Made available in DSpace on 2018-08-02T00:02:54Z (GMT). No. of bitstreams: 1 tese_10439_ARTUR GUIMARÃES MAIOLI20170710-111821.pdf: 23311759 bytes, checksum: 71248c6370f30765c8368835db6d11fb (MD5) Previous issue date: 2016-09-30 / A combustão smouldering é uma forma de combustão lenta, sem chama e que ocorre a relativamente baixas temperaturas. Ela é sustentada pelo calor liberado em reações heterogêneas decorrentes do ataque direto de oxigênio na superfície de combustíveis sólidos. Apesar das características relativamente baixas desse tipo de combustão, ela apresenta um perigo significativo. Este trabalho teve o objetivo de avaliar a combustão smouldering do xisto betuminoso em uma célula de combustão. Para isso foi utilizado o software de simulação gratuito OpenFOAM, com o solver biomassGasificationFoam, destinado à processos de conversão termoquímica de combustíveis sólidos em leito fixo. Os resultados foram comparados com dados experimentais da literatura. Os perfis de temperatua simulados apresentaram boa concordância com os experimentos, além de que foi possível a confirmação da estrutura de combustão reaction leading, onde a zona de reação avança de forma mais rápida do que a zona de transferência de calor. Foi avaliado também a importânica do fornecimento de oxigênio na velocidade de propagação da frente de chama, confirmando que esse parâmetro governa essa velocidade. Por fim, foi realizado um estudo paramétrico para avaliar a influência de parâmetros físicos na evolução da temperatura do leito e na velocidade de propagação da frente de chama.

Made available in DSpace on 2018-08-02T00:03:12Z (GMT). No. of bitstreams: 1 tese_9112_CARLOS EDUARDO SILVA ABREU.pdf: 1527404 bytes, checksum: 6d25418e60b02423f34ab3c331567ad0 (MD5) Previous issue date: 2015-07-28 / A necessidade da busca por fontes alternativas de energia que auxiliem na geração energética associada ao processamento térmico de algum produto de maneira sustentável ou racionalizada é um assunto de extrema importância. Além disso, com o fator ambiental que após a lei nº 12.305/10 de destinação de resíduos sólidos, a qual prevê a redução na geração de resíduos urbanos o gerenciamento de resíduos torna-se condição incontornável na gestão ou implantação de qualquer sistema ou processo. Tendo em vista essa demanda, o Lodo de Fossa Séptica (LFS) é utilizado nesse trabalho com o intuito de realizar uma análise referente ao potencial de geração de energia, e, ao mesmo tempo, sugerindo um modo auto-sustentável de tratamento termoquímico visando a redução do seu volume. Portanto, a influência da umidade do material e do tipo de configuração do leito de combustão (co-corrente ou contra-corrente) foi estudada. Inicialmente, foi realizada uma análise do poder calorífico superior (PCS) do lodo em função da sua umidade, e os resultados obtidos mostraram que para uma redução da umidade de 20% até que o lodo esteja completamente seco, ou seja, a 0%, o PCS elevou-se de 7487 até 8480 kJ.kg-1, o que representa um aumento de, aproximadamente, 14% no potencial energético do LFS. Em seguida, foi realizada a análise da combustão smouldering contra-corrente do lodo em função da umidade. Tal análise mostrou que a redução da umidade acarreta no aumento da temperatura máxima obtida no processo (962 até 1026°C) e, além disso, gera um aumento da velocidade de propagação da frente de combustão, de 2,43 até 2,99 mm.min-1. A análise referente ao processo co-corrente apresentou resultados similares, de forma que, com a redução da umidade elevou-se a temperatura máxima de operação e a velocidade de propagação da frente de combustão. Finalmente, comparou-se os resultados do processo contra-corrente e co-corrente, apontando que para o mesmo teor de umidade, o processo co-corrente apresentou maiores temperaturas e menores velocidades de propagação da frente de combustão. Paralelamente às análises supracitadas, foi verificado o teor de material inerte no lodo comparando a massa da amostra antes e após o experimento. Todos os ensaios apresentaram teor próximo de 52% de matéria inerte.

Made available in DSpace on 2018-08-02T00:03:13Z (GMT). No. of bitstreams: 1 tese_9216_JADERSON NUNES PRETTI.pdf: 4692062 bytes, checksum: 7088a108ff1b2538b7a95be7acd6c458 (MD5) Previous issue date: 2015-08-31 / Com o constante aumento da demanda energética é necessário o estudo de fontes alternativas de energia bem como técnicas para sua conversão em trabalho útil em diferentes escalas de consumo. Outro fator importante é que a humanidade esta produzindo cada vez mais resíduos sólidos, e neste, existe um potencial energético que não pode ser negligenciado. Neste contexto, a combustão se mostra uma boa alternativa para o reaproveitamento energético desses resíduos, no entanto, é indispensável um entendimento do processo, bem como das variáveis de operação. Portanto, este trabalho tem como objetivo apresentar uma modelagem para as equações de energia que governam a transferência de calor em um meio poroso reativo das fases sólida e gasosa e, ao mesmo tempo, simular o processo de combustão smouldering em meio poroso utilizando um software de simulação gratuito, o OpenFOAM, principal ferramenta utilizada neste trabalho. É apresentado para o leitor uma concisa descrição do pacote de simulação utilizado juntamente com suas principais características. Os resultados simulados são comparados com resultados experimentais obtidos pela célula de combustão instrumentada desenvolvida no Laboratório de Combustíveis e Combustão da Universidade Federal do Espírito Santo para estudos da combustão em meio poroso. Por último, apresenta-se a influência de parâmetros físicos, como espessura da frente, fração volumétrica de sólido e velocidade de resfriamento, na evolução da temperatura simulada no interior do leito.

Smouldering combustion governs the burning of many materials in the built and natural environments. Smouldering is flameless, heterogeneous combustion which occurs when oxygen reacts with the surface of a solid fuel. Understanding the conditions which will result in the ignition and smouldering of a porous fuel is important and the phenomena involved are complex and coupled, involving heat and mass transfer, and chemical kinetics. This thesis reports experimental studies of the ignition, spread, suppression and emissions from reactions in porous media. Similar experimental techniques are shown in this thesis to be applicable when studying a wide range of solids which undergo self-sustaining reactions. This thesis is presented in a manuscript style. Each chapter takes the form of an independent paper which has been prepared for journal publication and as such, each chapter can stand on its own as a piece of research. A final chapter summarizes the findings and conclusions and suggests further areas of research. Chapter 1 presents a study of self-sustaining decomposition of ammonium nitrate containing inorganic fertilizer. This is of importance to the shipping industry which transports these materials in large quantities. Upon exposure to a heat source, ammonium nitrate may undergo exothermic decomposition which can propagate through the material, posing safety and economic threats. This reaction does not involve oxygenbased chemistry, but has many similarities to the propagation of a smoulder front in a porous material. Small-scale experiments to investigate the self-sustaining decomposition (SSD) behaviour of NPK (nitrogen, potassium, phosphorous) 16.16.16 fertilizer were undertaken. Experiments showed that this material will undergo self-sustaining decomposition and are used to formulate a reaction framework. Findings were applied to the events that occurred aboard the Ostedijk in 2007. Chapter 2 is a study of smoulder in polyurethane foam to study the relationship between sample size, critical heat flux and spread rate. Smouldering fires are the leading cause of residential fire deaths in developed countries and polyurethane foam is ubiquitous in the modern world. The critical heat flux for ignition was found to decrease with increasing sample size and the spread rate was found to be a function of the sample size, smoulder propagation depth and the applied heat flux. This is the first time that results on the effect of sample size on smouldering have been reported in the literature and these can be used to aid the extrapolation of small-scale flammability testing results to large scale scenarios. Chapter 3 presents an experimental investigation into the ignition of porous fuels by hot particles. This is related to the problem of spotting ember ignition in wildland fires which is a major, but poorly understood, spread mechanism. The process of spotting occurs in wildland fires when fire-lofted embers or hot particles land downwind, leading to ignition of new, discrete fires. The work studies the ignition of a fuel as a function of ember size and temperature. Metal particles are used as a proxy for burning embers and powdered cellulose to represent the forest fuel. Relationships between the size and temperature of the particle required for flaming and smouldering ignitions are found. These results are used to assess the ability of hot-spot ignition theory to determine the particle size–temperature relationship required for ignition of a cellulose fuel bed. Chapter 4 is an investigation into the suppression of smouldering coal. Subsurface coal fires are a significant global problem with fires in China alone estimated to consume up to 200 million tons of coal per year. As global demand for coal increases, accidental fires are a waste of a useful energy resource as well as a source of pollution and greenhouse gases. The results are the first attempt reported in the literature to study the suppression of these fires under controlled laboratory conditions. The ignition, spread and suppression of subsurface coal fires were studied using small-scale laboratory experiments. Time to ignition was seen to depend on particle size with small and large particles resulting in long times to ignition, while medium sized particles resulted in the shortest time to ignition. The maximum temperature, spread rate and mass lost were found to be independent of particle size above a critical particle size. The effectiveness of three systems for delivery of a suppression agent were assessed – direct injection, shower and spray. The effect of particle size on the water required for extinguishing using a spray was found to be weak. Chapter 5 presents an experimental investigation of the smouldering behaviour of peat. This is of particular interest in understanding the impact of smouldering fires on the earth system. The longer burn durations and different combustion dynamics of smouldering compared to flaming means that they have been shown to consume large amounts of biomass in, and contribute significantly to the emissions from, natural fires occurring in peatlands. The dynamics of smouldering peat in shallow, strong fronts was studied in the Fire Propagation Apparatus and a smoulder reaction framework with two burning regimes is presented. The first regime is peat smouldering and was found to be controlled by the applied heat flux and the second regime corresponded to char smouldering and was more sensitive to the flow of oxidizer. Chapter 6 complements Chapter 5 with an analysis of the CO and CO2 emissions for smouldering and flaming peat. This data can be used with large-scale measurement techniques to improve emission estimates. The emissions are found to be dependent of the burning regime and the type of combustion with flaming resulting in higher fluxes of CO2 and lower fluxes of CO compared to peat smouldering. Char smouldering resulted in the highest yields of CO and CO2. The large majority of emissions (85% of CO2 and 97% of CO) are released during the smoulder phase of the reaction. This highlights the differences in the chemical processes occurring under these two modes of combustion. Chapter 7 summarizes the research undertaken in this thesis and presents possible further work.

A model examining underground smouldering peat combustion is presented. A one-step chemical reaction is considered where the gas and solid are assumed to be in thermal equilibrium. The full model allows porosity, permeability and gas density to vary and considers a buoyant velocity field determined by Darcy's law. Due to the low bulk thermal conductivity of peat, the diffusion of oxygen through it is characterised by a Lewis number much less than one. This results in thermal-diffusive instabilities. These instabilities can cause flame balls to arise in gaseous combustion and a fingering regime to arise in solid combustion. Analytical solutions to simplified spherically symmetrical equations are derived. These equations assume diffusion to be the dominant transport mechanism as well as taking that the porosity, gas molecular weight and gas density all remain constant. The underlying structure of the combustion region is found to be analogous to that of a flame ball. When studied in cylindrical symmetry a single, stable finger can be modelled propagating against an imposed air flow. The effects of heat losses, velocity magnitude and the Lewis number can be studied and results are compared to existing experimental smouldering combustion data. Although no detailed experiments have studied this phenomenon in peat, predicted results capture key qualitative trends found in both filtration combustion of polyurethane foam and in the fingering combustion of paper. In addition to this, when the imposed air flow is reduced to zero a propagating combustion front is predicted, analogous to a self-travelling flame ball. When the velocity field is determined by Darcy's law the dimensionless permeability of the peat plays a key role in determining the range of values over which fingering combustion can occur. Whilst there is little impact of taking the gas molecular weight to be constant, when porosity is allowed to vary and a relationship between porosity and permeability is included an over-blowing extinction limit is identified. This limit is not found in the constant-porosity model where a low-fuel extinction limit is predicted. Peats of differing ages and locations can possess significantly different characteristics. However, the fingering regime is predicted to occur within the range of parameters in which peat soils lie. Experiments suggest that fingering combustion can take the form of both sparse fingers and a complex fingering regime. The cylindrically symmetrical model can not capture tip-splitting. Hence the model does not explicitly account for the distance between two neighbouring fingers. However, an estimate for this value can be made if peat smouldering were to occur in a regime of multiple fingering. An averaged continuum model describing the spread of an ember storm is also presented. The dominant mechanism determining the spread-rate of the fire is the lofting and landing of embers and individual fires are taken to grow in an elliptical manner under the influence of the wind. When an ember storm is spreading at a steady speed, its spread rate is found to be described by a single similarity solution.

As wildfires increase in frequency, severity, and areal extent in western Canada’s boreal region, wildfire managers are challenged with maintaining current levels of effectiveness. Review of recent wildfire events have identified a need for an improved understanding of vegetation management as a means to mitigate risk of future fires in the wildland-urban and wildland- industry interfaces. Peatlands cover 21% of the land area in continental western Canada; however, there is a lack of peatland-specific fuel modification strategies. The unique ecohydrological feedbacks that operate in these ecosystems provide an opportunity to implement novel peatland-specific treatments in these areas. This thesis examines the effectiveness of novel peatland-specific fuel modification treatments derived from seismic line analogs in reducing the smouldering potential of near-surface moss and peat. An ecohydrological assessment of seismic lines bisecting bogs revealed that alterations to canopy structure and physical peat properties at the time of seismic line establishment leads to persistent changes to the ecohydrological structure and functioning of these systems, marked by limited regeneration of vegetation, dominance of Sphagnum groundcover, and greater near-surface volumetric water contents. Such traits are desirable in fuel modification strategies and therefore, we incorporated the seismic line framework into conventional fuel reduction approaches to create novel peatland-specific fuel modification treatments, involving alterations to canopy structure (thinning and clearing) and physical peat properties (compression). The short-term effects are compression-induced changes to hydrophysical properties including elevated mean near-surface volumetric water contents. Ecological and hydrological indicators of moss moisture stress suggest long-term effects likely include an expansion of Sphagnum moss ground cover within thinned and cleared areas. Ultimately, both short- and long-term effects contribute to the reduction of smouldering potential in near-surface moss and peat. We propose that these peatland-specific fuel modification treatments be incorporated into current FireSmart fuel strategies to reduce wildfire smouldering risk at the wildland-urban and wildland-industry interfaces. / Thesis / Master of Science (MSc)

To build multi story buildings out of timber is of a common interest in the building sector. Timber as a building material has many profits, such as the low cost, the availability and the ability to recycle it, the low carbon footprint and the workability. Although, when it comes to fire protection of buildings with a timber based structure there are challenges regarding prevention of the spread of fire while timber surface is exposed to fire. There have been cases in which timber buildings have caught fire leading to severe fire spread and ruined buildings. One example concerns a student modulus accommodation in Luleå that caught fire in august 2013. The fire started on the fourth floor after which a vertical fire spread occurred in concealed spaces between the volume modules. According to the fire investigation lack of knowledge regarding performance of detailed building solutions has led to the poor fire performance of the building. This master thesis mainly consists of a model scale tests that is prepared and performed according to the standard EN 1363-1. The purpose of the test is to investigate the performance of various cavity barriers exposed to fire. The main objective is to examine which temperatures that can be expected at different positions at various cavity barriers when using model scale test as a test method. There are two main kinds of cavity barriers: barriers that are airtight and closed inside the voids of the construction; and ventilated barriers. The most common cavity barriers are the ones that are airtight and closed. The material can be solid wood, gypsum board or mineral wool. The installation areas for these cavity barriers are anywhere, besides where the concealed spaces shall be ventilated and in every joint that shall be sealed using sealant. The ventilated cavity barriers are mounted in concealed spaces where the ventilating function is provided. These concealed spaces are often situated in, for example, ventilated attics, facades and roofs. The purpose of the ventilated barriers is to maintain the air flow in the cavity during regular conditions but also to form a protecting barrier between fire compartments when exposed to fire. The model scale test includes test apparatuses such as thermocouples and a fire resistance furnace with plate thermometers and burners. In addition, a test rig consisting of test specimens and the products to be tested are essential.  In this report, two model scale tests have been performed and prepared according to EN 1363‑1. The test period endured for four hours and the thermocouples measured the temperatures during the whole time. During the first hour the test specimens were exposed to the standard ISO 834 fire curve by controlling the burners in the furnace. After one hour the burners were turned off and the specimens were no longer exposed to fire. The measurements of the temperatures continued during three more hours. After the first two of these three hours the furnace was opened to confer more oxygen in the purpose to record any changes in the temperatures. Results of the performed experiments have indicated parameters that affect the performance of the cavity barriers. The cavity surface itself has an influence to the fire spread. The number of barriers in the cavity and the material properties of the material that is used as the cavity barrier lead to the different protection by those cavity barriers. Some of the tested barriers were plastic covered, which had effect on the performance of the cavity barriers. The dimensions of the barriers, moreover the width and the thickness, are important parameters for the proper function of the barrier. The test results indicate that glowing combustion occurs in the cavity between various cavity barriers.  It can be seen that the temperature rises when the furnace is opened. This indicates the appearance of smouldering since the combustion increases when the amount of oxygen increases, which leads to a temperature rise. Furthermore, the appearance of smouldering (glowing combustion) can be indicated by the observation of the damages of the specimens after the test. The temperatures that may be expected at the unexposed side of the cavity barrier depend on the surface material of the cavity, dimensions, and the material of the cavity barriers. Smouldering is a consequence of the temperature rise in closed cavities between cavity barriers. The performed test endured for approximately four hours and this indicates that fires in cavities can stay for a long time. To ensure the performance of various cavity barriers and verification by a model scale test it is important to perform further experiment and analyses to investigate the effects of the various parameters. To ensure the effectiveness of the performance of the cavity barriers they should be tested in cavities with various widths and various heights. Further investigation of the risk for smouldering is needed with measuring the amount of oxygen and the pressure.

Submitted by Maykon Nascimento (maykon.albani@hotmail.com) on 2016-02-25T18:44:09Z No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertacao Monhol 2015.pdf: 4387300 bytes, checksum: f1407d1b8975e9e2878b9c25ad0c2ec3 (MD5) / Approved for entry into archive by Patricia Barros (patricia.barros@ufes.br) on 2016-03-03T12:28:28Z (GMT) No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertacao Monhol 2015.pdf: 4387300 bytes, checksum: f1407d1b8975e9e2878b9c25ad0c2ec3 (MD5) / Made available in DSpace on 2016-03-03T12:28:28Z (GMT). No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertacao Monhol 2015.pdf: 4387300 bytes, checksum: f1407d1b8975e9e2878b9c25ad0c2ec3 (MD5) Previous issue date: 2015 / A propagação de uma frente de combustão ocorre numa variedade de situações e para diferentes propósitos industriais. O desempenho desses processos precisa melhorar e ao mesmo tempo reduzir os níveis de emissões para atender às normas de emissões internacionais. Para isso é necessário um certo grau de conhecimento tanto do processo como dos fenômenos da combustão. Em todos as situações envolvendo a combustão, a propagação é iniciada por uma fonte de calor e, após a ignição do combustível, a frente de combustão alcança o combustível adjacente. Estudos anteriores mostraram a ignição e propagação de uma frente de combustão como um fenômeno complexo que depende de processos químicos, térmicos e físicos. O presente trabalho abordou os desafios encontrados durante uma abordagem empírica para análise da propagação de uma frente de combustão em leito fixo. A partir da utilização de combustíveis simulados foram analisados: a influência da composição do combustível no comportamento da ignição do mesmo, as características da propagação da frente de combustão (regime de combustão, retração do leito e estrutura da frente) e a influência da ignição do combustível na propagação da frente de combustão. Foi possível realizar um mapeamento, para diferentes composições, do comportamento da ignição de combustíveis sólidos. A partir dos resultados de propagação da frente verificou-se que ocorrem basicamente três estágios de combustão no leito: ignição, propagação e oxidação do carbono fixo remanescente. Através das análises de gás notou-se a existência de dois regimes de combustão no leito: limitada pela reação e limitada pelo oxigênio. Foi obtido que em leitos com alta porcentagem de material inerte, onde há maior estabilidade, há uma maior influência da ignição na frente de combustão. Assim, mostrou-se como esses conhecimentos são úteis em diversas aplicações e processos industriais. / The combustion front propagation occurs in a variety of situations and for different industrial purposes. The performance of these processes needs to be improved and at the same time to reduce emission levels to meet the international standards. For this purpose, is needed a certain degree of knowledge of both processes of combustion phenomena. In all situations involving combustion phenomena, the propagation is initiated by a source of heat, and after fuel ignition, combustion front reaches the adjacent fuel. Previous studies have shown the ignition and the combustion front propagation as a complex phenomenon which depends on chemical, thermal and physical processes. This work focuses on the challenges encountered during an empirical approach to analyze the propagation of a combustion front in fixed bed. From the use of simulated fuels, it were analyzed: the influence of fuel composition on the behavior of its ignition, the characteristics of the combustion front propagation (combustion regime, shrinkage of the bed and the front structure) and the influence of fuel ignition in the propagation of the combustion front. It was possible to perform a mapping of ignition behavior of the solid fuel for different compositions. From the results of front propagation, it was found that, basically, three combustion stages occur in the bed: Ignition, Propagation and Oxidation of the remaining fixed carbon. Through gas analysis it was noted that there were two reaction modes present in the bed: reaction limited and oxygen limited. It was obtained than in bed with high content of inert materials, where there is greater stability, there is a greater influence from the ignition to the combustion front. Thus, it was shown how these skills are useful in various applications and industrial processes.

Modern buildings increasingly include the usage of innovative materials aimed at improving sustainability and reducing the carbon footprint of the built environment. Phase Change Materials (PCMs) are one such group of novel materials which reduce building energy consumption. These materials are typically flammable and contained within wall linings yet there has been no detailed assessment of their fire performance. Current standard fire test methods provide means to compare similar materials but do not deliver knowledge on how they would behave in the event of a real fire. Thus, the aim of this thesis is to develop a novel testing framework to assess the behaviour of these materials in realistic fire scenarios. For PCMs, a flammability study is conducted in the bench-scale cone calorimeter to evaluate the fire risk associated with these materials. Then, micro-scale Thermogravimetric Analysis (TGA) is used to identify the fundamental chemical reactions to be able to confidently interpret the flammability results. Finally, intermediate-scale standard fire tests are conducted to evaluate the applicability of the bench-scale results to realistic fire scenarios. These take the form of modified Lateral Ignition and Flame spread Test (LIFT) and Single Burning Item (SBI) tests to understand flame spread and compartment fires respectively. Finally, a simplified method to combine this knowledge for use in building design is proposed. This method allows the balancing of potential energy benefits with quantified fire performance to achieve the specified goals of the designer. Hemp-lime insulation is a material which has also becoming increasingly popular in the drive towards sustainability. The porous nature of the material means that smouldering combustions are the dominant reaction mode but there is currently no standardised test method for this type of behaviour. Thus, hemp-lime materials also represent an unquantified risk. The work in this thesis defines a simple, accessible and economically viable bench-scale method for quantifying the fire risk associated with rigid porous materials. This is applicable for both downward opposed flow and upward forward flow smoulder propagation conditions. The behaviour is then interpreted using micro-scale thermogravimetric analysis to understand the underlying pyrolysis and oxidation reactions. Designers can utilise this framework to quantify the smouldering risk associated with hemp-lime materials to enable their usage in the built environment. The holistic fire risk assessment performed in this thesis has quantified the behaviour of PCMs and hemp-lime insulation applicable to realistic fire scenarios. The simplified design method empowers designers to be able to realise innovative buildings through fundamental understanding of the fire behaviour of these materials. The outcomes of this thesis allow designers to mitigate the fire risk associated with these materials and achieve optimised engineering solutions. Furthermore, the novel fire testing frameworks provide the economically viable means to assess the fire performance of future PCMs and hemp-lime products which ensures lasting relevance of this research in the future.