Submitted by Nestor Proenza Perez null (nestor@feg.unesp.br) on 2016-07-25T14:02:32Z No. of bitstreams: 1 TESIS VERSÃO FINAL NESTOR PROENZA.pdf: 3806431 bytes, checksum: e67652e66d5b48b5104953feec776a66 (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-07-28T12:09:11Z (GMT) No. of bitstreams: 1 perez_np_dr_guara.pdf: 3806431 bytes, checksum: e67652e66d5b48b5104953feec776a66 (MD5) / Made available in DSpace on 2016-07-28T12:09:11Z (GMT). No. of bitstreams: 1 perez_np_dr_guara.pdf: 3806431 bytes, checksum: e67652e66d5b48b5104953feec776a66 (MD5) Previous issue date: 2016-06-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Neste trabalho foi realizada a caracterização física, geométrica e fluidodinâmica do bagaço de cana-de-açúcar visando o projeto e dimensionamento de um gaseificador de leito fluidizado borbulhante para pequena e média capacidade térmica (até 25 MW térmicos). As principais propriedades físicas e químicas como massa específica real, aparente e a granel, assim como os teores de umidade, cinzas, material volátil e carbono fixo presentes neste material foram determinadas aplicando normas vigentes para este tipo de resíduo. Também foi realizada uma caracterização geométrica através de técnicas de análise de imagens, determinando-se a esfericidade e razão de aspecto para todas as faixas de diâmetro de partículas estudadas, obtendo-se um valor médio de 0,39 no caso da esfericidade para o bagaço em seu estado natural. Através do estudo fluidodinâmico verificou-se que partículas de bagaço de cana com diâmetros característicos entre 0,59 – 9,5 mm não são fluidizáveis, apresentando uma tendência a coesão e formação de canais preferenciais. Foi constatado que o emprego dos modelos existentes até agora para a previsão da velocidade mínima de fluidização (Vmf), tanto para partículas de bagaço, quanto para misturas delas com material inerte, não preveem de forma adequada este parâmetro. Indicando erros entre 85% e mais de 100% em cada um desses caso, pelo que foram deselvolvidos dois novos modelos específicos para partículas de bagaço de cana e para misturas delas com areia, os quais previram com melhor exatidão os valores da (Vmf), com um erro máximo de 6,3%, para partículas de bagaço, e de até 30% para 88% das 25 condições experimentais testadas no caso de misturas. Conclui-se também que, para garantir uma boa fluidização, a fração em massa máxima de bagaço na mistura deve ser entre 2 - 5%. Uma nova metodologia é proposta baseada nos novos modelos desenvolvidos para a determinação da (Vmf), tornando possível o projeto e dimensionamento de gaseificadores de leito fluidizado borbulhante, sendo determinado que reatores trabalhando com misturas de bagaço e areia são 30% maiores que reatores empregando somente partículas de bagaço de cana-de-açúcar com uma eficiência a frio de 58,5%. / In this work is carried out a physical, geometric and fluid-dynamics characterization of sugarcane bagasse, aiming to design and sizing a bubbling fluidized bed gasifier for small and medium power (up to 25 MW thermal). The main physical and chemical properties as real density, bulk density and apparent density, as well as, the content of moisture, ash, volatile matter and fixed carbon present in the bagasse, were determined by applying the standars norms suitable for this type of residue. It was also made a geometric characterization by image analysis techniques, being determined the sphericity and aspect ratio for all diameter ranger of studied particles, obtaining an average value of 0.39 in the case of sphericity for bagasse in it is natural form. Through the fluid dynamic study it was found that bagasse particles with typical diameters between 0,59 – 9,5 mm are not fluidizable, showing a tendency to cohesion and formation of preferential channels. It has been found that the use of the existing models to date for determination of the minimum fluidization velocity for bagasse particles and for mixtures of them with inert, do not predict the right way this parameter, introduced errors of up to 85% to over 100% in both cases, therefore were developed two new models specifically for sugarcane bagasse particles and mixtures of them with sand, with a maximum error of 6.3% in the first case, and 30% for the 88% of the 25 experimental conditions tested in the case of mixtures. Concluding that to ensure a good fluidization, the maximum mass fraction of bagasse in the mixture should be between 2 - 5%. A new methodology is proposed based on the new models developed, making possible the design and dimensioning of the bubbling fluidized bed gasifier, determining that reactors working with mixtures of sugarcane bagasse and sand are 30% higher than reactors employing solely sugarcane bagasse particles, with a cold gas efficiency of 58.5%.

This thesis constitutes fundamental experimental and computational investigations on gasification and combustion in a packed bed of biomass. Packed bed gasification-combustion in counter-current mode is used in two applications -(1) Gasifier stove in reverse downdraft mode (or equivalently, top-lit updraft mode) that constitutes the idea behind efficient and clean burning domestic stoves. (2) Combustion-on moving grate for boiler application, studied widely in Europe. While a large part of the present study is around domestic stoves, a crucial part of the study aims to address the second application as an extension of the approach taken in the first part to clarify conflicting conclusions of earlier studies and explain the aero-thermochemical behavior over the entire range of superficial velocities, V s (this is velocity of air through the empty cross section of the reactor). Operational differences between the two applications lie in the range of superficial velocity -3.5 to 6 cm/s for domestic stoves and 15 to 30 cm/s for grate combustion. Lower values of Vs are chosen for domestic stoves to limit the particulate emissions; higher values of V s for combustion-on-grate to maximize the conversion rate. Present work deals with a fan based gasifier stove, Oorja, built by BP, India (currently transferred to FEPL, Pune) and disseminated to over 400,000 households between 2005 and 2009. The technology was developed at CGPL, IISc and transferred to BP for commercialization. Work reported in this thesis was started to resolve issues of higher CO emissions in char mode operation and occasional smoking during transition from flaming to char mode. The contribution of the thesis is split into two parts. (a) Use of the principles of gasification to improve the performance of the stoves to the highest possible level, balancing between efficiency and ash fusion issues for domestic and industrial applications and (b) fundamental studies to unravel the flame structure in the two-phase gasification-combustion process over the entire range of Vs. Improving the stove performance It has been known that in most free-convection based stoves, like three stone fire and others developed over the last two decades, the amount of energy extracted from the stove by a cooking pot, usually measured as water boiling efficiency, is between 15 to 35 % with CO emissions of more than 1.5 g/MJ. Oorja stove had demonstrated water boiling efficiency of 50 % and CO emissions of 0.75 g/MJ. Operational issues noticed in the field provided an opportunity to further improve the performance by conducting detailed thermo-chemical studies. Towards this, the components of water boiling efficiency in different phases and from different modes of heat transfer were determined. Optimizing the ratio of air flow rate between combustion air from top and gasification air through the grate (denoted by R) was the key to improving the performance. The maximum water boiling efficiency obtained was 62% with 0.53 g/MJ CO for a 320 mm diameter vessel; under these conditions, the first phase, termed flaming mode, involving pyrolysis-gasification-gas phase combustion contributed 45% to the total efficiency and 0.4 g/MJ CO at R = 4.8 and the second phase, termed char mode, involving char surface oxidation-gasification-gas phase combustion contributed 17% and 0.13 g/MJ CO at R = 1.9. Under optimal air flow conditions, efficiency depends on the size of the vessel used; reactive flow calculations were performed with fast chemistry (using mixture fraction approach) in a zone that includes the free space of the combustion chamber and the vessel to obtain the heat transfer efficiency and bring out the effect of vessel size. Experiments aimed at evaluating the performance of the stove on either side of stoichiometry, revealed that while the stove could be operated on the rich side, it was not possible to operate it on the lean side -it was always tending towards the stoichiometric point with enhanced power. Computational studies showed that increased air flow from the top caused enhanced recirculation around the fuel bed bringing more oxygen that reacted closer to the surface and transferred additional heat enhancing the pyrolysis rate, explaining the observed shift towards stoichiometry. An examination of literature showed that the energy balance for stoves had long remained unexplained (unaccounted losses in stoves were up to 40 %). Using the different components of efficiency obtained from experiments and computations, a heat balance was established to within 5%. This vast improvement in the heat balance is due to the fact that the unaccounted loss in the earlier estimates was essentially due to poor combustion, but was not so recognized. The very significant increase in combustion efficiency in this class of stoves allowed the possibility of estimating other components reasonably accurately. This is a direct consequence of the two stage gasification-combustion process yielding steady flow of gases which contain 80% (gasification efficiency) of the input energy enabling near-stoichiometric combustion with the help of controlled supply of combustion air. Fundamental studies Experiments with wood chips (615 kg/m3) and pellets (1260 kg/m3) showed that particle density has no effect on single particle and packed bed combustion in flaming mode beyond the role played through the surface energy balance (involving the product of fuel density and propagation rate, ˙r). Same is true for single char particles. A transport controlled combustion model taking into account the ash build up over the char surface confirmed this behaviour and showed that the phenomenon follows d2 law, where d is the equivalent diameter of the fuel particle, consistent with the experimental results. But packed bed of char particles showed distinct dependence on particle density. Differences were traced to poor thermal environment faced by low density wood char pieces compared to pellet char leading to variations in the volumetric heat release rate. A composite picture of the operational behaviour of the packed bed flame propagation was obtained from the measurements of exit gas composition, bed temperature, temperature of gas phase and condensed phase surface using 100 µm thermocouples, O 2 drop across the flame front using lambda sensor as a function of Vs. The packed bed studies were conducted in insulated steel and glass reactors. These studies clearly showed distinctive regimes in the bed behavior. In the first regime from Vs = 3 to 17 cm/s, (a) the propagation rate increases with Vs, (b) the fractions of CO, H2 are at least 10%, CH4 drops from 3 to 1%, (c) the oxygen fraction is near zero, (d) the gas phase temperature in the bed is constant at about 1600 K, (e) the condensed phase surface temperature increase from 850 K to 1600 K and (f) oxygen fraction drops from 0.21 to 0.0 within a single particle depth and coincides with the gas phase ignition. The inferences drawn from these data are that (i) the process is diffuusion controlled (ii) the bed operates in fuel rich mode, (iii) char participates only in reduction reactions. In the second domain from V s = 17 cm/s up to about 50 cm/s, (a) the propagation rate is nearly constant (b) the mass fractions of CO and H2 drops to less than 5%, CH4 decreases further, (c) oxygen fraction remains near zero, (d) CO 2 increases, (e) gas phase and surface temperatures are nearly equal and increase from 1600 K to 2200 K and match with the equilibrium temperature at that equivalence ratio, (f) oxygen fraction drops from 0.21 to 0 in one particle depth like in the first regime indicating diffuusion limitedness in this regime as well, (g) unlike in the first regime, volatiles from biomass are convected up to the next layer suppressing a local flame and char oxidation dominates. Beyond Vs = 50 cm/s, the propagation ceased to occur. The precise value of the extinction V s depended on the rate of increase of Vs in this range. A faster change initiated the extinction earlier. Observations showed that extinction began at some location around the periphery and spread laterally. Extinction at one layer was adequate to complete the extinction process. To explain the observed behaviour a simple zero-dimensional model tracking the heating of a fresh biomass particle upstream of the propagating flame front because of radiative heat transfer was set up. This equation was coupled with the equation for single particle flaming combustion to explain the behavior in the first regime. In order to explain the observed flattening of propagation rate in the second regime, it was found essential to account for the effect of the ash layer building on the oxidizing char particle and the temperature dependence of ash emissivity, on the radiative heat transfer to fresh biomass. The results of the model coupled with the experimental data from all sources on a corrected propagation rate vs. V s showed a universal behaviour that is considered a very important recognition of the packed bed propagation behaviour. Combining theory and experiments was essential to explain the extinction. The features are: (a) the presence of ash layer over the surface is shown to be responsible for maintaining a steady char conversion in a single particle at low stream speeds, (b) the feature that the ash layer would be blown away at stream velocities of 2.5 to 3 m/s in a single particle combustion, (c) with V s close to 50 cm/s, local velocities of air flow through the bed can reach 2 to 3 m/s, this value being sensitive to the bed arrangement (with slight shifting or settling of one particle leading to increase of the local velocity at the periphery). Thus, the high local speeds of flow through the bed (more than 2 m/s) was considered responsible for removal of ash layer such that radiation losses would be dominant and cause local extinction of the reaction front at the char surface. Thus, this study has led to a comprehensive understanding of the gasification-combustion behavior of packed bed in stoves and on grates. It has also led to the evolution of parameters for obtaining high efficiency and low emissions (HELE) from stoves -both domestic and industrial. Most interestingly, it has resulted in recognition of an universal behavior of flame propagation rate through packed bed of biomass.

Automated start–up and shutdown procedures increase the profitability and safety of a process, but are difficult to implement due to the complex nature of the concepts that must be incorporated. Generic components used specifically for the implementation of automated startup and shutdown procedures were defined to streamline the implementation process. The generic components developed are based on Sequential Function Charts and were applied to the startup of a fixed–bed gasification unit, for which a dynamic simulation model was developed. The application showed that the automated startup can be defined by a few generic components and that the flexibility of the startup procedure is increased through the incorporation of a fault accommodation module. The use of a visual–based definition of sequential processes increases the understanding of the complex scheduling procedures as well as the efficiency of the development of these automated procedures. In addition, iterative learning was incorporated into the generic definition to optimise controller performance during the non–linear phases of operation. / Dissertation (MEng (Control Engineering))--University of Pretoria, 2006. / Chemical Engineering / MEng / Unrestricted

Today the large scale introduction of biomass gasification is hampered by health, safety and environmental issues which present a major barrier in the deployment of this technology. The condensate in particular resulting from producer gas cooling before use in gas engines is highly toxic and carcinogenic which, if not adequately controlled, can lead to detrimental impacts on human health and the environment. The study was therefore aimed at assessment of pollution levels resulting from biomass gasification organic condensates. The study involved assessing the concentration of polycyclic aromatic hydrocarbons (PAHs) and BTEX (i.e. benzene, toluene, ethylbenzene and xylene) in the condensate deemed toxic and carcinogenic, mention their impact on human health and the environment as well as recommend measures aimed at minimizing pollution levels resulting from biomass gasification.   The gasifier installation at Makerere University was run in downdraft mode using maize cobs as biomass fuel. The producer gas was cooled using a water cooled condenser connected to the exhaust pipe of the gasifier. The condensate was then transferred into sampling bottles made of opaque glass to minimize photochemical reactions in water samples and preserved in a cooler at 2oC to 6oC until the time for analysis to minimize volatilization and bacterial degradation of the hydrocarbons. The capillary gas chromatography with mass spectrometric detector (CGCMSD) was used to analyze the condensate for the selected hydrocarbons. The procedures involved preparation of PAHs and BTEX standard solutions using standard mixtures and internal standards, calibration of the CGCMSD, extraction of the aromatic hydrocarbons using hexane, performing a surrogate analysis to assess percent recoveries and injecting a 2 µl aliquot of the final solution of each test sample in a CGCMSD for analysis. Identification of targeted hydrocarbons was based on the retention time match and mass spectra match against the calibration standards while quantitation was done by use of internal standards.   The average concentration of naphthalene was 204.3 mg/m3, benzene-16.8 mg/m3,toluene-105.5 mg/m3, ethylbenzene-200.9 mg/m3, 1,2-dimethyl benzene-209.5 mg/m3 and 1,3+1,4-dimethyl benzene-790.4 mg/m3. Acenaphthylene, acenaphthene, fluorene, phenanthrene and anthracene were not detected in the condensate by the CGCMSD due to their concentration levels being below the detection limit of the CGCMSD. The concentrations of naphthalene and xylene were considerably high compared to the recommended permissible exposure limits thus posing risks on both human health and the environment. It is therefore important to treat the condensate before disposal to the environment. On the other hand, the concentrations of benzene, toluene and ethylbenzene were below the permissible exposure limit and therefore for this study, the liquid effluent was considered to meet the regulatory standards. The recommendations aimed at minimizing pollution levels during biomass gasification were also discussed.

Biochar systems have been beneficial to Kenyan residents living in the rural areas, particularly in Kwale, following recent research interventions. Biochar system starts from the biomass feedstock sourcing, its production method, and finally its application to soil. The aim of this study is to assess the climate change impacts of the application of biochar in smallholder farms and households in rural Kenya, against the traditional agriculture and cooking practices under realistic conditions and from a life cycle perspective. The scope of this study includes the biomass sourcing identification, biomass availability measurement, cooking practice observation and biochar application during planting season (April to May) at one of the rural areas, the Waa Ward in Kwale County under The Biochar Project. Field observation was carried out to identify and measure on-farm biomass availability and cooking performance. The identification and measurement of biomass weight were conducted through survey and manual scale, respectively. While the cooking performance was observed with uncontrolled Kitchen Performance Test (KPT) method. A life cycle assessment was conducted to evaluate the climate change impact of biochar system in Kwale. The biochar production method, also called the improved system in this study, is compared against the traditional system. This study focuses at the cookstove used for the two systems, Gastov and three-stone open fire. Gastov is a type of Top-Lit UpDraft (TLUD) natural draft gasifier cookstove investigated. The biomass measurement established the biomass and energy availability on-farms in Kwale. Meanwhile, the KPT found that Gastov required lesser fuel for cooking due to higher thermal efficiency in comparison to three-stone open fire. The LCA results showed that the improved system performs better than the traditional system in terms of climate change impacts and that the improved system potentially offset GHG emissions caused by traditional system as well as generates a net carbon credit. Lastly, the ‘hotspot’ of the improved system was identified in the cooking process, although it was also significantly better than the traditional cooking process. The sensitivity analysis showed that both fraction of stable carbon and fraction of non- renewable biomass (fNRB) were major factors in the biochar system in Kwale, Kenya. The conclusion is that the biochar system presents more advantages as applied in Kwale compared to the traditional system through biomass management, improved cooking method, and biochar application to soil.

In  Kenya, lack of clean cooking services affect around 80 % of the population. A range of improved cookstoves (ICS) have been produced to address this. This study aims to investigate the long-term usage of an improved stove, the biochar producing gasifier. The stove was distributed to 150 rural households divided between three regions in Kenya, in a research project in 2016. This follow-up study looked at areas of stove satisfaction and dissatisfaction among participants, as well as identifying key factors which separate users from non-users. All 150 were asked a few questions over the phone and 30 were visited for in-depth, survey-based interviews. Most households used the traditional three stone open fire stove for everyday purposes, sometimes complemented by the gasifier or other ICSs[CS1] [CS2] . 60 % of households used the gasifier at least monthly. Users and non-users rated the gasifier stove similarly. They varied in terms of stove ownership with users owning on average half a stove more than non-users. User households were generally larger. The gasifier was a fuel efficient stove and created little smoke, but was considered too small and required tiresome fuel preparation. The reported problems cannot be fixed unless thoroughly changing the stove design and possibly the gasification process itself, and without addressing them the gasifier is unlikely to replace the three stone stove. The study recognizes the potential of the gasifier as an improved stove, but calls for creative redesign in order to achieve mass adoption. / I Kenya påverkar bristen på matlagningsutrustning som är säker ur hälso- och miljösynpunkt runt 80 % av befolkningen. Traditionellt lagas mat över öppen  eld. En mängd spisar har producerats i syfte att förändra detta. I denna studie undersöktes långtidsanvändningen av en spis, en biokolsproducerande förgasningsspis. Spisen delades ut till 150 hushåll på landsbygden, jämnt fördelade på tre regioner i landet i ett forskningsprojekt år 2016-7. Denna uppföljningsstudie tittar på vilka aspekter hos spisen som forskningsdeltagarna tyckt om respektive funnit utmanande, samt vad som skiljde användare från de som slutat använda spisen. En kort telefonintervju gjordes med alla, och med 30 gjordes djupgående, enkätbaserade intervjuer. Resultaten visade att de flesta hushåll lagade mat över öppen eld till vardags, ibland kompletterat med förgasningsspisen eller andra spisar. 60 % av hushållen använde förgasningsspisen  minst en gång i månaden. Användare och icke-användare hade liknande åsikter om förgasningsspisen. Användare ägde i genomsnitt en halv spis mer än icke-användare. Hushåll som använde förgasningsspisen var generellt sett större. Förgasningsspisen ansågs vara en bränslesnål spis och bara skapa en liten mängd rök, men ansågs vara för liten. Den krävde också mer ansträngande bränsleförberedning. De rapporterade problemen går inte att åtgärda utan att ändra förgasningsspisens design i grunden och eventuellt själva förgasningprocessen, och utan att åtgärda dem kommer förgasningsspisen sannolikt inte att ersätta matlagning över öppen eld. Studien understryker förgasningsspisen potential, men kräver kreativ omdesign för att uppnå massanvändning.

The thesis, through experimental and numerical investigations reports on the work related to packed bed reactors in co-current configuration for biomass gasification. This study has extensively focused on the gasification operating regimes and addressing the issues of presence of tar, an undesirable component for engine application. Systematically, the influence of fuel properties on the gasification process has been studied using single particle analysis and also in packed bed reactors. Studies related to the effect of fuel properties - size, surface area volume ratio and density on the reactor performance are addressed. The influence of these parameters on the propagation rate which indirectly influences the residence time, tar generation, gas compositions is explicitly elucidated. Most of the reported work in literature primarily focuses on counter-current configurations and analysis on propagation flame front/ignition mass flux and temperature profiles mostly under the combustion regime. In this work, flame propagation front movement, bed movement and effective movement for a co-current packed bed reactor of different reactor capacities and a generalized approach towards establishing ‘effective propagation rate’ has been proposed. The work also reports on the importance of particle size and sharing of air from the top and through nozzles on tar generation in the open top down draft reactor configuration. Firstly, pyrolysis, an important component of the thermochemical conversion process has been studied using the flaming time for different biomass samples having varying size, shape and density. The elaborate experiments on the single particle study provides an insight into the reasons for high tar generation for wood flakes/coconut shells and also identifies the importance of the fuel particle geometry related to surface area and volume ratio. Effect of density by comparing the flaming rate of wood flakes and coconut shells with the wood sphere for an equivalent diameter is highlighted. It is observed that the tar level in the raw gas is about 80% higher in the case of wood flakes and similar values for coconut shells compared with wood pieces. The analysis suggests that the time for pyrolysis is lower with a higher surface area particle and is subjected to nearly fast pyrolysis process resulting in higher tar fraction with low char yield. Similarly, time for pyrolysis increases with density as observed from the experimental measurements by using coconut shells and wood flakes and concludes the influence on the performance of packed bed reactors. Studies on co-current reactor under various operating conditions from closed top reactor to open top reburn configuration suggests improved residence time reduces tar generation. This study establishes, increased residence time with staged air flow has a better control on residence time and yields lower tar in the raw gas. Studies on the influence of air mass flux on the propagation rate, peak temperature, and gas quality, establishes the need to consider bed movement in the case of co-current packed bed reactor. It is also observed that flame front propagation rate initially increases as the air mass flux is increased, reaches a peak and subsequently decreases. With increase in air mass flux, fuel consumption increases and thereby the bed movement. The importance of bed movement and its effect on the propagation front movement has been established. To account for variation in the fuel density, normalized propagation rate or the ignition mass flux is a better way to present the result. The peak flame front propagation rates are 0.089 mm/s for 10 % moist wood at an air mas flux of 0.130 kg/m2-s and while 0.095 mm/s for bone-dry wood at an air mass flux of 0.134 kg/m2-s. These peak propagation rates occur with the air mass flux in the range of 0.130 to 0.134 kg/m2-s. The present results compare well with those available in the literature on the effective propagation rate with the variation of air mass flux, and deviations are linked to fuel properties. The propagation rate correlates with mass flux as ̇ . during the increasing regime of the front movement. The extinction of flame propagation or the front receding has been established both experimentally supported from the model analysis and is found to be at an air mass flux of 0.235 kg/m2-s. The volume fraction of various gaseous species at the reactor exits obtained from the experiment is 14.89±0.28 % CO2, 15.75±0.43 % CO and 11.09±1.99 % H2 respectively with the balance being CH4 and N2. The model analysis using an in-house program developed for packed bed reactor provide a comprehensive understanding with respect to the performance of packed bed reactor under gasification conditions. The model addresses the dependence on air mass flux on gas composition and propagation rate and is used to validate the experimental results. Based on the energy balance in the reaction front, the analysis clearly identifies the reasons for stable propagation front and receding front in a co-current reactor. From the experiments and modelling studies, it is evident that turn-down ratio of a downdraft gasification system is scientifically established. Both the experimental and the numerical studies presented in the current work establishes that the physical properties of the fuel have an impact on the performance of the co-current reactor and for the first time, the importance of bed movement on the propagation rate is identified.

Die Arbeit zeigt wichtige Nutzungswege von fester Biomasse in Form von Holzhackschnitzel (HHS). Einleitend wird das Potenzial und der derzeitige Stand dargestellt. Es werden die physikalischen und chemischen Eigenschaften mit dem Schwerpunkt Wassergehalt in bezug auf die energetische Nutzung der HHS behandelt. Kerne der Nutzungswege bilden dabei die Vergasung im Gleichstromvergaser und die Co-Verbrennung in der Zirkulierenden Wirbelschicht. Mit Hilfe eines Versuchsvergasers werden die Auswirkungen von HHS-Eigenschaften auf den Betrieb untersucht. Der Modellvergaser IGEL bietet durch seine Konstruktion die Möglichkeit, innere Vorgänge zu beleuchten und Messungen in verschiedenen Vergaserebenen durchzuführen. Die Auswirkungen von verschiedenen Brennstoffchargen mit unterschiedlichem Wassergehalt führten zu Änderungen in der Gaszusammensetzung. Eigene Untersuchungen ermittelten einen Grenzwassergehalt, mit dem der Vergaser noch betrieben werden kann. Die Experimente an der Pilotanlage mit zirkulierender atmosphärischer Wirbelschicht befass-ten sich mit der wichtigen Frage, ob und welches NOx-Minderungspotenzial beim Einsatz von Biomasse vorliegt. Die mathematische Modellierung verdeutlicht die Nutzbarkeit von Simulationsprogrammen bei der Untersuchung von Einflüssen der Co-Verbrennung auf die NOx-Bildung. Hier wurden die Gesichtspunkte der Luftzahl, der Luftstufung, des Wassergehaltes, das Mischungsverhältnis und die Brennstoffstufung betrachtet. Eine Wirtschaftlichkeitsbetrachtung führt zu dem Ergebnis, dass Anlagen zur reinen Stromerzeugung mit Biomasse nur nahe der gesetzlichen Höchstleistung von 20 MWel zur Einspeisevergütung von wirtschaftlich betrieben werden können. Die ökologisch und ökonomisch günstigste Variante stellt die Co-Verbrennung in vorhandenen Anlagen dar. Die Kalkulationen zu den in Deutschland benötigten 20-MWel-Anlagen verdeutlichen, dass bei den gegenwärtig geplanten Heizkraftwerken das Potenzial an HHS schnell aufgebraucht ist.

As the need for both sustainable energy production and waste minimization increases, the gasification of biomass becomes an increasingly important process. What would otherwise be considered waste can now be used as fuel, and the benefits of volume reduction through gasification are seen in the increased lifespan of landfills. Fluidized-bed gasification is a particularly robust technology, and allows for the conversion of most types of waste biomass. Within a fluidized-bed gasifier, thermal medium (sand) is heated to operating temperature (around 1350°F) and begins to fluidize due to the rapid expansion of air entering the bottom of the reactor. This fluidization allows for excellent heat transfer and contact between gases and solids, and prevents localized "hot spots" within the gasifier, thereby reducing the occurrence of ash agglomeration within the gasifier. Solids enter the middle of the gasifier and are rapidly dried and devolatilized, and the products of this step are subsequently oxidized and then reduced in the remainder of the gasifier. A syngas composed mainly of N2, H2O, CO2, CO, CH4, and H2 exits the top of the gasifier. A computer model was developed to predict the syngas composition and flow rate, as well as ash composition and mass flow rate from a fluidized-bed gasifier. A review of the literature was performed to determine the most appropriate modeling approach. A chemical kinetic model was chosen, and developed in MATLAB using the Newton-Raphson method to solve sets of 18 simultaneous equations. These equations account for mass and energy balances throughout the gasifier. The chemical kinetic rate expressions for these reactions were sourced from the literature, and some values modified to better fit the predicted gas composition to literature data.

Im Rahmen der vorliegenden Arbeit werden dynamische Modelle eines IGCC-Kraftwerkes mit CO2-Abtrennung unter Verwendung des Modellierungstools Modelica/Dymola entwickelt. Dabei liegt der Schwerpunkt auf dem Gaspfad der Gasreinigung. Es ist vorteilhaft, für verschiedene Aufgaben, Modelle mit unterschiedlicher Tiefe zu verwenden. Mit den detaillierten Modellen werden Simulationen der Teilprozesse durchgeführt. Für den Aufbau eines Gesamtsystems werden vereinfachte Modelle verwendet. Anhand des Gesamtsystems werden drei Regelkonzepte (Gleitdruckregelung, Leistungsregelung der Gasturbine, Leistungsregelung des Vergasers) untersucht und bewertet. Des Weiteren werden drei Störfallszenarien (Ausfall des Sättigers im Brennstoffsystem, Betriebsstörung in der Vergaserinsel, Unterbrechung der Stickstoffzumischung im Brennstoffsystem) getestet.