Biomass is among the primary alternative energy sources that supplements the fossil fuels to meet today’s energy demand. Gasification is an efficient and environmental friendly technology for converting the energy content in the biomass into a combustible gas mixture, which can be used in various applications. The composition of this gas mixture varies greatly depending on the gasification agent, gasifier design and its operation parameters and can be classified as low and medium LHV gasified biomass. The wide range of possible gas composition between each of these classes and even within each class itself can be a challenge in the combustion for heat and/or power production. The difficulty is primarily associated with the range in the combustion properties that may affect the stability and the emission levels. Therefore, this thesis is intended to provide data of combustion properties for improving the operation or design of atmospheric combustion devices operated with such gas mixtures. The first part of this thesis presents a series of experimental work on combustion of low LHV gasified biomass (a simulated gas mixture of CO/H2/CH4/CO2/N2) with variation in the content of H2O and tar compound (simulated by C6H6). The laminar flame speed, lean blowoff limit and emission levels of low LHV gasified biomass based on the premixed combustion concept are reported in paper I and III. The results show that the presence of H2O and C6H6 in gasified biomass can give positive effects on these combustion parameters (laminar flame speed, lean blowoff limit and emission levels), but also that there are limits for these effects. Addition of a low percentage of H2O in the gasified biomass resulted in almost constant laminar flame speed and combustion temperature of the gas mixture, while its NOx emission and blowoff temperature were decreased. The opposite condition was found when H2O content was further increased. The blowoff limit was shifted to richer fuel equivalence ratio as H2O increased. A temperature limit was observed where CO emission could be maintained at low concentration. With C6H6 addition, the laminar flame speed first decreased, achieved a minimum value, and then increased with further addition of C6H6. The combustion temperature and NOx emission were increased, CO emission was reduced, and blowoff occurs at slightly higher equivalence ratio and temperature when C6H6 content is increased. The comparison with natural gas (simulated by CH4) is also made as can be found in paper I and II. Lower laminar flame speed, combustion temperature, slightly higher CO emission, lower NOx emission and leaner blowoff limit were obtained for low LHV gas mixture in comparison to natural gas. In the second part of the thesis, the focus is put on the combustion of a wide range of gasified biomass types, ranging from low to medium LHV gas mixture (paper IV). The correlation between laminar flame speed or lean blowoff limit and the composition of various gas mixtures was investigated (paper IV). It was found that H2 and content of diluents have higher influence on the laminar flame speed of the gas mixture compared to its CO and hydrocarbon contents. For lean blowoff limit, the diluents have the greatest impact followed by H2 and CO. The mathematical correlations derived from the study can be used to for models of these two combustion parameters for a wide range of gasified biomass fuel compositions. / <p>QC 20130411</p>

There is a great interest to develop biomass combustion systems for industrial and utility applications. Improved biomass energy conversion systems are designed to provide better combustion efficiencies and environmental friendly conditions, as well as the fuel flexibility options in various applications. The gas derived from the gasification process of biomass is considered as one of the potential candidates to substitute traditional fuels in a combustion process. However, the gascomposition from the gasification process may have a wide range of variation depending on the methods and fuel sources. The better understanding of the combustion features for the Gasified Biomass Gas(GBG) is essential for the development of combustion devices to be operated efficiently and safely at the user-end. The objective of the current study is therefore aiming to achieve data associated with the combustion features of GBG fuel for improving the efficiency and stability of combustion process. The numerical result is achieved from the kinetic models of premixed combustion with a wide range of operating ranges and variety of gas compositions. The numerical result is compared with experimental data to provide a better understanding of the combustion process for GBG fuel. In this thesis the laminar flame speed and ignition delay time of the GBG fuel are analyzed, using 1-D premixed flame model and constant volume model respectively. The result from different kinetics are evaluated and compared with experimental data. The influences of initial temperature, pressure and equivalence ratio are considered, as well as the variation of gas compositions. While the general agreement is reached between the numerical result and experimental data for laminarflame speed prediction, deviations are discovered at fuel-rich region and increased initial temperature. For the ignition delay time, deviations are found in the low-temperature and low pressure regime. The empirical equations considering the influence of initial temperature,pressure and equivalence ratio are developed for laminar flame speed and ignition delay times. The influence of major compositions such as CO, H2 and hydrocarbons are discussed in details in the thesis. Furthermore, a simplified kinetic model is developed and optimized based on the evaluation of existing kinetics for GBG fuel combustion. The simplified kinetic model is expected to be used for simulating the complexc ombustion process of GBG fuel in future studies. / <p>QC 20150511</p>

<p>Nanotechnology is a relatively new research topic that attracts increasing interest from scientists and engineers all over the world, due to its novel applications. The use of nanomaterials has extended to a broad range of applications, for example chemical synthesis, microporous media synthesis and catalytic combustion, contributing to achievement of improved or promising results. Microemulsion (ME) is considered a powerful tool for synthesis of nanomaterials, due to its unique properties. This thesis concentrates on the use of the ME as a catalyst synthesis route for obtaining metal nanoparticles for two challenging concepts: Hydrogen production by a membrane reactor and selective catalytic oxidation (SCO) of ammonia in gasified biomass.</p><p>Particularly for the scope of the fist concept presented in this thesis, palladium nanoparticles were synthesised from ME in order to be deposited on zeolite composite membranes to improve the H₂ / CO₂ separation (hydrogen production) ability. The membranes impregnated with Pd nanoparticles were then tested in a metal reactor for the permeance and selectivity towards H₂ and CO₂. Regarding the second concept, cerium-lanthanum oxide nanoparticles were prepared by conventional methods and from ME in order to be tested for their activity towards SCO of ammonia in gasified biomass.</p><p>The environmental importance of these two applications under investigation is great, since both are involved in processes contributing to the minimisation of the harmful exhaust gases released to the atmosphere from numerous industrial applications, such as the oil industry and heat-and-power production (for example combustion of natural gas or biomass in a gas turbine cycle). Regarding these applications, separation and capture of CO₂ from exhaust gases and oxidation of the fuel-bound ammonia in gasified biomass directly to nitrogen, minimising at the same time NO_xformation, are rated as very important technologies. The results obtained from this work and presented analytically in this thesis are considered successful and at the same time promising, since further research on the ME method can even lead to improvement of the current achievements.</p><p>The first part (Chapter 2) of the thesis gives a general background on the ME method and the applications in the two concepts under investigation. Additionally, it describes how the nanoparticles corresponding to the concepts were synthesised.</p><p>The second part (Chapter 3) of the thesis describes the different Pd-nanoparticle impregnation methods on the zeolite composite membranes and the results obtained form the permeation tests. In parallel with impregnation methods, various aspects that affect the Pd impregnation efficiency and the membrane performance such as duration, temperature and calcination conditions are discussed thoroughly.</p><p>The third and final part of the thesis (Chapter 4) concerns the preparation of the cerium-lanthanum oxide catalysts and the activity tests (under simulated gasified biomass fuel conditions) carried out in order to monitor the activity of these catalysts towards the SCO of ammonia. Additionally, a comparison of the activity between identical catalysts prepared by conventional methods and the ME method is discussed.</p>

Nanotechnology is a relatively new research topic that attracts increasing interest from scientists and engineers all over the world, due to its novel applications. The use of nanomaterials has extended to a broad range of applications, for example chemical synthesis, microporous media synthesis and catalytic combustion, contributing to achievement of improved or promising results. Microemulsion (ME) is considered a powerful tool for synthesis of nanomaterials, due to its unique properties. This thesis concentrates on the use of the ME as a catalyst synthesis route for obtaining metal nanoparticles for two challenging concepts: Hydrogen production by a membrane reactor and selective catalytic oxidation (SCO) of ammonia in gasified biomass. Particularly for the scope of the fist concept presented in this thesis, palladium nanoparticles were synthesised from ME in order to be deposited on zeolite composite membranes to improve the H2 / CO2 separation (hydrogen production) ability. The membranes impregnated with Pd nanoparticles were then tested in a metal reactor for the permeance and selectivity towards H2 and CO2. Regarding the second concept, cerium-lanthanum oxide nanoparticles were prepared by conventional methods and from ME in order to be tested for their activity towards SCO of ammonia in gasified biomass. The environmental importance of these two applications under investigation is great, since both are involved in processes contributing to the minimisation of the harmful exhaust gases released to the atmosphere from numerous industrial applications, such as the oil industry and heat-and-power production (for example combustion of natural gas or biomass in a gas turbine cycle). Regarding these applications, separation and capture of CO2 from exhaust gases and oxidation of the fuel-bound ammonia in gasified biomass directly to nitrogen, minimising at the same time NOx formation, are rated as very important technologies. The results obtained from this work and presented analytically in this thesis are considered successful and at the same time promising, since further research on the ME method can even lead to improvement of the current achievements. The first part (Chapter 2) of the thesis gives a general background on the ME method and the applications in the two concepts under investigation. Additionally, it describes how the nanoparticles corresponding to the concepts were synthesised. The second part (Chapter 3) of the thesis describes the different Pd-nanoparticle impregnation methods on the zeolite composite membranes and the results obtained form the permeation tests. In parallel with impregnation methods, various aspects that affect the Pd impregnation efficiency and the membrane performance such as duration, temperature and calcination conditions are discussed thoroughly. The third and final part of the thesis (Chapter 4) concerns the preparation of the cerium-lanthanum oxide catalysts and the activity tests (under simulated gasified biomass fuel conditions) carried out in order to monitor the activity of these catalysts towards the SCO of ammonia. Additionally, a comparison of the activity between identical catalysts prepared by conventional methods and the ME method is discussed. / QC 20101216

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. / QC 20100504