<p>CO₂ concentration in the atmosphere poses a great threat to life on earth as we know it. The reduction of CO₂ concentration is key to avoid the critical turning point of 1.5^oC temperature increase highlighted by Intergovernmental Panel on Climate Change (IPCC). Gasification using CO₂ as reacting agent can potentially reduce the CO₂ concentration in the atmosphere. Naturally, biomass such as corn, uses great amounts of CO₂ for photosynthesis and produces O₂; hence, energy and fuel production using biomass can potentially be classified as carbon neutral. Moreover, if CO₂ is used as the gasifying agent, gasification can effectively be carbon-negative and collaborate to the reduction of CO2 in the atmosphere.</p> <p>The major setback of using CO₂ biomass gasification is the energy-intensive reaction between C + CO₂ -> 2CO. This reaction at atmospheric pressure and room temperature is heavily tilted towards producing char and CO2. The current investigation describes efforts to favor the right hand side of the reaction by using simple impregnation techniques and cost-effective catalysts to reduce the energy requirements of the reaction. Also, parameters such as pressure are explored to tilt the balance towards the production of CO. Corn stover is selected as the biomass for the present research due to its wide use and availability in the US.</p> <p>The results show that by using catalysts such as iron nitrate and sodium aluminate, the temperature required to achieve substantial char conversion is reduced. Also, increasing the pressure of the reactor, the temperature can be substantially decreased by 100 K and 150 K. The structure and chemical composition of the chars is studied to explain the differences in the reaction rate between chars. Further, chemical kinetics are calculated to compare the present work with previous work in the literature. Finally, data-driven analysis of the gasification data is explored. The appendices provide supplementary information on the application of deep learning to CO₂ recycling using turbulent flames and efforts to reduce the flame spread rate over a pool of Jet A by using Multi Walled Carbon Nanotubes (MWCNTS).</p>

Orientador: José Luz Silveira / Banca: Celso Eduardo Tuna / Banca: José Antonio Perrella / Banca: Wendell de Queiróz Lamas / Banca: Ricardo Alan Verdú Ramos / Resumo: Os níveis significativamente elevados dos subprodutos disponíveis (bagaço e palha) no processamento da cana-de-açúcar oferecem um potencial atrativo para o uso de sistemas que utilizem um gaseificador de biomassa integrado a um ciclo combinado (BIG - GTCC). Neste trabalho propõe-se estudar a incorporação do processo de gaseificação de biomassa para uso em sistema de cogeração com ciclo combinado aplicado ao setor sucroalcooleiro. Foram realizados estudos energéticos, econômicos e ecológicos da incorporação do sistema BIG - GTCC como alternativa para o aumento da oferta de produção de eletricidade em uma típica indústria sucroalcooleira do Brasil. Propõe-se o suo de uma tecnologia de pré-tratamento do bagaço para superar os problemas técnicos existentes ao alimentar, de forma contínua, o reator de gaseificação de bagaço. Na análise econômica, determina-se, inicialmente, o custo de produção de gás de síntese, permitindo alocar os custos de produção de eletricidade, energia mecânica e calor de processo no sistema proposto, considerando três configurações. Na etapa final, são determinadas as emissões de poluentes, o dióxido de carbono equivalente, o indicador de poluição e a eficiência ecológica da planta utilizando o processo de gaseificação com ciclo combinado ao setor. Conclui-se que a aplicação do processo de gaseificação apenas do excedente de bagaço em fluxo de arraste com pré-tratamento de torrefação apresenta-se como a melhor das opções propostas, tanto do ponto de vista termodinâmico, como do econômico e do ecológico / Abstract: The significantly elevated levels of byproducts (bagasse and trash) currently available in the sugar cane industries offer an attractive potential for the use of the BIG - GTCC in the sugar industry. This work aims to make an energetic, economic and ecological studies of the BIG -GTCC (Biomass Integrated Gasifier - Gas Turbine Combined Cycle) system incorporation in the sugar cane industry, as an alternative to increase the levels of electricity generation in this sector. A new technology for the bagasse pre-treatment is proposed in order to overcome the technical problems observed during the continuous feeding of gasifier with sugarcane bagasse as a setting for coupling the gasifier with the sugarcane mill. An energetic analysis of the proposed system was performed. The study also identified the production cost of the synthesis gas, as well as allocated the electricity, heat, and mechanical energy production cost in the proposed system, considering the three studied cases. In the final phase, the pollutant emissions, the carbon dioxide equivalent, the pollution indicator, and the ecological efficiency of the incorporation of the cogeneration process with combined cycle in the traditional Brazilian sugar industries were determined. The main result of the study was that the application of the configuration, where only the surplus bagasse of the conventional plant is gasified in an entrained flow reactor, after pretreatment of the bagasse through a torrefaction process, appears to be economically, ecologically, and technically the best of the proposed options / Doutor

Call number: LD2668 .T4 1979 U57 / Master of Science

In recent years, there is a rapid growing interest in the use of biomethane for the transport sector. A new method of combining anaerobic digestion and biomass gasification is proposed.The feasibility study shows that more biomethane can be produced; resulting in an increase in the revenue compared to individual biogas plants. The GoBiGas project,which is initiated by Göteborg Energi, adopted another method based on gasification, water gas shift and methanation to enable biomethane production from forest residue. The aim of the present study is to investigate the economic viability of the new method when compared with the GoBiGas (Gothenburg Biomass Gasification) process. For this study, a model of GoBiGas process was developed in Aspen Plus to perform the technical analysis, in which the overall efficiency and exergy efficiency were calculated at different moisture contents of biomass. For the economic analysis, the annual revenue was also estimated during the study. The results show that the overall efficiency of the new method is higher than the efficiency of the GoBiGas process and there is more production of biomethane from the new process.

Fossil fuels continue to deplete with use as they are irreplaceable. In addition, the environmental impact with the continuous use of these conventional fuels has generated global concern due to the production of harmful emission gases. An alternative source of energy has become inevitable. Technological advancements in the area of biomass use for both aviation and power generation are at different levels of development. There is however the need for an integrated approach to assess gas turbine engine behaviour in terms of performance, emission and economics when they are running on biofuels. The current research work is concerned with finding alternative fuel resources for use on stationary gas turbine engines for power generation with the necessary identification of suitable biofuels using a multidisciplinary approach. A techno-economic, environmental and risk assessment (TERA) model comprising the performance, emissions, economics and risk modules has been developed. There had been several simulations of two gas turbine engines (GTEs) to ascertain the effects of both ambient and operating conditions and the effect of fuel types on the engines. These simulations were done with the use of an in-house code-the Turbomatch and a code developed for the steam cycle which is employed for the combined cycle simulation. Cont/d.

Increasing the share of biomass, preferably by replacing fossil fuels, is one way to mitigate the present climate change. Fossil coal can be directly replaced by co-combustion of coal and biomass and fossil engine fuels (gasoline and diesel) could potentially partly be replaced by synthetic renewable fuels produced via entrained flow gasification of biomass. The use of biomass in these processes is so far limited, partly because of the fibrous and hygroscopic nature of biomass which leads to problem in storing, transportation, handling and feeding. This thesis demonstrates how the challenging characteristics of raw biomass are mitigated by the pretreatment method torrefaction. Torrefaction is a process where biomass is heated in an oxygen deficient atmosphere to typically between 240 and 350°C for a time period of 2 minutes to 1 hour. Most of the torrefaction R&amp;D in the literature have so far been performed with bench-scale batch reactors. For the purpose of carefully studying continuous torrefaction, a 20 kg/h torrefaction pilot plant was therefore designed, constructed and evaluated. The overall conclusion from this thesis is that the many benefits of torrefied biomass are valid also when produced with a continuous pilot plant and for typically Swedish forest biomasses. Some of the documented improved biomass properties are increased heating value, increased energy density, higher friability (lower milling energy) and less hydrophilic biomass (less moisture uptake). Most of the improvements can be attributed to the decomposition of hemicellulose and cellulose during torrefaction. The most common variables for describing the torrefaction degree are mass yield or anhydrous weight loss but both are challenging to determine for continuous processes. We therefore evaluated three different methods (one existing and two new suggestions) to determine degree of torrefaction that not require measurement of mass loss. The degree of torrefaction based on analyzed higher heating value of the raw and torrefied biomass (DTFHHV) predicted mass yield most accurate and had lowest combined uncertainty. Pelletizing biomass enhance transportation and handling but results from pelletization of torrefied biomass is still very limited in the literature and mainly reported from single pellet presses. A pelletization study of torrefied spruce with a ring die in pilot scale was therefore performed. The bulk energy density was found to be 14.6 GJ/m3 for pelletized torrefied spruce (mass yield 75%), a 40% increase compared to regular white pellets and therefore are torrefied pellets more favorable for long distance transports. More optimization of the torrefied biomass and the pelletization process is though needed for acquiring industrial quality pellets with lower amount of fines and higher pellet durability than attained in the present study. Powders from milled raw biomass are generally problematic for feeding and handling and torrefied biomass has been proposed to mitigate these issues. The influence of torrefaction and pelletization on powder and particle properties after milling was therefore studied. The results show that powder from torrefied biomass were enhanced with higher bulk densities, lower angle of repose as well as smaller less elongated particles with less surface roughness. Even higher powder qualities were achieved by pelletizing the torrefied biomass before milling, i.e. another reason for commercial torrefied biomass to be pelletized. Entrained flow gasification (EFG) is a promising option for conversion of biomass to other more convenient renewable energy carriers such as electricity, liquid biofuels and green petrochemicals. Also for EFGs are torrefied fuels very limited studied. Raw and torrefied logging residues were successfully gasified in a pilot scale pressurized entrained flow biomass gasifier at 2 bar(a) with a fuel feed corresponding to 270 kWth. Significantly lower methane content (50% decrease) in the syngas was also demonstrated for the torrefied fuel with mass yield 49%. The low milling energy consumption for the torrefied fuels compared to the raw fuel was beneficial for the gasification plant efficiency.

<p>Tanzania has a characteristic developing economy, which is dependent on agricultural productivity.  About 90% of the total primary energy consumption of the country is from biomass.  Since the biomass is mostly consumed at the household level in form of wood fuel, it is marginally contributing to the commercial energy supply.  However, the country has abundant energy resources from hydro, biomass, natural gas, coal, uranium, solar, wind and geothermal.  Due to reasons that include the limited technological capacity, most of these resources have not received satisfactory harnessing.  For instance: out of the estimated 4.7GW macro hydro potential only 561MW have been developed; and none of the 650MW geothermal potential is being harnessed.  Furthermore, besides the huge potential of biomass (12 million tons of oil equivalent), natural gas (45 million cubic metres), coal (1,200 million tones), high solar insolation (4.5 – 6.5 kWh/m²), 1,424km of coastal strip, and availability of good wind regime (> 4 m/s wind speed), they are marginally contributing to the production of commercial energy.  Ongoing exploration work also reveals that the country has an active system of petroleum and uranium.  On the other hand, after commissioning the 229km natural gas pipeline from SongoSongo Island to Dar es Salaam, there are efforts to ensure a wider application in electricity generation, households, automotive and industry.</p><p> </p><p>Due to existing environmental concerns, biomass resource is an attractive future energy for the world, Tanzania inclusive.  This calls for putting in place sustainable energy technologies, like gasification, for their harnessing.  The high temperature gasification (HTAG) of biomass is a candidate technology since it has shown to produce improved syngas quality in terms of gas heating value that has less tar.</p><p> </p><p>This work was therefore initiated in order to contribute to efforts on realizing a commercial application of biomass in Tanzania.  Particularly, the work aimed at establishing characteristic properties of selected biomass feedstock from Tanzania.  The characteristic properties are necessary input to thermochemical process designers and researchers.  Furthermore, since the properties are origin-specific, this will provide baseline data for technology transfer from north to south.  The characteristic properties that were established were chemical composition, and thermal degradation behaviour.  Furthermore, laboratory scale high temperature gasification of the biomasses was undertaken.</p><p> </p><p>Chemical composition characteristics was established to palm waste, coffee husks, cashew nut shells (CNS), rice husks and bran, bagasse, sisal waste, jatropha seeds, and mango stem.  Results showed that the oxygen content ranged from 27.40 to 42.70% where as that of carbon and hydrogen ranged from 35.60 to 56.90% and 4.50 to 7.50% respectively.  On the other hand, the elemental composition of nitrogen, sulphur and chlorine was marginal.  These properties are comparable to findings from other researchers.  Based on the results of thermal degradation characteristics, it was evident that the cashew nut shells (CNS) was the most reactive amongst the analyzed materials since during the devolatilization stage the first derivative TG (DTG) peak due to hemicellulose degradation reached (-5.52%/minute) compared palm stem whose first peak was -4.81%/minute.  DTG first peak for the remaining materials was indistinct.</p><p> </p><p>Results from the laboratory gasification experiments that were done to the coffee husks showed that gasification at higher temperature (900°C) had an overall higher gasification rate.  For instance, during the inert nitrogen condition, 7% of coffee husk remained for the case of 900°C whereas the residue mass for the gasification at 800 and 700°C was 10 and 17% respectively.  Steam injection to the biomass under high temperature gasification evolved the highest volumetric concentration of carbon monoxide.  The CO peak evolution at 900°C steam only was 23.47 vol. % CO whereas that at 700°C was 21.25 vol. % CO.  Comparatively, the CO peaks for cases without steam at 900°C and 2, 3, and 4% oxygen concentrations were 4.59, 5.93, and 5.63% respectively.  The reaction mechanism of coffee husks gasification was highly correlated to zero reaction order exhibiting apparent activation energy and the frequency factor 161 kJ/mol and 3.89x10⁴/minute respectively.</p> / QC 20100923

Pressurised entrained-flow gasification (PEFG) of woody biomass has the potential to produce high purity syngas for the production of vital chemicals, e.g., biofuels. However, ash-related issues such as reactor blockages and refractory corrosion need to be addressed before this potential can be realised from a technical perspective. These undesirable consequences can be brought about by slag formation involving inorganic ash-forming elements and the chemical transformations that they undergo during fuel conversion. The objective of this study was to elucidate the ash transformations of the major ash-forming elements and the slag formation process. A pilot-scale PEFG reactor was used as the basis of the study, gasifying different woody biomass-based fuels including wood, bark, and a bark/peat mixture. Different ash fractions were collected and chemically analysed. Reactor slags had elemental distributions differing from that of the fuel ash, indicating the occurrence of fractionation of ash material during fuel conversion. Fly ash particles from a bark campaign were also heterogeneous with particles exhibiting differing compositions and physical properties; e.g., molten and crystalline formations. Si was consistently enriched in the reactor slags compared to other major ash-forming elements, while analyses of other ash fractions indicated that K was likely volatilised to a significant extent. In terms of slag behaviour, near-wall temperatures of approximately 1050-1200 °C inside the reactor were insufficient to form flowing ash slag for continuous extraction of ash material during firing the woody biomass fuels alone. However, fuel blending of a bark fuel with a silica-rich peat changed the chemical composition of the reactor slags and bulk slag flow behaviour was evident. Thermochemical equilibrium calculations supported the importance of Si in melt formation and in lowering solidus and liquidus temperatures of Ca-rich slag compositions that are typical from clean wood and bark. Viscosity estimations also showed the impact that solids have upon slag flow behaviour and corresponded qualitatively to the experimental observations. Corrosion of reactor refractory was observed. The mullite-based refractory of the reactor formed a slag with the fuel ash slag, which caused the former to flux away. Reactor blockages were also resultant because of the high viscosity of this slag near the outlet.  A preliminary study into the corrosion of different refractories was also carried out, based on firing a bark/peat mixture.  Alumina-rich refractories consisting of corundum, hibonite, mullite, and andalusite tended to form anorthite and exhibited varying degrees of degradation. Infiltration of slag was evident for all the samples and was a severe mode of degradation for some refractories. For fused-cast periclase and spinel-based refractories, slag infiltration was limited to voids and no extensive signs of refractory dissolution were found. This is also supported by a thermochemical equilibrium calculations mimicking slag infiltration that incorporated viscosity estimations. The findings from this thesis contribute towards the development of woody biomass PEFG by highlighting issues concerning ash fractionation, slag behaviours and ash\slash refractory interaction that should be investigated further.

With the current trend of CO2 mitigation in process industries, the primary goal of this thesis is to promote biomass as an energy and reduction agent source to substitute fossil sources in the steel industry. The criteria for this substitution are that the steel process retains the same function and the integrated energy efficiency is as high as possible. This work focuses on advanced gasification of biomass and waste for substitution of fossil fuels in steel industry heat treatment furnaces. To achieve this, two approaches are included in this work. The first investigates the gasification performance of pretreated biomass and waste experimentally using thermogravimetric analysis (TGA) and a pilot plant gasifier. The second assesses the integration of the advanced gasification system with a steel heat treatment furnace. First, the pyrolysis and char gasification characteristics of several pretreated biomass and waste types (unpretreated biomass, steam-exploded biomass, and hydrothermal carbonized biomass) were analyzed with TGA. The important aspects of pyrolysis and char gasification of pretreated biomass were identified. Then, with the objective of studying the gasification performance of pretreated biomass, unpretreated biomass pellets (gray pellets), steam-exploded biomass pellets (black pellets), and two types of hydrothermal carbonized biomass pellets (spent grain biocoal and horse manure biocoal) were gasified in a fixed bed updraft gasifier with high-temperature air/steam as the gasifying agent. The gasification performance was analyzed in terms of syngas composition, lower heating value (LHV), gas yield, cold gas efficiency (CGE), tar content and composition, and particle content and size distribution. Moreover, the effects on the reactions occurring in the gasifier were identified with the aid of temperature profiles and gas ratios. Further, the interaction between fuel residence time in the bed (bed height), conversion, conversion rate/specific gasification rate, and superficial velocity (hearth load) was revealed. Due to the effect of bed height on the gasification performance, the bed pressure drop is an important parameter related to the operation of a fixed bed gasifier. Considering the limited studies on this relationship, an available pressure drop prediction correlation for turbulent flow in a bed with cylindrical pellets was extended to a gasifier bed with shrinking cylindrical pellets under any flow condition. Moreover, simplified graphical representations based on the developed correlation, which could be used as an effective guide for selecting a suitable pellet size and designing a grate, were introduced. Then, with the identified positive effects of pretreated biomass on the gasification performance, the possibility of fuel switching in a steel industry heat treatment furnace was evaluated by effective integration with a multi-stage gasification system. The performance was evaluated in terms of gasifier system efficiency, furnace efficiency, and overall system efficiency with various heat integration options. The heat integration performance was identified based on pinch analysis. Finally, the efficiency of the co-production of bio-coke and bio-H2 was analyzed to increase the added value of the whole process. It was found that 1) the steam gasification of pretreated biomass is more beneficial in terms of the energy value of the syngas, 2) diluting the gasifying agent and/or lowering the agent temperature compensates for the ash slagging problem in biocoal gasification, 3) the furnace efficiency can be improved by switching the fuel from natural gas (NG) to syngas, 4) the gasifier system efficiency can be improved by recovering the furnace flue gas heat for the pretreatment, and 5) the co-production of bio-coke and bio-H2 significantly improves the system efficiency. / <p>QC 20160825</p>

<p style="text-align: justify;">U disertaciji je prikazan matematički model<br />gasifikacije otpadnih automobilskih pneumatika.<br />Modelom je istražen uticaj količine ubačenog vazduha<br />i vodene pare u gasifikator i temperatura gasifikacije<br />na prinos gasovitih produkata. Numerička procedura<br />je rije&scaron;ena Newton-Raphson metodom a brojne<br />vrijednosti molskih udjela gasovitih komponenata u<br />ravnotežnoj mje&scaron;avini dobijene su kori&scaron;ćenjem<br />programskog jezika C.<br />U drugom dijelu disertacije prikazano je<br />eksperimentalno ispitivanje pirolize otpadnih<br />automobilskih pneumatika. Eksperimentalni rezultati<br />ukazuju da na prinos gasa, odnosno na prinos čvrstog<br />(koksnog) ostatka značajno utiču parametri: veličina<br />čestice otpadne gume, temperatura pirolize i brzina<br />zagrijavanja uzorka.</p> / <p>The dissertation presents a mathematical model of<br />gasification of waste automotive tires. The model<br />examined the impact of the amount of the loaded air and<br />water vapor in the gasifier and gasification temperature<br />to yield gaseous products. The numerical procedure is<br />resolved Newton-Raphson method and the numerical<br />values of mole portions of gaseous components in the<br />equilibrium mixture obtained using the programming<br />language C.<br />In the second part of the thesis is shown<br />experimentally testing pyrolysis of waste automotive<br />tires. Experimental results indicate that the yield of gas,<br />or to yield a solid (coke) significantly affect the rest of the<br />parameters: the size of the particles of waste rubber<br />pyrolysis temperature and heating rate of the sample.</p>