Through biomass gasification, biomass can be converted at high temperature to a product gas rich in carbon monoxide, hydrogen, and methane. After cleaning and upgrading, the product gas can be converted to biofuels such as hydrogen; methanol; dimethyl ether; and synthetic diesel, gasoline, and natural gas. Particulate matter (PM) is formed as a contaminant in the gasification process, and the aim of this work was to develop and apply a method for sampling and characterization of PM in the hot product gas.   A particle measurement system consisting of a dilution probe combined in series with a bed of granular activated carbon for tar adsorption was developed, with the aim of extracting a sample of the hot product gas without changing the size distribution and composition of the PM. The mass size distribution and concentration, as well as the morphology and elementary composition, of PM in the size range 10 nm to 10 µm in the product gas from a bubbling fluidized bed (BFB) gasifier, a circulating fluidized bed (CFB) gasifier and an indirect BFB gasifier using various types of biomass as fuel were determined.   All gasifiers and fuels displayed a bimodal particle mass size distribution with a fine mode in the <0.5 µm size range and a coarse mode in the >0.5 µm size range. Compared with the mass concentration of the coarse mode the mass concentration of the fine mode was low from all gasifiers. The evaluation of the results for the fine-mode PM was complicated by condensing potassium chloride for the CFB gasifier when using miscanthus as fuel and by condensing tars for the indirect BFB gasifier when using wood C as fuel. The mass concentration of the coarse-mode PM was higher from the CFB gasifier than from the two BFB gasifiers. The coarse-mode PM from the BFB gasifier when using wood A as fuel was dominated by char. In the CFB gasifier the coarse-mode PM was mainly ash and bed material when using all fuels. The coarse-mode PM from the indirect BFB gasifier when using wood C as fuel was mainly ash.

Environmental concerns and energy security are two major forces driving the fossil fuel based energy system towards renewable energy. In this context, hydrogen is gaining more and more attention in this 21st century. Presently, hydrogen is produced from reformation of fossil fuels, a process that could not address above two problems. For this it needs to be produced from a renewable carbon neutral energy source. Biomass has been identified as such a renewable energy source. Conversion of biomass through thermo-chemical gasification process in the presence of steam could provide a viable renewable source of hydrogen. This thesis presents an innovative system based on chemical looping gasification for producing hydrogen-enriched gas from biomass. The other merit of this system is that it produces a pure stream of carbon dioxide by conducting in-process capture and regeneration of sorbent. A laboratory scale chemical looping gasification (CLG) system based on a circulating fluidized bed (CFB) is developed and tested. Experiments conducted to gasify sawdust in CFB-CLG system shows that it could produce a gas with as much as 80% hydrogen and as little as 5% carbon dioxide. A kinetic model is developed to predict the performance of the gasifier of a CFB-CLG system, and is validated against experimental results. To understand the science of biomass gasification in the presence of steam and CaO, a number of additional studies are conducted. It show that for higher hydrogen and lower carbon dioxide concentration in the product gas, the optimum values of steam to biomass ratio, sorbent to biomass ratio, and operating temperature are 0.83, 2.0 and 670oC respectively. In CFB-CLG system the sorbent goes through a series of successive calcination-carbonation cycles. Calcination studies in presence of three alternate media, nitrogen, carbon dioxide and steam show, that steam calcination is best among them. An empirical relation for calcination in presence of three media is developed. Owing to the sintering, irrespective of medium used for calcination, the conversion of CaO reduces progressively as it goes through alternate calcination-carbonation cycles. An additional empirical equation is developed to predict the loss in sorbent’s ability during carbonation.

Im Rahmen der Arbeit werden Modelle zur Beschreibung des stationären und instationären Betriebsverhaltens der Komponenten der Vergasungsinsel - Bunker, Druckschleuse, Einspeisebehälter, Vergaser, Quench, Venturi-Wäscher, Teilverdampfer und Abscheider - in der Modellierungsumgebung Modelica/Dymola entwickelt. Im Vordergrund steht dabei die Entwicklung eines Modells des SFGT-Vergasers, das den Wärmeeintrag in den Kühlschirm berücksichtigt. Die verwendete Modellierungstiefe der einzelnen Komponenten ermöglicht die Erfassung des Einflusses aller wesentlichen Größen. Damit wird sowohl die genaue Beschreibung einzelner Anlagenkomponenten der Vergasungsinsel als auch die Beschreibung der gegenseitigen Wechselwirkungen ermöglicht. Mit dem entwickelten Modell des SFGT-Vergasers werden umfassende Untersuchungen zum Wärmeeintrag in den Kühlschirm durchgeführt.

No description available.

The significant generation of municipal solid waste (MSW) has become a controversial global issue. Pyrolysis and gasification technologies for treating rejects from solid waste disposal sites (SWDSs), for which over 50 % of MSW is attributed to combustible species, have attracted considerable attention. MSW is an alternative energy source that can partly replace fossil resources; there is an increasing awareness that global warming caused by the utilization of fossil resources is occurring. The goal of this thesis is to realize the efficient and rational utilization of MSW and decrease the harmful impact of pollutants, such as dioxin, HCl, and CO2, on the environment. To achieve this goal, some fundamental studies have been experimentally and numerically conducted to enhance the understanding of the properties of municipal solid waste thermal conversion. In this thesis, the pyrolysis behaviors of single pelletized recovered fuel were tested. A detailed comparison of the pyrolysis behaviors of typical recovered solid waste and biomass particles was conducted. A swelling phenomenon with a swelling ratio of approximately 1.6 was observed on the surface of pelletized recovered fuels. Subsequently, a particle model was constructed to describe the thermal conversion process for large recovered fuel particles that are composed of a high fraction of polyethylene (PE) and a comparable low fraction of cardboard. The results indicate that an understanding of the heat transfer mechanism in highly porous and molten structures and the selection of a heat transfer model are crucial for accurate prediction of the conversion process. MSW pyrolysis is a promising method for producing liquid products. With the exception of lignocellulosic materials, such as printing paper and cardboard, PE, polystyrene (PS), polypropylene (PP), polyethylene terephthalate (PET), and polyvinyl chloride (PVC) are the six main polymers in domestic waste in Europe. Characterization studies of the products obtained from these individual components, such as PE, PET, PVC, printing paper, and cardboard, have been conducted on a pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) system and a fixed-bed reactor. The possible pathways for the formation of the main primary/secondary products in rapid and conventional pyrolysis were also discussed. MSW steam gasification with CaO was performed in a batch-type fixed-bed gasifier to examine the effect of CaO addition on the heat transfer properties, pollutant removal, and devolatilization and char gasification behaviors in the presence of steam. A new carbon capture and recycle (CCR) system combined with an integrated municipal solid waste system was proposed. The foundation of the system is the development of a novel method to remediate CO2 using a high-temperature process of reforming CH4 and/or O2 and/or H2O without catalysts. Thermodynamic and experimental studies were performed. High temperatures significantly promoted the multi-reforming process while preventing the problem of catalyst deactivation. Potential improvements in the efficiency of the novel technology can be achieved by optimizing the reforming reactants. Landfill gas (LFG) and fuel gas from bio-waste treatment contain a considerable fraction of CH4, which may be a source of CH4 for this process. / <p>QC20141028</p>

It is recognised that the reactions with steam and CO2 are the rate limiting step during coal gasification, and a vast number of studies has been dedicated to the kinetics of these reactions. Most studies were carried out by using a single reactant (CO2 or H2O), either pure or diluted with an inert gas. Research using gas mixtures of CO2 and steam and their effects on gasification kinetics have been undertaken but are limited. The objective of this study is to determine the effects of CO2 on the steam gasification rate of a typical Highveld seam 4 coal. The South African medium ranked high volatile bituminous coal was charred at 950 °C. 2.0 g samples of ± 1 mm particles were analysed in a modified large particle thermo gravimetric analyser under various reactant gas concentrations. Experiments were conducted at atmospheric pressure (87.5 kPa) and temperatures from 775 to 900 °C, such that the conversion rate was controlled by chemical reaction. Reagent mixtures of steam-N2, steam-CO2 and CO2-N2 at concentrations of 25-75 mol%, 50-50 mol%, 75-25 mol% and 100 mol% were investigated. Arrhenius plots for steam and CO2 gasification produced activation energy values of 225 ± 23 kJ/mol and 243 ± 32 kJ/mol respectively. The calculated reaction orders with respect to reagent partial pressure were 0.44 ± 0.08 and 0.56 ± 0.07 for steam and CO2 respectively. Comparisons of the experimental data showed a higher reaction rate for the steam-CO2 mixtures compared to steam-N2 experiments. The semi empirical Wen model (m = 0.85) with an additive Langmuir-Hinshelwood styled rate equation predicted the mixed reagent gasification accurately. Reaction constants that were determined from the pure reactant experiments could directly be applied to predict the results for the experiments with mixtures of steam and CO2. The conclusion was made that under the investigated conditions steam and CO2 reacts simultaneously on different active sites on the char surface. / Thesis (MIng (Chemical Engineering))--North-West University, Potchefstroom Campus, 2013.

It is recognised that the reactions with steam and CO2 are the rate limiting step during coal gasification, and a vast number of studies has been dedicated to the kinetics of these reactions. Most studies were carried out by using a single reactant (CO2 or H2O), either pure or diluted with an inert gas. Research using gas mixtures of CO2 and steam and their effects on gasification kinetics have been undertaken but are limited. The objective of this study is to determine the effects of CO2 on the steam gasification rate of a typical Highveld seam 4 coal. The South African medium ranked high volatile bituminous coal was charred at 950 °C. 2.0 g samples of ± 1 mm particles were analysed in a modified large particle thermo gravimetric analyser under various reactant gas concentrations. Experiments were conducted at atmospheric pressure (87.5 kPa) and temperatures from 775 to 900 °C, such that the conversion rate was controlled by chemical reaction. Reagent mixtures of steam-N2, steam-CO2 and CO2-N2 at concentrations of 25-75 mol%, 50-50 mol%, 75-25 mol% and 100 mol% were investigated. Arrhenius plots for steam and CO2 gasification produced activation energy values of 225 ± 23 kJ/mol and 243 ± 32 kJ/mol respectively. The calculated reaction orders with respect to reagent partial pressure were 0.44 ± 0.08 and 0.56 ± 0.07 for steam and CO2 respectively. Comparisons of the experimental data showed a higher reaction rate for the steam-CO2 mixtures compared to steam-N2 experiments. The semi empirical Wen model (m = 0.85) with an additive Langmuir-Hinshelwood styled rate equation predicted the mixed reagent gasification accurately. Reaction constants that were determined from the pure reactant experiments could directly be applied to predict the results for the experiments with mixtures of steam and CO2. The conclusion was made that under the investigated conditions steam and CO2 reacts simultaneously on different active sites on the char surface. / Thesis (MIng (Chemical Engineering))--North-West University, Potchefstroom Campus, 2013.

Coal, as energy resource, possesses numerous characteristics and properties which all have an influence on its gasification behaviour. The two properties considered critically important when evaluating a coal source for gasification are its mineral content and slagging behaviour. Research has indicated that slag formation can be inhibited or even prevented by the addition of a fluxing agent. It is thus of great importance to understand the mineral interaction during gasification, in order to select a suitable fluxing agent for the prevention of slagging and clinker formation in the gasifier. The aim of this dissertation is to evaluate the slagging properties of a coal source with the addition of iron as a fluxing agent and to study the transformation of the mineral and added iron during gasification. A pre-determined amount of elemental iron (between 2 and 20 percentage by mass) was added to three different coal samples obtained from Sasol's operations in South Africa. The transformation of the iron in conjunction with the possible iron-containing minerals present in the coal was studied by means of Mossbauer spectroscopy. Typical characterisation analyses were also carried out on the original coal samples. The ash fusion temperature analyses (AFT) were used to study the slagging behaviour of the iron-spiked coal samples. Even though AFT analyses only provide an average flow property, it gives a good indication of the changes that the iron addition induces in coal properties. FactSage modelling was carried out in conjunction with the Mossbauer and AFT analyses. The AFT analysis on all of the samples indicated that the iron addition led to a 20% decrease in the AFT of all three the coal samples. The decrease observed, can be attributed to three main reasons: Formation of lower melting iron-containing phases, bridging of oxygen bonds by FeO and Fe203and the lowering of the viscosity by the iron-oxides, mainly hematite. Mossbauer spectra of the three original coal samples indicated that pyrite was the only iron-bearing mineral present / Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2009.

The production of synthetic fuels (synfuels) in coal–to–liquids (CTL) facilities has contributed to global warming due to the huge CO2 emissions of the process. This corresponds to inefficient carbon conversion, a problem growing in importance particularly given the limited lifespan of coal reserves. These simultaneous challenges of environmental sustainability and energy security associated with CTL facilities have been defined in earlier studies. To reduce the environmental impact and improve the carbon conversion of existing CTL facilities, this paper proposes the concept of a nuclear–assisted CTL plant where a hybrid sulphur (HyS) plant powered by 10 modules of the high temperature nuclear reactor (HTR) splits water to produce hydrogen (nuclear hydrogen) and oxygen, which are in turn utilised in the CTL plant. A synthesis gas (syngas) plant mass–analysis model described in this paper demonstrates that the water–gas shift (WGS) and combustion reactions occurring in hypothetical gasifiers contribute 67% and 33% to the CO2 emissions, respectively. The nuclear–assisted CTL plant concept that we have developed is entirely based on the elimination of the WGS reaction, and the consequent benefits are investigated. In this kind of plant, the nuclear hydrogen is mixed with the outlet stream of the Rectisol unit and the oxygen forms part of the feed to the gasifier. The significant potential benefits include a 75% reduction in CO2 emissions, a 40% reduction in the coal requirement for the gasification plant and a 50% reduction in installed syngas plant costs, all to achieve the same syngas output. In addition, we have developed a financial model for use as a strategic decision analysis (SDA) tool that compares the relative syngas manufacturing costs for conventional and nuclear–assisted syngas plants. Our model predicts that syngas manufactured in the nuclear–assisted CTL plant would cost 21% more than that produced in the conventional CTL plant when the average cost of producing nuclear hydrogen is US$3/kg H2. The model also evaluates the cost of CO2 avoided as $58/t CO2. Sensitivity analyses performed on the costing model reveal, however, that the cost of CO2 avoided is zero at a hydrogen production cost of US$2/kg H2 or at a delivered coal cost of US$128/t coal. The economic advantages of the nuclear–assisted plant are lost above the threshold cost of $100/t CO2. However, the cost of CO2 avoided in our model works out to below this threshold for the range of critical assumptions considered in the sensitivity analyses. Consequently, this paper demonstrates the practicality, feasibility and economic attractiveness of the nuclear–assisted CTL plant. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2011.

Coal, as energy resource, possesses numerous characteristics and properties which all have an influence on its gasification behaviour. The two properties considered critically important when evaluating a coal source for gasification are its mineral content and slagging behaviour. Research has indicated that slag formation can be inhibited or even prevented by the addition of a fluxing agent. It is thus of great importance to understand the mineral interaction during gasification, in order to select a suitable fluxing agent for the prevention of slagging and clinker formation in the gasifier. The aim of this dissertation is to evaluate the slagging properties of a coal source with the addition of iron as a fluxing agent and to study the transformation of the mineral and added iron during gasification. A pre-determined amount of elemental iron (between 2 and 20 percentage by mass) was added to three different coal samples obtained from Sasol's operations in South Africa. The transformation of the iron in conjunction with the possible iron-containing minerals present in the coal was studied by means of Mossbauer spectroscopy. Typical characterisation analyses were also carried out on the original coal samples. The ash fusion temperature analyses (AFT) were used to study the slagging behaviour of the iron-spiked coal samples. Even though AFT analyses only provide an average flow property, it gives a good indication of the changes that the iron addition induces in coal properties. FactSage modelling was carried out in conjunction with the Mossbauer and AFT analyses. The AFT analysis on all of the samples indicated that the iron addition led to a 20% decrease in the AFT of all three the coal samples. The decrease observed, can be attributed to three main reasons: Formation of lower melting iron-containing phases, bridging of oxygen bonds by FeO and Fe203and the lowering of the viscosity by the iron-oxides, mainly hematite. Mossbauer spectra of the three original coal samples indicated that pyrite was the only iron-bearing mineral present / Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2009.