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Pyrolysis is an attractive alternative for the conversion of solid fuels to valuable chemicals and bio-fuels. In order to obtain more H2 and syngas from pyrolysis of coal and biomass, microwave has been adopted to enhance the co-pyrolysis of coal and biomass, which has been investigated systematically in this study. Firstly, conventional pyrolysis of coal and biomass was carried out using a vertical tube furnace. Characterizations of pyrolytic gas, liquid and solid products were conducted to study the different properties of products from the pyrolysis of coal and biomass. More gas products were produced at higher temperatures and biomass samples produced more H2 and syngas than coals. Bio-oils produced from conventional pyrolysis of biomass samples have relatively simpler compositions compared with those produced from conventional pyrolysis of coals. Char samples produced from conventional pyrolysis of coal and biomass samples show different morphologies due to the different nature of original coal and biomass. Secondly, microwave-induced pyrolysis of coal and biomass was carried out and compared with the results of conventional pyrolysis. Microwave-induced pyrolysis was found to produce pyrolytic gas products with higher contents of H2 and syngas than conventional pyrolysis. The bio-oils produced from microwave-induced pyrolysis were not as complicated as those from conventional pyrolysis. The reason for this is believed to be that both microwave irradiation and the longer residence time favour more complete decomposition of large hydrocarbon molecules in coal and biomass, which subsequently results in less complicated composition compared with bio-oil produced via conventional pyrolysis. Char samples from microwave-induced pyrolysis undergo more complete pyrolysis than char samples from conventional pyrolysis, and results in less volatiles remaining. Because of the thermal annealing process by microwave at the later stage of pyrolysis, char samples produced by microwave-induced pyrolysis have higher peak temperatures and burnout temperatures than those produced by conventional pyrolysis. In char samples prepared via microwave-induced pyrolysis of coal and biomass, special structures are found, such as nano-scale fibers in char samples from gumwood and pine, spheres in char samples from coals as well as coal and biomass blends. Based on the analysis of energy balance, it is evident that microwave-induced pyrolysis is a cost-effective and energy saving method for solid fuel conversion.

Pyrolysis of biomass is a promising and sustainable approach to produce value-added chemicals and biofuels. In order to achieve a high yield of hydrogen-rich syngas from pyrolysis of biomass, the microwave-enhanced pyrolysis of biomass coupled with catalytic reforming was studied systematically in this research. Firstly, microwave-enhanced pyrolysis of biomass was carried out and compared with conventional pyrolysis under the same processing conditions. Characterisations of biomass, pyrolytic char, bio-oil and biogas were conducted to investigate the differences between microwave-enhanced and conventional pyrolysis. It was found that certain types of carbon nano materials were formed on the surface of microwave pyrolytic chars. More biogas was produced via microwave heating, in which the highest H2 content reached 48.2vol.% during the course of microwave-enhanced pyrolysis of bamboo at 800°C. Most of the syngas contents produced from microwave-enhanced pyrolysis of biomass were above 80vol.% at 800°C. Generally, biomass could be converted into biofuel efficiently with microwave-enhanced process. Secondly, in order to increase hydrogen production, microwave-enhanced pyrolysis coupled with catalytic reforming (MPCCR) at 600°C was studied. In catalyst screening, Ni and Fe were applied as active compounds loaded onto different supports such as molecular sieves (13X), Al2O3 and natural minerals. In addition, activated carbon was employed as a reforming agent. It was found that Ni-13X catalyst resulted in a low yield of bio-oil and high yield of biogas around 75wt.%, which was the highest among all the catalysts investigated. It was also observed that activated carbon played a significant role in increasing biogas product and reducing bio-oil yield to less than 1wt.% in both conventional and microwave-enhanced pyrolysis coupled with reforming. MPCCR with Ni-13X and activated carbon enhanced cracking reactions of bio-oil, and subsequently lowed bio-oil yields and narrowed products distribution simultaneously. The maximum H2 content reached 55vol.% by MPCCR of bamboo using activated carbon as the reforming agent. Compared with conventional reforming, there was a sharp increase of H2 yield via microwave-enhanced reforming, resulting in a hydrogen-rich syngas with a high ratio of H2 to CO. Therefore, it is concluded that microwave irradiation enhances the reforming process. Finally, in this study, a novel method for catalyst-free synthesis of multi-walled carbon nanotubes (MWCNTs) from biomass was developed. MWCNTs with a diameter of 50 nm and a wall thickness around 5 nm have been successfully prepared via microwave-enhanced pyrolysis of gumwood at 500 °C. The mechanism for the growth of such carbon nanotubes (CNTs) was proposed as follows: volatiles were released from the biomass and left behind char particles; these char particles then acted as substrates, mineral matter in char particles (originating from biomass) acted as the catalyst, and the volatiles released act as the carbon source gas; the volatiles then underwent thermal and/or catalytic cracking on the surface of char to form amorphous carbon nanospheres; the carbon nanospheres subsequently self-assembled to form multi-walled CNTs under the effects of microwave irradiation. In summary, microwave-enhanced pyrolysis of biomass has the potential to produce high yield of hydrogen-rich syngas not only at high temperatures but also at low temperatures when it is coupled with catalytic reforming processes. It has also been demonstrated that microwave-enhanced pyrolysis of biomass could be used to produce MWCNTs at low temperatures. It can therefore be concluded that microwave-enhanced pyrolysis of biomass is an effective and efficient approach for the conversion of biomass into value-added products under mild conditions.

Utilisation of biomass is identified as one of the promising solutions to reduce society’s dependence on fossil fuels and mitigate climate change caused by the exploitation of fossil fuels. By using the concept of biorefinery, biomass can be converted into value-added products such as biofuels, biochemical products and biomaterials in a greener and sustainable way. To enhance the efficiency of biorefinery, the concept of integrated biorefinery which focuses on the integration of various biomass conversion technologies is utilised. To date, various biomass conversion pathways are available to convert biomass into a wide range of products. Due to the substantial amount of potential products and conversion technologies, determining of chemical products and processing routes in an integrated biorefinery have become more challenging. Hence, there is a need for a methodology capable of evaluating the integrated process in order to identify the optimal products as well as the optimal conversion pathways that produce the identified products. This thesis presents a novel approach which integrates process with product design techniques for integrated biorefineries. In the proposed approach, integration between synthesis of integrated biorefinery and computer-aided molecular design (CAMD) techniques is presented. By using CAMD techniques, optimal chemical product in terms of target properties which fulfils the required product needs is designed. On the other hand, in order to identify the conversion pathways that produce the identified optimal chemical product in an integrated biorefinery, chemical reaction pathway map (CRPM) and superstructural mathematical optimisation approach have been utilised. Furthermore, this thesis also presents various chemical product design approaches. In order to solve chemical design problems where multiple product needs are required to be considered and optimised, a novel multi-objective optimisation approach for chemical product design has been presented. By using fuzzy optimisation approach, the developed multi-objective optimisation approach identifies optimal chemical product based on multiple product properties. In addition, fuzzy optimisation approach has been further extended to address chemical product design problems where the accuracy of property prediction model is taken into account. A robust chemical product design approach is developed to design optimal chemical products with consideration of accuracy of property prediction model. Furthermore, together with CAMD techniques and superstructural mathematical optimisation approach, the developed multi-objective optimisation approach has been utilised for the design of mixtures in an integrated biorefinery. For this purpose, a systematic optimisation approach has been developed to identify optimal mixture based on multiple desired product needs as well as the optimal conversion pathways that convert biomass into the optimal mixture. Finally, possible extensions and future opportunities for the realm of the research work have been highlighted in the later part of this thesis.

The use of biomass derived solid fuels for electricity generation in combustion, gasification and pyrolysis plant has received increasing levels of interest for commercial operation in recent years. However, there are limited tools available which allow a prediction of the performance of these fuels during thermochemical transformation given an understanding of their original chemical structure. As such, this investigation has concentrated on the derivation of a simply utilised classification system able to predict a series of important fuel combustion characteristics given an understanding of both the organic and inorganic chemical and structural composition of any lignocellulosic biomass fuel. A prediction of volatile matter content and char yields during pyrolysis has been made using correlation with aromatic carbon, potassium and calcium contents using both thermogravimetric slow heating and simulated pulverised fuel (PF) entrained flow rapid heating. Alongside this, investigation of the impact of biomass composition, namely aromaticity and alkali/alkaline earth metal concentrations, on char structure and oxidative char reactivity of simulated PF chars has been conducted. Experimental investigation has involved the pre-treatment of a wide range of commercially available biomass fuels including softwood, hardwood, herbaceous and agricultural waste materials to remove both lignin and ion exchangeable mineral species. In addition to this, torrefaction has been utilised to increase the aromatic character of chosen fuels. This has allowed a quantification of the impact of aromaticity and mineral matter concentration on pyrolysis and char combustion reactions to be derived for a wide range of fuel aromaticity and mineral matter contents. Considerable success has been achieved in the classification of an array of lignocellulosic biomass. Accurate prediction of pyrolysis char and volatile matter yields under both slow and rapid entrained flow drop tube heating conditions have been attained using simple empirical correlations with fuel aromatic carbon and alkali/alkaline earth mineral species concentrations (K+Ca being utilised here). This classification system has relied upon the clear linear correlation observed between aromatic carbon content and char yield in the absence of mineral matter influences (R2 of 0.98 and 0.95 being observed for demineralised biomass under slow and rapid heating pyrolysis respectively). In addition to this, the relative enhancement of char yield due to mineral matter interaction with varying concentration of K and Ca within the fuel has been quantified and is used to calculate total char yields. The empirical relationship derived under slow heating takes the following form: Slow Heating Char Yield=(1×Aromatic Carbon )+(16.1 ×(K+Ca) ) Where slow heating char yield is the char yield wt% on a dry ash free basis (daf), aromatic carbon is the wt% daf aromatic carbon content of the biomass and K+Ca is the wt% K+Ca content of the raw fuel on a dry basis. This relationship applies below K+Ca contents of 0.6 wt% db, beyond this a fixed additional char yield of 9.76 wt% daf can be applied as a quantification of the influence of enhanced char yield due to mineral activity as the second term in the above equation. For rapid heating entrained flow pyrolysis the empirical prediction of char yield is conducted as follows: Rapid Heating Char Yield=(0.58×Aromatic Carbon )+(2.43 ×(K+Ca) ) Strong linear correlations of predicted vs. observed char yield have been derived with correlation coefficient R2 = 0.96 and 0.99 with mean relative errors of 7.8 and 8.4% for slow and rapid heating pyrolysis respectively. Furthermore, the influence of biomass aromaticity and active mineral content on char formation processes, the form of chars generated under PF like devolatilisation conditions and their subsequent oxidation reactivity has been studied in detail. Both alkali/alkaline earth mineral matter content (primarily K and Ca) and aromaticity are instrumental in determining the porosity, morphology and surface area of simulated PF chars. Due to its tendency to soften during heat treatment lignin is shown to produce low surface area, non-porous chars under slow heating and this behaviour drives a reduction in char surface area and combustion reactivity with increasing aromatic carbon content. Although char surface areas have been seen to be negatively correlated with increasing potassium and calcium content this may be due to ash blockage of char pore structures. However, the likelihood of a negative impact of mineral enhanced charring has been discussed. K catalysis of combustion reactions is clearly evident in apparent and inherent char reactivities; however, easy quantitative assessment of this influence has been prevented by the clear complexity of mineral behaviour during the pyrolysis process. The development of char structure and reactivity as a function of char combustion degree has also been investigated under entrained flow combustion conditions. The results of this study indicate that by accurately quantifying aromatic carbon, potassium and calcium contents, all lignocellulosic fuels can be classified in terms of their behaviour during pyrolysis (volatile matter and char yields), the form of char structures generated (surface area and porosity) and char combustion reactivity. It is hoped that this relative classification will shed light on the predicted performance of biomass fuels for use in combustion driven power generation infrastructure, especially in pulverised fuel applications.

Biomass combustion has increasingly been used in pulverised fuel coal fired power stations as a way of addressing a wide range of emissions reduction targets. The reuse of existing equipment such as coal mills is essential to minimise the costs of conversion. However the fundamental fracture mechanics involved in biomass comminution are completely different to coal. Thus a thorough knowledge of the comminution properties of all biomass types in coal and biomass mills is necessary in order to minimise operational issues and to optimise milling and combustion. This thesis provides extensive novel characterisation on densified biomass before and after milling. The study analysed 9 densified biomasses, 2 non-densified biomasses, and a sample coal in five different mills; planetary ball mill, Hardgrove Grindability Index testing mill, Bond Work Index ball mill, cutting mill, and a ring-roller mill. Milling was found to have little impact on particle shape, even when an order of magnitude change in particle size was observed. Particle shape is inherent to the particles which comprise a pellet, and is determined by the pre-densified comminution processes. Milling had little impact on compositional particles of herbaceous or wood pellets. Olive cake had the most spherical of all the materials. Thermal pre-treatments of woody biomass not only saw a significant improvement in grindability in all mills, but also enhanced shape factors. The Hardgrove Grindability Index is a poor indicator of the grindability of biomass. The Bond Work Index can be used to analyse the choking potential of biomass pellets prior to full scale mill trials. To optimise milling in coal mills, biomass pellets should be composed of particles close to the required size so that only the pellet comminution stage occurs. The milling behaviour of densified biomass in a laboratory scale ring-roller mill with dynamic classification was investigated for the first time. The milling studies showed that knowledge of a materials critical particle size for comminution through compression is essential to understand its milling behaviour in different mills. The results presented in this thesis not only provide new insight and addresses significant gaps in knowledge, they also provide useful and practical guidance for addressing operational issues such as mill choking, as well as ways to optimise biomass comminution in laboratory and full scale mills, such as mill classifier optimisation based on real particle characteristics.

This thesis examines two important physical phenomena that occur when solid fuels are exposed to external radiative heating: (1) the pyrolysis process in reaching ignition conditions and (2) the natural convection around one or more radiatively heated fuel samples. A vegetation fire (bushfire, wildfire, or forest fire) preheating the vegetation which is in its path is a particular example which occurs in nature. However there are many more applications where modelling the pyrolysis process and/or the natural convection is of practical use. For the pyrolysis phenomena, a one-dimensional time dependent pyrolysis model is proposed. The mathematical model is solved numerically and results are used to analyse the influence of the size of a wood-based fuel sample, the heating rate it is exposed to, and its initial moisture content in the process of the sample reaching the conditions where it can produce enough pyrolysate vapour to support a flame (flash point). In many pyrolysis models in the open literature it is assumed that the fuel samples are dry. In the present study it is found that the initial moisture content has a marked effect for a fuel sample reaching its flash point. For the convection phenomena, a two-dimensional steady model, which explores the natural convection around one or more solid fuels, is also presented. The flame front is represented by a radiating panel. This means that the solid fuels receive a non-uniform heating rate depending on their geometry and location in relation to the panel. Changes in temperature and velocity profiles are monitored for varying heating rates and sample sizes (or, equivalently, the Rayleigh number Ra). Additionally, in the case of multiple fuel samples, changes in the distance between the fuels is also taken into account. For multiple fuels in arbitrary locations it is possible that one sample will block some of the radiation from the panel from reaching another sample. This means that the fuel sample will receive a reduced heating rate. This reduction in heating is also incorporated in the natural convection model. Both the pyrolysis and natural convection models are solved numerically using the finite element software package COMSOL Multiphysics. A comparison of COMSOL is performed with benchmark solutions provided by the open literature. A good agreement in the numerical results is observed.

In this work, both experimental and computational studies have been performed to investigate the flame dynamics and combustion instability of a laboratory buoyant jet diffusion flame from different prospects. The motivation behind this study was to obtain a better understanding of the dynamics of jet diffusion flames, as part of a long-term effort in achieving flexible fuel utilisation such as interchangeable fuels and achieving more effective combustion control such as better combustion efficiency.In the experimental study of jet diffusion flames, the influences of parameters such as nozzle exit diameter, fuel flow rate, fuel types and burner geometries have been investigated, where the focus was on the effects of fuel mixture on the flame dynamics. The frequency spectra, flame vortex development and flickering frequencies were measured using flow visualisation techniques and data acquisition systems. It was observed that the fuel jet velocity and the type of burner had a weak influence on the pulsation frequency for all the tested diameters. In contrast it has been found that both the ambient condition and fuel variability do have significant effects on the flame flickering frequency. Flame structure and dynamics are very different for the methane, propane and mixed fuel jet flames. Since the measurements of variables such as entrainment properties are difficult to obtain under experimental conditions, it is more effective to deal with such problems numerically. In the second part of this study, the dynamics of the buoyant jet diffusion flame has been investigated by idealised axisymmetric direct numerical simulations (DNS). The physical problem is a fuel jet issuing vertically into an oxidant ambient. Taking the advantages of idealised computational conditions, the effects of nozzle velocity profile, initial momentum thickness, Froude number, Reynolds number and co-flow on the near-field dynamics of a jet diffusion flame have been investigated. The computational cases have shown the development of different vortical structures, which suggest that vortical structures depend on both buoyancy and jet nozzle velocity profile. The flickering frequency and flickering energy results provide supportive evidence of the above finding. The results of the co-flow case indicate no significant flame-vortex interaction, and the flame oscillation is being suppressed. In general, the study suggested that the velocity shear plays a significant role in the near-field flame dynamics, apart from the buoyancy effects.

This research project is to investigate the control of the wave power device, known as the 'Manchester Bobber' (MB), and to optimise the output by tuning its drive-train parameters. The work starts with building a numerical model and developing a control strategy. The work sequentially progressed to obtain the experimental results from a physical model in order to make a comparison with the numerical results.An assessment of three different control strategies is made. These are reactive control, latching control, and two methods of torque control based on either time-averaged velocity or a pre-defined static characteristic. It is found that reactive control and latching control are not feasibly applicable to the MB wave energy device due to the configuration of the device. It is also found that the historical data approach is able to reduce the problem of high rate of change of electromagnetic torque but with a subdued output performance. A method based on a static characteristic, similar to the approach used to control wind turbines, is shown to significantly enhance the power output performance although this imposes a high rate of change of electromagnetic torque.The findings of the numerical simulation are supported by experimental measurements obtained in the wave tank. The parameters used in the numerical model (i.e. hydrodynamic damping co-efficient, added mass co-efficient and Froude-Krylov force co-efficient) are calibrated by comparing with the experimental measurements.Two drive-train parameters, the number of generator poles and flywheel inertia, are optimised in order to both maximise output power and minimise rate of change of electromagnetic torque. The proportional gain and integral time constant of the PI controller are tuned to further reduce the maximum rate of change of electromagnetic torque, so that the device is protected from the high mechanical stress. It is found that the annual energy production from the device at a range of locations is found to be almost linear with the annual average significant wave height of each site.

Agricultural residues from Thailand, namely stalk and rhizome of cassava plants, were employed as raw materials for bio-oil production via fast pyrolysis technology. There were two main objectives of this project. The first one was to determine the optimum pyrolysis temperature for maximising the organics yield and to investigate the properties of the bio-oils produced. To achieve this objective, pyrolysis experiments were conducted using a bench-scale (150 g/h) reactor system, followed by bio-oil analysis. It was found that the reactor bed temperature that could give the highest organics yield for both materials was 490±15ºC. At all temperatures studied, the rhizome gave about 2-4% higher organics yields than the stalk. The bio-oil derived from the rhizome had lower oxygen content, higher calorific value and better stability, thus indicating better quality than that produced from the stalk. The second objective was to improve the bio-oil properties in terms of heating value, viscosity and storage stability by the incorporation of catalyst into the pyrolysis process. Catalytic pyrolysis was initially performed in a micro-scale reactor to screen a large number of catalysts. Subsequently, seven catalysts were selected for experiments with larger-scale (150 g/h) pyrolysis unit. The catalysts were zeolite and related materials (ZSM-5, Al-MCM-41 and Al-MSU-F), commercial catalysts (Criterion-534 and MI-575), copper chromite and ash. Additionally, the combination of two catalysts in series was investigated. These were Criterion-534/ZSM-5 and Al-MSU-F/ZSM-5. The results showed that all catalysts could improve the bio-oils properties as they enhanced cracking and deoxygenation reactions and in some cases such as ZSM-5, Criterion-534 and Criterion-534/ZSM-5, valuable chemicals like hydrocarbons and light phenols were produced. The highest concentration of these compounds was obtained with Criterion-534/ZSM-5.