Large scale self-heating of wood pellets in storage is a major concern worldwide during long term storage due to the potential for fire with safety concerns for both personnel and plant. Additionally, any adverse publicity resulting from an incident involving biomass is likely to result in negative effects to the biomass industry as a whole. Self-heating could lead to serious accidental fires, causing enormous damage and danger to workers. The aim of the research in this thesis was to provide underpinning data and understanding in order to implement safe storage of wood pellets at Drax Power Ltd. Thus, the self-heating rates at different temperatures, and under different levels of inerting, were experimentally determined, and the thermal properties were measured for wood pellets produced for Drax Power Ltd. In addition, the thesis covers measurements at three scales; laboratory, temporary storage of approximately 40,000 tonnes through to largescale storage at approximately 280,000 tonnes spread equally over 4 domes… the largest storage of pellets ever investigated. The factors such as moisture content, pellet age and environment temperature were investigated and their impacts on the self-heating process were analysed. Moisture content has a significant effect on effective on self-heating but ventilation of the store was found to be more critical. Pellets age and environment temperature are two major factors impacting the self-heating and off-gassing process. The self-heating rate is significantly increased at higher a temperature and eventually will lead to a thermal runaway when the ambient temperature is high enough. Based on all measured properties, a self-heating model was developed to predict the self-heating process and thermal runaway in large wood pellet dome of ~120,000m3. This work contributed to the inerting of nitrogen gas to maintain an atmospheric (and therefore assumed within biomass) oxygen content less than 10% and monitoring protocols with the focus on carbon monoxide along with the understanding of temperature tracking for the large-scale dome storage of wood pellets, which is now used by Drax Power Ltd. Safety of all personnel working with biomass is paramount concern for Drax Power Ltd., which this thesis contributed to personal exposure monitoring and standard setting for gas exposure, mainly carbon monoxide and dioxide along with dust exposure. The handling of pellets through the supply chain and on site can cause the pellets to degrade and fine wood particles and dust is present within bulk pellets. Any release of wood dust into the atmosphere can pose a risk to health. Wood dust can cause serious health problems. Wood dust is a recognised respiratory irritant, sensitizer, asthmagen and for a limited number of species, a potential carcinogen (hard woods). Contact with wood dust can also lead to skin sensitisation and dermatitis. Drax Power Ltd, recognises it’s duties under Health and Safety and is committed to minimising the risk to health from wood dust in its premises. Both hardwood and softwoods dusts have a Workplace Exposure Limit (WEL) of 5mg/m3, which must not be exceeded. These are limits placed on the amount of dust in the air over an eight–hour shift. However the Control of Substance Hazardous to Health Regulations 2002 (as amended) requires exposure to wood dust to be “As low as reasonably practicable” (ALARP). Drax Power Ltd will manage exposure to wood dust to as low as reasonably practicable. The primary means of preventing exposure, is by containment of wood dust within the materials handling and processing plant. Dust control equipment such as Local Exhaust Equipment (LEV), will be used in conjunction with handling and processing plant to ensure that dust levels are kept to as low as is reasonably practicable. For certain operational and maintenance tasks it is necessary to use additional procedural controls to ensure that the risk of exposure to wood dust are managed effectively.

Biofuels were first used, as motor fuel (bioethanol) in 1860 in Germany and soon after, biofuels became the main rival for petroleum. But the abundance and the low price of fossil fuels had severe impact on the use of biofuels. Decades later, in 1970s, the shortage of fossil fuels due to the geopolitical conflicts, and the subsequent rise in the price of crude oil in 2000s, alongside energy security and climate change concerns, once again attracted the attention of governments to the use of biofuels. As a result of investment in biofuel production, the share of biofuels among the total renewable energy sources has increased since the beginning of the new century. The crop-based fuels (the so-called first generation biofuels) were considered as panacea to solve energy problems and environmental concerns. At the same time, research in advanced biofuel production methods, i.e. the second (non-food crops and residues) and the third (algae) generation has increased. However, in 2007-2008, biofuels were blamed for pushing up food prices, failing to meet environmental standards, and destroying natural habitats. As such, the use of first generation biofuels has been controversial. As for the second and the third generation biofuels, there is a need for further technological breakthrough. Currently, they cannot compete with crude oil economically, and are not commercially viable yet. In addition, fracking and the discovery of the new shale gas resources add further complication to this already complicated case. Although there is vast number of publications on biofuels, and they have been discussed extensively, to date, very little effort has been made to integrate the knowledge to provide new ideas to inform policy. The aim of this study is to investigate, bring together, and analyse the current biofuel science and regulations to provide recommendations for policy-makers in the UK/EU. Therefore, an extensive and critical literature review of the refereed journals, books, relevant publications, and official policy documents was carried out in this study, and views of the experts in three different sectors (academic, governmental, and industrial/private) were collated and analysed. The participants were recruited based on purposive sampling, and the semi-structured qualitative interviewing method was adopted. The participants’ views were analysed in relation to the published literature in order to drive an inclusive and integrated insight to develop novel recommendations for the biofuels agenda and extend the knowledge about this platform. This thesis suggests that, while the first generation biofuels are problematic, it is likely that they will remain dominant until 2022. The fate of the second generation biofuels is mainly determined by the advances in technology, and this type could become dominant beyond 2022. The potential of algae for the third generation biofuels is being increasingly recognised; however, to date, it is difficult to predict any time period for this method to become a commercial reality. The future of biofuels is very much related to the price of fossil fuels. If the global supply of fossil fuels continues to be tight, the price of crude oil may go above US$100 per barrel beyond 2030. Increasing crude oil prices is interpreted as increasing demand for biofuels in the future. A robust development in biofuels research and technology, and tighter mandatory policies for biofuel blending is forecasted. But, if shale gas resources are used extensively in the coming years, the price of crude oil may decrease/stay under US$ 100 per barrel and as a result, at least the current level of investment in biofuels technology may be kept. However, a backing away from investing in biofuels and re-focusing on other climate mitigation methods beyond 2030 is also possible but very unlikely. Based on the results of this study, there is no single, simple and generic solution for the issues surrounding biofuels. In this context, a range of recommendations are provided, a major one is for the UK/EU policy makers to push for the establishment of an international biofuels governing body, supported by the UN, to oversee sustained global biofuels production and consumption.

Charcoal has rapidly become the most widely used domestic source of urban energy for cooking and heating in sub-Saharan Africa, yet much of the sector is informally, or not at all regulated, with consequential detrimental impacts on livelihoods and the environment. Across Africa, 75% of urban growth is occurring in urban areas with populations of less than 1 million. Yet, these charcoal markets, their value chains, and the actors' livelihood outcomes are severely under researched. This thesis focuses on Zomba, a city of 164,000 people in southern Malawi. The research applies questionnaires, semi-structured interviews and a suite of rapid rural appraisal techniques to investigate actors' motivations, roles and livelihood outcomes along the charcoal value chain, examining processes at market, community and individual scales. By viewing the charcoal sector through a livelihoods lens, this thesis attempts to provide evidence and examine its implications for debate surrounding emerging charcoal policies across sub-Saharan Africa. The core findings of this thesis demonstrate that engaging in the production and transportation of charcoal strengthened actors' financial assets and delivered other benefits, such as improved access to goods and services and opportunities for livelihood diversification. These benefits contributed to reducing actors' vulnerability and improved their livelihoods. However, benefits were dependent on resource availability and a lack of charcoal resource management in the region has led to unsustainable harvesting practices. This resulted in localised forest degradation and charcoal-livelihood benefits were subsequently unsustainable in the longer-term. Lack of an environmentally sustainable commercial sector and enforcement of punitive regulations increased actors' vulnerability to reduced income, undermining market and livelihood security whilst having little positive impact on forest resource protection. This thesis provides original insights into the rural components of the value chain of small urban charcoal markets, the motivations of actors and livelihood outcomes. Combining a Value Chain Analysis with the Sustainable Livelihoods Framework supported an analysis of livelihood outcomes amongst actors along the chain and within the same node. The findings identify gendered nuances in participation and livelihood outcomes and in the distribution of enforcements amongst actors. This study confirms the importance of the charcoal sector for rural income generation, provides new context-specific insights into the contribution of charcoal to forest degradation and raises concerns over the levels of rent-seeking activities by authorities.

No description available.

A suite of coals covering a range of properties was gasified in a pressurised thermogravimetric analyser (PTGA) at 950°C and 2.5 MPa. The reactivities of the coals to steam were measured to determine any relationships between coal properties and reactivity. Some of the coals were pre-pyrolysed to produce chars, and the reactivity of these chars was measured both in steam and CO2. The results show that no simple relationships exist but trends can be shown whereby reactivity increases with decreasing carbon content, increasing volatile matter and decreasing mean vitrinite reflectance. Coal minerals, notably CaO, also increased reactivity to some extent in coals of low carbon content, yet carbon content itself influenced reactivity more than mineral content. The effect of pre-pyrolysis of the coals on reactivity appears to be dependent on coal rank, with higher rank coals (carbon content above 83%) showing an increase in reactivity whereas lower rank coals show a marked decrease.

The combustion process of liquid conventional and biofuels depend on factors ranging from the thermophysicochemical properties associated with such fuels to the combustion infrastructure used to burn them. A third class of fuels commonly referred to as surrogate fuels can be obtained by mixing conventional and biofuels. It is thought that the existence of oxygen atoms in biofuels play a crucial role in the way they burn in a stream of air, in uencing not only the e ciency of the combustion process of such class of fuels but also the emissions. The mechanisms through which the existing oxygen atoms in uence the combustion process of biofuels (and its surrogates) are still debatable and unestablished. This thesis sheds light on the points mentioned in the paragraph above. Extensive computational and experimental work was done to elucidate the combustion process of conventional, surrogate and biofuels. Some of the reaction mechanisms used in modelling the current reactive ow simulation are already tested while others were developed during the course of this work. The computational results have shown good agreement with the available experimental data. One of the most important observations and ndings reported in this work was that when comprehensive reaction models were used, the injected fuels burned at a slower rate compared to the situation when reduced models were employed. While such comprehensive models predicted better ame structure and far better by-products compared to the existing experimental results, it has also led to di erences in some parameters, especially the temperature eld. The computational prediction has also shown that biodiesel produces a marginally higher rate of COx compared to diesel which was also observed experimentally using a Compression Ignition Engine (CIE). Having said so, the experimental work also showed that surrogate fuels perform far better than pure diesel and biodiesel in CIE) in terms of emissions. The experimental work further addressed some phyisical and spectral analysis of diesel, biodiesel and nine blends as well as assessing the performance of a combination of these fuels in a compression ignition engine. The results are in line with what has reported in the literature but also sheds light on important features related to surrogate fuels and explain better the expected structure of such blends which may in uence the way they burn under di erent environments. With regards to the harmfull emissions of the combustion of liquid fuels, biodiesel was found to produce harmful emissions in a lower quantity compared to conventional diesel which is in line with the ndings of many experimental data. The computational ndings have also predicted less energy content and temperature range for biofuels of order 10-15% which is also in agreement with many experimental ndings cited in the literature.

A study is made of the influence chemical structure of fuel has upon combustion performance through tracing the generation of carbon monoxide and oxides of nitrogen in lean, premixed, hydrocarbon air flames. The study includes both analytical and experimental investigations. On the analytical side, a kinetic model is developed to predict both CO and NO time histories in one-dimensional, premixed flames. The model is based upon the assumption of partial equilibrium in the post-flame zone while the fuel oxidation in the main reaction zone is allowed for by using a global oxidation rate equation. NO formation is assumed to be entirely via the Zeldovitch mechanism and to start in the post-flame zone. The utility of the model is judged through comparison between theoretical results and experimental data. On the experimental side, a simple burner system, supporting a one-dimensional premixed flame was designed and built. All fuels selected for investigation were pure hydrocarbons representing the main hydrocarbon types usually found in practical fuels; namely paraffins, olefins, naphthenes and aromatics. The hydrogen-to-carbon ratio ranged from 1 to 2.67 and the carbon number from 3 to 12. The experiments were performed at 1, 2 and 3 atm pressure levels and 140°C inlet temperature, while the equivalence ratio was in the range 0.6 to 0.9. Flames were sampled for most stable species by a water- cooled stainless steel sampling probe. The experimental results show that the fuel structure signifi- cantly affects CO time-histories in the investigated flames mainly through influencing its generation rather than its burnout. CO burnout is shown to be mainly controlled by radical recombination processes, and the experimentally derived CO global oxidation rate equations are found not to be universally applicable. The results also show that the fuel structure influences prompt NOx formation within, and very near, the main reaction zone but that it does not influence post-equilibrium NOx formation if account is taken of differences in the flame temperatures. N02 is found to constitute a large percentage of total NOx measured especially at lower temperature and equivalence ratios. Comparison between experimental and theoretical results show that the prescribed kinetic model can satisfactorily predict CO levels for different fuels and under different conditions if the fuel oxidation global rate equation is correctly defined for different fuels. On the other hand, agreement between predicted and measured NO profiles has been obtained at atmospheric pressure only. At high pressure, the predicted levels were much smaller than those measured experimentally, and this disagreement is attributed to the fact that proper account is not taken of the NO and N02 formation kinetics in the main reaction zone.

The reactivity of cellulose in alkylimidazolium hydrogen sulfate-water ([CnCmim][HSO4]/H2O) mixtures during a biomass deconstruction process at 120 °C was investigated. Two types of sample, Miscanthus and a model polymer cellulose, Microcrystalline Sigmacell-Cellulose (MCC), were used. The studied variables included: [HSO4]-ionic liquids with different acidities, 1-butylimidazolium hydrogen sulfate, [HC4im][HSO4], and 1-butyl-3-methylimidazolium hydrogen sulfate, [C4C1im][HSO4]; acid-to-water ([CnCmim][HSO4]/H2O) ratio, and incubation period. A number of analysis tools and chemical methods were employed to characterise the resultant cellulose products: Scanning Electron Microscopy and Energy Dispersed X-Ray (SEM-EDX), Infrared Spectroscopy, Matrix Assisted Laser Desorption/Ionisation with Time of Flight (MALDI-TOF) Mass Spectroscopy, CHNS elemental analysis, viscosity measurement, compositional analysis and enzymatic saccharification. Deconstruction of Miscanthus in a [HC4im][HSO4]/H2O mixture at 120 °C for 22 h successfully separated cellulose, hemicellulose and lignin. A study on the purification of cellulose sample found that inadequate washing allowed the [HC4im][HSO4] traces to be physically adsorbed. After an extensive washing, indirect evidence, indicating that [HSO4]- anions had chemically adsorbed, was revealed. An investigation involving incubation of MCC in [CnCmim][HSO4]/H2O mixtures at 120 °C was conducted, replicating the deconstruction process. MALDI-TOF analysis demonstrated that the '[HSO4]' anion had chemically adsorbed on the surface of cellulose, forming sulfur-containing oligosaccharides. However, the type of bond responsible for chemisorption could not be identified. The [HSO4]- anion was the active species for chemisorption, regardless of different acidities of ionic liquids. Incubating MCC in [CnCmim][HSO4]/H2O mixtures at 120 °C also exhibited an interesting interplay between chemisorption and depolymerisation. A positive relationship was predominant in the presence of lower water content. Increasing water content displayed a negative relationship.

Concentrated solar energy provides thermal energy that can be utilised for thermochemical conversion of biomass to produce liquid fuel and gases. This creates an efficient and a carbon-free process. The fast pyrolysis of biomass is an endothermic thermal process that occurs within 400-550oC at fast heating rates of >300 oC/second in the absence of oxygen. This temperature is within the range produced in a parabolic trough arrangement. The process of biomass gasification is the conversion of biomass fuels to non-condensable gases usually for chemical feedstock or as fuel using a fluidising medium. Solar intermittence is a major issue; this can be resolved by proposing a continuous process from concentrated solar energy to fuels or chemical feedstock. Computational fluid dynamics has proven to be a tool for design and optimisation of reactors. The Eulerian-Eulerian multiphase model using ANSYS Fluent has shown to be cost-effective at describing the characteristics of complex processes. The project entails using parabolic trough for fast pyrolysis of biomass; it is integrated with a gasification process with utilities produced entirely from solar energy. The scope of the project are: (i) A Computational fluid dynamic (CFD) model analysis of the novel reactor is to be developed to model biomass pyrolysis (ii) Investigate the potentials of integrating the proposed solar reactor with a conventional circulating fluidised bed (CFB) gasifier to create a highly efficient and sustainable closed loop thermo-solar process (iii) Validate the circulating fluidised bed model with an experimental scale Circulating fluidised bed (CFB) gasifier at Aston University’s European Bioenergy Research Institute. The report studied the use of CFD modelling to investigate fast pyrolysis of switch grass biomass using a solar parabolic trough receiver/reactor equipped with a novel gas-separation system. The separator controls the effect of tar-cracking reactions and achieves high separation efficiency compared to other gas-solid separation methods. The study assumes an average heat flux concentrated along the receiver/reactor. Pyrolysis reaction was represented as a single global first order Arrhenius type reaction with volatiles separated into condensable (bio-oil) and non-condensable products. The drying of moisture of the switch grass was represented as a mass transfer process. The separation efficiency achieved by the conical deflector was about 99%. The proposed reactor at the considered operating conditions can achieve overall energy efficiency of 42%; the product yield consist of 51.5% bio-oil, 43.7% char and 4.8% non-condensable gases. The average reactor temperature, gas residence time, and maximum devolatilisation efficiency were 450 °C, 1.5 s, and 60% respectively. There was good agreement in comparison with experimental findings from literature. A sensitivity analysis was conducted to study the effect of heat flux conditions, heat transfer, sweeping gas temperature, and particle size. The heat flux distribution showed that non-homogeneous provides a greater heating rate and temperature compared to the homogeneous flux. Radiation negligibly affects the final product composition; the radiation heats the biomass mainly rather than cause devolatilisation. The larger the biomass diameter the more bio-oil is produced, when a uniform particle temperature is assumed. An experimental study was conducted for the validation of the hydrodynamic model of a circulating fluidised bed. The experiment measured the pressure profiles and the solid recirculation rate. The experiment result showed that particle size has a negative correlation to the ease of fluidisation. High fluidising gas flowrate has a positive impact on the fluidising regime and pressure in the riser. The following parameters were compared with experimental results: grid size, turbulence model, drag laws, wall treatment, and wall shear properties (specularity coefficient and restitution coefficient). The results proved the optimum hydrodynamic model through comparison of pressure profiles of the model with experimental results. The gasification of char in a circulating fluidised was studied using the optimum hydrodynamic model validated from experiment. The model considered the effect of turbulence on the species evolution and tar reforming with char. Over the range of operating conditions, the results looked into the hydrodynamics and product yield of the gasifier. The product yields obtained for the base case was CO (12%), CO2 (19%), H2 (6%), CH4 (0.7%), and N2 (63%). The results proved that for smaller particles the evolution of species are dominated by kinetics. The catalytic effect of char showed improvement in tar yield and CGE to 15.12g/Nm3 and 67.74%. The product yields showed improvement with the compositions of CO2 and H2 due to reforming reactions. The yields and efficiency were in qualitative agreement with results from literature. The proposed models described will provide details on the procedures for future design of integrated solar biomass thermochemical conversion systems.

There is an ever-increasing use of sustainable, bio-derived feedstocks in fuel oils including hydrogenated vegetable oil (HVO) from agricultural or recycled sources. HVO fuels consist of a narrow alkane distribution mainly octadecane (C18) and hexadecane (C16). Such fuels crystallise easily, which can lead to vehicle failures in cold weather conditions. This thesis examines the interplay between crystallisation kinetics, crystal structure and phase behaviour using model C18/C16 alkane mixtures. Computational systematic search modelling in combination with high resolution synchrotron X-ray powder data yields its crystallographic structure for C18 and C16 together with their volume thermal expansion coefficients: 4.39±(1.94)× 〖10〗^(-4) ˚C-1 and4.17±(2.48)× 〖10〗^(-4) ˚C-1. Morphological analysis of C18 crystals reveals a plate-like morphology dominated by the {001} habit plane with smaller side faces (depending upon supersaturation). Analysis of C18/C16 binary phase diagram reveals five single phases (liquid, R1, Mdcp, Op and T18) and five three-phase-equilibrium invariants (eutectic and peritectic at high temperature, eutectoid and peritectoid at low temperature). Kinetic studies reveal the crossover behaviour of the R1 existed in a transient to metastable to stable phase, which the stability is affected by both composition and alkane chain length. Studies of the ternary C18/C16/kerosene system reveal a variety of different structures with compositions close to that of its pure components forming solid-solution in triclinic structures, whilst high relative fractions result in its formation of multiple phases (triclinic and two higher symmetry structures). Rotator induced crystallisation observed in melt phase crystallisation is also formed in solution crystallisation but only for C18/C16 mixtures with its metastability depending on the composition. Solubility studies reveal the closest to the ideal condition with highest solubility in n-dodecane followed by kerosene and toluene respectively. Calculated activity coefficients reflect the non-identical phase formation in the solution phase with higher deviations for C18 molar compositions of x=0.1, 0.5-0.7. Solvents type is not found to have any significant effect on its solid for structure behaviour for C18/C16 mixtures. Crystallisation of C18/C16 mixtures for most compositions in the three solvents are found to be mediated by progressive nucleation mechanism. Cases of instantaneous nucleation are also seen in particularly compositions with higher C18 concentration. Progressive nucleation reveals well correlated with wider metastable zone width and concomitant larger interfacial tension (1.33-1.64 mJ/m^2 ). Higher solubility is found to accelerate the instantaneous nucleation by increasing effective solute concentration, whilst inhibit the progressive nucleation by causing larger interfacial tension.