This project is aimed towards an understanding of ash deposition during air firing of high percentages of biomass with coal. Biomass resources are widely used as sustainable, renewable and environmentally friendly materials. There has been an increase in the use of biomass for power generation by means of co-firing with coal as well as by the combustion of 100% biomass. Despite the advantages of biomass in reducing carbon emissions from the electricity sector, the co-firing of high percentages of biomass can potentially aggravate ash related problems in the boiler. In order to develop mitigation strategies for the formation of deposits, an understanding of the ash behaviour during the combustion of high percentages of biomass is required. To understand ash deposition, the influence of the inorganics, crystal types, and complex compound formation should not be neglected. In this work, ash samples from El Cerrejon coal and pine, wheat straw, white wood pellet biomass were characterised for their inorganic composition by X-ray fluorescence (XRF) and wet chemical methods. Relationships between these two methods were found and a modification to the standard test method has been recommended to improve the accuracy of the XRF method. Furthermore, the melting behaviour of ashes from pure El Cerrejon coal, biomasses, and their blends were studied through ash fusion tests and via a method using a simultaneous thermal analyser coupled to mass spectrometer (STA-MS) for the evolved gas analysis. The inorganic composition were used to calculate indices to determine the slagging and fouling potential of pure fuel ash, ash blends and ash produced by ashing blended fuels (fuel blends ash). Base-to-acid ratio (Rb/a) results indicate that pine ash has a higher slagging potential than coal ash, which is not consistent with the experimental ash fusion measurements. Viscosity models appear to perform better for high-coal content blends than high-biomass content fuel, and further refinement is required for modelling the viscosity of pure biomass ash as well as high co-firing percentages. Thermodynamic modelling of slag formation was undertaken using the FactSage model and verified by XRD analysis for the solid phase. XRD showed complex interactions between inorganics which changed with biomass type, blend ratio and temperature. The FactSage model was successful in predicting the changes of gas, solid and liquid phases during pure biomass, coal and co-combustion, and for most of the blends studied the prediction of slag formation was within 100°C of the measured experimental ash melting window.

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Food security and alternative fuel production are a poignant concern for sustainable development. It is desirable to attain high nutritional value without comprising on the supply of raw materials for biofuel production. The residual biomass in biofuel processing of Jatropha curcas Linn is called Jatropha meal. Its utilisation is limited due to a constituent, a natural carcinogen: phorbol ester, although it also contains a high level of nutrients, potentially useful as feed stock or fertiliser. This research aims to develop technology for detoxifying phorbol esters in jatropha meal while maintaining the protein content. Experiment was conducted by passing air through a plasma microreactor to produce ozone while a ceramic diffuser was used to generate microbubble. The air flow rate was set to 2 L/min before the sample was loaded into the reactor. The ignition voltage of plasma was 4 kV while the working voltage was 3.8 kV. The mixture was treated with ozone for 1 to 5 hours. Indonesian variety of Jatropha meal was used as sample. HPLC technique was used to determine phorbol ester content and Bradford Assay was used for protein quantification. It was observed that only 40% reduction of synthetic phorbol ester was achieved after 30 minutes of aeration (without ozone activation) while 64% of degradation was detected after 5 minutes of ozonolysis (with ozone activation). A 97% reduction of natural phorbol ester (obtained from Indonesian Jatropha meal) content after 5 hours of ozonolysis resulted in a final phorbol ester concentration of 0.11 mg/g in jatropha meal sample. This value is also phorbol ester concentration found in the non-toxic Mexican variety which has become the limiting level for of jatropha edibility. Further, it is observed that the protein content remains stable after 5 hours of ozonolysis. It was reported that total protein concentration ranged from 18-32% which meets the requirements for sufficient nutritional content. Various benefits offered by developed technology in this research promise to overcome the conflict between oil and food supply. A higher economic value of jatropha meal as biofuel processing residual can be achieved.

There are, on average, over twenty-five accidental gas explosions every year in the UK, each requiring an investigation to determine the origin and cause, in order to satisfy regulatory requirements, or for the purposes of criminal or civil litigation. The most important conclusion to be drawn from the investigation is the identification of the source of the gas release. This is most often determined through interpretation of the severity of pressure and thermal damage to the building and its contents. Guidance in reference books states that gas explosions exhibit characteristic pressure and thermal damage dependent upon the concentration of the fuel/air mixture prior to ignition. It is believed that a number of investigations have resulted in the incorrect apportion of blame as a consequence of the misinterpretation of forensic evidence. The key objectives of the study were to answer three questions. Firstly, can ignition of a fuel lean or fuel rich mixture cause significant structural damage to a building? Secondly, is it possible to determine the gas concentration in a building, prior to ignition, from the severity of the thermal damage? Thirdly, do materials exposed to a transient flame front always exhibit thermal damage? The results of four experimental programmes, and over one hundred and fifty explosion tests, are reported in this thesis. Explosion tests were conducted in explosion chambers ranging from 1 m3 to 180 m3. Experiments were conducted in single and interconnected enclosures, with and without obstacles (including furniture) and with a number of ‘marker’ boards to assess the severity of thermal damage. A number of parameters were varied; including, fuel type, concentration, distribution of gas, congestion, ignition position and vent size and failure pressure. The results demonstrate that under the right conditions, fuel lean and fuel rich explosions can cause overpressures that have the potential to structurally damage buildings (> 200 mbar). A number of mechanisms have been proposed, detailing the manner in which gas explosions propagate from one room to another. This knowledge provides a valuable new insight into how complex a vented explosion in a typical building can be, and how the design and construction of a building can affect the magnitude of the explosion. Several causes of the development of high overpressures have been identified; the ignition of a flammable cloud outside the vent opening(s), the sudden increase in mass combustion as a turbulent mixture in a secondary compartment is ignited by a propagating flame front passing through an interconnecting doorway, and the highly turbulent ‘jetting’ expanding flame, driven by the venting process, propagating through a doorway and towards a vent opening in a secondary enclosure. Evidence is presented that shows it is possible to generate pressures capable of causing structural damage to buildings with volume blockages of as little as 0.57%, if vent openings do not allow sufficient outflow. However, the obstacle geometry, and its location to other obstacles and the enclosure, were found to be critical in the development, or otherwise, of damaging overpressures. The experiments have demonstrated that it is possible to use the severity and extent of thermal damage to wall coverings and wood surfaces, sustained during a gas explosion, to provide useful information on the gas concentration, its distribution throughout the building prior to ignition and the depth of any flammable layer. It is demonstrated that it is possible to assess the severity of the thermal damage to various materials in order to estimate the natural gas concentration prior to the explosion to the nearest 2%. The most suitable materials, in terms of forensic indicators, appear to be softwood covered with either gloss varnish or white oil based gloss paint. Such surfaces are common in buildings as door frames, window frames, etc. However, it is shown that quick drying paints are less susceptible to thermal damage and may cause the misinterpretation of evidence which could lead to an incorrect diagnosis of the origin and cause of an explosion. In tests where a flammable gas/air layer was present, thermal damage may be observed above the nominal layer boundary (for natural gas), down to the lowest level where the concentration was originally above 8% ± 1%. It is shown to be possible to estimate the layer depth from the damage to an accuracy of approximately 15 cm. The results of the experimental programmes presented in this thesis, provide new knowledge and understanding of the development of gas explosions in buildings and how this knowledge may be used to better interpret forensic evidence found in a gas explosion.

The mechanism of blow-off has been investigated because of the increased importance of this phenomenon consequent upon the conversion of the Gas Industry from high burning velocity manufactured gas to relatively low burning velocity natural gas. Burning velocity is regarded as the primary variable controlling flame stability, and correlations have therefore been sought between burning velocity and blow-off flow rate. For this purpose, burning velocities have been determined by the cooled flat flame method, and blow-off flow rates have been measured for inverted flames and for conical burner flames.

Current environmental issues and resource demands are driving the global development of renewable energy. The work described in this thesis applies green and energy efficient microwave technology to transform lignocellulosic biomass into solid and liquid fuels suitable for application in coal burning power plants or upgrading into transportation fuels. Current thermochemical biofuel production (e.g. pyrolysis and gasification) suffer many drawbacks such as high energy consumption and poor flexibility. Herein, it is shown that by applying novel low temperature microwave processing, fuels can be produced at temperatures up to 190 oC lower than required in equivalent conventional thermal treatments. Studies on the microwave activation of the major components of biomass give insight into the mode of action. 180 oC was identified as the key temperature in the degradation of cellulose. Softening of the amorphous region of cellulose at this temperature enables microwave induced rearrangement increasing the efficiency of microwave interaction resulting in acid catalysed decomposition. It was shown possible to produce high calorific value chars at 150 oC lower than previously expected. A reduction of 100 oC was observed in the degradation temperature of hemicellulose. The technology is versatile, effective on a variety of biomass species, and has a favourable energy balance. In studies on whole biomass, the processing conditions and energy usage were found to be favourable when compared with conventional methods. Chars were produced at low temperatures with increased calorific values and material properties in parallel with high quality bio-oils. Pilot scale trials were also carried out proving the technology to be scalable and open to industrial application. This thesis shows for the first time the possibility to produce biofuels via microwave processing, while operating at temperatures below 300 oC. The impact of these findings is being further investigated at the dedicated microwave facility at the University of York.

A direct carbon fuel cell (DCFC) is a special type of high temperature fuel cell that uses solid carbon as fuel and air as oxidant. Researches in the area of the DCFC have focused on using fuel derived from petroleum products, coal and activated carbon but this current research investigates the use of biomass carbon fuel in a single cell DCFC. Six different biomasses were investigated (miscanthus, switchgrass, wheat, spruce, poplar and willow). The biomasses were subjected to pyrolysis reaction at 800oC, 7oC/min with particle sizes of 0.50 mm to 1.00 mm, yielding 25 wt.% biomass carbon. The two electrolyte systems investigated were; molten carbonate electrolyte direct carbon fuel cell (MCDCFC) and solid oxide electrolyte direct carbon fuel cell (SODCFC) and these were tested using hand and ball milled biomass carbon fuels (HM and BM). The overall electrochemical reactions of the biomass carbon fuels in the SODCFC were better than those of the MCDCFC. The BM biomass fuels performed better in the SODCFC while the HM biomass fuels performed better in the MCDCFC. In terms of the open circuit voltage, miscanthus fuel (1.24 V) had the best value for SODCFC while willow fuel (0.83 V) for MCDCFC. The best peak power density was recorded for miscanthus fuel (77.41 mW/cm2) in the SODCFC and willow fuel (18.48 mW/cm2) in the MCDCFC. Miscanthus fuel (180.52 mA/cm2) gave the maximum current density for the SODCFC while spruce fuel (73.02 mA/cm2) for the MCDCFC. For the current density at 80% voltage efficiency miscanthus fuel (100 mA/cm2) was superior for the SODCFC and willow fuel (6.67 mA/cm2) for MCDCFC. Miscanthus fuel (0.66 V) showed the highest voltage at peak power for the SODCFC and willow fuel (0.48 V) for the MCDCFC. The overall energy strategy considering two major routes of electricity generation from biomass were investigated. The first route is the burning of biomass in a power plant to generate 6.5 MJ of electricity and the second is the DCFC integrated route using biomass to generate 12.8 MJ of electricity. The DCFC integrated route gave superior outputs of energy generation with an overall conversion efficiency of 70% when compared with the 35% of the first route.

Pulverised biomass is being used in electric power generation, either co-fired with coal or increasingly as 100% biomass. However, there is minimal information in the literature on the mechanism of flame propagation in pulverised biomass. In the present work the explosion technique was used to obtain fundamental information on the rate of flame propagation, the lean limits of flame propagation and related explosion characteristics of coarse biomass. A large part of this research involved the modification of the ISO 1m3 method to enable it to be used with coarse fibrous biomass powders. The technique that worked was to follow the Hartmann method and place the dust inside the vessel using a hemispherical bowl and then disperse this dust with a blast of air. This was demonstrated to work with coarse woody biomass and the calibration was established using cornflour and referenced to the standard method. The MEC and Kst for dusts were shown to have a dependence on the particle size. However, very coarse particles still propagated a flame, with no evidence that this was due to preferentially burning of the finer particles. Biomass particles of 300-500µm were shown to be flammable, i.e. as large as kerosene mist and large than coal particles will propagate a flame. For coarse woody biomass the Kst values were very low <20 bar m/s in many cases, but the peak pressure was high and hence the explosion would destroy biomass handling plant. This work found that the unburnt material was compressed into a layer against the wall of the vessel ahead of the flame front, thus preventing it from interacting with the flame front. It was postulated that large particles lagged the main flame due to interaction with the explosion induced wind. This led to large particles being pyrolysed behind the flame front and then to arrive last at the wall and so appear as on outer pyrolysed layer on the material compressed against the wall. This explanation also enabled an explanation to be given for the very rich mixtures that could burn with dusts than could not burn if the material was a gas.

The availability and sustainability of biomass is very crucial in the production of energy using biomass. Currently nearly two thirds of the biomass in the UK is being imported due to the limited supply of indigenous resources. The Green House Gas (GHG) emissions from importing these fuels are very high. The imported feed stocks studied here (PKE, shea, olive and DDGS) exhibited high N and ash contents and also high slagging and fouling tendencies which are undesirable fuel traits. The high N contents and S content (in the case of DDGS) emit NOx and SOx emissions respectively which cause acid rain and photochemical smog and are harmful to human health. Due to the poor quality of these fuels for use in boilers and furnaces, and the need for Green House Gas savings, indigenous fuels with better combustion properties need to be produced. Energy crops like SRC willow and Miscanthus have remarkably better fuel properties (eg low ash and nitrogen contents) and there is potential to grow them in the UK. In order to help farmers to increase the yields and grow these crops in a more sustainable way, some agronomic studies have been carried out. The influence of 6 different fertilizer treatments with varying nitrogen levels, (0, 150 and 250 Kg/hectare), the addiition of K (150Kg N + 100Kg K), the addition of S (150 Kg N + 80 Kg S) and sewage pellets on SRC willow are studied. These crops are sampled twice a year for 3 years. It was found that fertilizer treatments do have an impact on the fuel properties (eg the application of N and K increase the C content and the CV of the fuel). Different parts of the crop also exhibit different fuel properties (eg leaves have higher nitrogen and ash contents which are undesirable qualities during combustion) hence it is important to avoid such parts. Sampling time also has a very big impact as the composition of the crop changes over the growth period. The optimum harvest time for SRC willow would be spring, after senescence when the leaves have fallen and some of the nutrients have translocated into the soil for the next growing season. Different genotypes of SRC willow with varying biochemical compositions were also studied to enable farmers to try and breed different genotypes with desired fuel properties for the next generation. 6 genotypes with varying biochemical composition (highest and lowest hemicelluloses, cellulose and lignin contents) were studied. From these, one genotype S.elaeagnos Scop showed remarkably different properties compared to the other 5 genotypes. All the genotypes except S.elaeagnos Scop had very high ash melting temperatures (>1500oC) and low slagging and fouling tendencies. S.elaeagnos Scop exhibits good grinding properties. The pyrolysis products of SRC willow are highly sensitive to its hemicelluloses and lignin contents. Due to its different properties S.elaeagnos Scop is of great interest for further investigation especially for its grinding ability. Overall, there is a potential for the UK to grow its own SRC willow. A larger dataset is required for the fertilizer application experiment to make firm conclusions since it is insufficiently small at the moment. A larger selection of genotypes would also need to be studied in order to help farmers breed a larger variety of SRC willow.

Present work concerns the interaction of chemistry and turbulence in a turbulent reacting flow. Both self-ignition and flame propagation are studied. For self-ignition study, the combined effects of temperature/concentration inhomogeneities and turbulence were studied numerically. For this purpose two statistic turbulent combustion models, namely Linear Eddy Model (LEM) and Reference Scalar Field (RSF), were applied for simulations of statistically homogeneous reacting media. because these two models allow the calculation of the averaged reaction rates in fluctuating media from the first principles. Self-ignition delays, species concentration and temperature evolutions were computed for three kinds of initial conditions, where temperature pdfs were given as Dirac's 8 peak pdf, rectangular and bimodal shapes. The results obtained from the two models mentioned above were compared. The effect of heat loss on ignition delay was also studied with the RSF model. For the study of turbulent flame propagation, RSF model was applied to the problem of I-D flame propagation in a spherical fan-stirred bomb. This problem is selected because of its simplest possible flow field, hence reduced computation cost and easy implementation. For turbulent convection different conditionally averaged velocity models were introduced and evaluated. Pressure during gas explosion, and averaged mean values such as temperature and species concentration were calculated. The evolution of temperature pdf was also obtained from statistics of the reference scalar field. Flame radii and turbulent mass burning rates were determined from the calculated pressure rise and the mass burning rates were compared with two existing correlations of Bradley et al. and Zimont as well as with measurements. Two types of reactive mixtures were studied, one was the methane/air flame and the other one was DTBPIN2 decomposition flame. Experiments with both mixtures were carried out in a spherical fan-stirred bomb. In particular, pressure trace during explosion was recorded and this provided reference data for the modelling studies. Methane/air combustion was simulated with a reduced two-step chemical kinetics mechanism instead of the single-step kinetics commonly used for turbulent reacting flows modelling. The two-step kinetics employed was developed according to the experimental observations of two-stage oxidation of hydrocarbons, in which the first stage is related to the consumption of the fuel and the second stage represents the oxidation of CO and H2• Firstly, the kinetics was "calibrated" in the laminar situations to produce a reasonable agreement with measured flame speed. Then the kinetics was used with turbulent models to simulate the turbulent explosions. While DTBPIN2 decomposition flame is described by a single step kinetics and the reaction constants have been well-studied. So for simulation ofDTBPIN2 flame, any ambiguity resulting in uncertainties in chemical mechanism is avoided.