the concentration of SO3 in the combustion gases. However, the level of SO3 content in the flue gases reached a maximum at about 4% excess oxygen concentration in the flue gases. It was established that ignition properties of fuels have an effect on the oxidation of S02. Ignition delay v temperature curves for the fuels employed in the research programme were determined. This was done with the help of Ignition-Delay apparatus (PART II). It was found that fuels having shorter ignition delay times at. temperatures. prevailing near flame zone produced less SO3 under identical combustion conditions. The results of the effect of residence time of combustion gases in the high temperature zone showed that in the first instance amount of SO3 formed was in excess of those predicted from thermodynamic considerations involving molecular oxygen. Sulphur trioxide thus formed began to dissociate back into sulphur dioxide and oxygen as the gases continued to pass along the combustion chamber. It was thought that oxygen atoms, produced in the flame, being a reactive oxidising species are responsible for the oxidation of SO2. The theory proposed to explain the experimental results appear to be that of a consecutive reaction [see full text for details].

No description available.